ACETATE CONCENTRATIONS AND OXIDATION IN SALT-MARSH SEDIMENTS

Acetate concentrations and rates of acetate oxidation and sulfate redu ction were measured in Spartina alterniflora sediments in New Hampshir e and Massachusetts. Pore water extracted from cores by squeezing or c entrifugation contained >0.1 mM acetate and in some instances > 1.0 mM . Pore water sampled nondestructively contained much less acetate, oft en <0.01 mM. Acetate was associated with roots, and concentrations var ied with changes in plant physiology. Acetate turnover was very low wh ether whole-core or slurry incubations were used. Radiotracers injecte d directly into soils yielded rates of sulfate reduction and acetate o xidation not significantly different from core incubation techniques. Regardless of incubation method, acetate oxidation did not account for a substantial percentage of sulfate reduction. These results differ ma rkedly from data for unvegetated coastal sediments where acetate level s are low, oxidation rate constants are high, and acetate oxidation ra tes greatly exceed rates of sulfate reduction. The discrepancy between rates of acetate oxidation and sulfate reduction in these marsh soils may be due to the use of substrates other than acetate by sulfate red ucers or to artifacts associated with measurements of organic use by r hizosphere bacteria.