Microbial community dynamics in a two-stage treatment wetland: Insights from treating seasonal ski resort wastewater

Microbial community studies in treatment wetlands (TW) have not investigated cold-climate TW and have focused primarily on laboratory mesocosms. This study determined microbial community composition and dynamics using 16s rRNA sequencing in a partially-saturated two-stage, vertical-flow pilot TW treating ski resort wastewater from December–April. Indicator species analysis found organisms capable of the primary nitrogen transformations observed in each stage at 3 °C, with nitrifiers in the unsaturated second stage and heterotrophic denitrifiers in the first stage where recycled nitrate is removed. During seasonal TW operation, microbial communities developed significant differences between TW stages and α-diversity decreased. Microbial communities were compared to batch mesocosm TW communities, which were significantly different from the pilot. The study is the first to discern community dynamics and key microorganisms during seasonal loading of a cold-climate, field-scale TW. Results raise questions regarding comparability of mesocosms to pilot systems and indicate more field-scale TW investigations are needed. [Display omitted] •Spatial and temporal differences indicated potential community specialization.•Observed bacteria show nitrifying and denitrifying processes partitioned by stage.•Cold climate selected for psychrophiles and maintained efficient nitrogen removal.•Periodic operation with low nutrients enhanced diversity and caused temporal shifts.•Mesocosm TWs were functional proxies of field system but had distinct communities.