Survey of the benthic macroinvertebrate community of Lake Pepin and a study of the influence of various physical factors on the distribution of selected taxa

Abstract

The macroinvertebrate community of Lake Pepin on the Upper Mississippi River was sampled twice during the summer of 1977 in order to determine. The taxonomic groups present and what portion of the total standing crop each group represented. Using a petite Ponar dredge, 118 and 127 samples were collected during Sampling Periods I and II, respectively. A total of 38,874 individuals, representing 54 taxa, were collected. It was determined that the family Chironomidae comprised 56% of the benthic standing crop. Chironomus sp., and more specifically the pollution-tolerant midge C. plumosus, represented over 53% of the total number of individuals. Other dominant taxa were the Oligochaeta (40.37%), the Sphaeriidae (1%), and the Hirudinea (0.23%). The remaining taxonomic groups represented 5.43% of the standing crop. Only 18 nymphs of the genus Hexagenia were collected during the study. The pronounced domination of the benthic community by C. plumosus and the rare occurrence of the once prominent mayfly, Hexagenia, reflects the continued perturbation of the influent water of Lake Pepin. In addition to the survey, correlation coefficients were calculated in order to determine the relationship between seven selected taxonomic groups and various physical factors (substrate particle size, dissolved oxygen, depth, and the % total sediment organics). Statistical analyses indicated that invertebrate distribution was effected by the physical factors examined and was often a function of feeding habit, physiological adaptations, and stage of larval development. Multiple correlation analyses determined that the physical factors investigated played a significant role in influencing the selected taxa.