The effects of infiltration-based stormwater best management practices on the hydrology and phosphorus budget of a eutrophic urban lake

Small GE, Niederluecke EQ, Shrestha P, Janke BD, Finlay JC. The effects of infiltration-based stormwater best management practices on the hydrology and phosphorus budget of a eutrophic urban lake. Lake Reserv Manage. 35:38-50. Urban lakes can provide a variety of ecosystem services but managing water quality in urban environments is a challenge due to greatly altered hydrology and nutrient cycling. Stormwater best management practices (BMPs) are commonly used to reduce inputs of total phosphorus (TP) to urban lakes through interception and infiltration of stormwater runoff. However, the indirect effects of stormwater infiltration on urban lake water quality are not well understood. We used a heuristic hydrology and phosphorus model of an urban lake to explore how changes in hydraulic flushing due to stormwater management can affect water quality. We applied the model to Como Lake, a 28 ha shallow lake in Saint Paul, Minnesota, USA, which is impaired due to excess TP. The model was calibrated using 17 yr of data, including 10 yr post-BMP implementation. We then used the model to estimate the effect of a range of simulated BMP implementations on the lake's hydrology and P budget. BMP implementation reduced external TP loads to the lake, but reductions in water-column TP concentrations were partially undermined by reduced flushing in the summer months, when water column concentrations were highest, leading to reduced downstream TP export and the increased relative importance of evaporation. While the benefits of BMPs can often extend beyond lake P management, these results suggest that simply quantifying reductions in TP loading due to BMPs while ignoring altered hydrology could lead to overestimating water quality benefits.