SULFATE REDUCTION IN THE HYPOLIMNION AND SEDIMENTS OF LAKE KINNERET, ISRAEL

1. Lake Kinneret is a warm (13-30 degrees C) monomictic lake. Between January and June a heavy annual bloom of the dinoflagellate Peridinium gatunense dominates phytoplankton biomass (250 g m(-2)). At the begin ning of the summer, degradation and decomposition of the Peridinium bi omass occurs, serving as a trigger for intense sulphate reduction in t he hypolimnion and sediments. 2. The rates of sulphate reduction in th e sediments varied seasonally from 12 to 1700 nmol SO4-2 reduced cm(-3 )day(-1) in December and July, respectively. The availability of organ ic matter and sulphate is high in June after the crash of the Peridini um bloom and the beginning of stratification and is lowest in December before overturn. 3. Sulphate concentrations in the hypolimnion range between 0.52 mM and 0.20 mM during mixing (January-April) and before o verturn (December), respectively. The depletion in sulphate in the hyp olimnion is stoichiometrically correlated to the increase in sulphide. The lake is not depleted of sulphate at any time, so the sulphate red uction process in Lake Kinneret is not limited by sulphate concentrati ons except in the sediments just before overturn.