Many streams along the Minnesota coast of Lake Superior have been listed as impaired from either high turbidity or high fish mercury concentrations or both. Both turbidity and total mercury have been shown to be strongly correlated to total suspended sediment in many disturbed watersheds. Turbidity and total mercury concentrations and loads were estimated in four western Lake Superior watersheds from 2005-2006 using automated in-stream turbidity measurements. Regression models were developed relating this near-continuous turbidity data to grab sample measures of mercury during differing flow regimes. Total mercury values ranged from 1 to 28 ng l -1 throughout the open water season and showed a close relationship to total suspended sediment (r 2 = 0.85, n = 23; p < 0.001) and a less robust but still significant relationship with turbidity (r 2 = 0.40, n = 34; p < 0.001) for all four streams. Mercury loads to Lake Superior were estimated to range from 8 to 97 g yr -1 with watershed yields ranging from 0.5 to 4.3 μg m -2 yr -1. Continuous turbidity monitoring appears to be a reasonable surrogate for both suspended sediment and total mercury concentration, providing information when manual sample collection is cost-prohibitive or logistically difficult, and across a wide range of flows.
Bibliographical noteFunding Information:
This work is the result of research sponsored by the Minnesota Sea Grant College Program, supported by the NOAA office of Sea Grant, United States Department of Commerce, under grant No. NA03OAR4170048. The U.S. Government is authorized to reproduce and distribute reprints for government purposes, not withstanding any copyright notation that may appear hereon. This paper is journal reprint No. JR 580 of the Minnesota Sea Grant College Program. The authors also thank Western Lake Superior Sanitary District for funding the mercury analyses; additional support provided under the Coastal Zone Management Act, by NOAA’s Office of Ocean and Coastal Resource Management in cooperation with Minnesota’s Lake Superior Coastal Program (Project No. 306-09-10 to RA), the Natural Resources Research Institute, and the city of Duluth, Minnesota Stormwater Utility. Jesse Anderson of the Minnesota Pollution Control Agency, Tim Tuominen of the Western Lake Superior Sanitary District, and Todd Carlson of city of Duluth’s Public Works and Utilities Department provided valuable technical assistance and advice, and the manuscript was improved by two anonymous reviewers. This is contribution No. 516 from the Center for Water and the Environment, Natural Resources Research Institute, University of Minnesota Duluth.
- total suspended sediment
- urban runoff