CONSERVATION TILLAGE PRACTICES  AND  THE  BIOLOGICAL  INTEGRITY  OF
TRIBUTARY STREAMS OF THE UPPER MISSISSIPPI RIVER

Roger J. Haro 1, Andrew F. Burgess 1, and Prasanna H. Gowda 2.
1 River Studies Center, University of Wisconsin-La Crosse, La Crosse, WI 54601; and 
2 Department of Soil, Water and Climate, University of Minnesota-Twin Cities 
Campus, 1991 Upper Bufford Circle, St. Paul, MN 55108.

Land-use practices associated with intensive agriculture in the Upper Mississippi River 
(UMR) Basin greatly alter aquatic ecosystems, both locally and in receiving waters 
thousands of kilometers downstream (the Gulf of Mexico). Large-scale best 
management practices, such as conservation tillage, are effective for preserving on-
site soil resources.  However, their off-site benefits to local stream ecosystems are 
not well documented.  We estimated sediment erosion rates for 32 subwatersheds in 
two major UMR tributary basins (Lower Minnesota River, Minnesota and the 
Maquoketa River, Iowa) from tillage practice data derived from LANDSTAT TM 
images and from additional spatial data required by the Universal Soil Loss Equation. 
In 1998, we sampled benthic macroinvertebrate communities and evaluated local 
stream conditions in the downstream reaches of each subwatershed.  We developed 
Benthic Macroinvertebrate Indices of Biological Integrity (BM-IBI) for each basin and 
determined scores for all reaches.  The linear relationship between BM-IBI scores and 
estimates of sediment erosion rate were statistically significant, however, our study 
basins exhibited opposite trends.  In both basins, BM-IBI scores were positively 
related to the percentage of upstream area under conservation tillage.  Results 
suggest that large-scale changes in agricultural land-use practices can affect the local 
biological integrity of streams even in highly disturbed basins.

Keywords:  Mississippi River tributaries, tillage practices, benthic macroinvertebrates
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