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22 SPECIES EXTIRPATIONS OVERVIEW OF RIVER-FLOODPLAIN ECOLOGY IN THE UPPER MISSISSIPPI RIVER BASIN As with exotic species introductions, plant extirpations are not well documented. It is likely that massive develop- ment in the UMRS floodplain eradicated many terrestrial and wetland species. Degradation in the aquatic environ- ment has caused the decline of many wetland and aquatic species, though the impact has not been adequately documented. Mussels are the most devastated faunal group in the UMR. In the Illinois River they have been reduced from 47 to only 24 species. and total abundance has been reduced (Cummings, 1991). Similar trends are evident on the upper Mississippi River. Commercial shelling, which was once very active on both rivers (Carlander, 1954; Starrett, 1971). has declined significantly, and harvest has even been pro- hibited by State regulators in minois, Fishes have suffered significantly from the perturba- tion of the river-floodplain ecosystem. Although wholesale extinctions are uncommon. in lhe Illinois River 10 percent (13 of 131 species) have probably been extirpated (Page and others, 1992). In the Mississippi River. blocked migration routes have nearly eliminated skipjack herring from the upper floodplain reach. and paddlefish migrations have been intenupted (Pflieger. 1975). Walleye movements have also been disrupted (John Pitlo, personal commun., 1993). CONTAMINANTS Toxic contaminants and fish consumption advisories are widespread in the UMRS (Wiener and others, 1984; Dukerschein and others, 1992). Near large urban areas (Minneapolis. Minnesota; Davenport, Iowa; St, Louis, Mis- souri; Chicago, Illinois: and Peoria, lllinois), industrial con- taminants are common. Sewage effluents were very high in the Illinois River following the diversion of Lake Michigan water in 1900 (Mills and others, 1966), A zone of degrada- tion spread slowly down the river until the river had been severely degraded as far south as the LaGrange Lock and Dam. Sewage and storm-water treatment improved water quality dramatically but at a huge economic cost ($10 bil- lion). Regulatory controls have improved water quality but not sediment conditions. Throughout the remainder of the basin, most contami- nants are of agricultural origin and occur in concentrations at or near maximum advisable levels (Goolsby and others. 1993; Pereira and Hostettler, 1992). While point source pol- lutants have been effectively regulated. nonpoint pollutants are largely uncontrolled, Papers in Wiener and others (1984) provide a detailed summary of UMRS contaminants. although the work should be updated to reflect recent changes. ECOLOGICAL OBSERVATIONS FROM THE "GREAT FLOOD OF 1993" Flood stages in 1993 were greater than ever recorded in most places in the basin (Parrett and others, 1993), The force of the water scoured banks, levees, and floodplains, Flood flows also deposited sediments throughout the flood- plain and in some places may have restored sand habitats lost through the years. The newly created habitats will increase habitat diversity if the areas affected by the flood are left to recover naturally. Floodplain herbaceous plants were destroyed in the areas suffering flooding late into the summer. Because the flood lasted throughout most of the growing season, most plants were not able to grow at all before the onset of fall senescence. Inundated herbaceous plants provided large amounts of organic energy for detritivores. Wetland and aquatic plants are expected to recover quickly when hydro- logic conditions stabilize. The effect on trees is unknown but will be carefully monitored. Aquatic invertebrates sampled in the minois River were very abundant at the moving edge of the rising flood. The highest density and diversity were found in the shal- lowest water in flooded vegetation. Many fishes are adapted to reproduce during the rising portion of the flood pulse. In the lower Illinois River, repro- ductive success for most lacustrine and some river fishes was higher than previously documented. In 1993 the skip- jack herring was found in Pool 4 for the first time since 1989. when LTRMP fish sampling was initiated (Mark Stapyro, personal commun., 1993), Because Lock and Dam 19, which normally blocks fish migrations, was overtopped by floodwaters. skipjack herring and other fish species moved freely throughout the UMRS. Birds were variably affected, depending on the habitats they prefer. Waterfowl were spread widely over the inun- dated floodplain but may have suffered from reduced plant food availability. Piscivorous birds appeared to thrive; they occurred in large numbers in isolated floodplain puddles and at the moving edge of the river. where they fed on the abundant small fishes. A detrimental effect of the inundation of levee districts was the drowning of small mammals, reptiles, and amphibi- ans. Larger mammals were caught in a few cases, but most were able to escape unhanned. Many instances of wildlife wandering into urban areas were reported as animals were forced out of their homes on the floodplain. Floodwaters quickly filled levee districts and inun- dated the relatively immobile small animals. In natural sys- tems, animals usually have time to escape flooding because the waters move slowly across the floodplain rather than breaking through manmade barriers.