TPO 28 - Question 6

A sample Answer to this speaking in text:

The professor talks about two ways lakes disappear. The first way is by natural processes. Plants are growing in the lake. When they die, they become muddy substance and fall into the bottom of the lake. Then new plants grow and die and the muddy substance will accumulate. Gradually, the lake will be filled with muddy substance and there is no room for water. The second way is by human activities. Farmers need water to irrigate their fields so they use pump to get water from the lakes. If the lakes don’t have enough refill. Say if there is not enough rain or there is no stream to come into the lakes, the lakes will eventually dry up.

1. So, when we look at lakes, they seem to be permanent, we assume they'll be around forever.
2. But in fact, lakes aren't permanent; they can actually disappear.
3. Sometimes they disappear through natural processes, and sometimes because of human activities.
4. First let's look at one way that lakes can disappear naturally, and that is, by gradually getting filled in with organic sediment.
5. This often happens with lakes that have lots of plants growing in them.
6. When the plants die, they break down into a muddy substance, which falls to the bottom of the lake, they're then replaced by new plants, which eventually also die and fall to the bottom.
7. And over the years, all this dead plant material builds up on the bottom of the lake, and as builds up, it starts to fill up the lake, and there's less and less room for water, and eventually the lake gets completely filled in, and disappears.
8. OK, lakes can also disappear, pretty rapidly sometimes, as a result of human activities.
9. For example, we know that farmers need water to irrigate their crops.
10. And sometimes to get that water, they pump that water out of a nearby lake.
11. They install pipes that run from the lake to their farms, and they pump the water out of the lake and into their fields.
12. Now that's ok if the lake is continually being refilled with rainwater or with water from streams that run into the lake, but if there isn't enough rainwater or stream water to replace the water the farmers take out of the lake, the lake will eventually dry up.