Soil and microbial properties of green infrastructure stormwater management systems

Abstract

Green infrastructure (GI) refers to environmental design features or engineered systems in an interconnected natural and urban space that provide multifunctional ecosystem services. However, there is great uncertainty and variation in the function of different GI features related to carbon and nitrogen cycling processes that are essential for sustained plant growth and water quality. The objective of this study was to evaluate the effects of GI designs (enhanced tree pits (ETP), street-side infiltration swales (SSIS), and vegetation swales (VS)), including surface area, and watershed area ratio (WAR), on the biogeochemical processes and properties (organic carbon (Corg), total nitrogen (Ntotal), pH, salts, total petroleum hydrocarbons (TPH), Pb, Zn, moisture content (MC), texture, microbial biomass carbon and nitrogen content, potential net nitrogen mineralization and nitrification, microbial respiration, and denitrification potential) of GI engineered soils. Results showed that GI sites did not have significant levels of contamination with metals or TPH and that GI with larger surface area had significantly lower TPH, Pb, and Zn. Microbial biomass and activity were positively correlated with Corg, Ntotal, pH, MC, TPH, and WAR. Denitrification potential was higher in the ETP and SSIS (3 mg N kg−1 h−1) compared to the VS (0.5 mg N kg−1 h−1). Microbial biomass carbon and nitrogen contents were significantly higher in ETP followed by SSIS then VS. These results suggest that relatively young (<10 years) GI sites provide significant levels of microbial biomass and activity that are important for carbon and nitrogen cycling.