Subsurface landfill leachate - home to complex and dynamic eukaryotic communities

The heterogeneity in eukaryotic and bacteria community structure in surface and subsurface sediment samples downgradient of the Banisveld landfill (The Netherlands) was studied using a culturing-independent molecular approach. Along a transect covering the most polluted part of the aquifer, sediment was sampled at 1-m intervals, until a depth of 5.5 m, at four distances from the landfill. At two distances, replicate sediment sampling was performed. Two drillings were placed in a nearby clean area as reference. Denaturing Gradient Gel Electrophoresis banding patterns revealed high bacterial and eukaryotic diversity and complex community structures. Bacteria and eukaryotic community profiles in polluted samples grouped distinct from those in clean samples. Bacteria community profiles in surface samples clustered together and separately from subsurface community profiles. Belowground bacteria profiles clustered location-specific. Eukaryotic community structure did not significantly relate to distance from the landfill or depth. Eukaryotic 18S rRNA gene diversity decreased with depth, and was significantly lower in polluted samples than in clean samples. No significant spatial autocorrelation of bacteria or eukaryotic communities was observed over 1-m depth intervals per sampling location. Spatial heterogeneity in sediment-associated microbial community appears much larger than in groundwater. We discuss how on the one hand spatial heterogeneity may complicate the assessment of microbial community structure and functioning, while on the other hand it may provide better opportunities for natural attenuation.