| Abstract [eng] |
Eutrophication is a process, when aquatic bodies are affected by high nutrients loads, which is followed by rapid reproduction of micro- and macralgae. Transitional systems as estuaries, including Curonian lagoon, constantly face high loads of nutrients so there eutrophication process is a common phenomena. Under certain conditions – establishment of hypoxia and elevated sedimentation of organic matter to surface sediment – reductive processes are initiated and then dissolved phosphorus liberated to pore water due to reduction of solid phase iron. Therefore the goal of the master thesis is to evaluate fluxes (net and diffusive) and biogeochemical transformations of manganese and iron in the reduced sediment of the Curonian lagoon. The object of this research is to estimate fluxes (net and diffusive) and biogeochemical transformations of manganese and iron. Water and sediment samples were collected during February, April, August and November in 2015, representing different seasons. The highest concentration of solid phase reduced iron Fe(II) were found in 5 – 10 cm depth, while lowest – in 0 – 0,5 cm depth. Highest concentrations of solid phase oxidized iron Fe(III) – in 0 – 0,5 cm depth, lowest – in 5 – 10 cm depth. The highest concentrations of solid phase manganese Mn(IV) – in 5 – 10 cm depth, while lowest – in 0 – 0,5 depth, except for winter season where highest concentrations of Mn(IV) were found in 0 – 0,5 cm depth. The highest concentrations of dissolved Mn2+ and Fe2+ were found in 8,5 cm depth. There were no statistically significant differences between different seasons. The diffusive fluxes of both manganese and iron was always directed from sediment to near bottom water, with highest efflux in autumn. The direction of net flux of manganese and iron varied among seasons. The highest net flux of manganese from bottom water to sediment was observed during summer, while highest efflux of iron occurred during winter. Comparasion both net and diffusive fluxes, suggest that dissolved manganese and iron accumulated in bottom water during winter and spring seasons. In winter – spring period, both iron and manganese reduction was a dominant process, in summer – manganese reduction and iron oxidation, whereas in autumn season – both manganese and iron oxidation. Organic matter had a statistically significant effect to solid phase iron (Fe(II) and Fe(III)), Mn2+, and diffusive flux of manganese and net flux of iron. Bottom water temperature had a statistically significant effect to diffusive flux of manganese and iron, bottom oxygen concentration was important factor to diffusive flux of manganese and iron, net flux of iron flux, nitrates - to net fluxes of manganese and iron. |
