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This lecture is going to be very
dependent upon the PowerPoint slides,

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because if I take the time to draw
the cycles on the board,

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we'd be here forever.  So I would
say sit back and relax because you

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have the slides.
They're on the Web.

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And try to focus on what the
take-home message is.

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OK, but before we go on to
biogeochemical cycles,

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I want to just briefly review some
of the things that we learned in the

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second lecture.
I got feedback from many of you,

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actually, on the things that were
difficult to understand from that

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lecture, and those are important for
understanding these cycles.

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And the one thing that some people
were confused by was this anaerobic

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respiration.  Remember,
I drew this on the board,

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and it showed a lot of reduction
reactions.

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And I think that was confusing for
some people, so let's just go over

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that very quickly.
You've learned in Graham's lectures,

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and in my lectures,
that anaerobic respiration,

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respiration of organisms where there
is oxygen, that oxygen is the

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terminal electron receptor here in
that electron transport chain and

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it's reduced to water.
So in aerobic environments,

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when organisms respire oxygen it's
reduced to water.

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If there's no oxygen around,
the organisms, and in this case it's

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always bacteria,
look for the next thermodynamically

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favorable electron acceptor.
And so, whatever is dominant in

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that environment and is most
thermodynamically favorable,

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they'll use.  So, the sulfate
reducing organisms use sulfate and

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reduce at [H2S?
.  Denied trying denitrifying

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organisms use nitrate and reduce it
to these forms of reduced nitrate or

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reduce nitrogen.
And we talked about iron bacteria

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[epi?] plus three,
and reduce it to epi plus two.

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Some can use manganese, etc.
Whatever's there,

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and it's thermodynamically favorable,
they'll use.  OK,

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so that clarifies that.
Some of the people said,

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you kept talking about symmetry.
You kept talking about symmetry.

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I didn't see any symmetry, and in
hindsight I can understand why,

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because it just threw that out and I
didn't really point it out.

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So what I was talking about was as
we went through these processes,

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you see here, these elements,
sulfate and nitrogen,

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nitrate, are being reduced.
There are other processes,

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particularly chemosynthesis in which
these reduced compounds,

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here's H2S and ammonia or be
oxidized.  So that's the symmetry

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that I was talking about.
And if you didn't have that,

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if all the organisms were reducing
things, the whole system would run

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down.  You have to have organisms
that are also oxidizing things.

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And that's a key component of all
of these, or not all of the

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biogeochemical cycles,
but particularly the cycles of

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nitrogen and sulfur,
which have this [redox?

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chemistry.  So that's a symmetry
that I was talking about.

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OK, now so let's talk about how we
think about biogeochemical cycles.

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Did you see the slide in the back?
Try to turn the lights off?  That

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was a double question.
Can you see the slide in the back?

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Yes?  OK.  So this is a generic map
of the components of biogeochemical

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cycles.  And we can think of the
earth as a giant chemical factory in

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the sense that has what we call
compartments, or reservoirs,

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or pools of a particular element.
Or it might be water that we are

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analyzing, and then there are fluxes
between these pools.

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So here's a flux, an arrow.
So typically these are diagrammed

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with boxes and arrows connecting
them.  And you don't have to use all

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of these boxes.
It could be we are just looking at

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land, atmosphere,
and ocean.  I mean,

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you can construct whatever model you
want cities.  And these are just

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some useful conversion factors for
the amount of things that we're

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going to have flowing between these
compartments.  And here,

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again, this is something we defined
earlier when we were talking about

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productivity.  The main residence
time of, say, an element,

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say, carbon in the terrestrial
biomass, is the pool size,

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the amount of carbon that they're
divided by the mean flux in or out

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of the pool, OK?
It's exactly the same concept we

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talked about for carbon.
And then the fractional turnover,

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one over the mean residence time is
simply the fraction.

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If we're talking about carbon again
in trees, it's the fraction that's

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removed per unit time.
OK, so you can see that when we talk

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about mean residence time of an
element  in one of these reservoirs,

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if the whole system is in a steady
state, in other words,

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if the amount in a reservoir is
changing, the flux in is going to be

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the same as the flux out,
right?  You know that.  Just like a

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bathtub, if you have water flowing
in, water flowing out,

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the level will say the same if the
flow rate and is the same

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as the flow rate out.
But often in nature,

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you don't have that exactly.
And if you don't, the size of these

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reservoirs is either increasing or
decreasing.  So when you're

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analyzing these systems,
your most of the time trying to get

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the very rough estimate of main
residence time.

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So if the flow in and the flow out
isn't the same,

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you can either average them and use
that as your flux,

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or you could define your residence
time with respect to the flow

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in or the flow out.
So, these are just gross

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approximations.
What we want to understand is the

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residence time thousands of years,
millions of years, days, rough

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approximation.
And the other thing I want to say

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before we go on,
is that all of these cycles,

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we're going to talk about them
element by element: phosphorus,

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carbon, whatever.
But they're all tightly coupled in

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the system.  And we'll bring that up
again later.  Before we go on,

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let's just look at the solar energy
budget, which is driving this whole

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system, mostly,
there is some geothermal energy,

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energy for the Earth's, the magma
that is also driving biogeochemical

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cycles.  But the solar energy is the
primary driver.

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And if you say that the total energy
from the sun is 100%,

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it's that energy that is used in
evaporation, and winds,

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and photosynthesis that is the
important component driving the

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cycles.  And you'll see that
photosynthesis is a tiny fraction.

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The energy that plants harvest is a
tiny fraction of the total energy

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that is driving the Earth's system.
And yet, this photosynthesis, which

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is the basis of the biosphere,
has an enormous effect on the

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conditions on Earth.
That's an interesting nonlinearity

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of the system.
OK, so let's start with the

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geological cycle,
which is the slowest moving,

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people don't even think of it as a
cycle because while we are on Earth

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we don't see rocks flying through,
well, sometimes you see rocks in a

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landslide or whatever,
but for the most part you don't

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think of rocks as cycling.
But they do.  And if they didn't,

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the system would run down much
faster than it is.

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And we've all heard about plate
tectonics, that the surface of the

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Earth is made up of these plates
that are slowly shifting.

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And when they shift you have
earthquakes, like we've had recently

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a lot of.  And also,
you have volcanic eruptions that

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bring material from the inside of
the Earth up to the surface

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and it overflows.
And that's part of this geological

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cycle.  So, here's a really
oversimplified,

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when the geology professor in our
department so that ever showing this

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he had a heart attack by how
simplified it is.

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But it's just so you get the idea.
When he started editing it, there

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are so many arrows you can never
cope with that.

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But just get the idea.
There's geothermal energy coming in

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from the inner core of the Earth
where you have magma.

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Think volcanic eruption,
lava, which ultimately becomes

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surface rocks.
And they're eroded by weathering by

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rain, and then elements from that go
into the soils.

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Soils eventually become sedimentary
rocks.  We're talking over really,

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really long time periods, which
become metamorphic rocks.

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Some of those are uplifted,
and some of them are melted and

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become magma.
But it is a cycle,

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a very, very slow cycle.
In fact, somewhere I read 70%,

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you do not need to know this.  This
is not geology class.

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But just so you have an idea,
75% of the rocks now on the surface

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of the earth have been uplifted.
So it's almost as if the Earth is,

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on average, maybe halfway through a
cycle.  So, this erosion here,

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and weathering, as we talked about
last time is critical for making

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nutrients available to the biosphere.
And the force of this weathering is

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incredibly powerful.
One number that I found it one

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textbook that I never knew before is
that Niagara Falls is eroding at 3

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feet per year.
The cusp of the falls from the water

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is moving back 3 feet per year.
That's fast.  Another little

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factoid when I gave this lecture one
year, students asked what is going

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to burn out first on the Earth,
the sun or the geothermal energy?

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And of course I have no idea.
We over someday.

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The Earth is going to be history
because without the sun and without

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the geothermal energy there's no
source of energy.

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So I went to my colleagues in this
department, Earth Atmosphere and

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Planetary Sciences,
and said, which is going to burn out

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first?  And they said,
roughly the same time.  And we have

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about 2 billion years,
so not to worry yet.

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But it is, we are only here for a
period of time.

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So, that's the geologic cycle.
Now, let's move onto the water

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cycle, and then we're going to go
through the element cycles of

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nitrogen, phosphorus,
and carbon.  But the water cycle is

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obviously important in carrying
those elements through their cycles.

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And the cycle is actually fairly
well understood.

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As a fairly because not all of
these things, when you're talking

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about global averages of things it's
very difficult.

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But the weather service is very
interested in the global water cycle.

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So there's been a lot of study done.
So in terms of reservoirs,

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these numbers of black at the amount
of water in a reservoir.

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And the numbers and blue are the
number of fluxes annually of the

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amounts of water moving
from one to another.

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So, there is a lot of water and
groundwater.  There's a lot of water

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and ice, and there's a lot of water
in the oceans.

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And there's very little water in
the atmosphere.

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These are the annual fluxes.
So you can see, if I animated this

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right, so 111,
these are in terms of square

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kilometers of water,
that's a lot of water.

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So, 111 minus 71 gives you 40.
So that's the rainfall.

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This is the evapotranspiration,
and the net result is 40,000 that is

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flowing into the oceans.
And in the oceans, here's the

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evaporation and here's the rainfall
going in with just a net of 40

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that's transported from the oceans
to land.  So you have 40,

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00 going into the oceans, and 40,
00 coming back, fairly nicely

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balanced.  That's good.
And so, let's just use this as an

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example to say,
what's the residence time of water.

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Let's just calculate this.  We can
just approximated.

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So the mean residence time is equal
to the pool size divided by the flux,

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right?  So what's the pool size?
Well, how much water there in the

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ocean?
Thank you.  [35?

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times 109.  And,
what's the flux?

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Well, we have 425,

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00 evaporating and we have 40 going
here.  So, I would add this and that

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so it's balanced.
So, I would use 425.

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4.25 times 105 equals just roughly
how many years?  3,000

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years roughly.
So we would say the residence time,

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the average molecule, the average
water molecules floating through

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this system would spend on average
thousands of years in the oceans

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before it would evaporate and get
back into the system.

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So you should now think about what
the average residence time is,

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for example, in the atmosphere.
And you can see when the pool is

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very small relative to the fluxes,
the residence time is going to be

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very short, right?
That's something to remember.

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When the pool is huge relative to
the fluxes, the residence time is

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going to be very long.
So, you should think about that as

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you go through your notes.
But, in oceans, the residence time

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is thousands of years in groundwater.
The residence time,

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again, can be very long,
which is why we don't want to

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contaminate our groundwater because
it's going to take a really long

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time to flush that through.
Lakes: the residence time is on the

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order of decades,
streams on the order of weeks,

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and atmosphere I'll let you
calculate it and figure it out.

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OK, let's move on now to an element
cycle, the global phosphorous

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cycle.

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First of all, there's no [redox?
chemistry in the cycle.  That's

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important.  OK,
that's the first thing to remember.

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And it's called a sedimentary cycle
because there is no atmospheric

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component.  There is essentially no
phosphorus in the atmosphere.

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Everything in this field, there's
always an exception.

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There is something called phosphine
that comes out of bogs that is

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really interesting.
But it's not a huge amount,

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so it doesn't really matter in this
analysis.  And,

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let's look at it here.
We have a fair amount of phosphorus

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in land plants.
And there's internal cycling here.

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We have the mining of phosphorus
from rocks.

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00:19:00,000 --> 00:19:04,000
This is a fertilizer.
No, that's not a mine; that's a

220
00:19:04,000 --> 00:19:08,000
house.  Sorry.
The mine is invisible.

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00:19:08,000 --> 00:19:12,000
Here's the mine.  So, the
phosphorus is being mined.

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00:19:12,000 --> 00:19:17,000
It's put on crops as fertilizer.
The crops are eaten by the people

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00:19:17,000 --> 00:19:21,000
in the house, and the phosphorus
ends up in sewage.

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00:19:21,000 --> 00:19:25,000
Even if it's treated,
it ends up in the rivers,

225
00:19:25,000 --> 00:19:30,000
and it ends up flowing into the
oceans.

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00:19:30,000 --> 00:19:35,000
And there's a little bit in dust
transport here,

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00:19:35,000 --> 00:19:40,000
but if you look at this whole system,
it's basically the phosphorous cycle

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00:19:40,000 --> 00:19:46,000
is a one-way flow to the oceans.
The only return of the cycle is via

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00:19:46,000 --> 00:19:51,000
the sedimentary cycle where you go
from sediments.

230
00:19:51,000 --> 00:19:57,000
Those are sedimentary rocks until
you go to mineable rock

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00:19:57,000 --> 00:20:02,000
and through uplifting.
And this is on geological timescales.

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00:20:02,000 --> 00:20:08,000
So, on the earth today,
the global phosphorous cycle is

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00:20:08,000 --> 00:20:13,000
really not a cycle.
It's a one-way flow to the oceans.

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00:20:13,000 --> 00:20:18,000
Well, it's a cycle, but it's an
extremely unbalanced cycle because

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00:20:18,000 --> 00:20:24,000
eventually this one will come back.
It cycles very rapidly in the biota,

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00:20:24,000 --> 00:20:29,000
internal cycling in the ocean.
So, it comes of the river, it's

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00:20:29,000 --> 00:20:34,000
taken up by phytoplankton,
there you can buy zooplankton,

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00:20:34,000 --> 00:20:40,000
and then the phosphorus is excreted
or bacteria [UNINTELLIGIBLE] on dead

239
00:20:40,000 --> 00:20:49,000
organisms take up the phosphorous.
It's excreted as organic phosphorous,

240
00:20:49,000 --> 00:21:02,000
and it cycles rapidly through
this system.  OK.

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00:21:02,000 --> 00:21:15,000
So the other important feature of
this one way flow, and also

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00:21:15,000 --> 00:21:33,000
humans have altered.

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00:21:33,000 --> 00:21:40,000
In other words,
humans are responsible for this,

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00:21:40,000 --> 00:21:47,000
basically, one-way flow by mining
the phosphorus and putting it into

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00:21:47,000 --> 00:21:54,000
the agricultural system.
OK, yeah, and there's the return

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00:21:54,000 --> 00:22:01,000
flux.
OK, moving on to the nitrogen cycle,

247
00:22:01,000 --> 00:22:07,000
which is much more complicated
because it is [redox?

248
00:22:07,000 --> 00:22:14,000
chemistry, OK?  And, humans have
also had a major,

249
00:22:14,000 --> 00:22:20,000
major, major effect on the global
nitrogen cycle.

250
00:22:20,000 --> 00:22:27,000
So, let's first look at the global
estrogen transformation.

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00:22:27,000 --> 00:22:31,000
So this isn't a pools and fluxes
diagram.  This is a summary for you

252
00:22:31,000 --> 00:22:36,000
of things you already know.
You already know this.  It just

253
00:22:36,000 --> 00:22:40,000
looks different than what you
learned in the second lecture.

254
00:22:40,000 --> 00:22:45,000
So let's just go through it very
quickly.  If we think of the

255
00:22:45,000 --> 00:22:50,000
compounds of nitrogen as being
either reduced or oxidized and we

256
00:22:50,000 --> 00:22:54,000
think of the environment where they
might be found as either being

257
00:22:54,000 --> 00:22:59,000
aerobic or oxic,
having oxygen, or anaerobic and oxic,

258
00:22:59,000 --> 00:23:05,000
not having oxygen.
We can draw a schematic of these

259
00:23:05,000 --> 00:23:11,000
processes that hopefully makes good
sense.  If we start with organic

260
00:23:11,000 --> 00:23:17,000
nitrogen, but say it's a dead whale
that you saw is organic nitrogen,

261
00:23:17,000 --> 00:23:23,000
bacteria work on it, and through
this process which you haven't

262
00:23:23,000 --> 00:23:29,000
really learned about explicitly at,
can convert that to free ammonia.

263
00:23:29,000 --> 00:23:34,000
That ammonia can be used in
chemosynthesis,

264
00:23:34,000 --> 00:23:40,000
which you learned about.
OK, the specific type of

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00:23:40,000 --> 00:23:45,000
chemosynthesis is called
nitrification,

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00:23:45,000 --> 00:23:51,000
where this ammonia is converted to
nitrite.  Is that an oxidation or a

267
00:23:51,000 --> 00:23:56,000
reduction?  Shout it out.
Yes, yes.  It's an oxidation.

268
00:23:56,000 --> 00:24:02,000
This was obvious because you can
actually see the oxygen.

269
00:24:02,000 --> 00:24:06,000
So, in that, nitrite also in
chemosynthesis can be further

270
00:24:06,000 --> 00:24:11,000
oxidized to nitrate.
And chemosynthesis, so this is an

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00:24:11,000 --> 00:24:16,000
energy releasing process for these
bacteria.  Now,

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00:24:16,000 --> 00:24:20,000
so here we now have nitrogen in an
oxidized form,

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00:24:20,000 --> 00:24:25,000
and we are in an anoxic environment,
and that should immediately tell you,

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00:24:25,000 --> 00:24:30,000
oh, that's an electron acceptor for
the anaerobic bacteria which are

275
00:24:30,000 --> 00:24:35,000
going to dump their electrons on
this and convert it to NO or N2O.

276
00:24:35,000 --> 00:24:40,000
These are gases,
and nitrogen gas.

277
00:24:40,000 --> 00:24:45,000
This is denitrification or
anaerobic respiration,

278
00:24:45,000 --> 00:24:50,000
which we already talked about.
And it also can be converted

279
00:24:50,000 --> 00:24:55,000
through nitrogen fixation,
N2 gas can be converted to ammonia.

280
00:24:55,000 --> 00:25:00,000
We already talked about this,
too.

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00:25:00,000 --> 00:25:04,000
Remember, bacteria and cyanobacteria
are the only organisms that can take

282
00:25:04,000 --> 00:25:09,000
nitrogen gas from the atmosphere and
converted to ammonia for the use of

283
00:25:09,000 --> 00:25:13,000
other organisms.
OK, and then there's one other

284
00:25:13,000 --> 00:25:18,000
thing here which is called
assimilatory nitrate reduction.

285
00:25:18,000 --> 00:25:22,000
And that is when organisms just
take up nitrate,

286
00:25:22,000 --> 00:25:27,000
and inside them, and they reduce it
so that they can,

287
00:25:27,000 --> 00:25:31,000
they have to reduce it to ammonia in
order to reduce it for

288
00:25:31,000 --> 00:25:38,000
protein synthesis.
So that's another route for nitrate

289
00:25:38,000 --> 00:25:46,000
to become organic nitrogen in an
oxidized environment.

290
00:25:46,000 --> 00:25:54,000
So these are the important
biological transformations in the

291
00:25:54,000 --> 00:26:03,000
cycle.  So, here's the cycle in all
of its complexity.

292
00:26:03,000 --> 00:26:10,000
And redox is important.
That's a feature.  I'm going to

293
00:26:10,000 --> 00:26:18,000
list these things,
and then we'll look at them on the

294
00:26:18,000 --> 00:26:25,000
diagram, has a gaseous phase,
in other words, is an important

295
00:26:25,000 --> 00:26:33,000
atmosphere component,
N2, NO, N2O, and by the way,

296
00:26:33,000 --> 00:26:41,000
this is a very powerful greenhouse
gas.

297
00:26:41,000 --> 00:26:52,000
So, the balance or imbalance in the
nitrogen cycle that results in more

298
00:26:52,000 --> 00:27:03,000
or less N2O is very important for
global climate regulation.

299
00:27:03,000 --> 00:27:29,000
Nitrogen fixation by microbes and
humans: very important.

300
00:27:29,000 --> 00:27:37,000
And denitrification by microbes is
the only way to return nitrogen to

301
00:27:37,000 --> 00:27:45,000
the atmosphere.
If you didn't have denitrification,

302
00:27:45,000 --> 00:27:54,000
this process that you learned in my
second lecture that you thought was

303
00:27:54,000 --> 00:28:02,000
just some weird way things get
through life, is incredibly

304
00:28:02,000 --> 00:28:11,000
important in maintaining the global
nitrogen cycle.

305
00:28:11,000 --> 00:28:18,000
So, let's look at this,
the details here.  So, in terms of

306
00:28:18,000 --> 00:28:26,000
nitrogen fixation,
that's taking N2 gas and converting

307
00:28:26,000 --> 00:28:33,000
it to ammonia.
Biological fixation by plants,

308
00:28:33,000 --> 00:28:39,000
or it's really not by plants.  It's
by the symbiotic microbes in their

309
00:28:39,000 --> 00:28:46,000
roots is 140 times 1012 of grams per
year.  The industrial electrician

310
00:28:46,000 --> 00:28:52,000
fixation, that is,
what's done by humans,

311
00:28:52,000 --> 00:28:59,000
there's a process called the Haber
process that's incredibly energy

312
00:28:59,000 --> 00:29:05,000
intensive.  It takes a lot of fossil
fuel to break that nitrogen

313
00:29:05,000 --> 00:29:11,000
triple bond.
In other words,

314
00:29:11,000 --> 00:29:15,000
to take nitrogen gas and convert it
to ammonia, you have to break this

315
00:29:15,000 --> 00:29:19,000
triple bond which is very energy
intensive.  But they figured that

316
00:29:19,000 --> 00:29:23,000
out during World War II basically,
or was it World War I?  Anyway, one

317
00:29:23,000 --> 00:29:27,000
of the wars, how to break that bond,
and that was the beginning of the

318
00:29:27,000 --> 00:29:32,000
nitrogen fertilizer industry.
So, this is human nitrogen fixation

319
00:29:32,000 --> 00:29:38,000
that is used to fertilize crops.
So this is a huge fraction of the

320
00:29:38,000 --> 00:29:43,000
natural fixation.
I mean, this adds a huge amount of

321
00:29:43,000 --> 00:29:49,000
nitrogen flux to the system.
OK, in this flux here, this is

322
00:29:49,000 --> 00:29:54,000
cultivated legume.
So, this would be agricultural bean

323
00:29:54,000 --> 00:30:00,000
plants that naturally have nitrogen
fixers in them,

324
00:30:00,000 --> 00:30:06,000
and that also import nitrogen into
the system.

325
00:30:06,000 --> 00:30:12,000
So, we consider that part of the
human flux.  OK,

326
00:30:12,000 --> 00:30:18,000
to balance this, we have
denitrification,

327
00:30:18,000 --> 00:30:25,000
which as I said is done by microbes
on land and in the ocean.

328
00:30:25,000 --> 00:30:31,000
So, looking at this, is it balanced?
Is nitrogen fixation on a global

329
00:30:31,000 --> 00:30:37,000
scale and denitrification balanced?
Did I hear a no?

330
00:30:37,000 --> 00:30:43,000
Which is greater?
Denitrification, yeah.

331
00:30:43,000 --> 00:30:48,000
If you add this, this, and this,
you get 260.  Is that right?  Yeah,

332
00:30:48,000 --> 00:30:54,000
and then you add this, this, and
this you get 310.

333
00:30:54,000 --> 00:31:00,000
So, there's more nitrogen going
into the atmosphere than

334
00:31:00,000 --> 00:31:06,000
we're taking out.
And people don't understand this.

335
00:31:06,000 --> 00:31:13,000
They think the denitrification has
been disproportionately stimulated

336
00:31:13,000 --> 00:31:19,000
by this huge flux of nitrogen into
the system.  But this is an

337
00:31:19,000 --> 00:31:26,000
important imbalance that a lot of
people are studying very

338
00:31:26,000 --> 00:31:32,000
hard.  OK, yeah.
That's the major feature that you

339
00:31:32,000 --> 00:31:36,000
want to look at in the system.
And then, if we compare, this

340
00:31:36,000 --> 00:31:41,000
figure is from your textbook
comparing the biological nitrogen

341
00:31:41,000 --> 00:31:45,000
fixation.  Plus,
lightning fixes it a little bit.

342
00:31:45,000 --> 00:31:50,000
Compared to the human, you can see
that humans are now responsible for

343
00:31:50,000 --> 00:31:54,000
an equal amount of nitrogen flux on
a global scale as the natural system.

344
00:31:54,000 --> 00:31:59,000
This is a dramatic perturbation,
and that's only in the last 50 years

345
00:31:59,000 --> 00:32:04,000
or so, dramatic perturbation
to the system.

346
00:32:04,000 --> 00:32:09,000
This amount that we are doing is,
140 gigatons is equivalent to 10

347
00:32:09,000 --> 00:32:15,000
million trucks of dry nitrogen
fertilizer that we are putting into

348
00:32:15,000 --> 00:32:20,000
the system with completely unknown
effects.  OK, the next series of

349
00:32:20,000 --> 00:32:26,000
slides are just to illustrate in one
ecosystem the importance of the

350
00:32:26,000 --> 00:32:32,000
biota and maintaining nitrogen in
the ecosystem.

351
00:32:32,000 --> 00:32:35,000
And I'll also just show you the
importance of experiments in ecology.

352
00:32:35,000 --> 00:32:39,000
And this is the Hubbard Brook
Experimental Forest,

353
00:32:39,000 --> 00:32:43,000
which is up in New Hampshire.
Some of you might have even visited

354
00:32:43,000 --> 00:32:47,000
there.  This was my first job as a
graduate student was actually

355
00:32:47,000 --> 00:32:50,000
working in the forest.
I was measuring phosphorous

356
00:32:50,000 --> 00:32:54,000
concentrations in the streams.
And what they do there, just like

357
00:32:54,000 --> 00:32:58,000
that experimental lake study I
showed you, here,

358
00:32:58,000 --> 00:33:02,000
they have permits from the forest
service to clear cut

359
00:33:02,000 --> 00:33:06,000
entire watersheds.
A watershed is just an area that

360
00:33:06,000 --> 00:33:10,000
collects the rainfall and directs it
into a single stream.

361
00:33:10,000 --> 00:33:14,000
You can collect the rain and
measure what's in it,

362
00:33:14,000 --> 00:33:18,000
and you can collect the water coming
out and measure what's in it.

363
00:33:18,000 --> 00:33:22,000
And the difference is what the
ecosystem is actually doing.

364
00:33:22,000 --> 00:33:26,000
So, what they did was they had
these two watersheds that were the

365
00:33:26,000 --> 00:33:30,000
same, and they clear cut one of them.
And they asked with the influence

366
00:33:30,000 --> 00:33:34,000
of this clear cutting was on the
quality of the water coming

367
00:33:34,000 --> 00:33:38,000
out of the system.
And to make a long story very short,

368
00:33:38,000 --> 00:33:42,000
it's a really fascinating study
that's been going on for four years

369
00:33:42,000 --> 00:33:47,000
that I want to tell you because then
you'll know how old I am.

370
00:33:47,000 --> 00:33:51,000
But, here's the control watershed,
and here's the water coming out of

371
00:33:51,000 --> 00:33:56,000
the devegetated one,
showing massive [reflux?

372
00:33:56,000 --> 00:34:01,000
of nitrate from the system as well
as other cations.

373
00:34:01,000 --> 00:34:04,000
And your textbook does a terrible
job of not explaining this.

374
00:34:04,000 --> 00:34:08,000
And I don't have time to go into
the details.  But,

375
00:34:08,000 --> 00:34:12,000
the major reason this is lost,
the vegetation is really important

376
00:34:12,000 --> 00:34:16,000
in that, but it's important in also
maintaining the microbial community

377
00:34:16,000 --> 00:34:20,000
in the soil.  And when it's cut down,
the microbial community changes.

378
00:34:20,000 --> 00:34:24,000
And that is very important and
resulting in the loss.

379
00:34:24,000 --> 00:34:28,000
It's a beautiful study,
which unfortunately we don't have

380
00:34:28,000 --> 00:34:32,000
time to go into.
But if you're interested,

381
00:34:32,000 --> 00:34:36,000
I can point you in the right
direction.  OK,

382
00:34:36,000 --> 00:34:40,000
now, let's go into the really
important, well,

383
00:34:40,000 --> 00:34:44,000
they're all important because
they're all coupled.

384
00:34:44,000 --> 00:34:48,000
But this is the one that's getting
a lot of attention,

385
00:34:48,000 --> 00:34:52,000
the global carbon cycle.
And it's getting a lot of attention

386
00:34:52,000 --> 00:34:56,000
because we have had an incredibly
significant impact on it,

387
00:34:56,000 --> 00:35:01,000
and we are worried about that
causing major global warming.

388
00:35:01,000 --> 00:35:05,000
And as an aside,
I'll just tell you that I actually

389
00:35:05,000 --> 00:35:10,000
think the global nitrogen cycle is a
sleeping giant,

390
00:35:10,000 --> 00:35:14,000
and that the public doesn't know
much about that right now.

391
00:35:14,000 --> 00:35:19,000
But in the scientific community,
we know the perturbation we've had

392
00:35:19,000 --> 00:35:23,000
on that cycle could end up being
equally, if not more,

393
00:35:23,000 --> 00:35:28,000
traumatic for the Earth's climate as
this.  But that's an aside.

394
00:35:28,000 --> 00:35:33,000
So let's focus on this now.
So, here's the global not carbon

395
00:35:33,000 --> 00:35:38,000
cycle, which you've seen now several
times in my lectures.

396
00:35:38,000 --> 00:35:43,000
So here's gross primary
productivity, and respiration by

397
00:35:43,000 --> 00:35:48,000
land plants, respiration by the
soils.  These are RA and RH that we

398
00:35:48,000 --> 00:35:53,000
talked about before.
And in this, we have their balance,

399
00:35:53,000 --> 00:35:58,000
roughly balanced, and then you have
uptake by the oceans,

400
00:35:58,000 --> 00:36:03,000
and loss of CO2 by the oceans.
Your textbook says this is all a

401
00:36:03,000 --> 00:36:07,000
physical and chemical process that's
absolutely wrong.

402
00:36:07,000 --> 00:36:11,000
The biota are central to that,
and that's another lecture.  But you

403
00:36:11,000 --> 00:36:15,000
already know that,
that the phytoplankton are sucking a

404
00:36:15,000 --> 00:36:20,000
lot of CO2 in through photosynthesis.
So let's look at the budget here.

405
00:36:20,000 --> 00:36:24,000
And, this is the introduction of
CO2 into the atmosphere by burning

406
00:36:24,000 --> 00:36:28,000
fossil fuel, and the introduction of
CO2 into the atmosphere by

407
00:36:28,000 --> 00:36:34,000
destruction of vegetation.
So, we have 7.

408
00:36:34,000 --> 00:36:42,000
gigatons going into the atmosphere
due to human perturbation.

409
00:36:42,000 --> 00:36:49,000
The annual increase of CO2 in the
atmosphere is 3.

410
00:36:49,000 --> 00:36:57,000
gigatons.  So, 3.
gigatons annual increase,

411
00:36:57,000 --> 00:37:03,000
and, let's see.
If we look at the difference here

412
00:37:03,000 --> 00:37:07,000
between respiration and
photosynthesis we see that there's 2

413
00:37:07,000 --> 00:37:11,000
gigatons going into the vegetation,
actually net into the vegetation.

414
00:37:11,000 --> 00:37:15,000
And if we look at this,
we see that there's two going into

415
00:37:15,000 --> 00:37:19,000
the ocean.  So,
if we ask, of all of this

416
00:37:19,000 --> 00:37:23,000
anthropogenic CO2 where's it going?
3.5 is going to increase in the

417
00:37:23,000 --> 00:37:27,000
atmosphere.  Two is going to
vegetation, and two is

418
00:37:27,000 --> 00:37:33,000
going to the ocean.
And it's this that we are very

419
00:37:33,000 --> 00:37:39,000
concerned about because it's causing
a dramatic increase in the CO2 in

420
00:37:39,000 --> 00:37:45,000
the atmosphere.
Even though these are tiny fluxes

421
00:37:45,000 --> 00:37:51,000
relative to the global biological
fluxes, these tiny fluxes lead to a

422
00:37:51,000 --> 00:37:57,000
significant increase because the
pool is so small of CO2

423
00:37:57,000 --> 00:38:02,000
in the atmosphere.
So, this is a trace of CO2 since

424
00:38:02,000 --> 00:38:06,000
1960.  Here's a question for you to
think about.  I'm not going to

425
00:38:06,000 --> 00:38:11,000
answer it.  Its summer and winter
are out of phase in the Northern and

426
00:38:11,000 --> 00:38:15,000
Southern Hemisphere,
why isn't this just smooth?

427
00:38:15,000 --> 00:38:19,000
This cycle that we see here is an
annual cycle of the Earth breathing.

428
00:38:19,000 --> 00:38:24,000
Remember I showed you that the
first lecture showing photosynthesis

429
00:38:24,000 --> 00:38:28,000
greater than respiration during the
summer, and the reverse

430
00:38:28,000 --> 00:38:33,000
during the winter.
Think about why it isn't just smooth

431
00:38:33,000 --> 00:38:38,000
and canceled out by the two
hemispheres.  OK,

432
00:38:38,000 --> 00:38:42,000
and if we look at that same graph,
this is atmospheric CO2 from ice

433
00:38:42,000 --> 00:38:47,000
core data as a function of time.
This is today, and this is time

434
00:38:47,000 --> 00:38:52,000
before present going backwards.
This is 450,000 years ago.  We can

435
00:38:52,000 --> 00:38:56,000
see that CO2 in the atmosphere,
and this is measured in, you take a

436
00:38:56,000 --> 00:39:01,000
deep ice core in Greenland,
or something, and you measure the

437
00:39:01,000 --> 00:39:06,000
CO2 concentration at different
slices of the core.

438
00:39:06,000 --> 00:39:11,000
And it tells you what the Earth was
like back then.

439
00:39:11,000 --> 00:39:16,000
And, this just dramatically shows
you what we are doing just that the

440
00:39:16,000 --> 00:39:21,000
last hundred years.
We have increased CO2 in the

441
00:39:21,000 --> 00:39:26,000
atmosphere dramatically by burning
fossil fuels.  And CO2 is a

442
00:39:26,000 --> 00:39:31,000
greenhouse gas,
and so we are very concerned about

443
00:39:31,000 --> 00:39:36,000
that.
OK, this is just read showing that

444
00:39:36,000 --> 00:39:40,000
slide from last time of upwelling to
remind you that the biogeochemical

445
00:39:40,000 --> 00:39:45,000
cycles of these elements are tightly
coupled.  Remember,

446
00:39:45,000 --> 00:39:49,000
we talked about nutrients,
nitrogen, phosphorus, being upwelled

447
00:39:49,000 --> 00:39:54,000
from the deep water,
phytoplankton taking them up,

448
00:39:54,000 --> 00:39:58,000
drawing down CO2 and then we had
oxygen and CO2 going back

449
00:39:58,000 --> 00:40:03,000
and forth in the water.
So, the oxygen cycle,

450
00:40:03,000 --> 00:40:09,000
which we haven't even talked about
is tightly coupled also to the CO2

451
00:40:09,000 --> 00:40:14,000
cycle.  I'm not going to show this
there.  OK, moving on,

452
00:40:14,000 --> 00:40:19,000
and I know this is quick,
but this is in your readings.

453
00:40:19,000 --> 00:40:25,000
There is a newspaper article about
the Biosphere 2 experiment which now

454
00:40:25,000 --> 00:40:30,000
is pretty dated.
To make a long story short,

455
00:40:30,000 --> 00:40:36,000
many years ago a very rich person
built the system out in the middle

456
00:40:36,000 --> 00:40:41,000
of the Arizona desert.
And it had seven ecosystems in it.

457
00:40:41,000 --> 00:40:45,000
It was sealed.  It was closed.  And,
he put people at,

458
00:40:45,000 --> 00:40:49,000
which were called biospherians,
and the idea was to see whether

459
00:40:49,000 --> 00:40:54,000
humans could create a closed
biosphere that would sustain human

460
00:40:54,000 --> 00:40:58,000
life.  And, it was a miserable
failure, which is sad because it

461
00:40:58,000 --> 00:41:02,000
costs a lot of money,
and has since been taken over by

462
00:41:02,000 --> 00:41:07,000
Columbia University to use it as an
experimental facility.

463
00:41:07,000 --> 00:41:11,000
But the one thing that they learned,
here's what happened.  They put the

464
00:41:11,000 --> 00:41:16,000
people in.  And it turned out that
there was not enough photosynthesis

465
00:41:16,000 --> 00:41:21,000
to supply enough oxygen for the
people to breathe.

466
00:41:21,000 --> 00:41:25,000
Oxygen levels steadily went down.
And the reason for that, they

467
00:41:25,000 --> 00:41:30,000
learned later,
was that they had put way too much

468
00:41:30,000 --> 00:41:35,000
rich soil in the system.
So, the bacteria in the soil were

469
00:41:35,000 --> 00:41:39,000
sucking the oxygen out of the
atmosphere.  And there were

470
00:41:39,000 --> 00:41:44,000
subsidizing the system with rich
soil so that people would have

471
00:41:44,000 --> 00:41:49,000
enough food.  But there was a puzzle,
because if this was the case,

472
00:41:49,000 --> 00:41:53,000
because the cycles are coupled,
you should expect to see the same

473
00:41:53,000 --> 00:41:58,000
amount of, if this oxygen is coming
from photosynthesis,

474
00:41:58,000 --> 00:42:03,000
you should see the same amount of
CO2 coming into the system.

475
00:42:03,000 --> 00:42:07,000
And you should see an increase in
CO2 in the atmosphere.

476
00:42:07,000 --> 00:42:11,000
And they didn't.  In other words,
they saw oxygen going down, but they

477
00:42:11,000 --> 00:42:16,000
didn't see surplus CO2 in the
atmosphere.  And it took a bright

478
00:42:16,000 --> 00:42:20,000
graduate student from Columbia
University to go in there and figure

479
00:42:20,000 --> 00:42:25,000
out what was going on.
And it turned out that,

480
00:42:25,000 --> 00:42:29,000
so why didn't CO2 increase?
It turned out that this CO2,

481
00:42:29,000 --> 00:42:34,000
which was coming out of the system
from respiration in the soil was

482
00:42:34,000 --> 00:42:38,000
actually binding to the calcium
hydroxide in the cement and making

483
00:42:38,000 --> 00:42:43,000
calcium carbonate.
So, the cement,

484
00:42:43,000 --> 00:42:47,000
another human invention,
was playing an important role here.

485
00:42:47,000 --> 00:42:51,000
The point is that none of this,
this is only understandable in

486
00:42:51,000 --> 00:42:55,000
hindsight, because it didn't work.
You can go in and figure out, what

487
00:42:55,000 --> 00:42:59,000
the heck, where did these imbalances
come from?  So,

488
00:42:59,000 --> 00:43:03,000
it was a very interesting study,
and we learned that it's not easy to

489
00:43:03,000 --> 00:43:08,000
mimic natural biosphere
on a very small scale.

490
00:43:08,000 --> 00:43:12,000
OK, I'm going to skip that one,
and come to this real quickly,

491
00:43:12,000 --> 00:43:17,000
because this was just on the news
this morning as I was driving into

492
00:43:17,000 --> 00:43:22,000
work.  I thought,
perfect for this lecture.

493
00:43:22,000 --> 00:43:27,000
The UN just announced this
millennium ecosystem assessment.

494
00:43:27,000 --> 00:43:32,000
It's on the web.
And 2,000 scientists have been

495
00:43:32,000 --> 00:43:36,000
working on this for over ten years
trying to assess the state of the

496
00:43:36,000 --> 00:43:40,000
global ecosystems and their
capability to support future

497
00:43:40,000 --> 00:43:44,000
generations, i.
. you guys.  And they say the next

498
00:43:44,000 --> 00:43:49,000
50 years, and those are the 50 years
that you guys are in charge,

499
00:43:49,000 --> 00:43:53,000
are absolutely critical for whether
or not these systems will sustain,

500
00:43:53,000 --> 00:43:57,000
be able to sustain human populations.
So you can go to the web if you're

501
00:43:57,000 --> 00:44:02,000
interested in that.
OK, quickly to our civil and

502
00:44:02,000 --> 00:44:06,000
environmental engineering major,
I'm just going to say that our new

503
00:44:06,000 --> 00:44:11,000
motto is nature,
tools, and toys, that nature is

504
00:44:11,000 --> 00:44:16,000
ecology.  There is a two series
ecology course.

505
00:44:16,000 --> 00:44:20,000
Tools are mechanics: basics,
fundamentals for analyzing systems.

506
00:44:20,000 --> 00:44:25,000
And toys is design.  The part of
the curriculum is going to be

507
00:44:25,000 --> 00:44:30,000
designing instrumentation for
studying environmental systems.

508
00:44:30,000 --> 00:44:35,000
And there are these brochures here
and in the back.

509
00:44:35,000 --> 00:44:40,000
So I encourage you to pick those up
if you're at all interested in that

510
00:44:40,000 --> 00:44:45,000
major.  Now, let me show you this
cool clip.  Don't leave yet.

511
00:44:45,000 --> 00:44:51,000
This is worth it.  It's only two
minutes, and its nature at its best.

512
00:44:51,000 --> 00:44:56,000
So, all I need to do here is hit
play.  And this is the soccer

513
00:44:56,000 --> 00:45:02,000
player's look like this.
Oh, why didn't that work.

514
00:45:02,000 --> 00:45:22,000
[Miophon?] our little

515
00:45:22,000 --> 00:45:51,000
bugs in the sand.

516
00:45:51,000 --> 00:46:08,000
That's my favorite part.

517
00:46:08,000 --> 00:46:21,000
Life is a geological agent.

518
00:46:21,000 --> 00:46:25,000
See, that would have been a great
kick off for spring break,

519
00:46:25,000 --> 00:46:30,000
but welcome back from spring break.
All right, I'll see you in a few

520
00:46:30,000 --> 00:46:33,000
weeks.