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Excessive Loading of Nutrients and Sediments
IJC Criteria: An impairment will be listed when there are persistent water quality problems (e.g. dissolved oxygen depletion of bottom waters, nuisance algal blooms or accumulation, decreased water clarity, etc.) attributed to cultural eutrophication.
Although persistent water quality problems associated with eutrophication are not observed currently in the estuary, the high levels of nutrients and sediments being delivered to Lake Superior is an important concern. Therefore, the RAP will use a modification of the IJC eutrophication criterion to reflect local conditions.
Adaptation of IJC Criterion to Fit Local Conditions: High nutrient and sediment levels in the St. Louis River estuary lead to excessive loadings to Lake Superior, although these high nutrient levels do not seem to be expressed as eutrophication in the Area of Concern.
SLR RAP Rationale for Listing: Prior to the improvements in wastewater treatment in the late 1970's in this area, water quality and biological investigations characterized the St. Louis estuary as eutrophic. At this time, the Western Lake Superior Sanitary District (WLSSD) treatment plant was built and the Superior wastewater treatment plant was upgraded. Since that time, many indicators of trophic status have shown improvements. For instance, concentrations of total phosphorus, ammonia, and organic nitrogen have decreased in the St. Louis Bay. The loading of phosphorus to the estuary from point sources has been reduced substantially. Further work is needed to ascertain the effects of nonpoint source loadings to the system and to Lake Superior. Despite the reductions in point source loadings, phosphorus concentrations in the estuary remain at levels where eutrophic conditions might be expected. However, algal biomass has been lower than would be expected given these high phosphorus concentrations. Chlorophyll a concentrations measured in the estuary have been similar to levels found in mesotrophic or oligotrophic waters. Several investigators have proposed that reduced light penetration due to turbidity and color may be a limiting factor for algal growth in the estuary. Although persistent water quality problems associated with eutrophication are not observed currently in the estuary, the high levels of nutrients and sediments being delivered to Lake Superior is an important concern. Therefore, the RAP will use a modification of the IJC eutrophication criterion to reflect local conditions.
Draft Proposed Restoration Goals for the Beneficial Use Impairments in the St. Louis River Area of Concern
6.
Excessive Loading of Nutrients and Sediments Goals
Meetings to Develop Restoration Goals for the Beneficial Use Impairements
Excessive Loading of
Nutrients and Sediments (BUI #6) workgroup
November 6, 2003 Minutes - meeting postponed
February 17, 2004 Minutes
March 11, 2004 Minutes
The SLRCAC Board of Directors discussed BUI restoration goals at two quarterly meetings: March 24, 2004 Minutes and May 26, 2004 Minutes.