2.U 



Atjiialic Ecosystems — Our Livinii Resources 



Habitat loss on a stretch of the 

 Mississippi River modified for 

 navigation (shown here) contrasts 

 with a diverse complex of habitats 

 on less developed areas of the 

 Upper Mississippi River (iff plate 

 previous page). 



algae i,see Moe), and protozoa (see Lipscomb), 

 little is known of the national trends in their 



populations, diversity, or biomass. Our knowl- 

 edge of these groups is poor even though they 

 provide basic functions of photosynthesis, pro- 

 duction, and decomposition critical to the nor- 

 mal functioning of aquatic ecosystems. 



Without increased monitoring, some very 

 basic attributes of aquatic systems may be 

 unknowingly lost or severely degraded. Groups 

 of species that seem insignificant actually are 

 critical parts of a food web that supports valu- 

 able commercial and sport species. Subtle 

 changes such as losses of island habitat and 

 constant water depth or level may lead to dras- 

 tic declines in productivity or diversity (see 

 Wlosinski et al.; Wilcox and Meeker). The loss 

 of some of these integral pieces of ecosystems 

 may be impossible to restore. The unsuccessful 

 attempt to restore self-sustaining lake trout pop- 

 ulations in the Great Lakes, despite massive 

 efforts, exemplifies this (see Hansen and Peck). 



Habitat 



Changes in the 



Upper 



Mississippi 



River 



Floodplain 



by 



Joseph H. Wlosinski 



Douglas A. Olseii 



Carol Lowenberg 



Thomas W. Owens 



Jim Rogala 



Mark iMiistrup 



National Biological Service 



The U.S. Congress recognized the Upper 

 Mississippi River (UMR) as a nationally 

 significant ecosystem in 1986. The UMR 

 extends noithward from the confluence of the 

 Mississippi and Ohio rivers to the Twin Cities. 

 Minnesota, a distance of more than 1,360 km 

 (850 mi). The floodplain (area between the 

 bluffs) of the UMR includes 854,000 ha 

 (2,1 l(),()()0 acres) of land and water. The 

 Mississippi River is a major migration corridor 

 for waterfowl and provides habitat for more 

 than 150 fish and 40 freshwater mussel species. 



Since 1824 the federal government has 

 implemented numerous changes on the UMR. 

 The river was first modified by removing snags 

 and then sandbars, with changes progressing to 

 rock excavation, elimination of rapids, closing 

 of side channels, and the construction of hun- 

 dreds of wing dams. 27 navigation dams, and 

 hundreds of kilometers of levees. Reservoirs 

 formed by the navigation dams are known local- 

 ly as pools (Fig. 1), which are numbered from 

 north to south. Construction of the dams (most- 

 ly during the 1930"s) significantly altered the 

 northern 1,040 km (650 m) of the UMR (north 

 of St. Louis, Missouri) by increasing the 

 amount of open water and marsh areas. Wing 

 dams and levees have altered aquatic habitats 

 south of St. Louis (the open river) by reducing 

 open-water habitats and isolating the river from 

 much of the floodplain. Most of the changes to 

 the river ecosystem were either designed for 

 navigational improvements or to control the 

 movement of river water. Here we investigate 

 some of the habitat changes at various levels of 

 resolution. 



Spatial data were analyzed by using a geo- 

 graphic infonnation system (GIS). Floodplain 

 areas (bluff to bluff) and systemic land- 



cover/land-use data were obtained from Landsat 

 Thematic Mapper data collected in 1989. Land- 

 cover/land-use data from 1891 were created 



Fig. I. The Upper Mississippi River. Numbers indicate 

 reservoirs formed by navigation dams and known locally as 

 pools. 



