Quantifying rates of methanogenesis and methanotrophy in Lake Kinneret sediments (Israel) using pore-water profiles

Full seasonal sets of chemical and isotope profiles from the pore water of Lake Kinneret (Sea of Galilee, Israel) were produced to study methanogenesis and methanotrophy processes and the couplings between methane (CH(4)), sulfur, and iron. Sulfate is depleted within the upper 10 cm of the sediment mainly by traditional bacterial sulfate reduction by organic matter. Maximum sulfate reduction rates calculated from sulfate concentration profiles are found at the water-sediment interface (0-1 cm - 1.4 x 10(-12) +/- 0.2 x 10(-12) mol cm(-3) s(-1)). CH(4) concentrations and modeling of dissolved inorganic carbon (DIC) and its stable carbon isotope (delta(13)C(DIC)) suggest that maximum methanogenesis rates of 2.5 x 10(-13) +/- 1.5 x 10(-13) mol cm(-3) s(-1) occur at 5-12-cm depth in the sediments, and that it ends at 20 cm. Of the produced CH(4), 50-75% is converted to gas bubbles of CH(4) before it reaches the bottom water. Model results suggest the occurrence of anaerobic oxidation of CH(4) (AOM) in the deep sediments of the lake below the zone of methanogenesis.