Release Characteristics of Mercury from Submersed Typical Herbaceous Plants in the Water-Level Fluctuation Zone of the Three Gorges Reservoir Area

Abstract

In suit inundation experiments of three typical herbaceous plants were conducted in field to investigate the mercury release characteristics of plants grown in the water-level fluctuation zone of the Three Gorges Reservoir after flooding by regulating the water level. To realize this objective, this study mainly focused on the dynamic change of total mercury (THg) concentrations in plants after inundation, the release rate and flux of THg from plants and its release load in this region. The results showed that the release process of THg in plants fitted exponential curve, suggesting that mercury release rate was quick in the initial inundation period and then flat afterwards as the decomposing plants. The THg release amounts (followed the order of Alternanthera philoxeroides > Polygonum lapathifolium > Cynodon dactylon) were probably influenced by initial C/N ratio and THg concentrations of plants. The decrement of THg concentrations in per unit mass of plants residue was found to be generally proportional to their initial C/N ratio, while the THg release amounts were generally proportional to the initial THg concentrations of plants. The total release loads of three plants (Alternanthera philoxeroides, Polygonum lapathifolium, Cynodon dactylon) were estimated to be 167.31, 78.13 and 88.33 mg·hm-2, respectively, according to their weight distribution and biomass in the water-level fluctuation zone of the Three Gorges Reservoir Area.