托福tpo53听力lecture2 Two Kinds of Pollution

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Two Kinds of Pollution托福听力原文翻译及问题答案

一、Two Kinds of Pollution托福听力原文：

NARRATOR:Listen to part of a lecture in an environmental science class.FEMALE PROFESSOR:The Chesapeake Bay,on the east coast of the United States,is huge—the largest estuary in the U.S.—and it's very important to local economies.

But,like many of the world's waterways,the Chesapeake is being polluted;and efforts to stop that from happening have not been entirely successful.And that's partly because of the type of pollution affecting the Chesapeake…which may not be what you might predict.

Uh,first let's mention that the sources of pollution are of two general types.And let’s begin with what's known as“point source pollution”Point source pollution has an identifiable source,and you can find the specific point where,say,one particular pipe is dumping pollutants into the bay—and then treat the water right there where the pollution’s coming from.

And that's what's happened over the past 30 years or so.Modifications have been made at factories and sewage treatment plants to treat polluted water before it's released into public waterways.But there's also something we call“non-point source pollution.”

Nowadays,the most serious pollution threat doesn’t come from any particular source,like a factory or sewage treatment plant,but originates from many sources over a large area.And this non-point source pollution is a challenge to deal with,because it doesn’t just enter the bay through one pipe—you can't identify precisely where it's coming from.

And to be specific,the biggest problem now facing the Chesapeake Bay is due not to toxins,but to nutrients contained in chemical fertilizers used on farms all over the region.These nutrients—like phosphorus and especially nitrogen—wash away in what we call agricultural runoff.That’s when water from a hard rain or from melting snow carries these chemicals down to streams and into the bay,

and there they stimulate the explosive growth of algae.And that uses up much of the oxygen in the water,oxygen that fish and other aquatic organisms need to stay alive.So,since there's no single place you can treat the runoff before it reaches the bay,any efforts to reduce this non-point source pollution generally need to be aimed at keeping pollution out of the streams in the first place.

But before we go into that,let's look at the role of nitrogen fertilizer in modern farming.Until about 60 years ago,before a great increase in industrialization,this wasn’t a problem.In the past,farmers used natural fertilizers and rotated crops so that,in addition to commercial food crops,like corn and wheat,they might plant legumes,like alfalfa and clover,for animal feed.

But these legumes also enriched the soil—by converting nitrogen in the atmosphere into nitrates—a form of nitrogen the crops like wheat or corn could use as a nutrient.And,these and other“cover crops,”planted to hold the soil after the wheat or corn was harvested—they stored much of the surplus nitrogen during the time of the year when the runoff tended to be greatest.But farming practices changed as farmers came under pressure to use more and more chemical fertilizer in order to increase crop production on the same amount of land.But more isn’t always better,at least in terms of chemical fertilizer in the environment.And,along the way,farmers switched from legumes…to animal feeds more suited to intensive,large-scale animal production.

And the excess nitrogen,once trapped by these cover crops,either washed away in the next big rain or went down into the groundwater and,either way,eventually ended up in the streams and the bay.And that,as we said,means more algae in the water and less oxygen for the fish and other aquatic life to breathe.

So what’s being done?Well,two things.

First,after the main crops are harvested,more farmers are planting cover crops again—other kinds,like rye and barley—that hold the nitrogen and keep it from washing out of the soil during the months when that’s most likely to occur.And the second strategy is to plant“buffer zones”at the edges of streams—not crops,but natural areas…trees.The roots of these trees can absorb the excess nitrogen in the runoff before it reaches the streams.Farmers sometimes object to letting trees grow on land where they might otherwise be cultivating crops.But there’s a government program that compensates them,that pays them for creating these buffer zones between their fields and the streams that eventually feed into bays like the Chesapeake.And it's beginning to show some success.

二、Two Kinds of Pollution托福听力中文翻译：

旁白：听一节环境科学课上的讲座。女教授：切萨皮克湾位于美国东海岸，是美国最大的河口，对当地经济非常重要。

但是，像世界上许多水道一样，切萨皮克正在受到污染；阻止这种情况发生的努力并没有完全成功。这部分是因为影响切萨皮克的污染类型……这可能不是你所能预测的。

呃，首先让我们提到污染源有两种类型。让我们从所谓的“点源污染”开始，点源污染有一个可识别的来源，你可以找到一个特定的点，比如说，一条特定的管道将污染物倾倒到海湾中，然后在那里处理污染来源的水。

这就是过去30年左右发生的事情。工厂和污水处理厂已经进行了改造，以便在污水排入公共水道之前对其进行处理。但也有一些我们称之为“非点源污染”

如今，最严重的污染威胁并非来自工厂或污水处理厂等任何特定来源，而是来自大面积的许多来源。这种非点源污染是一个需要解决的挑战，因为它不仅仅是通过一条管道进入海湾，你无法准确识别它的来源。

具体来说，切萨皮克湾目前面临的最大问题不是毒素，而是该地区农场使用的化肥中所含的营养素。这些营养物质，如磷，尤其是氮，在我们所称的农业径流中被冲走。当大雨或融化的雪带来的水将这些化学物质带到小溪和海湾时，

在那里它们刺激藻类的爆炸性生长。这消耗了水中的大部分氧气，鱼类和其他水生生物生存所需的氧气。因此，由于没有一个地方可以在径流到达海湾之前对其进行处理，任何减少这种非点源污染的努力通常都需要首先将污染控制在溪流之外。

但在我们开始之前，让我们看看氮肥在现代农业中的作用。直到大约60年前，工业化大幅度增长之前，这还不是一个问题。过去，农民使用天然肥料和轮作作物，因此除了商业粮食作物，如玉米和小麦，他们还可以种植豆类，如苜蓿和三叶草，作为动物饲料。

但这些豆科植物也通过将大气中的氮转化为硝酸盐来丰富土壤，硝酸盐是小麦或玉米等作物可以用作养分的一种氮。而且，这些和其他“覆盖作物”在小麦或玉米收获后种植以保持土壤，它们在一年中径流最大的时候储存了大量剩余氮。但是，随着农民面临越来越多的化肥使用压力，为了在同样数量的土地上增加作物产量，农业做法发生了变化。但更多并不总是更好的，至少在环境中的化肥方面。一路上，农民们从豆类转向更适合集约化、大规模动物生产的动物饲料。

而过量的氮一旦被这些覆盖作物吸收，要么在下一场大雨中被冲走，要么流入地下水，最终流入溪流和海湾。正如我们所说，这意味着水中的藻类增多，鱼类和其他水生生物呼吸的氧气减少。

那么正在做什么？嗯，有两件事。

首先，在主要作物收获后，更多的农民种植其他作物，如黑麦和大麦，这些作物可以保持氮，并在最有可能发生氮流失的月份防止氮从土壤中冲走。第二个策略是在溪流边缘种植“缓冲区”，而不是作物，而是自然区域……树木。这些树的根部可以在径流到达溪流之前吸收多余的氮。农民有时反对让树木生长在他们可能种植作物的土地上。但有一项政府计划对他们进行补偿，为他们在田地和河流之间建立缓冲区，最终流入切萨皮克湾等海湾提供资金。它开始显示出一些成功。

三、Two Kinds of Pollution托福听力问题：

Q1:1.What is the lecture mainly about?

A.The difference between point source and nonpoint source pollution

B.The source and treatment of a serious type of pollution affecting the Chesapeake Bay

C.The causes for the large decrease in algae in the Chesapeake Bay

D.The development of farming methods during the past century

Q2:2.What is one of the reasons that the professor mentions pollution that comes from a pipe?

A.To compare point source pollution with nonpoint source pollution

B.To blame factories and sewage treatment plants for producing most water pollution

C.To demonstrate that agricultural runoff is a point source pollutant

D.To suggest new methods that may someday begin to reduce water pollution

Q3:3.According to the professor,why has it been difficult for fish and many other organisms to live in the Chesapeake Bay?

A.Toxic chemicals in the water have poisoned many of them.

B.Runoff from farmland has made the water very muddy.

C.Water flow from streams has been unreliable.

D.Oxygen levels in the water have been reduced.

Q4:4.What is the professor's attitude about the use of chemical fertilizer?

A.She is surprised that some farmers have stopped using it.

B.She is convinced that its use should be increased substantially.

C.She worries that farmers may be using too much of it.

D.She regrets that it was not more useful for increasing crop production.

Q5:5.What two practices does the professor suggest for reducing the amount of nitrogen that enters a bay such as the Chesapeake?[Click on 2 answers]

A.Planting trees along the sides of streams

B.Building water treatment facilities where streams enter the bay

C.Planting cover crops that take up excess nitrogen in the soil

D.Letting farm animals graze in areas near streams and the bay

6.According to the professor,why were farmers reluctant to create buffer zones near streams?

A.They were not convinced that buffer zones effectively control pollution.

B.They feared that creating buffer zones might decrease farm income.

C.Government approval for creating buffer zones was at first difficult to obtain.

D.Planting trees was much more expensive than planting the usual crops.

四、Two Kinds of Pollution托福听力答案：

A1:正确答案：B

A2:正确答案：A

A3:正确答案：D

A4:正确答案：C

A5:正确答案：AC

A6:正确答案：B

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