Aquatic Habitat Mapping in the St. Louis River Estuary

Abstract

The goal of this project has been to use data from recent aquatic vegetation sampling in the St. Louis River estuary to refine aquatic habitat maps for four restoration sites and four reference sites that can serve as models for restoration design and management. These aquatic habitat maps are designed for use by resource managers working to restore impaired habitats. St. Louis River estuary restoration plans are part of the multi-agency St. Louis River Area of Concern Remedial Action Plan (RAP) to restore fish and wildlife habitats and remove impairments that led to listing the St. Louis River as a Great Lakes Area of Concern (MPCA and WDNR 2013). This 12,000-acre freshwater estuary was designated an Area of Concern in the 1980s because legacy contaminants and disturbances led to nine key impairments, including loss of fish and wildlife habitat. Current restoration plans rely on aquatic habitat maps prepared for the 2002 Lower St. Louis River Habitat Plan (Appendix 1, Map 1); the original aquatic habitat polygons were drawn using minimal data on aquatic vegetation (SLRCAC 2002). The classification of aquatic habitats used in the 2002 Habitat Plan was qualitative, based primarily on the extensive expertise of local fisheries biologists. Since 2008, biologists in Minnesota and Wisconsin have conducted field surveys yielding over 3000 samples for aquatic and wetland vegetation in 23 key restoration and reference sites within the estuary. The objectives of this project were to 1) identify restoration site mapping priorities and appropriate reference sites, and compile existing data on aquatic vegetation, water depths, and wind fetch as characterized by relative exposure index (REI) for the estuary; 2) run hydrodynamic models for at least four scenarios of river discharge and Lake Superior water levels and extract data on water velocities and temperatures at vegetation sample sites; 3) use multivariate analyses to classify aquatic habitats based on aquatic and wetland plant communities and associated environmental data, and prepare habitat maps and supporting data for four restoration sites and four reference sites; and 4) share progress on this project with estuary resource managers at least five times during the project period, at meetings of the St. Louis River Estuary Habitat Work Group.