字幕列表 影片播放 列印英文字幕 Hi. It's Mr. Andersen and this is environmental science video 5. It is on water resources. Our body is filled with over 60 percent water. And this does not seem like a big deal because the earth is covered with over 70 percent water. The problem with that is that most of that is sea water that we cannot use. And the freshwater that remains, most of it is going to be frozen in ice caps and glaciers. And so the percent that is really fresh water on the surface is a small percent of the water on our planet and it is finite. The amount of water we have on our planet has never changed. Now as the sun provides energy to the earth the water will move around through the hydrologic or the water cycle but we have a finite amount of water. And most of it is going to be sea water. We have a little bit of fresh water. The sea water moves around through ocean currents. The fresh water could be divided into ground water, water underneath the surface and then surface water which is on the surface. Now we need that water. We need it domestically in the home to take a shower or to drink. But we also need it in industry to make our goods. And most of it actually goes to agriculture to make the food that we eat. The problem with water on our planet is that it is unevenly distributed. In some areas there is lots of water. In some areas however there is going to be scarcity. And so humans have had to learn how to store water, move it around and in the future we may have to desalinate some of that sea water so that we can use it as fresh water. Now where is that ground water stored? It is underneath the ground in aquifers that we can deplete. What about the surface water? Well it can be stored in reservoirs that occur naturally or ones that are created as we produce dams. And then we can move it around through aqueducts and even to the planet itself through irrigation. But we have a finite amount and so conservation is incredibly important. And economics have contributed to water loss and could help us to actually solve this water conservation problem. And so the hydrologic cycle works like this. Anywhere there is water on the surface we can have evaporation. That gets cooled and eventually leads to condensation and precipitation. Once it is on the surface we call that surface water. It is running over the surface. That could be lakes and swamps and rivers. After we have that water hit the ground it can however be infiltrated into the soil and the ground itself. To give you an example of that imagine I have a beaker here. Is it full? Well maybe full of air. If I put marbles in it, is it full? No you can see there is spaces in it. What if I fill it up with sand? Is it full? No. There is still spaces in there. If I fill it up with water now we are starting to fill up that beaker. And that is what infiltration is. As the water flows down into the soil we call that now ground water. Let's say it is not filling that whole beaker. It is right here. That point at which we have saturation in the ground water is called the water table. Most of our planet is covered with water, unfortunately it is seawater. It has salt dissolved in it. If you drink it you will die. If we put it on our fields the crops are going to die. Now it moves around using currents. We talked about that in the last video on the atmosphere, it is cells in the atmosphere and coriolis effect. So we have these general trends in circulation. But also salinity affects it. And so if we look at an area right here it is a high salt concentration because we have a lot of evaporation. But up here we have a lot of melting of that glacial ice. And so we are going to have a low salt concentration. And so the salt concentration and differences in heat create these thermohaline circulations that really make that whole ocean on our planet one system. Now if we look at fresh water it can be divided into water that is above the surface, we call that surface water and then ground water. But what is interesting is if we look to the sides of that stream you can see the water table in the ground water. And so if you dig a hole right here it is just going to fill in with water because of all of that ground water around it. Now this is an aquifer. It is storage of that water in the ground water. We call this unconfined aquifer because the water can move between the surface and the aquifer itself. If I were to dig down a little bit we could find what is called a confined aquifer. And that is going to be stuck between this impermeable rock down here and above it. Now let's say we want to get to that ground water on the surface. If we want some of the surface water we simply pump it out of the stream. But if we want to get water out of that ground water we could dig a well. Now the water, we could either pump out the water or sometimes we will have what is called an artisan well where there is either enough gravity above it or enough pressure in the ground water so it actually comes out. But as we use that well, just like using a stream the water table is going to drop. And so we are going to start to deplete that aquifer. Now an important term in filling an aquifer is something called recharge. So as we get water and infiltration we are going to fill up that aquifer. But if the outputs, in other words if we pull out more water then we are putting in, we are going to deplete the aquifer. And what are we using all of this fresh water for? Well if we break it out using a pie chart most of it is actually for agriculture. The growing of our food. We use some of it for industry. And then some of it domestically in the house. The problem again is that it is unevenly distributed on our planet. Brazil is going to have plenty of water. But if we look in the desert southwest of the US or in the Sahara there is not going to be any water right there. And so what have humans done? We have started to store water. So reservoirs are an example of that. A big example would be the Three Gorges Dam that was built in China. It was finished in 2006. And so this is what that river, the Yangtze River looked like before they built the dam. And then they built the dam, finished in 2006. You can see what it looks like then. So we are storing the water behind the dam. What is nice about that, now we have water that we can use at will. We also can get energy from it, as we run that water through a generator. We can control flooding downstream. And also we can use that for irrigation. Or the Three Gorges Dam they are using to increase shipping on the Yangtze River. So it sounds great. What is the problem? Well there is going to be destruction wherever that water went. So we are decreasing 20 percent of the forest in this Yangtze River. We are displacing over 1,000,000 people that used live there. We also have evaporation of the water off the surface. And then we are going to have nutrients that start to deposit there that would have normally moved their way down the river. And that is going to disrupt wildlife. And so fish obviously cannot spawn, move up and down in the stream. But it is also going to change the temperature of the water. An example. There is a freshwater dolphin that went extinct in the Yangtze River and the Three Gorges Dam may have contributed to that. We can also store it underground. That is naturally stored in what are called aquifers. One of the largest ones on the planet is the Oglala Aquifer. It is going to be found in the midwest. And so here it is in Nebraska. But it goes all the way down to Texas and up into South Dakota. It is a huge aquifer. So if we look at the amount of water stored underground it is over 1000 feet of infiltrated saturated water underneath the ground that we can use. And you can see right here that there is tons of irrigation going on. This is in Kansas. They are using center pivot irrigation so they can grow their crops. It seems great but what happens again is that we can deplete that. So if we look at, this is during a 15 year period of time, there is an increase in the aquifer in certain areas but most of the time we are seeing depletion. And sometimes that aquifer has kind of disappeared. And a lot of scientists think in the next 100 years the Oglala Aquifer is just going to disappear. Why is that a problem? It could take another 6000 years to fill it up again through natural recharge. Now we also have to move water around. So looking to California is a great example of that. So if we look in California they need a lot of water in the central valley and then in the south, Los Angeles and San Diego. So they built this huge system where they can move water where it is, in the mountains, and they can move it through these aqueducts to where it is needed. Now you can see that is controversial. So people in this area are saying you are depleting our rivers. In this area we are saying we have more population. We are growing your food so we need more of that water. And this conversation becomes more heightened when we move into drought. And California is in an awful drought right now. Drought occurs when you receive way less then the normal amount of water. And so as we use that for agriculture, irrigation movement is super important. So how do we move the water actually to the plant. The easiest way to do that is using furrow irrigation. You can see it is easy. You just dig a trench. What is the problem? We have efficiency rates of around 60 percent. What is that? That is how much of the water is actually going to the plant without being evaporated and infiltrated into the soil. So we could move to flood irrigation. Higher efficiency but it is going to damage the plant a lot of the time. We could move towards a spray irrigation, high efficiency, but what are we doing? You can see we are adding equipment. This is the center pivot. So that costs money. Or we could move to drip irrigation. And you can see that it is going to 95 percent efficient but it is going to cost the farmer a lot more money to do that kind of irrigation. As we move into drought situations desalination becomes an option. We can remove the water from sea water. One way to do this is through distillation. What you do is you heat up the water and it evaporates. It is kind of like the hydrologic cycle. You then cool it down usually through pipes and what you do is you remove the water. What is a problem? It costs a huge amount of money. We could also do that through reverse osmosis. This is a reverse osmosis plant over on the side. What you do is put a membrane right here and then we squeeze the water and as you squeeze the water you move the water through but you leave the salts behind. Now we have fresh water. What is the problem. It costs a lot of money. About 1 percent of the people on our planet are using water that is created through desalination. But by 2025 we should have 14 percent of the people on our planet in water scarcity and so desalination may be an issue. Now how did we get to this problem? It seems like we have an unlimited amount of water? And remember our model the earth provides the life support for society and the economy on the inside. And so the economy got us to this point. The decisions that we as governments made got us to this point. Where is the big mistake we made? Well water does not cost enough. It is low cost water. In other words governments are subsidizing the cost of water so farmers and industry and you are not really paying the amount that water costs. And as a result you are not going to conserve it because it is just pennies on the gallon. It is incredibly cheap. And so how could we solve this problem? People might not like it but if we increase the price of water people are going to start to conserve. And we can also use incentives. In other words we can pay people, pay farmers for example to use irrigation that is going to be more efficient or to conserve water. That is another way that economics can start to solve this problem of water conservation. And so did you learn the following? I would pause the video at this point and try to fill in all the blanks. But let me do that for you. Remember the water resources move through the hydrologic cycle. We have sea water. We have fresh water. Ocean circulation and desalination could help us solve this problem. The fresh water can be ground water or surface water. We use it for domestic, industry and agriculture, would be what is here. We can store the surface water through reservoirs, aquifers is ground water. And then we are going to use aqueducts and irrigation to help us move that water around. But again, conservation is incredibly important. Economics are going to drive that. And I hope that was helpful.