Chesapeake Bay - Watershed Stream Health:

Introduction

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Bottom-dwellers, also known as benthic macroinvertebrates, are freshwater organisms including snails, mussels, and insects that live in and on the stream and river bottom. They are routinely monitored throughout the Chesapeake Bay watershed by the states and other organizations.The abundance and diversity of these organisms are good indicators of local stream health because they have more limited movement than fish and they respond quickly to pollutants such as nutrients and sediment and other environmental stressors. The health of bottom-dwellers is threatened by pollutants introduced into streams and rivers by sources such as mining, agriculture, stormwater, fossil fuel combustion, and household and industrial wastewater treatment facilities. These human activities can add nitrogen and phosphorus to the water, which lead to algal blooms and low dissolved oxygen in slow-moving streams. Mining, agriculture, and development also can add fine sediment to streams, which smothers benthic organisms and contributes to low dissolved oxygen. Mining adds toxic chemicals to the water that directly kill these bottom-dwellers.



 

Stream Health Map

Water quality in Chesapeake Bay is linked to the health of the 64,000 square miles of land and associated streams and rivers that comprise its watershed. Land-based activities (e.g., development, agriculture) can add pollution, such as nutrients and sediment, to local streams and rivers, which ultimately flow into Chesapeake Bay. The new stream health indicator (Benthic Index of Biotic Integrity (BIBI) illustrates this link between stream health and land-based activities. For example, stream health conditions tend to be very poor to fair in areas that have extreme land disturbance, such as new construction, which results in high levels of pollution, altered water flow, and poor quantity and quality of streamside vegetation. Such unhealthy streams tend to be clustered around large urban areas such as metropolitan Washington, D.C. in the lower Potomac River watershed, and in areas that have land-uses dominated by agriculture (e.g., Eastern Shore of Maryland) and mining (e.g., parts of Pennsylvania and West Virginia). In contrast, stream health conditions tend to be good to excellent in areas with little land disturbance that offer low levels of pollution and natural in-stream and streamside habitat. Such healthy areas tend to be clustered around forested and prairie areas, such as the upper Potomac River watershed. The health of streams is variable throughout the Bay watershed and can vary even within a smaller subwatershed (e.g., the Potomac River watershed). Exceptions to these generalizations linking land-based activities to stream health are expected and are due to complexities within the ecosystem. Overall, 1,632 of the sites had very poor or poor health conditions and 1,056 sites had good or excellent conditions, out of a total of 3,291 sampling sites. Developing this indicator provides an important tool for managers and watershed groups who are focusing efforts to restore degraded streams and protect the quality of the healthiest ones.

 Interactive Google Map with data overlay

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Methods

Most monitoring programs in the Chesapeake Bay watershed collect samples of bottom-dwellers (benthic macroinvertebrates) with somewhat similar field methods and calculate a common suite of indicators from the data. However, the programs use state-specific protocols to score and evaluate these indicators in order to identify "impaired" waters for regulatory requirements. The purpose of this new stream health indicator is to evaluate benthic community health in a uniform manner and in the context of the entire Chesapeake Bay watershed. This approach incorporates the data into an overall watershed-wide Benthic IBI that is classified at the scientific family level. This method allows the results to be compared across state boundaries. This indicator is a first step toward a regional benthic community health assessment. Future work will continue to improve upon this indicator by standardizing methodologies, developing ways to combine results from different sampling designs (targeted vs. random samples), and incorporating data that were not available for analysis this year.

Further Information

Chesapeake Bay Program Stream Health Indicator website

Stream health indicator methods

State Assessments:

Delaware
Maryland
New York
Pennsylvania
Virginia
West Virginia