Wetlands Characteristics and Boundaries (1995) / Chapter Skim
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2 ECOLOGY OF WETLAND ECOSYSTEMS
2 ECOLOGY OF WETLAND ECOSYSTEMS
Pages 20-42
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From page 20... ...
In very large wetlands, such as extensive peatlands, marshlands, bottomlands, and river floodplains, internal spatial variation can be great. Examples include the Great Dismal Swamp, which consists of at least four major wetland plant communities integrated with lakes and streams (Kirk, 1979~; the Everglades, which includes sloughs, sawgrass prairies, and wet shrub islands (Kushlan, 1990; Davis and Ogden, 1994~; the Mississippi delta, which has swamps, marshes, lakes, and rivers (Day et al., 1977~; and peatlands of northern Minnesota 20
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From page 21... ...
It begins with an overview of the nature of wetland ecosystems and the response of wetlands to various alterations, progresses to a summary of the functions of wetlands, and it closes with a consideration of boundaries between wetlands and terrestrial ecosystems. THE NATURE OF WETLANDS Because wetlands are neither aquatic nor terrestrial, they have not been easily assimilated by the well-established scientific disciplines of terrestrial and aquatic ecology.
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From page 22... ...
Most wetlands share with terrestrial ecosystems a flora dominated by vascular plants, although the species composition of wetlands generally differs from that of uplands. Wetlands often are found at the interface of terrestrial ecosystems (such as upland forests and grasslands)
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From page 23... ...
For example, the biotic component of a wetland also can affect hydrology by increasing or decreasing water level or flow. Low rates of decomposition in some types of wetlands can cause basins to fill with undecomposed plant material, thus altering hydrologic conditions.
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From page 24... ...
criticize the practice of stabilizing water level in managed wetlands. They point out that resource managers can be misled by the notion that most wetland wildlife species require year-round standing water for their life cycles.
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From page 25... ...
Even so, not all organic matter that enters or is formed by photosynthesis in wetlands remains within the wetland boundary. Many wetlands export organic carbon to streams and estuaries at a rate substantially higher than that of terrestrial ecosystems (Mulholland and Kuenzler, 1979~.
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From page 26... ...
ad Bourns punt pue _ .
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From page 27... ...
acorns punoJO pU~lI0M ~ 11o it ~ t' It .
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From page 28... ...
28 ia Q a, G)
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From page 29... ...
1 1 1 1 1 1 1 1 r,0 o rat ret 3: m=E ~O a ~80 ..
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From page 32... ...
When production and decomposition rates are high, as is especially likely in flowing water or in wetlands that have pulsed hydroperiods, nutrient cycling is rapid. When rates of production and decomposition are low, as is most likely in nutrient-poor wetlands such as ombrotrophic bogs, nutrient cycling can be slow.
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From page 33... ...
Reproduced with permission from Mitsch and Gosselink (1993) , Van Nostrand Reinhold.
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From page 34... ...
Functions of wetlands often have effects beyond the wetland boundary. For example, wetlands store surface water, and the effect of this function downstream is a reduction in flood peak.
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From page 35... ...
Even so, wetlands perform some functions, such as maintenance of breeding habitat for some bird species (Brinson et al., 1981) , that are either unique or particularly efficient in proportion to their size.
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From page 36... ...
Thus, the landscape gives proper context for the evaluation of some wetland functions. Maintenance of biodiversity, water quality, and natural hydrologic flow regimes in part depends on the total wetland area and on the types of wetlands within regions (Preston and Bedford, 1988~.
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From page 37... ...
For example, Moyle and Sato (1991) found that habitat heterogeneity is closely related to species diversity of fish communities, presumably because a more variable habitat provides a wider range of biological niches.
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From page 38... ...
In many watersheds, wetlands process dissolved and suspended materials from an area much greater than their own, which explains their disproportionately strong influence on water quality. In watersheds subject to human activities, the importance of wetlands on water quality is exaggerated by two factors: disturbances to uplands that increase erosion and augment the fertility of the landscape, and reduction of wetland area through filling, diking, and draining.
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From page 39... ...
Culex pipiens Chlorion cyaneum Tabanus americanus Simulium spp. Drosophila melanogaster Dolomedes triton Nephila clavipes Limnochares americana Eggs hatch 7-15 days; adults feed on water Adult and nymph stage Entire life cycle Entire life cycle All but a few weeks All but pupal and part of adult stages All but pupal stage None None None None None 10 months All but winter Entire life cycle Larval stage Two or three years One year or more All but short adult stage Nymphs develop slowly Egg to nymph Egg to nymph Overwinter Egg through naiad Egg through nymph Egg through nymph Nymphs overwinter Nymphs overwinter Eggs and nymphs overwinter until July None All but adult Eggs hatch 2-5 weeks; nymphs Eggs hatch 1-5 days; larvae pupate 1-2 weeks none Two years Egg and pupal stage None Most of life None Much of life cycle
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From page 40... ...
of marsh in the delta disappears annually because of land subsidence, sediment starvation, and saltwater intrusion (Kusler et al., 1994~. Changes in land use and water diversions that decrease freshwater flows in rivers and streams similarly threaten many estuarine wetlands by reducing the quantity of fresh water.
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From page 41... ...
For gentle gradients, or where microtopography causes wetlands to be interspersed with uplands on very fine scales, the boundary of a wetland can be especially difficult to determine (Appendix B hydric pine flatwoods of southwest Florida, and Chapter 8J.
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From page 42... ...
Wetlands and associated terrestrial ecosystems are also interdependent, but alterations in terrestrial ecosystems usually affect wetlands more than the reverse. Watersheds and water bodies associated with wetlands control the quantity and quality of water reaching wetlands, and thus affect wetland functions.
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