USING MICROBIAL COMMUNITY PROFILES FOR DELINEATION AND LONG-TERM MONITORING OF A LANDFILL LEACHATE-CONTAMINATED AQUIFER

Groundwater contaminated by landfill leachate provides an excellent opportunity for studying the interaction between microbiological communities and their biogeochemical environment. Leachate typically contains high concentrations of organic matter, nutrients, and metals, and when introduced to an aerobic groundwater, distinctly changes the subsurface microbial community. Quantifying the attenuation progress of contaminated groundwater at leaking landfill sites is challenging, and depends on the constituents present in leachate, the site-specific subsurface environment, and the spatial and temporal scales over which the site will be monitored. In this work we sampled groundwater monitoring wells around a leaking municipal waste disposal site over space and time for microbial communities and hydrochemistry. Community profiles for Archaea, Bacteria, and Geobacteraceae were generated using the 16S rRNA gene and terminal restriction fragment length polymorphism (T-RFLP), and temporal community dynamics were quantified using the Jaccard Index of similarity. On a general level, changes in microbial community structure between successive sampling events followed significant Mann-Kendall trends in hydrochemistry (i.e. significantly increasing, decreasing) for leachate indicators (inc. total organic carbon, alkalinity, and specific conductance) in fringe and contaminated monitoring locations. Thus, if leachate indicators were significantly increasing, microbial community similarity increased throughout the year. Furthermore, relationships between trends in specific hydrochemical components (inc. organics, nutrients, electron acceptors, etc.) and microbial similarity were the strongest in the most contaminated portion of the groundwater and weakest in unimpacted locations with Bacterial communities correlated to substrate concentrations and essential macronutrients, and Geobacteraceae correlated to substrate concentrations, electron acceptors, nutrients, and reaction byproducts. Our findings support the use of microbial community structure, as monitored using molecular methods, to improve our knowledge of the state of the groundwater system at a leachate-contaminated site, and indicate the progress toward attenuation.