Journal of Student Research 2018

83 Urban Photsphorus Runoff and Loading to Half Moon Lake, Wisconsin having an improved impact. However, further investigation is required to determine which BMPs resulted in the greatest infiltration. Although mean summer total P concentration declined only slightly, mean summer SRP concentrations decreased substantially after BMP implementation. I had expected the various BMPs to trap particulates and reduce the total P concentration. I observed that particulates and turbidity (not measured) were usually highest in the first few samples and then declined after peak flow. This pattern suggested that perhaps initial runoff could have exceeded the rate of infiltration into rock islands and grass buffers, resulting in some flushing of particulates into Half Moon Lake. Thus, re-evaluation of particulate runoff and BMPs to trap particles and total P more efficiently may be needed to reduce total P loading from this subwatershed. Exact mechanisms and causes for the reduction in the mean SRP concentration post-BMP are not known. SRP approximates PO 4 -P that can be directly available for algal uptake. Thus, reducing SRP loading to Half Moon Lake was very beneficial. SRP concentration was consistently low during storm events in 2017 and did not vary compared to the greater fluctuation in total P concentration. Maybe exposure of runoff to the various rock islands and grass buffers was causing adsorption and retention of some of the SRP. Another possibility is that construction of numerous rock islands resulted in less fertilization of grass areas and gardens which decreased SRP runoff. Luther Hospital also reduced runoff by constructing a parking ramp with multiple levels. More information is needed on land use practices before and after the Luther Hospital campus upgrade to better understand SRP runoff dynamics in this subwatershed.