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.