Organic matter diagenesis in acidic mine lakes

The significance of organic matter origin for carbon oxidation via sulfate and iron reduction in the sediments of three acid mine lakes is analyzed. C arbon reactivity was estimated by fitting first-order expressions to measur ed rates. Carbon oxidation rates via sulfate and ferric iron reduction rang ed from 3.4 to 4.7 mmol m(-2) d(-1) and resembled those reported for freshw ater lakes. The estimated reaction constants increased from about 10(-3) a( -1) at the interface to the former mine grounds to 0.05 to 0.2 a(-1) at the current sediment-water interface. Aquatic organic matter accounted for an estimated 45...75% of total carbon oxidation rates while it amounted only t o about 5...14% of the total organic matter that had been deposited. The re sults of this study suggest that in highly acidic mine lakes the reactivity of the deposited organic matter can rapidly increase after flooding, enhan cing carbon oxidation and internal neutralization rates in the sediments.