vvEPA
United States
Environmental Protection
Agency
Office of Water
(4503F)
EPA841-K-94-005a
September 1994
Watershed Protection:
TMDL Note #2
Bioassessment and TMDLs
Background
Why is
ecological
regionalization
important?
Total Maximum Daily Loads (TMDLs) allocate allowable loads among different
pollution sources so that appropriate control actions can be taken, water quality
standards achieved, and human health and aquatic resources protected. To attain
applicable water quality standards effectively, all sources of pollution to surface
waters must be considered, including nonchemical stresses such as habitat
alteration and hydromodification. This requires incorporating evalua|ions of the
physical and biological components of aquatic ecosystems. Biological
assessments (bioassessments) are well-suited to identifying aquatic life use
impairments and evaluating their relative magnitude.
Bioassessment is the evaluation of ecosystem condition using integrated
assessments of habitat and biological communities and comparing the results of
the assessments to empirically defined reference conditions. Once an
impairment is'identified, other techniques, such as chemical sampling and
toxicity testing might be needed to determine the cause(s) of impairment and
sources of stress so that appropriate mitigation strategies can be designed and
implemented. Bioassessments performed through time provide information
about the ecological integrity (i.e., the condition of an unimpaired ecosystem as
measured by combined chemical, physical, and biological attributes [Barbour et
al., 1992]) of the waterbody and can indicate whether pollution control actions ,
are achieving the biological endpoints that might be specified by a TMDL.
They are particularly valuable for assessing the effects of physical habitat
degradation on biological resources. Bioassessments can lead to substantially ;
more accurate water resources assessments by explicitly linking biological and
physical habitat evaluations with chemical water quality determinations.
The TMDL process is a geographically-based approach to preparing load and
wasteload allocations for sources of stress that might impair waterbody integrity.1;
The geographic nature of this process can be complemented and enhanced by
using ecological regionalization as part of bioassessment activities.
Ecosystems with similar spatial patterns can be grouped into ecoregions, which
can be developed using mapped variables, such as hydrologic units, land-surface
form, soil type, potential natural vegetation, and land use. Naturally occurring
biotic'assemblages would be expected to differ among ecoregions but to be
relatively similar within a given region. One of the key tests for determining the
validity of ecoregions is to establish that variability within regions is less than
between regions. The ecoregion concept provides a geographic framework for
more efficient aquatic resource management. A logical result of applying
regionalization is that similar water quality standards, criteria, and monitoring
strategies are likely to be valid throughout a particular ecoregion, but should be
modified to accommodate differences between regions (Gallant et al., 1989).
Ecoregionalization provides a means of identifying sites that represent valid
reference conditions for an entire region for biosurveys and assessments. This
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How can
bioassessment
be used in the
TMDL process?
can obviate the need to identify site-specific reference (i.e., minimally impaired)
locations. These might not exist in many watersheds affected by urbanization
and agriculture.
/. Identification of Water Quality-Limited Waters that Require TMDLs
The first step in the water quality-based approach is to identify waterbodies that
do not meet water quality standards after required controls have been installed.
See Figure 1. This requires reviewing water quality standards, evaluating
monitoring data, and determining whether adequate controls are in place.
Biological community and habitat impairments are identified by comparing
biological monitoring data from waters of concern against a reference condition
(i.e.,"pristine" or minimally impaired waters) (Plafkin et al., 1989). The ability to
complete bioassessments relatively rapidly enables states to meet the biennial
reporting requirement for a list of waters still needing TMDLs and priority
waterbodies.
2. Priority Ranking and Targeting Listed Waters
For the second step, a state prioritizes its list of waters needing TMDLs and
targets those waters for development of TMDLs within a specified period. While
individual states define their own ranking process, the Environmental Protection
Agency (USEPA) has encouraged the adoption of ranking processes that integrate
the pollution control activities in a state with other resource management
programs and activities that directly or indirectly relate to water quality.
Bioassessment data can be used in the ranking and targeting process to determine
the relative vulnerability or fragility of particular waterbodies as aquatic habitat.
USEPA guidance (1991) lists this as a factor
states might consider.
Ecoregionalization in Ohio
Ecoregtonallzation has been effectively used in Ohio to
increase the utility of bioassessments for reporting
under Clean Water Act §305(b). The development of
ecoreglons has allowed Ohio to identify previously
undetected water quality impairment using btocriteria
and bioassessments. A comparison of the waterbody
impairments identified using biocriteria with waterbody
chemical exceedances based on the Ohio Water
Quality Standards was performed as part of Ohio's
1990 305(b) reporting. It showed that biological
impairment was evident in 49.8 percent of the
waterbody segments where no ambient chemical water
quality exceedances were observed (Yoder, 1991).
Biological and chemical assessments both indicated
impairment (or lack of impairment) in slightly greater
than 47 percent of the waterbody segments. The
development of ecoregions and subecoregions was
fundamental to the ability of biological assessments, in
concert with biocriteria, to generate these results
(Yoder, 1991; Shepard, 1993),
3. TMDL Development
This third step of the TMDL process involves
the compilation and analysis of all available
data, as well as any modeling that might be
needed to prepare a TMDL for the stressor of
concern. TMDLs can and should be developed
for nonchemical stressors that are identified
through biosurveys and habitat assessments.
For example, biosurveys and habitat
assessments are excellent tools for identifying
where damaged riparian zones should be
repaired in order to reduce stream temperature
and bank erosion in cool and cold-water
streams. These techniques can be useful for
indicating where sediment loadings should be
reduced to reduce stream channel
embeddedness in trout and salmon spawning
reaches. They can also indicate the size of
impacted habitat.
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"Identification of threatened
good quality waters is an
important part of this
approach" --
Bioassessment can
identify such waters and
establish reference conditions
Assessment of aquatic
life use attainment
based on
biological
surveys
tdfnttftcauon of Water Quallty-
Llmtted Waters
Review wattr quality standards
Evaluate monitoring data
Determine If adequate controls
are In place
Assessment of Water QuaiHy-
Based Control Actions
Monitor polnt/nonpolnt sources
Audit NPS controls for effectiveness
Evaluate TMDL for protection
of wattrbody daslgnatad uses
Prioritization of
impaired waters is
best accomplished
through assessment of
biological condition
Aquatic life use and
biocriteria are part
of WQ standards
Bioassessment of
receiving waters is
an important link to
ecological integrity
Priority Ranking and Targeting
Integrate priority ranking with other
water quality planning and management
activities
Use priority ranking to target
waterbodles for TMDLs
Use of bioassessment
should be included in the
updated plan.
Enhanced if ecological
regionalization is
applied
Implementation of Control
Actions
Update watarquaHtymanagtmant
plan
Issue water quality-based permits
Implamant nonpolnt source controls
(section 319 management plans)
Development of Control
Actions through TMDLs
Apply geographic approach
applicable
Establish schedule for phased
approach, H nacesuary
Complete TMDL development
BMP selection and siting best accomplished
by incorporating bio- and habitat assessment
Adapted from Flour* 1, Guidance forth* Implementation
QfWBtorQuality-BuodDadsIon<: Tho TMDL Proem
TMDLs can be
developed for non-
chemical stressors
Figure 1. Using bioassessment in the TMDL process
4. Implementation of Control Actions
After TMDLs are developed, states must choose appropriate control actions, then
site and implement them so that specific sources of stress can meet the
allocations specified by the TMDL. Bioassessment and habitat data can be
useful for selecting and siting required controls. For example, bioassessment and
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References
habitat data might show that a particular stream reach is impaired due, in part, to
poor habitat conditions and that those conditions are caused by sediment
originating from streambank erosion upstream. Reestablishing vegetated riparian
buffer zones would be a reasonable control action for this case, which would
have the additional benefits of reducing stream temperature as the vegetation
matured and increasing the food base for macroinvertebrates because
allochthonous material would be added to the stream.
5. Assessment of Water Quality-Based Control Actions
Bioassessment can be used as,one component of an integrated monitoring
approach to measure pollutant inputs from point and nonpoint sources following
implementation of control actions. For example, bioassessment can be used to
determine the biological and habitat effects of a streambank fencing program to
reduce streambank erosion in agricultural areas or the effects of controls applied
to combined sewer overflows. Collection of monitoring data is essential for
evaluating whether the TMDL that is developed for a waterbody is successful at
protecting designated use(s).
Harbour, M.T., J.B. Stribling, and J.R. Karr. 1992. Biological criteria:
.'• Technical guidance for streams. Draft. United States Environmental
Protection Agency, Office of Science and Technology, Washington, DC.
Gallant, A.L., T.R. Whittier, D.P. Larsen, J.M. Omernik, and R.M. Hughes.
1989. Regionalization as a tool for managing environmental resources.
EPA 600/3-89/060. United States Environmental Protection Agency,
Environmental Research Laboratory, Corvallis, OR.
Plafkin, J.L., M.T. Barbour, K.D. Porter, S.PC Gross, and R.M. Hughes. 1989.
Rapid bioassessment protocols for use 'in streams and rivers: Benthic
macroinvertebrates and fish. EPA 440/4-89/001. United States
Environmental Protection Agency, Office of Water, Washington, DC.
Shepard, L. 1993. Application of biocriteria under sections 303(c) and 303(d) of
the Clean Water Act. Memorandum from L. Shepard, Water Quality
Standards Coordinator, United States Environmental Protection Agency,
Region 7, to Susan Jackson and George Gibson, United States
Environmental Protection Agency, Office of Science and Technology.
January 8, 1993.
USEPA. 1991. Guidance for the implementation of water quality-based
decisions: The TMDL process. EPA 440/4-91-001. United States
Environmental Protection Agency, Office of Water Regulations and
Standards, Washington, DC.
Yoder, C.O. 1991. Answering some concerns about biological criteria based on
experiences in Ohio. In Water Quality Standards for the 21st Century.
Proceedings of a Conference. United States Environmental Protection
Agency, Office of Water.
Any Questions or Comments? Please, contact Theresa Tuafio, Watershed
Branch, Office of Water, U.S. Environmental Protection Agency, 401 M
Street SW, Washington, DC 20460, phone 202/260-7079, fax 202/260-7024.
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