Abstract
The diurnal variation in the microgradients of O2, H2S, and Eh were studied in the benthic cyanobacterial mats of a hypersaline desert lake (Solar Lake, Sinai). The results were related to light intensity, light penetration into the mat, temperature, pH, NH4+, photosynthetic activity, pigments, and the zonation of the microbial community. Extreme diurnal variation was found, with an O2 peak of 0.5 mM at 1 to 2 mm of depth below the mat surface during day and a H2S peak of 2.5 mM at 2 to 3 mm of depth at night. At the O2-H2S interface, the two compounds coexisted over a depth interval of 0.2 to 1 mm and with a turnover time of a few minutes. The photic zone reached 2.5 mm into the mat in summer, and the main 14CO2 light fixation took place at 1 to 2 mm of depth. During winter, light and photosynthesis were restricted to the uppermost 1 mm. The quantitative dynamics of O2 and H2S were calculated from the chemical gradients and from the measured diffusion coefficients.
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