Seasonal Hydroclimatic and Soil Biogeochemical Drivers of N and P Availability in a Constructed Stormwater Wetland

Abstract

Constructed stormwater wetlands are green stormwater infrastructure (GSI) practices with potential to treat stormwater nutrient pollution. GSI nutrient removal performance is controlled by GSI soil nutrient cycles, which depend on soil hydrologic and biogeochemical conditions. The objective of this study was to characterize spatial and temporal patterns in soil dissolved nutrients, and their relationships with soil conditions, at a constructed stormwater wetland in Milwaukee, Wisconsin. Ion exchange membranes were used to measure soil nutrient availability, which was combined with precipitation, air and soil temperature, soil moisture, and soil oxygen data. Nitrate was intermittent: 17% and 25% of the study period accounted for 50% and 67% of the total nitrate availability in the Upland and Lowland, respectively. Time-series data suggest this intermittency resulted from summertime N mineralization. Orthophosphate was higher in the well-aerated Upland than in the periodically anoxic Lowland with a larger contributing area. Regression results indicate that relationships between nutrient availability and environmental drivers depended on the nutrient and landscape position. Modeling spatiotemporal variability of GSI soil nutrient dynamics may improve system performance and prediction.