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Thursday, June 7, 2007 - 8:00 AM
348
Ecological Responses to Alum Treatment in Spring Lake, Michigan
Mary E. Ogdahl and Alan D. Steinman. Annis Water Resources Institute, Grand Valley State University, Lake Michigan Center, 740 W. Shoreline Dr., Muskegon, MI 49441
Internal loading can be a major contributor of phosphorus in shallow, eutrophic lakes, often compounding water quality issues that impact lake ecology. As a management technique, alum is commonly applied to lakes with high rates of internal phosphorus loading. Spring Lake, Michigan, has some of the highest water column phosphorus concentrations in western Michigan, and is notorious for summer blooms of Microcystis. In fall 2005, Spring Lake was dosed with alum to bind internally-loaded phosphorus. We measured internal loading rates, ambient nutrient concentrations, benthic invertebrate densities, chlorophyll a, and other physical/chemical parameters 2 years preceding and 8 months following treatment. Alum significantly reduced phosphorus flux under anaerobic conditions; mean post-alum rates ranged from -0.52 to 0.88 mg TP m-2 d-1, compared to pre-alum rates of 12 to 34 mg m-2 d-1. Ambient phosphorus declined significantly following alum treatment, with mean surface concentrations falling from 98 to 30 μg TP L-1. However, chlorophyll a concentrations did not decline and transparency remained low following alum application. Benthic invertebrate densities declined significantly, from 4800 to 1100 individuals m-2. Our pre- and post-alum treatment results indicate that alum triggered ecological responses in Spring Lake; however, further monitoring is necessary to identify long-term effects.