GEOGRAPHIC AND HYDROLOGIC PATTERNS BIOLOGICAL AND WATER-QUALITY CONDITIONS

By David A. Peterson, Stephen D. Porter, and Scott V. Mize
U.S. Geological Survey, Wyoming Water Science Center
2617 E. Lincolnway
Cheyenne, Wyo. 82001

Macroinvertebrate, periphyton, and water-chemistry data were analyzed from streams and rivers sampled by the USGS NAWQA P rogram in the central United States. Tolerance values based on macro invertebrate abundance and richness were significantly lower ( larger proportion of intolerant organisms) in streams draining the Rocky Mountain region than in other areas of the central U.S. , whereas macroinvertebrate tolerance values were significantly higher, and EPT richness values were significantly lower, in streams draining the western dry plains and coastal plains regions than in other areas. Algal-community indicators of tolerance (nutrient and organic enrichment) were similarly high in the western dry plains and coastal regions, and algal-tolerance values were significantly lower in streams draining the Rocky Mountain and Ozarks regions. Algal-tolerance values were highly correlated (positively) with water chemistry (nutrient and suspended-sediment concentrations); however, periphyton biomass (biovolume) did not differ significantly among geographic regions and was not significantly correlated with water chemistry. Periphyton biomass was relatively larger in streams during low-flow than high-flow years, as were tolerance values for both macroinvertebrate and periphyton communities. Results from this analysis illustrate the importance of understanding the influence of natural hydrologic and geographic variability on biological and water-chemistry indicators of stream condition.

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