Seasonal investigations were conducted at sites in the Marano and Grado lagoon where Manila Clams were previously seeded using benthic chambers. Total dissolved Hg (THg), methylmercury (MeHg) and dissolved gasoues Hg (DGM) were considered. Diurnal benthic fluxes were found to significantly exceed the diffusive fluxes at all sites. Annually, up to 99% of MeHg is recycled to the water column while Hg recycling avearaged 45%. MeHg poses the highest risk for potential bioaccumulation in clams but it is partially mitigated by Hg reduction. Hg benthic recycling appears more active in the Grado part, hence, the western part appears more suitable for clam farming.
COBISS.SI-ID: 2569295
Hg transformations, methylation and demethylation, and sulphate reduction were studied in sediments of Marano and Grado lagoon using radiotracer methods. Hg methylation rate constants were the highest in summer and generally decresed with depth. Demethylation rate constants were much higher and it occured via the oxidative pathway except in winter when the the reductive pathway increased in importance. Methylation and demethylation rate constanst correlated positively with sulphate reduction and pore water Hg concentrations and inversely with Hg sediment-water partition coefficient indicating the importance of sulphate reduction and Hg dissolution on Hg cycling. In laboratory experiments, methylation was inhibited by amendment of molybdate and nitrate. Spring/summer conditions stimulated methylation and autumn demethylation. SRB tended to be responsible for methylation and oxidative demethylation while while during winter the iron-reducing bacterai seemed to contribute to methylation.
COBISS.SI-ID: 3494778
The spatial distribution of Hg and its relationship with MeHg, organic matter and several geochemical parametres were studied in surafce sediments of the Marano and Grado lagoon (Italy). Hg is primarily associated with fine-grained sediments originated from the fluvial source but Hg sulphides were found also in the eastern coarse sandy fractions. Spatial distribution of MeHg did not show such a clear trend. The good correlation between MeHg and humic acid contents and origin indicated that MeHg is preferentially associated with autochthonous (less aromatic) humic acids.
COBISS.SI-ID: 2520399
The key organic constituents of marine macroaggregates (macrogels) of prevalently phytoplankton origin, periodically occurring in the northern Adriatic Sea, are proteins, lipids and especially polysaccharides. The enzymatic hydrolysis of the macroaggregate matrix revealed the simultaneous degradation of polysaccharides and proteins, while lipids seem largely preserved. In the "fresh" surface macroaggregate samples a pronounced degradation of the alfa- compared to beta-gycosidic linkages were observed. Degradation of the colloidal fraction proceeded faster in the higher molecular weght fractions. N-containing polysaccharides can be important constituents of the higher MW fraction while the lower MW constituents can mostly be composed of poly- and oligosaccharides. Since the polysaccharide component in the higher MW fraction is more degradable compared to N-containing polysaccharies, the higher MW fraction represents a possible path of organic N preservation. Hence, different macroaggregate fractions are subjected to compositional selective reactivity with important implications for macroaggregate persistence in the sea water column and deposition.
COBISS.SI-ID: 2258511