THE RELATIONSHIP OF MICROBIAL DIVERSITY TO PLUME GEOCHEMISTRY IN AN ANOXIC LANDFILL LEACHATE PLUME, NORMAN OKLAHOMA

The variability of electron acceptors and microbial populations was studied in a landfill-leachate plume at the Norman Landfill, a closed municipal landfill on Canadian River alluvium and the site of long-term biogeochemical investigations of plume evolution. Temporal variability in plume geochemistry after 5 years shows electron acceptors (i.e. sulfate) and degradation products (i.e. methane) change significantly at the water table and plume fringes where recharge and advective flux of less-contaminated groundwater provide sources of electron acceptors. Sulfate concentrations are variable, ranging from > 950 mg/L near the water table to < 1 mg/L only 2 m deeper in the center of the anoxic plume. Near the lower boundary of the plume, where upgradient groundwater mixes with the sulfate-depleted plume, sulfate ranges from 10 to 60 mg/L. Since 1997, the 2-D area of sulfate-depletion has more than doubled and methane concentrations have reached 30 mg/L in the center of the plume. To determine if changes in plume geochemistry are correlated with presence or dominance of different microbial groups, terminal restriction length polymorphism analysis (T-RFLP) was used to obtain DNA fingerprints of bacteria and methanogens present in water and sediment from the same plume section. Microbial populations are affected by factors such as proximity to the water table or groundwater mixing fronts, driven largely by variability of electron acceptors, nutrients, and the quality of electron donors. Bacterial abundances in water are highest near plume fringes, where electron acceptors such as sulfate are available; however, the greatest diversity is observed within the plume. In contrast, the greatest diversity of bacteria in the sediment is outside the plume. In general, the distribution of methanogens is less variable than bacteria. At all sites, non-acetoclastic methanogens are found in both sediment and water fractions, whereas acetoclastic methanogens are present only in water samples within the plume. These patterns of methanogens indicate the availability of electron donors, such as organic acids, may be controlling their distribution. We are conducting further studies to examine how availability of electron donors and acceptors influences microbial structure and function in this dynamic hydrogeochemical system.