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当前位置: Science » 植物&动物 » Science:海狸池塘会加大下游水域的汞含量


摘要 : 加拿大的海狸水坝改变了风景,把涓涓溪流变成了静止的池塘和洪泛的森林。而今,研究人员发现这些水坝带来的改变还不止这些。瑞典的科学家已经证明,海狸池塘能够在夏季使下游水流中的甲基汞水平升高至基准水平的3.5倍——甲基汞是一种带巨毒的汞。


加拿大的海狸水坝改变了风景,把涓涓溪流变成了静止的池塘和洪泛的森林。而今,研究人员发现这些水坝带来的改变还不止这些。瑞典的科学家已经证明,海狸池塘能够在夏季使下游水流中的甲基汞水平升高至基准水平的3.5倍——甲基汞是一种带巨毒的汞。虽然汞是一种自然存在于环境中的神经毒素,但当人们燃烧煤炭等化石燃料时,也会向大气中释放汞。一旦汞通过某种方式回到陆地或水中,土壤中的细菌便能够把它转换成它更具毒性的“近亲”,即甲基汞。正如研究人员上个月在《环境科学与技术》网络版上所报告的,这种细菌滋长于堆积在海狸水坝后部的那些富含腐烂植被的积水沉积物中。但甲基汞的上升似乎是暂时的。令人惊讶的是,在海狸搬回旧水坝时这种情况不会发生:研究中,重新被海狸占领的 水坝其上下游的甲基汞水平几乎相同 。科学家们说,这可能意味着水下那些供养细菌的植物最后腐烂消失了,没给细菌留下什么食物。他们还补充说,该研究结果为欧洲和北美保留老水坝的做法提供了支持,因为 海狸们正在重回这些水坝 ——在过去150多年间,它们的数量已急剧下降。接下来,研究人员希望可以弄明白甲基汞是如何在生态系统中循环,以及它们是否会在鱼类和其它生物中聚积。


Beaver ponds boost mercury levels downstream


Beaver dams transform landscapes, turning stretches of flowing streams into still ponds and flooding forests. Now, researchers have found the dams are transformative in more ways than one. Scientists in Sweden have shown that beaver ponds can cause levels of methylmercury—a particularly toxic form of mercury—to rise in downstream waters by as much as 3.5 times the background levels during summer months. Although mercury, a neurotoxin, occurs naturally in the environment, it is also released into the atmosphere when humans burn coal and other fossil fuels. once it finds its way back to land or water, bacteria in the soil can convert it into its more toxic cousin, methylmercury. As the researchers reported online last month in Environmental Science & Technology, this kind of bacteria thrives in the waterlogged sediments, rich with decaying vegetation, that pile up behind beaver dams. But the increase in methylmercury appears to be temporary. Surprisingly, it doesn’t occur when beavers move back into old dams: Methylmercury levels above and below recolonized dams were nearly identical in the study. This could mean the submerged vegetation that was feeding the bacteria finally rotted away, leaving them with less food, scientists say. They add that their findings support the practice of leaving old dams in place in Europe and North America wher beavers—whose numbers have plummeted over the last 150 years—are making a comeback. Next, the researchers hope to figure out how methylmercury works its way through the ecosystem and whether or not it’s accumulating in fish and other organisms.

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