三峡库区消落带优势草本植物淹水后汞的释放特征

为研究三峡库区消落带植物淹水后汞的释放特征,选取狗牙根、酸模叶蓼、空心莲子草这3种优势草本植物在库区现场进行原位淹水试验,研究这3种植物淹水后总汞(THg)含量动态变化特征,分析其释放通量与速率,估算其THg释放负荷.结果表明,3种植物在淹水过程中THg浓度的下降速率呈现先快后慢的趋势,表明淹水前期植物中THg随植物腐解快速释放,随后释放基本稳定.3种植物的THg释放量存在显著差异,且表现为酸模叶蓼空心莲子草狗牙根.3种植物的THg释放量可能受植物初始C/N和THg浓度的影响.植物初始C/N越高,单位质量THg释放量越小.而植物初始THg浓度越高,单位质量植物THg释放量越大.结合3种植物在三峡库区消落带的分布权重和生物量,估算出酸模叶蓼、空心莲子草、狗牙根完全分解后的THg释放负荷分别为167.31、78.13、88.33 mg·hm~(-2).

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

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.