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Linking Watershed Land-use Patterns to Estuarine Indicators

Dennis Whigham
Smithsonian Environmental Research Center
Edgewater, MD

Science question

Direct and indirect effects of human activities have taken a toll on the nation's estuaries yet few direct linkages have been identified between human activities on land and responses in estuarine ecosystems. The Atlantic Slope Consortium (ASC) is one of five national projects funded in EPA's Estuarine and Great Lakes (EaGLe) initiative within the Science to Achieve Results (STAR) program. The goal of the EaGLe's initiative is to 'develop the next generation of ecological indicators that can be used in a comprehensive coastal monitoring program across the country's coasts'.

The research

ASC scientists have identified potential abiotic and biotic indicators in Chesapeake Bay subestuaries that are linked to watershed land-use patterns, especially the amount of development. Linkages between development and degradation of estuarine indicators is a key finding of the ASC project, especially the finding that relatively small amounts of development result in significant degradation. Two examples illustrate the linkages identified thus far. Smithsonian Institution scientists found that there was a 26% probability that the diversity of birds that breed in estuarine wetlands would decrease with as little as 10% development of land within 500 meters of the wetland (Diagram 1). The probability increased to 79% when the amount of development increased to only 17%. The same research group also found a significant relationship between the amount of watershed development and PCP levels in White Perch (a commercially important species). With less than 20% development of watersheds PCP levels were above the consumption levels recommended by EPA (Diagram 2). Other potential estuarine indicators that have been identified by the ASC research team are the abundance of juvenile blue crabs, concentrations of nitrogen in water, the abundance and nutrient status of Common Reed - an invasive wetland species - in estuarine wetlands, the diversity of the fish community in nearshore habitats, and the abundance of birds that forage in shallow estuarine habitats.

Contributions to environmental outcomes

The ASC research is providing a comprehensive list of potential estuarine indicators. They are also obtaining the first comprehensive information on thresholds of watershed disturbance that result in a degradation of estuarine resources. Threshold information is important because it can potentially be used to determine how much watershed development can occur in order to avoid estuarine degradation. Threshold information could also be used to identify areas where successful management and restoration would have the potential to reverse the consequences of previous development.





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