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<br />
<br />Flooding and Aquatic Ecosystems
<br />
<br />Richard S. Wydoski
<br />u.s. Fish and Wildlife Service {retired}
<br />
<br />Edmund J. Wick
<br />TETRA TECH, Inc.
<br />
<br />Periodic natural flooding is important in maintaining the function
<br />and integrity of all aquatic ecosystems even though catastrophic
<br />events sometimes pose hazards to these systems. The relation of
<br />flooding to large river ecosystems is emphasized in this chapter,
<br />but the ecological concepts apply to all aquatic systems. Biologi-
<br />cal, chemical, and physical linkages between terrestrial, riparian,
<br />and aquatic ecosystems are described as well as the ecological ef-
<br />fects of various human activities on aquatic ecosystems. A case
<br />review involves four endemic fishes that are endangered in the ~
<br />~ Colorado Riv~ basin of the western United States. During the
<br />past century, water development in this basin to serve agriculture,
<br />logging, mining, industry, and domestic uses has altered the tim-
<br />ing and magnitude of greamflows. This in turn disrupted sediment
<br />transport, riparian vegetation, and connectivity of the river and
<br />floodplain. River-floodplain connectivity during historically peak
<br />spring flows of the upper basin rivers was an important compo-
<br />nent of the life histo(Y strategy of the .@zorback sucker. A balance
<br />must be attained between land-use practices and consumptive uses
<br />of water with preservation and maintenance of ecological function,
<br />integrity, productivity, biodiversity, and heterogeneity in large rivers
<br />and other aquatic syst:tms. Management decisions related to river-
<br />floodplain systems must be made with full consideration of the eco-
<br />logical,economical, political, and sociological factors. A systems
<br />approach is recommended for applying "adaptive management"
<br />that allows actions to be taken based on the best available informa-
<br />tion while providing for refinem.ent as pertinent new information
<br />becomes available.
<br />
<br />Introduction
<br />
<br />Fre.shwater constitutes less than 1 %
<br />of the Earth's water supply and
<br />only, !lbout 25% of surface fresh-
<br />water is contained in streams and
<br />rivers (Feth, 1973). Because of their
<br />paucity, streams and rivers are es-
<br />pecially important compared with
<br />other aquatic ecosystems.
<br />The natural streamflow regime
<br />of virtually all rivers is inherently
<br />variable and this variability is crit-
<br />ical to majntaining the. integrity of
<br />river-floodplain ecosystems (Heede
<br />and Rinne, 1990; Poff et al., 1997).
<br />FluctuatiOlls in streamflows in a
<br />river environment provide a wide
<br />array of habitats for plants, inver-
<br />tebrates, amphibians, rep~les, fish,
<br />birds, and mammals that occupy
<br />aquatic and riparian ecosystems
<br />(Clark, 1978; Kozlowski, 1984).
<br />Instream flows are important to fish for passage, spawning,incubation,
<br />rearing, feeding, and resting (Schnick et aI., 1982; Stalnaker and Wick,
<br />Chapter 16, this volume). Variable streamflows in rivers are linked directly
<br />to the physical, chemical, and biological characteristics of flowing water
<br />environments (Church, 1992; Davies et al., 1994).
<br />Flooding of natural aquatic ecosystems occurs when a larger-than-
<br />average volume of water enters a water body. Flooding can affect all types
<br />of aquatic systems, including wetlands, small streams, large rivers, lakes,
<br />estuaries, and seacoasts. The primary reservoir for floodwaters is precip-
<br />itation as rainfall from the atmosphere and the secondary reservoir is ac-
<br />cumulated snow and ice on the surface oflandscapes (Baker et aI., 1988).
<br />The magnitude and frequency of flooding are influenced by the size of the
<br />drainage area, climate, amount and rate of precipitation, accumulation of
<br />snow and ice, air and soil temperature, amount and species ofterrestrial
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