United Stales
Environmental Protection
Environmental Research
Laboratory-Co rvallis
August 1993
<&EPA Wetlands Research Update
Prepared by:
Richard Sumner, Regional Liaison
Wetlands Research Program
Mary E. Kentula, Manager
Wetlands Research Program
The Update Is prepared to keep those who are inferos tod in the U.S.
Environmental Protection Agency's Wetlands Research Program (WRP) abreast of
our activities and accomplishments.
The WRP is in the second year of implementing
research towards the development of a risk-based
approach to wetlands protection (Leibowitz et al.
1992a). The specific research objectives of WRP
are: 1) Determine how wetlands contribute to envi-
ronmental quality, both individually and as an ag-
gregate within the landscape; 2) quantify the
effects of stressors and landscape factors on wet-
land function to assess the risks posed by the as-
sociated loss and degradation of wetlands; 3}
develop risk management options through the use
of site prioritization and performance criteria for
wetlands restoration; and 4) design and test a
monitoring system that can assess wetland condi-
tion and the effectiveness of risk reduction activi-
The implementation of a risk-based approach to
wetlands protection requires information on the in-
teraction of wetlands with other ecosystems within
broad geographic areas, including ecoregions
(Omemik 1987) and watersheds. Empirical analy-
sis and overlay analysis (i.e Geographic Informa-
tion System - GIS) are two approaches being
evaluated by WRP for use in landscape-scale
Results from an Illinois study suggest that
empirically-derived Information can be
used to geographically target environmen-
tal management activities, Including wet*
lands restoration, where the goal Is a
remediation of regional water quality prob-
Stream water quality and watershed character-
istics were examined for 64 watersheds in Illi-
nois. Statistical relationships were established
between water quality (e.g., summer and win-
ter nitrate-nitrite concentrations) and watershed
characteristics (e.g., percent of area in agricul-
ture). A hypothetical management scenario
then was specified for each watershed, where-
in 50 hectares of agricultural land were re-
stored to wetlands. The empirical relationships
were used to evaluate the change in nutrient
concentrations that resulted from the simulated
conversions. The study concluded that target-
ing restoration activities in selected watersheds
would induce greater water quality improve-
ment than implementing the activities at ran-
dom within watersheds. A manuscript
describing the study has been submitted for
Watersheds or other landscape units also can be
prioritized for ecosystem protection and restoration
activities through a GIS-based approach. Exam-
ples are given in a recent WRP publication that

Wetlands Research Update, Page 2 of 8
describes the "Synoptic Approach" (Leibowitz
et al. 1992b). GIS-based approaches are
useful when time and data, availability preclude
the use of an empirical approach. However,
empirical results are more reliable because
hypotheses can be tested to ensure that
management scenarios are not based on false
The WRP will continue its evaluation of the
two assessment approaches in new studies on
the prairie pothole wetlands of North Dakota,
and on. wetlands in Delaware. By the end of
1993, a GIS-based assessment of North
Dakota's wetland resources will have been
initiated using the Synoptic Approach.
Empirical studies also are planned as psirt of a
comprehensive effort on prairie pothole
wetlands (See Risk Reduction Project),
including cooperators such as the U.S.
Geological Survey (USGS). The USGS will be
supplying the Project with information about
the response of prairie pothole wetlands to
climatic variability. This kind of information
provides an understanding of the factors
responsible for the formation and maintenance
of wetlands within the study areia. The
information also allows results obtained during
a recent drought within the region to be
extrapolated to wetter conditions.
Concurrent with work in North Dakota, the
WRP will enter into a second interagency
agreement with the USGS in Delaware. The
cooperative study will examine a
hydrogeomorphic classification system for
landscape units within the state, and whether
wetlands within different units exhibit differing
capacities to perform a water quality
improvement function.
The WRP has commissioned'several new
studies designed to demonstrate and refine
WRP's "An Approach to Improving Decision
Making in Wetlands Restoration and Creation"
(Kentula et al. 1992). The work will culminate
in a series of new publications discussing
methods for (1) characterizing populations of
wetlands to establish their reference condition,
(2) analyzing the information gathered to
establish management goals, performance
criteria, and monitoring protocols for wetland
restoration projects, and (3) prioritizing areas
ecologically suitable for wetlands and riparian
A recently implemented study builds upon past
WRP work conducted in Oregon. The Oregon
Wetland Study (OWS) will produce detailed
characterizations of a sample of approximately
100 natural, created, and restored freshwater
wetlands located in the Portland, Oregon
Metropolitan Area (Magee et al. 1993).
Short-term trends in wetland loss, of small
(5 acre or less) isolated wetlands, has
been documented in a rapidly urbanizing
Preliminary work on the OWS compared the
U.S. Fish and Wildlife Service's National
Wetlands Inventory of 1981-1982 (aerial
photograph dates) with the results of a WRP
inventory conducted during the summer of
1992. Approximately 40% of the 233
wetlands in the entire resource population
had been converted to other land uses
during the ten year period. Most of the
wetlands were small in size. Although
conversion to urban uses was the
predominant cause of wetland destruction,
23% was due to conversion to agricultural
land. The conversions are significant given
that an independent study within the same
ecoregion documents high waterbird use of
small wetlands in farmland settings (Budeau
In addition to the findings on trends in wetland
loss, the OWS will generate information on: (1)
how natural wetlands compare with projects, (2)
the relationship between land use and wetland
function,.and (3) design and performance criteria
for projects.
The approach and results from the OWS
provide a model for a companion study in the
Puget Sound area of Washington, scheduled for
implementation late in 1993. Cooperators from
the University of Washington will work on the
WRP-sponsored study to examine how reference
wetland condition can be used as a tool for
designing and monitoring wetland mitigation
banks. Reference sites have been used for
evaluating the condition of certain types of
ecosystems, particularly small streams and rivers
(Hughes et al. 1986). Approaches for
establishing reference wetland condition are
expected to be more problematic given the
variability within this type of ecosystem.
Three more WRP-sponsored studies that will
help restoration planning efforts are being
conducted in the San Luis Rey River watershed

Wetlands Research Update, Page 3 of 8
of California, and the Upper Arkansas River
watershed of Colorado. The overall objective
of the studies is the development of methods
for prioritizing the ecological suitability of sites
for riparian restoration.
Restoration planning for entire
watersheds must be performed at
several scales of Increasing complexity
and precision. Both environmental and
human factors must be considered
when prioritizing sites to maximize the
ecological function and sustainability of
Studies in the San Luis Rey River and
' Upper Arkansas River watersheds are
being conducted in cooperation with the
University of California, Berkeley and Utah
State University. One recently completed
task was the stratification of the San Luis
Rey watershed by geomorphic setting,
using an overlay of existing primary source
data. The information was used to
develop a preliminary list of environmental
indicators for evaluating the restoration .
potential of stream reaches. More
intensive field sampling is being
conducted within the reaches showing
higher restoration potential. A second
task was the gathering of low-level
videography data for both watersheds.
Videography is being evaluated as part of
a complementary approach for identifying
stream reaches with potential for riparian
Publications describing results from these
studies should become available beginning in
the summer of 1994.
Information on the relationship between
stressors and degradation of wetland function
is needed for a risk-based approach to
wetlands protection. New research sponsored
by the Project will produce indicators for
characterizing wetland condition and function
by wetland type, along a gradient of
environmental disturbance. One major study
currently underway explores the role of
bottomland hardwood riparian systems as
buffers for maintaining water quality.
Preliminary findings of research show
significant reductions in concentrations
of herbicides in runoff moving through
mature riparian systems of the
Southeastern Coastal Plain. Nevertheless,
the concentrations of herbicides entering
surface waters adjacent to riparian buffers
can remain significant. The fate of the
herbicides within the riparian system is
being studied.
The role of riparian forest buffer systems in
maintaining water quality in intensively
managed agricultural watersheds is the
subject of a cooperative study with the
University of Georgia. Field work is being
conducted at a research watershed
managed by the USOA Southeast Watershed
Research Laboratory at Trfton, Georgia.
Researchers are examining the movement of
alachlor and atrazine from a conventional
corn production system through a mature
riparian buffer system. They also are
following the movement of the same
chemicals through riparian systems that are
managed differently (e.g., clearcutting versus
selective cutting). Results of these studies
will be correlated with information gleaned
from surveys of macroinvertebrates
conducted within the various riparian buffer
systems, as well as within surface waters
affected by different farm practices. The
organisms might prove to be important
environmental indicators for monitoring the
condition of riparian buffers receiving
herbicide polluted waters.
A similar study effort is being conducted in North
Dakota. Researchers are exploring whether
vegetation buffers surrounding prairie pothole
wetlands reduce sediment input and thereby
sustain wetland integrity and function.
Close field coordination between WRP and
the U.S. Fish and Wildlife Services
(USFWS) Northern Prairie Wildlife
Research Center is facilitating access and
the timely instrumentation of prairie
wetlands for evaluating the effects of
sedimentation on wetlands within areas of
differing farm practices.
In an initial study, semipermanent wetlands
with a range of adjacent upland buffer widths
and upland agricultural practices were
selected within the Glaciated Plains and
Missouri Coteau Ecoregions for field
sampling. In a second study, 20 seasonal
wetlands in the Missouri Coteau were
selected for controls (e.g., USDA
Conservation Reserve Program enrollments

Wetlands Research Update, Page 4 of 8
or native prairie watersheds) or for
treatments (e.g., tilled watershed or tillage
with vegetated buffer strip). Data collected
from the sites by cooperators from the
USFWS will be analyzed to quantify
changes in wetland condition attributed to
sedimentation. Researchers then will
attempt to correlate sedimentation rates
within the wetland to farm practices
conducted adjacent to the wetlands.
Information generated by the Project will help
wetland managers better understand the
capacity of individual wetlands to withstand
disturbance. It should prove useful to states
developing management strategies and the
bioeriteria needed to sustain wetlands for their
aquatic life use.
The WRP's proposed risk-based framework
for wetlands protection has three components:
risk assessment, risk management, and
monitoring (Leibowitz et al. 1992a). The goal
of the Risk Reduction Project is to formalize the
risk framework and to develop technical tools
(e.g., indicators for risk assessment
approaches) necessary for implementation.
The previously described WRP projects will
contribute and interact with the Risk Reduction
Project to produce integrated risk
assessments, beginning with prairie pothole
wetlands in North Dakota.
The WRP's integrated study of prairie
pothole wetlands will entail multiple risk
assessment approaches at several spatial
scales, including model-based, synoptic, and
field sampling approaches. The Landscape
Function Project will provide the broad
perspective by deriving landscape-scale
indicators of function (e.g., the mosaic of
wetland types needed to support habitat)
useful for setting wetland management goals
(i.e., value). At the same time, the Wetland
Function Project will quantify the responses of
individual wetlands to stressors (e.g., functional
loss caused by sedimentation) and will assess
possible technical approaches for managing
the risks to the wetland resource (e.g.,
environmental buffers for controlling nonpoint
source pollution). The Wetland
Characterization and Restoration Project will
gather field data with which modeling and
assessment analysis can be performed. The
Project also will evaluate the replacement
potential of different wetland types.
The WRP anticipates making significant
headway on its risk reduction studies because of
the recent assignment of a senior scientist to lead
the Project. Dr. Jim Wigington is working with
the other project leaders and scientists to draft a
project work plan. The plan will outline specific
research and assessment activities that will be
conducted in the prairie wetlands. It will be
submitted for peer review in early 1994.
the Environmental Monitoring and Assessment
Program (EMAP) is designed to characterize the
condition of the Nation's ecological resources on
regional and national scales and over long
periods of time. The wetland-resource
component of EMAP (EMAP-Wetlands) is
developing a program, in cooperation with the
USFWS, to assess the status and trends of
wetland condition and extent (Leibowitz et al.
1991). The USFWS National Wetlands Inventory
(NWI) will provide EMAP-Wetlands with
information about the geographic coverage and
extent of wetlands. The EMAP-Wetlands program
then will couple the NWI information with
probability-based sampling to estimate wetland
condition by wetland class. Pilot studies for the
Program have been implemented in the Midwest
(prairie pothole wetlands) and Louisiana (coastal
salt marsh).
Results from a pilot study in the prairie
pothole region suggest that the proportion
of wet basins, number of species of
emergent hydrophytes, and sedimentation
rates may be good indicators of palustrine
emergent wetland condition in the
Midwest. Results from a pilot study in the
coastal salt marsh of Louisiana suggest
that plant biomass and plant stem
height/diameter may be good indicators of
salt marsh condition.
EMAP-Wetlands and the USFWS Northern -
Prairie Research Station developed an
interagency agreement to develop indicators
and measurement protocols for evaluating
the condition of prairie pothole wetlands.
Beginning in 1992, indicators were tested in
temporary, seasonal, and semi-permanent
wetlands within 4-square mile plots. Plots
. were selected in both intensely developed
(farmed) and sparsely developed (prairie
grass) landscapes in four ecoregions. A
similar pilot study was initiated in 1991 to
develop indicators of coastal salt marsh
condition. Three hydrologic basins in the

Wetlands Research Update, Page 5 of 8
Mississippi Delta have been sampled in
cooperation with Louisiana State
University. In each basin six minimally
impacted and six degraded sites were
identified based upon their vegetation-to-
open water ratio. Measurements taken at
the coastal sites include characteristics of
landscape (e.g., land cover mosaic),
vegetation (e.g., plant species), soils (e.g.,
organic content), and hydrology (e.g.,
redox potential).
Regional demonstration studies in the
Midwest (prairie potholes) and the Gulf of
Mexico (salt marsh) are planned for 1994. A
primary objective of the demonstrations will be
the evaluation of the variability of 'pilot project"
indicators across broad geographic regions.
The EMAP-Wetlands Program will be ready for
implementation once the demonstration
projects are completed. Statistical summaries
describing the condition of the wetland classes
then would be prepared annually. EMAP-
Wetlands and the USPWS would periodically
prepare assessment reports describing status
and trends in wetlands acreage (NWI) and
condition (EMAP). Information from the reports
would be used to relate changes in wetlands to
management practices, global climate change,
sea level rise, and other stress or influences on
the wetland ecosystem.
The Project continues work on evaluating the
performance of constructed wetlands built
primarily for the purpose of treating municipal
wastewater. Work is progressing in four areas.
A wetlands treatment database is being
developed using dBase IV software. The
database will be a collection of existing
information from all wetlands in North America
known to be treating wastewater, except for
agricultural and acid mine drainage systems
(Knight et al. 1992). The reliability and cost of
both free water surface and subsurface flow
wetlands are discussed in a recent publication
supported by the project (Reed and Brown,
A study of pilot scale subsurface flow
wetlands is being conducted at Tennessee
Technological University. Objectives of this
project are the evaluation of: the kinetics of
BOD removal and nitrogen removal, including
the effects of seasonal temperature changes;
the factors affecting nitrogen removal; the
plugging of rock media pores; the effect of
system configuration on treatment performance;
and the effect of water level fluctuations on
treatment performance.
A study to evaluate the performance of on site
(individual home) subsurface flow wetlands is
being conducted by the Arkansas Environmental
Academy. The study will monitor six to eight on
site systems for a variety of water quality
parameters. Monitoring should begin in August
1993, and continue into 1995.
The final study is an evaluation of free water
surface wetlands to determine their habitat
quality. Preliminary findings from the studies
suggest that the habitat quality of some of the
systems resembles the quality associated with
neighboring natural wetlands (McAllister 1992
and McAllister 1993).
Over the last year, the WRP contributed
resources and expertise to the following activities
and studies performed in collaboration with the
EPA Regional Offices and several of the states.
*	Distribution of a Permit Tracking System
(Holland and Kentula 1991) to states interested in
compiling wetland restoration information from
permit/project files. Results generated from the
"PTS" can be used to set geographic priorities
and goals for future projects.
*	Publication of a report documenting the
importance of irrigated wetlands as bird habitat in
the Colorado Plateau region (Adamus 1993). The
report describes significant indicators of habitat
function, and a documented procedure for rapidly
evaluating the suitability of irrigated wetland
habitat for birds.
*	The drafting of the Oregon Freshwater
Wetlands Assessment Methodology. The Oregon
Division of State Lands is basing the Oregon
Method, in part, on information gleaned from the
'Method for the Comparative Evaluation of
Nontidal Wetlands in New Hampshire" (Ammann
and Stone 1991). The Oregon Method differs
from the New Hampshire Method, as the former
places greater emphasis on the disciplines of
landscape ecology and ecological risk
assessment. Draft copies of the Oregon Method
are scheduled for distribution in the fall of 1993.

Wetlands Research Update, Page 6 of 8
*	The development of environmental indicators
for wetlands evaluation. A study is being
completed by the University of Massachusetts
at Amherst, in cooperation with EPA Region 1
(Boston). Expected outputs from the study
are: (1) Ah "example" state wetland assessment
methodology that can be used as a template
by states wanting to develop their own
standard methodology, and (2) a list of
indicators of wetland function within urban
landscapes that can be integrated into state
wetland assessment methodologies. Products
dre scheduled for completion during the
summer of 1994.
*	The development of technical approaches
for'prioritizing riparian restoration and
protection efforts within the Delaware River
Basin, Kansas. The study is being completed
by the Kansas Biological Survey, in
cooperation with EPA Region 7 (Kansas City).
Study results should help advance the
development of Best Management Practices
that properly reflect the assimilative capacity of
riparian systems for controlling nonpoint
source pollution in agricultural settings. A
workshop was conducted in June 1993 in
Topeka to review preliminary criteria. Final
products are expected during the spring of
*	The development of technical approaches
for prioritizing wetland restoration projects
within the Tensas Basin, Louisiana. The study
is being completed by the USDA Soil
Conservation Service, in cooperation with EPA
Region 6 (Dallas). It employs the use of best
professional judgment and WRP's Synoptic
Approach. The project will complement local
efforts to complete a Comprehensive Tensas
River Basin Plan. A final project report is
scheduled for December 1993.
*	An evaluation of the Synoptic Approach as a
tool for prioritizing wetlands restoration
activities in northeastern Illinois. The study is
being completed by the USFWS Chicago
Metro Wetlands Office. Final products are
scheduled for completion in early 1994.
*	The development of technical approaches
for establishing wetlands biocriteria in
Minnesota. Coordination continues with EPA
Region 5 (Chicago) and the State of Minnesota
for the development of a study plan for
analyzing water quality and macroinvertebrate
data collected at reference wetland sites within
the North Central Hardwoods Ecoregion of
*	An evaluation of plants and amphibians as
environmental indicators of wetland disturbance
within urban settings (King County, Washington).
The study is being completed by the University of
Washington, in cooperation with EPA Region 10
(Seattle). Final reports are scheduled for early
*	The development of approaches for
establishing reference wetlands condition within
the Southeastern Plains Ecoregion of South
Carolina and North Carolina. A sampling plan for
the study should be completed in late 1994.
Project planning continues with EPA Region 4
(Atlanta), the states of North Carolina and South
Carolina, and EPA's Health and Ecological
Criteria Division (Washington, DC).
*	The development of approaches for selecting
and characterizing a reference population of
vernal pool wetlands within the Central Valley of
California. Information gathered from the sites
would be used to establish wetland restoration
goals and monitoring protocols. A sampling
design and evaluation report should be
completed late in 1994.
*	The description of a conceptual model for
ecological risk assessment for bottomland
hardwoods in the Tifton-Vidalia Upland of
Georgia. The report was completed by the
University of Georgia. It was commissioned to
assist research planning efforts within the Risk
Reduction Project. The report will be published
as an EPA document in September 1993.
*	Project oversight for two extramural study
efforts in the Sandhills region of Nebraska. Both
projects will be completed by the University of
Nebraska. They are entitled, "The influence of
landscape scale on avian abundance and
richness in Sandhills Wetlands", and "The
dynamics of Sandhills wetlands and the hydraulic
connection with the High Plains Aquifer".
*	The preparation of a quality assurance plan for
the Estuarine Habitat Assessment Protocol. The
project is being completed by the University of
Washington, in cooperation with EPA Region 10.
A final project report is scheduled for completion
in August 1993.

Wetlands Research Update, Page 7 of 8
The WRP program welcomes Dr. Jim
Wigington. Jim brings to the Program his
expertise and experience as a forest
hydrologist. His previous research' at EPA's
Corvaltis Laboratory was on the topic of
watershed response to acid deposition. The
Program bids farewell to Dr. Janet Keough.
She left EPA's Duluth Laboratory to return to
the U.S. Fish and Wildlife Service's National
Wetlands Research Center in Lafayette,
If this Update was mailed to you, you're on
our mailing list and will continue to receive
Program information. If you wish to be added
to our mailing list, please contact the Wetlands
Research Program (Attn: Kristina Miller), EPA
Environmental Research Laboratory, 200 SE
35th Street, Corvallis, OR 97333. Inquiries
about specific research projects can be
directed to Richard Sumner at the above
address. He will direct the inquiry to the
appropriate principal investigator.
Detenbeck, N.E., C.E. Johnston, and G.J. Niemi.
1993. Wetland effects on lake water quality in the
Minneapolis/St. Paul metropolitan area.
Landscape Ecology. 8(1): 39-61.
Holland, C.C. and M.E. Kentula. 1991. The
Permit Tracking System (PTS): A User's Manual.
EPA/600/8-91/054. U.S. Environmental Protection
Agency, Environmental Research Laboratory,
Corvallis, OR.
Hughes, R.M., D.P. Larson, and J.M. Omemik.
1986. Regional reference sites: a method for
assessing stream potentials. Environmental
Management 10(5): 629-635.
Kentula. M.E.. R.E. Brooks, S.E. Gwin, C.C.
Holland, A.D. Sherman, and J.C. Sifneos. 1992.
An approach to improving decision making in
wetland restoration and creation. Edited by A.J.
Hairston. EPA/600/R-92/150. U.S. Environmental
Protection Agency, Environmental Research
Laboratory, Corvallis, OR.
Knight, R.L., R.H. Kadlec, and S.C. Reed. 1992.
Wetlands Treatment Data Base. In: Proceedings
of the 65th Annual Conference of the Water
Environment Federation, New Orleans,
September 1992, Volume IX, 'General Topics,'
WEF Order No. C2009.
The following publications with journal
citations may be obtained through library
sources. Inquiries about EPA publications may
be directed to EPA's Center for Environmental
Research Information (CERI), 26 West Martin
Luther King Boulevard, Cincinnati, OH 45268.
Telephone (513) 569-7562.
Adamus, P.R. 1993. Irrigated wetlands of the
Colorado Plateau: Information synthesis and
habitat evaluation method. EPA/600/R-93/071.
U.S. Environmental Protection Agency,
Environmental Research Laboratoiy, Corvallis,
Ammann, A.P. and A. Ltndley Stone. 1991.
Method for the Comparative Evaluation of
Nontidal Wetlands in New Hampshire.
NHDES-WRD-1991-3. New Hampshire
Department of Environmental Services,
Concord, NH.
Budeau, D. 1993. Migratory waterfowl and
shorebirds refuel in Willamette Valley farmed
wetlands. Oregon's Wildlife Resources.
Volume 3, Number 1. Oregon State University
Extension, Corvallis, OR.
Leibowitz, N.L, L Squired, and J.P. Baker. 1-991.
Research plan for monitoring wetland
ecosystems. EPA/600/3-91/010. U.S.
Environmental Protection Agency, Environmental
Research Laboratory, Corvallis, OR.
Leibowitz, S.G., E.M. Preston, LY. Arnaut, N.E.
Detenbeck, CA Hagley, M.E. Kentula, R.K.
Olson, W.D. Sanville, and R.R. Sumner. 1992(a).
Wetlands Research Plan FY92-96: An Integrated
Risk-Based Approach. Edited by Joan P. Baker.
EPA/600/R-92/060. U.S. Environmental
Protection Agency, Environmental Research
Laboratory, Corvallis, OR.
Leibowitz, S.G., B. Abbruzzese, P.R. Adamus,
LE. Hughes, J.T. Irish. 1992(b). A synoptic
approach to cumulative impact assessment: A.
proposed methodology. Edited by S.C.
McCannell and A. J. Hairston. EPA/600/R-
92/167. U.S. Environmental Protection Agency,
Environmental Research Laboratory, Corvallis,
Magee, T.K., S.E. Gwin, R.G. Gibson, C.C.
Holland, J.E Honea, P.W. Shaffer, J.C. Sifneos.
and M.E. Kentula. 1993. Research plan and

Wetlands Research Update, Page 8 of 8
methods manual for the Oregon Wetland
Study. Document production by K. Miller.
EPA/600/R-93/072. U.S. Environmental
Protection Agency, Environmental Research
Laboratory, Corvallis, OR.
McAllister, LS. 1993. Habitat quality
assessment of two wetland treatment systems
in the arid West - A pilot study. EPA/600/R-
93/117. U.S. Environmental Protection Agency,
Environmental Research Laboratory, Corvallis,
McAllister, LS. 1992. Habitat quality
assessment of two wetland treatment systems
in Mississippi - A pilot study. EPA/600/R-
92/229. U.S. Environmental Protection Agency,
Environmental Research Laboratory, Corvallis,
Omernik, J.M. 1987. Ecoregions of the
conterminous United States. Annals of the
Association of American Geographers. 77:118-
Reed, S.C. and D.S. Brown. 1992.
Constructed wetland design - the first
generation. Water Environment Research.
Volume 64(6): 776-781.
United States
Environmental Protection Agency
Corvallis Environmental Research Laboratory
200 Southwest 35th Street
Corvallis, Oregon 97333