In the 21st Century, most urban lakes will receive more phosphorus than necessary and the phosphorus levels are projected to be even higher in the future (Schueler 2001). Urban watersheds, like the Riley-Purgatory-Bluff Creek Watershed, typically export 5 to 20 times the amount of phosphorus than less developed watersheds due to an increase in the amount of impervious cover (streets, sidewalks, and driveways) and surface runoff for a watershed (Athayde et al. 1983, Dennis 1985). Phosphorus pollution is the primary component influencing eutrophication in freshwater resources. Excess phosphorus can lead to increased algal growth, turbid water, and loss of biodiversity and desirable aquatic habitat. Potential sources of phosphorus pollution in the District include: stormwater runoff, sediment erosion, grass clippings, lawn fertilizer, and pet waste. Stormwater ponds are the most commonly used method for controlling pollutants, such as phosphorus and nitrogen, which are found in stormwater runoff (Borden et al. 2001).
The Riley-Purgatory-Bluff Creek Watershed District stormwater pond project began in 2010, with initial data collection conducted in the summers of 2010 and 2011 and the second phase beginning in 2012. The purpose of the project is to ascertain if stormwater ponds are possible sources of pollution within the District and identify the ‘bad’ ponds with exceptionally high total phosphorus concentrations that could be targeted for remediation projects. By improving the water quality of these ‘bad’ ponds, the many lakes and creeks within the District will ultimately benefit from reduced total phosphorus levels in stormwater.
The stormwater pond project was conducted by District staff in partnership with city staff from Bloomington, Chanhassen, Eden Prairie, Minnetonka, and Shorewood.