Influence of Wing Dam Notching on Aquatic Macroinvertebrates in Pool 13, Upper Mississippi River: The Prenotching Study

摘要

Benthic and colonizing macroinvertebrates and physicochemical characteristics were studied at six wing dams and an adjacent side channel in the prenotching phase of a project to determine the effects of wing dam notching on aquatic macroinvertebrates. Water temperature and dissolved oxygen concentration were uniform with depth in each sampling period but varied among periods. Current velocity varied with sampling period because staff gauge, i.e. discharge, varied with time. Current velocity decreased with depth. The substrate was mainly medium sand because bottom current velocities ranged from 22 to 43 cm/s during 1978. Fifty-six taxa of macroinvertebrates were collected with a Ponar grab sampler in 1978. Oligochaeta, the most abundant class, comprised 51% of benthic invertebrate density. Hexagenia bilineata (Say), Hexagenia limbata (Serville), and early instars of Hexagenia spp. made up 64% of the benthic biomass. Total benthic invertebrate, oligochaete, Hexagenia spp., and chironomid density, and biomass and number of benthic taxa each were positively, significantly related to percent silt-clay in the substrate. All of these macroinvertebrate categories were negatively, significantly related to percent sand in the substrate. The wing dams were islands of rock in a sea of sand. Basket samplers collected 26.5 times more macroinvertebrate numbers and 14.3 times more biomass than the Ponar grab sampler made earlier. These differences were related to habitat, i.e. basket samplers collected invertebrates from a lotic-erosional habitat, and the Ponar grab sampler sampled a lotic-depositional habitat.