Stimulation of sulfate-reducing activity at salt-saturation in the salterns of Ribandar, Goa, India
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In order to address the question if Sulphate Reducing Activity (SRA) ever gets arrested at salt saturation, it was measured at 0-2, 2-5 and 5-10 cm depth in sediment cores from the salt pans of Ribandar (Goa) using 35S – sulphate. 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 of SRA under mesohaline (85 psu) and hypersaline conditions (330 psu) as are available in the salt pans during salt producing season. Variation in culturable abundance of SRB governed 98 and 75% of the variation in SRA at hypersaline and mesohaline conditions respectively.. Though SRA of 3.34 nM.g-1.hr-1 could be measured at hypersaline conditions of 330 psu, higher SRA of 116.03 nM.g-1.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 (Oren, 1999), we hypothesize that SRA is not totally arrested at salt saturation but could rather get retarded. Further, our studies show that availability of an extraneous carbon source could serves to stimulate and thus counter the retardation. Our finding suggest that SRA in saturated salt pans is apparently more carbon than sulfate limited.
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