Base Cation Retention in Green Stormwater Infrastructure Soils: Contrasting Effects of Soil Characteristics, Catchment area, and Age

Stormwater runoff contains cations that are derived from the urban landscape, either through eroded materials and/or deicing agents. Excess accumulation of cations in green stormwater infrastructure (GSI) has the potential to decrease soil infiltration rates and plant water uptake, both hydrological processes promoted by GSI, or promote leaching of heavy metals and nutrients. To understand cation retention in GSI soils and the potential for negative impacts, this study evaluated base cation concentrations in GSI soils and their soil, catchment, and hydrologic controls. We tested three factors that we hypothesized to control cation retention in GSI soils: 1) soil texture and organic matter (OM); 2) the ratio of catchment area to GSI infiltration area; and 3) GSI age. Soil samples were collected in GSI sites that varied across gradients of catchment:GSI area ratio (1-10) and age (0.5-10 years) and in reference soils for comparison (floodplain, field, forest, and prairie). The samples were analyzed for cations (sodium (Na), calcium (Ca), magnesium (Mg), and potassium (K)), OM, and soil texture. GSI soils were most similar to floodplain soils, but distinct from field, forest, and prairie soils. GSI soils were consistently more elevated in Ca and Mg relative to field, forest, and prairie soils, in comparison to Na and K. However, the highest Na concentrations were observed in GSI. Correlative analysis revealed that soil texture was related to Ca, Mg, and K in GSI soils. Silt percentage was negatively correlated with Ca, Mg, and K and clay percentage was negatively correlated with Ca and Mg. With respect to catchment and hydrologic controls, the area ratio was positively correlated with Na concentrations only. Furthermore, older GSI were found to have higher concentrations of Ca and K than younger GSI soils. Our findings will improve the understanding of ecohydrological systems in engineered, urban environments and provide data that can be used to optimize GSI sustainability and performance.