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Health and Environmental Effects Research


Section 303 of the 1972 Clean Water Act requires States, Territories, and Tribes to develop lists of waters that are impaired based on biological, chemical, or physical criteria. For impaired waters, the Clean Water Act mandates that States, Territories, and Tribes impose limits on the amount of pollutants that a waterbody can receive; this limit is known as a Total Maximum Daily Load, or TMDL. In cases in which the impairment is judged to exist based on biological criteria, it is necessary to diagnose the cause(s) of impairment prior to the establishment of a TMDL. The nationwide scope of this problem is enormous: approximately 44% of stream or river miles; 49% of lakes, reservoirs, and ponds; 98% of Great Lakes shoreline waters; and 42% of estuaries have been designated as impaired based on biological criteria.

To determine the causes of biological impairment, waterbodies must be considered within the context of their watershed; consequently, EPA's research plan to study aquatic stressors includes development of methods and tools to enable this work. The Aquatic Stressors research plan lays out five projects which share the goal of supporting the TMDL process and improving the current state of the science of monitoring and assessment. Research in under this topic includes development of the following:

View information about the Implementation Plan for Diagnostics Research within the Aquatic Stressors PDF file. (PDF, 197 pp, 3.21 MB, About PDF).


EPA worker testing water

An EPA scientist testing water quality.

Development of a conceptual model and a framework for information management

The first step in achieving the goals of EPA's plan for Diagnostics Research is to formulate a conceptual framework that can be used to describe relationships between stressors and the responses of aquatic systems to those stressors. Efforts are also underway to produce a seamless nationwide database containing watershed boundaries and other geospatial data and a database containing information about stressor-response relationships for non-toxic stressors. Progress in this area will support the development of criteria aimed at protecting aquatic systems from stressors such as nutrients and suspended and bedded sediments.

Development of a classification framework

EPA researchers are working to develop a classification system to group aquatic systems based on how systems respond to different types or levels of stressors. This classification system would be based on a spatial hierarchy, ranging in scale from habitat to waterbody to watershed to region and would assist in the setting of TMDLs by reducing the number of unique cases that would need to be considered.

Development of diagnostics and case studies to test their application

Tools under development include models useful in determining the source(s) of biological impairment, in allocating causality among multiple stressors, in diagnosing interactions among multiple stressors, and in forecasting the effects of remediation efforts. Once developed and as these tools are being developed, EPA plans to test them in regional case studies. Case studies are particularly useful because they allow scientists to address high priority environmental problems and because they provide a mechanism of demonstrating and testing the effectiveness of newly developed diagnostics. Examples of case studies include research on the Great Lakes coastal watersheds, wetlands, and nearshore zones; on shallow estuarine systems in the Northeast Atlantic; and on shallow estuarine systems in the Gulf of Mexico.

Development of generic models with which to evaluate the interactions of multiple stressors

The objective of this research is to assess the likelihood that synergistic and/or antagonistic ecological effects will occur from the interactions of multiple stressors. This work is fundamental to the TMDL-setting process and restoration efforts because a change in the level of one type of stressor may cause a shift in a system's vulnerability to a different stressor. For example, in a turbid coastal wetland, a reduction in the input of suspended solids without an accompanying reduction in nitrogen loading from an upstream animal feed lot could reveal a eutrophication problem that was previously masked due to light limitations. Progress in this area will assist the States and Tribes in developing viable restoration and remediation plans for aquatic systems that are affected by multiple stressors.

Development of a decision-support system

The objective of this research is to develop a decision-support system for diagnosing the causes of biological impairment at multiple scales. This system will be based on the conceptual models that outline expected cause-effect relationships involving single and multiple stressors. This system will describe how to use existing EPA databases, methods, and models; and new tools will be incorporated into the system as they are developed. This work will facilitate an integrated and common approach to assessment and diagnosis at the regional scale and will make the process of setting TMDLs more efficient.

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