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CHAPTER 2: ECOLOGICAL OVERVIEW-POSTFLOOD RECOVERY AND ECOSYSTEM MANAGEMENT 23 MANAGEMENT CONSIDERATIONS ACQUISITION AND PROTECTION OF ECOLOGICALLY IMPORTANT HABITATS Approximately half the floodplain in the Illinois River (Mills and others, 1966: Bellrose and others, 1983) has been drained and leveed. primarily for agriculture, as was much of the floodplain of the upper Mississippi River and the entire floodplain in the middle Mississippi River. In contrast to the Minnesota and Wisconsin reaches of the UMRS. where the U,S, Fish and Wildlife Refuge is concentrated. the Illinois River and the rest of the UMRS have much more area of agriculturally developed floodplains, Land acquisi- tions should be encouraged, but some areas may offer better potential for management than others. The ecology of newly acquired areas should be intensively monitored to under- stand and better manage the large river-floodplain ecosys- tems. Monitoring should also identify management problems in time to take corrective action. Floodplain forests in the upper Mississippi River sys- tem have been negatively affected by disruption of historic hydrologic cycles, Mast-producing forest communities are adapted to the hill and swale floodplain topography and are distributed in relation to the average seasonal pattern of dry- ing and flooding. While inundation by surface waters is an important consideration, impoundment by navigation dams has mised the water table. The result over the last 50 years is the development of a dominance of silver maple (Nelson and others. 1994), While it may be impossible to counteract the effects on the water table. valuable forest resources may be present in the upper pool reach of the navigation pools, Tributary inflows provide highly diverse microhabitats within the larger view of the river-floodplain ecosystem. Their channels are dynamic and meander extensively through the low-relief topography of the alluvial floodplain, They suppon forest stands of great species diversity, hut perhaps more imponant. they suppon variability in age structure of a forest stand. Tributary channel migrations cut banks and fell mature trees; the openings provide space for new trees further away from the cut bank and on the oppo- site bank. where depositional processes dominate. The meandering tributaries also slow current velocities, allow- ing sediments to drop out in stream or in tributary delta fans that create new terrestrial habitats for colonization by young trees, Many river-floodplain birds are dependent on forests of varying age. Tributary streams should be sought out and dechannelized to optimize the ecological diversity they can provide, Mesic prairies were once a major portion of the river- floodplain ecosystem. bUlthey were the first areas to be convened to agricultural fields (Nelson and others. 1994) and therefore the first to be sequestered behind levees, The highly productive prairie habitats provide seasonal energy pulses to the river community when riverine fauna migrate into the newly flooded habitat. The energy pathway begins when plants are inundated and are colonized by microflora and microfauna. Microbial energy is incorporated by inver- tebrate detritivores and ultimately by venebrates of all classes (fish. reptiles and amphibians. birds. mammals), The mesic prairie community may survive best at midpool reaches of the navigation pools because they may be more tolerant of the raised water table and provide the energetic benefits associated with flooding described above. Deepwater wetland habitats are rare but important components of the river-floodplain ecosystem. They sup- port diverse populations of plants along an elevation gradi- ent determined by river-floodplain geomorphology and hydrology. Migratory birds and riverine fishes have evolved behaviors adapted to seasonal hydrologic cycles that typi- cally provide access to these habitats, Bimodal flooding in the Mississippi River may panition availability of energy resources (wetland plants), so that some summer production is available to birds migrating south in the fall and another ponion. higher on the floodplain. is available for birds migrating nonh in the spring, Flooding also provides access to off-channel habitats for riverine fish species adapted to spawning. rearing. and overwintering in protected backwa- ters (Welcomme. 1979; Bayley. 1991: Bodensteiner and Lewis. 1992), These habitats (and side channels that some- times exhibit backwater characteristics) have been severely degraded by sedimentation. Large floodplain depressions. oxbows. and historic side channels behind levees should be considered for their potential wetland value, The lower pool reach of the navigation pools provides a hydrologically disturbed but potentially valuable habitat, Waler-Ievel stability is maintained by the dam in a pool managed with dam point control. This can reduce operating costs for waterfowl management activities by eliminating pumping costs when rewatering managed wetlands. It can also provide greater hydrologic predictability. thereby allowing beller refined water level management plans, It may also be possible to use ground water to rewater the areas in the fall. thereby reducing sedimentation by elimi- nating turbid river water inputs, The impounded portion of the navigation pool also provides the greatest opponunity for recreational boating because of the predictability of water levels. The most intensive management should be concentrated in the most hydrologically disturbed ponions of the pool. Midpool floodplain habitats are valuable beca~se of their potential to suppon wetland habitats. Changing control points of pools regulated at mid pool would not only reduce the negative impacts of drawdowns, it would also provide more floodable acreage and greater energetic potential to the river community.