Oxygen, organic matter, and sediment granulometry as controls on hyporheic animal communities

Abstract

We hypothesized that dissolved oxygen, sediment granulometry, and sediment organic content jointly limit hyporheic animal communities. To test this hypothesis, we took 167 samples of hyporheic invertebrates at 14 sites in the eastern United States with a Bou-Rouch pump (100 μm mesh net) and measured sediment grain size and organic content, dissolved oxygen, and other chemical variables at these sites. Invertebrate communities were dense (almost 600 animals per 3-L sample) and typically dominated by copepods, nematodes, and annelids. Nonetheless, many other groups of invertebrates were encountered regularly, and both density and community composition varied widely across sites. Many invertebrate taxa were found infrequently where oxygen concentrations were low or sediment grain size was small. Further, at sites where oxygen concentrations were higher than 1 mg/L, densities of many invertebrates were positively correlated with sediment organic content. In addition, many invertebrate taxa were most abundant in coarse sediments. These results support our hypothesis. Nevertheless, the correlations we observed were weak, suggesting that other factors also are important in regulating hyporheic animal communities.