In vitro studies on sulphate reduction and acidification in sediments of shallow soft water lakes

SUMMARY. 1. The sulphate reduction capacity of six shallow soft water sediments, differing in pH and organic matter content, was studied under controlled pH adjustments ranging from pH 3 to pH 8.
2. In the acid sediments, relatively rich in organic matter, the sulphate reduction capacity reached values of 0.09-0.12 μmol g^?1 d^?1. In the circumneutral mineral sediments the values ranged between 0.04 and 0.08 μmol g^?1 d^?1.
3. The latter group of sediments was very sensitive to the effects of experimental acidification as sulphate reduction was almost fully inhibited when pH decreased from 7 to 5. In the acid sediments inhibition occurred at lower pH values, in the range pH 5 to pH 3.
4. Sulphate reduction governed the production of free sulphides, whereas putrefaction processes were only of minor importance. It is suggested that in acid sediments, relatively rich in organic matter, the sulphate reducing bacterial population is less sensitive to acidification than in circumneutral mineral sediments.
5. The presence of organic matter appeared to be important in counteracting the inhibiting effects of acidification on sulphate reduction. This is important for the in situ sulphate reduction in sediments of soft waters which become enriched with organic matter during the long-term process of acidification.