Paleolimnology Provides Early Warnings of Nutrient Stress in the St. Louis River Estuary AOC

Session: 32. - Long-Term Monitoring: Achievements, Challenges, and Solutions

Elizabeth Alexson, Natural Resources Research Institute, University of Minnesota Duluth, [email protected]
Euan Reavie, University of Minnesota Duluth, [email protected]
Richard Axler, Ctr. Water & the Environment, Natural Resources Res. Inst., [email protected]
Sergiy Yements, Natural Resources Research Institute, University of Minnesota Duluth, [email protected]
Pavel Krasutsky, Natural Resources Research Institute, University of Minnesota Duluth, [email protected]
Mark Edlund, St. Croix Watershed Research Station, Science Museum of Minnesota, [email protected]
Robert Pillsbury, University of Wisconsin-Oshkosh, Biology Dept., [email protected]
Diane Desotelle, Desotelle Consulting, [email protected]

Abstract

A paleolimnological investigation provided insight on long-term environmental impacts and remediation in order to support delisting of the St. Louis River Estuary (SLRE) Area of Concern. Various sedimentary indicators (pigments, diatom communities, and diatom-inferred phosphorus) were analyzed from six cores taken throughout the SLRE and another from western Lake Superior. Reductions in eutrophic diatom taxa such as Cyclotella meneghiniana after 1970 in certain cores suggested improvement in water quality over the last 40 years. However, in cores taken from estuarine bay environments, persistence of eutrophic taxa such as Cyclostephanos dubius and Stephanodiscus binderanus indicate ongoing nutrient problems. Increased diatom-inferred phosphorus and cyanobacterial pigments corroborate this trend. While it appears some of the legacy nutrient pool has been remediated, modern stressors like internal phosphorus loading and climate change may be contributing to ongoing water quality impairments. The trajectory of these recent changes serves as an early warning of future conditions.

1. Keyword
paleolimnology

2. Keyword
diatoms

3. Keyword
St. Louis River AOC