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DISTINGUISHING AND QUANTIFYING NATURAL AND ANTHROPOGENIC NUTRIENT LOADING TO PACIFIC NORTHWEST ESTUARIES
Citation:
BROWN, C. A. AND J. E. KALDY, III. DISTINGUISHING AND QUANTIFYING NATURAL AND ANTHROPOGENIC NUTRIENT LOADING TO PACIFIC NORTHWEST ESTUARIES. Presented at OW/ORD Seminar Series, Washington, DC, September 13, 2006.
Description:
Many coastal ecosystems are experiencing environmental problems due to excess nutrients, particularly nitrogen. Identifying the sources of dissolved inorganic nitrogen (DIN) in estuaries is complicated by the multiple sources and pathways, temporal variability in inputs, and variations in transport. Our research is showing that in contrast to the East and Gulf coasts of the United States, many of the estuaries in the Pacific Northwest have high nitrogen loading associated with natural sources. Natural sources of nitrogen include seasonal nearshore coastal upwelling as well as nitrogen fixation associated with native red alder (Alnus rubra) stands in the watershed. We present evidence that these natural sources of nitrogen are important at a regional scale. In this presentation, we quantify the nutrient loading to an estuary in the Pacific Northwest and identify the sources of nitrogen including natural and anthropogenic sources. We are using a novel approach combining a transport model with natural abundance stable isotopes (¿ 15N) to identify nitrogen sources within an estuary. These tools are applicable across a regional scale, and address the critical issue of distinguishing natural and anthropogenic sources in the development of nutrient criteria.