Natural treatment systems (NTS) are engineered designs that are increasingly used to address stormwater pollution to urban surface waters. When runoff enters an NTS, the combined action of vegetation, soil media and microorganisms reduces runoff volume and improves stormwater quality. However, a deeper understanding of the NTS components that offer pollutant attenuation, particularly soil microorganisms, is lacking. For an NTS to be effective, pollutants should be continuously removed and not be significantly released in future storm events. This is relevant to nitrogen (N) within NTS, and particularly nitrate, a pollutant linked to eutrophication of surface waters and groundwater contamination. Nitrate is permanently removed via denitrification, with intermediate production of the greenhouse gas N2O. Denitrification in NTS has been widely studied, but the microorganisms behind N transformation processes are seldom directly examined. Some studies suggest that denitrification gene abundances are positively correlated with inundation time. But, the potential effects of sequestered pollutants on NTS microorganisms are uncertain. Here, we focus on heavy metals as they are effectively retained in soil media and, in high concentrations, negatively affect soil microbial processes. The goal is to evaluate at the field scale how NTS soil microorganisms respond to environmental perturbations, such as heavy metal pollution, and how this affects N cycling, particularly nitrate removal and N2O release. The study includes sampling at model NTS, where soil cores are collected for physicochemical and microbial analysis, and greenhouse gas fluxes are evaluated. The overall project includes multiple sampling campaigns, analysis of bacterial community phylogenetic composition and diversity, and functional gene abundance and activity of nitrifiers and denitrifiers. Initial results suggest that: drainage area characteristics may be related to metals in soil media; nitrifying and denitrifying enzyme activities are positively related to microbial abundance and N; nitrifying enzyme activity is negatively related to bioavailable lead and vanadium concentrations; and N2O release is influenced by soil texture. New insights into the impacts of environmental conditions and stormwater-derived pollutants on bacterial communities and their metabolic capabilities can inform NTS designs for nitrate removal, mitigated N2O emissions, and other beneficial bacterially-mediated processes.

Natural treatment systems for urban stormwater runoff: Relationships between soil microbial communities, environmental conditions, accumulated pollutants, and nitrogen cycling

2019 Fall National Meeting

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