Design of green stormwater infrastructure in cold climates: Material selection, phosphorus dynamics, and road salt effects

Urbanization has led to increased impervious surface area in watersheds globally, contributing to increased stormwater discharge and nutrient loading to aquatic ecosystems. Freshwater ecosystems like Lake Champlain have been negatively impacted by harmful algal blooms driven by excess phosphorus (P) loading. Additionally, salinization from chloride (Cl-) in road salts used in developed areas is a growing concern for freshwater ecosystems in cold climates. Green stormwater infrastructure (GSI) is a best management practice (BMP) intended to mitigate increased runoff and nutrient loading. Many states require the incorporation of GSI in new development plans, but better guidance is needed for the materials used in GSI to achieve desired water quality goals. Two popular GSI types are subsurface gravel wetlands and bioretention cells; however, measured performance of these GSI types has been variable for P. In my first thesis chapter, I examine the effects of different materials on P and Cl- dynamics in subsurface gravel wetlands and the effects of Cl- on two wetland plant species. My results demonstrate that some materials being used in subsurface gravel wetlands may lead to increased soluble reactive P leaching, compromising water quality goals. Chloride data suggest no significant retention by gravel wetland substrates, and that plant sensitivity to field Cl- concentrations differs by species. In a second study, I tested several drinking water treatment residuals from EPA Region 1 for their P removal capacities in the context of bioretention cells. Results illustrate variable, but largely high P removal capacities, with arsenic leaching below the threshold of concern, providing additional evidence that these materials could broadly support enhanced P removal by bioretention systems.