NUTRIENT DYNAMICS IN A STORMWATER MANAGEMENT COMPLEX AT GRAND VALLEY STATE UNIVERSITY, ALLENDALE, MICHIGAN

Grand Valley State University (GVSU) is a liberal arts university located in western Michigan with approximately 25,000 students. The university was founded in 1960 as a “commuter campus”. The infrastructure needed to support the students and cars has resulted in large amounts of stormwater runoff which impacts nearby ravine systems. Stormwater management structures have been implemented since the early 2000’s to reduce offsite impacts. In 2011, a 44-acre stormwater management complex was completed.

Over the summer of 2012, automated water samplers were used collect suspended solids and nutrient data to evaluate the overall efficiency of the newly constructed detention ponds. Completion of the detention ponds decreased stormwater input into one of the largest ravines by roughly 25 percent. Over 200 samples were analyzed for orthophosphate, nitrate, and chloride during rain events and between rain events, to determine baseline conditions. Samples were collected at the inlet and outlet of the stormwater management complex.

Baseline conditions were observed during periods of little precipitation and used for comparison of nutrient concentrations. Average orthophosphate concentrations decreased from 0.58 ppm at the inlet to 0.21 ppm at the outlet. Average nitrate concentrations decreased from 1.95 ppm at the inlet to 0.45 ppm at the outlet, and may be due to fertilizer-derived nutrients. Average chloride concentration increased from 133.5 ppm at the inlet to 189.8 ppm at the outlet, likely due to water evaporation as water moved through the stormwater management complex. Chloride and orthophosphate concentrations may be elevated due to irrigation water derived from a well in the Marshall Formation aquifer.

Rain event samples were taken at 5-minute intervals during periods of precipitation greater than 0.1 inches per hour. Average orthophosphate concentrations decreased from 0.12 ppm at the inlet to 0.02 ppm at the outlet. Average nitrate concentrations decreased from 0.73 ppm at the inlet to 0.51 ppm at the outlet. Average chloride concentration increased from 24.46 ppm at the inlet to 72.67 ppm at the outlet. Rain event concentrations of orthophosphate, chloride, and nitrate were generally lower than baseline conditions due to dilution of the water in the stormwater management complex.