United States
Environmental Protection
Agency
Science Advisory Board
EPA-SAB-EPEC-98-003
January 1998
http://www.epa.gov/sab
Ecological Impacts And
Evaluation Criteria For The Use
Of Structures In Marsh
Management
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The Science Advisory Board (SAB) of the U.S. Environmental Protection Agency is a body of
independent experts who provide advice to the EPA Administrator on scientific and engi-
neering issues. The SAB was established in its present form by the Congress in 1978. The
SAB's approximately 100 members and more than 300 consultants include scientists, engineers, and
other specialists drawn from a broad range of disciplines-physics, chemistry, biology, mathematics,
engineering, ecology, economics, medicine, and other fields. Members are appointed by the Admin-
istrator to two-year terms. The SAB meets in public session, and its committees and review panels
are designed to include a diverse and technically balanced range of views, as required by the Federal
Advisory Committee Act (FACA).
The Board's principal mission is to review the quality and relevance of the scientific information
being used to support Agency decisions, review research programs and strategies, and provide broad
strategic advice on scientific and technological matters. In addition, the Board occasionally conducts
special studies at the request of the Administrator to examine comprehensive issues such as future
environmental problems or new approaches to analyze and compare risks to human health and the
environment.
Cover photo by R. Flaak
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Ecological Impacts And Evaluation Criteria
For The Use Of Structures In
Marsh Management
Stephanie Sanzone and Anne McElroy, Editors
Marsh Management Subcommittee
Ecological Processes and Effects Committee
EPA Science Advisory Board
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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, DC 20460
January 22, 1998
EPA-SAB-EPEC-98-003
Honorable Carol M. Browner
Administrator
U.S. Environmental Protection Agency
401 M Street, S.W.
Washington, DC 20460
Subject: Ecological Impacts and Evaluation Criteria for the Use of Structures in Marsh Management
Dear Ms. Browner:
In 1994, at the request of the Office of Wetlands, Oceans, and Watersheds (OWOW), the
Science Advisory Board (SAB) established a Marsh Management Subcommittee to review the state of the
science underlying the use of structures to manipulate marsh hydrology. This approach to marsh
management, termed Structural Marsh Management (SMM), entails the use of structures such as canal
plugs, weirs, tide gates, and levees to manipulate local hydrology in tidal and Great Lakes marshes. The
genesis of the request to the SAB was OWOW's interest in assessing the scientific basis for a consistent
Agency, and ultimately national, approach to the evaluation of proposed SMM projects, which are
currently being implemented most widely in coastal Louisiana under the federal Coastal Wetlands
Planning, Protection, and Restoration Act (CWPPRA). As part of the CWPPRA process, the various
federal and state agencies with a role in the evaluation of proposed restoration projects, including SMM
projects, have expressed differing views on the ecological desirability of SMM.
Historically, structural manipulation of marsh hydrology, including impoundment, has been
used to enhance habitat for waterfowl and wildlife, provide physical buffers against wave or tidal
scouring, control mosquito populations, create nursery habitat for fish and macroinvertebrates, and
treat wastewater and storm water. More recently, SMM has been undertaken for the specific purpose of
protecting or creating emergent vegetated wetlands in coastal Louisiana, where the rapid rate of deterio-
ration of extensive coastal wetlands and marine encroachment has prompted protective efforts by
landowners and public resource agencies.
In the Charge to the Subcommittee, which was developed by OWOW with input from the
U.S. Fish and Wildlife Service, the National Marine Fisheries Service, the U.S. Army Corps of Engi-
neers, and the Soil Conservation Service (now the Natural Resources Conservation Service), the Sub-
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committee was asked to evaluate the impacts of SMM on emergent marsh vegetation, natural marsh-
sustaining processes, and fish and wildlife. In addition, the Subcommittee was asked to assess the
cumulative impacts of numerous large-scale SMM projects in a region, identify high priority research
and monitoring needs, and suggest scientific or technical evaluation criteria that the Agency could use to
evaluate proposed SMM projects. To address the Charge, the Subcommittee worked over a two-year
period, holding two public meetings, a site visit to coastal Louisiana, a writing session, and several
rounds of draft review and revision. The SAB report provides a summary of the state of the science on
the ecological consequences of SMM from a national perspective, science based-evaluation criteria for
SMM projects, monitoring and research recommendations, and a discussion of SMM issues in various
regions of the country.
In agreeing to evaluate the science underlying SMM, the Subcommittee was very aware of the
contentious nature of the issue, and the political and management implications of any report on this
subject. The Subcommittee recognizes that ecological considerations are not the only factors that must
be utilized by the Agency in developing any proposed policy on SMM. The Subcommittee is also aware
that consensus among the federal agencies with a role in SMM may be a longer-term goal. Nonetheless,
we urge the Agency to consider fully the findings of this report in developing and adopting an Agency
policy on SMM.
We would like to emphasize the following Subcommittee conclusions:
a) The collective experience around the country has shown that unintended, unantici-
pated, and sometimes undesirable effects have resulted from structural management of marsh hydrology.
\)\ Although marsh management practices have evolved over the years to include more
sophisticated structures and management approaches for controlling water levels, there is insufficient
information at present to determine whether these new structural approaches are inherently better than
those used in the past.
c) SMM projects may be irreversible (e.g., in cases where the marsh has subsided behind
levees or spoil banks) and thus imply a perpetual, and often costly, commitment to the management and
maintenance of control structures.
d) Past SMM projects have shown that while it is relatively easy to change marsh hydrol-
ogy, it is much more difficult to control or manage the changes or to predict fully the consequences of
proposed modifications.
With these cautionary notes as a backdrop, the Subcommittee urges the Agency to evaluate all
proposed SMM projects carefully against the criteria in this report, taking into account the potential
impacts of projects from an ecosystem, rather than single-species or single-resource, perspective. Al-
though specific choices regarding SMM should be based on local circumstances, management objectives,
and trade-offs; the Subcommittee proposes the following science-based principles for SMM to achieve
sustainable wetlands:
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a Wetlands systems that are providing a suite of wetland functions and are self-sustaining
should be left undisturbed and not subject to SMM.
b) Only if restoration of hydrology or physical processes is not feasible should SMM be
considered as an approach to restore/improve the wetland.
c) The decision of whether or not to use SMM should reflect a firm scientific understand-
ing of the causes of marsh degradation, both in a local and regional context, and should take into
account regional differences in marsh dynamics. The Proposed Guidelines for Ecological Risk Assess-
ment (EPA, 1996) should guide the evaluation of risks to the system with and without the proposed
SMM.
d) Preference should be given to SMM strategies that restore, to the degree possible,
natural wetland processes and functions and provide for at least periodic hydrologic connectivity with
surrounding ecosystems.
e) In large part, SMM techniques are experimental and should only be applied with
appropriate experimental design, including monitoring of both the managed site and control sites to
assess the impacts of the SMM on marsh processes and long-term marsh viability and to determine
whether the project is meeting management and design objectives.
In summary, the Subcommittee has attempted to synthesize the large body of scientific litera-
ture on the ecological consequences of changing marsh hydrology, including what is known and not
known, and to emphasize the development of science-based criteria that should guide evaluation of
proposed SMM projects. We hope the report will assist you and the Agency in developing a scientifi-
cally based policy for SMM, and we look forward to your reply.
Sincerely,
Dr. Joan M. Daisey, Chair
Executive Committee
Dr. Mark A. Harwell, Chair Dr. Anne McElroy, Chair
Ecological Processes and Marsh Management Subcommittee
Effects Committee
Enclosure
IV
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NOTICE
This report has been written as part of the activities of the Science Advisory Board, a public
advisory group providing extramural scientific information and advice to the Administrator and other
officials of the Environmental Protection Agency. The Board is structured to provide balanced, expert
assessment of scientific matters related to problems facing the Agency. This report has not been re-
viewed for approval by the Agency and, hence, the contents of this report do not necessarily represent
the views and policies of the Environmental Protection Agency, nor of other agencies in the Executive
Branch of the Federal government, nor does mention of trade names or commercial products constitute
a recommendation for use.
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ABSTRACT
The Marsh Management Subcommittee of the Science Advisory Board's Ecological Processes
and Effects Committee reviewed the state of the science for structural marsh management (SMM). The
Agency requested this review in support of their plans to develop an interim Agency position on SMM,
with a long-term goal of developing a national marsh management policy. The Subcommittee used the
term "structural marsh management" to distinguish this fairly narrow set of management approaches
from the broader set of practices that are commonly associated with the term marsh management. The
Agency's definition for marsh management is "the use of structures (such as canal plugs, weirs, gates,
culverts, levees and spoil banks) to manipulate local hydrology in coastal marshes." The Agency
specified in the Charge for the Subcommittee to include in its review wetlands influenced by the tide,
and lands and waters associated with the Great Lakes.
The Subcommittee found that the collective experience on SMM around the country has shown
that unintended, unanticipated, and sometimes undesirable effects have often resulted from structural
management of marsh hydrology. The Subcommittee found it difficult to generalize about the ecologi-
cal impacts of SMM because of differences in the physical environment, status of wetland resources, or
management objectives in different wetland areas. The Subcommittee recommends that the application
of a marsh management policy should be done at least at the region-specific, ecosystem-specific, or basin-
specific level. The Subcommittee urges caution in the adoption or approval of SMM projects in order to
avoid counterproductive results on the long-term sustainability of imperiled tidal and Great Lakes
wetlands. The Subcommittee also recommends that Agency decisions regarding proposed SMM projects
take into account the potential impacts of the project from an ecosystem, rather than single-species or
single-resource, perspective.
In addition to providing a summary of the state of the science on the ecological consequences of
SMM from a national perspective, the report recommends a number of scientific/technical criteria that
should be used to evaluate proposed SMM projects, highlights priority monitoring and research issues,
and discusses SMM issues that are relevant in various regions of the country.
Keywords: coastal marshes, hydrology, marsh management, structural marsh
management
VI
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U.S. ENVIRONMENTAL PROTECTION AGENCY
SCIENCE ADVISORY BOARD
ECOLOGICAL PROCESSES AND EFFECTS COMMITTEE
MARSH MANAGEMENT SUBCOMMITTEE
CHAIR
Dr. Anne McElroy, State University of New York at Stony Brook, Stony Brook, NY
MEMBERS
Dr. Frederic K. Pfaender, Carolina Federation for Environmental Studies, University of North Carolina,
Chapel Hill, NC
Dr. William H. Smith, School of Forestry and Environmental Studies, Yale University, New Haven, CT
CONSULTANTS
Dr. Donald Boesch, Center for Environmental and Estuarine Studies, University of Maryland, Cambridge, MD
Dr. Robert Buchsbaum, Massachusetts Audubon, Wenham, MD
Dr. Grant Gilmore, Harbor Branch Oceanographic Institution, Fort Pierce, FL
Dr. James G. Gosselink, Professor Emeritus, Center for Wetland Resources, Louisiana State University,
Baton Rouge, LA
Dr. Douglas A. Wilcox (Federal Liaison), National Biological Service, Great Lakes Science Center,
AM Arbor, MI
Dr. Philip Williams, Philip Williams and Associates, San Francisco, CA
Dr. Joy B. Zedler, Pacific Estuarine Research Laboratory, San Diego State University, San Diego, CA
SCIENCE ADVISORY BOARD STAFF
Ms. Stephanie Sanzone, Designated Federal Official, US EPA, Science Advisory Board (1400) 401 M Street, SW,
Washington, DC 20460
Ms. Constance Valentine, Staff Secretary, US EPA, Science Advisory Board (1400), 401 M Street, SW,
Washington, DC 20460
Acknowledgments- In addition, other Science Advisory Board Staff Members contributed to the development
and/or completion of this report. These include Robert Flaak, who staffed the site visit to Louisiana; Dorothy
Clark, who provided meeting support; Roslyn Edson, who provided final edits; and Wanda Fields, who typed the
final edits to the report. The subcommittee also thanks the Agency staff, in particular Fran Eargle and the
members of the Team for Ecosystem Restoration in the Wetlands Division, for their assistance in
gathering and organizing a large number of scientific and policy background documents.
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1. Executive Summary 1
2. Introduction 5
2.1 Charge to the Subcommittee 5
2.2 Scope of the Report 5
3. State of the Science: The National
Perspective 7
3.1 Impacts of SMM on Marsh-Sustaining Processes 8
3.1.1 Marsh Hydrology 9
3.1.2 Marsh Vegetation and Primary Production 9
3.1.3 Sedimentation and Soil Formation 11
3.1.4 Water and Soil Chemistry 11
3.2 Impacts of SMM on Fish and Wildlife 13
3.2.1 Migratory and Anadromous Fish 13
3.2.2 Waterfowl/Wading Birds 14
3.2.3 Other Wildlife 15
3.3 Cumulative Impacts of SMM 16
3.4 Engineering Design Issues 17
4. Evaluation Criteria 20
4.1 Science-Based Principles 20
4.2 Scientific/Technical Criteria 20
4.3 Management Considerations 23
5. Monitoring and Research Priorities 25
6. Regional Experiences with SSM 27
6.1 Louisiana Coastal Wetlands 27
6.1.1 Resource Status 27
6.1.2 Management Objectives 28
6.2 New England Salt Marshes 29
6.2.1 Resource Status 29
6.2.2 Management Objectives 31
6.3 East Coast Coastal Marshes 32
6.3.1 Resource Status 32
6.3.2 Management Objectives 33
6.4 Eastern Florida Marshes 33
6.4.1 Resource Status 33
6.4.2 Management Objectives 34
6.5 Great Lakes Marshes 35
6.5.1 Resource Status 35
6.5.2 Management Objectives 37
6.6 Southern California Coastal Marshes 37
6.6.1 Resource Status 37
6.6.2 Management Objectives 38
6.7 San Francisco Bay/Delta Wetlands 39
6.7.1 Resource Status 39
6.7.2 Management Objectives 40
7. Summary and Conclusions 41
8. References Cited 44
Appendix A: Charge to the
Subcommittee 51
IX
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At the request of the Environmental
Protection Agency's Office of Wetlands,
Oceans and Watersheds, the Ecological
Processes and Effects Committee of the Science
Advisory Board (SAB) established a Marsh
Management Subcommittee (the Subcommittee)
to review the state of the science for structural
marsh management in support of Agency plans to
develop an interim Agency position on SMM,
with a long-term goal of developing a national
marsh management policy. The Charge to the
Subcommittee (Appendix A) defines marsh
management as "the use of structures (such as
canal plugs, weirs, gates, culverts, levees and spoil
banks) to manipulate local hydrology in coastal
marshes." The Charge notes further that "marsh
management or tidal impoundments for the
purpose of this review will include those wetlands
influenced by the tide and lands and waters
associated with the Great Lakes." The
Subcommittee subsequently decided to use the
term "structural marsh management" (SMM) to
distinguish this fairly narrow set of management
approaches from the broader set of practices that
are commonly associated with the term marsh
management.
Historically, structural manipulation of marsh
hydrology, including impoundment, has been
used to enhance habitat for waterfowl and
wildlife, provide physical buffers against wave or
tidal scouring, control mosquito populations,
create nursery habitat for fish and
macroinvertebrates, and treat wastewater and
storm water. More recently, SMM has been
undertaken for the specific purpose of protecting
or creating emergent vegetated wetlands in coastal
Louisiana, where the rapid rate of deterioration of
extensive coastal wetlands and marine
encroachment has prompted protective efforts by
landowners and public resource agencies. In the
Charge, the Subcommittee was asked to evaluate
the impacts of SMM on emergent marsh
vegetation, natural marsh-sustaining processes,
and fish and wildlife. In addition, the
Subcommittee was asked to assess the cumulative
impacts of numerous large-scale SMM projects in
a region, identify high priority research and
monitoring needs, and suggest scientific or
technical criteria that the Agency could use to
evaluate proposed SMM projects.
Although most experience with SMM is based
on efforts primarily designed to accomplish a
purpose other than the protection or creation of
emergent vegetated wetlands, the collective
experience around the country has shown that
unintended, unanticipated, and sometimes
undesirable effects have often resulted from
structural management of marsh hydrology.
Differences in the physical environment, status of
wetland resources, and management objectives
make it clear that the application of a marsh
management policy needs to be at least region-,
ecosystem-, or basin-specific. Further, the impact
of SMM on marsh-sustaining processes depends
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on the type of management scheme employed.
For these reasons, it is difficult to generalize
about the ecological impacts of SMM. However,
the interruption of daily, monthly, and seasonal
hydrologic cycles as a result of SMM inevitably
influences important elements of the ecosystem
such as sediment chemical processes, water
column chemistry, the distribution and migration
of aquatic and semi-aquatic organisms, and
material import and export from the marsh.
Because of the substantial uncertainties about
the impacts of SMM and because not all SMM
projects are reversible, the Subcommittee urges
caution in the adoption or approval of SMM
projects in order to avoid counterproductive
results on the long-term sustainability of
imperiled tidal and Great Lakes wetlands.
Further, we strongly recommend that Agency
decisions regarding proposed SMM projects take
into account the potential impacts of the project
from an ecosystem, rather than single-species or
single-resource, perspective. We recognize that
ecological sustainability is not the only
consideration in the evaluation of SMM projects.
However, insofar as the Agency's goals are to
ensure long-term marsh survival and productivity,
the Subcommittee proposes five science-based
principles with regard to SMM (Figure ES-1).
The Subcommittee's responses to the specific
questions in the Charge are summarized
below:
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The available scientific studies on the efficacy
of SMM are highly equivocal. Emergent wetland
area has been maintained or increased in some
SMM projects, but unchanged or decreased in
others, relative to similar unmanaged areas. In
salt and brackish marshes in regions undergoing
rapid subsidence, SMM generally restricts the
supply of mineral sediments needed to accrete
soil, does not seem to protect wetlands, and may
even hasten their demise. There may be a better
case for the application of SMM in protecting
tidal freshwater wetlands with highly organic or
even floating soils. However, critical scientific
appraisals of the effectiveness of SMM in such
environments have yet to be performed. (See
Section 3.1.)
Depending on the extent of intervention,
SMM may impact natural marsh-sustaining
processes greatly or little at all. If SMM is applied
to protect vanishing marshes or restore lost
marshes, it must seek to do so by altering the
physical, biological, and chemical processes
operable. However, it is difficult to manipulate
one process deemed necessary for sustaining or
restoring a marsh (e.g., current flows or salinity)
without also affecting others (e.g., sediment
supply, water and sediment chemistry). Therein
lie the controversies regarding the long-term
effectiveness of SMM. In those cases in which
SMM has been successful in protecting or
expanding vegetated wetlands, the long-term
effectiveness of SMM (and thus sustainability) in
the face of geomorphic trends and sea-level rise
remains in question. In any case, it is clear that
SMM requires a perpetual management
commitment to maintain its effectiveness. (See
Section 3.1.)
In a wide variety of cases and regions, SMM
has been shown negatively to affect estuarine
fisheries by creating an artificial separation
between the wetland and the estuary or lake,
reducing either the access to or escape from the
habitat. This impact has been reduced, but not
eliminated, by improvements to the design of
weirs and gates. In addition, impoundments
within the managed marsh may result in degraded
water quality (e.g., salinity, temperature, and
dissolved oxygen extremes, and mobilization of
sulfate), occasionally with drastic results for
marsh biota. SMM can enhance the habitat value
for waterfowl and other wildlife and has been
widely used for that purpose. It is not clear,
however, whether SMM results in increases in the
regional or continental populations of these
resources. On the other hand, wading birds and
other organisms that depend on periodic exposure
of the marsh surface for effective feeding and prey
capture, and endangered birds that nest or feed in
specific types of vegetation, may be negatively
affected by SMM. (See Section 3.2.)
Collateral and cumulative effects of SMM are
poorly understood and virtually unqualified.
Potential cumulative effects relate to the reduced
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water exchange between the managed marsh and
adjacent wetlands and waters, altered patterns of
sediment transport and deposition, altered
movement of nutrients, pollutants, and organisms
into and out of the marsh, and the ability to
support regional biodiversity and rare or
endangered species. Assessment of cumulative
effects of SMM should be of central concern in
areas where SMM is widely practiced or proposed
for expansion. Presently, however, this
assessment is based on highly subjective and
qualitative approaches, rather than sound data
and models. Research in this area should be a
high priority for federal and state agencies. (See
Section 3.3.)
High priority research areas include: the
development and testing of alternative
management techniques that maintain the
hydrological connections between marshes and
coastal ecosystems; improved SMM technologies
(e.g., improvements to control structure design
and hydrological modeling of marshes); the effects
of SMM on marsh morphology and productivity;
and the cumulative effects of numerous SMM
projects within a watershed or region. The
Subcommittee recommends that monitoring be
required for SMM projects and suggests
parameters that should be measured. Routine
monitoring of SMM projects involves
characterization of the physical, chemical, and
biological attributes of the marsh ecosystem to
identify how the projects affect the ecosystem
structure and function, and is clearly distinct
from compliance monitoring. Monitoring of
SMM projects is important because it provides a
mechanism for the development of new SMM
approaches. (See Section 5.)
The Subcommittee suggests that the Agency
develop both generic national criteria and criteria
relevant to specific regions of the country. These
criteria should be consistent with the science-
based principles discussed above. The
Subcommittee has identified a number of
scientific and management evaluation criteria that
should be used when evaluating proposed SMM
projects, including: the historic quality and
productivity of the marsh; the current state of the
marsh; the suitability of the modifications for the
proposed site; the relationship of the proposed
project to long-term, regional restoration goals;
the ability of the SMM design to cope with
extreme weather events; the potential for
cumulative impacts; and the ecological impacts
were the project to fail or be abandoned. (See
Section 4.)
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2.1 Charge to the Subcommittee
At the request of the Office of Water's Office of
Wetlands, Oceans and Watersheds, the Ecological
Processes and Effects Committee of the Science
Advisory Board (SAB) established a Marsh
Management Subcommittee (the Subcommittee)
to review the state of the science for structural
marsh management in support of Agency plans to
develop an interim Agency position on SMM,
with a long-term goal of developing a national
marsh management policy. The Charge to the
Subcommittee (Appendix A) defines marsh
management as "the use of structures (such as
canal plugs, weirs, gates, culverts, levees and spoil
banks) to manipulate local hydrology in coastal
marshes." The Charge notes further that "marsh
management or tidal impoundments for the
purpose of this review will include those wetlands
influenced by the tide and lands and waters
associated with the Great Lakes." The
Subcommittee subsequently decided to use the
term "structural marsh management" (SMM) to
distinguish this fairly narrow set of management
approaches from the broader set of practices that
are commonly associated with the term marsh
management. The Charge included the following
specific questions to the Subcommittee:
a) Does SMM protect or create emergent
vegetated wetlands? In regard to this evaluation,
consider two conditions in the response: i) areas
where net sediment deficit occurs (i.e., soil
building does not keep up with relative sea level
rise), and ii) areas where there has been extensive
human-induced wetlands deterioration.
b) To what extent does SMM impact the physical,
biological and/or chemical aspects of natural
marsh-sustaining processes? With regard to this
evaluation, consider long-term marsh survival and
productivity, including accretion of organic and
inorganic sediments.
c) What are the impacts of SMM, if any, to
estuarine fisheries, waterfowl, and other fish and
wildlife? If there are impacts, provide an analysis
of the extent of these impacts.
d) What are the cumulative effects of numerous
large-scale SMM projects with respect to emergent
vegetation, accretion, fish and wildlife, and other
resources?
e) What are the gaps and the highest priorities for
research studies related to the effects of SMM
projects, and for routine monitoring of such
projects?
f) What scientific or technical criteria should EPA
use as part of the basis for case-specific decision-
making; or, as an alternative, what approach
should EPA take to develop such criteria?
2.2 Scope of the Report
In accepting the request, the SAB agreed to
consider the state-of-the-science underlying SMM
and to recommend criteria for evaluating the
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potential ecological effects of marsh management
projects in various types of marsh systems and
regions of the country. While recognizing that
much of the impetus for an Agency policy on
SMM arises from concerns in coastal Louisiana,
the Subcommittee was constituted to reflect a
balance of geographic expertise, and the report is
intended to provide guidance that the Agency can
apply in marsh ecosystems around the country.
The Subcommittee held public meetings in
Washington, DC on July 21 and September 7-8,
1994, to receive comments from federal and state
agencies with marsh management responsibilities,
as well as from non-governmental organizations
and members of the public. A large volume of
technical material and public comments was
supplied to the Subcommittee as a result of these
meetings, including a summary and proceedings
from an EPA-sponsored workshop on SMM held
in Louisiana in August 1994. In addition, several
Subcommittee members visited marsh sites in
coastal Louisiana in February 1995 to observe
first-hand several marsh management projects
underway in that area.
Much has been written on SMM, and the
Subcommittee did not attempt to compile an
exhaustive summary of all relevant technical
studies. Rather, this report includes references to
key scientific studies of SMM in various regions
of the country. The Subcommittee, focusing on
published reports in refereed scientific journals,
has attempted to summarize the state-of-the-
science as it relates to SMM, including what is
known and not known about the ecological
impacts of intentional or unintentional changes to
marsh hydrology. An overview of SMM issues
on the national level (Section 3) is complemented
by more detailed discussions of the circumstances
and concerns in various regions of the country
(Section 6). Recommendations for monitoring
and priority research to improve our
understanding of the impacts of SMM are also
included (Section 5).
A primary focus of this report is on scientific
and technical criteria that should guide the
assessment of ecological impacts of proposed
SMM projects (Section 4). In most cases, SMM
has resulted in trade-offs in which certain wetland
values have been maintained at the expense of
other values. The determination of management
objectives is a reflection of societal choices at the
national, state, and local levels, rather than a
scientific debate, and as such is not the domain of
the SAB. However, the selection of management
objectives needs to be informed by a scientific
assessment of what is feasible and what are the
likely trade-offs. The Subcommittee agrees that
region-specific characteristics, including the
extent, location, connectivity, and condition of
wetland resources, as well as differences in local
goals and priorities, will affect decisions on where
and when to implement SMM. Despite these
region-specific factors, however, the
Subcommittee has proposed a number of criteria
for evaluating the ecological desirability and
feasibility of proposed SMM projects (Section 4).
These proposed criteria, developed in response to
elements (a) through (d) of the Charge to the
Subcommittee, are intended to allow the Agency
to assess the regional impacts of a proposed SMM
project on wetland ecological values and
functions. In addition, the report discusses a
number of management considerations that the
Subcommittee finds are directly related to
whether or not a SMM project is likely to achieve
its management objectives.
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The Charge to the Subcommittee includes a series
of questions regarding the impacts of SMM on
specific biological, physical or chemical
components of marsh ecosystems. In the past,
federal and state agencies have often been charged
with the protection or management of a
particular component of the marsh ecosystem
(e.g., the navigable waters, fishery resources, or
wildlife species). In some cases this has resulted in
different agencies having conflicting goals for the
management of wetland areas. Although the
Subcommittee has organized the subsequent
discussion around the charge questions, we urge
the Agency, in concert with the other relevant
federal and state agencies, to take an ecosystem,
rather than species-specific or single-resource,
approach to the management of wetlands that
focuses on the sustainability and long-term
viability of the resource. Further, the
Subcommittee recognizes that regional differences
in the physical environment, status of wetland
resources, and management objectives, as well as
variations in SMM practices around the country,
make it difficult to generalize about the ecological
impacts of SMM. Much of the present debate
over SMM is dominated by concerns over the
extensive loss of wetlands in coastal Louisiana.
This section, therefore, summarizes the range of
ecological responses to SMM that have been
observed under a variety of conditions. A
description of the specific SMM issues in different
coastal regions is contained in Section 6, and
highlighted in Figure 1. (see page 8)
3.1 Impacts of SMM on
Marsh-Sustaining Processes
Historical objectives for SMM have included
enhancement of habitat for waterfowl and
wildlife, physical buffers against wave or tidal
scouring, mosquito control, creation of nursery
habitat for fish and macroinvertebrates, and
wastewater and stormwater treatment. More
recently, SMM has been undertaken for the
specific purpose of protecting or creating
emergent vegetated wetlands in coastal Louisiana,
where the rapid rate of deterioration of extensive
coastal wetlands and marine encroachment has
prompted protective efforts by landowners and
public resource agencies. SMM may also be used
to create inland, nontidal wetlands for wastewater
treatment, stormwater/desilting detention basins,
and other uses; the application of SMM in this
context, however, is outside the scope of this
report.
Although most experience with SMM is based
on efforts aimed at accomplishing a purpose other
than the protection or creation of emergent
vegetated wetlands, the collective experience
around the country has shown that unintended,
unanticipated, and sometimes undesirable effects
have often resulted from structural management
of marsh hydrology. Differences in the physical
environment (e.g., hydrologic and geomorphic
conditions), status of wetland resources, and
management objectives make it clear that the
application of a SMM policy needs to be at least
-------
region-, ecosystem-, or basin-specific. Further, the
impact of SMM on marsh-sustaining processes
depends on the type of management scheme
employed. However, a number of general
conclusions emerge from the scientific literature
regarding the effects of SMM on marsh vegetation
and natural marsh-sustaining processes, as well as
effects of SMM on fish and wildlife that rely on
marshes for food, habitat, and refuge.
Marsh-sustaining processes include hydrology
(water level, and fluctuations thereof, water
residence times, waves, and currents); plant
recruitment, growth, and decay; soil formation
(including deposition and erosion of organic and
-------
inorganic matter); nutrient cycling and exchange
with other ecosystems; water and soil chemistry
(including biogeochemical processes in the soil);
and competition and predation. All of these can
be altered by structural management of water
level.
3.1.1 Marsh Hydrology
SMM is defined as the use of structures to modify
marsh hydrology. Since hydrology drives the
other physical, chemical, and biological processes
in a wetland, it is inevitable that SMM impacts all
aspects of wetland function. Hydrologic
modification, through active manipulation of
water level changes, alters the flux of nutrients
and other chemical constituents into and out of
the marsh as the amount, frequency, and duration
of flooding change (Swenson and Turner, 1987;
Boumans and Day, 1994). The modification of
daily, monthly, and seasonal hydrologic cycles
also influences soil chemical processes and
oxidation-reduction (redox) status, water column
chemistry, the distribution and migration of
aquatic and semi-aquatic organisms, and
particulate material import and export from the
marsh. In addition, deep water basins or canals
created within the marsh act as sediment and
detrital traps, contributing to anoxic and
eutrophic depressions, and provide habitat for
larger estuarine predators that prey on diminutive
marsh resident species and juveniles of transient
species (Harrington and Harrington, 1982; Rey et
al, 1990b).
Despite the fact that hydrology drives all of
these marsh-sustaining processes, little is known
about the effects of SMM design elements on such
basic hydrologic parameters as water level control
and water residence time. Careful documentation
of the relationship between gate cross section
(relative to impounded area) and water level
equilibration rates under different water head
conditions does not exist, and studies of the
effects of gates on water residence time are
similarly lacking. Considerable research has gone
into documenting the effects of hydrology (water
level and water level fluctuation, and flushing/
residence time) on wetland plants; however,
without the link between SMM design and
hydrology, this information is not helpful for
assessing the impacts of SMM. The importance of
engineering design considerations in the success or
failure of SMM projects is discussed in Section
3.4.
3.1.2 Marsh Vegetation and Primary
Production
Theoretically, SMM can protect or create
emergent vegetated wetlands under the right
conditions. Natural processes of water flow and
inundation, soil formation, and plant growth are
responsible for creating existing wetlands. The
loss of wetlands is usually associated with a
change in those processes, which disrupts the
dynamic equilibrium. It may be possible, then, to
restore these processes or to manage them in a
way that enhances the survival and propagation of
wetlands. To do so requires an understanding of
marsh ecosystem processes, their interactions, and
how structures affect them. At least in the short
term, SMM has in some cases succeeded in
increasing marsh plant cover, usually following
draw-downs of water level, which allows seed
germination in previously submerged soils. In
wetland areas adjacent to the Great Lakes, for
example, SMM has been used to recreate lost
natural barriers to wave erosion and has allowed
marsh vegetation to become established.
9
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in
In
composition
and
of
Similarly, marsh plant coverage may be increased
by drawdowns in impounded marshes at
Rockefeller State Wildlife Refuge in coastal
Louisiana. However, there are few scientific
studies comparing the long-term effects of SMM
relative to unmanaged reference sites, and the
effectiveness of SMM in protecting or creating
emergent marsh over the long term has not been
well documented.
Historical comparisons of areas in coastal
Louisiana structurally managed for waterfowl
Phragmites encroaching on salt marsh at Rough
Meadow Sanctuary near Plum Island Sound,
Massachusetts
Photo by FL Buchsbaum
10
habitat with similar reference areas have
demonstrated that water level control has
frequently not protected or restored emergent
vegetated wetlands (although it may result in a
proliferation of submerged aquatic vegetation)
and in a number of cases has accelerated the loss
of emergent wetlands. For example, in one such
study, an evaluation of 16 managed sites in
Louisiana showed that water level management
was effective at increasing marsh acreage at fewer
than half of the sites (Cahoon and Groat, 1990).
In a somewhat similar environment (e.g.,
relatively rapid subsidence, small tidal range, and
limited sediment supply), the hydrologic barrier
caused by a roadway across the marsh has
unwittingly contributed to the rapid breakup of
marshes at the Blackwater Wildlife Refuge on the
Chesapeake Bay (Stevenson et al., 1985).
Furthermore, in systems that receive little
freshwater input (e.g., in southern California),
impoundment of wetlands can lead to hypersaline
conditions and massive diebacks of the most
sensitive halophyte plant species (Ibarra Obando,
1990, 1993; Ibarra Obando and Poumian-Tapia,
1991;Zedleretal, 1992).
Most experience, however, is based on SMM
efforts aimed at accomplishing a primary purpose
other than the protection or creation of emergent
vegetated wetlands. Thus, it should not be
expected that these efforts also protected or
created emergent wetlands. Recent marsh
management techniques have improved in
sophistication, and active management of water
levels may improve the ability to create emergent
vegetated marsh. Although it is not clear why
some projects succeed in growing marsh plants, at
least in the short term, while others do not, the
ability to draw down water levels, especially in
the spring to stimulate seed germination and
-------
growth of perennial species, seems to be one of
the more important factors (Keddy et al, 1989;
Leek, 1989; van der Valk and Pederson, 1989).
The implications of this and other ecological
management objectives for the design of SMM
structures are discussed in Section 3.4.
The Subcommittee notes, however, that the
presence of emergent vegetation should not be the
sole measure of marsh productivity and
sustainability. Where the primary management
goal is implicitly or explicitly the maximization
of waterfowl or shorebird use, this often requires
the maintenance of open water or mudflats as
well as vegetated areas. In areas with existing
emergent marsh, SMM often results in shifts in
species composition and diversity of plant
communities in response to altered salinity, water
level, and flooding regime (frequency and
duration) (Chabreck and Junkin, 1989; Turner et
al., 1989; Cahoon and Groat, 1990; Reed, 1995).
In some areas, invasion by aggressive, exotic plant
species has been observed following
implementation of SMM (e.g., Roman et al.,
1984). Monospecific stands of these aggressive
species are generally considered of less value to
wildlife than the more diverse natural marsh
community.
In addition to shifts in marsh plant species
composition, changes in flooding regime that
favor growth of emergent vegetation may affect
overall primary productivity. Prolonged
inundation affects periphyton and epibenthic
algal and bacterial communities, as does shading
by vascular plant canopies. Scientific studies
indicate that for some wetland systems these algal
mats may be more important as food sources for
wetland fauna than many wetland vascular plants
(Rey et al., 1990c; Browder et al., 1994).
3.1.3 Sedimentation and Soil Formation
In natural systems, the long-term viability of a
marsh requires that inputs of inorganic and
organic sediments be sufficient to offset substrate
compaction, erosion, and relative sea-level rise. If
marsh elevation is not maintained, marsh
vegetation is inundated and drowned. SMM may
interrupt the supply of inorganic sediment from
the watershed or the ocean. If the decline in
inorganic sediment supply is not offset by an
increase in accretion of organic material,
subsidence within the managed area will result.
In San Francisco Bay, for example, managed
marsh areas typically have subsided about four
feet behind levees constructed to protect the areas
from storm surge flooding or for waterfowl
management. In a managed system, water levels
can be manipulated to compensate for subsidence,
but at the cost of continued intervention.
Without adequate soil formation, this effort is
ultimately a losing battle. Conversely, in areas
with a net sediment surplus, loss of tidal flushing
can result in elevation of the marsh surface and
conversion to upland, terrestrial habitat, either as
a result of accumulation of organic detritus (e.g.,
mangrove forest litter in Florida impoundments;
Rey et al., 1990c) or from increased supply of
sediments from the watershed as a result of
urbanization (e.g., in southern California). In
summary, the impact of SMM on marsh sediment
accretion depends on the nature of the sediment
supply to the marsh in question.
3.1.4 Water and Soil Chemistry
Both water column and sediment chemistry
change in response to changes in hydrologic
cycles, principally by changing the salinity and
11
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oxidation-reduction (redox) status of sediments
and processes controlling organic carbon
decomposition. Redox cycles change because of
changes in the exposure of the marsh sediments to
the atmosphere. Thus, depending on the
management scheme, SMM has been shown to
lower redox potentials in some instances and
result in more oxidized soils in others (Cahoon
and Groat, 1990); this change in redox potential
has implications for the cycling of H2S and NH,
(e.g., Carlson et al, 1983; Nickerson and
Thibodeau, 1985). The redox state at any given
time will control the mobility of many metals,
plant nutrients, toxic organics, and sediment.
SMM strategies that drain marshes and create dry
Water control structures may affect water
quality, e.g., by changing water residence times
and deposition of organic and inorganic matter.
Photo by R. Flaak
12
ground will increase the redox potential and
foster the more oxidized conditions that in turn
lead to: release into the water column of metals
generally bound to sulfides in anaerobic
sediments; increased oxidation of organic matter
that binds organics and metals and helps to hold
fine grain sediments together; and release of plant
nutrients (nitrogen and phosphorus) into the
water column, which can give rise to excess
growth of algae in adjacent waters. SMM
practices that change water levels to submerge
land will lower the redox potential and lead to
binding and concentration of metal sulfides in the
sediments, increased denitrification, and
accumulation of organic material and some
nutrients. Aside from redox changes, water level
manipulation can also change sediment
accumulation rates, thereby affecting the
availability of those materials that bind to
sediments (e.g., metals and toxic organics).
With regard to water quality, impoundment
tends to increase the range of environmental
extremes in a marsh (e.g., salinity, temperature,
and dissolved oxygen). Reduced or no tidal
flushing in the managed marsh may increase
deposition of organic matter, inducing algal
blooms and subsequent low levels of dissolved
oxygen or anoxic conditions in the water column.
Changes in wetland water quality resulting from
impoundment construction or management may
require mediation mechanisms to prevent
mortality of indigenous flora and fauna. As an
example, natural low-energy hydrological
conditions at impounded mangrove forest sites
may be augmented seasonally during low water
quality periods by pumping large volumes of
open estuarine waters through the impoundment
and out of bottom water release structures to the
open estuary (Rey et al., 1990a).
-------
3.2 Impacts of SMM on Fish and Wildlife
To varying degrees, SMM creates an artificial
separation between the open water body (estuary
or lake) and wetland, thus interfering directly or
indirectly with transport and migration of
organisms. Direct interference occurs with
aquatic organisms that ride water currents
passively or migrate actively into or out of the
marsh for feeding, habitatrefugia, or spawning.
Indirect interference occurs with terrestrial and
avian organisms that feed on the marsh surface
when it is exposed at low tide but cannot feed
when the marsh is flooded (e.g., certain insects,
wading birds, reptiles, and certain mammals)
(Lewis et al, 1985; Gilmore, 1987). Fish and
wildlife are sensitive to changes in marsh
hydrology, sedimentation, and water chemistry as
well.
3.2.1 Migratory and Anadromous Fish
Structural marsh management of tidal and Great
Lakes wetlands has generally had a negative
impact on migratory fishery resources, i.e., those
resources based on species that use the wetland-
shallow water complex for spawning or as a
nursery and then leave this environment to open
water as they mature. This impact appears
largely to be the result of restrictions of access to
the managed marsh, which is the means of seeding
the nursery with larvae, postlarvae, or juveniles.
Loss of access to spawning, refuge, and foraging
habitat, as well as changes in the availability of
preferred forage organisms, has detrimental effects
on a number of fish, shrimp, and crab species
(Harrington and Harrington, 1982; Gilmore et
al., 1982a; Rey et al., 1990b; Rogers et al., 1992;
Rogers et al., 1994; Herke et al., 1992; Herke et
al., 1996). While those animals recruited into the
managed marsh may actually do quite well, they
are less likely to escape at the appropriate time in
their development and join the fishery or
breeding stocks. Further, since use of diked
wetlands as fisheries habitat is generally restricted
to species that enter as larvae passing through
screens, fish and invertebrate species diversity in
pump-controlled diked wetlands may be
considerably lower than in undiked systems
(Johnson, 1989; Navarro and Johnson, 1992).
Another concern is the blockage of
anadromous fish runs by dams, dikes, and
culverts, which has been a major source of decline
of these fish, one of which, the short-nosed
sturgeon, is on the federal endangered species list.
Although large dams on major rivers are generally
upstream of coastal marshes, the tidal portions of
A great egret (Casmerodius albus) in diked
wetland along the shore of western Lake Erie.
Photo by D. Wilcox
13
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An
'<• " '' ier
"r* mt
>'.-' . f- '< 'Vfef
for
In i' of
many rivers and streams are impacted by culverts,
dikes, and tidegates, all of which may impede the
passage of fish. Various modifications in water
control structures or flow management schemes
have been used to reduce the effects of this
"ingress-egress" problem, including slotted weirs
and specially designed culverts and gates (Rogers
et al, 1994). However, these modified structures
are not used in many instances, and there is
general consensus that some detrimental effects
are unavoidable.
As mentioned in Section 3.1.4, impoundments
within the managed marsh may also result in
degraded water quality (e.g., salinity, temperature,
and dissolved oxygen extremes, mobilization of
sulfate), occasionally with drastic results for
marsh biota (DeVoe and Baughman, 1986;
Portnoy, 1991; Greene and Van Handel, 1992).
Open Marsh Water Management site at Cranes
Beach near Essex, Massachusetts.
Photo by Northeast Massachusetts Mosquito Control
and Wetlands Management District
14
There is a conundrum here, though, in that if
deteriorating marsh is not protected or restored,
the wetland habitat needed to sustain these fishery
resources may be lost altogether. Thus, in some
cases it may be necessary to make some
concessions regarding reduced value for fisheries
over the short-term, if this will ensure the
sustainability of the habitat over the long term.
This would require that adequate fish passages be
included in the project design. However, the
concern remains that intensely managed wetland
systems may not be sustainable, i.e. able to be
maintained independently.
3.2.2 WaterfowlAVading Birds
SMM certainly can be applied in a way that
enhances the value and attractiveness of the
habitat for waterfowl. Typically, this result is
achieved by the promotion of conditions for
growth of certain submerged,aquatic vegetation
or emergent plants that provide food resources
(Chabreck, 1976; Chabreck and Junkm, 1989). It
is less clear that these benefits extend to
waterfowl populations, however, or whether they
merely serve to concentrate existing populations.
Migratory waterfowl populations could be
controlled by birth, mortality, or growth in areas
other than the habitat in question, e.g., at inland
nesting sites or subtropical overwintering sites.
In addition, while wetlands managed for
waterfowl provide wintering habitat for
migratory species, it is not clear how these
wetlands compare in value with natural tidal
marsh or waterfowl habitat in non-tidal areas.
Similarly, existing salt ponds and seasonal
wetlands in agricultural areas provide good bird
feeding and resting areas, but a systematic
comparison of their habitat values relative to
-------
those of natural marsh plain ponds and natural
seasonal wetlands is lacking.
Waterfowl benefit from impoundments when
the relative amount of open water in a marsh
system is increased (Weller, 1988). Effects on
waders (e.g., herons and egrets) and shorebirds are
variable, depending on the depth of the
impoundment. Deeper impoundments or steep
bank impoundments and mosquito ditches may
not provide the shallow water and muddy shores
waders need for foraging areas. The long-term
benefit to waterfowl of diked systems is
problematic, since these systems evolve to
Phrugmires- dominated marshes along much of the
east coast, thought to be of lower habitat value to
waterfowl. Hence a diked marsh requires
continued, intensive management to maintain its
value to waterfowl.
In recent years, an alternative approach called
Open Marsh Water Management (OMWM),
which may have greater benefits for shorebirds
and wildlife, has been employed in a number of
New England and mid-Atlantic states. OMWM is
a method of mosquito control with two overall
goals: controlling salt marsh mosquitoes and
maintaining the productivity of marshes for
wildlife. In the past, salt pannes, small pools on
the marsh surface that are often important feeding
areas for birds, had been drained in the name of
mosquito control. OMWM retains and deepens
these pannes to serve as reservoirs for small fish
that then reach mosquito breeding areas through
a system of shallow canals dug into the marsh
surface and consume mosquito larvae. In the
mid-Atlantic states where OMWM was first
developed, several-acre ponds were dug to serve as
fish reservoirs. In New England in recent years,
OMWM has also been used as a way to restore
salt pannes. Further knowledge of the salt panne
functions would help to determine if this trade-
off has net benefits for wildlife.
3.2.3 Other Wildlife
Impacts of SMM on wildlife, including various
terrestrial and aquatic invertebrates (crustaceans,
insects, mollusks, and polychaetes), reptiles,
songbirds, raptors, and mammals, may be great if
major changes in the plant community or
hydrology take place with impounding (e.g.,
Gilmore and Snedaker, 1993). Many indigenous
wetland invertebrates (e.g., fiddler crabs) require
periodic exposure to the atmosphere and may
drown if kept inundated for several days. In
addition, resident crustaceans or fish populations
that require intertidal substrate exposure to the
atmosphere as part of their life cycle can be
eliminated under SMM scenarios (Provost, 1967;
1977; Rey et al, 1990c; Taylor, 1990). Effective
feeding behavior and prey capture by wading
birds and many wetland reptiles are often
dependent on periodic marsh surface exposure
which does not occur in flooded impoundments
(Kushlan, 1986; Bancroft et al., 1994; Ogden,
1994). The same may be true of mammalian
species that feed in coastal wetlands (e.g.,
raccoons, otters, and bobcats). Further,
vegetative shifts resulting from SMM can
eliminate habitat for endangered birds that have
specific nesting and feeding requirements (e.g.,
light-footed clapper rail). The extinction of the
dusky seaside sparrow was caused in part by the
elimination of indigenous vegetative habitat due
to marsh impoundment within the Merritt Island
Wildlife Refuge in Flonda (Kale, 1981; Walters,
1992). On the other hand, lengthy drawdowns of
diked marshes may completely eliminate less
mobile, wholly aquatic organisms, including some
that are endangered or of commercial value.
15
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3.3 Cumulative Impacts of SMM
While many assessments of SMM focus on
induced changes within the managed area (e.g.,
changes to plant and animal species composition
and diversity, marsh productivity, and marsh
surface elevation), SMM may have implications
far beyond the confines of the project area. It is
of critical importance to understand the effects of
the site-specific SMM on surrounding
environments and the interactive effects of
numerous SMM projects within the same
hydrological unit (watershed, estuary, lagoon, or
embayment) (Gosselink and Lee, 1989).
Assessment of such collateral and cumulative
effects is particularly critical in regions in which
SMM has been extensively applied. In
documentation supplied to the Subcommittee,
Good (1994) estimated that 15.8% of the coastal
wetlands of South Carolina, 13.1% of those in
California, and 11.6% of those in Louisiana were
under various types of SMM. SMM is even more
extensive in particular estuaries or hydrological
units. For example, 75% of the salt marshes
adjacent to the Indian River Lagoon (Florida)
were impounded for mosquito control during the
1950s and 1960s and in some hydrological basins
of coastal Louisiana, e.g., the Calcasieu-Sabine
Basin, the majority of marshes are under SMM.
The question of cumulative effects of SMM is
particularly relevant in coastal Louisiana, where
great increases in SMM are proposed by
landowners and as part of restoration efforts
under the Coastal Wetlands Planning, Protection
and Restoration Act (CWPPRA). In a draft
Environmental Impact Statement on marsh
management, the New Orleans District of the
U.S. Army Corps of Engineers (1995) estimated
that while previously issued permits for marsh
management (1977 to 1995) encompass nearly half
16
a million acres, candidate CWPPRA marsh
management and hydrological restoration projects
(which may involve erecting barriers to flow, but
are not generally intended to control water level)
could add an additional half-million acres to the
total.
Cumulative effects of SMM have received little
study and have been identified as an important
knowledge gap (Cahoon and Groat, 1990).
Although there are no careful studies of the
consequences of large areas of impoundments on
hydrology in Louisiana, elsewhere the effects are
dramatic. When the great marshes in New
England were diked in the last century, the
harbors filled with sediments as a result of the
decrease in tidal prism (Gosselink et al, 1974). In
San Francisco Bay, tidal sloughs were silted in
after adjacent marsh plains were diked off for
agriculture, salt ponds, or duck-hunting clubs
(Coats et al., 1989).
Potential collateral or cumulative effects of
SMM projects include the following:
a) SMM reduces the volume and/or frequency
of water exchange resulting from tidal action or
wind forcing (seiches) between the managed
marsh, adjacent wetlands, and coastal water
bodies. Thus, water-level fluctuations and
currents may be affected in adjacent unmanaged
marshes or more broadly in the estuary, lagoon,
or embayment. Additional SMM projects in the
same hydrologic system would further affect
water-level fluctuations and flow. In the
microtidal, shallow lagoons of the Gulf Coast and
Florida, where SMM is most widely applied,
placing extensive wetlands under SMM could
affect the tidal prism and, thus, the currents,
salinity, and tidal exchange of materials and
organisms. Even if the tidal prism is not affected,
tidal amplitude and exchanges may be increased in
-------
other unmanaged marshes (Cahoon and Groat,
1990).
b) In addition to reducing the tidal influx of
sediments into the managed area, SMM may alter
patterns of sediment transport and deposition
elsewhere. If many management areas are
implemented in a region, much of the freshwater
and sediment entering the upper reaches of the
water body may flow past the managed marshes,
thus altering the flushing rates and sediment
distribution within the region (Cahoon and
Groat, 1990). Also, if tidal flows are increased
outside of the managed areas, greater resuspension
of bottom sediments and bank erosion may
result.
c) Water quality, including nutrient flux, may
be affected beyond the managed marshes as well
as within them. The nutrient- and pollutant-
trapping capacity of the wetlands may be reduced.
Waters depressed in dissolved oxygen may be
released from semi-impounded areas. Conversely,
oxygen-demanding organic matter may be
trapped in the managed areas, and organic loading
to surface waters could be reduced.
d) Where migration of fish and crustaceans
between ocean and estuarine habitats and coastal
wetlands is decreased by SMM, multiple SMM
projects that significantly reduce the available
marsh habitat within an estuary or lagoon will
impact the overall fisheries productivity of that
ecosystem.
e) The numbers of certain types of wildlife,
including waterfowl, may be increased in a
particular tract of marsh under SMM. While
often cited as a beneficial effect of SMM, it is
unclear whether this increase represents actual
increases in the populations of these species
within the region, or whether it merely reflects
aggregation to a preferred habitat.
f) Biodiversity and the conservation of rare or
endangered resources may be affected as the
proportion of marshes under SMM increases in a
region.
In addition to these environmental and natural
resource concerns, there are additional
socioeconomic concerns-beyond the scope of the
Subcommittee's assessment-relative to
cumulative impacts of SMM. These include
interference with access via navigable waterways,
ownership and use of the living resources
impounded by SMM, and riparian rights.
The cumulative effects of SMM should be of
central concern in areas where SMM is widely
practiced or is proposed for expansion, yet they
are poorly understood, much less quantified. It is
therefore troubling to see plans being developed
for expansive, adjacent, or interlinked SMM (e.g.,
some CWPPRA projects: Gagliano, 1994) based
on highly subjective and qualitative reasoning,
rather than sound scientific data and models.
3.4 Engineering Design Issues
A key element of SMM is the correct design of
drainage structures to manage key hydrologic
processes. Strategies for controlling water levels
in the managed marsh fall into two categories:
those that rely on gravity drainage and those that
utilize pumps. Passive control structures range
from fixed crest weirs (which are seldom used
anymore) to a range of types of variable crest
weirs with and without culverts (see, for example,
Broussard, 1988; Clark and Hartman, 1990).
Since hydrologic processes are the major driving
force in wetlands, the design characteristics of
17
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SMM projects to control these processes,
particularly with respect to capacity of the
damage system, are critical to project success. In
the absence of powered pumps, successful
drawdown requires a natural gravity head and
appropriate structures that can be manipulated to
•iown
>ef
Examples of two water
control structures in use
in coastal Louisiana.
Photos by R. Flaak
18
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take advantage of notoriously fickle weather and
tide conditions to maintain the required water
gradient (e.g., north winds associated with the
passage of cold fronts build up a temporary head
differential that can allow drainage of an
impounded marsh). However, in impounded
areas where vertical accretion does not keep pace
with relative sea level rise, the gradient from the
impoundment into adjacent waters is slowly lost,
reducing and then eliminating the effectiveness of
gravity drainage over time.
Several formulae are used to calculate the
appropriate cross-sectional area of water control
gates in a managed marsh (considering such
factors as marsh area, the desired range of
managed water levels and culvert cross-sectional
area) (Broussard, 1988; Louisiana Department of
Natural Resources and Soil Conservation Service,
1988; Clark and Hartman, 1990). In many cases,
however, SMM control structures built using
these formulae do not provide adequate rates of
drawdown to meet ecological management
objectives. For example, a drawdown to enhance
seed germination, a common feature of many
marsh management plans, often requires water
level reductions of a foot or more in a short time.
Even if much of the impounded area is marsh,
thus reducing the volume of water to be drained
compared to open water ponds, the calculated
drawdown period using standard formulae may
be as long as three weeks. In addition, it is
imperative to be able to drain an area rapidly after
storm surges that introduce saline water into low
salinity areas. Even assuming that weather
conditions allow maintenance of the necessary
hydrologic head, a three-week drawdown period
is long enough to kill all salt-intolerant
vegetation. In contrast, water levels in open,
unmanaged Gulf Coast marshes can drop one to
two feet in 24 to 48 hours when a high pressure
weather system with north winds moves through
the area (a common occurrence).
In one of the few studies to relate drawdown
effectiveness to drainage capacity, Hess et al.
(1989) documented response to attempted
drawdowns in 10 managed areas in coastal
Louisiana, ranging from 19 to 639 acres in size.
They reported successful drawdowns (dried pond
bottoms within the impoundment) in 6 out of 12
years, depending largely on weather conditions.
They found that the larger semi-impoundments
drained more slowly than small ones, even
though the control gates number and size had
been designed for the larger area. For example, a
47 acre impoundment could be completely
dewatered in two days of exceptionally low tides.
Under the same tidal conditions, however, only 2
to 4 inches of water could be drained off the
larger semi-impoundments. Despite the enhanced
drainage capacity of these semi-impoundments,
averaging 215% larger than the National
Resources Conservation Service guidelines, the
authors found gravity drainage in the larger semi-
impoundments to be only adequate.
In summary, the Subcommittee recommends
that much more attention be given to hydraulic
and hydrologic design criteria for SMM projects,
especially to the quantitative drainage capacity
under different weather conditions. In general,
drainage capacity should always be oversized in
SMM projects since it is easy to stop down a
culvert but impossible to increase its capacity
beyond the construction size. The Subcommittee
notes, however, that project success requires not
only adequate engineering design, but competent
construction, as well as maintenance and
management over the life of the project.
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4.1 Science-Based Principles
Before discussing the criteria that might be
employed to evaluate any specific SMM proposal,
the Subcommittee wishes to provide an overall
framework and set of principles that should guide
the ecological evaluation of SMM projects
generally. For purposes of discussion, we have
grouped wetlands into three categories: a) wetland
systems that are already functioning in some self-
sustaining manner; b) wetland systems that have
been compromised to the point where they are
significantly degraded or are not self-sustaining;
and c) wetland systems being created as part of
mitigation for loss of wetlands elsewhere.
Although the focus of the Charge to the
Subcommittee is on assessing the performance,
rationale, and criteria for converting existing tidal
systems to managed systems, the general principles
and evaluation criteria in the report offer
significant guidance for choices on strategies for
wetlands management, restoration, and
conservation, including alternative restoration
strategies for large areas of diked former tidal
wetlands that are now becoming available for
restoration.
The lesson from past SMM projects is that
while it is relatively easy to change marsh
hydrology, it is much more difficult to control or
manage the changes or to predict fully the
consequences of proposed modifications. Further,
not all marsh management projects are reversible;
i.e., it may not be possible to return a marsh to
20
pre-SMM conditions simply by removing marsh
management structures if, for example, subsidence
has occurred. A failed or abandoned SMM project
can create conditions that prevent the subsequent
evolution of a marsh (e.g., where levees have
failed, creating large open water areas exposed to
strong wave action). Because of the substantial
uncertainties in the impacts of SMM, caution is
warranted in the adoption or approval of SMM
projects in order to avoid counterproductive
results on the long-term ecological sustainability
of imperiled tidal and Great Lakes wetlands. In
situations where SMM is deemed necessary,
proposed projects should be carefully designed and
evaluated to ensure that they will accomplish the
desired results. The Subcommittee proposes five
science-based principles with regard to SMM (see
Figure 2).
4.2 Scientific/Technical Criteria
From an ecological viewpoint, changes to a
wetland ecosystem, i.e., the presence of an
ecosystem that is different from what existed
previously, does not necessarily mean that the
wetland is "degraded" or of lower ecological value.
However, the decision to manage a wetland for
specific characteristics inherently reflects a societal
judgment regarding the desired state for the
wetland. The scientific criteria in this section are
designed to allow consideration of the full suite of
current, as well as possible future, ecological
functions of a marsh for which SMM is proposed.
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Although the Subcommittee is impressed with
the need to consider large-scale manipulations of
wetlands in some circumstances, we believe that
adequate technical information does not exist to
create a general policy delineating where and
when specific modifications should be applied.
Obviously, the scale of marsh management
projects varies from region to region, with the
scale often being dictated by the size of the
remaining marshes. Similarly, the potential for
cumulative impacts depends largely on the extent
of previous modifications to wetland resources in
a region and the nature and scope of proposed
future projects. Therefore, the Agency may wish
to develop two general groups of criteria, the first
group to include generic criteria that will have
relevance to all wetland ecosystems in the nation
and the second group to include criteria specific
to certain regions. These criteria should be based
on a thorough review of national and regional
wetland ecosystem literature and should be
reviewed by experts from various parts of the
country to determine which criteria are
significant and valid for specific regions.
However, the Subcommittee recommends that, at
a minimum, the following questions should be
addressed prior to implementation of any SMM
project:
An assessment should be provided that will
indicate the historic significance and present state
of the marsh ecosystem. Is the present marsh
functioning to provide selected ecological and
societal values? Is the marsh presently
dysfunctional with regard to selected ecological
values? Does the proposal involve restoration or
21
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reestablishment of a degraded or destroyed
marsh? In its present condition, is the marsh at-
risk for future viability because of: insufficient
sediment, excess sediment, inadequate tidal
flooding, excess tidal flooding, exotic organism
expansion, changing salinity, or degradation of
water quality?
As the wetland ecosystem is largely controlled
by hydrologic processes, wetland ecosystem
function will change with impoundment.
Therefore, proposals to manage a wetland
impoundment or to create an impoundment in a
wetland should document the functions being
provided by the existing wetland, as well as the
new functional role of the wetland once
impounded or manipulated.
What are the physical boundaries of the
management proposal? How is the subject marsh
related to associated ecosystems? What is the
viability and ecological status of abutting
systems/properties? How long will it take to
construct management structures? How long will
they be maintained? To what degree will the
project require continual input of human
resources, materials, or energy? What is the
proposed time-line for management activity (i.e.,
the useful life of the structure)?
In structural management of marsh systems,
the spatial and temporal scales of change, both
those of the natural background on which the
plan is imposed and those that are part of the
management plan, need to be characterized and
considered in the formation of alternatives.
Change is a natural part of the evolution of
natural systems, and restoration or management
proposals that seek to return to conditions in
some past time may not be feasible or sensible.
This is especially true in wetland systems that
have been the sites of previous, unsuccessful
management efforts. Land uses (e.g.,
development) surrounding the wetlands may also
limit what can be done.
Are the management proposals consistent with
available regional, local, or site-specific hydrologic
models? Data should be evaluated on site
characteristics, including: natural hydrologic
conditions (tidal periodicity/amplitude, riverine
flow), historical vegetative community,
quantitative assessment of indigenous tidal marsh
aquatic fauna, substrate characteristics,
background water quality data, and interactions
with adjacent ecosystems. Paleoecological studies
and seed bank studies may also be useful to
characterize past and potential plant communities
to guide managers in decisions on management
and restoration of vegetation. The goal should be
to determine how the original natural wetland at
a site developed and functioned; this information
should then be related to natural and
anthropogenic changes in the region that might
determine how many of the original wetland
functions and site characteristics can still be
restored.
SMM projects should be evaluated in the
context of ecosystem management; i.e., is the
proposal in conformance with or in conflict with
long-term regional, estuary-wide, or larger
ecosystem restoration strategies? Is holistic
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consideration given to the structure and function
of the ecosystem. What is the successional status
of the marsh? Does the proposal seek to "hold
the marsh in a certain successional stage (often a
reality when upland development no longer
allows natural marsh migration)? What is the
impact of the proposal on species composition,
food web structure, energy flow, and nutrient
cycling? What impacts on physical and ecological
processes are expected or possible, both within
and adjacent to the managed site?
Marsh ecosystems are dynamic systems subject
to predictable and stochastic perturbations. Is the
SMM proposal flexible? Can it be readily altered/
modified to accommodate changes related to
natural or anthropogenic forces?
Monitoring of relevant and quantifiable
parameters is essential to evaluate success in
reaching the goals of the project, to evaluate
impacts on other components of the system and/
or on surrounding ecosystems, and to provide the
technical basis for future modifications.
Although the elements of an appropriate
monitoring program will depend on the
particular system being studied, suggested
minimum requirements are outlined in Section 5.
or other co-occurring human projects in a given
locale must be evaluated. This assessment should
take into account region-specific factors such as
the extent and condition of the marshes and the
combined acreage of marsh currently under (or
proposed for) SMM.
As discussed in Section 3.4, the design criteria
for the control structure(s) should be evaluated to
determine whether the system will allow adequate
water level control, including rates of drawdown
required to meet ecological management
objectives.
As discussed in Section 3.3, the cumulative
impact of multiple marsh management proposals
Structural failures (including those resulting
from extreme storm events, such as storm surges
and river floods) typically include levee
subsidence or undermining of control structures,
mechanical failure can include debris obstruction
of culverts or tidegates, and operational failures
can include erroneous weir settings or lack of
scheduled maintenance.
4.3 Management Considerations
Studies evaluating the factors that contribute to
the success or failure of SMM projects (see, for
example, Cahoon and Groat, 1990; Josselyn et al,
1993; Holderman, 1994) indicate the importance
of evaluating a number of management aspects of
a proposed project. Although the establishment
of management and implementation requirements
for SMM projects is a policy decision, these
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management issues have a direct impact on the
ecological consequences of SMM projects.
Therefore, the Subcommittee recommends that,
in addition to assessing the potential
environmental impacts of a proposed SMM
project design, the Agency consider the
following:
a) Does the project include a clearly defined set
of goals and criteria for judging the success or
failure of the management approach?
b) Is there a management plan for the project
that explains the design rationale, documents the
baseline conditions, establishes performance
criteria, identifies expected operation and
maintenance, and identifies responsible and
interested parties?
c) Is there a management system in place with
an agency or other entity with the authority,
expertise, staffing, and funding to implement the
plan for the lifetime of the project?
d) Is there evidence that the proposed
management regime will achieve its objectives
based on past experience?
e) If the proposed management is
experimental in nature, what is the experimental
design, what hypotheses are to be tested, and how
will the project test them?
f) Are there alternate locations that are better
suited for restoring natural physical processes or
achieving the proposed objectives (e.g., can the
management objectives be achieved by conversion
of upland sites presently outside the area of
potential tidal influence)?
g) Does the proposal include contingency
plans to modify the design or discontinue
structural management in the event that desired
results are not being achieved, or the cost of
maintaining the levee/control structure system
becomes too great in the face of relative sea level
rise? What will be the impacts of
decommissioning?
24
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Very few studies have systematically looked at the
effects of SMM relative to unmanaged reference
marshes, not only on vegetative growth, but on
other marsh functions, and over a 10- to 20-year
time frame. Thus, there is a general lack of
scientific documentation that the structural
approaches used in the past have achieved
sustainable improvements in marshes. Although
marsh management practices have evolved over
the years to include more sophisticated structures
and management approaches for controlling
marsh water levels, at present there is insufficient
information to determine whether these new
structural approaches are inherently better than
those used in the past.
Given these uncertainties, proposed SMM
projects should be considered carefully using the
science-based evaluation criteria in the previous
section. In addition, SMM projects should include
a monitoring plan that will provide data with
which to assess the impacts of the project on
marsh processes and long-term viability, to
determine whether the project is meeting
management and design objectives, and to provide
guidance for improving the design of future SMM
projects. Monitoring prior to construction of
SMM could provide temporal response measures.
Routine monitoring of SMM projects should
evaluate marsh biota (e.g., see PERL, 1990), as
well as physical processes and contaminants. In
many cases, very little is known of the quality of
inflowing waters or resident sediments. Thus,
monitoring efforts should include stream gauges
just upstream of managed wetlands. In addition,
remote recorders are recommended for
monitoring of salinity, oxygen, and temperature,
with proper safeguards to minimize vandalism.
Although parameters to be measured will
depend in part on the particular system being
managed, the monitoring plan should include, at a
minimum: a) monitoring of water level and flow,
salinity, dissolved oxygen, temperature, and
nutrients; b) cover and composition of emergent
and submergent vegetation; c) soil accretion rates
(organic and inorganic) and land elevation
changes; d) system productivity (although this
parameter may be unrealistic in monitoring of
small sites); and e) fish and wildlife utilization of
the marsh. Monitoring should also include fecal
coliform bacteria and toxic contaminants on a
case-by-case basis in areas where such pollutants
are suspected (e.g., in urban lagoons). Data for
these parameters should be compared with similar
data obtained in non-managed marsh areas in the
ecoregion. Absent this information, monitoring
data should also be collected in non-managed
areas.
The highest priority for research is to develop
alternative SMM techniques that maintain the
hydrologic connections between marshes and
coastal ecosystems, while meeting objectives such
as restoring and protecting coastal marsh
vegetation, providing wildlife habitat, and
25
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controlling mosquito populations. Long-term
(multi-annual, decade-long) multi-disciplinary
comparative studies of impounded and
unimpounded coastal wetlands will allow
predicted successional changes to be studied and
documented, and management approaches to be
refined. Previously impounded marshes offer
tremendous opportunities for interdisciplinary
study of the effects of hydrologic manipulation
compared simultaneously with natural systems.
To this end, efforts should be made to obtain
past, present, and continuing aerial photographs
of study sites at the largest scale affordable.
In order to improve our understanding of the
impacts of SMM, the following specific research
areas should be addressed by the Agency, in
concert with other federal and state agencies and
research institutions:
Highest Priority Research Areas
Marsh Hydrology
Control structures: assess the effects of
impoundment control structure size and design
on marsh hydrology (e.g., water level, flux, and
water residence time) and develop ecological
criteria to judge design and performance of
control structures.
Hydrologic models: develop and/or improve
hydrologic models of marshes to improve
prediction of conditions (including salinity)
within the managed marsh under different
closure and freshwater inflow regimes.
Management technology/engineering:
develop and test new technologies applicable to
active marsh management (e.g., environmental
sensors, flow regulators, and control structure
design to allow ingress/egress of organisms that
utilize the marsh).
26
Marsh morphology: assess the effects of SMM
on marsh morphology within the managed area
(e.g., changes to tidal channel geometry, tidal
creek density, edge/marsh ratios, and creek
length/area).
Ecosystem Management
Productivity: examine the effects of SMM on
marsh productivity, including the effect of
flooding on plant growth and the relative
importance of different types of primary
producers (e.g., vascular plants, periphyton,
cyanobacterial or algal mats, and
phytoplankton).
Cumulative effects: assess the effects of
multiple SMM projects within a single
hydrologic unit such as an estuary or watershed,
including impacts on circulation patterns, flows,
and geomorphology of streams, water bottoms,
and marshes.
Other Priority Research Areas
Sediment/Soil Geochemistry
Marsh soil formation: assess the effects of
SMM on mineral versus organic sedimentation
rates and net accretion rates.
Geochemistry: assess the effects of SMM on
soil geochemistry, especially of drawdowns
(e.g., oxidation rates, oxidation-reduction
potentials, and related soil chemistry).
Marsh Vegetation and Fauna
Exotic species: evaluate the occurrence and
role of exotic plants and animals in managed
marshes, factors affecting their distribution, and
their effects on native biota.
Wildlife Support: assess the relative role of
managed vs. unmanaged marsh in the support of
wildlife species and the preservation of regional
biodiversity.
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The Subcommittee has attempted to summarize
the ecological impacts of previous SMM and to
propose a consistent set of evaluation criteria for
proposed SMM projects that could be applied
from a national perspective. We recognize,
however, that SMM practices and objectives vary
in different parts of the country. Moreover, the
nature of the wetland resource-its condition,
extent, geomorphology, and dominant biota-and
the extent to which it has been modified by
human activities vary from region to region. For
these reasons, both the evaluation of proposed
SMM projects and the identification of priority
research questions must be informed by the
particular regional characteristics of the wetland
resource to be managed and a historical
perspective on how and why the resource has
been altered. This section, although not all-
inclusive, provides a sample of the differing marsh
management issues in a number of coastal regions
of the United States.
6.1 Louisiana Coastal Wetlands
6.1.1 Resource Status
Approximately 40% of U.S. coastal wetlands are
found in Louisiana. From the 1930s to 1990, the
coastal zone of Louisiana lost an estimated 3950
square kilometers (1526 square miles) of wetlands.
This loss constituted about 80% of the total
national coastal wetland loss (Boesch et al, 1994).
Wetland loss rates in the Louisiana coastal zone
for the period 1983 to 1990 have been estimated
at 66 km2/yr (Dunbar et al., 1992), representing a
serious threat to the wetland resource.
The loss of emergent wetlands in coastal
Louisiana is the result of a complex set of
circumstances, among which is the rapid
subsidence of the coast, leading to submergence of
marshes and intrusion of marine (salt) water. A
comprehensive assessment of factors contributing
to wetland loss in the region, and possible
th*
•
i
Several members of the SAB Marsh Management
Subcommittee examine a water control structure
during a site visit to coastal Louisiana.
Photo by R. Flaak
27
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T.t
to wetland loss in the region, and possible
management responses, was recently published
(Boesch et al, 1994). Submergence results from
the net imbalance of aggrading processes (mineral
sedimentation and in-place organic production)
compared to subsidence. The subsidence rate,
itself, can be addressed in some instances where it
can be shown that factors such as local faulting
and subsurface withdrawals are contributing to
the submergence. The primary focus of
management solutions, however, should be on
ways to increase marsh surface accretion. In areas
where mineral sediments are in short supply,
water level manipulation has been used and
advocated to increase marsh plant expansion and
growth, thereby increasing organic production to
balance subsidence.
Cumulative effects of SMM are a particular
concern in coastal Louisiana because of the extent
of wetland loss occurring and the scale of existing
and proposed SMM schemes (e.g., Cahoon and
Groat, 1990; Day et al., 1990; Gaghano, 1994, Fig.
7,8). In some coastal basins, half of the remaining
coastal wetlands are currently under SMM. In
addition, the area permitted for marsh
management in Louisiana seriously
underestimates the total area affected by
impoundment since there is-strong interaction
with the extensive dredged canal-spoil bank
system in the coastal marshes. The hydrology of
entire coastal basins has been extensively
replumbed by multiple actions, including ditches
that drain and channelize adjacent uplands
(Gosselink et al., 1979), navigation and oil well
access canals and their associated spoil banks, and
marsh management projects. These have changed
flow directions, channelized flows that were
historically over-marsh flows, and replaced
natural shallow, sinuous channels with deep
straight ones (Gosselink, 1984). In the isolated
managed areas, water levels are stabilized, with
fewer but longer flood events and fewer but
longer unflooded events. There are no detailed
studies of the consequences of large areas of
impoundments on hydrology in Louisiana.
6.1.2 Management Objectives
The most extensive wetland areas under SMM
exist in coastal Louisiana. The current focus of
SMM in that area primarily is to stem the loss of
emergent marsh by slowing erosion of marsh
sediments, increasing production of organic
sediments, and increasing the areal extent of
marsh grass. The results of SMM in Louisiana in
terms of the effects on marsh loss and salinity
intrusion have been mixed, however, and not yet
well documented (Reed, 1994). Historical
comparisons of areas structurally managed for
waterfowl habitat with similar reference areas
have shown that: 1) water level control has
generally not protected or restored emergent
vegetated wetlands (although it may result in a
proliferation of submerged aquatic vegetation)
and in a number of cases has accelerated the loss
of emergent wetlands; 2) the effect of SMM on
salinity is variable, but in most cases the change is
not ecologically significant (i.e., does not affect
the composition of the biota or significantly
affect geochemical processes); and 3) soil
aggradation is less in managed than in unmanaged
areas (Turner et al., 1989; Cahoon and Groat,
1990; Reed, 1992; Boumans and Day, 1994).
Some reports, on the other hand, have reported
success not only in protecting wetlands, but also
in promoting expansion of emergent wetlands
(Chabreck, 1994; Klett and Faille, 1994). In
general, these reports are less well documented
and are often promotional rather than analytical.
28
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The clearest cases for vegetative expansion have
been in low salinity regions of the Chenier Plain
of Louisiana (Cameron-Creole, Rockefeller
Wildlife Refuge) where long-duration drawdowns
have been used to allow emergent plants to
extend coverage. However, it is unclear whether
the expanded wetlands survive re-inundation.
In some areas, notably the Mermentau basin,
which is operated as a large freshwater lake for
rice irrigation, the U.S. Army Corps of Engineers
is increasingly unable to meet its target water
level elevations, apparently because the head
differential across the control structures no longer
exists with sufficient frequency (Gosselink et al,
1979). Thus, the most effective management areas
employ pumps to move water. Examples in the
Rockefeller Wildlife Refuge show that under
these circumstances a vigorous carpet of marsh
grass can be maintained indefinitely. There are
no data, however, to show whether or not the
marsh substrate has accreted in these
impoundments.
There is growing consensus within the
technical community in Louisiana that "active
marsh management which involves water-level
control structures and drawdowns is primarily
considered for implementation in highly organic
marshes in which hydrologic alterations have
adversely impacted what was historically a
naturally fresh, low-energy environment" (SMM
Workshop, August 1994). In these marshes,
organic accretion processes have the most
potential to benefit wetlands. Many of the
marshes in coastal Louisiana (perhaps 250,000
acres) are floating, their mats entirely organic, and
expansion from the edge of existing mats has been
documented in impoundments (O'Neil, 1949;
Sasser, 1994). In brackish and saline marshes, the
need for mineral sediment input for healthy
marsh vegetation growth and substrate accretion
(e.g., Nyman et al., 1990) mitigates against long-
term success of structural management projects,
which curtail mineral sediment input (Gaboon
and Turner, 1989; Taylor et al., 1989; Reed, 1992;
Boumans and Day, 1994).
6.2 New England Salt Marshes
6.2.1 Resource Status
Although SMM is not currently practiced on a
large scale in New England, salt marshes have
been diked in the past to limit tidal flushing and
reduce salinity in marsh areas in order to create
brackish or freshwater habitat for waterfowl,
provide flood control, and create conditions that
would favor Spartina patens over Spartina
alterniflora. (S. patens is the preferred species for
salt marsh hay, which is still harvested from some
New England salt marshes for livestock fodder).
These dikes typically had a tide gate that would
shut at high tide, but allow drainage of water at
low tide, so that impoundments did not develop.
Inadvertent diking of marshes has also occurred as
a result of road and railroad construction.
This past SMM has often resulted in the
transformation of well-functioning saline
wetlands to brackish or freshwater marshes
dominated by exotic alien emergents and
considered degraded in terms of wetlands
functions (Roman et al., 1984). There are regional
effects, such as widespread replacement of
Spartina by the freshwater exotic Phragmites, but
they occur in individual marshes based on
individual hydrologic conditions. As of yet, no
widespread declines of any salt marsh species have
been definitively attributed to such
transformations through monitoring or research
efforts. Based on circumstantial evidence,
29
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, . is
' -.
-.'
• • •: ;-'s in
Researchers study
Phragmites stands near
Plum Island Sound,
Massachusetts
Photo by R. Buchbaum
however, there is a widely held belief in the
region that the replacement of salt marsh
vegetation by Phragmites has resulted in the loss
of habitat for marsh birds, such as rails,
shorebirds, herons, bitterns, and sharp-tailed
sparrows, since these species are rarely observed
within the dense monocultures of Phagmites.
SMM in New England has had negative
impacts on migratory fish. These may be
attributed to outright blockage-e.g., blockage of
fish runs by water control structures, which has
been a major source of decline in New England of
anadromous species such as alewives, blueback
herring, shad, rainbow smelt, sturgeon, and
Atlantic salmon (Reback and DiCarlo, 1972)-but
also to lowered dissolved oxygen and possibly the
mobilization of sulfate (Portnoy et al, 1987).
Studies on the Herring River, an estuarine river of
Cape Cod National Seashore that was diked and a
tide gate installed, have documented changes in
water quality parameters, accretion of peat,
geochemistry of sulfur and other elements, and
the species composition of primary producers
(Portnoy et al., 1987; Portnoy, 1991). The area
behind the tide gate now has reduced tidal
flushing and lowered salinities. It has experienced
subsidence, periods of hypoxia and anoxia during
summer, and mobilization of iron and sulfate.
When the salt marsh peat is exposed to air, it
decomposes more rapidly, leading to higher
biochemical oxygen demand when the area is
reflushed during storm events (Portnoy, 1991).
Pyrite oxidation increases dissolved sulfate
concentrations, reducing pH to nearly 4 in some
instances (Portnoy et al., 1987). These conditions
have resulted in periodic fish kills and are likely
affecting local recruitment of alewives and
blueback herring. In addition, a die-off of
American eels in the diked Herring River basin
has been attributed to low pH from sulfuric acid
formation when sulfate in marsh peat is
alternately exposed to the air and inundated with
fresh water (Portnoy et al., 1987).
The subsidence of peat in tidally restricted
areas has made it unlikely that simply restoring
the tidal flushing alone will bring back a Spartina
marsh in all cases (Roman et al., 1984; Portnoy, et
al., 1987). In New England, marshes receive
inorganic sediments from both the ocean and the
rivers, although the extent of these inputs is
probably less than in other parts of the country.
Winter storms may be a major source of sediment
from the ocean, and spring floods are a major
source of sediment from land; tide gates affect this
balance. Marsh accretion that enables marsh to
keep up with rising sea level is dependent both on
primary production and the input of inorganic
sediment, although the extent to which inorganic
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sediments provide essential constituents, such as
metals that complex sulfate and therefore enhance
primary production, is an open question.
6.2.2 Management Objectives
Restoring natural tidal flushing is now a major
priority of salt marsh managers in much of New
England because Phragmites- dominated marshes
are considered of less functional value and
therefore degraded compared to the natural
marshes (Roman et al, 1984), although there is
little scientific documentation of this in East
Coast marshes other than the obvious loss of
plant diversity. Roman et al. (1984) estimate that
10 percent of Connecticut marshes are
"threatened" by tidal restriction. Removal of tidal
restrictions results in a rapid reduction of
brackish species and a return of the natural salt
marsh species within a few years (Sinicrope et al.,
1990; Peck et al., 1994). In the Parker River
National Wildlife Refuge in northern
Massachusetts, impoundments that were created
in former salt marsh habitats to create black duck
breeding habitat are now plagued by two exotic
emergents, Phragmites australis and Lythrum
salicaria, to the point where the impoundments
are currently being managed with herbicides,
prescribed burning, and water level
manipulations. Despite the general interest in
restoring salt marshes in much of New England,
wetlands regulations in Massachusetts require that
a thorough analysis of wetlands functions in
impounded marshes be carried out before any
restoration activity is allowed to proceed.
In the future, managing marshes in relation to
sea-level rise is something that may need to be
addressed in New England, particularly since
upland buffers are often developed, leaving no
place for marshes to migrate naturally. The
merits of structural management of hydrology
have been debated in relation to one proposal in
Saugus, Massachusetts, but no SMM has been
implemented. The major current effort in New
England is to restore degraded marshes by
restoring their natural hydrology and salinity
levels.
In recent years, Open Marsh Water
Management (OMWM) systems have been
implemented in New England (Hruby et al.,
1985). This method of mosquito control relies on
maintaining some open water to act as reservoirs
for mosquito-eating fish (primarily the
mummichog, Fundulus heteroclitus, in New
England) and a system of radial canals that allow
the fish access to mosquito breeding areas.
OMWM systems in New England, which are
small-scale (e.g., typically less than one acre), have
little impact on vegetation, and a clear preference
for these areas by shorebirds has not been
demonstrated (Brush et al., 1986). Habitat use by
birds is more closely related to the relative
amount of open water on a marsh than to
31
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whether an area is an OMWM or control marsh.
However, the creation of additional habitat and
access to the marsh surface for the mummichog is
beneficial because this small fish has a vital role in
the ecology of New England marshes and
estuaries, being one of the major transfer agents
of marsh productivity from the marsh surface to
higher trophic levels.
6.3 East Coast Coastal Marshes
6.3.1 Resource Status
SMM has been practiced in East Coast marshes
(New Jersey through Georgia) for a variety of
purposes. These include enhanced habitat for
waterfowl, mosquito control, and agriculture.
Only recently has protection or enhancement of
the vegetated wetland itself been an objective.
Table 1 presents estimates of the total acreage of
coastal wetlands in which there is structural
management of water level and relates these
estimates to the total acreage of coastal wetlands.
The total area of "managed" wetlands is small
compared to that in coastal Louisiana (388,000
acres) and comprises a significant fraction of the
coastal wetlands only in South Carolina and
Delaware.
In South Carolina, most "managed" marshes
are in impoundments that had been under
cultivation for rice prior to the early 1900s. These
impoundments range from those in which tidal
exchange with the surrounding estuarine waters is
totally cut off, to those that are more or less
freely open to the estuary, and to those in which
exchange and water level are managed for some
specified purpose. Such impoundments have been
studied in some depth (DeVoe and Baughman,
1986). On the positive side, they provide habitat
for migratory waterfowl and other wildlife
species, while there may be negative effects on
estuarine-dependent fish and shellfish populations
and on water quality, particularly if tidal
exchange is limited.
The situation in Delaware differs in that water
level control in marshes has been pursued
originally for the purposes of mosquito control
and waterfowl habitat enhancement rather than
agriculture. Many mid-Atlantic marshes,
including those in New Jersey, Maryland, and
Delaware, have been subjected to parallel grid
ditching for mosquito control. This activity has
had the effect of dewatering marsh ponds and
pannes, resulting in undesirable vegetation
changes and often not producing the desired effect
of mosquito reduction (Meredith, 1994). To
promote source reduction of mosquitoes in order
to reduce the application of pesticides, the use of
Open Marsh Water Management (OMWM) is
increasing in the region.
The areas of managed marshes listed in New
Jersey, Delaware, Maryland, and Virginia consist
mostly of impoundments for waterfowl
enhancement. These managed marshes have been
little studied in terms of the effects of
impoundments on marsh loss, sediment accretion,
or fish and shellfish utilization. They are viewed
by wildlife biologists as important habitat for
wading birds and some endangered species (e.g.,
black-necked stilt) and are favored sites for
birdwatchers (Josh Standt, Maryland Department
of Natural Resources, personal communication).
Marshes in parts of the Chesapeake Bay are
undergoing rapid rates of loss much like those of
coastal Louisiana. For example, the Blackwater
Wildlife Refuge has lost over 7,000 acres since the
1940s (Glenn Carowan, US Fish and Wildlife
Service, personal communication). This region,
like coastal Louisiana, is characterized by a small
32
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tidal range and relatively high subsidence rates,
and both areas exhibit break up of marshes from
within as a result of a deficiency in soil
accumulation compared to relative sea-level rise
(Stevenson et al, 1985). Marshes that have been
unwittingly impounded by a road crossing
Blackwater marshes seem to have accelerated rates
of marsh loss.
6.3.2 Management Objectives
In general, there are no plans to increase greatly
the area of coastal marshes under SMM in
Atlantic states, and a number of states have legal
and regulatory restrictions on reclaiming
abandoned and open impoundments. Rather,
managers seem concerned that EPA policies will
restrict them from repairing and modifying
existing structures. In South Carolina, for
example, the emphasis is on repairing and
improving the management of actively managed
impoundments rather than attempts to impound
or otherwise control water levels in
unimpounded wetlands. In that regard, DeVoe
and Baughman (1986) pointed out the need for
better manipulation of water exchange between
impoundments and adjacent natural wetlands. In
general, SMM is not being pursued for the
purposes of creating or preserving tidal wetlands.
There is also some interest in applying water
level management in marshes that have become
dysfunctional as a result of human activities (for
example, portions of the Blackwater Wildlife
Refuge and marshes dewatered by mosquito
ditching). Managers profess to be committed to
"ecosystem management" of wetlands, which is
meant to embody multipurpose management
with the sustainability of the habitat as a central
goal. Delaware officials speak of their Integrated
Marsh Management approach, which combines
OMWM, local eradication of the plant pest
Phragmites, and restoration of dysfunctional
impoundments.
6.4 Eastern Florida Marshes
6.4.1 Resource Status
Marshes along the east coast of Florida exhibit
varying mixtures of vegetation, from dense
mangrove forest, to a mixture of mangrove and
marsh grass species, to predominantly marsh grass
meadows and ponds. These marsh/mangrove
ecosystems have been altered by previous efforts
to impound the marsh. For example, thousands
of acres of marsh/mangrove vegetation were
inundated and drowned with impoundment
construction along the Indian River Lagoon on
the east coast of Florida during the 1950s and
1960s as water level heights were not controlled
to allow plant community survival (Harrington
and Harrington, 1982; Gilmore et al., 1982a).
Where vegetation was not eliminated,
impoundment often induced successional changes
from low salt marsh grasses to mangrove forests.
Submerged seagrass meadows grew in
impoundments where salterns and salt marshes
once thrived. Subsequent control of water levels,
i.e., lower water levels during impoundment
closure and inundation periods, has permitted
marsh/mangrove regrowth, and extensive
mangrove forests have developed (basin forest)
(Rey et al., 1990a, 1990c; Gilmore and Snedaker,
1993). However, long-term successional changes
from herbaceous marsh/saltern systems to
mangrove forest communities through the
influence of both impoundment management and
regional sea level rise are predicted.
Long-term survival of indigenous marsh/
mangrove biota under impoundment may be
33
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threatened by high detrital deposition from
mangrove forest litter production and reduced
detrital transport from the system. Lower levels
of biological and hydrological transport of
organic materials from impounded marsh and
mangrove forest ecosystems will tend to increase
organic and inorganic material accretion.
Impacts of impoundment on indigenous
marsh/mangrove fish and crustacean species (e.g.,
snook, tarpon, striped mullet, red and black
drum, shrimp, and blue crab) have resulted either
from direct death of mangrove or salt marsh
grasses following prolonged impoundment
flooding, limited access to passive/active
migration, or loss of feeding sites or preferred
food organisms (Harrington and Harrington,
1982; Gilmore et al, 1982a, 1982b; Lewis et al,
1985; Gilmore, 1987). Cumulative fish and
wildlife impacts from standing water associated
with impounding marsh and mangrove forest
communities are directly associated with
vegetative and hydrological changes. Sediment
and organic material accretion, tidal water
column reduction, and water quality declines
associated with eutrophication in subtropical/
tropical climates cause available aquatic habitat to
decline in quality and quantity. Only those
aquatic organisms adapted to eutrophic, anoxic
conditions will survive (Peterson and Gilmore,
1991). It is likely, therefore, that without major
anthropogenic energy subsidies, species diversity
will decline in impounded mangrove forest
aquatic communities, with periodic mass
mortalities of sensitive aquatic organisms. This
successional scenario has already been
documented at various locations in Indian River
Lagoon impounded wetlands (Greene and Van
Handel, 1992).
Marsh and mangrove forest aquatic species
that require summer tidal variations in order to
complete their life history, reproduction, or
effective feeding will eventually be eliminated
from impounded wetlands. Those indigenous
species showing population declines and
sensitivity to impounding are the marsh killifish
(Fundulus confluentus: Gilmore, 1987), rivulus
(Rivulus marmoratus: Taylor, 1988), and various
species of fiddler crabs (Uca spp.). Other species
that require shallow mud, algal and salt flats with
salt marsh grasses for breeding and/or feeding will
also decline in numbers as the mangrove forest
canopy shades out these photophilic vegetative
species. Species impacted by this plant
community succession include the sheepshead
minnow (Cyprinodon variegatus) and palaemonid
shrimp (Palaemonetes spp.), as well as the various
wading birds (e.g., white ibis, snowy egret, wood
stork, and roseate spoonbill) that prey on these
species in open waters and shallow flats (Gilmore,
1987). Reptilian, avian, and mammalian species
that are adapted to open herbaceous marsh
systems will decline as mangrove forest systems
succeed. The dusky seaside sparrow, now extinct,
was significantly reduced in number because of
the vegetational changes and succession induced
by wetland impoundment (Kale, 1981; Walters,
1992).
6.4.2 Management Objectives
A variety of state and federal agencies have
participated in the review, permitting, and
implementation of wetland management plans for
the east coast of Florida over the past 25 years. In
1982, the Governor formed the Subcommittee on
Managed Marshes to advise state and federal
permitting agencies on technical wetland
management issues. Most recently, two of the
regional water management districts (St. Johns
34
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River and South Florida) have taken the lead in
the development of a management plan for the
Indian River Lagoon as part of the State's Surface
Water Improvement and Management (SWIM)
Program. The basic goal of the wetland portion
of the SWIM plan is "to attain and maintain a
functioning macrophyte-based ecosystem which
supports endangered and threatened species,
fisheries and wildlife" (Steward et al., 1994). The
major management objective of the SWIM plan is
to rehabilitate the ecological function of
impounded wetlands without compromising
mosquito control, either by breaching
impoundment dikes and using open marsh
management (for northern temperate wetlands) or
by the use of numerous gated culverts that can be
opened seasonally to tidal influence (for the
southern marshes dominated by mangrove
forests). The seasonal change in hydrology and
water management is called Rotational
Impoundment Management (RIM).
Other important management objectives in
the SWIM plan are the preservation of existing
marshes, principally through land acquisition, and
the creation of wetlands where feasible. Wetland
creation is often controversial and will require
understanding of the association of wetland
function with geomorphology, hydrology, and
other site characteristics.
6.5 Great Lakes Marshes
6.5.1 Resource Status
Including the connecting channels and islands, the
Great Lakes have 10,900 miles of shoreline. Over
1300 individual wetlands cover an area of more
than 470 square miles. A large area of wetland has
been lost to development and drainage for
agriculture, especially in certain regions, and
many existing wetlands have been degraded by
human activities (Wilcox, 1995). Although few
wetlands could be considered pristine, a number
of those in Lake Superior and northern Lakes
Huron and Michigan appear to be less degraded
111
••' '
."•
' • ' '
flie /,'
Diked wetlands along the
shore of western Lake Erie
managed by periodic
drawdowns.
Photo by D. Wilcox
35
-------
than those of Lakes Erie and Ontario. SMM is
practiced at a few locations in Lakes Superior,
Michigan, Huron, and Ontario. It is widely
practiced on the Canadian side of Lake St. Clair
and the U.S. side of Lake Erie.
In the past, dike construction was a common
response to the degradation of wetlands that
occurred when protective barrier beaches and
sand spits were eroded and not rebuilt because of
an inadequate supply of sediments in the littoral
drift. Such lack of sediment supply is generally
caused by armoring of the shoreline to protect
property from erosion. In addition, revetments
and wetland dike structures are less capable of
absorbing wave energy during storms and thus
transfer this energy downshore where its effect on
unprotected beaches, sand spits, or wetlands is
magnified.
Biological communities in diked Great Lakes
wetlands have been altered by isolation from the
lakes. Reduced active transport of plant seeds and
propagules into a diked wetland, in concert with
the restricted amplitude of controlled water levels
and active management for desired plant species,
reduces the diversity of vegetation types and plant
species richness (Stuckey, 1975, 1989). Ingress
and egress of fauna are limited to organisms that
can fly or traverse the dike by land. Many of
these fauna can benefit from such management
(Kroll and Meeks, 1985; McLaughlin and Harris,
1990), and since management efforts are generally
directed toward developing waterfowl food or
habitat, waterfowl almost always receive benefits.
However, exclusion of certain fauna that may be
important parts of food webs, either as prey or
predators, can further alter biological
communities. These effects can be long-lasting if
hydrologic connection with the lake is not
restored.
Use of diked wetlands as fisheries habitat in
the Great Lakes is generally restricted to species
that enter as larvae passing through screens when
pumps or culverts are used to fill the wetlands
(Navarro and Johnson, 1992). As a result, fish
species diversity in diked wetlands is considerably
lower than in undiked systems (Johnson, 1989);
many of the more than 40 species of Great Lakes
fish that require wetland habitat in one or more
life-history stages (Johnson, 1989; Jude and
Pappas, 1992) are excluded; and overall
populations of certain species, such as northern
pike, may be greatly reduced because of lack of
access to wetland spawning areas (Herdendorf,
1987). Common carp that enter diked wetlands as
larvae grow to adult size and cannot return to
open waters of the lake in mid to late summer as
they typically do. While feeding, these large carp
can uproot or destroy wetland plants, and they
stir up sediments and create turbidity problems
that further reduce the ability of plants to thrive
(Crivelli, 1983). In diked wetlands where carp are
a problem, habitat values for target fauna, such as
waterfowl, are diminished. Thus, structural
management of Great Lakes coastal marshes may
allow for enhancement of certain wetland
functions and values for a limited period of time,
but the overall wetland ecosystem can be severely
compromised by this practice as it is currently
conducted.
Numerous large-scale marsh management
projects in one region, such as along the Ohio
shoreline of Lake Erie, can have cumulative
effects of endangering or eliminating populations
of certain fish species that require access to
wetlands, reducing the overall diversity of
wetland plant species and faunal organisms that
depend on lost plants, and reducing or altering
36
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sediment supplies in the littoral drift of the lake.
6.5.2 Management Objectives
SMM has been shown to be successful as a
restoration technique to create and protect
emergent vegetation in coastal areas around the
Great Lakes. However, the species composition
and diversity of the plant communities can differ
from pre-management conditions, with a noted
increase in non-indigenous plants, and other
ecosystem values are nearly always compromised
(Lowden, 1969; Stuckey, 1975, 1989; Kroll and
Meeks, 1985; Bartolotta, 1989; Harris et al, 1991).
As practiced in the Great Lakes, structural
management consists of constructing dikes
around wetlands or isolating an embayment
wetland from the lake by placing a dike across the
mouth of the bay. Water-level control is thus
attained and used to create drawdown conditions
that stimulate growth of emergent plants from
the seed bank. Under most circumstances,
hydrologic connection with the lake is not
restored. Because water levels in the Great Lakes
vary widely on scales of centuries, decades, years,
seasons, and hours (seiches), wetland managers
find it difficult to restore emergent vegetation in
wetlands that have been degraded by other human
activities. Given an adequate span of time, natural
lake-level cycles would result in low-water years
with drawdown conditions that would stimulate
the seed bank. However, since these time scales
generally do not match management goals, SMM
has been chosen as an alternative.
6.6 Southern California Coastal Marshes
6.6.1 Resource Status
Very few coastal wetlands remain in southern
California, largely as a result of urbanization. In
San Diego County, for example, 85 percent of the
historical tidal salt marsh is gone (Macdonald,
This photo of a con-
structed (mitigation) marsh
in San Diego Bay shows
the kinds of structures that
affect many of the region's
wetlands. A freeway on
the left blocks access to
fresh water inflows. An
abandoned railroad and
power lines on the right
block access to tidal flows.
Tidal influx is limited to
flows through a flood
control channel, which is
seen on the horizon; the
levee of the flood control
channel has a notch that
allows tidal inflows,
although a shallow wier
(submerged except at low
tide) impairs drainage.
Photo by J. Zedler
37
-------
1990). The coastal watersheds are characterized by
highly erodible soils, steep slopes, and ample
disturbance associated with urbanization. All of
southern California's coastal wetlands receive
some unnatural freshwater inflows, as the region
imports water from northern California and from
the Colorado River. Some of this water makes its
way into coastal streams through irrigation runoff
or other means. Virtually every coastal wetland
has a roadway crossing it; most have three (Coast
Highway, Santa Fe Railroad, and Interstate
Freeway 5). These structures act as breached
levees-they have cut off tidal channels, although
a single bridge allows some tidal flow. The result
of these "levees" is reduced tidal action and
increased sedimentation, both at the ocean inlet
(from long shore transport) and from the
watershed (entrained sediments).
The effect of this inadvertent impounding of
tidal wetlands has been to increase the range of
environmental extremes (e.g., water and soil
salinity, dissolved oxygen concentration in the
water column, and water temperature). Wetlands
become hypersaline when there is little runoff or
brackish if there is excess inflow from irrigation
runoff or other stream flows (e.g., reservoir
discharge; raw sewage from Mexico to Tijuana
Estuary). Hypersahne soils, as high as 100 ppt
interstitial soil water, have developed in some
locations (Zedler et al, 1992), causing massive
diebacks in the more sensitive halophyte
populations. Hyposaline soils (e.g., those under
20 ppt) allow invasions by brackish marsh
vegetation (e.g., Typha domingensis, Scirpus
californicus) which shades and out-competes the
native salt marsh plants. Three species are most
tolerant of these conditions, and one of them
(Salicornia virginica) becomes the dominant of
impounded wetlands. In watersheds with high
runoff from urban or agricultural uses (e.g., San
Elijo Lagoon), the water levels may become too
high to support emergent vegetation. A
comparison of 26 wetlands in southern California
shows that the wetlands that are most often fully
tidal support up to 19 native halophytes, while
the least frequently tidal systems retain as few as 3
(PERL, 1990). While some impoundment may
lead to increased vascular plant productivity
(Zedler et al., 1980), algal mats are rare beneath
these canopies, and total primary productivity
may not be enhanced.
In addition to impacting marsh vegetation,
salinity, temperature, and dissolved oxygen
extremes stress fish and invertebrates, causing
heavy mortality. Lack of tidal flushing eliminates
habitat for endangered birds that have specific
nesting and feeding requirements (e.g., light-
footed clapper rail, Belding's Savannah sparrow)
and allows the accumulation of nutrients
(eutrophication) and algal blooms, the decay of
which contributes to anoxia through the water
column. The cumulative impact of reduced tidal
influence has been a loss in biodiversity, a loss in
productivity of sport and commercial fisheries, a
loss in bait fisheries, a loss in recreational
clamming, and various nuisance problems (e.g.,
algal blooms, odors, midges, and mosquitoes)
(Zedler at al., 1992; Nordby and Zedler, 1991;
Zedler, 1996b).
6.6.2 Management Objectives
Because very few coastal wetlands remain, the
primary focus of marsh management activities in
southern California has been on marsh
protection, restoration, and creation. These
efforts have been greatly hampered by the lack of
38
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a regional plan for wetland management,
including identification of sites that need to be
restored and sites that might serve mitigation
needs (Zedler, 1996a). Most projects merely
"remodel" existing wetlands, rather than creating
new wetlands from upland. Mitigation projects
are undertaken piecemeal, often without regard
for the hydrologic suitability of the site. For
example, Southern California Edison is required
to "substantially restore" 150 acres of wetland
with an emphasis on fish production to mitigate
losses to coastal fisheries caused by the San
Onofre Nuclear Generating Station. The site
chosen for this project, San Dieguito Lagoon,
cannot be made fully tidal without continual
maintenance of the ocean mouth. Since closure is
detrimental to fish populations (Nordby and
Zedler, 1991; Zedler, 1996b), the project has a low
likelihood of achieving its mandate.
6.7 San Francisco Bay/Delta Wetlands
6.7.1 Resource Status
Ninety-five percent of San Francisco Bay's
550,000 acres of tidal wetlands has been converted
to agricultural uses, salt ponds, duck clubs, or
urban development. Since 1965, further
conversion of tidal wetlands in the salinity-
influenced portion of the estuary has been
prevented by legislation. In the freshwater tidal
area (the Delta), all but a few isolated remnants of
tidal marsh have been converted to agricultural
land. Large-scale elimination of fresh and brackish
tidal marshes has significantly changed the food
web in the estuary. Elimination of tidal marshes
has also removed a major sediment sink, resulting
in greater sediment recirculation and higher
turbidity in the estuary. Vulnerability of SMM
sites to catastrophic failure in the event of
earthquakes and floods can significantly increase
tidal prism and estuarine hydrodynamics.
Tubb's Island Managed
Wetlands, San Pablo Bay
National Wildlife Refuge,
Sonoma County, California.
Photo by Phillip Williams and
Associates, Ltd.
39
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6.7.2 Management Objectives
Within the last decade there has been growing
interest in restoring large areas of former San
Francisco Bay/Delta wetlands, with substantial
land acquisitions now underway. In the Delta
region, a key impetus for wetland restoration is
the protection of freshwater diversions from
salinity intrusion caused by tidal inundation of
subsided reclaimed land, as well as restoring
fishery habitat. In Suisun Marsh, the brackish
zone of the estuary, the main concern is the long-
term future of 40,000 acres of private wetlands
managed for waterfowl habitat in the face of
increased saltwater intrusion and deteriorating
levees. In San Pablo Bay, up to 20,000 acres of
former salt ponds and agricultural land are being
purchased by a mix of state, federal, and local
nonprofit organizations for restoration as
wetlands. In the South Bay, up to 40,000 acres of
salt ponds may eventually become available for
restoration as wetlands.
One of the most important resource
management issues in the region is the attempt to
ameliorate the impacts on the estuary of water
diversions. EPA is presently engaged in setting
flow standards to maintain the ecosystem based
on its present day functioning. Because of the loss
of most of the tidal wetlands connected to the
estuary, only about 10 to 20% of organic carbon
input to the estuary comes from marshes
compared to 50% generated in the water column
by phytoplankton (Jassby et al, 1992). With full
tidal as opposed to managed wetland restoration,
there is a significant potential for increasing
inputs of organic carbon, which is a measure of
the source of food for phytoplankton and other
biota in the estuarine food web.
As proposals for large-scale restoration
projects have matured, an important controversy
over wetland restoration strategy has emerged.
Because of drastic losses of all types of wetlands in
California, there is now competition for different
wetland restoration goals in diked former tidal
marshes, such as waterfowl habitat or seasonal
wetlands. An example of this controversy
concerned the recently constructed 300-acre
Sonoma Baylands tidal restoration project, where
56 acres of seasonal wetland existed in the
hayfields on a site that was formerly a tidal
wetland. The U.S. Fish and Wildlife Service
argued that mitigation was required for the loss of
the seasonal wetland upon restoration of tidal
influence. Maintenance of existing "accidental"
wetland values on potential tidal restoration
areas, such as salt ponds or poorly drained fields,
implicitly requires a commitment to a structural
marsh management system. This is because the
hydrology and geomorphology sustaining these
accidental transient wetlands are artificial
creations of the former management practices and
must be maintained indefinitely to preserve the
new status quo.
40
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Although most experience with SMM is based on
efforts primarily designed to accomplish a
purpose other than the protection or creation of
emergent vegetated wetlands, the collective
experience around the country has shown that
unintended, unanticipated, and sometimes
undesirable effects have often resulted from
structural management of marsh hydrology.
Differences in the physical environment, status of
wetland resources, and management objectives
make it clear that the application of a marsh
management policy needs to be at least region-,
ecosystem-, or basin-specific. Further, the impact
of SMM on marsh-sustaining processes depends
on the type of management scheme employed.
For these reasons, it is difficult to generalize
about the ecological impacts of SMM. However,
the interruption of daily, monthly, and seasonal
hydrologic cycles as a result of SMM inevitably
influences important elements of the ecosystem
such as sediment chemical processes, water
column chemistry, the distribution and migration
of aquatic and semi-aquatic organisms, and
material import and export from the marsh.
Because of the substantial uncertainties about
the impacts of SMM and because not all SMM
projects are reversible, the Subcommittee urges
caution in the adoption or approval of SMM
projects in order to avoid counterproductive
results on the long-term sustainability of
imperiled tidal and Great Lakes wetlands.
Further, we strongly recommend that Agency
decisions regarding proposed SMM projects take
into account the potential impacts of the project
from an ecosystem, rather than single-species or
single-resource, perspective. All proposed SMM
projects should be carefully evaluated in the
context of the science-based principles and
evaluation criteria described in this report. SMM
projects implemented following this careful
evaluation should include environmental
monitoring to assess the impacts of the project on
marsh processes and long-term viability, to
determine whether the project is meeting
management and design objectives, and to provide
guidance for improving the design of future SMM
projects. In addition, the Subcommittee has
identified priority research questions that should
be addressed by the Agency, in concert with
other federal and state agencies and research
institutions, in order to improve our
understanding of the effects of SMM on various
ecosystem processes and functions.
The Subcommittee's responses to the specific
questions in the Charge are summarized below:
a) Does SMM protect or create emergent
vegetated wetlands? In regard to this
evaluation, consider two conditions in the
response: i) areas where net sediment deficit
occurs (i.e., soil building does not keep up with
relative sea level rise), and ii) areas where there
has been extensive human-induced wetlands
41
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deterioration.
The available scientific studies on the efficacy
of SMM are highly equivocal. Emergent wetland
area has been maintained or increased in some
SMM projects, but unchanged or decreased in
others, relative to similar unmanaged areas. In salt
and brackish marshes in regions undergoing rapid
subsidence, SMM generally restricts the supply of
mineral sediments needed to accrete soil, does not
seem to protect wetlands, and may even hasten
their demise. There may be a better case for the
application of SMM in protecting tidal freshwater
wetlands with highly organic or even floating
soils. However, critical scientific appraisals of the
effectiveness of SMM in such environments have
yet to be performed. (See Section 3.1.)
b) To what extent does SMM impact the
physical, biological and/or chemical aspects of
natural marsh-sustaining processes? With
regard to this evaluation, consider long-term
marsh survival and productivity, including
accretion of organic and inorganic sediments.
Depending on the extent of invasiveness,
SMM may impact natural marsh-sustaining
processes greatly or little at all. If SMM is applied
to protect vanishing marshes or restore lost
marshes, it must seek to do so by altering the
physical, biological, and chemical processes
operable. However, it is difficult to manipulate
one process deemed necessary for sustaining or
restoring a marsh (e.g., current flows or salinity)
without also affecting others (e.g., sediment
supply, water and sediment chemistry). Therein
lie the controversies regarding the long-term
effectiveness of SMM. In those cases in which
SMM has been successful in protecting or
expanding vegetated wetlands, the long-term
effectiveness of SMM (and thus sustainability) in
the face of geomorphic trends and sea-level rise
42
remains in question. In any case, it is clear that
SMM requires a perpetual management
commitment to maintain effectiveness. (See
Section 3.1.)
c) What are the impacts of SMM, if any,
to estuarine fisheries, waterfowl, and other fish
and wildlife? If there are impacts, provide an
analysis of the extent of these impacts.
In a wide variety of cases and regions, SMM
has been shown negatively to affect estuarine
fisheries by creating an artificial separation
between the wetland and the estuary or lake,
reducing either the access to or escape from the
habitat. This impact has been reduced, but not
eliminated, by improvements to the design of
weirs and gates. In addition, impoundments
within the managed marsh may result in degraded
water quality (e.g., salinity, temperature, and
dissolved oxygen extremes, and mobilization of
sulfate), occasionally with drastic results for
marsh biota. SMM can enhance the habitat value
for waterfowl and other wildlife and has been
widely used for that purpose. It is not clear,
however, whether SMM results in increases in the
regional or continental populations of these
resources. On the other hand, wading birds and
other organisms that depend on periodic exposure
of the marsh surface for effective feeding and prey
capture, and endangered birds that nest or feed in
specific types of vegetation, may be negatively
affected by SMM. (See Section 3.2.)
d) What are the cumulative effects of
numerous large-scale SMM projects with
respect to emergent vegetation, accretion, fish
and wildlife, and other resources?
Collateral and cumulative effects of SMM are
poorly understood and virtually unquantified.
Potential cumulative effects relate to the reduced
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water exchange between the managed marsh and
adjacent wetlands and waters, altered patterns of
sediment transport and deposition, altered
movement of nutrients, pollutants, and organisms
into and out of the marsh, and the ability to
support regional biodiversity and rare or
endangered species. Assessment of cumulative
effects of SMM should be of central concern in
areas where SMM is widely practiced or proposed
for expansion. Presently, however, this
assessment is based on highly subjective and
qualitative approaches, rather than sound data
and models. Research in this area should be a high
priority for federal and state agencies. (See
Section 3.3.)
e) What are the gaps and the highest
priorities for research studies related to the
effects of SMM projects, and for routine
monitoring of such projects?
High priority research areas include: the
development and testing of alternative
management techniques that maintain the
hydrological connections between marshes and
coastal ecosystems; improved SMM technologies
(e.g., improvements to control structure design
and hydrological modeling of marshes); the
effects of SMM on marsh morphology and
productivity; and the cumulative effects of
numerous SMM projects within a watershed or
region. The Subcommittee recommends that
monitoring be required for SMM projects and
suggests parameters that should be measured. (See
Section 5.)
f) What scientific or technical criteria
should EPA use as part of the basis for case-
specific decision-making; or, as an alternative,
what approach should EPA take to develop
such criteria?
The Subcommittee suggests that the Agency
develop both generic national criteria and criteria
relevant to specific regions of the country. These
criteria should be consistent with the science-
based principles discussed above. The
Subcommittee has identified a number of
scientific and management evaluation criteria that
should be used when evaluating proposed SMM
projects, including: the historic quality and
productivity of the marsh; the current state of the
marsh; the suitability of the modifications for the
proposed site; the relationship of the proposed
project to long-term, regional restoration goals;
the ability of the SMM design to cope with
extreme weather events; the potential for
cumulative impacts; and the ecological impacts
were the project to fail or be abandoned. (See
Section 4.)
43
-------
Bancroft, F.T., A.M. Strong, R.J. Sawicki, W.
Hoffman, and S.D. Jewell. 1994.
Relationships among wading bird foraging
patterns, colony locations, and hydrology in
the Everglades, pp. 615-658. In S.M. Davis
and J.C. Ogden (eds.), Everglades: The
ecosystem and its restoration. St. Lucie Press.
Bartolotta, R.J. 1978. Vascular flora and the
succession of plant communities of the eastern
dikes bordering Sandusky Bay and western
Lake Erie. Ohio State University, Columbus,
OH. CLEAR Technical Report No. 100.
Boesch, D.F., M.N. Josselyn, A.J. Mehta, J.T.
Morris, W.K. Nuttle, C.A. Simenstad, and
D.J.P. Swift. 1994. Scientific assessment of
coastal wetland loss, restoration and
management in Louisiana. J. Coastal Research
Special Issue 20: 1103.
Boumans, R.M. and J.W. Day, Jr. 1994.
Effects of two Louisiana marsh management
plans on water and materials flux and short-
term sedimentation. Wetlands 14:247-261.
Broussard, L.J. 1988. Report on current
marsh management engineering practices. U.S.
Department of Agriculture, Soil Conservation
Service, Alexandria, LA. Prepared for the
Department of Natural Resources, Coastal
Management Division, Baton Rouge, LA.
Browder, J.A., P.J. Gleason, and D.R.
Swift. 1994. Periphyton in the Everglades:
Spatial variation, environmental correlates, and
ecological implications, pp. 379-418. In SM.
Davis and J.C. Ogden (eds.), Everglades: The
ecosystem and its restoration. St. Lucie Press.
Brush, R., R.A. Lent, T. Hruby,
B.A. Harrington, R.M. Marshall, and W.G.
Montgomery. 1986. Habitat use by salt marsh
birds and response to Open Marsh Water
Management. Colonial Waterbirds 9:189-195.
Cahoon, D.R. and C. G. Groat (eds.).
1990. A Study of Marsh Management Practice
in Coastal Louisiana. U.S. Department of
Interior, Minerals Management Service (MMS
90-0075). 4 volumes.
Cahoon, D.R. and R.E. Turner. 1989.
Accretion and canal impacts in a rapidly
subsiding wetland II: Feldspar marker horizon
technique. Estuaries 12:260-268.
Carlson, P.R., L.A. Yarbro, C.F.
Zimmermann, and J.R. Montgomery. 1983.
Pore water chemistry of an overwash
mangrove island. Fla. Sci. 46:239-249.
Chabreck, R.H. 1976. Management of
wetlands for wildlife improvement, p. 226-
233. In M. Wiley (ed.), Estuarine Processes:
Uses, Stresses, and Adaptation to the Estuary.
Academic Press, New York.
Chabreck, R.H. 1994. Marsh management in
Louisiana for production of emergent and
aquatic plants. Prepared for Louisiana
Landowners Association, Inc., Baton Rouge,
Louisiana. 83p.
44
-------
Chabreck, R.H. and G.M. Junkm. 1989.
Marsh impoundments for the management of
wildlife and plants in Louisiana, pp. 112-119.
In W.G. Duffy and D. Clark (eds.), Marsh
Management in Coastal Louisiana: Effects and
Issues - Proceedings of a Symposium. U.S.
FWS Biological Report 89(22): 151-163.
Clark, D. and R. Hartman. 1990.
Engineering and construction techniques of
marsh management structures, pp. 87-163. In
D.R. Cahoon and C.G. Groat (eds.), A Study
of Marsh Management Practices in Coastal
Louisiana. Final report submitted to Minerals
Management Service, New Orleans, LA.
Coats, R., M. Swanson, and P. Williams.
1989. Hydrologic analysis for coastal wetland
restoration. Environmental Management
13:715-727.
Crivelli, A.J. 1983. The destruction of aquatic
vegetation by carp. Hydrobiologia 106:37-41.
Day, R.H., R.K. Holz, and J.W. Day, Jr.
1990. An inventory of wetland impoundments
in the coastal zone of Louisiana, USA:
historical trends. Environmental Management
14:229-240.
DeVoe, M.R. and D.S. Baughman (eds.).
1986. South Carolina Coastal Wetland
Impoundments: Ecological Characterization,
Management, Status and Use. South Carolina
Sea Grant Consortium, Charleston, SC. 3
volumes.
Dunbar, J.B., L.D. Bntsch, and E.B. Kemp.
1992. Land Loss Rates, Report 3: Louisiana
Coastal Plain. Technical Report No. GL-90-2.
U.S. Army Corps of Engineers, Waterways
Experiment Station, Vicksburg, MS.
Gagliano, S.M. 1994. Marsh management in
coastal Louisiana: what works where. 18 pp. In
Summary Report of the Workshop on
Structural Marsh Management, August 16-18,
1994. New Orleans, LA.
Gilmore, R.G. 1987. Fish, macrocrustacean and
avian population dynamics and cohabitation in
tidally influenced impounded subtropical
wetlands, pp. 373-394. In W.R. Whitman and
W.H. Meredith (eds.), Proceedings of a
Symposium on Waterfowl and Wetlands
Management in the Coastal Zone of the
Atlantic Flyway. Delaware Dept. Of Natural
Resources and Envir. Control, Dover,
Delaware.
Gilmore, R.G. and S.C. Snedaker. 1993.
Chapter 5: Mangrove Forests, pp. 165-198. In
W.H. Martin, S.G. Boyce, and A.C.
Echtemacht (Eds.), Biodiversity of the
southeastern United States/lowland terrestrial
communities. John Wiley and Sons, Inc.
Gilmore, R.G., D.W. Cooke, and C.J. Donohoe.
1982a. A comparison of the fish populations
and habitat in open and closed salt marsh
impoundments in east-central Florida.
Northeast Gulf Science 5:25-37.
Gilmore, R.G., C.J. Donohoe, and D.W. Cooke.
1982b. Observations on the distribution and
biology of east-central Florida populations of
the common snook, Centropomus undecimalis
(Bloch). Fla. Sci. Spec. Suppl Issue 46:313-336.
Good, W. 1994. The [Louisiana] Office of
Coastal Restoration and Management's View
of EPA Region VTs Recent Activities
Concerning Marsh Management. Presentation
to the SAB Marsh Management Subcommittee,
July 21, 1994. 19p.
Gosselink, J.G. 1984. The ecology of delta
marshes of coastal Louisiana: a community
profile. U.S. Fish and Wildlife Service, FWS/
OBS-84/09.
45
-------
Gosselink, J.G. and L. C. Lee. 1989. Cumulative
impact assessment in bottomland hardwood
forests. Wetlands 9:83-174.
Gosselink, J.G., E.P. Odum, and R.M. Pope.
1974. The value of the tidal marsh. Louisiana
State University, Center for Wetland
Resources, Baton Rouge, LA, LSU-SG-74-03.
Gosselink, J.G., C.L. Cordes, and J.W. Parsons.
1979. An ecological characterization study of
the Chenier Plain coastal ecosystem of
Louisiana and Texas. 3 vols., U.S. Fish and
Wildlife Service, Washington, D.C., FWS/
OBS-78/9 through 78/11.
Greene, L.E. and E. Van Handel. 1992. Sulfide
sensitivity in fishes of the Indian River
Lagoon, Florida. J. Am. Mosquito Control
Assoc. 8:95-96.
Harrington, R.H. and E.S. Harrington. 1982.
Effects on fishes and their forage organisms of
impounding a Florida salt marsh to prevent
breeding by salt marsh mosquitos. Bull. Mar.
Sci. 32:523-531.
Harris, J.J., L. McAllister, and D. McLaughlin.
1991. Impacts of nutrients, sediments, and
turbidity on coastal marshes of Green Bay,
Lake Michigan. Great Lakes Wetlands 2:1-3.
Herdendorf, C.E. 1987. The ecology of Lake
Erie coastal marshes: a community profile.
U.S. Fish and Wildlife Service Biological
Report 85(7.9).
Herke, W.H., E.E. Knudsen, P.A. Knudsen, and
B.D. Rogers. 1992. Effects of semi-impoundment
of Louisiana marsh on fish and crustacean nursery
use and export. North American Journal of Fisheries
Management 12:151-160.
Herke, W.H., B.D. Rogers, V.L. Wnght, and
W.H. Bradshaw. 1996. Postlarval Penueus
aztecus and P. setiferous transport into, and
distribution within, adjacent weired and
unweired ponds. Wetlands 16:197-207.
Hess, T.J., R.F. Faille, R.J. Moertle, and K.P.
Guidry. 1989. Results of an intensive marsh
management program at Little Pecan Wildlife
Management Area. pp. 278-310. In W.G.
Duffy and D. Clark (eds.), Marsh Management
in Coastal Louisiana: Effects and Issues -
Proceedings of a Symposium. U.S. FWS
Biological Report 89(22): 151-163.
Holderman, R. 1994. Eighteen years of wetland
restoration and enhancement: lessons from the
California Coastal Conservancy. Presentation
to the SAB Marsh Management Subcommittee,
July 21, 1994. 7p.
Hruby, T., W.G. Montgomery, R.A. Lent, and
M. Dobson. 1985. Open Marsh Water
Management in Massachusetts: adapting the
technique to local conditions and its impact on
mosquito larvae during the first season. J.
Amer. Mosquito Control Assoc. 1:85-88.
Ibarra Obando, S.E. 1990. Lagunas costeras de
Baja California. Ciencia y Desarrollo 16:39-49.
Ibarra Obando, S.E. 1993. Plantas marinas y
pesquerias costeras. Ciencia y Desarrollo 18:36-
40.
Ibarra Obando, S.E. and M. Poumian-Tapia.
1991. The effect of tidal exclusion on salt
marsh vegetation in Baj a California, Mexico.
Wetlands Ecology and Management 1:131-148.
Jassby, A.D., B. Herbold, and P.B. Moyle.
1992. Status and Trends Report on Aquatic
Resources of the San Francisco Estuary.
Prepared by the University of California at
Davis for the San Francisco Estuary Project,
U.S. Environmental Protection Agency. 257p
and appendices.
46
-------
Johnson, D.L. 1989. Lake Erie wetlands:
fisheries considerations, pp. 257-273. In K.A.
Krieger (ed.), Lake Erie and its estuarine
systems: issues, resources, status, and
management. NOAA and U.S. EPA,
Washington, DC.
Josselyn, M., S. Chamberlain, K. Goodnight, H.
Hopkins, and A. Fiorello. 1993. Evaluation
of Coastal Conservance Enhancement Projects:
1978-1992. Report to the California State
Coastal Conservancy, July 1993. 22p and
appendices.
Jude, D.J. and J. Pappas. 1992. Fish utilization
of Great Lakes coastal wetlands. /. Great Lakes
Research 18:651-672.
Kale, H.W. 1981. Dusky seaside sparrow:
gone forever? Florida Naturalist 54:3-4.
Keddy, P.A., I.C. Wisheu, B. Shipley, and C.
Gaudet. 1989. Seed banks and vegetation
management for conservation: toward
predictive community ecology, pp. 347-363.
In M.A. Leek, V.T. Parker, and R.L. Simpson
(eds.), The Ecology of Soil Seed Banks.
Academic Press, Inc., San Diego, CA.
Klett, S. and R. Faille. 1994. Cameron Creole
Watershed Project. In Summary Report of the
Workshop on Structural Marsh Management,
August 16-18, 1994. New Orleans, LA.
Kroll, R.W. and R.L. Meeks. 1985. Muskrat
population recovery following habitat re-
establishment near southwestern Lake Erie.
Wildl. Soc. Bull. 13:483-486.
Kushlan, J.A. 1986. Responses of wading birds
to seasonally fluctuating water levels: strategies
and their limits. Colon. Waterbirds 9:155-162.
Leek, M.A. 1989. Wetland seed banks, pp. 283-
305. In M.A. Leek, V.T. Parker, and R.L.
Simpson (eds.), The Ecology of Soil Seed
Banks. Academic Press, Inc., San Diego, CA.
Lewis, R.R., III, R.G. Gilmore, Jr., D.W. Crewz,
and W.E. Odum. 1985. Mangrove habitat and
fishery resources of Florida, pp. 281-336. In
W. Seaman, Jr. (Ed.), Florida Aquatic Habitat
and Fishery Resources. Fla. Chapter,
American Fish. Soc., Kissimmee, Florida.
543p.
Louisiana Department of Natural Resources and
U.S. Soil Conservation Service. 1988.
Louisiana Coastal Resources Program Marsh
Management Manual. Louisiana Department
of Natural Resources, Coastal Management
Division, Baton Rouge, LA.
Lowden, R.M. 1969. A Vascular Flora of
Winous Point, Ottawa and Sandusky
Counties, Ohio. OhioJ. Sci. 69:257-486.
Macdonald, K.B. 1990. South San Diego Bay
Enhancement Plan Volume One/Resources
Atlas: Marine Ecological Characterization, Bay
History and Physical Environment. San Diego
Unified Port District, San Diego.
McLaughlm, D.B. and H.J. Hams. 1990.
Aquatic insect emergence in two Great Lakes
marshes. Wetlands Ecology and Management
1:111-121.
Meredith, W.H. 1994. Tidal Marsh Management
in Delaware: An Overview of Activities,
Programs, Plans and Policies. Presentation to
the EPA Science Advisory Board, July 21,
1994. Delaware Dept. of Natural Resources,
Dover.
Navarre, J.E. and D.L. Johnson. 1992. Ecology
of Stocked Northern Pike in Two Lake Erie
Controlled Wetlands. Wetlands 12:171-177.
Nickerson, N.H. and F.R. Thibodeau. 1985.
Association between pore water sulfide
concentrations and the distribution of
mangroves. Biogeochemistry 1:183-192.
47
-------
Nordby, C.S. and J.B. Zedler. 1991. Responses
of fishes and benthos to hydrologic
disturbances in Tijuana Estuary and Los
Penasquitos Lagoon, California. Estuaries
14:80-93.
Nyman, J.A., R.D. DeLaune, and W.H. Patrick,
Jr. 1990. Wetland soil formation in the
rapidly subsiding Mississippi River Deltaic
Plain: mineral and organic matter
relationships. Estuarine, Coastal and Shelf
Science 31:57-69.
Ogden, J.C. 1994. Chapter 22: A comparison of
wading bird nesting colony dynamics (1931-
1946 and 1974-1989) as an indication of
ecosystem conditions in the southern
Everglades, pp. 533-570. In S.M. Davis and
J.C. Ogden (eds.), Everglades: the ecosystem
and its restoration. St. Lucie Press.
O'Neil, T. 1949. The muskrat in the Louisiana
coastal marshes. Louisiana Wildlife and
Fisheries Commission, New Orleans. 159p.
Pacific Estuarine Research Laboratory (PERL).
1990. A Manual for Assessing Restored and
Natural Coastal Wetlands with Examples from
Southern California. California Sea Grant
Report No. T-CSGCP-021. La Jolla,
California. 105p.
Peck, M.A., P.E. Fell, E.A. Allen, J.A. Gieg, C.R.
Guthke, and M.D. Newkirk. 1994.
Evaluation of tidal marsh restoration:
comparison of selected macroinvertebrate
populations on a restored impounded valley
marsh and an unimpounded valley marsh
within the same salt marsh system in
Connecticut, USA. Envir. Manag. 18:283-293.
Peterson, M.S. and R.G. Gilmore, Jr. 1991.
Eco-physiology of juvenile snook Centropomus
undecimalis (Bloch): life-history implications.
Bull. Mar. Sci. 48:46-57.
Portnoy, J.W. 1991. Summer oxygen depletion
in a diked New England estuary. Estuaries
14:122-129.
Portnoy, J.W., C.T. Roman, and M.A. Soukup.
1987. Hydrologic and chemical impacts of
diking and drainage of a small estuary (Cape
Cod National Seashore): effects on wildlife and
fisheries, pp. 254-265. In Proceedings from a
Symposium on Waterfowl and Wetlands
Management in the Coastal Zone of the
Atlantic Flyway.
Provost, M.W. 1967. Managing impounded salt
marsh for mosquito control and estuarine
resource conservation, pp. 163-171. In
Proceedings of a Marsh Estuarine Symposium,
Louisiana State University, Baton Rouge.
Provost, M.W. 1977. Source reduction in salt
marsh mosquito control: past and future.
Mosquito News 37:689-698.
Reed, D.J. 1992. Effects of weirs on sediment
deposition in Louisiana coastal marshes.
Environmental Management 16:55-65.
Reed, D.J. 1994. Marsh management in coastal
Louisiana: impact on vegetation, accretion and
fisheries productivity. A Briefing Document
for EPA Region VI. 63p.
Reed, D.J. (Ed.) 1995. Current Status and
Historical Trends of Hydrologic Modification,
Reduction in Sediment Availability and
Habitat Loss/Modification in the Barataria and
Terrebonne Estuarine Systems. Barrataria-
Terrebonne National Estuary Program,
Thibodaux, Louisiana. Vol. BTNEP Pub. No.
20. 330p.
Rey, J.R., R.A. Grossman, and T.R. Kain. 1990a.
Vegetation dynamics in impounded marshes
along the Indian River Lagoon, Florida, USA.
Environmental Management 14:397-409.
48
-------
Rey, J.R., J. Shaffer, D. Tremain, R.A. Grossman,
and T.R. Kam. 1990b. Effects of re-
establishing tidal connections in two
impounded subtropical marshes on fishes and
physical conditions. Wetlands 10:27-45.
Rey, J.R., J. Shaffer, R. Grossman, and D.
Tremain. 1990c. Above ground primary
production in impounded, ditched, and natural
Batis-Salicornia marshes along the Indian River
Lagoon, Florida, U.S.A. Wetlands 10:151-171.
Rogers, D.R., W.H. Herke, and E.E. Knudsen.
1992. Effects of three different water-control
structures on the movements and standing
stocks of coastal fishes and macrocrustaceans.
Wetlands 12:106-120.
Rogers, D.R., B.D. Rogers, and W.H. Herke.
1994. Structural marsh management effects on
coastal fishes and crustaceans. Environmental
Management 18:351-369.
Roman, C.T., W.A. Niering, and R.S. Warren.
1984. Salt marsh vegetation change in response
to tidal restriction. Environmental
Management 8:141-150.
Sasser, C.E. 1994. Floating Marshes in the
Barataria and Terrebonne Basins, Louisiana.
Louisiana State University, Coastal Ecology
Institute, Baton Rouge. Prepared for U.S.
Environmental Protection Agency, Dallas,
Texas, LSU-CEI-94-02.
Seback, K.E. and IS. DiCarlo. 1972. Final
Completion Report--Anadromous Fish
Project. Massachusetts Division of Marine
Fisheries, Publication No. 6496 (115-50-12-72-
CR).
Sinicrope, T.L., P.G. Hine, R.S. Warren, and
W.A. Niering. 1990. Restoration of an
impounded salt marsh in New England.
Estuaries 13:25-30.
Stevenson, J.C., M.S. Kearney, and E.G.
Pendelton. 1985. Sedimentation and erosion
in a Chesapeake Bay brackish marsh system.
Marine Geology 67:213-235.
Steward, J., R. Virnstein, D. Haunert, and F.
Lund. 1994. Surface Water Improvement and
Management (SWIM) Plan for the Indian River
Lagoon. St. Johns River Water Management
District and South Florida Water Management
District. 120p, Appendix.
Stuckey, R.L. 1975. A floristic analysis of the
vascular plants of a marsh at Perry's Victory
Monument, Lake Erie. Michigan Botanist
14:144-166.
Stuckey, R.L. 1989. Western Lake Erie aquatic
and wetland vascular-plant flora: its origin and
change, pp.205-256. In K.A. Krieger (ed.),
Lake Erie and its Estuarine Systems: Issues,
Resources, Status, and Management. NOM
and USEPA, Washington, DC.
Swenson, E.M. and R.E. Turner. 1987. Spoil
banks: effects on a coastal marsh water-level
regime. Estuarine, Coastal and Shelf Science
24:599-609.
Taylor, D.S. 1988. Observations on the ecology
of the killifish Rivulus marmoratus
(Cyprinodontidae) in an infrequently flooded
mangrove swamp. Northeast Gulf Sci. 10:63-68.
Taylor, D.S. 1990. Adaptive specializations of
the cypriondont fish Rivulus marmoratus. Fla.
Sci. 53:239-248.
Taylor, N.C., J.W. Day, and G.E. Neusaenger.
1989. Ecological characterization of Jean
Lafitte National Historic Park, Louisiana: basis
for a management plan. pp. 247-277'. In W.G.
Duffy and D. Clark (eds.), Marsh Management
in Coastal Louisiana: Effects and Issues -
Proceedings of a Symposium. U.S. FWS
Biological Report 89(22): 151-163.
49
-------
Turner, R.E., J.W. Day, Jr. and J.G. Gosselink.
1989. Weirs and their effects in coastal
Louisiana wetlands (exclusive of fisheries). In
W.G. Duffy and D. Clark (eds.), Marsh
Management in Coastal Louisiana: Effects and
Issues—Proceedings of a Symposium. U.S.
FWS Biological Report 89(22): 151-163.
U.S. Environmental Protection Agency. 1996.
Proposed Guidelines for Ecological Risk
Assessment. Office of Research and
Development, Washington, D.C. EPA/630/R-
95/002b.
van der Valk, A.G. and R.L. Pederson. 1989.
Seed banks and the management and
restoration of natural vegetation, pp. 329-346.
In M.A. Leek, V.T. Parker, and R.L. Simpson
(eds.), The Ecology of Soil Seed Banks.
Academic Press, Inc., San Diego, CA.
Walters, M.J. 1992. A shadow and a song.
Chelsea Green Publishing Co., Post Mills,
Vermont. 239p.
Weller, M.W. 1988. Issues and approaches in
assessing cumulative impacts on waterbird
habitat in wetlands. Environmental
Management 12:695-700.
Wilcox, D.A. 1995. The role of wetlands as
nearshore habitat in Lake Huron, p. 223-245.
In M. Munawar, T. Edsall, and J. Leach (eds.),
The Lake Huron Ecosystem: Ecology,
Fisheries, and Management. Ecovision World
Monograph Series, SPB Academic Publishing,
Amsterdam, The Netherlands.
Zedler, J.B. 1996a. Ecological issues in wetland
mitigation: an introduction to the forum.
Ecological Applications 6:33-37.
Zedler, J.B., principal author. 1996b. Tidal
wetland restoration: A scientific perspective
and southern California focus. California Sea
Grant College System, University of
California, La Jolla, California. Report No. T-
038.
Zedler, J.B., T.P. Wmfield, and P. Williams.
1980. Salt marsh productivity with natural
and altered tidal circulation. Oecologia (Berl.)
44:236-240.
Zedler, J.B., C.S. Nordby, and B.E. Kus. 1992.
The Ecology of Tijuana Estuary: A National
Estuarine Research Reserve. NOAA Office of
Coastal Resource Management, Sanctuaries and
Reserves Division, Washington, DC. 151p.
50
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Appendix A: Charge to the Subcommittee
Science Advisory Board Proposed Project
Subject: Marsh Management Practices
Requesting Organization: Office of Water, Assistant Administrator for
Office of Water
Operational/Program Contact: Fran Eargle, Wetlands Division
Background:
Marsh management generally refers to practices that selectively modify attributes, individually or in
combination, to induce hydrologic changes in a marsh. Marsh management is held to be a viable
restoration technology in coastal areas where erosion and subsidence is a critical resource problem.
However, the environmental merits of implementing these practices, as well as the potential cumulative
and secondary impacts of these projects, are widely debated among the scientific community. In
addition, there is often debate about whether a particular project design will yield environmental
benefits or cause environmental harm. These practices are regulated under Section 404 of the Clean
Water Act because they typically involve the discharge of dredged and fill material into waters of the
U.S. Federal funding of these marsh management projects under the Coastal Wetlands, Planning,
Protection and Restoration Act (CWPPRA, P.L. 101-646) has also recently been a very contentious
issue. To make informed permit and funding decisions, EPA needs clarification on the underlying
science regarding marsh management.
Because of the contentious nature of marsh management, permit decisions are often subjected to
delays, especially if these permits are elevated to Headquarters. For example, within the last year this
issue has been problematic in coastal Louisiana, where three 404(q) elevations regarding marsh
management have been initiated, one by EPA and two by National Marine Fisheries Service (NMFS).
In addition, federal funding of marsh management projects under CWPPRA has been challenged by
some Agencies. This has resulted in polarized federal agency positions and deadlock in reaching
consensus on restoration strategies to restore coastal Louisiana wetlands, which continue to be lost at a
rate of approximately 25 square miles per year.
To address these concerns, an EPA position on marsh management (as an interim step to establish a
uniform Federal policy) is desired to clarify what is and what is not acceptable to EPA. This would
expedite the permit review process and define EPA's position regarding federal funding of marsh
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management projects, consistent with the best available science. This would be consistent with the
Administration's Wetlands Plan which established a position that the Federal government be efficient,
flexible and fair in conducting the wetlands regulatory program. The Administration's Plan also
provides, as one of its basic principles, that wetlands policy should be based on the best available science.
The Administration supports the reduction of the impact of regulation on the public, while meeting the
objectives of wetlands protection in a technically sound manner. Recently, Federal agencies (Fish and
Wildlife Service and NMFS) developed individual agency positions on marsh management. For a long
term goal, EPA will seek to work with other Federal agencies to establish a unified Federal policy to
reduce confusion and provide federal consistency. However, we believe that a scientific review of this
issue is critical to the development of an environmentally sound policy.
In developing a position on marsh management in Region 6, a briefing document was prepared that
provides a compilation of literature, and summarizes a status of the science in regard to marsh
management practices entitled, "Marsh Management in Coastal Louisiana: impact on vegetation,
accretion, and fisheries productivity." In addition, we are seeking assistance from the SAB to assist the
Office of Water to identify scenarios for differentiating sound marsh practices from environmentally
damaging practices, and to develop criteria for scientific evaluation of marsh management practices.
Charge:
Marsh management is defined as the use of structures (such as canal plugs, weirs, gates, culverts, levees
and spoil banks) to manipulate local hydrology in coastal marshes. Marsh management or tidal
impoundments for the purpose of this review will include those wetlands influenced by the tide and
lands and waters associated with the Great Lakes. As a general rule, the purpose of structural marsh
management projects is to at least partially isolate a marsh from natural or altered hydrologic processes,
thereby partly or totally impounding a discrete parcel of wetland acreage. This may be done for
objectives such as: wetlands protection, enhancement or restoration; aquaculture; mariculture;
agriculture; waterfowl hunting and management; enhancement of wildlife and/or local fisheries; and/or
protection of property rights. Considering the range of both differences and similarities that exist
between marsh types the Office of Water is requesting the Science Advisory Board to perform a review
of marsh management practices to assist the Agency in answering the following questions:
1. Does structural marsh management protect or create emergent vegetated wetlands? In regard to this
evaluation, consider two conditions in the response 1) areas where net sediment deficit occurs (i.e. sea
level rise) and 2) in areas where there has been extensive human-induced wetlands deterioration.
2. To what extent does structural marsh management impact the physical, biological and/or chemical
aspects of natural marsh-sustaining processes? With regard to this evaluation, consider long-term marsh
survival and productivity, including accretion of organic and inorganic sediments.
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3. What are the impacts of marsh management, if any, to estuarine fisheries, waterfowl, and other fish
and wildlife? If there are impacts, provide an analysis of the extent of these impacts.
4. What are the cumulative effects of numerous large-scale marsh management projects with respect to
emergent vegetation, accretion, fish and wildlife, and other resources?
5. What are the gaps and the highest priorities for research studies related to the effects of structural
marsh management projects, and for routine monitoring of such projects?
6. What scientific or technical criteria should EPA use as part of the basis for case-specific decision-
making; or, as an alternative, what approach should EPA take to develop such criteria?
Committee: Ecological Processes and Effects Committee
Schedule: July 1994
Prepared By: Fran Eargle
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