Stimulation of sulfate-reducing activity at salt-saturation in the salterns of Ribandar, Goa, India

Abstract

In order to address the question if sulfate-reducing activity (SRA) ever becomes arrested at salt saturation, it was measured at 0-2, 2-5 and 5-10 cm depth in sediment cores from the saltpans of Ribandar (Goa) using (35)S-sulfate. The activity was related to the abundance of culturable sulfate-reducing bacteria (SRB) and the prevailing environmental conditions. The salinity in these ponds ranged from 10 to 350 psu during the salt producing season. The present study compares the rates ofSRAunder mesohaline (85 psu) and hypersaline conditions (330 psu) as are available in the saltpans during the salt producing season. Variation in culturable abundance of SRB governed 98 percent and 75 percent of the variation in SRA at hypersaline and mesohaline conditions, respectively. Though SRA of 3.34 nM center dot g(-1) center dot hr(-1) could be measured at hypersaline conditions of 330 psu, higher SRA of 116.03 nM center dot g(-1) center dot hr(-1) could be measured in mesohaline conditions of 85 psu. These values seem to be higher than the rates reported for Black Sea or tropical mangrove forests. The present study shows that SRA is optimal between a salinity of 60 to 120 psu. Contrary to earlier reports, we hypothesize that SRA is not totally arrested at salt saturation but could instead get retarded. Further, our studies show that availability of an extraneous carbon source could serve to stimulate, and thus counter, the retardation. Our findings suggest that SRA in saturated saltpans is apparently more carbon limited than sulfate limited.