Stability of environmental reference conditions as indicated by stream macroinvertebrate communities: a case study in the central United States

We examined macroinvertebrate community data from Missouri reference streams collected approximately 12years apart to evaluate whether substantial changes in community metrics and/or taxonomic composition occurred over that period. We used analysis of variance to test whether metrics differed between years or between other variables and used non-metric multidimensional scaling to examine compositional differences among samples and the environmental variables that were most associated with these differences. Metrics primarily varied on a seasonal basis, largely reflecting life history patterns of dominant groups such as chironomids and the Ephemeroptera, Plecoptera, and Trichoptera orders. Variation between the time periods generally reflected atypically high abundance of chironomids in the spring of 1999/2000, but we did not observe reduced community quality between the earlier and later survey periods. Taxonomic composition was most related to seasonal differences and to the land cover characteristics of the study sites. No long-term compositional changes were evident, but water quality variables did not clearly differ and changes in land cover were slight between the survey periods. Reference stream conditions remained as indicative of high environmental quality in the later samples as in the earlier samples.