Biogeochemical Cycles

Hi. It’s Mr. Andersen and this is environmental
science video 11. It is on biogeochemical cycles. This is a picture of George Rhoads.
You have probably never seen him before but you may have seen his work. If you have ever
seen a giant kinetic sculpture at a museum where billiard balls are lifted up and then
they move down again, he invented that and has installed lots of those around the world.
Here is a planning document. In this one he is trying to show how energy from the sun
or within the earth can drive things like the water cycle and the rock cycle. And it
is a really good model for how nutrients move around on our planet. The carbon and the nitrogen
that we have is set and it just moves around between the living and nonliving world. #00:00:41-4# And so the matter on our planet is conserved.
We have a set amount and it moves between the biotic, or living, and abiotic world.
The living world is called the biosphere on our planet. And the nutrients that we need
are best remembered in this mnemonic, CHNOPS. Carbon, hydrogen, nitrogen, oxygen, phosphorus
and sulfur. If we look at the abiotic factors, that is going to be the atmosphere, lithosphere
and hydrosphere. And so these biogeochemical cycles are going to be how the nutrients move
between the living and nonliving. Now why is it such a long word? Bio, geo and chemical
are the biological, chemical and geological processes by which the nutrients move around.
You are probably most familiar with the water cycle. We will start there. Then talk about
the carbon cycle and following that the nitrogen cycle. One thing you are probably not familiar
with with the nitrogen cycle is the importance of bacteria and how they can nitrogen fix
or take nitrogen out of the atmosphere and put it into the living world. We will then
move to the phosphorus, one of the slowest turning cycles. It involves rock but no atmosphere.
Now both nitrogen and phosphorus are what are called limiting nutrients. That means
life really needs them and is waiting for them. And once it gets those nutrients then
it grows really really quickly. It is a good thing but sometimes can lead to eutrophication.
And then finally we will finish with the sulfur cycle. #00:01:57-7# And so the energy on our planet remember starts
in the sun, moves through producers to consumers, other consumers and eventually is lost as
heat. But as we move to matter everything on the planet is conserved. There is no sun
anymore. And so how do the producers get the nutrients that they need? It is from their
environment. From the atmosphere, from the hydrosphere, from the lithosphere. How do
consumers get the matter they need? By eating plants or eating consumers that ate plants.
How does the matter go back into the environment again? Through these biogeochemical cycles.
#00:02:30-8# And so what are the nutrients that life needs?
What are the billiard balls of life? Well a good mnemonic is CHNOPS. Carbon, hydrogen,
nitrogen, oxygen, phosphorus and sulfur. If we organize that into the five cycles we have
the water cycle, carbon cycle, nitrogen cycle, phosphorous cycle and sulfur cycle. So why
do we need all of this matter? We are filled with water. We also use the oxygen to release
energy and transfer energy with the hydrogen. We are built out of macromolecules. That is
what carbon is the building block of. The nitrogen and the sulfur are both big components
in the proteins that make us up. And then the phosphorous is found in DNA, RNA and the
ATP. And so if we do not have these nutrients, if we do not have these atoms then life cannot
exist. So we need to pull them out of our environment. #00:03:17-8# So let’s start with the water cycle. How
do plants get water? They are going to take it in through their roots. What about a cow?
They are simply going to drink the water. But how does it move through the abiotic parts
of our planet? First of all we are going to have evaporation off of oceans, lakes and
streams. And then we are going to have evapotranspiration. So it is evaporating but also it is being
transpired through the leaves of a plant. It is now moving from a liquid to a gas. What
eventually happens is that we are going to have condensation in the clouds. We have precipitation.
And then we have run off over the surface and through ground water. And the whole thing
begins again. #00:03:49-4# If we start with carbon, how does a plant
get carbon? It is going to be through photosynthesis. Both in plants on land and then phytoplankton
that are going to be found in the ocean. What about an animal like this cow, it is simply
gets the carbon through its diet. It eats the plant. Or if something eats a cow, like
you, you are taking the carbon from the meat of the cow. So what happens to that carbon?
It is eventually released through cellular respiration. It goes back into the atmosphere
again as carbon dioxide. So a lot of that carbon is going to be in the atmosphere as
carbon dioxide. Now we can also take that carbon and it can be covered by rock and we
can create coal and oil, fossil fuels. So we are storing that carbon in the rock. We
can extract it again by digging a well. And then we can have combustion where a factory
releases that carbon dioxide back into the atmosphere and the whole cycle continues again.
#00:04:37-8# The nitrogen cycle is a little different.
Most of the nitrogen is going to be found in the atmosphere as nitrogen gas. And to
get it into the living systems we have to do nitrogen fixation. So there are bacteria
that live lots of times on the roots of plants in these nodules and they are converting the
nitrogen in the atmosphere into usable ammonia. We could also put ammonia on our fields as
fertilizer. And then it is going to be assimilated. In other words plants are going to take it
in through their roots and we are going to get it from plants simply by eating them.
Now how does it get returned back to the atmosphere? It is kind of complex. What happens is we
have death. We then have decay. And so bacteria or fungi are going to convert that nitrogen
into ammonium. And then we have other bacteria, nitrifying bacteria that are going to convert
that ammonium into nitrites and then nitrates. Now the nitrates can be leached. They can
move into the water supply of our planet. Remember nitrogen is a limiting nutrient.
Plants, life, is just waiting for nitrogen to be there. And once we get nitrogen, for
example in this stream, you will get an algae bloom. We will get a bunch of algae growing
really, really quickly. Now that seems like a good thing but all of those algae are going
to quickly die. And eutrophication is this process by which they die and then other bacteria
have to break them down through respiration and it consumes all of the oxygen. So it is
not healthy for that water supply. But let’s keep watching the nitrogen. How does it get
back into the atmosphere? We will have denitrifying bacteria that are going to return it back
into the atmosphere. And so the whole thing can begin again. #00:06:05-4# Now the phosphorus cycle is going to turn
more slowly. It starts by having rock that have phosphorus being uplifted. We then have
weathering and erosion and that is going to move the phosphorus into the soil, into the
water supply. We could also add fertilizers. That is going to have phosphorus. And the
whole thing, since it is limiting can promote eutrophication. What happens to the phosphorus?
We then have assimilation where it is taken into plants. We can eat the plants and we
get it. What eventually happens is we die. So through excretion and decay we return that
phosphorus into the water supply. It eventually works its way to the ocean. And then it eventually
settles out in these sediments. And so it never goes to the atmosphere. It becomes part
of these phosphate rocks which are then uplifted again. And so it takes a long time for this
cycle to turn because we do not include the atmosphere. #00:06:49-0# And then finally we have the sulfur cycle.
Sulfur cycle is going to move from the oceans, the sulfur. We have bacteria that are going
to convert that into dimethyl sulfide which eventually becomes sulfur oxide or sulfur
dioxide. We can also increase sulfur dioxide through volcanism. So volcanoes are releasing
hydrogen sulfide which becomes sulfur dioxide. And then factories are going to release sulfur
dioxide as well. It is in the atmosphere now. How does it get back to the planet? It is
going to rain down as sulfuric acid and sulfates. We can then assimilate that, take it into
the living materials, same way, into plants and then into consumers. And finally it works
its way back through the water supply and now it is going to be sulfur in the oceans.
So the cycle can continue again. But we can also have that rock cycle forming some of
that into fossils fuels which can be extracted again and the cycle continues. #00:07:41-2# And so for each of these cycles you should
be able to figure out how do plants get it? How do animals get it? And then how does it
recycle back through the atmosphere, hydrosphere and lithosphere. #00:07:51-4# So did you learn the following? Could you
pause the video right now and fill in the blanks? Remember matter is conserved on our
planet. We have a set amount. It moves through the biotic and abiotic spheres. A good way
to remember the nutrients we need is CHNOPS. The biogeochemical cycles are how we move
it through abiotic and biotic. It is the water cycle, carbon cycle, nitrogen cycle, which
requires nitrogen fixation. Remember nitrogen and phosphorus are limiting nutrients which
can lead to eutrophication. The last cycle is the sulfur cycle. And I hope that was helpful.

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