Authors: Carrillo,U.; Gabellone, Néstor Adrián; Solari, Lía C.
The objective of this paper was to evaluate relationships between phytoplankton algae density and physical factors such as conductivity and temperature in lentic and lotic environments of Salado River basin. The information was obtained from 352 samples taken in San Miguel del Monte shallow lake, in the seepage Lacombe and in the Salado River (main channel and tributaries). Species with density higher than 4.000 individuals ml-1 were selected: eight cyanobacteria, four chlorophytes, three diatoms and one cryptomonadal. Temperature and conductivity optima and tolerance of species temperature were calculated. The chlorophytes showed highest optima temperature average (18,84 ºC) than the cyanobacteria (17,96 ºC) and diatoms (16,31 ºC). Optima temperature of Cryptomonas pusilla was high (19,86ºC). Diatoms and cryptomonadales showed conductivity optima average (5514 and 5599 μS cm-1) higher than chlorophytes and cyanobacteria (4506 and 3508 μS cm-1). Aphanocapsa delicatissima showed markedly low conductivity optima in the lakes (2002 μS cm-1) respect to the obtained in the Salado River (8989 μS cm-1). It must be emphasized that ranges observed in lotic environments were wider than those in lentic environments. The species optima may be useful for future interpretations of the phytoplankton ecology and also as biological indicator for waterquality assessment in the studied environments.
Keywords: Ciencias Naturales; Fitoplancton; temperatura; conductividad; óptimos/rangos de tolerancia.
Keywords: Ciencias Naturales; interacciones tróficas; microcosmos; algas palatables; peces planctivoros.
Authors: Quaíni, Karina Paola; Gabellone, Néstor Adrián; Solari, Lía C.
In lowland river basins with agricultural activities and periodically flood events, the exchange of materials and organisms between waterlogged soil and river are significant. One century conversion of natural systems to agriculture in the Argentine Pampas has resulted in significant changes of ecological properties of the valuable freshwater ecosystems of its region. For this reason it becomes essential to know soil basin responses to flood events and its reciprocal effects on the river. The aim of this paper was to determine the nitrate (NO3 -) and ammonium (NH4 +) dynamics on soil flooded waters with different land-use and topographic position, since the flood to the dry condition. «In situ» experiences were carried out on soils from Salado River basin (Valdés, 25 de Mayo). The treatments (4x3) were made according to: land-use (agricultural ‘a’ and cattle-agricultural ‘m’) and topographic position (ridge ‘L’ and middle ridge ‘ML’). NO3 - and NH4 +, chlorophyll ‘a’ and dissolved oxygen were measured in water. According to water time permanence on each site (calculated taking into account the slope in each site) five sample times were programmed: daily in L and fortnightly in ML. In all cases NO3 - values were higher than NH4 +. Water NO3 - and NH4 + concentrations were similar in ‘a’ and ‘m’ in both topographies. According to the topography and time of water permanence, NO3 - mean values were higher for L (five days), while the opposite occurred for NH4 +. Both ions dynamics showed differences according to topography and water time permanence, but not according to land-use. These results suggested that in flooded events of lowland river basins with farming land use, the nitrogen dynamic and its transport from the soil to the flooding water have significant importance and have a direct influence on phytoplankton biomass development. The NO3 - and NH4 + dynamics were different according to water time permanence over the soil: when the flood event was for long time, the system seem to have enough time to adapt to the new conditions, and so denitrification and nitrification processes are possible; but, when the flood event is short, time is not enough for the system to adapt, and thus, nitrification and denitrification processes does not seem to occur. Considering that some authors assumed soil basin agriculture as the former responsible for the increasing nutrient concentration in the river, these results suggest that because crop-pasture, cattle lands are important in this respect and should be considered from now on.
Keywords: Ciencias Naturales; Nitratos; Inundaciones; Topografía; amonio; suelos de uso agropecuario.
Polyphenols – products of organic-matter decomposition entering water bodies from autochthonous and especially allochthonous sources – affect primary producers, bacterioplankton, and zooplankton to consequently modify food webs. Cladocerans are widely used in research experiments because they constitute the most frequent prey of high-trophic-level organisms in the majority of lakes, and certain species symbolise the ecologic prototype of the generalist filter feeder. In our study area’s shallow lakes, cladocerans, though generally of low abundance, do attain significantly high biomasses. We accordingly evaluated the mortality of the cladoceran Daphnia menucoensis Paggi, 1996 exposed to different tannin concentrations along with the bacterial abundance. In two experiments D. menucoensis females exposed to high tannin concentrations reproduced inefficiently, exhibited high mortality, and manifested altered behaviour, such as reduced reflexes and diminished mobility. Though tannins apparently affected algal abundances, the cladoceran herbivory strongly reduced those numbers. Positive effects on bacteria, however, were not recorded. High-allochthonous-organic-matter-containing water bodies support trophic webs because bacterioplankton provide an alternative energetic base for the zooplankton, as possibly occurs in shallow lakes of the Salado-River basin, characterised by cyclic hydrologic periods alternating between draught and flooding and intensive land use. In conclusion, tannins diminish D. menucoensis’s survival, locomotion, and the capacity to respond to stimuli.
Keywords: TANNINS; ZOOPLANKTON; DAPHNIA MENUCOENSIS; BACTERIOPLANKTON; Bioquímica y Biología Molecular; Ciencias Biológicas; CIENCIAS NATURALES Y EXACTAS.
The structure and dynamic of planktonic rotifers were analysed in successive years in two shallow lakes (Lacombe and San Miguel del Monte) with different hydrological characteristics and aquatic macrophytes. Lacombe is characterized by the absence of tributaries, its small area and the presence of central annular stands of emergent macrophytes (Scirpus californicus) that reduce the open water sector. In this lake, during the study colonization by sumerged macrophytes occurred and an extensive clear water period was detected. San Miguel del Monte has two affluents and the emerged macrophytes (S. californicus) are observed in some littoral sectors. Two sampling stations were located in both lakes: one at the deeper part of the lake and the other in a sector with emergent macrophytes. Spatial-temporal changes of planktonic rotifers in the water column were examined. The perennial species found in these shallow lakes are considered to be common in eutrophic waters, eurytopic, and are widely distributed. The 59% of total species richness were common to both environments. The minor number of species recorded in Lacombe could be related to the structure of the egg banks in sediments and the impossibility of certain species to colonize from other water bodies. The occurrence of sumerged macrophytes (Potamogeton pectinatus and Myriophyllum quitense) in Lacombe favoured the presence of numerous periphytic species of Trichocercidae and Lecanidae in the open water sector. Records of some species (Brachionus havanaensis, B. plicatilis, Hexarthra fennica, Keratella cochlearis, Notholca acuminata and N. squamula) were related to their temperature or salinity preferences. Two rotifer peaks were recorded in Lacombe: one in later spring-early summer and other in autumn, whereas in San Miguel del Monte occurred in spring and early summer. In particular occasions during these seasons, the rotifer abundance diminished related to abundant local rainfall that stressed rotifer populations.
Contribución científica N° 782 del Instituto de Limnología "Dr. Raúl A. Ringuelet".
Keywords: Ciencias Naturales; Rotíferos; Plancton; rotifers, plankton, pampasic shallow lakes, temporal variations, causes.