Sediment Phosphorus Loading and Inactivation in Urban and Suburban Lakes

Riley-Purgatory-Bluff Creek Watershed District

Over the past five years, Wenck has been working with the City of Eagan, City of Eden Prairie, and the Riley-Purgatory-Bluff Creek Watershed District to measure phosphorus release from lake sediments and to develop restoration plans that address this important phosphorus source. During this period Wenck collected sediment cores to measure phosphorus release, mobile phosphorus in the sediments, and aluminum doses to inactivate sediment phosphorus. Study lakes ranged from small, shallow lakes such as LeMay Lake in the City of Eagan to deep, recreational lakes such as Lake Riley in the southwest corner of Eden Prairie. Since these lakes receive stormwater runoff, long term efficacy is an important feature of these projects. Wenck uses lake response models and sedimentation terms to define longevity, rank the lakes for alum efficacy, and provide long term context for the projects. To date, Wenck and our partners have treated five lakes, all of which are demonstrating significantly improved water quality following the alum treatments. In fact, all of the lakes are meeting water quality standards for the first time in over a decade.