(单词翻译:单击)
听力文本
From VOA Learning English, this is the Agriculture Report.
An area known as a dead zone develops every spring in the Gulf of Mexico near the mouth of the Mississippi River. It can spread as much as 13,600 square kilometers, extending all the way to the eastern Texas coast. Scientists know what causes the dead zone -- too much nitrogen, but the solution might be hard to accept.
Bayani Cardenas is a professor of water studies at the University of Texas at Austin. He says the movement of rivers usually removes material like nitrates. So he wondered why that natural filtration process does not remove nitrates from the Mississippi River.
Professor Cardenas says his recent study shows that more than 99 percent of the river's water does pass through the river's sediment which is on the shore or bottom of the river. But he says the study found that there is so much nitrogen in the river system that is simply can not filter all of it.
The water that has nitrogen still in it supports the growth of algae. As the algae dies, it sinks to the bottom of the river where it breaks down or decomposes. It then takes oxygen from the water. This condition is called hypoxia and it is deadly to fish and shrimp.
Where does all this nitrogen come from? The answer is farms. The Mississippi River system carries water from 33 American states and part of Canada to the gulf of Mexico. Along the way nitrogen and other chemicals used in farming enter the system. Farmers say these chemicals must be used to produce enough food for a growing world population.
Aaron Packman is a professor of Civil and Environmental Engineering at Northwestern University. He says farmers may be able to better control the amount of nitrate fertilizer they put on fields.
"How much fertilizer do you need to give you good yields and then how much is maybe a marginal gain from adding lots more fertilizer? There is really a question here: can you maybe [reduce the amount] and get close to the same level of yield without having such a negative impact?" said Packman.
The water in the Mississippi River system should be able to clean itself naturally as it flows down stream. But flood controls and other human-made structures have hurt this filtering process.
Storms in the next few month will mix the gulf water and the dead zone will disappear, but it will return next year. And scientists say it will grow larger in years to come, if something is not done to reduce the amount of nitrogen in the Mississippi River.
And that's the VOA Learning English Agriculture Report. For more agriculture stories, go to our website learningenglish.voanews.com. I'm Caty Weaver.
文本来自51voa，译文属可可原创，仅供学习交流使用，未经许可请勿转载
词汇解释
1.nitrate n. 硝酸盐 vt. 用硝酸处理
High levels of nitrate occur in the Midwest because of the heavy use of fertilizers.
因为大量使用化肥，中西部地区的硝酸盐含量很高。
2.filtration n. 过滤；筛选
This enzyme would make the filtration of beer easier.
这种酶会使啤酒更容易过滤。
3.decompose vi. 分解；使腐烂 vt. 分解；腐烂
The debris slowly decomposes into compost.
这堆碎屑慢慢地分解变成了堆肥。
4.hypoxia n. [医] 低氧；组织缺氧；氧不足
The oxygen sensing process enables animals to survive better at low oxygen levels, or 'hypoxia'.
这种氧感受机制使动物能在低氧或‘缺氧’条件下更好地生存。
5.marginal adj. 边缘的；临界的；末端的
This is a marginal improvement on October.
这是对10月份的一个小小的改进。
内容解析
1.As the algae dies, it sinks to the bottom of the river where it breaks down or decomposes.
break down 分解；发生故障；失败；毁掉；制服
Talks with business leaders broke down last night.
与商界领导人的谈判于昨晚失败了。
Over time, the protein in the eggshell breaks down into its constituent amino acids.
随着时间的推移,蛋壳中的蛋白质分解成其构成成分氨基酸。
参考译文
这里是美国之音慢速英语农业报道。
墨西哥湾的密西西比河河口的一个地方每年春天都会成为死水区，能扩散到13600平方公里，一直延伸到德克萨斯州东部沿海。科学家知道死水区的形成原因是含氮量太高，但解决方案难以被人接受。
巴雅尼·卡德纳斯是得克萨斯大学奥斯汀分校的水文研究教授，他说河流的移动通常会去掉硝酸盐等物质，所以他想知道为何自然的过滤过程不能将硝酸盐从密西西比河中移除掉。
卡德纳斯教授说他最近的研究表明99%以上的河水能通过河岸边或河床的沉积物，但他说研究发现河流系统的氮太多，无法完全过滤掉。
仍然富含氮的水能支持藻类的生长，藻类死亡后沉淀到河流的底部，然后分解，这样就从水中吸去氧气，这个过程叫做缺氧，这对鱼类和虾来说是致命的。
这些氮是哪里来的呢？答案是农场。密西西比河流域流经美国33个州和加拿大部分地区，一直流到墨西哥湾。一路上农场里的氮等化学物质流入水域，农民们说必须使用这些化学物质来生产食物，以满足日益增长的世界人口。
亚伦·帕克曼是美国西北大学土木与环境工程学教授，他说农民们也许能控制投放到田地里的氮肥量。
“多少氮肥才能获得好的收成呢？增加肥料的边际效益是多少呢？问题在于，如何在不产生负面影响的情况下减少施肥量，同时又达到同样好的产量呢？”
密西西比河水域的水在向下流的时候应该能够进行自洁，但防洪和其他人造设施破坏了这个过滤过程。
未来数月的暴雨将流入墨西哥湾水域，死水区将消失，但明年将再次出现。科学家说如果不采取措施减少密西西比河的含氮量，未来几年死水区的面积会扩大。
这就是美国之音慢速英语农业报道，登陆learningenglish.voanews.com获得更多农业报道，我是凯蒂·韦弗。
