Benthic invertebrates and sediment characteristics in Wahkiakum County Ferry channel, Washington, before and after dredging

In 1993, the Portland District of the U.S. Army Corps of Engineers contracted with the National Marine Fisheries Service to study benthic invertebrates and sediments in the Wahkiakum County Ferry Channel, Washington (River Mile 43.2), before and after dredging. Although the area of the dredging project was small, there was concern that benthic invertebrates, particularly the amphipods Corophium spp. (C. salmonis and C. spinicorne), would be adversely impacted. Corophium spp. are abundant in intertidal and shallow subtidal habitats of the Columbia River estuary and are seasonally important in the diets of juvenile salmonids and other fishes. The goals of the study were 1) to describe benthic invertebrate communities in the dredged portion of the ferry channel before and after dredging and 2) to assess recolonization of benthic invertebrates in the dredged portion of the ferry channel. We collected samples in a control area located about 3.2 km (2 mi) upstream from the ferry channel to help assess the effects of dredging. Specifically, we assessed benthic invertebrate species composition, standing crops, diversity, and equitability in both the ferry channel and the upstream control area. Contract no. 96930051