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Water: Monitoring & Assessment

Benefits and Applications of Wetland Bioassessments

Evaluating and Tracking Wetland Health

More than 25 years after it was passed, the Clean Water Act still challenges us to answer critical questions about the physical, chemical, and biological condition of the nation's waters. While great strides have been made to develop and implement methods to evaluate the condition of streams and lakes, research on wetlands has lagged behind. Considering that states and tribes collectively reported the quality of only 4 percent of the nation's wetlands in the National Water Quality Inventory: 1998 Report to Congress, the nation needs an effective means to measure wetland health.

One of the best indicators of an aquatic ecosystem's health is its biological integrity—its ability to "support and maintain a balanced adaptive community of organisms having a species composition, diversity, and functional organization comparable to that of natural habitats within a region." (Karr, J.R., and D.R. Dudley. 1981. Ecological perspective on water quality goals. Environmental Management 5:55–68.) Traditional water quality measurements of chemical concentrations do not accurately measure biological integrity because they do not account for physical or biological stressors, or even a wide enough array of chemical stressors. For example, typical chemical assessments will not detect wetland degradation from such non-chemical sources as erosion, flow alteration, or competition from introduced species. They also fail to detect degradation caused by a chemical omitted from measurement. Similarly, traditional wetland assessments, such as HGM, that emphasize physical attributes of wetlands fail to detect degradation from many chemical and biological stressors.

Many Stressors Can Damage Biological Communities
  • Invasive Species
  • Pesticides
  • Acidification
  • Toxic Chemicals
  • Nutrient Enrichment
  • Hydrologic Modification
  • Sedimentation
  • Habitat Alteration

In contrast, the biological community of a wetland reflects the cumulative response to a host of chemical, physical, and biological stressors that damage a wetland. Therefore, the most meaningful way to measure biological condition is to directly examine one or more biological assemblages, such as macroinvertebrates or vascular plants, and support that data with screening-level habitat and chemistry data.

Scientists can use bioassessment methods to directly measure biological integrity of wetlands and quickly screen wetlands for signs of impairment. For example, Minnesota Pollution and Control Agency--we would like to link to this case study, but have not sent it to you yet--is developing a Wetland Index of Biological Integrity (WIBI) based on wetland macroinvertebrates. While it is still under development, they can use WIBI to identify wetlands impacted by stormwater and agricultural runoff. In Figure 1, the three wetlands on the left are reference wetlands and the two wetlands on the right show signs of biological impairment. If a state or tribe detects a warning signal during this screening process, it can then conduct a more detailed and thorough assessment. Many states using bioassessments in streams are finding that they save time and resources by screening a large number of sites rapidly and then following up with more detailed (and expensive) biological studies and chemical and physical assessments when appropriate.


Evaluating Success of Restoration

States can evaluate the success of restoration activities and best management practices, such as buffer strips, by including follow-up assessments as a component of management plans. By periodically conducting bioassessments, states can track the condition of wetlands and learn which management activities work as planned and which do not work. With this knowledge, states can improve future management plans and save time and money by avoiding marginal activities. The USGS Biological Resources Division, NRCS Wetland Science Institute, and EPA Wetlands Division cooperatively worked on a project to develop bioassessment methods to evaluate restored wetlands in Maryland and Delaware.

Strengthening Water Quality Standards

The objective of the Clean Water Act (CWA) is to "maintain and restore the chemical, physical, and biological integrity of our Nation's waters," including wetlands (CWA Section 101 (a)). Under CWA Section 303, states and eligible tribes develop water quality standards (see Wetland Bioassessment Fact Sheet 7, Water Quality Standards) to ensure that their waters support beneficial uses such as aquatic life support, drinking water supply, fish consumption, swimming, and boating. States can use bioassessment methods to establish standards and criteria that are specifically appropriate for conditions found in wetlands. Criteria are the narrative or numeric descriptions of the conditions found in minimally impacted reference sites. By comparing the condition of a wetland to appropriate criteria, states can determine if the wetland is supporting its designated uses. In the absence of wetland-specific standards and criteria, states must rely on standards developed for lakes, streams, or other waterbodies that have different ecological conditions. In 1990, EPA published National Guidance, Water Quality Standards for Wetlands to help states create water quality standards for wetlands.

Certifying that Permits Maintain Water Quality

Under CWA Section 401, states have the authority to grant or deny "certification" for federally permitted or licensed activities that may result in a discharge to wetlands or other waterbodies. The certification decision is based on whether the proposed activity will comply with state water quality standards. Under this process, a state can use information from biological assessments to determine if a proposed activity would degrade water quality of a wetland or other waterbodies in a watershed. If a state grants certification, it is essentially saying that the proposed activity will comply with state water quality standards. Likewise, a state can deny certification if the project would harm the chemical, physical, or biological integrity of a wetland as defined by water quality standards. A state's Section 401 certification process is only as good as its underlying water quality standards. States can use bioassessments to refine narrative and numeric criteria to make them more suitable for conditions found in wetlands and subsequently improve the Section 401 certification process.

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