You are here:
Classification of Regional Patterns of Environmental Drivers and Benthic Habitats in Pacific Northwest Estuaries
Citation:
LEE, II, H. AND C. A. BROWN. Classification of Regional Patterns of Environmental Drivers and Benthic Habitats in Pacific Northwest Estuaries. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-09/140 (NTIS PB2012-110753), 2010.
Impact/Purpose:
To help determine the vulnerability of Pacific Northwest estuaries to excess nutrients, the Pacific Coastal Ecology Branch (PCEB) of the Western Ecology Division conducted a landscape analysis and field studies in Pacific Northwest estuaries.
Description:
While increased anthropogenic nutrient loading of coastal ecosystems is a growing ecological and economic problem both in the U.S. and globally, the extent of such excess nutrient loading in Pacific Northwest estuaries is poorly known. To help determine the vulnerability of Pacific Northwest estuaries to excess nutrients, the Pacific Coastal Ecology Branch (PCEB) of the Western Ecology Division conducted a landscape analysis and field studies in Pacific Northwest estuaries. The landscape analysis identified 103 Pacific Northwest estuaries (exclusive of Puget Sound), most of which are small. The watersheds associated with these estuaries had low population densities and were primarily forested with relatively low percentages of developed land. The 103 estuaries broke out into several classes based on their extent of oceanic exchange, with those with restricted flushing being the most vulnerable to excess nutrients. Previous research at PCEB had shown that seasonal intrusion of coastal upwelled water was the major nutrient source in the lower Yaquina Estuary during the summer. During the low river flow conditions of summer, riverine nutrients (i.e., terrestrially derived) were the dominant nutrient source only in the upper Yaquina Estuary. Oceanic nutrients are a natural source, while the terrestrial nutrients may be natural or a mix of natural and anthropogenic sources. To evaluate the generality of this pattern, nutrient source studies were conducted in seven Oregon estuaries (Alsea, Coos, Nestucca, Salmon River, Tillamook, Umpqua River, and Yaquina). Results demonstrated that the intrusion of high nutrient ocean water was the major nutrient source in the lower estuary for all seven estuaries. The next step was to evaluate whether the native seagrass, Zostera marina and four other key components of estuarine food webs were primarily exposed to ocean-derived or riverine-derived nutrients during the summer. The spatial distributions of these resources were determined both through aerial photography and field studies in each of the seven estuaries. Overlaying the spatial distributions of these species over the spatial patterns of nutrient sources showed that the bulk of the Z. marina, benthic macroalgae and both burrowing shrimp populations occurred in the oceanic segments of all seven estuaries. The exception to this pattern was the non-native seagrass, Z. japonica which was relatively abundant in both the oceanic and riverine segments. Compared to the other species, this non-native seagrass has a greater exposure to terrestrially derived nutrients and thus may be more susceptible to any future increases in terrestrial runoff of nutrients. Results from our studies and a growing body of literature suggest two key points for the management of nutrient enrichment in the Pacific Northwest. First, coastal Pacific Northwest coastal estuaries are, in general, not showing indications of eutrophication. Additionally, the majority of the populations of four of the five biotic resources we evaluated occurred in the oceanic segment of the estuaries, indicating a lower vulnerability to terrestrially derived nutrients. However, observations of phytoplankton blooms in the upper estuary segments of a few estuaries suggest that the riverine segments of estuaries may be experiencing localized nutrient enrichment. Second, environmental drivers such as coastal upwelling strongly indicate that regional approaches are needed to understand nutrient dynamics as well as in the development of management strategies and tools, such as the development of nutrient water quality criteria.