Distribution and Composition of Microbial Populations in a Landfill Leachate Contaminated Aquifer (Grindsted, Denmark) |
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Authors: | L Ludvigsen H-J Albrechtsen DB Ringelberg F Ekelund TH Christensen |
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Institution: | Department of Environmental Science and Engineering, Groundwater Research Centre, Building 115, Technical University of Denmark, DK-2800 Lyngby, Denmark |
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Abstract: | Abstract
To investigate whether landfill leachates affected the microbial biomass and/or community composition of the extant microbiota,
37 samples were collected along a 305-m transect of a shallow landfill-leachate polluted aquifer. The samples were analyzed
for total numbers of bacteria by use of the acridine orange direct count method (AODC). Numbers of dominant, specific groups
of bacteria and total numbers of protozoa were measured by use of the most probable number method (MPN). Viable biomass estimates
were obtained from measures of ATP and ester-linked phospholipid fatty acid (PLFA) concentrations. The estimated numbers of
total bacteria by direct counts were relatively constant throughout the aquifer, ranging from a low of 4.8 × 106 cells/g dry weight (dw) to a high of 5.3 × 107 cells/g dw. Viable biomass estimates based on PLFA concentrations were one to three orders of magnitude lower with the greatest
concentrations (up to 4 × 105 cells/g dw) occurring at the border of the landfill and in samples collected from thin lenses of clay and silt with sand
streaks. Cell number estimates based on ATP concentrations were also found to be lower than the direct count measurements
(<2.2 × 106 cells/g dw), and with the greatest concentrations close to the landfill. Methanogens (Archaea) and reducers of sulfate, iron,
manganese, and nitrate were all observed in the aquifer. Methanogens were found to be restricted to the most polluted and
reduced part of the aquifer at a maximum cell number of 5.4 × 104 cells/g dw. Populations of sulfate reducers decreased with an increase in horizontal distance from the landfill ranging from
a high of 9.0 × 103 cells/g dw to a low of 6 cells/g dw. Iron, manganese, and nitrate reducers were detected throughout the leachate plume all
at maximum cell numbers of 106 cells/g dw. Changes in PLFA profiles indicated that a shift in microbial community composition occurred with increasing horizontal
distance from the landfill. The types and patterns of lipid biomarkers suggested that increased proportions of sulfate- and
iron-reducing bacteria as well as certain microeukaryotes existed at the border of the landfill. The presence of these lipid
biomarkers correlated with the MPN results. There was, however, no significant correlation between the abundances of the specific
PLFA biomarkers and quantitative measurements of redox processes. The application of AODC, MPN, PLFA, and ATP analyses in
the characterization of the extant microbiota within the Grindsted aquifer revealed that as distance increased from the leachate
source, viable biomass decreased and community composition shifted. These results led to the conclusion that the landfill
leachate induced an increase in microbial cell numbers by altering the subsurface aquifer so that it was conducive to the
growth of methanogens and of iron-and sulfate-reducing bacteria and fungi.
Received: 11 June 1998; Accepted: 10 December 1998 |
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