Journal of Student Research 2018

Journal Student Research

82

Figure 9. Total phosphorus (P) and soluble reactive P (SRP) loading for storm sewer 2 during various years. Red column denotes before BMP implementation while blue columns represent year after BMP implementation.

For total P loading, decreased flow in conjunction with BMP implementation appeared to be the primary explanation for lower total P loading. For SRP, however, both lower flow and lower SRP concentration contributed to less SRP loading to Half Moon Lake during the post-BMP summers (Fig. 9). As cities like Eau Claire, Wisconsin, continue to develop, impervious surfaces will increase. This increase will lead to more runoff carrying pollutants, such as phosphorus, into lakes (Brezonik & Stadelmann 2002). As lakes receive excess nutrients they rapidly become eutrophic. Eutrophication is detrimental to lakes by deteriorating water quality and degrading habitat for wildlife (Søndergaard et al. 2003). BMPs such as construction of grassy swales and rock islands were implemented in the Storm Sewer 2 subwatershed during remodeling and expansion of the Luther Hospital complex which was completed in 2010 (Half Moon Lake Implementation Taskforce 2010). This research examined flow, P concentrations and P loading from one storm sewer two during 2017 for comparison with a long-term data base to evaluate the potential impacts of BMPs on urban loading to the lake. I hypothesized that BMPs should reduce flow into this storm sewer by increasing infiltration (Moore 2015, Jeppesen et al. 2005). Summer total P and SRP loading was reduced by 68% and 79%, respectively, suggesting that runoff detention and infiltration were