Bioretention column study of bacteria community response to salt-enriched artificial stormwater

Cold climate cities with green infrastructure depend on soil bacteria to remove nutrients from road salt-enriched stormwater. Our research examined how bacterial communities in laboratory columns containing bioretention media responded to varying concentrations of salt exposure from artificial stormwater and the effect of bacteria and salt on column effluent concentrations. We used a factorial design with two bacteria treatments (sterile, nonsterile) and three salt concentrations (935, 315, and 80 ppm), including a deionized water control. Columns were repeatedly saturated with stormwater or deionized and then drained throughout 5 wk, with the last week of effluent analyzed for water chemistry. To examine bacterial communities, we extracted DNA from column bioretention media at time 0 and at week 5 and used molecular profiling techniques to examine bacterial community changes. We found that bacterial community taxa changed between time 0 and week 5 and that there was significant separation between taxa among salt treatments. Bacteria evenness was significantly affected by stormwater treatment, but there were no differences in bacterial richness or diversity. Soil bacteria and salt treatments had a significant effect on the effluent concentration of NO₃, PO₄, Cu, Pb, and Zn based on ANOVA tests. The presence of bacteria reduced effluent NO₃ and Zn concentrations by as much as 150 and 25%, respectively, while having a mixed effect on effluent PO₄ concentrations. Our results demonstrate how stormwater can affect bacterial communities and how the presence of soil bacteria improves pollutant removal by green infrastructure.