engleski

Seasonal variation of organic compounds in a eutrophic oxbow lake

Seasonal variability of DOC, total dissolved carbohydrates TDCHO, total disoved free amino acids (TDFAA) and colloidal organic carbon (COC> kDa) in a eutrophic oxbow lake were studied biweekly between June 2003 and June 2004. During research period TDCHO were strongly related to DOC and concentrations of both compounds were higher in summer then in winter. Seasonal changes in the concentration of DOM and Chl-a of particulate mater indicate that organic matter impact the concentration of DOC. Excreted organic materials was another source of DOM during photosynthesis processes. The accumulation of dissolved organic matter in summer presumably involves enrichment in biorefractory compounds discharged by agriculture area around oxbow lake and an inability of bacteria/Cyanobacteria/algae to consume all the DOC produced. Increases in biological productivity and freshwater residence time and strong water stratification favored the accumulation of DOM. The data set provided on TDCHO is the first available for eutrophic freshwater ecosystem. In this study the carbohydrates accounted for 20-30% of DOC and were important constituents of DOM. In summer concentration of DOC and TDCHO were found to be higher in surface than bottom water, while DFAA did not show any significant variation in water columns. In winter all investigated variables showed reasonably uniform profile since the water column was completely mixed. Bioreactivity of organic matter and the carbon circulation thought the trophic food chain are strongly influenced by chemical composition and molecular size classes of DOM pool. High concentration of carbohydrates and high molecular mass colloidal particles favour the formation of aggregates. The dynamics of aggregates are also influenced by biological processes and by wind-induced mixing of the water column. The observed accumulation of DOM in summer along with an increased role of carbohydrates and colloidal matter may be critical factor for formation of mucilaginous aggregates.

DOC; total dissolved carbohydrates; total disoved free amino acids; colloidal organic carbon; eutrophic oxbow lake

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