Environmental

Oral

395202 - Using an Adaptive Aluminum Sulfate (alum) Application Approach to Improve Water Quality in Bald Eagle Lake, MN

Monday, June 4
10:30 AM - 12:00 PM
Location: Lakeshore B
Co-Authors: William James, Menominee, WI – University of Wisconsin-Stout; Brian Beck, Golden Valley, MN – Wenck Associates, Inc.; Matthew Kocian, Blaine, MN – Rice Creek Watershed District

Bald Eagle Lake is a highly used recreational lake in the northern suburbs of the Twin Cities Metropolitan Area that routinely experienced cyanobacteria blooms. The Rice Creek Watershed District (RCWD) has actively managed Bald Eagle Lake for over 30 years, but recently developed a targeted nutrient reduction program, including a TMDL, focused on achieving measurable improvements in lake water quality. One of the critical TMDL goals was quantify the roles of watershed and internal phosphorus loading in driving lake water quality. Laboratory-derived sediment P release was high at 10.8 mg/m2d, representing 44% of the P load to the lake. The RCWD decided to pursue an aluminum sulfate (alum) treatment to reduce sediment phosphorus release in Bald Eagle Lake. The alum dose required to inactivate 90% of the redox-sensitive P in the top 0-10 cm of profundal sediments was approximately 100 g Al/m2 based on laboratory jar tests. However, application of this rate throughout the lake was cost prohibitive. So, the 100 g Al/m2 rate was used for areas greater than 20 feet in depth and a lower rate of 50 g Al/m2 was used to inactivate the top 5 cm in the 15 to 20-foot depth zone. An adaptive alum application approach was used to achieve sediment aluminum targets and achieve the desired reductions in sediment phosphorus release. Half of the prescribed alum dose was applied to Bald Eagle Lake in the Spring of 2014 followed by sediment coring to measure changes in aluminum-bound phosphorus and sediment phosphorus release. Application zones and rates for the second (2016) application were adjusted based on the interim monitoring results. Following the completion of the alum applications, implementation of watershed BMPs and Curly-leaf pondweed management, Bald Eagle Lake is meeting State water quality standards for the first time is over 30 years.

Joseph Bischoff


Wenck Assocaites, Inc.

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William James

University of Wisconsin-Stout

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Matt Kocian

Rice Creek Watershed District

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395202 - Using an Adaptive Aluminum Sulfate (alum) Application Approach to Improve Water Quality in Bald Eagle Lake, MN



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