RESERVOIRS AS FUTURE SITES FOR ICHNOFACIES

The surface area in human constructed reservoirs now exceeds the surface area for natural lakes in North America (except for the Laurentian Great Lakes). Reservoirs differ from natural lakes not only in basic limnological patterns, but also in sedimentation patterns and sediment quality. Each of these factors influences the types and densities of burrowing invertebrates expected to be present and eventually the traces that will be left in the stratigraphic record. Reservoir sediments are generally poor in organic matter (≤ 1 %) limiting the depth distribution and abundance of conveyor belt taxa and other infaunal feeders; thus the depth of the mixed layer is often less than the amount of annual deposition. Most reservoir benthic invertebrates tend to be surface deposit gatherers or those that filter particles from the overlying water; pelecypods, chironomids (midge larvae), and burrowing mayfly naiads are typical taxa of mid-latitude reservoirs, but none are significant in sediment mixing. Patterns left by the deeper burrowing species (Hexagenia, Unionidae), therefore would be expected to be retained in the sediments.