Mitigation Banking: Theory And Practice

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Marshes can also filter out sediments that are already in the water column. The ability of marshes to filter sediments and maintain water clarity is of particular importance to the maintenance of clam and oyster production. Some marshes have been shown to act as sinks or traps for other pollutants and marsh plants take up nutrients deposited in marsh soils. Excess nutrient levels in an estuary can be a problem but the exact role of marshes in nutrient removal is not yet fully understood.

Nonvegetated wetlands are also important in the cycling of nutrients in the estuary and the filter feeding organisms present, particularly on tidal flats, remove suspended solids from the water column in amounts that may significantly affect water clarity. Flood Buffer. The peat substratum of some marshes acts as a giant sponge in receiving and releasing water. This characteristic is an effective buffer against coastal flooding, the effectiveness of which is a function of marsh type and size.

The higher elevation marshes are the more effective flood buffers. Nonvegetated wetlands, because of their intertidal location have little value in this regard. The following descriptions of wetland community types are identified and presented for management purposes.

The first twelve of these are the vegetated wetlands and of these the first ten are characterized by a single dominant species of emergent vegetation.

Mitigation Banking, Theory And Practice by David Salvesen | | Booktopia

Types eleven and twelve are brackish and freshwater marshes which have no clearly dominant species of vegetation. The five types of nonvegetated wetlands described here are identified mainly by physiographic position and sediment composition. No attempt is made to quantitatively separate the communities by particle size dominance since this is not necessary for value judgements on the level described in this publication. Associated vegetation: Saltmeadow hay, saltgrass, black needlerush, saltwort, sea lavender, marsh elder, groundsel tree, sea oxeye.

Growth habit: Stout, erect grass; long, smooth leaves, often with attached periwinkle snails; located at the waters edge. Tall form 4 to 6 feet along the water; short form 1 to 2 feet at or slightly higher than MHW. Annual production and detritus availability: Average yield is about 4 tons per acre per annum; optimum growth up to 10 tons per acre. Daily tides flux nearly throughout this community. Available detritus to the marine environment is optimum.

Operations Risk Management and Mitigation - from Assessment to Implementation

This type of marsh is recognized as an important spawning and nursery ground for fish. Waterfowl and wildlife utility: Roots and rhizomes eaten by waterfowl. Stems used in muskrat lodge construction. Nesting material for Forsters tern, clapper rail and willet. Potential erosion buffer: Most salt marshes and brackish water marshes are bordered by saltmarsh cordgrass along the waters edge. Underlying peat with a vast network of rhizomes and roots is very resistant to wave energy.

Water quality control and flood buffer: Marshes of this type can also serve as traps for sediment that originate from upland runoff. This also includes large debris that may accumulate on the marsh surface. Dominant vegetation: Saltmeadow hay Spartina patens L. Greene Saltgrass Distichlis spicata L. Associated vegetation: Saltmarsh cordgrass, black needlerush, marsh elder, groundsel tree, saltwort, sea oxeye.

Growth habit: Matted meadow-like stands with swirls or "cowlicks," individual plants wiry in appearance; saltgrass feet high. Physiographic position: About mean high tide to the limit of spring tides; saltgrass at lower elevations, saltmeadow hay predominates at the higher end of the range. Waterfowl and wildlife utility: Seeds eaten by birds; provides nesting area. Habitat for a snail Melampus important as food for birds.

Water quality control and flood buffer: In many cases, this community represents the oldest part of a marsh system. Peat may accumulate to great depths, making this type of marsh act as a giant sponge when flood waters wash over it. Denseness of vegetation and deep peat filter sediments and waste material. Production and detritus are less important to the marine environment than in Type I communities. Its contributions tend to favor the upland environment.

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Its values rank somewhat below Type I but, nevertheless, a Type II marsh should not be unnecessarily disturbed. Associated vegetation: Usually pure stands with saltmarsh cordgrass, saltgrass and saltmeadow hay near the margin. Growth habit: Dense monospecific stands; plant leafless, cylindrical hard stems tapering to a sharp pointed tip; brown to dark green in color, 3 to 5 feet high.

What is a mitigation bank?

Physiographic position: About mean high water to somewhat below spring tide limit. Seems to prefer sandy substratum. Annual production and detritus availability: 3 to 5 tons per acre per annum, decomposes more slowly than most of the marsh grasses.

Not flushed daily by tides. Waterfowl and wildlife utility: There is no evidence that waterfowl or wildlife utilize this type of plant directly as a food. Because of the dense, stiff stands, it has little wildlife value except for limited cover. Potential erosion buffer: The dense system of rhizomes and roots of black needlerush are highly resistant to erosion.

On sandy shores and low sand berms which support this community type, this characteristic is of high value. Water quality control and flood buffer: An effective trap for suspended sediments, but less effective than the densely matted saltmeadow community. Provides effective absorbent areas to buffer coastal flooding. It functions well as a sediment trap and erosion deterrent but ranks lower than the preceding types. The rhizomes of black needlerush are harder and tougher than the grasses that dominate Types I and II communities; therefore, needlerush is useful as an erosion deterrent.

Overall, the values of this marsh type rank below Types I and II. Dominant vegetation: Groundsel tree, highwater bush Baccharis halimifolia L. Growth habit: Shrubs 3 to 10 feet high along the margin of the marsh and upland plant communities. Physiographic position: Lower limit is approximately the upper limit of marsh marsh-upland ecotone.

Average density: May provide dense canopy over marsh. Individual shrub trunks usually spaced 3 to 10 feet apart. Annual production and detritus availability: Probably less than 2 tons per acre per annum. Detritus of little value. Waterfowl and wildlife utility: Provides diversity for wildlife in general and especially as a nesting area for small birds. No significant food value. Potential erosion buffer: Although not structurally suited as an assimilator of sediment and flood waters, it serves somewhat as a buffer to erosion on sand berms that often front small pocket marshes. Also functional as a trap for larger flotsam. Water quality control and flood buffer: Of minor consequence, but does trap larger material. See above. Values of this type rank below that of the preceding types.

However, this community does add diversity to the marsh ecosystem.

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Growth habit: Very tall feet , heavily stemmed, leafy grass with distinct branched fruiting head in the fall. Physiographic position: At or slightly above mean high water and extending to the upland margin. Most common in brackish or lower salinity marshes.