IN-SITU RATES OF SULFATE REDUCTION IN AN AQUIFER (ROMO, DENMARK) AND IMPLICATIONS FOR THE REACTIVITY OF ORGANIC-MATTER

Estimates of rates of organic matter degradation by bacterial sulfate reduction in aquifers are few, and all are obtained by indirect means. Here we present the first direct radiotracer measurements of in situ rates of sulfate reduction for an aquifer (Romo, Denmark). Sulfate red uction occurs in distinct reaction zones within the aquifer at rates t hat vary greatly over short lateral distances. In situ rates of sulfat e reduction are significantly higher than previous indirect estimates. In contrast, rates of sulfate reduction in aquifers are orders of mag nitude lower than in marine and limnic environments, emphasizing the l ow reactivity of natural organic matter in aquifers.