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第1段
1 .<-NARRATOR:-> Listen to a part of a lecture from a geology class.
请听地理课上的部分内容。
第2段
1 .<-FEMALE PROFESSOR:-> So, when we look at lakes, they seem to be permanent, we assume they'll be around forever.
我们在看待湖泊时，总是觉得它们似乎是永恒的，总是以为它们会永远存在。
2 .But in fact, lakes aren't permanent.
但是事实上，湖泊并不是永恒存在的，
3 .They can actually disappear.
它们实际上也会消失。
4 .Sometimes they disappear through natural processes and sometimes because of human activities.
有时候它们会随着自然过程而消失，有时会因为人类活动而消失。
第3段
1 .First, let's look at one way lakes can disappear naturally.
首先让我们来看看湖泊自然消失的方式，
2 .And that is by gradually getting filled in with organic sediment.
那就是渐渐被有机沉淀物填满的方式。
3 .This often happens with lakes that have lots of plants growing in them.
这种情况通常发生在有许多植物生长在其中的湖泊上。
4 .When the plants die, they break down into a muddy substance, which falls to the bottom of the lake.
当植物枯萎时，它们就会分解成泥状物质，沉到湖底。
5 .They're then replaced by new plants, which eventually also die and fall to the bottom.
然后就会被新的植物所代替，而这些新的植物最终也会枯萎并沉入湖底。
6 .And over the years, all this dead plant material builds up on the bottom of the lake.
许多年后，所有这些枯萎的植物便会在湖底不断堆积，
7 .And, as it builds up,
在堆积过程中
8 .it starts to fill up the lake,
它们便会开始充填湖泊，
9 .and there's less and less room left for water ...
而湖水所占空间也会越来越少，
10 .And eventually, the lake gets completely filled in.
当湖泊最终完全被填满时，
11 .And disappears.
它就消失了。
第4段
1 .OK. And lakes can also disappear¡ª
好了，有时候湖泊
2 .pretty rapidly sometimes¡ª
也会由于人类的活动
3 .as a result of human activities.
迅速消失。
4 .For example, we know that farmers need water to irrigate their crops.
比如，我们都知道农民需要水来灌溉庄稼。
5 .And sometimes, to get that water, they pump the water out of a nearby lake.
有时候为了获取水源，他们会从附近的湖泊中抽水出来。
6 .They install pipes that run from the lake to their farms, and they pump the water out of the lake and into their fields.
他们在湖泊和农田之间拉起水管，然后把湖里的水抽上来，湖水就会顺着水管流入他们的田里。
7 .That's OK if the lake is continually being refilled with rainwater,
如果这片湖泊能够持续被雨水
8 .or with water from streams that run into the lake.
或者汇入的溪水补充的话，也并无大碍，
9 .But if there isn't enough rainwater or stream water to replace the water the farmers take out of the lake,
但是如果没有足够的雨水或溪水来替代被农民抽出的湖水的话，
10 .the lake will eventually dry up.
这片湖泊将会渐渐枯竭。