贵州草海底栖动物汞分布及其对沉积物汞的响应特征

以国家自然保护区贵州草海湿地为研究对象,系统采集草海湖中深水区和湖边浅水区生长的底栖动物,测定其总汞和甲基汞,探讨底栖动物汞和甲基汞分布特征及其对沉积物汞的响应特征,并评估了其面临的汞污染风险.结果表明,底栖动物总汞含量范围为0.51~46.55 ng·g~(-1)(均值7.82 ng·g~(-1)),甲基汞含量范围为0.04~27.71 ng·g~(-1)(均值4.31 ng·g~(-1)),低于其他自然保护区报道的底栖动物的汞含量.对比发现,夏季底栖动物总汞和甲基汞含量均高于其他季节;湖边点底栖动物总汞和甲基汞含量均高于湖中点同种类底栖动物汞含量,这与沉积物中甲基汞含量的空间分布特征一致,却与沉积物总汞含量空间分布特征相反,且中华圆田螺甲基汞含量与沉积物甲基汞含量呈显著相关(r=0.52,P0.05),表明湖边浅水区沉积物汞的甲基化程度、生物可利用性都明显高于湖中深水区.湖中湖边沉积物有机质的含量差异以及湖边沉积物存在干湿交替可能导致了这种明显的差异.底栖动物对水体或沉积物总汞和甲基汞的富集系数均较高,这些高富集系数足以引起对草海湿地水生食物链中汞污染风险的重视.

Mercury Distribution of Benthonic Animals and Response to Mercury in Sediments in Caohai Wetland, Guizhou Province

Caohai wetland is a National Nature Reserve. Benthic animals were collected from the deep-water area in the middle of Caohai Lake and the shallow-water area in the surrounding marshes, and mercury and methyl mercury distributions in the benthic animals were analyzed and discussed. The risk of mercury pollution was evaluated. The concentrations of total mercury and methyl mercury in the benthonic animals were in the range of 0.51-46.55 ng·g^-1 with an average of 7.82 ng·g^-1 and 0.04-27.71 ng·g^-1 with an average of 4.31 ng·g^-1, respectively. This was lower than reports from other natural reserves. By contrast, the total mercury and methyl mercury in the benthic animals in summer were higher than in other seasons, which was consistent with the characteristics of methyl mercury distribution in sediments but opposite to the spatial distribution characteristics of total mercury in sediments. The methyl mercury contents in Cipangopaludina cathayensis were positively correlated with the content of methyl mercury in the sediments (r=0.52, P<0.05). The results showed methylation and the bioavailability of mercury in sediments from the shallow-water area were obviously higher than those from the deep-water area in the middle of Caohai Lake. The difference in organic matter content of the sediment or the wet-dry alternation (flooding-receding-flooding) in the surrounding shallow marshes was suspected to be associated with the obvious difference. The high enrichment coefficient of total mercury and methyl mercury in benthic animals were sufficient to raise the risk of mercury contamination in the aquatic food chain in the wetland.