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.
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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