A comparison of S-35-SO42- radiotracer techniques to determine sulphate reduction rates in laminated sediments

In order to find a simple and efficient method to determine sulphate reduct ion rates in environmental samples, we tested different S-35-SO42- radiotra cer techniques. The methods varied in the application of S-35-SO42- and sub sequent extraction of reduced S-35-sulphur species. Samples were either inc ubated as sediment slurries mixed with the radiotracer, or as undisturbed s ediment cores after core injection of the radiotracer. Reduced S-35-sulphur species were retrieved passively by diffusion or actively by reflux distil lation. The methods were applied to surface sediments derived from three aq uatic habitats situated in Germany: (1) a tideless brackish water, (2) a mi ning lake and (3) a natural freshwater lake. The best possible method was e xpected to yield the highest sulphate reduction rates, which were reproduci ble with respect to magnitude and depth distribution. At the same time, we aimed to keep the disturbance of samples as well as the expenditure of labo ur and equipment to a minimum. For all three types of aquatic habitats, the combination of core injection followed by diffusion was the most reliable and efficient method. This combination is therefore recommended for determi nation of sulphate reduction rates in laminated sediments. (C) 2000 Elsevie r Science B.V. All rights reserved.