网箱养鱼对水库水体甲基汞的影响

分别在2010年9月(暖季)和2011年3月(冷季),选取乌江渡水库网箱养鱼区和距离网箱100～200m的对照区(库心),对水体不同形态汞及其他相关参数进行了研究,以揭示网箱养鱼对水库汞地球化学行为的影响。结果表明,暖季养鱼区水体总汞含量为(2.04±0.53)ng·L-1,甲基汞含量为(0.146±0.231)ng·L-1,对照区水体总汞含量为(3.33±2.39)ng·L-1,甲基汞含量为(0.380±0.577)ng·L-1;冷季养鱼区水体总汞含量为(3.04±1.53)ng·L-1,甲基汞含量为(0.047±0.028)ng·L-1,对照区水体总汞含量为(3.24±1.23)ng·L-1,甲基汞含量为(0.046±0.013)ng·L-1;养鱼区与对照区总汞含量(n=35,P=0.875)、甲基汞含量(n=35,P=0.091)均无显著差异。结合对养鱼区与对照区水体中其他各参数(总氮、总磷、溶解性有机碳、叶绿素、温度、溶解氧等)综合分析表明,由于水库蓄水与泄水发电对水库水体的扰动及水库自身水体的交换作用导致水体呈混匀状态,网箱养鱼造成的水体甲基化程度差异不显著;而水库水体季节性分层造成的水体底部厌氧和温度的变化是影响水体甲基汞含量及分布的主要因素之一。

Influence of cage culture on methylmercury in water column of reservoir

To understand the influence of cage culture on the methylmercury production and distribution in water column of reservoir,water samples were collected from four cage culture sites in Wujiangdu Reservoir in September(warm season),2010 and in March(cool season),2011,taking the sites with a distance of 100-200 m from the culture sites and at the center of the reservoir as the reference sites.In warm season,the total mercury(THg) and methylmercury(MeHg) concentrations in cage culture sites were 2.04±0.53 ng·L-1 and 0.146±0.231 ng·L-1,and those in reference sites were 3.33±2.39 ng·L-1 and 0.380±0.577 ng·L-1,respectively;in cool season,the corresponding values were 3.04±1.53 ng·L-1 and 0.047±0.028 ng·L-1,and 3.24±1.23 ng·L-1 and 0.046±0.013 ng·L-1,respectively.No significant differences were observed in the concentrations of THg and MeHg(for THg,n=35,P=0.875,and for MeHg,n=35,P=0.091) between cage culture sites and corresponding reference sites.The analysis on the water parameters total phosphorus,total nitrogen,dissolved organic carbon,temperature,and chlorophyll-a at the cage culture sites and reference sites showed that the MeHg production and distribution in the water column were affected by the water discharge and water exchange activities in the reservoir rather than by the cage culture activities,whereas the anaerobic condition of bottom water and the variation of water temperature caused by the seasonal stratification of water column could be the main factors affecting the methylmercury production and distribution.