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

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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

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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

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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).

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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

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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

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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

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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

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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

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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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