Driving effects of dissolved organic carbon on cadmium release of the sediments by cyanobacterial decomposition

Abstract

The driving effects of dissolved organic carbon (DOC) on cadmium (Cd) release of the sediments by cyanobacterial decomposition were investigated, and the great shallow lakes (Taihu Lake, China) with the algae-type, grass-type, and grass-algal alternation areas were chosen as the study area. The results showed that DOC concentration in the overlying water and Cd content in sediments were the highest in the algae-type areas, amounting to 6.4 mg L−1 and 2.4 mg kg−1, respectively, while the DOC contents in the surface sediments showed higher in the algae-type and grass-type areas. The sediments from the grass-type and algal-type areas showed the strong Cd source state, and only the sediments from Zhushan Bay had the sink state. Most of the sediments had the low Cd release risk, and the values of the degree of Cd saturation (DCdS) and Cd release risk index (CdRI) showed a significant correlation with the DOC content in the sediments (P < 0.05). The Cd release contribution originated from the surface sediments, and F1 (the extractable state of Cd form) was the main Cd release form (the maximum value of 51 % from grass-type areas). Due to the algal decomposition and the complex external environment, the contribution values of F2 (the reducible state of Cd form) and F1 was similar (40 %–47 %) in the process of Cd release from the surface and bottom sediments in grass-algae alternation areas, as well as in some algae-type areas. This study provides theoretical foundation for Cd release control at the ecosystems level.