High chemoautotrophic primary production in Lake Kinneret, Israel: A neglected link in the carbon cycle of the lake

Intensive chemosynthetic microbial activity fueled by H₂S oxidation with dissolved O₂ was measured by ¹⁴C fixation in the dark and in presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea in Lake Kinneret waters. This process occurred in water collected below the photic zone (20 m) at the chemocline in the late autumn (November-January) and close to the sediment water interface in May when the chemocline starts to form. Averaged depth-integrated chemoautotrophic primary production at the chemocline was 16% and 24% of the photosynthetic primary production during May and autumn, respectively. The maximal rates were measured in December 1992, reaching values of >90% of the photosynthetic rate. The δ¹³C of particulate organic matter at the chemocline ranged between -27‰ and -39‰, the latter being associated with intensive chemosynthesis. These δ¹³C values support our earlier hypothesis that chemoautotrophic bacteria constitute, directly or indirectly (through the microbial loop), a ¹³C-depleted food source for the zooplankton in the lake during autumn and early winter. Mass and isotopic balance of carbon and H₂S suggest that chemosynthetic productivity may constitute 20%-25% of the primary production in Lake Kinneret annually.