Compensating for Wetland Losses Under the Clean Water Act (2001) / Chapter Skim
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3 Watershed Setting
3 Watershed Setting
Pages 46-59
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From page 46... ...
. In general, watershed organizational structure governs the flow of water and associated nutrients through these systems, the relationship between hydrological processes and the position of the wetland in the watershed, 46
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From page 47... ...
Wetlands occur in a variety of physical settings, including coastal lowlands, topographic depressions, broad flats on interstream divides, the base of slopes, and topographic highs with little slope (Winter and Woo 1990~. Location in the landscape influences geological characteristics, such as slope; thickness and permeability of soils; and the composition, stratigraphy, and hydraulic properties of the underlying strata, all of which influence surface and subsurface flows of water.
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From page 48... ...
One way to target mitigation sites to appropriate landscape positions is through the development of basinwide wetland restoration and mitigation plans. The evaluation of watershed position on the functions of existing wetlands and on restored, created, and enhanced wetlands has been aided by the development of new technology.
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From page 49... ...
To provide this water-quality function, the receiving wetland must also occur at a relatively lower topographic elevation in the watershed than the contributing uplands. Typical inland wetlands that occupy relatively lower landscape positions and provide water-quality functions include riparian or floodplain wetlands, isolated depressional wetlands (such as playas, prairie potholes, and vernal pools)
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From page 50... ...
and waste-water treatment wetlands (Ready and Smith 1987; Hammer 1989; Cooper and Findlater 1990; Moshiri 1993; Corbitt and Bowen 1994; DuBowy and Reaves 1994; Hammer 1997~. Constructed wetlands have much potential for assimilating nutrients and improving water quality in a watershed, but treatment wetlands and, to a lesser extent storm-water wetlands, often evolve to dense monoculture stands of Typha, Scirpus, or Phragmites, which will "effectively remove target contaminants from influent waters while providing habitat for a few muskrats, blackbirds and some songbirds but
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From page 51... ...
But such decisions can be effectively addressed only by applying appropriate functional assessment tools on a watershed scale. In the southeastern United States, there is a large acreage of inland nonriverine wetlands, such as pocosins and pine savannahs, that occur on broad flats and often exist at higher relative elevations in the watershed.
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From page 52... ...
Many species take advantage of, and actually require, alternative wetlands during periods of drought. To avoid extirpation from natural causes, a variety of isolated wetlands must be accessible by overland routes (see Box 3-2~.
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From page 53... ...
The biological portion of a functional wetland habitat forms a trophic structure that includes consumers as well as producers; hence, consideration must be given to environmental features of wetlands that are requisite for completion of the life cycle of wetland faunal inhabitants. On the basis of these facts and principles, the incorporation of animal populations requiring terrestrial movement into the design of compensatory wetlands requires that interwetland distances be taken into account (Semlitsch and Bodie 1998~.
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From page 54... ...
state that the advantages of using a reference wetland approach are (1) making explicit the goals of compensatory mitigation through identification of reference standards from data that typify sustainable conditions in a region, (2)
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From page 55... ...
Constructed, enhanced, or restored wetlands may be particularly vulnerable to external influences because they are still immature and may not have developed resilience to chronic change, catastrophic disturbance, and surrounding population growth and development that bring increased nutrient and contaminant loading and more frequent hydrological changes. For this reason, a site should be able to "evolve" with the landscape over time.
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From page 56... ...
36 C~ENS~G FOR ~~ LASSES HER ~ CLEAN ~~R ACT Over external factors that may impinge on Me long-term ecological sustain^~1ty of a mU1gat10n wetland include deleterious 1nOuences of natural pest species (eggs intense grazing by herbivores such as migratory or resident geese) and large-scale disturbances such as hurricanes' Are' seaJevel rise' and climate change Pee Box 3-3\ Me committee reco~1zes Mat it is 1mpracUcal to expect individual permittees to design for and be
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From page 57... ...
Other factors that result in both direct fill/destruction and indirect impacts and wetland losses include channelization, groundwater withdrawal, and flood-control practices. Losses Due to Urbanization Urbanization of watersheds is often extensive in headwater regions.
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From page 58... ...
Increased runoff from agricultural lands has generally caused a headward migration of stream channels in many areas. This leads to incised stream channels in many headwater regions (Costa 1975)
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From page 59... ...
CONCLUSIONS 1. Watershed organizational structure governs the flow of water and associated nutrients through a watershed, the relationship between hydrological processes and the position of a wetland in the watershed, and the relationship between wetland functions and watershed position.
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