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Benthic Habitat Mapping
Regional Monitoring Case Study
In the U.S. Environmental Protection Agency (EPA) regional monitoring program called the Mid-Atlantic Integrated Assessment (MAIA), the Virginian Province Benthic Index was calculated for each sampling location and used to map the distribution of degraded versus non-degraded benthic conditions (Paul et al. 2001, U.S. EPA 2002). This allowed for subsequent assessments of the spatial extent of degradation (percent of area) in large estuaries like Chesapeake and Delaware Bays, as well as in their component sub-systems. Initially, 41 candidate metrics were identified and tested for their ability to discriminate between sites that were known to be degraded and those that were known to be free of anthropogenic stress. After a series of iterative statistical tests, it was found that a combination of only 3 of the original 41 metrics was needed to consistently discriminate between degraded and non-degraded conditions:
The diversity metric contributed positively to the calculation of the Virginian Province Benthic Index, while the two abundance metrics contributed negatively. Sites with low diversity and high numbers of pollution-indicative tubificids and spionids, therefore, were assigned negative benthic index values and classified as degraded. Sites with high diversity and relatively low numbers of tubificids and spionids were assigned positive benthic index values and classified as non-degraded. Mapping of benthic community condition using various benthic indices has proven to be an effective tool for managers to evaluate both status and trends in estuarine systems at regional scales. These indices allow managers to compare the degree of habitat degradation in large estuarine systems (such as Delaware Bay) to smaller estuaries and tributaries (such as the Delaware River). As shown in this map, over half of the Potomac and York Rivers have negative indices, while the Choptank River and Chincoteague Bay are rated more positively. About a third of the Chesapeake Bay is also rated as degraded by the benthic index, but the mainstem of Chesapeake Bay generally fares better than its tributaries. Comparing the benthic community index with other measures of water and sediment quality helps to reveal cause-and-effect relationships (U.S. EPA 2002). Scientists are able to determine, for example, whether the benthic habitat degradation across large estuarine systems like Chesapeake and Delaware Bay, and within individual sub-systems (e.g., rivers and smaller estuaries), is due to chronically low dissolved oxygen levels, elevated sediment contamination, or a combination of both. This provides managers with the information they need for more effective targeting of future pollution prevention and control strategies. References Paul, J.F., K.J. Scott, D.E. Campbell, J.H. Gentile, C.S. Strobel, R.M. Valente, S.B. Weisberg, A.F. Holland, and J.A. Ranasinghe. 2001. "Developing and Applying a Benthic Index of Estuarine Condition for the Virginian Biogeographic Province." Ecological Indicators. Volume 1. Pages 83 to 99. U.S. Environmental Protection Agency. 2002. Mid-Atlantic Integrated Assessment 1997-98 Summary Report, EPA/620/R-02/003. U.S. Environmental Protection Agency, Atlantic Ecology Division. Narragansett, Rhode Island.
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