Human and climate-induced environmental changes can affect microbial ecosystem functions in unexpected ways. The occurrence of multiple, interacting environmental stressors (e.g., flooding, salinization, changes in residence time) is expected to increase in frequency, duration, and intensity. In most engineered and restored aquatic ecosystems, the contribution of microbial communities is often ignored even though microorganisms determine the types and rates of ecosystem functions. For example, microbial communities contain members that range in their tolerance to stress, and this can manifest in unaccounted variation in nitrogen removal functions. As such, it is essential to understand how contaminant mitigation strategies (e.g., denitrification) and the organisms that perform ecosystem functions respond to environmental changes. In this study, we characterize microbial community structure and nitrogen removal function in different urban aquatic ecosystems. To examine how environmental features of urban wetlands influence microbial community structure and function, we ran denitrification potential assays (acetylene block method) to quantify nitrogen removal rates and characterized bacterial community composition along riparian areas of an urbanized stream and constructed stormwater wetland. To examine consequences of punctuated environmental stressor effects on nitrogen removal potential, we ran a laboratory-based manipulation of moisture and salinity on constructed stormwater wetland sediments.
Results/Conclusions
There is enhanced potential denitrification rates in flooded and plant-dominated locations, which provides organic carbon needed to sustain the desired ecosystem function. In addition, experimental results revealed that salinity significantly reduced denitrification rates by ~100-fold in the most saturated environment. Last, we demonstrate that differences in potential denitrification rates are due in part to changes in bacterial community responses to environmental stressors such as moisture and salinity manipulation and organic carbon inputs. Characterizing this unaccounted microbial variation can improve efforts to construct and effectively manage microbiomes for enhanced delivery of ecosystem services. As microbial communities develop within built environments, identifying the degree to which functional traits associated with nitrogen removal and greenhouse gas production will be critical for sustainable design and management of urban soil and water resources.