Guidance for Stressor Identification of Biologically Impaired Aquatic Resources in Washington State
Section 303 of the federal Clean Water Act provides (1) guidance for setting water quality standards and (2) a framework to guide the remediation of waterbodies that do not comply with those guidelines. The Clean Water Act mandates that states and tribes sustain water quality at a level that maintains the integrity of its physical, chemical, and biological resources. The Clean Water Act also directs states to improve water quality at impaired sites.
Traditionally, water quality managers emphasized monitoring for physical and chemical pollutants for which numeric criteria have been adopted. When a water chemistry parameter such as dissolved oxygen, pH, turbidity, or temperature demonstrates impairment, managers take action to remedy the issue through the process of determining a Total Maximum Daily Load (TMDL). A TMDL sets the daily maximum amount of a pollutant that a waterbody can receive from all sources and still meet water quality standards. The goal of the Clean Water Act is not only to address the chemical integrity of the waterbody, but the physical and biological integrity as well. Over the past decade, in recognition of this issue, resource managers have begun to use biological data to make decisions.
Biological criteria can be a critical tool in detecting degradation of water quality. Biotic communities may exhibit the impacts of degradation even when common water quality parameters meet standards. This may indicate that other anthropogenic pollutants or activities are degrading water quality or that available water quality data are not robust enough to detect the impairment.
Organisms may respond to a vast number of complex factors and cumulative impacts for which current water quality standards are inadequate in detecting. For example, there are many chemicals making their way into waterways for which numeric water quality criteria have not been adopted. Likewise, there is no mechanism to measure impairments due to declines in habitat quality, alteration of flow, or changes in sedimentation patterns. Therefore, the United States Environmental Protection Agency (EPA) has provided guidance on the process of identifying stressors responsible for biotic impairment (EPA 2000).
The Stressor Identification (SI) process or Causal Analysis/Diagnosis Decision Information System (CADDIS) leads resource managers through a formal and rigorous process that identifies stressors causing biological impairment in aquatic systems. It provides structure for organizing scientific evidence that supports assessment conclusions (EPA 2000). Stressor Identification also has the benefit of being understandable to a wide variety of stakeholders, allowing them to address and improve water quality issues in their jurisdiction. The ability for people invested in the management and protection of natural resources to participate in identifying causes of impairment is a vital step in improving water quality more quickly.