Microbial community metabolic function in subsurface flow constructed wetlands of different designs

Microorganisms are central to the biogeochemical processes in constructed treatment wetlands. In this study we explored the spatial dynamics of microbial community metabolic function in several different constructed treatment wetland designs at the pilot-scale constructed wetlands of the UFZ Ecotechnology Research Facility in Langenreichenbach, Germany. The constructed wetland designs differed in terms of flow direction, degree of saturation, depth, and intensification. Internal sampling was conducted in April 2013 at different locations along the flow path of each system. The microbial community metabolic function was characterized via community level physiological profiling (CLPP). Microbial community activity (substrate utilization rate) and metabolic richness (number of carbon sources utilize) decreased dramatically with increasing distance along the flow path for most systems. Variation in the metabolic function of microbial communities was observed based on carbon source utilization patterns (CSUPs) and was found to be strongly influenced by system design and sample location within the wetland but not by the presence of plants or depth of media. Analysis of specific carbon source guilds highlighted increased utilization of polymers and carbohydrates in the early stages of all systems, pointing to the establishment of microbial communities optimized to best utilize more easily degradable compounds close to the inlet. Correlations between measures of microbial functionality (activity, richness, and diversity) and turbidity, total organic carbon (TOC), total nitrogen (TN) were observed in horizontal-flow systems but less so in vertical-flow systems. The results presented provide useful insight into the spatial dynamics of microbial community function in constructed wetlands. Potential opportunities for system optimization, based on the results of this study, are provided.