Distinguishing point and non-point sources of dissolved nutrients, metals, and legacy contaminants in the Detroit River.

ABSTRACT

Water quality impacts to the Laurentian Great Lakes create bi-national issues that have been subject of investigation since the 1970s. However, distinguishing upgradient sources of nutrients, metals and legacy contaminants in rivers remains a challenge, as they are derived from multiple sources and flows typically vary throughout the region. These complications are especially pertinent in the Lake Huron to Lake Erie corridor and Detroit River. The Detroit River supplies 90% of the water to the western basin of Lake Erie (5300 m3/s) and is subject to a variety of co-occurring potential sources (e.g., agriculture, urbanization, and upgradient water bodies) of water quality indicators that limit source disaggregation. To find the source signal in the noise we used an integrative interpretation of dissolved chemical and isotopic parameters with sediment chemical, isotopic, and contaminant indicators. The approach combines archival data to distinguish point and non-point sources, and upgradient water bodies as sources of nutrients, metals and contaminants to the Detroit River and ultimately the western basin of Lake Erie. Persistent organic pollutants and metals cluster together as an urban group. Regional dissolved orthro-phosphate (PO4) in the water column also groups with urban point sources rather than agricultural sources. Urbanization as the primary source of PO4 in the Detroit River highlights the need for continued research on urban impacts and assessments of broader best management practices protecting Lake Erie.