A QUANTITATIVE APPROACH FOR ASSESSING THE CHARACTER OF MITIGATED
FRESH WATER MARSHES AND SWAMPS IN FLORIDA
KEVIN L. ERWIN
2077 BAYSIDE PARKWAY
FT. MYERS, FLORIDA 33901
One of the principle questions that must be addressed when
assessing the success of a completed wetland mitigation project
is, to what extent does the reclaimed wetland provide biological
and hydrological functions similar to those made by the mitigated
wetland. In order to determine what the success criteria should
be for a particular wetland habitat related impact, the natural
system must first be evaluated in order to assertain its form,
function, and contribution to the ecosystem. This evaluation of
the wetland to be mitigated is also of great importance in the
design of the reclamation project itself.
The exact duplication of a mitigated wetland is probably not
possible. Therefore, we must be able to evaluate the reclaimed
wetland in a quantitative manner to assess its similarity of form
and function with a mitigated wetland.
The quantitative approach should begin with a thorough
evaluation of the ecosystem of which the subject wetland is a
part. This ecosystem usually includes the identification and
study of a watershed or drainage basin in which the subject
wetland area is located. The various contributions made by the
mitigated wetland must then be identified. These contributions,
many of which are typical for most wetland areas, include the
The mitigated wetlands' function within the ecosystem as a
flow way (to pass surface water flows), and the wetlands' ability
to uptake and/or absorb constituents within the water is, in
part, related t.o the storage capacity and detention times of the
area. The wetland may also provide an attenuation of peak water
discharges from storm events to the receiving water bodies. The
ability of a wetland system to store surface waters through the
dry season and drought conditions can directly benefit water
resources available for human consumption and fish and wildlife
The positive benefits of certain wetland systems to the
maintenance of water quality within an ecosystem is well
documented. It should be determined in what ways the mitigated
wetland performs such a function as part of a larger ecosystem.
The water quality of the subject wetland should also be evaluated
for future comparisons with the reclaimed wetland area. Once
baseline water quality data is collected, the reclaimed wetland
can be designed to replicate similar water quality conditions or
even an enhanced state.
Fish and Wildlife Values
The habitat evaluation procedure (HEP) as developed by the
U.S. Fish and Wildlife Service should be used to accurately
describe the quality of the habitat and its particular
contribution within the ecosystem.
Floral Species Composition
The importance of an accurate description of the plant
community structure of the subject wetland is second only to
understanding the area's hydrological function. An assessment of
existing or known proposed activities within the ecosystem, in
which the wetland is located, is imperative. Cumulative impacts
and synergistic effects of certain activities may require
rethinking the values placed upon the mitigated wetland.
Ideally, mitigation plans should be developed as part of an
approved land use plan for an ecosystem or manageable subunit.
Since the vast majority of the functions related to the
mitigated wetland are directly related to the hydrology of the
system, it is important to develop, at minimum, a basic
hydrological model for the wetland. Monitoring well and surface
water level data should be collected and whenever possible field
markings on vegetation such as lyhen lines should be marked and
the elevations recorded.
The water quality analysis in most cases follows the
criteria and procedures set forth by the Florida Department of
Environmental Regulation in Chapter 17-3, Florida Administrative
Code. Surface and groundwater samples should be taken quarterly
for an annual cycle which includes a full wet season and dry
A biological monitoring program should be designed to
compliment the water quality monitoring within a mitigated
wetland. The use of Hester Dendy samplers in stream situations
and net and core sampling in static water systems is recommended.
Since the target of the biological sampling is generally
macroinvertebrates it must be understood that seasonality and
habitat preference of most species will influence the sampling
procedure design. Sampling should be done quarterly, if
possible, spanning the dry/wet season cycle. Net and core
sampling should be undertaken in each of the major macrophyte
communities within the wetland since compartmentalization of
species will adversely bias an inadquately sampled system (Erwin,
1985). Samples collected within each macrophyte community over
the wet/dry season cycle should provide an accurate
characterization of species richness and diversity of the
The methodologies used to determine the characterization of
the wetlands floral composition depends upon whether the wetland
is a forested (swamp) or nonforested (marsh) wetland. In
nonforested wetlands line intercept transects (Phillips, 1959;
Smith, 1980) can be used to evaluate the mitigated wetland and
later provide comparison of degree of similarity with the
reclaimed system. The method consists of taking observations on
transect lines laid out over the study area. The identity of
plant species touching, overlying, or underlying the line is
recorded along with the distance that each species covers
(intercepts) the line. In this way the line can be thought of as
a two dimensional plane extending above and below the actual
transect line. The line intercept transect should run down
slope, perpendicular to the shoreline, thus enabling correlations
to be made between the distribution of cover and water depth
and/or hydroperiod. The individual intervals are totaled by
species and by transect to yield estimates of percent cover. The
line intercept method is rapid, objective, and relatively
accurate. This method is also well adapted for measuring changes
and vegetation across transitional zones and transects can be
randomly placed and replicated to obtain the desired precision.
When the line intercept transect data is displayed graphically,
each species will have a specific signature (Figure 1). To
facilitate both an intensive, accurate and repeatable
characterization of forested wetlands, the use of the "line
strip" (elongated quadrat) technique (Lindsey, 1955; Woodin and
Lindsey, 1954) should be used. All elongated quadrats should run
parallel to the slope to allow for correlations to be made on a
gradient from flooded through moist to dry conditions within the
wetland. Separate measurements should be taken for the over, mid
and understory percent closure, height and DPH of canopy trees.
This same methodology may also be applied to the reclaimed
forested wetland and expanded so data collection may address
survivability and growth rate.
Many other methodologies for quantitative data collection
and interpretation do exist with only a few mentioned in this
discussion. The investigator must take the time to evaluate the
available methodologies and select or develop the methodology
best suited to characterize the mitigated wetland given the
limitations which always are a part of any study. In many
instances it is the limitations placed upon the investigator that
have a greater influence on the methodology to be selected than
the study area itself. Therefore, it is important to recognize
some of these limitations.
Lack of Success Criteria
Since the restoration or exact duplication of a particular
wetland is not possible, the investigator must obtain acceptable
success criteria from which to judge the similarity of form and
function between the mitigated and reclaimed wetland systems.
In many instances it is not possible to provide the
investigator with the time necessary to conduct an investigation
over an annual wet/dry season cycle.
The techniques I have outlined here generally require
extensive field time and many hours of data entry and computer
So, what have we concluded in applying this approach to
wetlands mitigation? I believe the methodologies described do
provide an adequate characterization of the wetlands form and
function. Again, it is important that the investigator use
methodologies best suited for the particular system to be
Erwin, Kevin L. 1985. Agrico Fort Green reclamation project.
Third Annual Report. Agrico Mining Company, Mulberry,
Florida Administrastive Code, Chapter 17-3, Water Quality
Standards, 1983 Florida Department of Environmental
Regulation, Tallahassee, Florida.
Lindsey, A.A. 1955. Testing the line strip method against full
tallies in diverse forest types. Ecology 36:485-495.
Phillips, E.A. 1959. Methods of vegetation study. Holt,
Rinehart and Winston, Inc., New YOrk. 107 pp.
Smith, R.L. 1980. Ecology and field biology. Harper and
Row, New York. 805 pp.
Woodin, H.E. and A.A. Lindsey. 1954. Juniper-Pinyon east of
the continental divide as analyzed by the line strip method.