Evaluating Planting Strategies to Enhance Stormwater Pond Functionality: A Study on the Role of Vegetation in Nutrient Input and Treatment Rates

<title>Abstract</title> <p>Stormwater ponds (SWPs) are a common best management practice for mitigating flood risks and nutrient export from urban stormwater runoff, yet many fail to meet nutrient removal expectations. Many SWPs have mowed turfgrass banks. Planting SWP banks with vegetation or maintaining no-mow buffer zones (un-mowed, 1 to 2-m wide grass strips) may reduce nutrient inputs, while planting littoral zones may enhance nutrient treatment. We tested if (1) greater bank plant cover reduces nutrient inputs, (2) greater aquatic plant and algal cover enhance nutrient treatment, and (3) higher vegetation cover is associated with less algae—a characteristic of SWPs perceived as unsightly. We sampled 63 storm events across eight SWPs in Manatee and Sarasota Counties, Florida, USA. We estimated input and treatment rates for total dissolved nitrogen (TDN), total dissolved phosphorus (TDP), particulate nitrogen (PN), and particulate phosphorus (PP) for each storm event. Nutrient input and treatment rates showed high variability among storm events and nutrient forms. We found no evidence that greater bank plant cover decreased nutrient inputs (p ≥ 0.47), that greater aquatic plant and algal cover enhanced nutrient treatment (p ≥ 0.14), or that greater vegetation cover was associated with less algae (p ≥ 0.12). We found weak evidence of increased PP input rates in ponds with greater turfgrass cover (p = 0.05). Findings suggest that plantings alone are unlikely to meet nutrient removal goals and that protecting downstream water quality will require promoting both in-pond processes that enhance nutrient treatment and landscaping practices that reduce nutrient inputs.</p>