Average 2000-2010 Stream Health in the Chesapeake Bay Sub-watersheds
Author: Fred Irani
Date created: May 29, 2013
An effective way to measure the health of freshwater streams and rivers is to study the many tiny critters that live in these waters, called “benthic macro-invertebrates.” The abundance and diversity of snails, mussels, insects and other bottom-dwelling organisms are good indicators of the health of streams because they can’t move very far and they respond to pollution and environmental stresses. Benthic macroinvertebrates are generally harmed by direct and indirect effects of pollutants such as metals, acidity, sediment, pesticides, nitrogen and phosphorus. These pollutants come from sources such as mining, agriculture, urban and suburban runoff, automobile and power plant exhaust, and wastewater treatment facilities. Health of streams was evaluated by the Chesapeake Bay Basin-wide Benthic Index of Biotic Integrity (or “Chessie B-IBI”), which was developed from benthic macroinvertebrate data collected across the entire Chesapeake Bay watershed from over 20 federal, state, local, and river basin commission monitoring programs throughout the Chesapeake Bay basin. Each sampling event is scored on a standardized quantitative scale that allows scoring across jurisdictional boundaries. B-IBI scores were averaged for each site over all years of sampling (2000-2010) and then qualitatively categorized in one of the following categories – very poor, poor, fair, good or excellent for a total of 15,112 scored sites. An analysis was conducted on a subset of the 15,112 sites to investigate regional variation in the B-IBI scores. The subset of sites (8,871) were chosen where a random sampling design was used. By using only randomly selected sites, BIBI scores can be averaged across the smallest feasible watershed size without introducing bias associated with sampling designs that target areas with known degraded or high quality waters. For more information see: Buchanan, C., K. Foreman, J. Johnson, and A. Griggs. 2011. Development of a Basin-wide Benthic Index of Biotic Integrity for Non-Tidal Streams and Wadeable Rivers in the Chesapeake Bay Watershed: Final Report to the Chesapeake Bay Program Non- Tidal Water Quality Workgroup. ICPRB Report 11-1. Report prepared for the US Environmental Protection Agency, Chesapeake Bay Program.