Battle, J.M., J.K. Jackson, and B.W. Sweeney. 2007. Fundamental and Applied Limnology Archiv für Hydrobiology 168(1):39–54.
We sampled macroinvertebrates at four sites in the Open River section of the Upper Mississippi River near Cape Girardeau, Missouri (Rkm 106-114). In 1999, 2000, and 2002-2004, macroinvertebrates were sampled in the fine sediments downstream of four wing dikes with a Ponar dredge. In 1999 and 2001, macroinvertebrates on rocks were sampled on the upstream face of those same wing dikes with rock baskets. We identified 68 taxa in the fine sediments and 50 taxa on the rocks, with only 27 taxa being found in both. In both habitats, annual variability in population densities and community structure exceeded spatial variability. Macroinvertebrate densities in the fine sediments ranged from approximately 3700 to 11,700 individuals/m2 with oligochaetes comprising 77-95 % of total density. Non-metric Multidimensional Scaling ordination suggests that annual differences in the fine sediment assemblage reflect variation in hydrological conditions (high spring flow and low annual flow). Macroinvertebrate density on the rocks ranged from approximately 57,800 to 163,000 individuals/m2 with hydropsychid caddisflies (Hydropsyche bidenslorris and Potamyia flava) comprising 82-97 % of total density. This dominance of oligochaetes in fine bottom substrates and caddisflies on hard substrates is consistent with many other studies on big rivers in the Mississippi River Basin (e.g., Upper and Lower Mississippi, Ohio, Illinois, and Missouri Rivers), and may be the current “reference condition” for these big rivers. This makes traditional water quality monitoring and assessment efforts using macroinvertebrates more difficult because increased dominance by more pollution tolerant taxa is perceived as evidence of water or habitat degradation. However, macroinvertebrate assemblages in our study reach seem less stressed than other big rivers known to be impaired. Specifically, densities of the pollution-sensitive mayfly Hexagenia indicate that conditions in our study reach have improved markedly since the 1960s.