A community ecology approach to wetland mitigation assessment

Background/Question/Methods Design and evaluation of wetland mitigation projects have been challenging due to a range of monitoring and assessment protocols, varying project goals, and differing wetland construction. In order to evaluate wetlands for their capacity to perform important water quality functions such as denitrification, we must better understand the microbial communities responsible for this function and relate how these communities respond to environmental factors. This study examined vegetation and soil parameters from a set of 28 restored or created wetlands constructed by the Illinois Department of Transportation from 1992 to 2002. Microbial community composition was evaluated using DNA community “fingerprint” analyses. Molecular analyses targeted both the total bacterial community (using the 16S rRNA gene) and the populations potentially involved in denitrification (using the nosZ gene, a functional marker for denitrification). Constrained ordination was used to examine plant and microbial communities and their relationship to environmental factors.

Results/Conclusions Hydrology and fertility are the main ecological drivers that structure both microbial and plant communities. Microbial community composition was strongly affected by hydrology (redox potential, water depth, soil moisture) and fertility (soil organic matter, plant-available N). In a parallel way, plant assemblages were also influenced by hydrology, where aquatic species and emergent perennials clustered in areas inundated with water, while wet meadow forbs and floodplain forest species were present across a range of water levels. A successional gradient was detected where younger, less fertile sites generally had low sapling/shrub density and higher plant cover was observed in fertile, older sites. Based on these results, plant functional groups may be indicative of soil microbial community structure. Microbial functional diversity and the relationship with microbial and plant community composition was further examined. In addition, the landscape level variation on the plant and microbial relationship was investigated. Analyzing the composition of denitrifiers in relation to biological and ecological factors will allow for identification of monitoring criteria that are closely related to the nutrient removal potential of wetlands.