engleski

Carbon cycling in the peloid mud of Makirina bay (Croatia).

The decomposition of sedimentary organic matter with special emphasis on carbon biogeochemical cycling was studied in the Makirina Bay which is a small, shallow (0.2-1 m deep) lagoon in Central Dalmatia, Croatia. The recent sediment is represented by an up to 2 m thick layer of organic- and carbonate rich clayey silt with typical characteristics of peloid muds. The presence of framboidal pyrite indicates the existence of micro-environments with strongly reducing conditions even in the uppermost part of the sediment column, in spite of intensive bioturbation and irrigation due to macrobenthic organisms. Measurements of the Eh in the sediment column revealed a value of +60 mV at the sediment/water interface, decreasing rapidly to –300 mV in a depth of 2 cm and then stabilising around –400 mV below 10 cm. No bubble methane could be observed in-situ. In-situ benthic fluxes were measured in a benthic chamber and calculated from concentration vs. depth profiles of dissolved inorganic carbon (DIC), Ca2+, Mg2+, and dissolved nutrients in the pore water. The modelling of sources of carbon fluxes at the sediment/water interface using concentration and 13C-DIC data from depth profiles indicated the possibility of an intensive methane formation in the sediment. An incubation experiment with sediment slurries was thus performed to study the decompositon of sedimentary organic carbon in controlled laboratory conditions and to estimate whether and how methanogenesis proceeds. To determine the sources of fluxes of dissolved inorganic carbon (carbonate dissolution, decomposition of sedimentary organic matter and methanogenesis), stable carbon isotopes were used, as well as to asses the reaction pathway of methanogenesis and concurrent methane oxidation. It was found that in the incubation experiment at in-situ temperature, methane was formed probably by CO2 reduction although sulphate was still present in the solution. Methane oxidation occurred simultaneously so that the isotopic composition of methane and DIC was changed by 13C-depleted CO2 deriving from oxidised methane.

nije evidentirano

nije evidentirano