Characterization of pollutants and identification of microbial communities in the filter media of green infrastructures

Abstract

Green infrastructure (GI) technologies use natural mechanisms and processes associated with microorganisms, plants, and filter media to facilitate mass circulation and energy flow in the ecosystem. Despite the numerous studies focused on the functions and pollutant treatment performance of nature-based stormwater treatment technologies, studies concerning the effects of filter media characteristics on the diversity and abundance of microorganisms in green stormwater infrastructures are still lacking. In this study, the physico-chemical characteristics of filter media and accumulated sediments in an infiltration trench (IT) and bioretention facility (BI) were investigated. Moreover, the composition and distribution of different microbial communities in GIs designed for stormwater treatment were identified. As compared with BI, higher pollutant concentrations were noted on the filter media and sediments accumulated in IT due to the higher degree of anthropogenic activities in IT's catchment area. Inorganic filter media (i.e., gravel) tend to have greater pollutant trapping efficiency due to the accumulation of sediments in the macropores. On the other hand, organic filter materials (i.e., woodchips) may serve as carbon sources for fueling microbial processes and promote better moisture retention in the facility. Proteobacteria, which constituted 38.6% to 43.0% of the total bacterial population in IT and 37.9% to 41.4% of the total bacterial population in BI, was found to be the most dominant type of bacteria in the facilities. In terms of microbial diversity, BI exhibited a higher diversity index, which is most likely due to the presence of vegetative components forming a symbiotic relationship with microbial colonies. Generally, inorganic filter media are mainly used for improving the GI technologies' drainage and infiltration functions, whereas organic filter media provide suitable growth environments for different bacterial communities involved in important biogeochemical cycles.