EFFECTS OF SOILS, RIPARIAN ZONES, AND HYDROLOGY ON NUTRIENTS,
HERBICIDES, AND BIOLOGICAL RELATIONS IN MIDWESTERN AGRICULTURAL
STREAMS.  

Stephen D. Porter 1, Mitchell A. Harris 2, and Stephen K. Sorenson 3. 
U.S. Geological Survey, Water Resources Division, 1 Box 26046,
MS406, Denver, CO 80225; 2 221 North Broadway Avenue, Urbana, IL
61801; 3 12201 Sunrise Valley Drive, MS412, Reston, VA 20192.  

Chemical, biological, and habitat conditions were characterized
in 70 streams in the Midwest Corn Belt region during August 1997,
as part of the U.S. Geological Survey's National Water Quality
Assessment (NAWQA) Program.  The study was designed to evaluate
algal and macroinvertebrate responses to high agricultural
intensity in relation to nonpoint sources of nutrients and
herbicides, characteristics of basin soils, wooded-riparian
vegetation, and hydrology.  Concentrations and forms of
nutrients, herbicides and their metabolites, and seston
constituents varied significantly with regional differences in
soil drainage, ground-water and surface-water relations, density
of riparian trees, and preceding hydrologic conditions. 
Dissolved nitrate concentrations were relatively low in streams
with high diel productivity.  Stream productivity was positively
correlated with seston (phytoplankton) chlorophyll
concentrations, which were significantly larger in streams in
areas with poorly drained soils and low riparian-tree density. 
Concentrations of dissolved phosphorus were low in streams where
periphyton biomass was high.  Periphyton biomass was relatively
larger in streams with clear water and low abundances of
macroinvertebrate scrapers and collector-gatherers.  Periphyton
biomass decreased rapidly with modest increases in the abundance
of macroinvertebrate scrapers.  Differences in dissolved oxygen,
dissolved organic carbon, and stream velocity explained much of
the variance in macroinvertebrate community structure.  The total
number of macroinvertebrate species and number of mayfly,
caddisfly, and stonefly (EPT) taxa were largest in streams with
relatively large periphyton biomass in areas with moderately-well
drained soils and high riparian-tree density.  

Keywords:  algae, stream productivity, macroinvertebrates,
agricultural intensity, landscape factors