Spatial and Temporal Availability of Floodplain Habitat: Long-Term Changes at Pool 19, Mississippi River

Abstract

The 107-year record of daily water elevations for the upper Mississippi River (UMR) at Burlington, Iowa, was examined to assess changes in hydrologic patterns and floodplain availability resulting from dam and levee construction. Following completion of Lock and Dam 19 in 1913, mean low, mean high and overall mean water levels significantly increased (P <0.05). Floodplain habitat was permanently inundated. Establishment of extensive levee and drainage districts adjacent to Pool 19 resulted in additional loss of floodplain. Generalized annual hydrographs indicated the spring rise in water elevation had been shortened in the postdam period and an autumn rise evident in the predam hydrograph was absent in the postdam hydrograph. Temporal reduction in floodplain availability along with spatial losses caused by inundation and leveeing aggravates the situation for floodplain-dependent species. Detrimental consequences of floodplain loss can, however, be diminished through reduction of levee and drainage districts, thereby promoting interaction between floodplain habitat and the river system. INTRODUCTION Large rivers of the world are increasingly managed and impounded (Petts, 1984). An immediate impact of impoundment is readily apparent in the restriction of such migratory species as salmon (Mundie, 1979; Stanford and Ward, 1979) and the skipjack herring (Coker, 1930). Management, however, usually involves more than restriction of potamodromous movement because changes in hydrologic regime, habitat type, and floodplain availability frequently accompany dam construction. In large rivers, floodplains and regular floodplain inundations are critical to a variety of aquatic and terrestrial fauna (Davies, 1979; Goulding, 1980; Petts, 1984), and floodplain vegetation represents the major source of organic matter within such systems (Edwards and Meyer, 1987). The importance of the floodplain to large temperate-river ecosystems has been noted by Whitley and Campbell (1974), who reported that important fish species were eliminated from a reach of the Missouri River due to impoundment and subsequent loss of wetlands. Similar losses of the fishery occurred on the Illinois River when manmade levees eliminated interaction between the river and floodplain and backwater lake habitats (Starrett, 1972; Sparks and Starrett, 1975). The Mississippi River has been characterized as a completely modified floodplain river (Gerking, 1977; Welcomme, 1979; Cooper, 1980). The completion or closure in 1913 of Lock and Dam 19 at Keokuk, Iowa, was one of the first major perturbations of the upper Mississippi River (UMR) (Scarpino, 1985). Early studies of its impact described reduced passage of migratory fish species and associated mussel populations (Coker, 1914; Coker, 1930), reduction of the mussel fishery due to increased sedimentation (Ellis, 1931), and the influence of lake-like conditions on riverine planktonic populations (Galtsoff, 1923). Early records of postdam water elevations were not extensive enough to assess changes in hydrologic patterns and subsequent results of floodplain loss. Coker (1914) went so far as to speculate that although the dam restricted migra-