236 



Ai/iiatic EcosysWnis — Our Liviiti^ Hcsiiuives 



For further information: 



Joseph Wlosinski 



National Bioloyical Service 



Environnienlal Management 



Technical Center 



375 Lester Ave. 



Onalaska. Wl 54650 



water elevations during high discharges. Water- 

 SLiiface elevations at relatively low discharges 

 (60.000 cfs) have dropped about 2.4 m (8.0 ft) 

 over the record 133-year period at St. Louis. 

 Mis.souri. 0.5 m (1 .5 ft) over the 52-year record 

 at Chester, Illinois, and 1 .5 ni (5.0 ft) over the 

 60-year record at Thebes. Illinois. Water-sur- 

 face elevations at relatively high discharges 

 (780,000 cfs). however, have risen about 2.7 m 



(9 ft) over the record period at St. Louis, 1.5 m 



(5.0 ft) at Chester, and 1.1 m (3.6 ft) at Thebes. 



Reference 



McHcnrv. J.R.. J.C. Ritchie. CM. Cooper, and J. Verdon. 

 1984. Recent rates of sedimentation in the Upper 

 Mississippi River. Pages 99-118 in J.G. Wiener, R.V. 

 Anderson, and D.R. McConville. eds. Contaminants in 

 the Upper Mississippi River. Butterworth Publishers, 

 Boston, MA. 



Biota of the 



Upper 



Mississippi 



River 



Ecosystem 



by 

 James Wiener 

 Teresa Naimo 



Carl Korschgeu 



National Biological Service 



Robert Dahlgren 



U.S. Fish and Wildlife Service 



Jennifer Saner 



Kenneth Liibinski 



Sara Rogers 



National Biological Service 



Sandra Brewer 



University of Wisconsin- 

 LaCrosse 



The Mississippi River is one of the world's 

 major river systems in size, habitat and biot- 

 ic diversity, and biotic productivity. The naviga- 

 ble Upper Mississippi River, extending 1,370 

 km (850 mi) from St. Anthony Falls 

 (Minnesota) to the confluence with the Ohio 

 River, has been impounded by 27 locks and 

 dams to enhance commercial navigation. The 

 reach between two consecutive locks and dams 

 is termed a "pool." The upstream portions of 

 many pools are similar to the unimpounded 

 river, whereas the downstream reaches are sim- 

 ilar to reservoirs. 



The Upper Mississippi contains a diverse 

 array of wetland, open-water, and floodplain 

 habitats, including extensive national wildlife 

 and fish refuges. Human activities, though, have 

 greatly altered this river ecosystem; much of the 

 watershed is intensively cultivated, and many 

 tributary streams deliver substantial loads of 

 nutrients, pesticides, and sediment from fami- 

 land. Pollutants also enter the river from point 

 sources. 



We examine recent temporal trends in the 

 abundance of several key groups of organisms 

 in the Upper Mississippi River and show that 

 certain flora and fauna have declined along sub- 

 stantial reaches of the river. Our analysis is spa- 

 tially constrained by available data to the reach 

 of river extending from Pool 2 (near 

 Minneapolis-St. Paul. Minnesota) to Pool 19 

 (near Keokuk. Iowa). 



Information on the abundance of selected 

 riverine biota was obtained by compiling histor- 

 ical data and by censusing or sampling. 

 Bottom-dwelling invertebrates, collectively 

 termed benthic macroinvertebrates, were exten- 

 sively studied. Some of these organisms are 

 important in the diets of fish and wildlife and 

 are useful as biological indicators of toxic pol- 

 lution. Data on densities of fingernail clams 

 (Miisculiiim traiisversiim) from 1973 to 1992 

 were obtained from regional scientists, pub- 

 lished literature, and sampling (Wilson et al. 

 1994) in selected pools (pools are numbered 

 consecutively from upstream to downstream). 



In 1992 benthic macroinvertebrates were 

 sampled in soft sediments of five reaches of the 



Upper Mississippi and one reach of the Illinois 

 River to estimate densides of fingernail clams 

 and the burrowing mayfly iHe.xtigenia). In 1975 

 and 1990, benthic macroinvertebrates were 

 extensively sampled in five habitats (marsh, 

 bay, open water, side channel, and dredged side 

 channel) in Pool 8 of the Upper Mississippi 

 (near La Crosse, Wisconsin) to examine 

 changes in abundance, biomass, and communi- 

 ty structure (Brewer 1992). Data on the unionid 

 mussel fauna in the river were obtained from the 

 literature and other sources (Shimek 1921; 

 Grierand Mueller 1922; Ellis 1931a. b; Dawley 

 1947; Finke 1966; Coon et al. 1977; Fuller 

 1978, 1979; Mathiak 1979; Peny 1979; Thiel et 

 al. 1979; Ecological Analy.sts, Inc. 1981; Thiel 

 1981; Duncan and Thiel 1983; Holland-Bartels 

 1990). 



Wildcelery plants {Vallisiieria americana) 

 were sampled each August during 1980-84 and 

 1989-93 in quadrants along 12 0.8-km (0.5-mi) 

 transects in Lake Onalaska. a backwater lake in 

 Pool 7. Numbers of canvasback ducks {Aythya 

 valisiueria) in Pool 7 duiing fall migration were 

 determined by aerial surveys. Trends in the 

 abundance of mink (Mustek) rison) were 

 assessed by examining indices of mink harvest 

 per unit of trapping effort (total harvest/total 

 number of trappers) on the Upper Mississippi 

 River National Wildlife and Fish Refuge and in 

 states along the river corridor (Dahlgren 1990). 



Status and Trends 



Benthic Macroinvertebrates 



Densities of fingernail clams declined sig- 

 nificantly (f < 0.05) in five of eight pools exam- 

 ined (declines in Pools 2, 5, 7, 9, and 19; Figs. 

 I and 2) along 700 km (435 mi) of river from 

 Hastings, Minnesota, to Keokuk, Iowa. 

 Densities in Pool 19. which had the longest his- 

 torical record on fingernail clams, averaged 

 30,000/m- (2,800/ft-) "in 1985 and decreased to 

 zero in 1990 (Fig. 2). In 1992 densiUes of fin- 

 gernail clams were still low in sampled areas on 

 the Upper Mississippi and Illinois rivers, aver- 

 aging 5-94 individuals/m- (0.5-8.7/ft-). Only 



