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Water quality in the St. Louis River Area of Concern, Lake Superior: Historical and current conditions and delisting implications
Citation:
Bellinger, B., J. Hoffman, T. Angradi, Dave Bolgrien, M. Starry, C. Elonen, T. Jicha, L. Lehto, L. Seifert-Monson, M. Pearson, L. Anderson, AND B. Hill. Water quality in the St. Louis River Area of Concern, Lake Superior: Historical and current conditions and delisting implications. JOURNAL OF GREAT LAKES RESEARCH. International Association for Great Lakes Research, Ann Arbor, MI, 42(1):28-38, (2016).
Impact/Purpose:
Delisting Areas of Concern (AOCs) is an important goal for EPA under the Great Lakes Water Quality Agreement. To delist an AOC, individual Beneficial Use Impairments must be removed, which requires the AOC community to assess the BUI and determine if the beneficial use is no longer impaired. However, there is no standard approach to BUI assessment. In this study, we developed a generalized design for BUI assessment and tested the design by applying it to the BUI for excessive loadings of sediment and nutrients in the St. Louis River AOC. We found that the assessment design provided statistically-derived estimates of both spatial and temporal condition, and as such was well-suited to BUI assessment.
Description:
Water quality in the lower St. Louis River Area of Concern (AOC) from two stations over a 60 year period (19532013) and system-wide (20122013) was examined to determine if the AOC beneficial use impairment of excessive loading of sediment and nutrients could be considered for removal. Based on the time-series analysis, concentration and loading of total suspended solids and total phosphorus to Lake Superior decreased over time, and episodic hypoxia in the upper estuary was eliminated after 1975. Temporal patterns in nitrogen concentration and loading, particularly in the lower estuary, were confounded by Lake Superior nitrogen inputs and changes in wastewater treatment practices. For the system-wide assessment, site distribution was based on a probability survey design. In 2012 and 2013, monthly (May-October) variability was observed in water quality constituents. Based on area-weighted estimates, 60-85% of the estuary surface area was below criterion threshold concentrations for total phosphorus, total suspended solids, and chlorophyll a. Water quality of the western arm of Lake Superior in 2013 was indicative of oligotrophic conditions, satisfying delisting requirements. The long-term improvements in water quality followed improvements in watershed land-cover and uses and treatment of wastewater. The stratified system-wide survey provided statistically derived estimates of spatial and temporal condition and outlier sites. The data from this study supports the beneficial use impairment removal process for the St. Louis River.
