Stressor Gradients and Spatial Narratives of the St. Louis River Estuary

Abstract

The St. Louis River Estuary, a recently designated National Estuarine Research Reserve, is a complex mosaic of high quality aquatic habitat intermingled with areas of heavy industrial use, contaminated sediments, and effluents from the surrounding urban landscape. The estuary is Lake Superior’s largest U.S. tributary and home to the Duluth-Superior international seaport. The NOAA Sea Grant Program plays a significant role in promoting education, outreach and stewardship in Great Lakes coastal communities and environments. Geospatial thinking can enhance Sea Grant’s objectives, yet few tools exist to foster such an approach on a regional scale. In this project we conducted an estuary-wide sampling of water quality, wetland vegetation and macroinvertebrates, based on an anthropogenic stressor gradient that stratified sites from the relatively undisturbed riverine upper estuary to the working industrial and commercial harbor. Macroinvertebrate communities, plant communities, and water quality all showed some degree of association with the stressor gradient. The 17 water quality parameters we measured included five usually associated with suspended particulates and the rest with the “dissolved fraction” of the water. Dissolved “bioavailable” nitrogen (ammonium and nitrate), chloride, and specific electrical conductivity (a measure of total dissolved salts) were positively correlated with increased environmental stress (Bartsch 2012; Bartsch et al. submitted to JGLR 6/2014) as were suspended sediment and the sediment- associated parameters turbidity, water clarity, and total phosphorus when a factor relating to soil erosion potential was added to the original stressor gradient. These associations were evident for multiple combinations of flow regime and location in tributaries and at near-shore locations within the estuary. Wetland floristic quality was also negatively related to increasing human stress, with disturbed sites and industrial bays of the lower estuary having a greater prevalence of invasive plants and species tolerant of elevated nutrients and sediments. Conversely, sheltered bays and fringing marshes of the upper estuary had lower stress and higher floristic quality. In terms of macroinvertebrates, the Ephemoroptera or mayflies, a common indicator of environmental quality, showed a decline in abundance with increasing overall stress. Overall, these field efforts indicated good potential for developing more robust predictive models as more data becomes available and by improving the spatial resolution of some of the stressor elements - especially soil erosivity and NPDES discharges. By integrating scientific research with spatial narratives, geoquests and deep maps, we created socially and spatially rich tools to increase environmental literacy of the region. Spatial narratives for the St. Louis River Estuary were captured through five vignettes of key activities important to the area: fishing, shipping, wild ricing, recreation, and community; and through perspectives of the local people who told their stories about places and experiences related to these activities. Our research connected aquatic science research on human-based stressor gradients with spatially explicit vignettes of local resource issues and place-based games around those local issues to enhance spatial awareness, engagement with, and stewardship of the estuary.