Distribution and seasonal variability of organic matter in a small eutrophicated salt lake

Distribution and seasonal variability of dissolved organic carbon (DOC) and surface active substances (SAS) were studied along the depth profile (15 m) in a small eutrophicated and periodically anoxic sea lake (Rogoznica Lake, Eastern Adriatic coast) in 1996 and 1997. The range of DOC concentrations was characteristic fur productive coastal marine ecosystems (60% of samples in the range of 1-2 mg l(-1) and 40% between 2 and 3 mg l(-1)). Distribution of SAS concentrations was uniform and shifted coward higher concentrations in comparison to other coastal areas in the Adriatic Sea. Eutrophication in the lake is generated by nutrient recycling under anaerobic conditions. Systematically higher concentrations of chlorophyll a, DOC and SAS were determined at the chemocline in the bottom layer (10-12 m) than in the upper water layer (0.5-2 m). Seasonal variability of organic matter was discussed regarding distributions of microphytoplankton (cells >20 mum) and photosynthetic pigments as well as oxygen and salinity changes along the depth profile. The dissolved oxygen saturation reaching up to 300% in the water layer between 8 m and 10 m depths in May and June 1996, was correlated with enhanced concentrations of phytoplankton biomass (reflected as chi a and b, fucoxanthin, peridinin, zeaxanthin) and increased concentrations of DOC and SAS. (C) 2000 Academic Press.