Solar Lake (Sinai). 5. The sulfur cycle of the bcnthic cyanobacterial mats1

The littoral sediments of Solar Lake (Sinai) consist of cyanobacterial mats up to 1 m thick. The vertical distributions in these mats of sulfur compounds, organic carbon, carbonate, and of sulfate‐reducing and other anaerobic, heterotrophic bacteria are presented. The in situ rate of sulfate reduction, measured with a radiotracer technique, decreased 10,000‐fold from 5,400 nmol SO 4 2‐ cm −3 d −1 at the surface to <1 at the bottom of the mats. Turnover rates of inorganic sulfur compounds and of organic matter were estimated. A high influx down into the cyanobacterial mats of dissolved organic compounds produced by the epibenthic algae and bacteria could be deduced from the anaerobic respiration rates. A quantitative flow diagram of the sedimentary sulfur and carbon cycle is presented.