The effects of changes in flow on the ecological condition of two Arizona streams: analysis of trends in water chemistry and structure of biological assemblages

Analysis of climate observations have led researchers to predict that precipitation in the Southwest, USA will become more extreme in its variability. This prediction combined with increasing demand for water for human use support the claim that streams in the Southwest will experience flows lower than historic minima in the future. In order to protect stream communities, the effects of decreasing flow need to be studied. I investigated how changes in streamflow and base flow of the San Pedro River and West Clear Creek, AZ, affect water chemistry, fish, macroinvertebrates, and periphyton. Regression analysis showed the macroinvertebrate pollution-tolerance index and percent Collectors were significantly negatively related to flow. This indicates a depression of pollution-intolerant species with lower flows. Several other strong relationships were noted, however, long-term data are needed in order to make conclusions about the future effects of decreased flow on the biological assemblages of arid perennial streams.hydrology collectio