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Last modified
1/25/2010 6:46:43 PM
Creation date
10/5/2006 12:45:55 AM
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Template:
Floodplain Documents
County
Statewide
Basin
Statewide
Title
Overview of River-Floodplain Ecology in the Upper Mississippi River Basin
Date
12/9/1996
Prepared By
USGS
Floodplain - Doc Type
Educational/Technical/Reference Information
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<br /> <br />CHAPTER 2: ECOLOGICAL OVERVIEW-POSTFLOOD RECOVERY AND ECOSYSTEM MANAGEMENT 21 <br /> <br />habitats showed high diversity. sand islands being espe- <br />cially abundant. In 1989. approximately half of the flood- <br />plain was in agricultural production and river-floodplain <br />habitats were confined between an extensive levee system. <br />Biotic communities in the middle Mississippi River have <br />been changed by river-floodplain development and the loss <br />of side channel and forest habitat (see Chapter 3), <br />The Missouri River adds 137 million hectares to the <br />Mississippi drainage and increases the flow by an average <br />of 7 ,()()() cubic meters (Hesse and others. 1989), Because the <br />channel depths were greater below the Missouri River. river <br />engineering for navigation was conducted entirely with <br />channel training structures and side channel closures. Much <br />of the length has steep. riprap-annored banks that extend <br />down to a greatly incised channel. The riverbed profile at <br />St. Louis. Missouri, has downgraded by 12 feet. and the <br />width has constricted by half since 1837 (Simons and oth- <br />ers.1974). <br />The average river stage is 1-3 meters higher through- <br />out the year. but the pattern is comparable to the predam era <br />(fig, 2-2). Channel constriction by levees increases flood <br />stages (Simons and others. 1974) and isolates off-channel <br />aquatic habitats. Off-channel habitat is currently less than <br />5 percent of the total aquatic area in this reach. Sediment <br />delivery to this reach is reduced because dams on the Mis- <br />souri and upper Mississippi Rivers trap sediments in slack- <br />water environments. The number of islands has been <br />reduced by one-half since 1891. Areas below St. Louis are <br />also heavily affected by industrial pollutants (UMRBC, <br />1982), <br />Floodplain habitats in the fertile alluvial valleys were <br />leveed for agriculture and development beginning in the <br />1830's; they have been almost completely isolated from the <br />river since then. The alluvial delta between Cairo. Illinois. <br />and the Ohio River was constricted to a mile or less along <br />the main channel, following the construction of large levees. <br />Records prior to Euro-American colonization have not been <br />compiled yet. but thousands of acres of wetland habitat <br />were likely destroyed (Chapter 3), Approximately 100.000 <br />acres have been sequestered behind levees. <br /> <br />%TLAND HABITATS <br /> <br />Floodplain habitats of the middle Mississippi River <br />consist primarily of flood-tolerant forest species (LTRMP. <br />unpub, data. 1993), Aquatic plants are almost entirely <br />absent in the middle river (LTRMP, unpub, data). Channel <br />training structures eliminated slow-flowing side channels, <br />and downcutting eliminated channel border habitats. thus <br />eliminating river wetlands. The conversion of the floodplain <br />for agriculture eliminated floodplain wetlands and therefore <br />the most productive habitats. Remnant wetlands remain, but <br /> <br />most are carefully managed for waterfowl needs. A plant <br />species list is presented by Terpening and others (1974), <br /> <br />INVERTEBRATES <br /> <br />No comparative studies of invertebrate populations <br />between the past and present were found. Most bottom- <br />dwelling and epiphytic invertebrates have probably declined <br />in proportion with habitat. Epilithic invertebrate production <br />may be high because of the vast amount of rock substrate <br />used to control the channel. The Ohio shrimp has been <br />recently "rediscovered" in the Cape Girardeau reach (R, <br />Hrabik. personal commun,. 1994), <br /> <br />FISHES <br /> <br />Fish community composition has responded similarly <br />to Illinois River fish populations. but there is no sign of <br />recovery. Lacustrine species were once very common but <br />are currently only found in the protected areas of dike fields. <br />side channels. and tributary mouths, Although degraded. <br />middle Mississippi River tributaries offer importanl off- <br />channel habitat (R. Hrabik, personal commun.. 1993), <br /> <br />EXOTIC SPECIES <br /> <br />Introductions of exotic plant species are widespread. as <br />illustrated by the expansion of agricultural land, While there <br />are some detailed vegetation surveys available. none have <br />quantified exotic species introductions for the whole <br />UMRS. Purple loosestrife and water milfoil are examples of <br />nonnative plants that are spreading through the upper por- <br />tions of the UMRS (LTRMP. un pub, data). <br />The first and most widespread nonnative fish species <br />deliberately introduced to the UMR was the common carp, <br />It was brought from Europe, where it was a prized sportfish <br />and food fish, Other fishes introduced are redear sunfish. <br />white perch. bighead carp, and grass carp, The European <br />ruffe. the black carp. and a shovelnose/pallid sturgeon <br />hybrid are likely to be the next exotic introductions. <br />Invertebrate invaders are the Asiatic clam and the <br />European zebra mussel. The zebra mussel may be the big- <br />gest single threat because of its ability to survive in <br />extremely high densities (>90.()()() per square meter) <br />(Whitney and others. 1993), Native mussels are readily col- <br />onized by zebra mussels because they provide a hard sub- <br />Slrate for the zebra mussels to adhere to (Tucker and others, <br />1993), Mussels in the Great Lakes have been negatively <br />affected (Haag and others. 1993; Mackie. 1993). and the <br />same fate is expected wherever the zebra mussel develops <br />large populations. <br />
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