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240 Flooding and Aquatic Ecosystems Table 9.1. Aquatic habitats in a river and a floodplain" - Main channel habitats Deep and shallow runs Deep and shallow pools Riffles Shoreline eddies Shallow glides Backwaters Secondary channels Large woody debris Large protruding rocks Rocky, gravel. and sand bottoms Somewhat narrow riparian areas Undercut banks Floodplain Habitats Backwaters Embayments Ephemeral channels Lagoons Lakes (Cutoff or Oxbow Lake, Delta Lake, Ephemeral Lake. Gravel-Pit Lake. Intermittent Lake, Levee Lake, Pluvial Lake, Sink Lake, Vernal Lake) Ponds (Aestival Pond, Beaver Pond, Depression, Gravel-Pit Pond) Rather broad riparian areas ' Wetlands (aquamarsh. backswamp, bog. carr, emergent wetland, forested wetland, lotic wetland, marsh, scrub-shrub wetland, marsh. wet meadow. wooded swamp) "Habitats are defined in a glossary by Armantrout (1998). development impacts on some endemic fishes in the upper Colorado River basin of the western United States, and (4) the need to balance preservation and use of river-floodplain environments. Ecological Importance of Flooding to Aquatic Ecosystems, with an Emphasis on Large River Systems Flooding is important in maintaining the function and integrity of aquatic ecosystems even though catastrophic events will periodically pose a haz- ard to those ecosystems. The concepts describing the ecological impor- tance of flooding to large river ecosystems also apply to other aquatic sys- tems. Major alterations of large river-floodplain systems from human activ- ities occurred before ecological functioning of such systems was studied (Cummins, 1979). However, it was widely recognized that hydrological. physical, chemical, and thermal modifications in regulated rivers have a negative effect on aquatic organisms (Ward and Stanford, 1995). Today, flooding and floodplains are understood to be essential components of large river systems (Junk at aI., 1989; Ward and Stanford, 1983, 1995; Bayley, 1991, 1995; Sparks, 1995). Dynamic river-floodplain ecosystems provide a mosaic of aquatic habitats (Table 9.1), as do associated terrestrial upland areas and riparian corridors that support diverse plant and animal