高原湿地汞在生物链中的富集及传递特征-以贵州草海为例

Wetlands are sensitive ecosystems for methylation and biomagnification of mercury. Caohai wetland, located in Guizhou, is National Nature Reserve. Caohai wetland consists of various landscapes including deep water area, swamp, cyperus rotundus wetland and marshy grassland. Caohai is also rich in aquatic animals and plants resources，known as "kingdom of birds". Recent studies indicated that the sediment of Caohai had been polluted by Hg distinctly, which may lead to big challenge to the local wild animals and plants resources. In order to understand ecosystem risk of mercury in sediment and bioaccumulation features of mercury in food chains, the following researches will be carried: (1) In order to understand distribution features and ecological risk of mercury in ecosystem of Caohai wetland, total mercury and methylmercury will be measured in water, sediment and organisms in Caohai. (2) The bioavailability of mercury in the sediment and bioconcentration mechanisms of mercury in benthos will be studied by analyzing Hg(II) speciation in sediments and the digestive solubilization of mercury, as well as mercury exposure experiment of benthos. (3)The trophic levels and food sources of aquatic organisms will be identified using the stable isotopes of carbon and nitrogen. In combination with mercury concentrations in aquatic organisms and mercury isotope composition of organisms in typical food chains, transferring and bioaccumulation of mercury in food web will be studied. This study will be of great importance to understand geochemical cycling of Hg and to direct pollution control policy in wetlands of SW China.

湿地生态系统是汞甲基化及生物富集的敏感系统。贵州草海湿地为国家自然保护区，包括水域、沼泽、湿地和草甸，水生动植物种类丰富，素有"鸟的王国"之称。近年研究表明，草海沉积物遭受了较为严重的汞污染，对草海野生动植物造成威胁。为弄清草海汞污染沉积物的生态风险及汞在生物链中的传递特征，本项目拟开展以下研究：（1）通过测定草海湿地系统中水、沉积物、各类生物样品中汞和甲基汞，弄清草海湿地系统汞分布规律并评估其生态风险。（2）通过沉积物汞赋存形态分析，并结合体外消化液提取及底栖动物汞暴露实验，从多角度研究草海污染沉积物汞的生物有效性及底栖动物汞富集的影响因素。（3）利用碳氮同位素技术，弄清草海食物网中主要生物的营养结构及主要消费者的食物来源，结合各生物样品中汞及典型食物链中汞同位素组成探明汞在复杂食物网中的传递和富集过程。该研究对了解我国西南高原湿地汞的地球化学循环和污染防治具有重要的科学和现实意义。

湿地生态系统是汞甲基化及生物富集的敏感系统。本项目通过系统采集并测定草海各类样品中汞和甲基汞含量，弄清了草海湿地系统汞分布规律及其生态风险。通过沉积物汞赋存形态分析及底栖动物汞暴露实验等，从多角度研究了草海沉积物汞的生物有效性。利用碳氮同位素技术，结合典型食物链中汞同位素组成探明了汞在食物链中的传递和富集过程。主要得到以下研究结果：.（1）沉积物总汞及甲基汞浓度分别在 36.5~236.7 ng·g-1 和 0.02~1.07 ng·g-1 之间。水生植物总汞及甲基汞含量范围分别在5.18~40.06ng/g和 0.04~2.47ng/g（干重）之间。底栖动物、鱼类总汞及甲基汞含量范围分别在0.51~68.22ng/g和0.04~36.53ng/g之间；浮游生物总汞及甲基汞含量范围在27.03~624.50ng/g和0.02~173.55ng/g干重）之间；鸟类羽毛总汞及甲基汞分别在40.41~5057.76ng/g和0.75~112.63ng/g（干重）之间。部分肉食性鸟类汞含量超过或接近鸟类繁殖出现异常的阈值（5ug/g）, 表明草海部分鸟类面临一定的生态汞污染风险。.（2）通过系统对比草海深水域及浅水域中沉积物和生物样品中汞含量, 发现中间深水域沉积物总汞含量明显高于周边浅水域沉积物总汞含量。相反，周边沉积物甲基汞含量明高于中间深水域；且周边浅水域水生植物及底栖动物汞含量也明显高于中间深水域，表明周边浅水域汞的甲基化及汞的生物可利用性远高于中间深水域。沉积物总汞与有机质含量呈明显正相关性，周边浅水域的强络合有机结合态比例明显低于中间深水域，与沉积物总汞分布规律一致，但周边浅水域富里酸结合态汞比例却明显高于中间深水区域，表明周边浅水域沉积物中更高的富里酸结合态汞促进了汞的甲基化及生物可利用性。模拟实验结果表明，草海中间沉积物汞的生物可利用性也比周边沉积物高；在不同配方沉积物中，不含腐殖酸沉积物中汞的生物可利用性最低。.（3）草海沉积物及生物样品中δ13C值和δ15N值的变化范围分别为-30.44‰~-11.66‰和-1.88‰~20.68‰。 在典型食物链中，δ199 (‰)、Δ199(‰)及Δ201(‰)有向食物链顶端富集的趋势，表明在汞在食物链富集过程中，存在着汞同位素的质量和非质量分馏。非质量分馏Δ199 (‰)/Δ201(‰)比值约为1.1