Sulfate reduction in sediments colonized by cyanobacteria, Spencer Gulf, South Australia

Abstract

Sulfate reduction rates in laminated intertidal sediments colonized by cyanobacterial mats were determined by a glass-rod radiometric technique. Sulfate reduction rates were highest in the layers of sediment immediately below (c. 5 mm) the cyanobacterial mat. An annual sulfate reduction rate for the intertidal sediments was estimated at 6 5 mol m^-2. The individual sulfate reduction rates ranged from 2 to 104 mmol m^-2 day^-1, with the mean, median, mode and standard deviation being 21, 15, 2 and 21 mmol m^-2 day^-1, respectively; the mean of all standard errors (σ_x) for the sulfate reduction rates of replicate sets was 18%. The radiometrically determined sulfate reduction rates were consistent with δ³⁴S values. There was a significant linear correlation between the reciprocal of the absolute temperature of incubation and the sulfate reduction rate. Some diurnal variation in sulfate reduction rates (day-time > night-time) was most probably attributable to the higher day-time temperatures. A Q₁₀ range of 2.0-2.4 between 10 and 40ºC was calculated for sulfate reduction in sediment in which the porewater salinity was 121 × 10^-3 Multiple regression analyses showed that the daily sulfate reduction rates correlated significantly with salinity, temperature, porewater content and primary productivity. There was some covariance between the variables salinity, temperature and primary productivity. The estimated molar ratio between photosynthetically fixed carbon and reduced sulfate was 2:1. An equation relating sulfate reduction rate, primary productivity and environmental factors in marine environments may be useful in constructing mathematical descriptions of the sulfate-reducing process in marine environments.