From: kiran (Kiran R)
X-URL: http://www.hort.agri.umn.edu/h5015/97papers/lkessay.html.html
Subject: Island Wetlands: lkessay.html
Status: RO
INLAND WETLANDS
Leslie Knapp
The papers in this chapter pertain to inland wetlands, freshwater
wetlands that are not located along a coastline, generally occurring
along streams, rivers, lakes, and ponds. Fifteen plant communities
fall under this broad heading, including shallow open water, deep and
shallow marshes, sedge meadows, fresh meadows, low prairies,
calcareous fens, open bogs, coniferous bogs, shrub carrs, alder
thickets, lowland hardwood swamps, coniferous swamps, floodplain
forest, and seasonally flooded basins (Eggers &Reed, 1987).
Three of the papers in this chapter address wetland restoration or
creation. As our understanding and appreciation of wetlands has
expanded, so have the number and scope of federal, state, and local
laws to protect them. Regulatory agencies require mitigation in the
form of the restoration or enhancement of existing wetlands, or the
creation of new wetlands to offset wetland losses. Wetland mitigation
appears to promise the best of both worlds by allowing development to
occur in wetlands while ensuring that wetlands lost will be replaced.
However, arguments arise because no strong consensus has materialized
on exactly what constitutes a successful mitigation, and mitigation
attempts in general have yielded mixed results. Whether or not it is
possible to restore wetlands similar to those that existed
historically is uncertain. The challenge of wetland restoration is to
create wetlands comparable to those that existed over a century ago,
but within todays landscape. Also, "in-kind" replacement is preferred
and some wetland communities are extremely difficult or take centuries
to restore (Galatowitsch & van der Valk, 1994; Slavesen, 1991).
Much of what we know about wetlands derives from research and from the
hundreds of wetland mitigation projects undertaken each year. Each
mitigation project can contribute to the collective understanding of
how wetlands function and how they can be more successfully restored.
This strengthens the argument for the more consistent, long-term
monitoring of mitigation projects. Over time, experience will continue
to weed out the less successful mitigation methods and result in some
proven techniques that more closely resemble natural wetlands
(Galatowitsch & van der Valk, 1994; Slavesen, 1991).
The ecological, hydrological, and technical considerations in
planning, constructing, managing, and evaluating wetland restorations
needs to be examined and constantly evaluated as part of the wetland
restoration process (Galatowitsch & van der Valk, 1994) . The first,
and possibly most critical step, in the wetland restoration process
the selection of a site with appropriate hydrology. Unfortunately,
site characterization can fall prey to aggressive project schedules
and budgetary constraints, leading to mitigation projects that fail,
are less successful than they should be, or are more costly to
construct in order to overcome hydrology problems. Doyle discusses how
hydrology determines both the type of wetland restored and whether it
is self-sustaining. Siting considerations, data requirements, and
construction methods appropriate for the restoration of drained and
filled wetlands, as well as created wetlands are addressed. Doyle also
stresses the importance of identifying the characteristics of nearby
natural wetlands for incorporation in the design of mitigation
projects to produce similar processes and functions. This is
consistent with the goals set by Galatowitsch & van der Valk (1994)
for assessing the success of a wetland restoration by comparing
characteristics of the restoration to those of similar natural
wetlands. Eventually, this assessment may be based on comparisons of
the functioning of restored and natural wetlands in terms of criteria
such as primary and secondary production and rates of denitrification.
Biehn reviews the current technology of water control structures used
in wetland restoration and creation. The maintenance of appropriate
hydrology is affected by the selection and correct installation of the
these structures. Earthen structures, trickle tubes, spillways, drop
structures, and subsurface drainage manipulation are addressed. Biehn
provides a helpful overview of site considerations, lessons learned
from past projects, and information on the relative costs of various
water control structures.
Robertsons paper addresses another critical component in the
restoration process, wetland management. Robertson summarizes research
associated with prescribed burning as a restoration and management
tool in wetlands, reviews practical considerations of wetland burning
techniques, and provides a commentary on the use of fire to achieve
wetlands management goals. Although commonly used in upland
environments, the application of prescribed burning in wetlands
remains largely unresearched and the paucity of field data makes it
difficult to evaluate its effectiveness. Goals and prescribed burning
techniques for wetland sites differ from those for uplands, and the
determination of appropriate prescriptions to meet wetland management
goals is needed.
The next papers move from the topic of wetland mitigation and
restoration to the arena of wetlands constructed to improve water
quality and control flow. Although these wetlands are not
"restorations", they provide many benefits associated with wetlands
such as green space, habitat, water quality improvement, flood
control, and improved plant diversity while providing stormwater or
wastewater treatment. Mastey reviews design strategies for stormwater
wetlands and describes how a multiple pond system, consisting of a
deep forebay to remove suspended solids, a shallow emergent marsh to
remove fine sediment and nutrients, and a micro-pool for final
clearing and discharge can be an effective alternative to deep,
steep-sided detention ponds. Although more space is needed for
multi-pond system, benefits include improved water quality, improved
groundwater recharge due to ponding, increased plant diversity,
additional green space and wildlife habitat. Mastey also stresses the
landscape scale solution. This is consistent with the Afelbaum et als
(1994) experience with projects designed to reduce runoff volume and
pollutant loads through source control and the integration of
large-scale restored landscapes into developments to serve as the
stormwater management system consisting of upland prairie
biofiltration, natural swale conveyance systems, wetlands, and lakes.
Combined, these increase lag time and opportunities for pollutant
removal though settling and biofiltration and reduce the rate and
volume of runoff through enhanced infiltration opportunities.
Phillips reviews the use of constructed wetlands for wastewater
treatment, especially when used in conjunction with conventional
systems. Design elements can be incorporated in wastewater treatment
wetlands so that they become fully functioning ecosystems and can
contribute to the habitat needs of aquatic species. Phillips reviews
the types of treatment wetlands, area requirements, design
considerations, cleansing capabilities, and relative costs. BOD,
suspended solids, nitrogen and phosphorous removal capabilities and
methods to avert potential problems while maintaining low flow to the
receiving water body are addressed. As with all wetlands, water level
is the main consideration for plant survival and uptake.
References
Apfelbaum, S. I., J.D. Eppich, T. H. Prices, and M. Sands. 1994. The
Prairie Crossing Project: Attaining Water Quality and Stormwater
Management Goals in a Conservation Development. Using Ecological
Restoration to Meet Clean Water Act Goals.
Eggers, S. D. And D. M. Reed. 1987. Wetland Plants and Plant
Communities in Minnesota and Wisconsin. U.S. Army Corps of Engineers,
St. Paul, MN.
Galatowitsch, S. M. and A. G. van der Valk. 1994. Restoring Prairie
Wetlands, An Ecological Approach, Iowa State University, Ames, IA.
Salvesen, D. 1994. Wetlands, Mitigating and Regulating Development
Impacts. Urban Land Institute, Washington D.C.
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