Viability of Phytoplankton, Zooplankton, and Aquatic Macroinvertebrates in Dredged River Sediments of the Upper Mississippi River

Abstract

Sediment dredging is widely used to manage freshwater ecosystems, including maintaining river navigation corridors. Beneficial uses of the sediments are needed to reduce demands on new and existing stockpile sites. However, using dredged sediments in waterbodies outside the sediment source poses an ecological risk if aquatic organisms remain viable through desiccation‐resistant forms. We assessed viability of aquatic organisms in dredged river sediments from four locations along the Upper Mississippi River. We artificially re‐inundated sediments that had been dry for < 1, 1–5, and 5–10 years and sampled phytoplankton, zooplankton, and macroinvertebrate for 4 weeks. We hypothesized that richness and density of aquatic organisms would be negatively affected by duration of drying. Although individual samples of the most recently dredged material had the greatest richness and density of phytoplankton, zooplankton, and macroinvertebrates, mean richness and density was not different across sediment drying durations. Overall, richness and density of aquatic organisms was low in relation to in situ sampling especially following the first week of sediment re‐inundation. Our results suggest transporting sediments from main channel navigation dredging from the Upper Mississippi River to support beneficial uses in other waterbodies poses some ecological risk given our observations of viable organisms in dredged sediments. We present a multistep risk evaluation procedure that could be applied when considering beneficial uses for dredged sediments.