Impacts of Agricultural Drainage Outlets on Great Lakes Coastal Wetlands

Abstract

Great Lakes coastal wetlands are subject to many types of anthropogenic disturbances. Agricultural non-point source pollution is a major contributor to the eutrophication of coastal aquatic systems and agricultural pesticides and herbicides have been linked to losses of wetland biodiversity. Nutrients and pollutants are washed off the landscape during rain events and often times enter drainage systems that are connected to Great Lakes waters. The purpose of this study was to assess the effect that agricultural drainage systems have on coastal wetlands and to measure the subsequent alterations in coastal wetland biota. We sampled coastal wetland sites in Lake Huron and Lake Michigan near ( 1500 m) from drainage outlets for habitat conditions, aquatic macroinvertebrates and fish. Non-metric multi-dimensional scaling (NMDS) analysis in conjunction with a multi response permutation procedure (MRPP) revealed differences in macroinvertebrate community compositions located near drainage outlets when compared to sites far from outlets. Principal component analysis (PCA) of 16 abiotic parameters exposed variation in habitat conditions between sites near and far from outlets. Increased levels of nitrates, turbidity, and specific conductance were often associated with sites near outlets. These findings demonstrate the strong impact of agricultural drainage ditches on coastal wetlands and stress the importance of protective land use policy.