Max Planck Institute for Marine Microbiology
Publishes on Marine and coastal ecosystems, Groundwater and Isotope Geochemistry, Microbial Community Ecology and Physiology. 10 papers and 1.8k citations.
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Abstract A radiotracer technique for measuring in situ rates of sulfate reduction in marine sediments is described. Microliter portions of labeled‐sulfate solution are injected into undisturbed sediment cores, and the amount of labeled sulfide produced is analyzed. This tracer method is experimentally compared with a method that mixes label into the sediment. Controls and methodological problems of both methods are discussed.
The addition of 20 mM MoO(4) (molybdate) to a reduced marine sediment completely inhibited the SO(4) reduction activity by about 50 nmol g h (wet sediment). Acetate accumulated at a constant rate of about 25 nmol g h immediately after MoO(4) addition and gave a measure of the preceding utilization rate of acetate by the SO(4)-reducing bacteria. Similarly, propionate and butyrate (including isobutyrate) accumulated at constant rates of 3 to 7 and 2 to 4 nmol g h, respectively. The rate of H(2) accumulation was variable, and a range of 0 to 16 nmol g h was recorded. An immediate increase of the methanogenic activity by 2 to 3 nmol g h was apparently due to a release of the competition for H(2) by the absence of SO(4) reduction. If propionate and butyrate were completely oxidized by the SO(4)-reducing bacteria, the stoichiometry of the reactions would indicate that H(2), acetate, propionate, and butyrate account for 5 to 10, 40 to 50, 10 to 20, and 10 to 20%, respectively, of the electron donors for the SO(4)-reducing bacteria. If the oxidations were incomplete, however, the contributions by propionate and butyrate would only be 5 to 10% each, and the acetate could account for as much as two-thirds of the SO(4) reduction. The presence of MoO(4) seemed not to affect the fermentative and methanogenic activities; an MoO(4) inhibition technique seems promising in the search for the natural substrates of SO(4) reduction in sediments.
A mathematical model describing vertical sulfate gradients as a function of diffusion, bacterial reduction, and sedimentation is applied to calculate the steady‐state rates of sulfate reduction in coastal sediments. Diffusion coefficients of sulfate are determined experimentally in different sediment types and depths. The rate of sulfate reduction is also determined directly on sediment cores by a radiotracer technique. Experimentally determined rates are compared with those calculated from the model. The results of the model are shown to depend strongly on its assumptions about the kinetics of bacterial sulfate reduction.