三峡水库消落带土壤与优势植物淹水后对土-水系统汞形态的影响

三峡库区消落带落干期植被生长茂盛,蓄水后消落带被淹没,土壤-植物系统在长时间淹水情况下,随着体系内物理化学性质的改变,汞形态也会发生变化,从而对库区水生生态系统中汞含量以及形态带来一定的影响.为此,本研究选取三峡库区4种优势植物室内栽培,再进行室内模拟淹水试验,研究淹水后土壤、水体中甲基汞(Me Hg)以及其他形态汞的变化.结果表明,淹水过程中植物的存在有利于土壤Me Hg的生成,同时对上覆水不同形态汞浓度影响显著.狗牙根作为消落带优势种,由于其体内总汞及甲基汞含量较高,淹水后对土壤以及上覆水系统中甲基汞以及其他汞形态的影响最为明显.淹水第90 d,狗牙根+土+江水(B1)处理土壤Me Hg的含量最高,为(1 135.86±113.84)ng·kg~(-1),是不加植物的对照处理土+江水(CK2)中土壤Me Hg含量的2倍左右;上覆水总甲基汞(TMe Hg)、溶解态甲基汞(DMe Hg)、总汞(THg)、溶解态汞(DHg)和活性汞(RHg)均呈峰值偏左的抛物线状变化,在第30 d时达到峰值,其中B1处理上覆水TMe Hg、THg和DHg最高,分别为(2.88±0.06)、(40.29±2.42)和(35.51±3.77)ng·L~(-1),三者中溶解态汞是其主要存在形式.因此可以推测三峡库区消落带植物淹水后将增加水库汞污染负荷.

Effect of Soil and Dominant Plants on Mercury Speciation in Soil and Water System of Water-Level-Fluctuation Zone in the Three Gorges Area

Plentiful plants in the water-level-fluctuation-zone (WLFZ) of Three Gorges Reservoir (TGR) grow vigorously during the non-flooded period, especially the herbaceous ones. Then, the WLFZ is submerged gradually from the end of September. Soil-plant system that under a long time flooded condition may change the form of mercury, thus resulting in a secondary pollution of the water environment in TGR. To understand the characteristics of mercury species in soils and water after submerged, four kinds of typical plants from TGR were tested in the lab under submerged condition. The results indicated that the plants could promote the formation of soil methylmercury (MeHg), and had a significant effect on the different forms of mercury concentrations of the overlying water during inundation. Cynodon dactylon as the dominant species in WLFZ, because of its higher content of total mercury(THg) and methylmercury, the effect on MeHg and the other forms of mercury in the soil and the overlying water system was obvious.After 90 days, the soil MeHg level was the highest in Cynodon dactylon & soil & water treatment (B1)(1135.86±113.84) ng ·kg^-1]. It was approximately 2 times less than that of the soil MeHg in soil & water treatment (CK2).The variation characteristics of total mercury (THg), reactive mercury (RHg), dissolved mercury (DHg), total methylmercury (TMeHg) and dissolved methylmercury (DMeHg) of overlying water all showed a parabolic shape with a peak skewed to the left, and the peak was reached on the 30^th day. Meanwhile, TMeHg, THg and DHg in B1 treatment were the highest, which were (2.88±0.06),(40.29±2.42) and (35.51±3.77) ng ·L^-1 respectively, and TMeHg and THg in the overlying water were mainly in the form of dissolved state. Therefore, it could be inferred that the water consumption of the Three Gorges reservoir would increase the mercury pollution load of the reservoir.