The St. Louis River drains an area of 9412km2 into the western arm of Lake Superior. The river's lower section, including a 48.5km2 estuary, was designated as a Great Lakes Area of Concern due to degradation from industrial activities. Part of the estuary is occupied by the largest port in the Great Lakes. A GIS-based stressor index was previously developed to characterize anthropogenic stress within the watershed. The components of the stressor index were road density, point-source pollution permit density, population density, and percent agricultural and developed land. Water quality sampling was conducted at 27 sites in the estuary in tributaries and associated nearshore areas during multiple flow regimes in 2010-2011. Additional data were analyzed from 34 upper watershed sites sampled in 2009-2010. Stressor scores were significantly (p<0.1) and positively correlated with TSS, turbidity, TP, NO2-/NO3--N, dissolved oxygen saturation, pH, specific electrical conductivity, chloride, sulfate, and E. coli in the upper watershed. In the estuary, the index was significantly and positively correlated with NO2-/NO3--N, NH4+-N, and chloride at multiple flow regime and location combinations. Soil K factor (an erosivity index from recent NRCS SSURGO soil surveys) was found to have stronger relationships with sediment related parameters than the stressor gradient. Although originally designed to help stratify sampling across a gradient of landscape stress and identify reference areas for restoration projects, the stressor index was shown to have substantial predictive power for multiple water quality parameters.
Bibliographical noteFunding Information:
Jerry Henneck, Jeremy Erickson, Elaine Ruzycki, Andrea Crouse, Steve Koski and Brian Grunwald of the Natural Resources Research Institute (NRRI) assisted in both field work and laboratory analysis. Gerry Sjerven, Terry Brown and Paul Meysembourg from NRRI provided assistance with Geographic Information System analysis. Kang James from the University of Minnesota Duluth, Nick Danz and Jeff Schuldt from the University of Wisconsin Superior, and Joel Hoffman and Peder Yurista from the Environmental Protection Agency — Midcontinent Ecology Division (EPA-MED) provided advice on the project design and data analysis aspects of the project. Tom Hollenhorst from EPA-MED worked on the development of the stressor gradient and offered advice throughout the project. This work is the result of research sponsored by the Minnesota and Wisconsin Sea Grant College Programs supported by the NOAA office of Sea Grant, United States Department of Commerce, under grant No. NA10OAR4170069 . The funding source had no involvement in the study design; the collection, analysis, and interpretation of the data; or in the writing of the report and the decision to submit the article for publication. 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. 617 of the Minnesota and Wisconsin Sea Grant College Programs. This is contribution No. 582 of the Center for Water and the Environment, Natural Resources Research Institute.
© 2014 International Association for Great Lakes Research.
- Great Lakes
- Lake Superior
- Landscape stressor index
- St. Louis River AOC
- Water quality