三峡库区典型农田小流域水体汞的时空分布特征

Spatial and Temporal Distribution of Mercury in Water of a Small Typical Agricultural Watershed in the Three Gorges Reservoir Region

以三峡库区典型农田小流域——重庆涪陵王家沟为对象,分别于2012年11月~2013年9月对流域内不同类型水体总汞(THg)和总甲基汞(TMeHg)含量进行为期1 a的监测,探讨汞在农田流域水体中的时空分布特征.结果表明,流域内水体THg、TMeHg浓度范围分别为1.12~64.04 ng·L-1、0(未检出)~4.24 ng·L-1,均值分别为(13.54±10.55)ng·L-1、(0.22±0.42)ng·L-1,各类型水体THg均以颗粒态为主,雨水和池塘水TMeHg以颗粒态为主,井水和沟渠水则相反.在空间分布上,THg表现为雨水最高,池塘次之,井水最低,W2井相较于其他井THg浓度最高,各沟渠点水体THg浓度差异不大;TMeHg表现为沟渠水最高,池塘次之,井水最低,井水TMeHg浓度下游大于上游,各沟渠点水体TMeHg浓度差异大,甲基化率为沟渠水>池塘水>井水>雨水.在时间变化上,各类型水体THg浓度均表现为冷季高于暖季,TMeHg浓度则因水体类型而异.综合分析发现雨水是流域内汞的重要来源;农田流域颗粒物的迁移是汞、甲基汞迁移的主要途径,地表径流是影响流域对水库汞负荷贡献量的重要因素.

The distribution of mercury (Hg) in four different water bodies (streams, pond, precipitation and wells) of a small typical agricultural watershed in the Three Gorges Reservoir region was studied during the period from November 2011 to September 2012. Total mercury (THg) and methylmercury (TMeHg) concentrations ranged from 1. 12 ng·L - 1 to 64. 04 ng·L - 1 and from 0(undetected) to 4. 24 ng·L - 1 , with an average of (13. 54 ±10. 55) ng·L - 1 and (0. 22 ± 0. 42) ng·L - 1 , respectively. Particulate mercury (PHg) accounted for a major fraction of THg in these four water bodies, whereas for TMeHg dissolved fraction dominated in wells and streams, but not in pond and precipitation. An obvious spatial pattern of Hg distribution was observed with THg concentration in the order of precipitation >pond > streams > wells and streams > pond > precipitation > wells for TMeHg. The THg temporal distribution showed that THg concentrations in cold season were higher than that in warm season, but the temporal distribution of TMeHg varied with the water types. Comprehensive data analysis found that wet deposition was a significant source of Hg in this agricultural watershed and the particulate transport was the main way for Hg and MeHg transport in this watershed. In addition, surface runoff was an important process for Hg contribution from watershed to the Three Gorges Reservoir, but played a minor role for TMeHg load to the reservoir.