the sandier sediments located closer to the mouth of the estuary.
The coastal rivers of southern Oregon contain more fine-grained sediments than Oregon’s north coast rivers.
The composition of Coos River sediments may be moderately stressful to macroinvertebrates, a key biological community.
1996). Many determinants of estuarine sediment dynamics are naturally occurring, but human activities (e.g., shellfish culture, land use changes, dredging) can also change the way sediments are distributed (Bell et al. 2000; Pregnall 1993).
Sediments provide vital estuarine habitat for many organisms such as bivalves, snails, worms, echinoderms, crustaceans, etc. These organisms live in the sediment and often facilitate important ecological and geochemical processes in the estuary (Thrush et al. 2004). Sediments also facilitate the transport of nutrients and contaminants within aquatic ecosystems (Bartram and Ballance 1996; Swett 2010). This is particularly true of fine sediments (i.e., silt and clay), which are “responsible for a significant proportion of the annual transport of metals, phosphorus, chlorinated pesticides, and many industrial compounds such as polynuclear aromatic hydrocarbons, polychlorinated biphenyls, dioxins and furans” (Bartram and Ballance 1996).
The Coos estuary has been classified as one of the muddiest estuaries in Oregon (Lee II and Brown 2009) due to the relatively high percentage of “fines” (i.e., silt and clay)(Figures 1 and 2), a classification particularly applicable to the upper estuary. Data from the Oregon Department of Environmental Quality (ODEQ 1999, 2001, 2004, 2005, 2006) and the United States Army Corps of Engineers (USACE 2009) confirm that sediment in the estuary’s upper reaches (e.g., Haynes Inlet, Upper Bay, Isthmus Slough, and Catching Slough) is muddier than sediment near the mouth of the estuary (e.g., lower South Slough and Lower Bay Subsystems). Sediment composition is commonly classified using the Wenthworth Grade Scale, based on the particle size and cohesive properties of a material (Wenthworth 1922)(Table 1).
These conclusions are generally supported by Oregon’s newly developed estuary habitat classification maps using NOAA’s Coastal and Marine Ecological Classification Standard (CMECS) applied to Oregon estuaries by the Oregon Department of Land Conservation and Development (Figure 1).
Hubler (2008) suggests that elevated levels of fine sediments in some rivers and streams on the southern Oregon coast may be stressful to aquatic biota. In her report, fine sediment stress is categorized into four categories (Figure 3). Fines in the Coos River subsystem sampling sites exceeded Hubler’s lowest/least stress sediment category (0-10% fines) considered to be stressful to macroinvertebrate communities. However, the median sediment score in the Coos river did meet the moderate stress benchmark (11-20% fines). Thus, sediment stress in the Coos river is higher than the smaller estuaries (e.g., Necanicum, Nehalem) but lower than, or similar to, the estuaries associated with major coastal rivers (e.g., Coquille, Umpqua rivers)(Figure 4).
Bartram, J. and R. Ballance [Eds]. 1996. Water Quality Monitoring. A Practical Guide to the Design and Implementation of Fresh Water Quality Studies and Monitoring Programmes. Chapman & Hall, London.
Bell, Rob, Mal Green, Terry Hume, and Richard Gorman. 2000. Estuaries: What Regulates Sedimentation in Estuaries? Water and Atmosphere 8 (4): 13-16.
Coastal and Marine Ecological Classification Standard (CMECS). 2014. [Unpublished shapefiles for ArcGIS from the National Oceanographic and Atmospheric Association (NOAA)]. Accessed from the Estuarine and Coastal Sciences Laboratory of South Slough National Estuarine Research Reserve.
Pregnall, Maribel Marcy. 1993. Regrowth and Recruitment of Eel Grass (Zostera marina) and Recovery of Benthic Community Structure in Areas Disturbed by Commercial Oyster Culture in the South Slough National Estuarine Research Reserve, Oregon. [Master’s thesis]. Department of Environmental Sciences, Bard College, Annandale-On-Hudson, New York.
Stevenson, J., L. G. Ward, and M. S. Kearney. 1988. Sediment transport and trapping in marsh systems: implications of tidal flux studies. Marine Geology,80(1), 37-59.
Swett, Michael P. 2010. Assessment of Benthic Flux of Dissolved Organic Carbon in Estuaries Using the Eddy Correlation Technique. Master’s Thesis, University of Maine.
Thrush, S. F., J. E. Hewitt, V. J. Cummings, J. I. Ellis, C. Hatton, A. Lohrer, and A. Norkko. 2004. Muddy waters: elevating sediment input to coastal and estuarine habitats. Frontiers in Ecology and the Environment, 2(6), 299-306.
United States Army Corps of Engineers (USACE). 2009. Coos Bay Sediment Quality Evaluation Report. [report prepared by Wendy Briner and Mark Siipola of the Portland District USACE].
Wentworth, C. K. 1922. A scale of grade and class terms for clastic sediments. The Journal of Geology, 377-392.
Wright, L. D. 1977. Sediment transport and deposition at river mouths: a synthesis. Geological Society of America Bulletin, 88(6), 857-868.