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新东方网为大家带来2020托福听力练习：加固水坝有利鱼类繁殖（下载），希望对大家有所帮助!更多内容请随时关注新东方网!
In the early 19th century the fur industry reached what was then known as the Oregon Territories. Lewis and Clark found massive numbers of Pacific salmon and steelhead trout there, swimming among the beaver dams scattered across the Columbia River Basin.
But in an effort to starve American interests, Canada's Hudson's Bay Company tried to create a "fur desert" by killing off as many fur-bearing animals as they could. As a result, beavers had all but disappeared from the area by the year 1900. And once the beavers and their dams were gone, fish populations dropped.
Today, steelhead trout numbers in the region continue to fall. But scientists and government agencies are working to restore their habitats.
"We're looking for restoration approaches in these areas to recover ESA-listed species, but we really don't know what works and what doesn't." Nick Bouwes of the environmental consulting firm Eco Logical Research and Utah State University.
He says that the U.S. spends a billion dollars each year to restore watersheds, but without any real empirical information to guide those efforts. So Bouwes and his team tested the idea that by helping beavers, they could help the fish.
Dams naturally alter the flow of streams, providing fish with a variety of suitable habitats. But the watersheds have become so degraded that there's not enough woody vegetation available for the beavers to build strong dams. The flimsy ones they do build get washed away whenever there's a big storm.
"The idea was, can we reinforce these dams so that they maintain their integrity during high flows, and can be maintained by beavers to capture that sediment, to reconnect that floodplain?"
For seven years, the researchers compared Bridge Creek, which had lots of artificially strengthened dams, to Murderer's Creek, which had none. And in Bridge Creek, the fish flourished—despite the view held by some that beaver dams are bad for fish. The results are in the journal Scientific Reports.
"Beavers, they're really good at making a mess of a system, and it's that messiness that's exactly what we're looking for, by creating more complex fish habitat."
And costing just $11,000 for each kilometer of stream, artificial dam reinforcements are much cheaper than conventional restoration methods—since the beavers do most of the work for us. And that is a dam good deal.
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毛皮行业在19世纪早期进入到当时著名的奥勒冈领土。刘易斯和克拉克发现，大量的太平洋鲑鱼和硬头鳟在哥伦比亚河流域的海狸水坝中游来游去。
但是为了节制美国的利益，加拿大哈德逊湾公司试图创建一个“毛皮沙漠”，尽可能多地杀死毛皮类动物。因此，海狸在1900年时几乎消失殆尽。一旦海狸和它们创造出来的水坝都不见了，鱼类数量就会开始下降。
现在，该地区的硬头鳟数量仍在继续下跌。但是科学家和政府机构正在努力恢复它们的栖息地。
“我们正在这些领域寻找修复方法以恢复ESA名单上的物种，但我们真的不知道哪种方法有效，哪种方法没有作用。”这是环境咨询公司生态研究公司和犹他州立大学的研究人员尼克·鲍威斯所说。
他说，美国每年在恢复流域方面花费10亿美元，但是没有任何实证信息来指导这些努力。所以鲍威斯和他的团队测试了通过帮助海狸来帮助鱼类的办法。
大坝可以自然地改变河流的流动，为鱼类提供各种合适的栖息地。但由于水域质量严重下降，导致没有足够的木本植物供海狸建造坚固的水坝。只要有大风暴来袭，它们建造的劣质水坝就会被冲走。
“我们的想法是，能不能通过加强这些水坝使它们在高流动性期间保持完整性，由海狸采集沉积物去填补洪泛区来保持完整性?”
七年来，研究者将有过很多人工加固水坝经历的Bridge Creek与没有人工加固水坝经历的Murderer's Creek,相比较。虽然有观点认为海狸水坝对鱼类有害，不过在Bridge Creek，鱼类大量繁殖起来。这项研究成果刊登在《科学》杂志上。
“海狸非常擅长扰乱系统，而这种干扰正是我们所需要的，因为这样能创造出更多复合鱼类栖息地。”
与传统修复方法相比，每公里河流只需花费1.1万美元的人工加固大坝更加便宜，因为海狸为我们做了大部分工作。这是一桩相当划算的交易。
重点讲解：
1. kill off 全部杀死;灭绝;
例句：his spray will kill off any pests or insects.
这种喷雾能够消灭任何的害虫或者昆虫。
2. as a result 结果;后果;
例句：As a result, daily output has doubled.
结果日产量翻了一番。
3. wash away 冲垮;冲走;
例句：Flood waters washed away one of the main bridges in Pusan.
洪水冲垮了釜山的一座主要桥梁。
4. be good at 擅长的;精通的;能干的;
例句：I'm pretty good at water skiing.
我对滑水橇很在行。
以上是新东方网为大家带来的2020托福听力练习：加固水坝有利鱼类繁殖（下载），希望认真积极的备考，早日取得优异的成绩。更多内容请随时关注新东方网!
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