engleski

Seasonal variation of anoxic conditions in the Rogoznica lake

Seasonal variations of temperature, salinity and concentration of dissolved oxygen, as well as vertical distribution of dissolved organic matter, surface active substances, phytoplankton and reduced sulfur compounds in the small, intensely eutrophicated, 15 m deep sea-lake, Rogoznica Lake, were investigated during 1994, 1995 and 1996. Anoxic conditions in the Lake and high concentrations of sulfur compounds (up to 10^4 M, mainly in the form of sulfide) were detected below the 9 m depth in the periods of stable stratification in 1994 and 1995. At the boundary between oxic and anoxic conditions (chemocline), the presence of purple sulfur bacteria (genus Chromatium) and a maximum concentration of thiosulfate (8 x 10^-6 M) were detected. The stratification and mixing of lake water were greatly influenced by rainfall, as shown from decreased salinity in deeper waters. High phytoplankton activity over the entire water column and an extremely high production of oxygen (oxygen saturation up to 300%) probably prevented the expected development of anoxia during the spring of 1996.

dissolved organic matter; oxygen; sulfur; phytoplankton; stratification; Adriatic Sea

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