Effects of benthic macroinvertebrates on the exchange of solutes between sediments and freshwater

Results are presented from laboratory microcosm studies to assess the effects of benthic invertebrates (tubificid oligochaetes, chironomid larvae, and unionid bivalves) on chemical diagenesis of aquatic sediments and the exchange of solutes between sediment and overlying water. Photographs of the bioturbated zones of the microcosms are included. Because of their different modes of life, the various organisms modified the sediment physically in different ways, resulting in modification of the kinds, rate, and locations of chemical reactions within sediments, at the sediment/water interface, and at the burrow wall/water interface. The flux of solutes from pore waters was increased in the presence of irrigated burrows, and was greater than that predicted from the pore-water profiles. For some chemical species, part of this increased flux was due to the metabolic byproducts of the organisms, and the remainder was due to changes in sediment fabric, radial diffusion due to burrows, and enhanced decomposition of organic matter or dissolution of mineral matter.