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INTEGRATED ASSESSMENTS OF THE ENVIRONMENTAL CONDITION OF THE CHESAPEAKE BAY
Citation:
Paul, J F. AND S. Phillips. INTEGRATED ASSESSMENTS OF THE ENVIRONMENTAL CONDITION OF THE CHESAPEAKE BAY. Presented at EMAP Coastal Symposium on Coastal Monitoring, Pensacola, FL, April 24-27, 2001.
Description:
The Chesapeake Bay, the Nation's largest estuary, has experienced environmental degradation due to nutrient enrichment, contamination, loss of habitat, and over-harvesting of living resources. Resource managers need information on the extent of degradation to formulate restoration strategies. The presentation illustrates approaches our organizations are taking in conducting integrated resource assessments by reviewing examples for two problems in Chesapeake Bay (sediment contamination and nutrient loading). Sediment contamination is primarily found in small systems around the bay (i.e., harbors, embayments, and tidal rivers). The EP A EMAP approach to monitoring and assessment is to collect a suite of indicators at sites selected using a probability design. The design allows one to estimate areal extent of estuarine conditions, and the suite of indicators sampled pennits associations to be made between stressors and effects. Approximately 5% of the Bay has sediment with contaminants above the Long and Morgan ER -M levels, while 9% of the small systems exceed these levels. Research is currently underway to conduct integrated assessments relating landscape metrics to estuarine condition. Quantitative relationships have been developed which indicate that sediment contamination levels increase with urban land and point source loading in the local watershed, while they decrease with increasing nonforested wetlands acreage. Further work is being conducted to refine these relationships. Nutrient loading is a system-wide issue, contributing to hypoxia in the mainstem portion of the bay and the larger tributaries, as shown by data collected for the Chesapeake Bay Program. The USGS has conducted an integrated study of the nutrient sources and loadings in surrounding watersheds that are contributing to hypoxia in the Bay. The integrated approach includes relating nutrient sources to loadings delivered to the Bay, understanding the influence of ground water on the delivery, and examining how the nutrient loadings have changed over time. About 20 percent of the nutrients from sources in the watershed ultimately reach the Bay, based on results of a statistical model that links nutrient sources to loadings (SPARROW model). On average, about half of the nitrate from the non-point sources travels through the shallow ground-water system, but varies depending on the geology and source. Finally, nutrient loads to the Bay are not showing a large decrease over time in spite of nutrient reduction efforts. The lack of a trend is related to a lack of trend in stream flow and the buffering by ground water, both of which influence the delivery of nutrients to the Bay.