三峡库区消落带农业活动对土壤汞变化的影响

Effects of Agricultural Activities on Soil Mercury Changes in the Water-Level-Fluctuating Zone of the Three Gorges Reservoir

针对三峡库区消落带退水期农业生产是否会对库区环境带来不利影响的问题,以分布面积较大、农业活动较为频繁的重庆市开州区渠口镇消落带为研究区域,选择种植水稻、玉米、蔬菜和未农用的草地4类消落带地块为研究对象,调查了不同利用地块表层土壤汞(Hg)的变化特征.结果表明,研究区域内土壤THg、有效态Hg(Hg-wh)和甲基汞(MeHg)平均含量分别为25.80~68.74、0.44~0.88和0.08~0.85 ng·g-1.未耕作土地表层土壤THg、Hg-wh和MeHg含量均高于耕作土地表层土壤,说明耕作扰动能够加速土壤Hg的流失.未耕作土壤与耕作土地表层土壤MeHg含量随着落干时长的增加均呈现先升高后降低的趋势,峰值大约出现在落干后1~2个月内,约为淹水末期的4倍,之后逐渐降低至相对稳定的水平.MeHg占THg比例(%MeHg)也呈现类似规律,峰值出现在落干后1个月左右,降到稳定水平时与淹水末期含量无显著性差异(P>0.05).土壤%MeHg与Hg-wh含量呈显著性正相关关系(r=0.642,P<0.01),而与THg含量没有显著相关性(P>0.05),说明消落带土壤Hg甲基化主要受生物可利用性Hg形态的影响.

Farming in the water-level-fluctuating zone（ WLFZ） of the Three Gorges reservoir,China,may result in a wide range of environment problems when the sediment is exposed to air. In this study,Qukou,Chongqing,was selected as the research site due to its large WLFZ area and significant agricultural activities. Four kinds of land use types,including rice,maize,vegetables,and grassland,were selected to investigate the distribution of mercury（ Hg） in the surface soil. The results showed that the mean concentrations of soil total Hg（ THg）,bioavailable Hg（ Hg-wh）,and methylmercury（ MeHg） in the surface soil were 25. 80-68. 74 ng·g-1,0. 44-0. 88 ng·g-1,and 0. 08-0. 85 ng·g-1,respectively. The concentrations of THg,Hg-wh,and MeHg in non-cultivated soil were higher than those in cultivated soil, indicating that farming disturbances could accelerate soil Hg loss. The MeHg concentrations in both non-cultivated and cultivated soil increased up to the maximum value 1-2 months after drying,and then gradually decreased to a relatively stable level. The peak value was approximately four times higher than that at the end of flooding. The percentage of MeHg to THg（ %MeHg） was similar to the distribution of soil MeHg,and the peak value occurred at 1 month after drying. However,when %MeHg decreased to the stable level,no significant difference was found compared to the value at the end of flooding（ P 0. 05）. Furthermore,the soil %MeHg had a significantly positive correlation with Hg-wh（ r = 0. 642,P 0. 01）,while there was no significant correlation with THg（ P 0. 05）,suggesting that Hg methylation was mainly affected by the bioavailability of Hg in the seasonally inundated soil of the WLFZ.