High chemoautotrophic primary production in Lake Kinneret, Israel: A neglected link in the carbon cycle of the lake
Ora Hadas, Riki Pinkas, Jonathan Erez
Limnol. Oceanogr., 46(8), 2001, 1968–1976

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 ¹³C of particulate organic matter at the chemocline ranged between -27‰ and -39‰, the latter being associated with intensive chemosynthesis. These ¹³C 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.