text:
A well-fissured and faulted karst area at the Žveplenica sulphidic spring created suitable conditions for epigean copepods. Their presence in sulphidic water is a rare phenomenon. To understand the conditions related to sulphidic habitats in the region, two additional springs were analysed: the Studenec karst spring; and the Sovra artesian borehole, which contains dissolved sulphide. Water temperature, chemistry, and the stable isotopes of oxygen and hydrogen show that the Sovra borehole water has a different origin and history to that of the Žveplenica and Studenec springs water, which is derived from local precipitation. The low slope of the δ18O-δ2H regression line for the Žveplenica spring indicates a mixing of local precipitation water with geothermal sulphidic water that may explain the presence of live copepods. These harpacticoid and cyclopoid copepods must have survived anoxia and high sulphide for some time. The mean transit time for Žveplenica spring cannot be defined precisely from the available data, although the degree of attenuation of the isotopic signal indicates mean transit times of about 1.0 to 1.5 years. Sites similar to Žveplenica spring should be carefully analysed because not only do they provide insights into biodiversity, but they also represent an ecotone between the anoxic/ oxic and high/ low sulphide of these karst waters. Copepods in similar geological settings can be used as additional parameters to evaluate conditions in subsurface sulphidic habitats and their spatial connectivity and responses to hydrological events. This article is protected by copyright. All rights reserved.
This paper illustrates the hillslope storm runoff mechanisms and the effects of livestock in upland areas. The research site was a small upland catchment area on Dartmoor (Southwest England). It was shown that overland flow on the tracks and paths created by animals in the area responded very rapidly to rainfall, in the same order of magnitude as stream runoff. Livestock stocking densities were significantly different in different vegetation compositions. The topsoil bulk density values, moisture content and spatial track densities were significantly higher in areas associated with higher stocking rates. These areas reach a wetness threshold at an earlier state than surrounding, drier areas. When isolated, the wetter areas start discharging water only locally into downslope drier areas, but are not contributing to storm runoff in the stream. In areas with a high density of animal tracks, water is being discharged onto the track directly. The tracks comprised an ephemeral hydrological network contributing storm runoff to the stream quickly after rainfall. They transmit water rapidly downhill, short-circuiting local areas, reducing runoff lag time and increasing storm stream runoff. The runoff producing mechanism, in which soil conditions, vegetation types and path networks are a complex interplay of contributing factors, may be relevant to other uplands, especially when they act as water reservoir or source area for possible flooding events. Therefore, upland management policies need to take into account that the heterogeneity of hillslopes at local scales have implications for storm runoff at the catchment scale. This article is protected by copyright. All rights reserved.
More than half of the dry woodlands (forests and shrublands) of the world are in South America, mainly in Brazil and Argentina, where in the last years intense land use changes have occurred. This study evaluated how the transition from woody- to grass-dominated system affected key ecohydrological variables and biophysical processes over 20,000 hectares of dry forest in Central Argentina. We used a simplified surface energy balance model (S-SEBI) together with MODIS-NDVI data to analyse changes in above primary productivity, phenology, actual evapotranspiration, albedo and land surface temperature for four complete growing seasons (2004-2009).The removal of woody vegetation decreased aboveground primary productivity by 15-21%, with an effect that lasted at least 4 years, shortened the growing season between 1 and 3 months and reduced evapotranspiration by as much as 30%. Albedo and land surface temperature increased significantly after the woody to grassland conversion. Our findings highlight the role of woody vegetation in regulating water dynamics and ecosystem phenology, and show how changes in vegetative cover can influence regional climatic change. This article is protected by copyright. All rights reserved.
Feedbacks between vegetation spatial pattern and resource redistribution from bare areas (sources) to vegetation patches (sinks) are considered critical to the functioning of dryland ecosystems. However, experimental fieldworks testing the underlying assumptions and quantifying the feedbacks involved are very scarce. We hypothesized that the size and surface conditions of the upslope runoff-source areas control the transfer of resources to the downslope vegetation patch, and thereby vegetation performance. In a restored semiarid woodland in Alicante, SE Spain, we investigated the performance of planted shrubs (Olea europaea and Pistacia lentiscus) in response to the size, upslope length, internal connectivity, and soil surface properties of their respective upslope runoff-source areas (drainage microcatchments). Growth of O. europaea seedlings increased with drainage microcatchments size, while their water-stress level decreased with the upslope hillslope length. Lower plant density and higher bare-soil connectivity within the respective microcatchments improved the performance of O. europaea seedlings. Seedling survival was much lower for P. lentiscus than for O. europaea, and growth and water stress of alive P. lentiscus seedlings showed no significant relationships with any of the microcatchment properties assessed. Survival of P. lentiscus seedlings increased with hillslope length upslope the seedling location. Overall, results point to the interplay between the size and connectivity of the bare-soil upslope interpatch and the relative location on the hillslope as the most relevant control factors for seedling performance. Observed linkages between source-sink dynamics and plant performance provide valuable information for improving the design of conservation and restoration actions in semiarid lands. This article is protected by copyright. All rights reserved.
Both endangered and non-endangered unionid mussels are heterogeneously distributed within the Allegheny River, Pennsylvania. Mussel populations vary from high to low density downstream of Kinzua Dam, and the direction, amount, and range of hyporheic exchange (seepage) at the sediment-water interface was suspected to influence their distribution and abundance. Nineteen hydrogeomorphic variables, including quantification of seepage metrics, substrate size, river stage and discharge, and shear stress, were measured at 5 reaches on the Allegheny River within 80 km downstream of Kinzua Dam. Analysis revealed significant (α = 0.05) non-linear correlations between mussel population density and directional mean seepage (positive relationship), river width (positive relationship), and median substrate size (negative relationship). Specifically, seepage findings showed that increases in upward seepage and decreases in the overall range of seepage related to increases in mussel population density. River width, directional mean seepage, and median substrate size were also found to co-vary with marginal significance (α = 0.1), making their individual influences on mussel population density uncertain. Absolute mean seepage, water depth, hydraulic head, temperature differences between the surface water and substrate, and other substrate metrics besides median grain size were not found to significantly correlate to mussel population density. Considering the physical processes often linking seepage to other explanatory variables, future research in seepage-mussel relationships should work to isolate the mechanistic influence of hyporheic exchange independently from its common covariation with substrate size and geomorphology. This article is protected by copyright. All rights reserved.
In Brazil, as much as 50% of the native tropical savannas and woodlands (known as the Cerrado) have been converted to farmland under intensive agriculture. Land cover change at this scale has important implications for water and energy budgets, but at present these implications are poorly understood. A promising new technology for elucidating these relationships at large scales is remote sensing; but results obtained by this method need to be verified with ground-based measurements. For this study, we used remote sensing to estimate changes in energy budgets and evapotranspiration (ET) in São Paulo State following conversion of native Cerrado woodlands to cultivated land for sugar cane and eucalyptus. We applied the Surface Energy Balance Algorithm for Land (SEBAL) to ten TM–Landsat 5 images taken during 2005 at two locations (sugar cane fields and Cerrado woodlands). The SEBAL ET results were compared with ET data obtained via eddy covariance. There was good agreement between the two (R2 = 0.87), with no systematic over- or underestimation by SEBAL. Our SEBAL analysis indicated that land cover change causes strong shifts in albedo, land-surface temperature, and vegetation index—all of which affect energy balance and ET. Both the SEBAL and eddy covariance measurements indicate that ET for sugar cane is only about 70% of that for native woodlands. SEBAL estimates found that for cultivated eucalyptus plantations, ET was about 88% of that for Cerrado forests. Our results indicate that the SEBAL methodology is a reliable tool for estimating energy budgets and evapotranspiration in Cerrado landscapes and, further, that large-scale conversion of Cerrado woodlands to agricultural land significantly alters energy budgets and evapotranspiration. This article is protected by copyright. All rights reserved.
Though it is clear that mangrove forests have a positive effect on macrobenthos diversity in wetland ecosystems, these effects are not very clear under the condition of severe water pollution. The objective of this study is to investigate the effects of mangrove forests on macrobenthos diversity under severe water pollution in Shenzhen Bay, where water quality is strongly affected by industry and urbanization. For this purpose, we carried out a field study from December 2009 to July 2011 in the mangrove wetland in Shenzhen Bay, the only mangrove wetland located near a metropolis in mainland China. Samples were taken monthly from four habitats, namely, a reed fish pond, Gei wai ponds, mudflats, and a mangrove forest. The results show that the seawater in all four habitats is severely polluted and the total N, NO3-N, total phosphate, Cd, Pb, and COD are well over the Chinese national class IV level. The high level of organics (chemical oxygen demand and soil organic matter) and nutrients (nitrate nitrogen) has a significant positive influence (P <0.05) on the density and biomass of macrobenthos but a negative influence (P <0.05) on the diversity of the macrobenthos community. Despite the fact that the levels of organics and nutrients were also high in the mangrove habitat, the species biodiversity was also the most abundant of the four investigated habitats. This suggests that mangrove habitats have a remarkable positive effect on maintaining biological diversity compared to other habitats. Therefore, we suggest that efforts should be made to strengthen the protection of mangrove forests to maintain their biological diversity and promote a healthy ecological system. This article is protected by copyright. All rights reserved.
In the last decade, anthropogenically impacted (partially destroyed) spawning habitats of Atlantic salmon and anadromous brown trout have been restored in Western Norway. Mitigation measures have consisted of artificial gravel dumping and the restoration of fluvial processes induced by the removal of weirs. Reproduction enhancement has been documented in most cases, but the durability of restoration actions varied due to the flush out of spawning gravel in some cases. The aim of the present study was to evaluate the application of step-backwater modelling for a bimodal analysis of spawning suitability during low-flow conditions and bed stability during high-flow conditions. A successful model would provide a management tool to reach a longer durability of spawning restoration measures. Five different study sites were selected: three were classified as ´lake outlet´ and two as ´river´ sites. We performed a detailed analysis of the Froude number (-), cross sectional flow velocity (ms-1), and bottom shear stress (Nm-2). This allowed site specific power functions to be established in relation to discharge variations from 10 m3s-1 to 250 m3s-1. Friction slope Sf was determined as the trigger factor for both habitat suitability (Sf <0.05) and bed stability (Sf <0.002). Within the framework of a conceptual model (FSA) for discharge related spawning habitat restoration, flow-velocity exhibited better performance in addressing habitat suitability compared to the Froude number. Moreover, it was found that the consideration of geological long term and macroscale processes for artificial gravel dumping is recommended, including the application of the "critical discharge for spawning gravel". The increase in active width for ´lake outlet´ sites and the self-forming implementation of secondary channels in ´river´ reaches must be highlighted as optional restoration features. This article is protected by copyright. All rights reserved.
The Valdivian Rainforest Eco-region in Chile (35° - 48° S) has a high conservation priority worldwide. These forests are also keys for social welfare due to their supply of timber as well as ecosystem services. Forests in the Eco-region have been extensively converted to fast growing Pinus radiata and Eucalyptus spp. plantations for timber production promoted by public policies and timber companies. This study describes the results of detailed measurements of hydrology and streamwater chemistry in eight small watersheds in south central Chile, subjected to replacement of native temperate rainforest by exotic Eucalyptus plantations. In this system, watersheds have streamside buffers of native forest (SNFW) with varying widths. Results indicate that retention of SNFW counteracts hydrologic effects of Eucalyptus plantations, which are widely known to reduce water yields. A 1.4% rate of increase of the runoff coefficient for each meter of increase of SNFW was observed. In addition, a decrease in the concentrations of total nitrogen, dissolved inorganic nitrogen (DIN), nitrate- N and different sized fractions of particulate organic matter were found in streams draining these plantations as a function of increasing SNFW. Streamside buffer widths of 17-22 m for total nitrogen and DIN concentrations, and ≥36 m for sediments were required to provide comparable values to reference watersheds (100% native forest). The findings from this study suggest that SNFW may significantly reduce adverse effects from exotic-species forestry plantations on water provision in an area of south central Chile where exotic forest plantations are rapidly expanding. This article is protected by copyright. All rights reserved.
We investigated the impact of the 2011 severe drought on summer evapotranspiration (ET) and energy partitioning of a managed Old World bluestem grassland in the Southern Great Plains and compared the results with those from 2010, a hydrologically wet year. Measurements of CO2, latent heat (LE), and sensible heat (H) fluxes were made using an eddy covariance flux tower. In 2010, the total precipitation received during the summer months (June-August) was 82% above the 9-yr average precipitation and in 2011, it was only 8% of the 9-yr average precipitation. The amount of net radiation (Rn) available at the surface was higher in the wet year (54.3% of the incident radiation) compared with the drought year( 41.1% of the incident radiation). In 2010, LE consumed the majority of available energy resulting in a high evaporative fraction (EF). In 2011, less energy was converted to LE as soil moisture remained low, which also resulted in reduced plant growth. Thus, the energy partitioning in 2011 was dominated by H. Significant differences in bulk canopy conductance (Gs) were also observed between the two years. In both years, Gs was linearly correlated with soil volumetric water content in the top 4 cm of the soil profile. The gross primary production (GPP) was linearly correlated to ET. The water use efficiency (WUE) was 2.63 g C Kg-1 of water in 2010 and 0.69 g C Kg-1 of water in 2011. Results from this study showed that, in semi-arid grasslands, the ET and energy balance are strongly affected by water availability. This article is protected by copyright. All rights reserved.
The Brazilian Cerrado is recognised as one of the most threatened biomes in the world, as the region has experienced a striking change from natural Cerrado vegetation to intense cash crop production. This paper reviews the history of land conversion in the Cerrado and the development of soil properties and water resources under past and ongoing land use. We compared soil and water quality parameters from different land uses considering 80 soil and 15 water studies conducted in different regions across the Cerrado to provide quantitative evidence of soil and water alterations from land use change.
Following the conversion of native Cerrado, significant effects on soil pH, bulk density, and available P and K for croplands and less-pronounced effects on pastures were evident. Soil total N did not differ between land uses because most of the sites classified as croplands were nitrogen-fixing soybeans, which are not artificially fertilised with N. In contrast, water quality studies showed nitrogen enrichment in agricultural catchments, indicating fertiliser impacts and potential susceptibility to eutrophication. Regardless of the land use, P is widely absent because of the high-fixing capacities of deeply weathered soils and the filtering capacity of riparian vegetation. Pesticides, however, were consistently detected throughout the entire aquatic system. In several case studies, extremely high peak concentrations exceeded Brazilian and EU water quality limits, which were potentially accompanied by serious health implications. Land use intensification is likely to continue, particularly in regions where less annual rainfall and severe droughts are projected in the northeastern and western Cerrado. Thus, the leaching risk and displacement of agrochemicals are expected to increase, particularly because the current legislation has caused a reduction in riparian vegetation. We conclude that land use intensification is likely to seriously limit the Cerrado's future regarding both agricultural productivity and ecosystem stability. Because only limited data are available, we recommend further field studies to understand the interaction between terrestrial and aquatic systems. This study may serve as a valuable database for integrated modelling to investigate the impact of land use and climate change on soil and water resources and to test and develop mitigation measures for the Cerrado. This article is protected by copyright. All rights reserved.
The variability of coloured dissolved organic carbon (CDOC) in ten seepage and humic lakes was studied in an attempt to find out whether the morphometry of lake bodies and their catchment characteristics influence the studied factor during the ice-free season. The study was carried out in two consecutive years differed with annual sum of precipitation. Using an absorption coefficient at 320 nm as a proxy of CDOC content, and a coefficient of variation as a measure of its variability, we correlated these to lake and catchment features. The results showed that out of 11 studied characteristics, two (maximum and mean depth of the lake) were negatively correlated (−0.85 and −0.78, P < 0.01) and three (catchment size, drainage ratio and Schindler ratio) were positively correlated (0.64, 0.73, P < 0.05; 0.86, P < 0.01) to the studied variable. We have hence concluded that: (1) in more shallow lakes with greater catchment size, more intense mechanism of DOC loss exist during the summer, in contrast to deeper lakes with thermal stratification; (2) precipitation has a strong influence on CDOC inter-annual and seasonal variability, particularly in shallow lakes with high forest cover in their catchments. Copyright © 2014 John Wiley & Sons, Ltd.
Evapotranspiration (ET) dominates water fluxes in arid and semiarid ecosystems. The partitioning of ET into transpiration (T) and evaporation (E) has drawn increasing attention, particularly with respect to quantifying the control of shrub cover on water budget studies. The main objective of this study was to simulate the effects of shrub coverage spatial patterns on water partitioning into T and E and its relation to the simulation cell sizes. Correlation lengths of spatially distributed shrub cover in fine resolution grid cells were used to distinguish spatial patterns (i.e. patchiness) of shrub distributions. We then aggregated the fine resolution grid cells into larger cells of various hierarchies, calculated the potential T of each large cell as a portion of potential ET in the aggregated cell, and simulated the partitioning of actual ET into T and E. Results illustrated that simulated T increases with aggregated cell size, while E rate and total E do not change significantly (i.e. T/ET increases with aggregated cell size). The spatial distribution of shrub pattern influences the partitioning of ET: T increases with decreasing correlation length of shrub spatial pattern. Significant differences in T/ET are linked to the different correlation lengths, as a result of the highly non-linear relationship between potential T and % shrub cover, which indirectly take into account subsurface lateral flows in the root zone. Copyright © 2014 John Wiley & Sons, Ltd.
Streamflow variability, natural and human induced, has been suggested as a driver of life history differences among freshwater fish populations. During 1 year, we collected bimonthly and fortnightly samples from four populations of Iberian barbel, inhabiting permanent and temporary Mediterranean rivers with non-regulated and regulated flow regimes. We analysed data for fish age, growth and reproduction to (i) compare barbels' life cycles between permanent and temporary non-regulated rivers; (ii) assess the effect of two types of flow alteration in these traits; and (iii) identify flow variables significantly related with growth and reproductive cycles. Regional differences were related with the age of first maturation, growth rate and timing and duration of the reproductive season. Flow regulation promoted a decrease of fish growth rates, condition and gonad activity and an increase of maximum length and longevity. Seasonal variation of growth and gonad maturation were related with temperature and streamflow components. This study offers a multi-regional perspective of the relationship between fish biological cycles and streamflow variability, providing water resource managers with needed perspective about the effect of anthropogenic alteration of streamflow magnitudes. Copyright © 2014 John Wiley & Sons, Ltd.
The hyporheic zone bears key hydro-ecological functions such as hydrological connectivity of surface and groundwater ecosystems and biogeochemical regulation of substance dynamics. These functions are controlled by the sediment permeability that in turn is affected by biological and physical clogging. A number of conceptual models have been developed on the interactions and feedbacks between these functionalities; surprisingly, comprehensive field data are scarce. Thus, the aim of this study was to assess these functions and their vulnerability along a stressor gradient of nutrient and fine-sediment input at riffle scale. Three sampling sites along the Kharaa River (Northern Mongolia) were selected that represented conditions from being unaffected, affected by biological clogging and impaired by physical clogging. A significant impact on the hydrological connectivity was detected, as the vertical downward flux and the solute penetration depth decreased along the reaches. Simultaneously, the heterogeneity in biogeochemical patterns and the vertical extent of the oxygen gradients declined. Whilst biological clogging was apparently unstable and the biofilm supported the hyporheic organic carbon pool, it revealed to affect the two functions to a lesser extent when compared with physical clogging. In contrast, physical clogging seemed to be more permanent and restricted microbial metabolism to the uppermost centimetres, thus decreasing the active sediment depth. Moreover, fine-sediment particles enhanced the sediment surface area, thereby creating a high respiration potential that resulted in high values of community respiration and subsequent oxygen depletion. Concluding, the control of fine-sediment emissions has to be a priority issue in river restoration and catchment management. Copyright © 2014 John Wiley & Sons, Ltd.
Summer water temperatures are rising in many river systems in North America, and this warming trend is projected to intensify in the coming decades. Cold-water fish may alleviate thermal stress in summer by aggregating in discrete cold-water plumes that provide thermal refuge from high ambient river temperatures. Reliance on cold-water thermal refugia is expected to increase in a warming climate, and many river reaches already lack suitable thermal refugia as a result of an absence of thermal diversity. A comprehensive fish management strategy could proactively address this imminent threat to cold-water fish populations across North America by preserving existing thermal refugia, augmenting thermal anomalies to improve performance as refugia, and creating new thermal refugia in uniformly warm river reaches. We provide practical recommendations on how these measures can be accomplished based on insight derived from recent research focused on the Miramichi River, New Brunswick. Opportunities include limiting land use change, construction aggregate extraction (e.g. sand and gravel pits), and groundwater pumping/consumption. Existing thermal anomalies can be enhanced by controlling advective thermal mixing between cold-water tributaries and the river mainstem flow, installing riparian shading, and adding temporary structures for protection from avian predators. New refugia can be created by temporarily pumping groundwater to discrete points within the river during periods of thermal stress. These concepts are discussed in the context of a comprehensive thermal refugia management strategy. Copyright © 2014 John Wiley & Sons, Ltd.
Land use and land cover changes are important issues globally resulting in changing hydrological and ecological conditions. In addition to field sampling and measurements, we applied a model cascade comprising an ecohydrological model and a species distribution model. We developed five land use scenarios (three deforestation and two afforestation scenarios) for our Chinese study basin in the Poyang lake area. In detail, we assessed the impact of land use changes on the hydrologic regime and stream macroinvertebrate distributions for the most likely deforestation scenario.
Simulated deforestation scenarios result in higher streamflow and surface runoff compared with the base model. The spatial distribution of stream macroinvertebrates, a group of organisms well known as water quality indicators, was modelled to describe the effect of the changing environmental conditions on the freshwater ecosystem. For the deforestation scenario, species richness was reduced, and the occurrence of the stonefly Togoperla sp. decreased considerably. Copyright © 2014 John Wiley & Sons, Ltd.
An important issue in lake and reservoir management is to prevent algal proliferation and its problematic symptom: the algal blooms that deteriorate water quality and ruin its use. The aim of this study was to obtain a predictive model able to perform an early detection of algal abnormal proliferation using as a predictor the chlorophyll a (Chl a) concentration of previous days. For this purpose, some biological parameters (phytoplankton species expressed in biovolume) in addition to the most important chemical and physical–chemical parameters were considered. The implementation of the statistical learning method known as support vector machines (SVMs) allowed us to predict the Chl a concentration, one of the most frequently used estimators of algal biomass, and to study its evolution in the Trasona reservoir (Principality of Asturias, Northern Spain). In the first place, the main goal was to obtain the dependence relationship of chlorophyll concentration as a function of not only several chemical and physical–chemical variables but also the biological ones. This dependence relationship was useful in setting the significance order of the variables involved in the Chl a prediction. Secondly, a model for forecasting the algal abnormal proliferation is obtained. The agreement between experimental data and the model confirmed the good performance of the latter. Finally, conclusions of this innovative research work are exposed. Copyright © 2014 John Wiley & Sons, Ltd.
Snow cover is an important control in mountain environments and a shift of the snow-free period triggered by climate warming can strongly impact ecosystem dynamics. Changing snow patterns can have severe effects on alpine plant distribution and diversity. It thus becomes urgent to provide spatially explicit assessments of snow cover changes that can be incorporated into correlative or empirical species distribution models (SDMs).
Here, we provide for the first time a with a lower overestimation comparison of two physically based snow distribution models (PREVAH and SnowModel) to produce snow cover maps (SCMs) at a fine spatial resolution in a mountain landscape in Austria. SCMs have been evaluated with SPOT-HRVIR images and predictions of snow water equivalent from the two models with ground measurements. Finally, SCMs of the two models have been compared under a climate warming scenario for the end of the century.
The predictive performances of PREVAH and SnowModel were similar when validated with the SPOT images. However, the tendency to overestimate snow cover was slightly lower with SnowModel during the accumulation period, whereas it was lower with PREVAH during the melting period. The rate of true positives during the melting period was two times higher on average with SnowModel with a lower overestimation of snow water equivalent.
Our results allow for recommending the use of SnowModel in SDMs because it better captures persisting snow patches at the end of the snow season, which is important when modelling the response of species to long-lasting snow cover and evaluating whether they might survive under climate change. Copyright © 2014 John Wiley & Sons, Ltd.
Snowmelt from forested, mountainous environments in the western United States is a critical regional water resource for streamflow and ecological productivity. These landscapes are undergoing rapid changes from the combined effects of forest fires, insect infestation and climate change. Numerous observational studies demonstrate that trees control snowpack accumulation and ablation over scales of tens of metres. Representing forest heterogeneity in models is important for understanding how changes in climate and vegetation cover affect the snowpack; yet, many snow models simplify a forest into two categories: canopy covered and non-canopy covered. We combine existing parameterizations of mass and energy fluxes within a new three-dimensional framework informed by Airborne Laser Swath Mapping (ALSM)-derived canopy maps and evaluated with ALSM-derived snow depth maps to explicitly simulate snow cover in relation to heterogeneous canopy. Model results capture much of the observed snow variability depicted in the 1-m ALSM-derived snow depth maps. Observations and modelled results identify open areas <15 m from tree canopies as having more snow and more snow variability than areas >15 m from tree canopies, and modelled results predict that open areas <15 m from tree canopies have 30–40% more net snow water input than areas that are underneath tree canopies and 10–25% more net snow water input than areas that are >15 m from tree canopies. Furthermore, 1-m simulations give higher estimates for net snow water input than coarser resolution simulations, mainly in areas with fewer trees. These results suggest the importance of explicitly representing canopy edges in snow models. Copyright © 2014 John Wiley & Sons, Ltd.
Cloud deposition can contribute a significant amount of water and elements to montane forests and thus play an important role in the hydrological and biochemical cycles of these ecosystems. However, elevational pattern in cloud and throughfall input to forest ecosystems and the associated chemical element fluxes are poorly understood so far. We studied gross precipitation, throughfall and cloud water deposition, and the associated fluxes of elements (N, P, Ca, K, Mg and Na) in five mature stands of Norway spruce along an elevation transect from lowlands to the alpine treeline (420–1060 m) at Mt Brocken (Harz Mountains, Germany). We tested the hypotheses that water input increases with elevation despite a reduction in intercepting plant surfaces, leading to higher inputs of nitrogen and other elements to high-elevation forests than in lower-elevation stands. Gross precipitation (only snow-free period) rose by 75% towards the treeline, but water input with throughfall increased by 350% because of a large increase in cloud water deposition (from 2 mm at 420 m to 160–200 mm at 1000 m in the study period). Element fluxes with gross precipitation were not uniformly related to elevation across all six elements. However, element fluxes via throughfall showed a positive correlation with elevation for all elements. Thus, the upper montane spruce forests received ~50–150% higher atmospheric inputs of base cations and inorganic N and ~200% higher P inputs than lower-elevation forests. We conclude that elevation does have a large influence on the atmospheric water and element inputs in temperate mountain forests. Copyright © 2014 John Wiley & Sons, Ltd.
Climate variability and/or change control/s the local hydrologic cycle and consequently forest perturbations such as wildfires and bark beetle outbreaks. This case study addresses the following concerns: (a) the long-term trends in precipitation, potential and actual evapotranspiration, run-off, soil moisture content, number of wildfires, burned area, and bark beetle outbreaks and (b) the manner in which the fire occurrence, fire size, and beetle outbreaks are related to these hydrologic variables and multi-decadal climate indices in Mexico's north-western temperate forests. Using the daily measurements of precipitation and evaporation as well as the modelled interception loss and evapotranspiration, run-off and soil moisture content were computed using a mass balance budget model. Mann–Kendall, linear regression, and autoregressive integrated moving averaging techniques were used to evaluate the statistical significance of monotonic trends on the first momentum for the monthly and annual time series of hydro-climate (1945–2007), forest wildfire (1970–2012), and bark beetle infestation (1999–2012) data. The statistical analysis showed time series to be stationary in the first momentum. Recent wildfires and bark beetle population eruptions are associated with low modelled dry season soil moisture over several years. Drought spells, frosts, and pulses of high area burned, and high number of wildfires preceded acute discrete bark beetle population eruptions. Copyright © 2014 John Wiley & Sons, Ltd.
Many projects have been undertaken to restore urban rivers in arid regions. At the same time, passive discharge of urban water sources has stimulated redevelopment of wetlands and riparian forests along stretches of dewatered rivers. In Phoenix, Arizona, for example, some segments of the dewatered Salt River have been actively restored by planting and irrigation, whereas others have revegetated in response to runoff from storm drains and effluent drains. Our research documents how biotic communities differ between these actively restored and 'accidentally' restored areas, and between wetter and drier urban reaches. We addressed these objectives with a multi-taxa, multi-season sampling approach along reaches of the Salt River. We quantified plants using cover estimates in quadrats, birds using fixed radius, point-count surveys, and herpetofauna (amphibians and reptiles) using visual-encounter surveys. One notable finding was that wetland plants had greater richness and cover at accidentally restored sites compared with actively restored, dry urban, and non-urban reference sites. Birds and herpetofauna, however, were most species-rich at actively restored and non-urban reference sites, and riparian birds were more abundant at sites with perennial flows compared with ephemeral reaches. From a landscape perspective, the range of management approaches along the river (including laissez-faire) is sustaining a diverse riparian and wetland mosaic. Urban water subsidies are sustaining freshwater forests and marshlands, the latter a regionally declining ecosystem. In urbanized rivers of arid regions, mapping and conserving perennial stream flows arising from stormwater and effluent discharge can be an important complement to active restoration. Copyright © 2014 John Wiley & Sons, Ltd.
Large portions of Earth's terrestrial surface are arid or semiarid. As in these regions, the hydrological cycle and the vegetation dynamics are tightly interconnected, a coupled modelling of these two systems is needed to fully reproduce the ecosystem behaviour. In this paper, the performance of two parsimonious dynamic vegetation models, suitable for the inclusion in operational ecohydrological models and based on well-established but different approaches, is compared in a semiarid Aleppo Pine region. The first model [water use efficiency (WUE) model] links growth to transpiration through WUE; the second model [light use efficiency (LUE) model] simulates biomass increase in relation to absorbed photosynthetically active radiation and LUE. Furthermore, an analysis of the information contained in MODIS products is presented to indicate the best vegetation indices to be used as observational verification for the models. Enhanced Vegetation Index is reported in literature to be highly correlated with leaf area index, so it is compared with modelled LAImod (rWUE model = 0.45; rLUE model = 0.57). In contrast, Normalized Difference Vegetation Index appears highly linked to soil moisture, through the control exerted by this variable on chlorophyll production, and is therefore used to analyze LAI*mod, models' output corrected by plant water stress (rWUE model = 0.62; rLUE model = 0.59). Moderate-resolution imaging spectroradiometer Leaf Area Index and evapotranspiration are found to be unrealistic in the studied area. The performance of both models in this semiarid region is found to be reasonable. However, the LUE model presents the advantages of a better performance, the possibility to be used in a wider range of climates and to have been extensively tested in literature. Copyright © 2014 John Wiley & Sons, Ltd.
Accurate estimates and partition of evapotranspiration (ET) are difficult but critical for understanding terrestrial ecosystem processes and primary productivity. A multi-year, multi-technique study including the catchment water balance (12 years), a semi-empirical ET model (9 years), eddy covariance (9 years), canopy water balance (1 year) and sap flow (1 year) techniques was conducted to measure ET and its components within an intact forested watershed in the subtropical region of southern China. Over a 9-year period, the estimates of annual ET using the catchment water balance, eddy covariance and semi-empirical ET model techniques were in close agreement, averaging 809.9 ± 62.8, 803.8 ± 36.6 and 801.6 ± 46.9 mm per year, respectively, amounting to an average of approximately 50.2% of the mean annual precipitation. Qualitative similarities in seasonal and diurnal variation were observed between the sap flow and eddy covariance estimates of water flux. Sap flow estimates of transpiration were approximately 60.2% of the annual ET estimated with the eddy covariance technique. Interception evaporation was 31.7% of the total ET and was demonstrated to be a main contributor of total evaporation. Soil evaporation was calculated to be approximately 8.1% of the total annual ET and 4.7% of the annual precipitation. Furthermore, daytime transpiration exhibited a logarithmic increase with increases in the vapour pressure deficit (VPD) on daily scale in both the wet and dry seasons, and tended to level off when the VPD was >1 kPa because of the stomatal regulation of transpiration. Correspondingly, nighttime sap flow amounted to an average of approximately 6% of the total daily sap flow, and no significant correlations with the VPD, air temperature or relative humidity were found. Essential differences among the mechanisms of evaporation and transpiration were demonstrated, suggesting that soil evaporation is primarily a climate-driven process, with air temperature and wind speed as the predominant driving forces. Copyright © 2014 John Wiley & Sons, Ltd.
Dust deposition lowers the albedo of snow and can significantly alter snowpack energy balance. Investigation of aeolian dust deposition in the mountains of the western U.S. has shown that these effects advance the timing of snowpack melt and spring runoff across much of the region. These studies have primarily focused on alpine snowpacks with little to no overstory vegetation. To evaluate the impacts of aeolian dust on ecohydrological processes in forests, we conducted a manipulative experiment in a subalpine conifer forest in Utah's Wasatch Mountains. During the spring of 2010–2012, we added dust to the snow surface in forested plots every 1 to 2 weeks, roughly doubling the natural dust loading. We then measured snowpack ablation in control and dust addition plots, along with below-snowpack and warm season soil temperature (Tsoil), soil water content (θ), litter decomposition rate (D), soil respiration rate (Rs), and tree xylem water potential (ψ). Differences in ablation between control and dust addition plots were similar in magnitude to differences associated with the canopy structure of the forest. Seasonal patterns in Tsoil and θ were similar between dust treatments and canopy structure groups. D, Rs, and ψ varied little between dust treatments, but there were significant differences between years. During our 3-year study, an unusual level of interannual variability in snowfall had the greatest effect on the soil environment and ecosystem processes. The effects of aeolian dust on snowpack mass and energy balance in our forest were slightly smaller than those associated with canopy structure. Copyright © 2014 John Wiley & Sons, Ltd.
Along subtropical and tropical coastlines, Tillandsia usneoides L. (Spanish moss) can heavily cover tree crowns, altering the volume, timing and chemical composition of rainwater reaching soils as throughfall. It is well-established that throughfall amount, dissolved ion and dissolved organic matter (DOM) enrichment, as well as the chemical character of DOM, can influence a host of ecological processes – e.g. litter decomposition and fine root patterns. However, no study known to the authors has holistically examined the water storage capacity, dissolved ions and DOM derived from T. usneoides. This study examined 60 T. usneoides samples from two maritime live oak (Quercus virginiana Mill.) forest settings for water absorbency, maximum water storage capacity, dissolved solutes (Na+, NH4+, K+, Mg2+, Ca2+, F−, Cl−, NO3−, PO43−, SO42−, dissolved organic carbon, total dissolved nitrogen) and DOM optical properties using ultraviolet-visible and fluorescence spectrophotometry. Thirty samples were collected from each study site: downtown Savannah (SAV) and St. Catherine's Island (SCI), GA, USA. Results show that T. usneoides coverage can increase canopy water storage more markedly (up to 3 mm) than most other epiphyte communities, tree leaf forms or bark structures previously studied. Ion wash off/leaching was greater for N species from SAV samples; yet, base cation macronutrients (Mg2+, Ca2+) and sea salts (Na+, Cl−) were more enriched from SCI samples. Spectrophotometry revealed that T. usneoides leachates contained DOM with low-specific UV absorbance at 254 nm per unit carbon (SUVA254) and high percentage of protein-like fluorescent material compared with literature values for other throughfall and vegetation leachates. In other natural waters, these optical characteristics indicate highly biolabile DOM, suggesting that T. usneoides DOM may also be highly biolabile (i.e. highly relevant to soil microbial functions, like mineralization). Cluster analysis linked fluorescent DOM (FDOM) to ion concentrations of primarily anthropogenic source (F−, SO42−). Correlation analyses including both sites' data indicated that log-transformed FDOM intensities indirectly relate (p < 0.01, r = −0.5) – and enrichment of major sea salt ions directly relate (Na+: p < 0.000001, r = 0.83; Cl−: p < 0.000001, r = 0.80) – to T. usneoides maximum water absorbency. Copyright © 2014 John Wiley & Sons, Ltd.
Irrigated agriculture in south-east Australia has increased water availability to native flora and fauna by creating artificial open-water habitats and raising water tables across the landscape. However, it has also caused loss of floodplain woodlands and reductions in the frequency, extent and duration with which floodplains are inundated, resulting in habitat degradation. The effects of such changes on floodplain fauna such as woodland birds are poorly understood. This paper explores the hypothesis that water availability at landscape scales influences woodland bird density. It examines the density of selected bird species in remnant floodplain woodlands of two contrasting regions within the same drought-affected catchment and tests two predictions: (1) Increased water availability in the landscape resulting from greater surrounding irrigation land use intensity will be associated with higher bird density in floodplain woodlands and (2) lower flood frequency within a site will be associated with lower bird density in floodplain woodlands. Two contrasting levels of the effect of irrigation land use intensity on woodland bird density were found: firstly, a broad-scale positive relationship between irrigation water availability and bird density at a regional scale and, secondly, a within-region negative effect of very high intensity irrigation land use upon bird density. We suggest that these effects are mediated through the influence of water and land use on both food and habitat availability, and research is needed focusing on links between flood regime, vegetation condition and bird density in the absence of intensive irrigation land use to ascertain the importance of flooding to woodland birds. © 2014 Commonwealth of Australia. Ecohydrology © 2014 John Wiley & Sons, Ltd.
Transpiration in plants is a critical eco-hydrological process linking plant–atmosphere interactions and is very important in the arid environment because the surface runoff is of no practical importance in terms of the hydrological budget. Investigations on transpiration in arid land species under natural conditions have not been comprehensive, however. We present here the long-term transpiration of Haloxylon ammodendron, a dominant species growing at the southern edge of the Gurbantünggüt Desert, China, during the growing seasons from 2009 to 2011 using up-scaled sap flow monitoring with the thermal dissipation probe method. The sap flux density averaged 1·86 m3 m−2 day−1 during the measurement period for 3 years, and the transpiration per day based on ground area (EC) ranged from 0·05 to 0·27 mm day−1 and averaged 0·14 mm day−1, lower than that of other species largely because of the extremely arid environment. The canopy stomatal conductance averaged 16·75 mmol m−2 s−1 and maintained a constant low value under high vapour pressure deficit, which is essential for maintaining low transpiration compared with other species. High seasonal variation in EC was exhibited because of the plant's response to environmental factors at seasonal scale. EC showed much less variability at annual scale, however, because of the constant balance between the evaporative demand of the atmosphere and plant factors. These results contribute to a better understanding of the plant's transpiration in arid land and its response and adaptation to climatic changes at annual and seasonal scales. Copyright © 2014 John Wiley & Sons, Ltd.
Within dynamic alluvial riverine corridors, abandoned channels form and experience hydrogeomorphic processes that are distinct from similar elevation surfaces along active channels. Compared with the relatively well-studied role of fluvial disturbance on floodplain plant communities along active channels, the drivers of plant diversity and community dynamics along terrestrializing abandoned channels have received much less attention. In this study, we addressed several related questions within the context of the Sacramento River (California, USA): (1) Do abandoned channels host different plant species compared with the surrounding floodplain? (2) How do plant communities vary among abandoned channels in relation to time since cutoff and disturbance regime? (3) Do understory plant species within an abandoned channel display distinct zonation along a disturbance gradient from the wetted edge laterally to upland areas? Our results show that although species richness is similar to floodplain sites, abandoned channels support a different species pool, notably due to presence of more wetland-associated species, and this contributes to increase biodiversity within the fluvial corridor. We found substantial shifts in species composition that occurred since channel abandonment, likely related to decreases in the strength of hydromorphic disturbance through time. Lastly, we found that lateral environmental gradients within abandoned channel sites were significant, although much weaker drivers of understory vegetation patterns than typically found along active channel banks. These results argue for a management approach that preserves and promotes natural processes of channel migration and sediment dynamics. Copyright © 2014 John Wiley & Sons, Ltd.
Although it is recognized that streamside vegetation can reduce river bank erosion, the relative effectiveness of forest versus grassland has been unclear. To compare erosion resistance of the two vegetation types, we studied the free-flowing Elk River in British Columbia, Canada from 1993 to 2014, including major floods in June 1995 and 2013. Interpretation of aerial photographs from 1994 and 2000 were used to examine the correspondence between floodplain vegetation and the extent of channel change after the 1995 flood. Along a 23 km reach with alternating forest and grassland, 15 locations displayed substantial change as the river moved a channel width (45 m) or more with meander migration, or up to 200 m with channel avulsion. All ten locations with major change (>75 m) occurred where the floodplain zones were occupied by grasslands, sometimes with small shrubs. In contrast, channels flanked by forest were minimally altered (<15 m), and deciduous (black cottonwood, Populus trichocarpa) or mixed deciduous-coniferous groves were effective at resisting erosion. Some changes accompanied the 1995 flood and further changes followed as the destabilized banks were vulnerable to smaller floods in 1996 and 1997. Providing another comparison, a position that was dramatically scoured in 1995 when it was grassland had subsequent cottonwood colonization, and the 4 m trees resisted erosion from the 2013 flood. Thus, trees were more resistant than grassland to flood-associated bank erosion. We recommend that riparian forests should be conserved to provide bank stability and to maintain an equilibrium of river and floodplain dynamics. Copyright © 2014 John Wiley & Sons, Ltd.
Hydraulic redistribution plays a relevant role in the water relations of trees in climates with alternation between warm/dry and cold/wet periods. We aim to illustrate the ability of Mediterranean deep-rooted rainfed olive trees to maintain transpiration during the hot dry season and to redistribute soil water through roots, tending to temporarily homogenize soil moisture vertically. Sap flow was monitored by the heat field deformation method for 2·5 years in the stem, lignotuber, medium and shallow roots of an olive tree tracing the long-term variations in the patterns of transpiration, water uptake and hydraulic redistribution. During the same period, soil water content and meteorological data were measured and related to sap flow. Results show that hydraulic redistribution within the rhizosphere buffers the seasonal and long-term water deficits. Under high evaporative demand during the dry summer, the deeper roots connected to stem through the lignotuber uptake water supporting transpiration needs and reducing the intensive drying of the upper soil layers. Copyright © 2014 John Wiley & Sons, Ltd.
The influence of catchment attributes has been examined to find out whether variations in water quality indicators [electrical conductivity (EC), pH, turbidity, dissolved oxygen (DO), total dissolved solid (TDS), total nitrogen (TN), dissolved organic nitrogen (DON), dissolved inorganic nitrogen (DIN), temperature and nitrogen] could be explained by them for 24 wetlands in west Japan. Urban areas (%) were positively (P ≤ 0.05) correlated with EC (r = 0.67), TDS (r = 0.69), TN (r = 0.92), DON (r = 0.60), [NH4+] (r = 0.47) and with [NO2−] (r = 0.50). Forest areas (%) were inversely (P ≤ 0.05) correlated with EC (r = −0.62), TDS (r = −0.68), TN (r = −0.68) and [NH4+] (r = −0.55) and with DON (r = −0.43). Agricultural area (%) was positively (P ≤ 0.05) correlated with EC (r = 0.40), TDS (r = 0.45), TN (r = 0.44) and [NH4+] (r = 0.56) and with both areas (%) of grey lowland soil (r = 0.60) and diluvial sand (r = 0.58). Area (%) of regosol was positively correlated with DO (r = 0.42) but inversely with DON (r = −0.44, P ≤ 0.05). Rhyolite was positively (P ≤ 0.05) correlated with the TN (r = 0.46) but inversely with DON (r = −0.49) and [NH4+] (r = −0.47). Regression models were developed for the water quality indicators including EC (r2 = 0. 62), (r2 = 0.90), (r = 0.52), TN (r = 0.86), DIN (r2 = 0.74) and DON (r2 = 0.54) at 0.01 ≤ P ≤ 0.05. In the models, no significant contribution has been observed for catchment geometric features of the wetlands on water quality indicators. Copyright © 2014 John Wiley & Sons, Ltd.
The impounding of the Zambezi River by Kariba dam has regulated the river discharge of the Middle Zambezi river. This has been implicated in the failure of regeneration of Faidherbia albida in the downstream flood plain. This study aimed (1) to assess the effect of the altered flow regime of the river on the establishment and growth of F. albida on the Middle Zambezi floodplain and islands and (2) to test the potential of dendrochronology in detecting the age and long-term growth rates of F. albida in response to flow regime.
Results indicated an uneven age distribution of F. albida stands on relatively 'new islands', dominated by young trees, while the floodplain and the 'old island' exhibited an even-aged stand but with a lack of regeneration, and a dying-off of older trees. The lack of F. albida establishment on the floodplain was linked to the decreased occurrence of flooding events, associated with a decrease in alluvial deposits, soil moisture and groundwater recharge. These effects may be enhanced by impact from browsers on regeneration of trees. Tree-ring analyses revealed the presence of distinct annual growth rings in F. albida and the applicability of dendrochronology for estimating F. albida population dynamics. The trees on the 'new islands' are younger and grow faster than those on the floodplain. Lack of competition and possible favourable moisture conditions suggest beneficial conditions for establishment and growth of the trees on the islands. Copyright © 2014 John Wiley & Sons, Ltd.
The ecological and environmental consequences of large dam projects have received increasing attention in the recent decades. On the basis of daily water-level data, six periods of TM/ETM+ data and a digital elevation model, the eco-hydrological environments and vegetation area of East Dongting Lake, were compared for the years 1995–2011, spanning periods before and after the implementation of the Three Gorges Dam (TGD) in 2003. Vegetation area (including three types: forestry, reed and grass) continuously expanded, and the minimum elevation of vegetation-covered area (VCA) gradually decreased by 0·88 m from 1995 to 2011. Following the implementation of the TGD, the rates of both vegetation expansion (12·3 vs 14·1 km2 year−1) and the lowering of minimum elevation of VCA (3·1 vs 7·9 cm year−1) increased rapidly. Monthly water level decreased considerably from July to November, and annual submergence duration at elevations of 22–26 and 30 m was considerably decreased after the TGD was implemented. The average maximum submergence duration of VCA was 231 days. Almost equal linear equations describing elevation change from 1995 to 2011 indicated that the minimum elevation of VCA identified via analysis of TM/ETM+ images can be represented by the maximum submergence duration evaluated via daily water level. These data indicate that vegetation colonized the non-vegetation area (including mud beach or water body) more quickly after the implementation of the TGD, due to the drastic changes in eco-hydrological environments such as the decreasing water level and the minimum elevation of VCA. The present methodology might allow faster and more reliable assessment of inundation related landscape impacts on a basin scale and thereby contribute to biodiversity monitoring and policy assessment. Copyright © 2014 John Wiley & Sons, Ltd.
Properly quantifying evapotranspiration (ET) is a critical step in determining water and energy balances, especially in Arctic landscapes where spatial and temporal heterogeneity in soil water content and inundation is pronounced. Although the eddy covariance technique has gained popularity as an approach for estimating ET at aggregate scales, obtaining ET estimates at finer spatial scales remains problematic. Thus, ET is poorly estimated for highly variable tundra landscapes, despite the importance of this process for parameterization and validation of models. To overcome this methodological limitation, we developed an approach to measure diurnal ET by modifying a LI-8100A (LI-COR, Lincoln, NE, USA), a chamber-based instrument typically used for measuring soil CO2 fluxes. To enable the use of the LI-8100A for ET determinations, a calibration method was designed and implemented through laboratory and independent field measurements in Arctic and semi-arid locations. Once calibrated, the instrument was deployed June–September 2013 for diel measurements of ET on the Arctic coastal plain near Barrow, Alaska, USA. We validated the system by comparison to four adjacent plots measured by a LI-6400-09 soil CO2 flux system that was also calibrated to calculate water vapour flux. In conclusion, we determined that with calibration, the LI-8100A can make long-term, high-frequency measurements of ET, even in low flux, continuous-permafrost landscapes. This technique provides an opportunity to assess fine-scale ET and its topographic controls across low-centre and high-centre polygons and to rigorously compare such measurements with aggregate fluxes obtained with eddy covariance. Copyright © 2014 John Wiley & Sons, Ltd.
In semiarid montane regions, spatial patterns of shallow soil moisture (0–5 cm) are expected to depend on vegetation patterns and topographic attributes. In some cases, the vegetation patterns themselves depend on the topography, which makes the interaction of soil moisture, vegetation and topography especially complex. Such is the case in portions of the Colorado Front Range where many south-facing and north-facing slopes are primarily vegetated by mountain mahogany (Cercocarpus montanus) shrubs and ponderosa pine (Pinus ponderosa) trees, respectively. The objectives of this paper are the following: (1) to determine how the presence of a shrub or tree affects the shallow soil moisture on these distinct hillslopes and (2) to understand the main mechanisms through which the vegetation affects the shallow soil moisture. On opposing hillslopes in the Cache la Poudre catchment, soil moisture was monitored for intercanopy, shrub canopy and tree canopy locations. Throughfall, insolation, soil texture and hydrophobicity were also measured to understand the reasons for any soil moisture differences. The results suggest that the shallow soil moisture is more distinct between the canopy and intercanopy locations on the south-facing slope than the north-facing slope. On the south-facing slope, intercanopy locations are less shaded by the nearby canopy because of the shorter stature of the shrubs and the orientation of this hillslope towards the sun. Copyright © 2014 John Wiley & Sons, Ltd.
Summer drought frequency is expected to increase with climate change in forested regions of Europe. To examine the physiological impacts of low soil moisture on Norway spruce [Picea abies (L.) Karst.], we conducted an irrigation experiment in a Norway spruce-dominated forest. We monitored sap flow (Qs), stem circumference and soil water potential (Ψw), measured needle water potential (Ψl), and estimated potential evapotranspiration (PET) in control and irrigated plots. Soil water availability influenced the response of Qs to PET and the impact of Qs on maximum daily stem shrinkage (MDS). The positive relationship between Qs and PET was constrained below a threshold Ψw near −0.3 MPa. MDS was higher beyond this threshold, for a given value of Qs. Higher MDS and lower tree water status (ΔW) were observed at low Ψw in control plants, suggesting the lower water potential of stems' conducting tissues. Stem circumference increase (SCI) was 62% lower in control trees following the irrigation treatment. Slight SCI recovery was observed in these trees in response to early autumn rainfall, which caused ΔW to return to its predrought state. The results demonstrate that low water availability not only reduced Qs, ΔW, SCI, Ψl and increased MDS but also altered their mutual relations. Copyright © 2014 John Wiley & Sons, Ltd.
The North American east coast has experienced significant land-use and climate changes since the beginning of the 20th century. In this study, using the Dynamic Land Ecosystem Model 2.0 driven by time-series input data of land use, climate and atmospheric CO2, we examined how these driving forces have affected the spatiotemporal trends and variability of evapotranspiration (ET) in this region during 1901–2008. Annual ET in the North American east coast during this period was 648.3 ± 38.6 mm/year and demonstrated an increasing trend. Factorial model simulations indicated that climate variability explained 76% of the inter-annual ET variability. Although land-use change only explained 16% of the ET temporal variability, afforestation induced the upward trend of ET and increased annual ET by 12.8 mm/year. Elevated atmospheric CO2 reduced annual ET by 0.84 mm, and its potential impacts under future atmospheric CO2 levels could be much larger than estimates for the historical 1901–2008 period. Climate change determined the spatial pattern of ET changes across the entire study area, whereas land-use changes dramatically affected ET in watersheds with significant land conversions. In spite of the multiple benefits from afforestation, its impacts on water resources should be considered in future land-use policy making. Elevated ET may also affect fresh water availability for the increasing social and economic water demands. Copyright © 2014 John Wiley & Sons, Ltd.
A vast body of literature demonstrated that anthropogenic disturbances such as overgrazing and fire are key drivers of abrupt transition between vegetation types in ecosystems. In this study, we propose that the hydrological context (described in terms of rainfall, evapotranspiration and water yield) is a first-order, primordial determinant of the propensity of ecosystems to undergo transition. This implies that the anthropogenic disturbance is a second-order determinant that is strongly conditioned by the first one. Through the meta-analysis of existing studies, a collection of 685 geo-referenced study cases was organized to study the hydrological characteristics of three climatic regions and three ecosystems that vary in their relation between woody and grassy plants. Thus, humid, sub-humid and dry climatic regions, respectively, receiving >1000, 500–1000 and <500 mm year−1, were studied, and possible transition mechanisms among grasslands/savannas, shrublands and forests were analysed. The results showed that the ecohydrological context determines the probabilities of ecosystems transitions in different climatic regions and the prevalence of alternative transition mechanisms. We showed that transition of forests into other ecosystems is highly improbable in high-precipitation regions, more probable and likely subject to a bi-stable and reversible regime in sub-humid regions, and highly probable and irreversible in dry regions. Factors such as runoff, deep-water drainage, fire, flammable/nonflammable biomass and overgrazing were considered as hypothetical transition mechanisms. As a novel finding, we demonstrate that ecohydrology, as a determinant of transition, is a factor that operates at a hierarchical level higher than that of the human-driven disturbance. A synthetic graphical model was proposed to characterize resilience (the capacity of ecosystems to withstand transition) in the three study climatic regions. Copyright © 2014 John Wiley & Sons, Ltd.
Spatially heterogeneous and temporally variable nutrient concentrations (P, N) in near-surface aquifers are common and are driven by different factors such as climate, topography, vegetation, sediment compositions, and water level fluctuations. Nonetheless, the identification of discrete areas where similar concentrations patterns can be expected is still difficult, especially in patchy systems such as riparian zones of lowland rivers. To address this challenge, a floodplain aquifer of the river Spree (Germany) has been investigated by sampling groundwater with high vertical and horizontal resolutions. Vertical nutrient distributions measured by multi-level samplers with a 10 cm resolution indicate a biogeochemical layering of the aquifer. High concentrations in the upper 2 m can be attributed to a local redox gradient, which is induced by water level fluctuations and biological turnover processes, while the layer below is mainly influenced by medium-scale to large-scale groundwater flow patterns. High concentration in the upper part of the aquifer enforces groundwater sampling with a high horizontal resolution of 3 m from the near-surface groundwater. The results compared with highly resolved elevation and sediment data indicate that geomorphological features and water level fluctuations control the thickness of the unsaturated zone and the redox gradient. The strength of the gradient and the amount of degradable organic matter determine the intensity of nutrient release by chemical reactions and biological turnover. Copyright © 2014 John Wiley & Sons, Ltd.
At the scale of geomorphological units (riffles, pools, and gravel bars), the contribution of the hyporheic zone to the functioning of streams and rivers depends on the hydrological exchanges between surface water and groundwater. These exchanges are largely controlled by sediment structure and texture, which are difficult to assess with classical methods (shovelling and freeze coring). We aimed to evaluate the ability of a non-destructive method, ground-penetrating radar (GPR), to detect sediment structures associated with subsurface biologically active zones in a gravel-bed river. After GPR data acquisition and processing, a three-dimensional reconstruction of a gravel bar permitted the identification of two sediment facies: a cobble/gravel lithofacies denoted as 'coarse' and a sand/gravel lithofacies denoted as 'fine'. We installed piezometers along two longitudinal profiles (each corresponding to a lithofacies identified by GPR) and monitored hydraulic head and temperature for 20 days. Water and sediments were sampled along the two profiles to measure water physicochemistry, sediment characteristics, bacterial abundance and activity, and interstitial invertebrate assemblages. These measurements confirmed that the two profiles were characterized by distinct hydrological flow rates and associated biological activities. Rapid water transport in the coarse profile fuelled the hyporheic zone with organic matter, whereas water and organic matter supplies were lower in the fine profile. Consequently, the higher supply of organic matter in the coarse profile was associated with higher microbial activities and invertebrate density and diversity. Therefore, GPR could be an efficient tool to detect the sediment features playing a key role in hyporheic zone functioning. Copyright © 2014 John Wiley & Sons, Ltd.
Few studies have examined how insect outbreaks affect landscape-level hydrologic processes. We report the hydrologic effects of the invasive, exotic hemlock woolly adelgid (HWA) in a headwater catchment in the southern Appalachian Mountains. The study watershed experienced complete mortality of an evergreen tree species, Tsuga canadensis (L.) Carr. (eastern hemlock), after infestation was first detected in 2003. Hemlock mortality resulted in a ~6% reduction in basal area in the watershed, and this loss was primarily concentrated in riparian zones. We used a paired-watershed approach to quantify changes in water yield and peak stormflow using streamflow data from the infested watershed and a nearby watershed with significantly lower hemlock basal area. We hypothesized that yield would increase shortly after hemlock infestation but decrease over the longer-term. We found that annual yield did not increase significantly in any year after infestation but decreased significantly by 12·0 cm (~8%) in 2010. Monthly yield also decreased after infestation, but changes were limited to the dormant season. The decline in yield is likely to persist as hemlock is replaced by species with higher transpiration rates. Peakflow increased significantly after infestation during the two largest flow events in the post-infestation period. Changes in stormflow during extreme events may have been temporary as another evergreen, Rhododendron maximum, may have mitigated some of the changes after hemlock loss. Thus, streams draining watersheds where eastern hemlock has been lost due to HWA infestation demonstrate permanent reductions in yield and transient increases in peakflow during large-flow events. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.
The world's dams and reservoirs are aging. The ecological effects of a half-century or more of flow regulation and sediment alteration are becoming apparent. What remains of the highly dynamic channel and riparian ecosystem of the Missouri River described by Lewis and Clark has become static. Recent long-term studies have determined that some of the impacts on the Missouri River ecosystem turned out as predicted, such as the failure of cottonwood-dominated riparian forests to successfully establish and survive on a broad scale. Other changes were surprises, such as the effect of disease eliminating a formerly dominant tree species and the appearance of mainstem and tributary deltas affecting channel slope, floodplain hydrology, and vegetation. Restoration of the river's hydrologic and sediment regime has been delayed long enough that the chances of functional ecosystem restoration have been greatly reduced and complicated. Two phases are now needed to attempt to restore the riparian ecosystem: one to repair the effects of post-dam changes (channel incision, bank stabilization) and another to reestablish pre-dam flow and sediment regimes. The prospects for restoration of this valuable ecosystem, rich in history and in goods and services provided to the public, are dim. Time has diminished the chances that restoration or even rehabilitation can be achieved. Copyright © 2014 John Wiley & Sons, Ltd.
Airborne laser scanning systems (Light Detection And Ranging, LiDAR) are very well suited to the study of landscape and vegetation structure over large extents. Spatially distributed measurements describing the three-dimensional character of landscape surfaces and vegetation architecture can be used to understand eco-geomorphic and ecohydrological processes, and this is particularly pertinent in peatlands given the increasing recognition that these landscapes provide a variety of ecosystem services (water provision, flood mitigation and carbon sequestration). In using LiDAR data for monitoring peatlands, it is important to understand how well peatland surface structures (with fine length scales) can be described. Our approach integrates two laser scanning technologies, namely terrestrial laser scanning (TLS) and airborne LiDAR surveys, to assess how effective airborne LiDAR is at measuring these fine-scale microtopographic ecohydrological structures. By combining airborne and TLS, we demonstrate an improved spatial understanding of the signal measured by the airborne LiDAR. Critically, results demonstrate that LiDAR digital surface models are subject to specific errors related to short-sward ecosystem structure, causing the vegetation canopy height and surface-drainage network depth to be underestimated. TLS is shown to be effective at describing these structures over small extents, allowing the information content and accuracy of airborne LiDAR to be understood and quantified more appropriately. These findings have important implications for the appropriate degree of confidence ecohydrologists can apply to such data when using them as a surrogate for field measurements. They also illustrate the need to couple LiDAR data with ground validation data in order to improve assessment of ecohydrological function in such landscapes. Copyright © 2014 John Wiley & Sons, Ltd.
Large areas in the tropics and at mid-latitudes experience pronounced seasonality and inter-annual variability in rainfall and hence water availability. Despite the importance of these seasonally dry ecosystems (SDEs) for the global carbon cycling and in providing ecosystem services, a unifying ecohydrological framework to interpret the effects of climatic variability on SDEs is still lacking. A synthesis of existing data about plant functional adaptations in SDEs, covering some 400 species, shows that leaf phenological variations, rather than physiological traits, provide the dominant control on plant-water-carbon interactions. Motivated by this result, the combined implications of leaf phenology and climatic variability on plant water use strategies are here explored with a minimalist model of the coupled soil water and plant carbon balances. The analyses are extended to five locations with different hydroclimatic forcing, spanning seasonally dry tropical climates (without temperature seasonality) and Mediterranean climates (exhibiting out of phase seasonal patterns of rainfall and temperature). The most beneficial leaf phenology in terms of carbon uptake depends on the climatic regime: evergreen species are favoured by short dry seasons or access to persistent water stores, whereas high inter-annual variability of rainy season duration favours the coexistence of multiple drought-deciduous phenological strategies. We conclude that drought-deciduousness may provide a competitive advantage in face of predicted declines in rainfall totals, while reduced seasonality and access to deep water stores may favour evergreen species. This article has been contributed to by US Government employees and their work is in the public domain in the USA.
The Upper San Pedro River is one of the few remaining undammed rivers that maintain a vibrant riparian ecosystem in the southwest United States. However, its riparian forest is threatened by diminishing groundwater and surface water inputs, due to either changes in watershed characteristics such as changes in riparian and upland vegetation, or human activities such as regional groundwater pumping. We used satellite vegetation indices to quantify the green leaf density of the groundwater-dependent riparian forest from 1984 to 2012. The river was divided into a southern, upstream (mainly perennial flow) reach and a northern, downstream (mainly intermittent and ephemeral flow) reach. Pre-monsoon (June) Landsat normalized difference vegetation index (NDVI) values showed a 20% drop for the northern reach (P < 0·001) and no net change for the southern reach (P > 0·05). NDVI and enhanced vegetation index values were positively correlated (P < 0·05) with river flows, which decreased over the study period in the northern reach, and negatively correlated (P < 0·05) with air temperatures in both reaches, which have increased by 1·4 °C from 1932 to 2012. NDVI in the uplands around the river did not increase from 1984 to 2012, suggesting that increased evapotranspiration in the uplands was not a factor in reducing river flows. Climate change, regional groundwater pumping, changes in the intensity of monsoon rain events and lack of overbank flooding are feasible explanations for deterioration of the riparian forest in the northern reach. Copyright © 2014 John Wiley & Sons, Ltd.
Mining below groundwater tables is increasing globally, yet little is known of how associated large-scale modification of water tables impact functioning of surrounding ecosystems. We used measurements of foliage density (ρF) and sapwood-related sap flow (QS) to assess effects of depth to groundwater on Eucalyptus victrix, a tree species that is common in riparian zones in central and northern parts of Australia.
Foliage density (ρF) varied with season and among sites. Of itself, ρF provided a partial indicator of how trees responded to falling (more than 10 m) and rising (more than 9 m) water tables. Assessment of QS was highly informative. Across all sites, QS was least (90–130 l m−2 sapwood h−1) where groundwater was naturally deep (30 m) or had fallen substantially over the past 4 years (from 8 to 19 m). Fastest rates of QS (>245 l m−2 sapwood h−1) were recorded where groundwater had risen to a depth similar to a site where depth to groundwater remained stable at 6–7 m. Our analyses of daytime and night-time QS emphasize that water use by E. victrix is highly plastic and opportunistic. We discuss how empirical analysis of QS, coupled with a sound understanding of local hydrogeology, can help assess responses in ecosystem function to large-scale modification of groundwater levels – an important issue globally, as well as in Australia. Copyright © 2014 John Wiley & Sons, Ltd.
Since the Water Framework Directive (WFD) implementation, new biological indices based on macroinvertebrates have been developed, mainly focusing on multimetric approaches. This work checks the relationship among several biotic indices [Iberian Biological Monitoring Working Party (IBMWP), Indice Biotico Esteso, Indice Biologique Global Normalisé] and one multimetric index (METI) proposed for NW Spain rivers, and their behaviour using different physicochemical parameters throughout the different typologies defined for NW Spain rivers according to the WFD. It is also tested whether the reference sites and conditions established are representative enough of each typology comparing the IBMWP and METI in reference and non-reference sampling sites. As a whole, the METI showed the lowest correlations with the rest of the indices, whereas the IBMWP showed the highest and all indices displayed negative correlations with those variables, which caused pollution in all typologies. Furthermore, it has been found sites with an index value higher than that of the reference sites and therefore in a better status than the selected reference sites, revealing several shortcomings in the selection of the reference sites in NW Spain and proving that a good selection of the reference sites is extremely important to produce successful results. Finally, the IBMWP has proved to be a useful tool to assess freshwater ecosystems in NW Spain showing how a simple index can be satisfactorily used to monitor 'Ecological status'. Copyright © 2014 John Wiley & Sons, Ltd.
This paper compares two flow routing algorithms' influences on ecohydrological estimations in a northern peatland catchment, within the framework of an arctic-enabled version of the dynamic ecosystem model LPJ-GUESS. Accurate hydrological estimations are needed to fully capture vegetation dynamics and carbon fluxes in the subarctic peatland enviroment. A previously proposed distributed hydrological method based on the single flow (SF) algorithm extracted topographic indices has shown to improve runoff estimations in LPJ-GUESS. This paper investigates model performance differences caused by two flow routing algorithms, and importantly both permafrost processes and peatland hydrology are included in the model. The newly developed triangular form-based multiple flow (TFM) is selected due to its improved consideration of flow continuity and more realistic flow estimation over flat surfaces. A variety of measured data is included to assess both hydrological and ecological accuracy, and the results demonstrate that the choice of flow algorithm does matter for mesoscale ecohydrology applications. The allowance of flow convergence and consideration of flow partition differences from different terrain forms in the TFM algorithm yield better correspondence with the observed hydrological processes and also carbon fluxes. By directing flow to only one downslope cell together with its poorer depiction of flow over flat areas, the SF algorithm can result in too high runoff estimations for low-flat regions and overestimate carbon uptake and release in the peatland. The results of this study also highlight the need for care when selecting flow routing algorithms for biogeochemical estimations, especially within hydrologically and climatically sensitive environments. Copyright © 2014 John Wiley & Sons, Ltd.
The onshore movement of marine fog is a common occurrence during summer months along much of the contiguous US Pacific Coast. Because the fog season tends to occur during the precipitation-free dry season, any additional input of moisture or reduction in loss of moisture through evapotranspiration provided by the marine layer can be an important factor in local hydrologic systems. To quantify some of the effects of fog on regional dry-season hydrology, a study site within the Santa Cruz Mountains of central California was established. The fog-laden coastside and predominately fog-free San Francisco Bay side of the study area provide an excellent opportunity to assess the impacts of the presence and absence of fog on ecohydrological processes. Streamflow, fog drip, and soil moisture were measured from May to September. Fog drip was essentially nonexistent on the bayside and highly variable on the coastside. Maximum rates and seasonal totals of drip occurred within stands of mature conifers (Sequoia sempervirens and Pseudotsuga menziesii) along exposed, often windy ridgelines. Fog-drip totals up to 961 mm were recorded over 2·5 months. Consequently, frequent infiltration events to depths of 23 cm were documented. Over the course of the study, soil moisture levels at high-fog-drip locations either increased or were equivalent to spring conditions at the onset of data collection. Increases of flow in coastside streams, under otherwise receding conditions, were found to coincide with fog and fog-drip events. These results confirm that the presence of fog can significantly affect dry-season hydrologic conditions of some coastal locations. Copyright © 2014 John Wiley & Sons, Ltd.
Mountain regions are key for humanity's water supply, and their water yield depends on climatic, soil and vegetation effects. Here we explore the effects of vegetation composition and structure on the water balance of high elevation grasslands with different climatic conditions across the Alps. Using a total of 220 deep seepage collectors with intact soil-vegetation monoliths in different types of mountain grasslands in the Austrian, French and Swiss Alps, we solved the water balance equation for evapotranspiration (ET) and related the results to biomass, the abundance of certain plant functional types and structural and functional vegetation properties. While daily mean ET during the growing season was similar at all sites, ET to precipitation ratios were significantly higher and ET to potential ET ratios significantly lower at the drier French sites than at the more humid Swiss and Austrian site. Large variability of ET, seepage and soil moisture within all sites pointed at a high influence of vegetation on the water balance. While ET increased significantly with biomass at all sites, the influence of other vegetation properties was site specific. At the more humid, subalpine Austrian site the effects of vegetation on ET were stronger and more diverse than at the higher elevation Swiss site and the drier French sites, where climatic drivers dominated ET. The potential to influence ET and water yield of mountain areas by manipulating the plant canopy with systematic land management is therefore higher in regions with good growing conditions than in areas with harsh climate. Copyright © 2014 John Wiley & Sons, Ltd.
In a seasonally dry plant community of central Florida, USA, that experiences water limitation in the dry season and high water availability in the wet season, we first tested whether evergreen woody species shift from shallow water in the wet season to deep water in the dry season. Second, we tested whether deciduous woody species restrict water uptake to the shallow soil during the wet season and cease water uptake during the dry season. To address these questions, we measured water source use of two deciduous and three evergreen species over 13 months using stable isotopes. As hypothesized in previous studies, we showed that leaflessness in deciduous plants is an important source of stem water isotopic fractionation. Therefore, we compared stable isotope ratios of stem water only when deciduous species had leaves and found that all species, except the evergreen Lyonia ferruginea, used proportionally the same water sources. Early dry season water use was based on water availability for all species except L. ferruginea, and deep soil (50–150 cm) was the most important water source. During the late dry and wet seasons, water uptake from each soil layer was based on its respective proportion of fine roots. Nevertheless, deep water remained an important water source throughout the year. This study clearly demonstrates the limitations of using stable isotopes of stem water when comparing deciduous versus evergreen species. Further, this study is the first to directly quantify depth of water uptake via isotope analysis and couple these findings with root distribution. Copyright © 2014 John Wiley & Sons, Ltd.
There is various evidence that the presence of condensed water, e.g. dew, improves plant water relations. Because particularly plants in drier environments are expected to benefit from atmospheric water, it may be assumed that special adaptations promoting exploitation of dew water evolved in these habitats. Surface characteristics affect dewfall and retention of dew water. Leaf surface characteristics such as hairs (trichomes), which are often present in plants of arid environments, may therefore play a substantial role in dew harvesting. In this study, it is analysed to what extent (1) the presence of hygrophilic aerosoles promotes dewfall by reducing vapour saturation pressure ('early condensation'), (2) dew water can be stored within a dense trichome layer, (3) the presence of dew water increases humidity directly above the leaf surface, thereby reducing water loss from the leaf interior by decreasing the water potential gradient between leaf interior and exterior, and (4) dew evaporation reduces transpiration further by evaporative cooling. A physical framework is provided in this contribution that shows that these processes are in fact possible under natural conditions. Copyright © 2014 John Wiley & Sons, Ltd.
We introduce a novel methodology for measuring stand sapwood area (SA), which provides a useful indicator of evapotranspiration from forest stands. The method is demonstrated in a 73-year-old Eucalyptus regnans forest comprising 784 stems over a 5 ha area. We used photos of stump cross-sections to differentiate sapwood from heartwood and found 90% of stump segments to have a visible transition boundary. The digital images were corrected for lens distortion and scaled to an actual cross-sectional area, with resulting stump perimeters corresponding well with field-measured perimeters traced using string (root-mean-square error = 4 cm, R2 = 0.99). Calculated SA and basal area (BA) at stump height were coupled with tree and sapwood taper data to predict the SA:BA ratio at 1.3 m height (). Tree taper data were coupled with stump dimensions data in a mixed-effects model to predict each stump's BA at 1.3 m, and sapwood taper data from buttress logs were used to improve each stems . Using this procedure, we found our study site to have an of 0.21 and total stand SA at 1.3 m height of 9.3 m2 ha−1.
We quantified the bias in traditional estimates that use cores to measure sapwood thickness and diameter tape to calculate SA. We show traditional methods underestimate that increases with tree diameter and decreases with stem circularity, whereas our methodology gave more accurate measures of SA in large buttressing trees. Our methodology also provides a more efficient way of generating maps of SA variation across large forested catchments. Copyright © 2014 John Wiley & Sons, Ltd.
We demonstrate the potential of using freely available satellite data from the Landsat ETM+ sensor for generating carbon balance estimates for lowland peatlands. We used a lowland ombrotrophic peatland in the UK as our test site representing a range of peatland conditions. A literature survey was undertaken to identify the simplest classification schema that could be used to distinguish ecohydrological classes for carbon sequestration on the peatland surface. These were defined as: active raised bog, Eriophorum-dominated bog, milled unvegetated peat and drained or degraded bog, with bracken and Carr woodland to define the bog edges. A maximum likelihood classifier (MLC) was used to map the spatial distribution of the six classes on the peatland surface. A Landsat ETM+ band-5 derived brightness-texture layer created using geostatistical methods greatly improved classification accuracies. The results showed the best accuracy of the MLC, when compared to finer scale methods, with Landsat ETM+ bands alone was 74%, which increased to 93% when including the brightness-texture layer. An estimate of carbon sequestration status of the site was performed that showed good agreement with the results of a finer-scale-based estimate. The coarse-scale map estimating −12 000 kg carbon and fine scale map estimating +23 000 kg carbon per annum. We conclude that with further development of our tool, if textural measures are used alongside optical data in MLC, it is possible to achieve good quality estimates of carbon balance status for peatland landscapes. This represents a potentially powerful operational toolkit for land managers and policy makers who require spatially distributed information on carbon storage and release for carbon pricing and effective land management. Copyright © 2014 John Wiley & Sons, Ltd.
Classification systems are valuable to ecological management in that they organize information into consolidated units thereby providing efficient means to achieve conservation objectives. Of the many ways classifications benefit management, hypothesis generation has been discussed as the most important. However, in order to provide templates for developing and testing ecologically relevant hypotheses, classifications created using environmental variables must be linked to ecological patterns. Herein, we develop associations between a recent US hydrologic classification and fish traits in order to form a template for generating flow–ecology hypotheses and supporting environmental flow standard development. Tradeoffs in adaptive strategies for fish were observed across a spectrum of stable, perennial flow to unstable intermittent flow. In accordance with theory, periodic strategists were associated with stable, predictable flow, whereas opportunistic strategists were more affiliated with intermittent, variable flows. We developed linkages between the uniqueness of hydrologic character and ecological distinction among classes, which may translate into predictions between losses in hydrologic uniqueness and ecological community response. Comparisons of classification strength between hydrologic classifications and other frameworks suggested that spatially contiguous classifications with higher regionalization will tend to explain more variation in ecological patterns. Despite explaining less ecological variation than other frameworks, we contend that hydrologic classifications are still useful because they provide a conceptual linkage between hydrologic variation and ecological communities to support flow–ecology relationships. Mechanistic associations among fish traits and hydrologic classes support the presumption that environmental flow standards should be developed uniquely for stream classes and ecological communities, therein. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.
It was assumed that sediment release from a reservoir would trigger forestation and change the spatial pattern of tree recruitment in the downstream. This study tested these hypotheses by observation on a downstream sandbar of the Kurobe River. Prior to sediment release, Elaeagnus umbellata and Salix gilgiana were the most abundant tree species (33% and 64% of the total tree population) on the bar. The former colonized on elevated areas, whereas the latter mostly grew along the edges of river channels. After 2008 and 2009 sediment releases, a thick layer of fine sediment accumulated in active river channels and on low-elevated areas of the bar. The particle size of the accumulated sediment was significantly lower (p < 0·01) and the moisture content was higher (p < 0·01) than in the underlying substrate. Total nitrogen, carbon and phosphorus concentrations of the accumulated sediment were higher than in the covered portions. After sediment release, a seedling flushing of both species occurred on the bar where 87% was composed of S. gilgiana and the remaining 13% was of E. umbellata. Although most of the S. gilgiana seedlings recruited on low-lying areas, numerous individuals also grew on elevated margins of the channels and on areas dominated by E. umbellata. The accumulated sediment made changes in the substrate, which were favourable for the recruitment and spread of S. gilgiana. This study suggests that an alternative to sediment flushing for reservoir maintenance should be sought or the impacts on downstream environment should carefully be considered before an extensive sediment flushing operation. Copyright © 2014 John Wiley & Sons, Ltd.
The impact of extreme hydrologic disturbances on the quality of fine particulate organic carbon (FPOC) associated with sediments in low-gradient, agriculturally impacted streams remains poorly understood despite the significance of the FPOC pool to benthic food webs, organic matter budgets and nutrient cycles. We estimated immediate and long-term impacts of an extreme flow disturbance on FPOC quality using a 5-year dataset of the stable carbon isotopic signature and a new metric for carbon quality. Results of the study show that the stable isotopic signature of sediment carbon is significantly enriched in the year following the extreme event, which reflects the streams response to accrual of degraded soil carbon. Further, our FPOC metric was found to be inversely proportional to the isotopic signature, suggesting an immediate shift of the benthic ecosystem to lower quality carbon that is retained for more than 1 year before recovering to the pre-disturbance state. Following recovery, results show that the benthic ecosystem exports FPOC with quality that oscillates seasonally – the lowest quality observed in late spring and the highest quality in late fall. Although studies have addressed the response of high-quality algal biomass to fluvial shearing, this study is the first to assess the response of high-quality FPOC to an extreme hydrologic disturbance characterized by sediment deposition in an agriculturally impacted stream. Copyright © 2014 John Wiley & Sons, Ltd.
The subterranean part of the water cycle takes place in three different types of groundwater bodies: (1) unconsolidated sediments, (2) karstic aquifers and (3) fractured hard rock aquifers. Basically, different aquifer types require different investigation methods. However, the physico-chemical properties of groundwater can aid in the understanding of flow history and aquifer dynamics of each aquifer type. Although groundwater biology is sensitive to hydrochemistry, water temperature and flow velocity, the possible benefits of groundwater animals as 'hydrogeological agents' is still rarely considered by hydrogeologists. The main research focus of hydrogeologists and groundwater biologists is shallow groundwater bodies in unconsolidated sediments and karst aquifers. Fractured hard rock aquifers are still poorly considered by both disciplines. This commentary has three purposes: (1) to show the special characteristics of fractured hard rock aquifers in comparison to porous and karst groundwater bodies, and to describe the resulting methological gap hydrogeologists face when investigating such aquifer types; (2) to give an overview of current groundwater biological research with its focuses and shortcomings, including an introduction of rarely known but common groundwater inhabitants, namely free-living nematodes; and (3) to suggest a combination of methods, supported by a hypothetical example, and the possible benefits this combined knowledge from hydrogeologists and groundwater biologists can bring to both disciplines. Copyright © 2014 John Wiley & Sons, Ltd.
Saltwater intrusion has been recognized as a major driver of ecological regime shifts in coastal wetlands, but few studies have incorporated long-term salinity modelling data into the understanding of vegetation dynamics. This study uniquely combined artificial neural network (ANN) modelling and time series of aerial photographs to elucidate saltwater intrusion and mangrove encroachment into the freshwater floodplain of the Loxahatchee River over a period of six decades. Three ANN models were developed to simulate river salinity on a daily time step using freshwater inflow, rainfall and tide as inputs. With 8 years of measured data for training and testing, the ANN models demonstrated comparable or superior model performance for salinity simulation to their hydrodynamic counterparts. Modelling of historical salinity (1948–2011) using the ANNs indicated that the intensity of saltwater intrusion clearly correlated with watershed hydrology, which, in turn, was linked to historical watershed alterations and regional rainfall variability. Interpretation of the 1940, 1953, 1964, 1979, 1985 and 1995 aerial photographs revealed the progressive encroachment of mangroves and displacement of bald cypress and freshwater communities in the floodplain. The spatial extent of mangrove encroachment was related to the increasing mortality of bald cypress under the chronic effect of cumulative salinity exposure. The ecohydrological controls over vegetation changes in the Loxahatchee River support the ongoing ecosystem restoration programme, which aims to achieve incremental freshwater flow targets to protect and restore the floodplain ecosystem. Copyright © 2014 John Wiley & Sons, Ltd.
To assess the response of northern peatlands to hydrological changes, we analysed the response of a model designed to simulate peatland development at a millennial timescale, the Holocene Peat Model, to two hydrological drivers. The study is performed on two open ombrotrophic peatlands located in the James Bay region in North-eastern Canada. For both sites, two simulations were realized: one based on a precipitation reconstruction from pollen data, used as input in the model, and a second using a water-table depth reconstruction derived from testate amoebae to apply a forcing on the model. Simulated variations in carbon accumulation rates (CARs) and vegetation composition were analysed against palaeoecological datasets.
In both sites and for the two hydrological drivers, modelling results in CARs showed periods of net carbon loss that coincided with fluctuations in observed CARs, although net carbon loss cannot be traced in palaeoecological datasets per se. The comparison between plant macrofossil records and simulated vegetation distributions highlighted differences between precipitation and water-table depth-driven simulations. Thus, the methodology used was found useful to analyse the origin of vegetation shifts in macrofossil datasets. Copyright © 2014 John Wiley & Sons, Ltd.
The large-scale expansion of Moso bamboo forests in Japan raises concerns about how vegetation will affect the hydrological cycle and local water resources. However, information on transpiration (E) is limited to study on a single bamboo stand with low culm density (4 000 ha−1). The present study conducted a year-round measurement of E in a high-density (11 000 ha−1) stand using sap-flow measurements, and additional measurements were made during summer in the previously studied low-density stand and a neighbouring Japanese cedar stand for comparison. Annual E of the high-density stand was estimated at 455 mm. Although the value was greater than those reported for neighbouring coniferous forests (250–370 mm), it was lower than previous measurements made in the low-density stand (567 mm). The daytime sap flux density of the high-density stand was generally less than half that in the low-density stand, resulting in similar daily maximum E values in those stands. In addition, E typically peaked before midday in the high-density stand followed by a rapid decline; the midday suppression of E led to decreased total E in the stand. Based on present and previous measurements of E, combined with the lower rainfall interception (I) reported for bamboo stands, water loss through evapotranspiration would be comparable between bamboo and coniferous forests. Present results also suggest that the E of bamboo stands does not have strong positive relationships with stand structural parameters (e.g., culm density and sapwood area) but possibly depends more on the sites' microenvironments (e.g., solar radiation). Copyright © 2014 John Wiley & Sons, Ltd.
In recent years, it has become increasingly clear that two-way interactions between organisms and landscape-forming processes play a key role in the evolution of many aquatic ecosystems. To be able to compare sedimentation processes among different environments, a standardized method that is generally applicable is necessary. Current methods are usually designed for one environment only or are unreliable in the presence of vegetation. This paper presents the functionality of a plate sediment trap with a lid in combination with a filter paper, which enables the measurement of sedimentation rates in both permanently subaqueous environments and periodically flooded wetlands. We first present the trap design and demonstrate its functionality. No significant differences were found between replicates, nor was there any indication of a trap size effect on the sedimentation rate. Secondly, we demonstrate its applicability in periodically flooded and permanently subaqueous environments and in the presence or absence of vegetation. It is concluded that the use of a standardized method and equipment makes it possible to compare (bio)geomorphological changes in totally different environments. Copyright © 2014 John Wiley & Sons, Ltd.
Wetlands are ecosystems that play a key role in maintaining biodiversity and associated economies (e.g. agriculture and livestock) because they are reservoirs of water and carbon. Globally, these environments have been largely deteriorated, so their sustainable use takes on special importance. This study examined the effect on water recharge of the replacement of natural grassland by pine afforestation on hillsides adjacent to two Patagonian wetlands with contrasting rainfall. Results showed that independently of the rainfall at the site considered, canopies with high coverage values (90%) intercept 40% of the precipitation. This percentage is significantly reduced when canopy coverage is near 70%. Considering forested and grassland hillsides, groundwater drainage showed different patterns, consisting of only a few millimetres in the seasons recorded. Surface runoff was not a significant source of recharge for these systems in spring and summer, showing similar values in forested and grassland hillsides. Differences found in the recharge water variables between afforestation and grassland conditions cannot be directly associated with the vegetation in areas surrounding the wetlands. These systems showed high complexity, requiring site-specific analysis to determine what the impact of afforestation will be on their hydrology. Copyright © 2014 John Wiley & Sons, Ltd.
This study examines the morphological features, suspended sediment inputs and hydraulic conditions within a large river in association with ecological patterns before and after a tributary confluence. In order to examine these effects, the macroinvertebrate distributions from three reaches of the Paraguay and Bermejo Rivers (Paraguay–Argentina) are investigated. The Bermejo River is a tributary that supplies significant quantities of fine sediment to the Paraguay River, primarily in suspension. Two reaches were examined on the Paraguay River, upstream and downstream of the Bermejo River junction, with the third study reach located on the Bermejo River, upstream of the confluence with the Paraguay River. The results provide clear evidence that a significantly increased loading of fine sediment at a river confluence has effects on the distribution and potential movement of benthic invertebrates in the lotic environment by representing physical barriers at affected sites. These effects may be important at both local and regional scales, and such increases in suspended sediment (especially associated with anthropogenic change) may thus pose a major threat to ecosystem integrity that has been historically underestimated. Copyright © 2014 John Wiley & Sons, Ltd.
We sampled isolated trees and tree clusters from a blue oak, Quercus douglasii, savanna to determine the spatial heterogeneity of fine root biomass and soil carbon across the landscape as a function of tree size and configuration. We aimed to understand how fine root structure enables sustained ecosystem metabolism through a summer of limited moisture and high heat and facilitates resource acquisition during the short period of high resource supply. An additional goal was to provide a basis for upscaling root biomass and soil carbon to the landscape scale. We sampled trees of different size and tree clusters via a stratified sampling scheme that accounted for spatial heterogeneity in root biomass and soil carbon with lateral distance from the tree bole, or cluster centre, and soil depth. We upscaled these estimates using site-specific information from a lidar survey. We found that fine roots and soil carbon are spatially heterogeneous in their landscape distribution and greatly increase with tree size. We also found that Q. douglasii possesses a dimorphic fine root architecture, uniquely suited to the region's climatic constraints and exhibits morphological plasticity among trees of different size and physical setting. Copyright © 2014 John Wiley & Sons, Ltd.
This paper presents a methodological approach that can aid the assessment of variation in limnological variables in response to hydrological phases and seasonal temperature variation. The investigation was conducted in the Danube River floodplain, Kopački Rit, Croatia. The proposed approach facilitates a more accurate examination of the effects of first factor, while maintaining second factor less variable, and vice versa. Samples were collected in the floodplain channel and lake along a temporal connectivity gradient, and were grouped according to three hydrological phases (isolation, flow pulse and flood pulse) and according to three seasons (spring, summer and autumn). A permutational multivariate analysis of variance was used to analyse the hydrological effects within seasons, as well as seasonal effects within hydrological phases on selected limnological variables: pH, conductivity, dissolved oxygen, nitrites, nitrates, ammonium, total Kjeldahl nitrogen, total phosphorus, chlorophyll a concentrations and ratio of copiotrophic to oligotrophic bacteria. A multivariate data cloud was structured by hydrological phases during all investigated seasons, but not by all seasons during different hydrological phases. The strongest impact of hydrological phases on limnological variables occurred during summer. Seasonal effects were significant during the isolation and the flood pulse phases. The flow pulse phase somehow obscured the effects of seasonal change, resulting in temporal floodplain homogenization. One possible explanation is that water temperature determines potential limnological conditions, whereas hydrology determines actual conditions. Such results must be taken into account if the accurate effects of hydrology and seasonal change are to be assessed in temperate floodplain ecosystems. Copyright © 2014 John Wiley & Sons, Ltd.
This study presents a new hydraulic model for simulating the physical habitat of a river. The model is based on the quasi-steady assumption that the flow is steady, but the channel morphology changes during the computational time step. The model is also capable of simulating flow distribution in the lateral direction, making the model quasi-two-dimensional. The physical habitat simulations are carried out for a reach including a bend in the Dal River in Korea. Zacco platypus is used as the target fish. The habitat suitability index model for Zacco platypus, based on field monitoring, is used for the habitat simulation. The hydraulic model simulates morphological changes caused by a flood and the result is compared with the two-dimensional model. Simulation results obtained using the developed model compares favorably to calculations obtained using the two-dimensional model. Distributions of the habitat suitability index are provided for various flows by the present model. It is found that the morphological change by the flood increases the habitat suitability significantly by decreasing the flow depth and increasing the velocity in the study reach. In addition, the time change of the weighted usable area based on the mobile-bed computation is given, indicating that the flood decreases the habitat suitability seriously. Copyright © 2014 John Wiley & Sons, Ltd.
Restoration and protection of urban stream ecosystems require knowledge of the primary causes of their degradation. Conventional stormwater drainage has been identified as a primary source of stress to streams, but it remains unclear if the proximal stressor to stream biota can be represented by flow regime alone or requires a metric integrating the range of stressors associated with stormwater runoff or with urban land use more generally. We used the information-theoretic approach to assess whether various hydrologic indicators better predicted SIGNAL (a biotic index using macroinvertebrate families) than did attenuated imperviousness (AI; a landscape measure of connected imperviousness that inversely weights impervious areas by their distance from the nearest stormwater drain or stream) or total imperviousness (TI). The best models using hydrologic indicators were much less plausible than the overall best model, which used only AI. Predictors in the best hydrologic models characterized the magnitude of low-flow antecedent events, overall flow variability, and antecedent flow flashiness. TI was a poorer predictor than AI, but similarly plausible as some hydrologic models. The results suggest that although there are components of the flow regime that degrade stream ecosystems, AI is a better predictor because it integrates hydrologic and other stormwater-driven stressors, such as changes to water quality. Management of stream condition in our study area should focus on addressing conventional stormwater drainage and its associated alterations to hydrology and water quality. The identification of a single metric provides useful insights for others trying to identify simple predictors of complex phenomena. Copyright © 2014 John Wiley & Sons, Ltd.
Natural flow regimes are important predictors of variation in freshwater biodiversity, yet urbanization can significantly impact the volume and variability of water moving through a watershed. Moreover, there is limited quantitative understanding of spatial variation in the effects of urbanization on watershed hydrology and the impacts of this variation on aquatic species distributions and assemblage composition. We used a physically based watershed model (MIKE-SHE), a hydrodynamic river model (MIKE-11), and current landcover classifications to characterize flows at sites across the Big River watershed in eastern Missouri. Estimates of streamflow from the MIKE-SHE model based on current landcover classifications were then used to predict variation in fish species richness at 44 sites across the watershed. We also quantified the potential effects of five urbanization scenarios on streamflows throughout the watershed and used flow estimates from the urbanization hydrological models to predict changes in fish species richness as urban areas increase. Responses varied among sites, with some sites predicted to increase in species richness whereas others are predicted to decrease in species richness. This mosaic of responses is likely due to the inconsistent impact of urbanization on streamflows throughout the watershed. Results also differed among taxonomic groups. The number of species of Cyprinidae (minnows) is generally expected to increase within sites across the watershed, whereas the number of species of Centrachidae (bass and sunfish) is expected to decrease. This differential shift in cyprinid and centrarchid richness is predicted to have a compensatory effect, with overall richness remaining, on average, relatively constant among sites. Copyright © 2014 John Wiley & Sons, Ltd.
No abstract is available for this article.]]>
The human influence on the global hydrological cycle is now the dominant force behind changes in water resources across the world and in regulating the resilience of the Earth system. The rise in human pressures on global freshwater resources is in par with other anthropogenic changes in the Earth system (from climate to ecosystem change), which has prompted science to suggest that humanity has entered a new geological epoch, the Anthropocene. This paper focuses on the critical role of water for resilience of social-ecological systems across scales, by avoiding major regime shifts away from stable environmental conditions, and in safeguarding life-support systems for human wellbeing. It highlights the dramatic increase of water crowding: near-future challenges for global water security and expansion of food production in competition with carbon sequestration and biofuel production. It addresses the human alterations of rainfall stability, due to both land-use changes and climate change, the ongoing overuse of blue water, reflected in river depletion, expanding river basin closure, groundwater overexploitation and water pollution risks. The rising water turbulence in the Anthropocene changes the water research and policy agenda, from a water-resource efficiency to a water resilience focus. This includes integrated land and water stewardship to sustain wetness-dependent ecological functions at the landscape scale and a stronger emphasis on green water management for ecosystem services. A new paradigm of water governance emerges, encouraging land-use practices that explicitly take account of the multifunctional roles of water, with adequate attention to planetary freshwater boundaries and cross-scale interactions. © 2014 The Authors. Ecohydrology published by John Wiley & Sons, Ltd.
Ecological limit functions relating streamflow and aquatic ecosystems remain elusive despite decades of research. We investigated functional relationships between species richness and changes in streamflow characteristics at 662 fish sampling sites in the Tennessee River basin. Our approach included the following: (1) a brief summary of relevant literature on functional relations between fish and streamflow, (2) the development of ecological limit functions that describe the strongest discernible relationships between fish species richness and streamflow characteristics, (3) the evaluation of proposed definitions of hydrologic reference conditions, and (4) an investigation of the internal structures of wedge-shaped distributions underlying ecological limit functions.
Twenty-one ecological limit functions were developed across three ecoregions that relate the species richness of 11 fish groups and departures from hydrologic reference conditions using multivariate and quantile regression methods. Each negatively sloped function is described using up to four streamflow characteristics expressed in terms of cumulative departure from hydrologic reference conditions. Negative slopes indicate increased departure results in decreased species richness.
Sites with the highest measured fish species richness generally had near-reference hydrologic conditions for a given ecoregion. Hydrology did not generally differ between sites with the highest and lowest fish species richness, indicating that other environmental factors likely limit species richness at sites with reference hydrology.
Use of ecological limit functions to make decisions regarding proposed hydrologic regime changes, although commonly presented as a management tool, is not as straightforward or informative as often assumed. We contend that statistical evaluation of the internal wedge structure below limit functions may provide a probabilistic understanding of how aquatic ecology is influenced by altered hydrology and may serve as the basis for evaluating the potential effect of proposed hydrologic changes. Published 2013. This article is a U.S. Government work and is in the public domain in the USA. Ecohydrology published by John Wiley & Sons, Ltd.
Discharge fluctuation and extreme bed load movement, i.e. erosion and sedimentation occurring on short upper reaches of the river, are characteristic features of torrential rivers. This paper presents a biotechnical appraisal of a torrent catchment for implementing revetments methods, focusing on selected hydraulic characteristics of the flow. The Infiltration and Kinematic wave hydrological model (KINFIL) hydrological model (for design discharges) is used to verify these variables and also the Hydrologic Engineering Centre's River Analysis System and Sedimentation and River Hydraulics Two-Dimensional hydraulic models for channel flow. Data and computation for proposing nature-close remedial measures are demonstrated in a case study of the Jindrichovicky Brook, a mountain torrent located in the Ore Mountains (Czech Republic).
Particular attention is given to appropriate adaptation of the river for the invertebrate community. The hydraulic analysis is carried out in two sections of the river (section A: 'nature-close', restored in 2008, and section B: 'old style', regulated in the 1970s). The aim is to compute the major hydraulic characteristics (depths, velocities, shear stress values etc.). Then, a hydrobiological investigation is carried out in both sections to find how much the invertebrate communities extended their diversity and abundance as a consequence of better geomorphological diversity after restoration. It was found that, from the hydraulic point of view, the old section B is sufficiently robust and stable. However, it is clearly evident that this section can hardly be populated by fauna and if so, then only very sparsely and impermanently. Section A meets both priorities, hydraulic stability and an acceptable living environment for the benthic community. Copyright © 2013 John Wiley & Sons, Ltd.
This study conducts a comparative analysis of the effects of irrigation scheduling at two urban residential sites in the Phoenix, Arizona, metropolitan area: a xeriscaped site (gravel base with low water use plants) and a mesiscaped site (turf grass and shade trees). A model of soil moisture dynamics was calibrated to observed soil moisture data from irrigated and non-irrigated sensors at the xeric site and an irrigated sensor at the mesic site. Model simulations were conducted at both irrigated sites to investigate effects of irrigation scheduling; plant stress parameters; and precipitation variability on soil moisture dynamics, water balance partitioning, and plant water stress. Results indicated a substantial difference in soil water storage capacity at the two sites. At the xeric site, seasonal variation of irrigation input was shown to be critical in avoiding losses from the rooting zone, while reducing plant water stress. At the mesic site, sensitivity to irrigation scenarios was lower, though small amounts of water savings were achieved with seasonal applications. The model was then used to determine the minimum annual irrigation required to achieve specified levels of plant stress using long-term meteorological records. A bimodal schedule consisting of low winter and summer irrigation was identified as a means to conserve water while keeping moderate levels of dynamic water stress. Results from the quantitative model can potentially assist water and landscape managers in desert urban areas by identifying opportunities for water savings, while providing a deeper understanding of the ecohydrological differences between the two types of landscape designs. Copyright © 2014 John Wiley & Sons, Ltd.
Evapotranspiration (ET) of irrigated urban plants is a large yet uncertain component of urban water budgets in semi-arid regions. A detailed understanding of plot-scale ET and its sensitivity to plant species composition is necessary to improve estimates of urban water vapour fluxes and water balance. We used portable enclosed chambers and empirical equations to quantify ET from (1) unshaded urban lawns covered exclusively by turfgrass and (2) urban lawns comprised of open-grown trees and turfgrass groundcover in the Los Angeles Metropolitan area. Turfgrass at all locations had a non-limiting supply of soil water because of regular sprinkler irrigation. ET of irrigated turfgrass reached a maximum of 10. 4 ± 1·3 mm d−1 and was always higher than plot-scale tree transpiration, which did not exceed 1 mm d−1. In summer, total plot ET of the lawns with trees was lower than lawns without trees by 0·9–3·9 mm d−1. Turfgrass ET was highly sensitive to solar radiation, and the ratio of ET of lawns with trees to ET of lawns without trees decreased with tree canopy cover. Hence, reductions in turfgrass ET caused by shading effects of open-grown trees were more important in influencing total landscape ET than the addition of tree transpiration. This suggests that low-density planting of trees that partially shade irrigated urban lawns may be a water-saving measure in semi-arid irrigated environments. Copyright © 2013 John Wiley & Sons, Ltd.
The partitioning of precipitation into interception, stemflow and throughfall is an important hydrological process in forested systems, influenced heavily by climate and plant form. This study examined whether the rainfall partitioning pathways reflect the often cited influence of tree morphology, using two species in a semi-arid karst environment. Eucalyptus diversifolia ssp. diversifolia has a multi-stemmed habit, smooth bark and true leaves. In comparison, Allocasuarina verticillata has a single trunk, rough bark and long, thin, vertical phyllodes. We hypothesized that multiple stems and a smooth bark would be more effective at generating stemflow compared with single stems with a rough bark surface. To test this, rainfall, throughfall and stemflow were collected over two years, and stemflow funnelling ratios were calculated. The degree of similarity in overall rainfall partitioning for the two species was remarkable; although some divergence was found each month, the partitioning regressions converged. For E. diversifolia, gross rainfall partitioned into interception, throughfall and stemflow averaged 30.9%, 66.4% and 2.7%, respectively. For A. verticillata, rainfall partitioning of gross precipitation into interception, throughfall and stemflow averaged 31.4%, 65.9% and 2.7%, respectively. Maximum stemflow funnelling ratio for E. diversifolia was 74 and for A. verticillata was 147, indicating that water from stemflow is likely to play an important ecohydrological role in this environment. We further compared these findings to 31 global studies and discussed the importance of scale (individual tree vs plot) and canopy cover when reporting or interpreting rainfall partitioning results. Copyright © 2013 John Wiley & Sons, Ltd.
Water quality models are increasingly used to predict nutrient losses from anthropogenically impacted catchments, but comprehensive model calibration and transfer of model parameters are often difficult. The objectives of this study are (i) to assess the Hydrological Predictions for the Environment (HYPE) model for simulating runoff and inorganic nitrogen (IN) leaching in nested and spatially heterogeneous mesoscale catchments in central Germany and (ii) to investigate the temporal and spatial variations of IN leaching. A multi-site and multi-objective calibration approach using the parameter estimation tool PEST was employed. Results showed that parameters related to evapotranspiration were most sensitive for runoff simulation. The nitrogen balance was controlled by plant uptake and denitrification. Runoff was well reproduced for both calibration (1994–1999) and validation (1999–2004) periods at all three gauging stations, with the lowest Nash–Sutcliffe efficiency (NSE) of 0·86 and bias (PBIAS) of less than 15%. In addition, the model was tested successfully to predict the dynamics of soil water storage during extreme climatological events. IN concentrations showed increase in magnitude and decrease in dynamics from upstream to downstream of the catchment, reflecting the combined effects of nutrient inputs and IN in-stream retention. The dynamics of monthly IN loads were well represented by the model during the whole simulation period, with the lowest NSE and PBIAS of 0·69 and 33%, respectively. Results revealed seasonal dynamics of IN leaching due to the combined effects of hydrological and biogeochemical processes, which is consistent with runoff dynamics. This indicates the controlling role of hydrology on nitrogen transport processes. Copyright © 2013 John Wiley & Sons, Ltd.
Forests that recover from disturbance predominately via vegetative resprouting may be expected to have different catchment water balance dynamics following wildfire than forests recovering from seed. However, the impacts of wildfire on forest water use are largely unknown in resprouting forest types. This is despite their dominance across the majority of southern Australia's forested catchments and the large areas burnt in recent years. We hypothesized that postfire changes in evapotranspiration (Et) would be a function of fire severity and topography and that partitioning of Et would change after fire because of altered stand structure. We tested these hypotheses by monitoring Et and component fluxes across different topographic positions and fire severities in a mixed eucalypt species forest located in water supply catchments for the city of Melbourne. For this forest type, wildfire triggers vegetative resprouting from lignotubers and epicormic shoots on the bole and branches of the overstorey trees, in addition to prolific seedling germination. Monitoring was undertaken over 1–3 years following the 2009 Black Saturday wildfires. We found that Et was on average 41% lower in forest burnt at high severity compared with unburnt forest, whereas Et from forest burnt at moderate severity was only 3% lower than unburnt forest over 1–2 years postfire but on average 9% higher over 2–3 years postfire. Et losses were driven by tree and shrub mortality in conjunction with lower transpiration in surviving trees. Lower Et was partially offset by regenerating seedlings that drove increases in forest floor Et and interception loss. Finally, we found that topography, through its effects on evaporative demand and forest structure, was a strong determinant of total Et but did not affect the nature of postfire recovery. Copyright © 2014 John Wiley & Sons, Ltd.
In the literature, contrasting effects of plant species richness on the soil water balance are reported. Our objective was to assess the effects of plant species and functional richness and functional identity on soil water contents and water fluxes in the experimental grassland of the Jena Experiment. The Jena Experiment comprises 86 plots on which plant species richness (0, 1, 2, 4, 8, 16, and 60) and functional group composition (zero to four functional groups: legumes, grasses, tall herbs, and small herbs) were manipulated in a factorial design. We recorded meteorological data and soil water contents of the 0·0–0·3 and 0·3–0·7 m soil layers and calculated actual evapotranspiration (ETa), downward flux (DF), and capillary rise with a soil water balance model for the period 2003–2007. Missing water contents were estimated with a Bayesian hierarchical model. Species richness decreased water contents in subsoil during wet soil conditions. Presence of tall herbs increased soil water contents in topsoil during dry conditions and decreased soil water contents in subsoil during wet conditions. Presence of grasses generally decreased water contents in topsoil, particularly during dry phases; increased ETa and decreased DF from topsoil; and decreased ETa from subsoil. Presence of legumes, in contrast, decreased ETa and increased DF from topsoil and increased ETa from subsoil. Species richness probably resulted in complementary water use. Specific functional groups likely affected the water balance via specific root traits (e.g. shallow dense roots of grasses and deep taproots of tall herbs) or specific shading intensity caused by functional group effects on vegetation cover. Copyright © 2013 John Wiley & Sons, Ltd.
Swamps, bogs and fens are diverse wetland ecosystems found worldwide. Within each region, different ecological processes and species dominate them, yet water levels and saturation of sediments appear key to the maintenance of vegetation and the ecosystem as a whole. Consequently, understanding how vegetation responds to water levels in these ecosystems is critical to their future management. This paper describes the floristic patterns observed in an upland swamp on the Budderoo Plateau, Southern Highlands, NSW, and relates the distribution of the vegetation communities to groundwater depth, soil type and site attributes. Three distinct vegetation assemblages were identified associated with (1) the main swamp axis, (2) the swamp margin and (3) the adjacent hillslopes. Elevation above the central swamp axis was the variable most strongly related to vegetation structure. Relative changes in elevation create a drainage gradient that allows higher elevation areas (hillslope and swamp marginal zones) to drain more readily than areas in the main swamp axis. Variation in vegetation was also related to median groundwater depth. Finally, soil organic matter content was a contributing factor with the swamp axis and marginal zones mostly having fibric, highly organic soils in contrast to the sandy, loamy soils on the hillslopes. Copyright © 2014 John Wiley & Sons, Ltd.
Lake Koronia is a hypertrophic Ramsar site in northern Greece. Water level dropped progressively from approximately 6 m in the mid-1980s to 0·8 m in 2001 associated with over extraction of groundwater for agriculture, and the open water area has decreased from 4620 to 2930 ha, respectively. The resulting annual water level loss of 0·25–0·30 m year−1 was accompanied by expansion of Phragmites australis from a littoral fringe to dominance of exposed lake bottom areas from 97 ha in 1977 to 785 ha in 2005. The aim of this work was to apply an ecohydrological approach using remote sensing and geographic information system (GIS) to examine the movement of Phragmites relative to the water level retreat and to basin morphometry. Aerial expansion of Phragmites averaged 11–32 ha year−1 during the period of progressive water level decline but increased to 38–116 ha year−1 during a brief period of water level increase (2001–2003) as the plant colonized reflooded portions of the basin. The total area of Phragmites expanded 29% per annum during 1977–2005. Landward and lakeward margins of the Phragmites area followed water level retreat, moving 55 and 129 m, respectively, during the long period of progressive water level decline. Aerial movements of Phragmites in Lake Koronia are some of the highest reported in the literature. Mean water level within the Phragmites bed varied from 0·5 to 2·0 m during the period covered by this study. Very minor changes in basin slope, however, affected plant colonization rates, as evidenced by 200–250 ha/0·5 m water level drop at 0·18% basin slope to 360–1360 ha/0·5 m water level drop at 0·029% slope. The techniques applied to Lake Koronia for reconstructing past lake levels and associated distributions of Phragmites have broad application for understanding the dynamics of Phragmites elsewhere and anticipating periods of rapid plant expansion related to subtle changes in basin morphology. This study is useful for managing Phragmites populations in areas where efforts are being made to re-establish populations as well as where elimination of invasive populations is sought. Copyright © 2013 John Wiley & Sons, Ltd.
Flood inundation and retention are key hydrological characteristics of floodplain wetlands. This study developed a methodology for regional estimates of potential floodwater retention under floodplain inundation from ecologically significant flood return periods by coupling remote sensing and geographic information system technologies with spatial hydrological modelling. The Macquarie Marshes in Australia were selected as the case study area. Time series of Moderate Resolution Imaging Spectroradiometer 8-day composite imagery were related to peak flows (Ml day−1) of the 1-in-10 return period. Inundation extent in corresponding images was detected using the modified normalised difference water index (mNDWI). The potential maximum soil water retention was derived using a spatial hydrological modelling approach, which is driven by the Soil Conservation Service Curve Number (SCS CN) method. Soil and land cover data were collected and intersected to determine spatial distribution of CN using ArcGIS. The CN-based retention capacity map was then integrated with an inundation extent map to delineate the spatial pattern of retention under inundation. The results have ecological implications in relation to the response of broad eco-types in wetlands. This study has proved that the integration of remote sensing, geographic information system and spatial hydrologic modelling can be used to provide essential information as inputs to the management of environmental flows in terms of sustaining ecosystem function, biodiversity and habitat suitability. Copyright © 2013 John Wiley & Sons, Ltd.
The complete adaxial surface development and degradation due to weathering of two superhydrophobic leaf species with (black locust, Robinia pseudoacacia and bigtooth aspen, Populus grandidentata) and one without (quaking aspen, Populus tremuloides) a protective downy layer of trichomes was followed over one entire growing season using scanning electron microscopy and wetting property measurements. Scanning electron microscopy micrographs illustrate the initial development period of a dual-scale surface structure consisting of micrometre-sized papillae and nanoscale wax crystals, which was followed by a period of environmental degradation as nanoscale wax features were subjected to environmental stress. It was discovered that robust micropapillae protect nanoscale wax morphologies in-between them for quite some time allowing for a high tolerance to wear and erosion. Weather data was used to demonstrate the correlation between cumulative environmental stresses (temperature, relative humidity, precipitation and wind) and the loss of superhydrophobicity at the end of the growing season. Analysis of all binary combinations of the aforementioned environmental stress factors propose that cumulatively hot and humid weather have the most significant impact on degradation of nanoscale wax crystals and therefore result in the final loss of superhydrophobic behaviour. These findings were also tentatively linked to their importance in ecohydrology suggesting that canopy storage capacity, which has been previously correlated with leaf hydrophobicity, of superhydrophobic leaves may fluctuate considerably throughout an entire growing season. Copyright © 2013 John Wiley & Sons, Ltd.
Understanding the role of soils in regulating water flow through the unsaturated zone is critical in assessing the influence of vegetation on soil moisture dynamics and aquifer recharge. Because of fire, introduced ungulates and landscape-level invasion of non-native grasses, less than 10% of original dry forest (~730 mm precipitation annually) still exists on leeward Haleakalā, Maui, Hawaiian Islands. Native dry forest restoration at Auwahi has demonstrated the potential for dramatic revegetation, allowing a unique experimental comparison of hydrologic function between tracts of restored forest and adjacent grasslands. We hypothesized that even relatively recent forest restoration can assist in the recovery of impaired hydrologic function, potentially increasing aquifer recharge. To compare restored forest and grassland sites, we experimentally irrigated and measured soil moisture and temperature with subsurface instrumentation at four locations within the reforested area and four within the grassland, each with a 2·5 × 2·5-m plot. Compared with grassland areas, water in reforested sites moved to depth faster with larger magnitude changes in water content. The median first arrival velocity of water was greater by a factor of about 13 in the reforested sites compared with the grassland sites. This rapid transport of water to depths of 1 m or greater suggests increased potential aquifer recharge. Improved characterization of how vegetation and soils influence recharge is crucial for understanding the long-term impacts of forest restoration on aquifer recharge and water resources, especially in moisture-limited regions. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.