Mitigating Stormwater Runoff Using Rain Garden: Nitrogen and Phosphorus Dyanmics.

Rain gardens are designed to collect and treat urban stormwater runoff.  Because of this function, they have been considered a best management practice. However, there has been limited research on the quantitative effectiveness of rain gardens for water quality improvement. The purpose of this research was to measure the performance of rain gardens on the fate and transport of phosphorus (P) and nitrogen (N). Three residential rain gardens measuring approximately 20 m² were instrumented in River Falls, WI to evaluate the effect of vegetation type on rain garden performance. The three vegetation assemblages were native prairie, shrub, and broad-leaf plants. The stormwater that flows into each of the rain gardens was collected using surface water samplers.  Replicate suction cup lysimeters were installed at a depth of 60 cm in each rain garden to collect pore water.  Concentrations of soluble P, total P, and nitrate-N were measured for both inflow and leachate.