TEMPORAL CHANGES IN OXYGEN-DEMAND AND BACTERIAL SULFATE REDUCTION IN INLAND SHRIMP PONDS

Changes in sediment oxygen demand, sulfate reduction rates, and sulfat e reducing bacteria (SRB) abundances were monitored in nine 0.04-0.08 ha earthen shrimp ponds during a 17-week growing season, Organic matte r (feed) was added at two rates (standard and high) in a block design. The aquaculture site was located in an inland region and utilized sal ine groundwater of lower total dissolved salts and a proportionally hi gher sulfate concentration than undiluted seawater, Sediment oxygen de mand was measured in situ in an enclosed chamber, sulfate reduction ra tes were measured in cores using injected (SO42-)-S-35, and SRB counts were estimated using most probable number analyses. Over the growing season, sediment oxygen demand increased four-fold, SRB populations in creased by more than one order of magnitude, and sulfate reduction rat es increased over two orders of magnitude, with the highest values occ urring at the end of the season. Sulfide flux measurements within cham bers demonstrated that sulfide re-oxidation represented a greater prop ortion of sediment oxygen demand at the end of the season (mean 84%) t han at the beginning (< 2%). Sediment porewater sulfate concentrations were high at all depths (24.7-31.0 mM) and did not appear to limit su lfate reduction. Sediment profiles showed a reasonably strong correlat ion between organic matter content and sulfate reduction rates (r(2) = 0.66). Furthermore, significant differences (P < 0.05) in sulfate red uction were found between ponds that had been used for aquaculture in the previous season versus newly constructed ponds, Differences were c onsistent with the hypothesis that sulfate reduction was regulated by organic matter quantity and reactivity.