Temporal changes in oxygen demand and bacterial sulfate reduction in inland shrimp ponds

Changes in sediment oxygen demand, sulfate reduction rates, and sulfate reducing bacteria (SRB) abundances were monitored in nine 0.04-0.08 ha earthen shrimp ponds during a 17-week growing season. Organic matter (feed) was added at two rates (standard and high) in a block design. The aquaculture site was located in an inland region and utilized saline groundwater of lower total dissolved salts and a proportionally higher sulfate concentration than undiluted seawater. Sediment oxygen demand was measured in situ in an enclosed chamber, sulfate reduction rates were measured in cores using injected ³⁵SO₄/^2-, and SRB counts were estimated using most probable number analyses. Over the growing season, sediment oxygen demand increased four-fold, SRB populations increased by more than one order of magnitude, and sulfate reduction rates increased over two orders of magnitude, with the highest values occurring at the end of the season. Sulfide flux measurements within chambers demonstrated that sulfide re-oxidation represented a greater proportion of sediment oxygen demand at the end of the season (mean 84%) than at the beginning (< 2%). Sediment porewater sulfate concentrations were high at all depths (24.7-31.0 mM) and did not appear to limit sulfate reduction. Sediment profiles showed a reasonably strong correlation between organic matter content and sulfate reduction rates (r² = 0.66). Furthermore, significant differences (P < 0.05) in sulfate reduction were found between ponds that had been used for aquaculture in the previous season versus newly constructed ponds. Differences were consistent with the hypothesis that sulfate reduction was regulated by organic matter quantity and reactivity.