Effects of Black Spots of Dead-Cyanobacterial Mats on Fe-S-P Cycling in Sediments of Zhushan Bay, Lake Taihu
太湖竺山湾藻华黑水团区沉积物中Fe、S、P的含量及其形态变化

The purpose of the paper was to study the biogeochemical response of Fe-S-P in sediments in an extremely conditions (DO = 0.14 mg·L~(-1), Eh = -89.3 mV), which was caused by the dead-cyanobacterial mats. The results showed that organic matter concentration in surficial sediment was higher, and also the Org-P concentration in surface sediments increased 72 mg·kg~(-1) than those of natural sediments for the dead-cyanobacterial cells sedimentation on the sediment. The phosphorus bound Fe was dissolved in lower Eh and anoxia in water and it increased the content of activated Fe and PO_4~(3-)-P in sediments, also the concentration of Fe-P in sediment was lower than that of natural sediments. The concentration of PO_4~(3-) -P in interstitial water in sediments was higher than that of natural sediments, it would release to the overlying water and could be helpful to the next algae blooms outbreak. Also the activated Fe~(2+) concentration increased in the sediment in reducing environment (the Dithio-Fe increased 30 μmol than that the natural sediments); moreover, the increased Fe~(2+) caused the crystalline iron oxides to transform to the amorphous iron oxides. The anaerobic conditions of the water caused the AVS concentration increased and formed massive sulfides, including the production of H_2S, which would escape to the atmosphere, but it would be harmful to water column ecological health; the sulfides also increased in surficial sediment for the more production of AVS (the sulfides in dead-cyanobacterial mats district was 50 μmol·g~(-1) higher than natural water column) .