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CHAPTER 2: ECOLOGICAL OVERVIEW-POSTFLOOD RECOVERY AND ECOSYSTEM MANAGEMENT 9 takes place both within and beyond the floodplain (Bell rose, 1980). Neotropical songbirds are also important users of the flyway. Some species exploit seed and insect resources as they migrate through; others stay in the river-floodplain ecosystem to fledge their young, Woodpeckers (insecti- vores) are common in floodplain forests. where they feed on invertebrates. Kingfishers (piscivores) are common along land-water interfaces. where they feed on small fishes at the water surface. Turkeys, grouse, and other game birds occur in floodplain habitats during low-flow periods, Shorebirds 3re primarily insectivorous or piscivorous and exploit backwater and shoreline habitats, The smaller species such as sandpipers exploit invertebrates in shallow water or mudflat habitats, The larger species (egrets and herons) prey on small fishes in shallow aquatic habitats and ephemeral pools, This group of birds can sometimes be found nesting in large colonies in the tallest trees of the floodplain forest. Piscivorous rapters include bald eagles and osprey. Eagles occur in the UMRS year-round. but during the win- ter they concentrate in southern reaches, where the river remains ice-free. Hawks. owls. and falcons exploit flood- plain resources, and some migrate along the Mississippi flyway, MAMMALS Furbearers are the mammals most closely associated with the river-floodplain ecosystem, Beaver. muskrat. and other semi-aquatic species occur in off-channel habitats in the river-floodplain ecosystem. Raccoons, skunks, foxes, coyotes, and bats make up most of the carnivore species, while deer and cattle are the primary large herbivores in the system, Many large mammals have been extirpated by development. Small mammals include mice. shrews. and voles, They are abundant in floodplain habitats and support the commu- nity of carnivorous mammals and birds. lROPHIC DYNAMICS IN RIVER-FLOODPLAIN ECOSYSTEMS Energy pathways in UMR aquatic habitats are similar to those in other ecosystems in that energy flows from pri- mary producers (plants) through an invertebrate consumer community to a predator community, The UMR aquatic environment derives energy from production in both aquatic (algae and submersed aquatic plants) and terrestrial habitats (grasses and leaves) (Anderson and Day, 1986: Grubaugh and others. 1986; Fremling and others. 1989: Grubaugh and Anderson, 1989: Junk and others. 1989; Bayley, 1991), When floodwaters inundate terrestrial habitats, energy stored in floodplain plants is released to the aquatic environ- ment. A community of microbial organisms conditions the detrital resources for consumption by invertebrates. The energy is uhimately tnmsferred to higher consumers through invertebrate predation or recycled via nUlrient pathways, Energy transfers are rapid among faunal groups because animals migrate to the food rather than waiting for the food to come to them. Free-living invertebrates concen- trate in vegetated habitats at the water's edge: fishes. rep- tiles. amphibians. and birds concentrate there also to take advantage of the abundant food resources (Junk and others, 1989), MISSISSIPPI RIVER AQUATIC ECOLOGY: PAST AND PRESENT PAST GEOMORPHOLOGY The upper floodplain reach of the UMR extends from the headwaters to Clinton. Iowa (Pool 14). It is character- ized by a narrow river-floodplain terminating at steep bluffs (Hoops, 1993), Varying floodplain topography created by glacial and geologic processes. combined with seasonal flood pulses. created many off-channel permanent and ephemeral aquatic habitats. Deepwater wetlands were present where oxbows, side channel closures, and braided channels occurred. The unregulated river consisted of deep pools separated by shallow bars (shoals) and rapids: there were many rocks and snags (Carlander. 1954), The river exhibited a bimodal hydrograph (fig, 2-2), The lower floodplain reach of the UMR lies between Clinton. Iowa (Pool 14). and Alton. Illinois (Pool 26). It flows across glacial outwash below Clinton to Fulton. Illi- nois (Pool 14); between Fulton and Muscatine. Iowa (Pool 16). it flows over or near bedrock. Below Muscatine, the floodplain expands across a wide alluvial valley between high bluffs, Between Clarksville. Missouri (Pool 24). and Alton. Illinois (Pool 26). the average width of the valley floor is 5.6 miles. and the average slope is 0.5 foot per mile (Simons and others. 1975), The floodplain con- tained many wetlands of various sizes and shapes formed by channel migrations, natural levee fonnation, and scour. Wooded islands were common in floodplain reaches. A bimodal hydro graph persisted throughout this reach to the confluence with the Missouri River (fig. 2-2). Below the confluence of the upper Mississippi and Missouri Rivers. the middle Mississippi River takes on a much different character, The river flows through alluvial lowlands known as the American Bottoms to the confluence with the Ohio River, Missouri River flows contributed sig- nificant water and sediment inputs that made the middle Mississippi environment quite different from the upper Mis- sissippi and Illinois Rivers (Twain. 1896. and Dickens.