An analysis of algal, macroinvertebrate, and fish community indices for assessing low-level nutrient concentrations in wadeable Ozark streams

Biological indices for algae, macroinvertebrate, and fish communities can be effective for monitoring streams with high nutrient concentrations, but little is known regarding the efficacy of each community for monitoring low-level nutrient concentrations. The U.S. Geological Survey National Water-Quality Assessment Program collected nutrient (nitrogen and phosphorus) and biological samples from 30 Ozark streams in 2006 and compared biological metric and index response to a nutrient index calculated from log-transformed and normalized total nitrogen and total phosphorus concentrations. Biological metrics that were the best candidates for the three indices were identified with a process that included a combination of non-parametric multivariate-, univariate-, and visual-selection procedures. After consideration of 78 algal metrics, and 58 metrics each for macroinvertebrates and fish, 4 metrics were selected for each of the three biological indices. The algal index had higher correlations to the nutrient index and to agriculture land uses (i.e. poultry and cattle production) than did macroinvertebrate and fish indices. Our data suggest that the algal community may be most appropriate for monitoring exposure to low-level nutrient concentrations, perhaps, because nutrient uptake is more direct for primary producers than for consumers.