Can TMDL Models Reproduce the Nutrient Loading-Hypoxia Relationship?
Anthropogenic nutrient enrichment of estuaries is a problem dramatically transforming coastal ecosystems worldwide. Despite significant public and private sector resources dedicated to curbing point and non-point sources of nutrient loading, many of the symptoms of eutrophication, such as low bottom water dissolved oxygen (DO), have not abated. Recently, studies have suggested that many eutrophied estuaries have exhibited unexpected responses to nutrient reduction: hypoxic volume has continued to increase while nutrient loading has plateaued or decreased. The objective of this project was to construct a long-term time series of nutrient loading for the Chesapeake Bay (1950-present) from nutrient loading observations (i.e., Susquehanna, Potomac, and Patuxent), as well as proxies for other non-tidal rivers, long-term records of point sources, and proxies for changes in atmospheric loading. This loading reconstruction was then used to force the 4,000 segment Chesapeake Bay Program Environmental Modeling Package (CBEMP). Hydrodynamic simulations were limited to three freshwater states (i.e., normal, wet, and dry). Results indicate that while the model captures relative inter-annual variability in hypoxic volume in late July, late June/early July hypoxic volume may be more difficult to capture due to the inability of these models to accurately simulate stratification. Several improvements were also suggested for the sediment flux model of the CBEMP that are already being incorporated into management efforts in the Bay. Long-term trends in nutrient loading have also been analyzed and indicate a general increase in particulate loading (Particulate Phosphorus – PP, Particulate Nitrogen – PN, and Suspended Sediment – SS) while dissolved constituents have been on the decline.
This title belongs to WERF Research Report Series
ISBN: 9781780406497 (eBook)
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