Diagnosing Ecological Impairment
Under the Clean Water Act, States must list surface waters as impaired or threatened on 305(b) reports and 303(d) listings based on one or more of three types of criteria: biological criteria (narrative or numeric), chemical criteria, or physical attributes (e.g., habitat quality assessments). When impairment is determined based on biological criteria (26% of impairment decisions), States are also faced with the problem of diagnosing the cause of impairment before plans can be made to reduce the loading of pollutants through the total maximum daily loads (TMDL) process (http://www.epa.gov/owow/tmdl/ ). The nation-wide scope of this diagnostic task is enormous; approximately 21,000 water bodies have been designated as impaired (44% of stream or river miles, 49% of lakes, reservoirs, and ponds, 98% of Great Lakes shoreline waters, and 42% of estuaries. The U.S. EPA Clean Water Action Plan (1998) states that to improve overall efficiency of the TMDL process and to coordinate remediation activities, diagnosis of the causes of impairment is needed. Consequently, a clear need for diagnostic tools, methods and models exists.
This research emphasis the need to diagnose causes of biological impairment within an integrated framework linking watersheds with receiving water bodies to support the TMDL process. Four primary objectives support attainment of this goal:
- Provide a framework for interpreting cause-and-effect relationships
- development of conceptual ecosystem models that can be used to form the framework for diagnostic methods, tools and models; and
- classification schemes that explain variation in the ecological response of individuals, populations, communities, and ecosystems at the habitat, water body, watershed and regional scales and can be used to reduce the number of impaired water bodies to a more manageable number by grouping similar systems.
- Develop single-stressor diagnostic methods and models to determine the primary cause of biological impairment of aquatic ecosystems.
- Develop methods and models to allocate causality among multiple stressors and/or to diagnose interactions among them.
- Develop methods and models capable of forecasting to evaluate the ecological benefits of source reductions, to investigate stressor interactions, and to assess the gains and losses realized by various alternatives for restoration and remediation.
An ancillary objective is to provide to the Regions, States and Tribes tools with different levels of accuracy and sophistication dependent upon the cost benefit ratios of a given resource decision. Tools for diagnosing both single-stressor impacts and multiple stressor interactions are being piloted using regional case studies. These pilots will then be incorporated as example applications into decision-support systems. Ultimately, the decision-support systems will be linked to tools and models developed by ORD's National Risk Management Research laboratory (NRMRL; responsible for restoration research), forecasting not only future impacts based on no action, but also the results of alternative remediation scenarios.
To complete the four steps describing this critical path of research, three explicit research projects are being conducted by AED:
- establish a conceptual framework to guide implementation of diagnostics methods and models,
- develop classification schemes across habitat, water body, watershed and regional scales to provide a means for grouping similarly impaired systems,
- and perform case studies to develop and test methods and models for both single and multiple stressor scenarios, assess the likelihood of multiple stressor interactions, and establish the structure for a decision-support system.
Contact: Kay Ho