Reactive iron and its buffering capacity towards dissolved sulfide in sediments of Jiaozhou Bay, China.

Reactive iron (Fe) oxides in marine sediments play a critical role in removal of free sulfide. In this study, 0.5 and 6 N HCl-extractable Fe, acid volatile sulfide (AVS), and pyrite were examined in sediments at three sites of eutrophic Jiaozhou Bay to investigate the interactions of sulfur and Fe and possible influences of eutrophication on free sulfide removal. The results indicate that formation and accumulation of AVS and pyrite are limited by low availability of labile organic matter, despite eutrophication of the bay water. Quick buffering of free sulfide proceeded mainly via consumption of 0.5 N HCl-extractable Fe (labile Fe), however, the consumption did not result in a depletion of the Fe pool. High residual buffering capacity enables a quick removal of free sulfide in porewater, and thereby it is difficult for sulfide to accumulate and to cause detrimental effects on benthic organisms at the present steady state. Significant effects of eutrophication on Fe and sulfur geochemistry is restricted only to the estuarine sediments which were subject to direct wastewater discharges, whereas no such effects were observed in other sediments of the bay.

[Effects of Cd (II) on the growth of 8 species of marine microalgae].

Effects of Cd (II) on the growth of 8 species of marine microalgae were studied in batch culture experiment. The experimental results show that higher doses of Cd (II) inhibite the growth of Heterosigma akashiwo Hada. Chaetoceros curvisetus. Skeletonema costatum (Greville) Cleve, Pheodactylum tricornutum Bohlin, Prorocentrum micans. Gymnodinium sp., Platymonas helgolanidica, Platymonas subcordiforus. But, lower doses of Cd (II) (50 microg/L and 100 microg/L) promote the growth of Skeletonema costatum (Greville) Cleve and Platymonas helgolanidica. A growth model, with consideration of effect of Cd (II) on the growth of marine microalgae, was developed by incorporating Logistic growth model with Lorentz equation and GaussAmp equation. Lorentz equation can describe the effect of Cd (II) on the growth rate constant while GaussAmp equation can describe the effect of Cd (II) on the final biomass of microalgae. It was demonstrated that the growth model showed in accordance with the experimental data.