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Lecture 7a - Why do we care about soil?
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Biosphere 2 Science for the Future of Our Planet
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Soil Science - Foundations & Implications
How can soil be alive? In Module 7, discover the fascinating, microscopic world within soils and their critical role in Earth systems. Learn how soils provide functions and services that make them vital to our health and wellbeing. With Dr. Rachel Gallery, UA School of Natural Resources and the Environment, and Dr. Katerina Dontsova, UA Soil Water & Environmental Science, Biosphere 2.
Meet the Instructors
Kevin E. Bonine, PhDDirector of Education and Outreach
Biosphere 2
Hello, my name is Katerina Dontsova,
I am Associate Research Professor of Biogeochemistry and Biosphere 2.
I'm a soil scientist,
and Rachel and I are going to talk to you about soils.
We're going to tell you how they look,
how they form, why do we care about them,
what is the role of microorganisms in the soil,
what is it that we can do to make sure that future generations
can take advantage of the soils that feed us now?
In addition, we'll give you some examples of the current research that is happening,
that is examined in soils and their function.
So, the goals of this part of the module
is to demonstrate the basic importance of soils for human survival.
To learn about full components and their functions in this whole organism.
We want to show you that soils are living systems that change and
develop over time and that can be influenced by human activity.
And then finally, I'll discuss some examples of
the experiments that are examining soil formation.
So, the examples are: Landscape Evolution Observatories,
Geobiology project that was funded by NSF,
and additional project on Climate change and its effect on soils.
So to start with,
why do we care about soils?
There are several functions of the soils that make them essential for human survival.
And one of them is that the supply of water, and air,
and nutrients for the plants that feed us,
they also purify water.
So, they act as natural filters that promote
contaminants from the water as it percolates through the soils.
They support natural ecosystems and Rachel Galerix is going
to be talking about it a lot more in the next part of this module.
They also remove and store carbon from the atmosphere,
what is called carbon sequestration.
Was the climate change where CO2 in the atmosphere is the cause of the global warming?
When soils can store and remove carbon from the atmosphere,
that can mediate the effects of a climate change.
But first and foremost,
soils can make or break civilizations.
If you think about the Egyptian civilization,
and the Nile that brought in nutrients choose the soils and the delta,
that allowed Egyptian civilization to flourish,
you'll see what that means.
We can also think about Mesopotamia,
this is another example of ancient civilization.
There was a fertile land between the two rivers,
it's the birthplace of agriculture.
And the farming of the region dependent on irrigation from Tigris and Euphrates rivers.
Now, the high productivity of those soils allowed few people to produce enough food,
so that other people could work on something else,
those who are free to do art,
were free to create most,
those were free to start Triton.
But what happened over time is the soil from evaporating water,
turns the irrigation accumulated in the soil,
and by about 2300 B.C.
that agricultural production in Mesopotamia was reduced,
and it was much less than it was before.
And with that, the resource that had provided diminished,
and the civilization diminished with it.
So, the official definition of the soil is,
that soil is a natural body,
it's made up of mineral and organic matter,
it covers much of the Earth's surface,
it contains living matter,
and it can support vegetation and this comes from the soil taxonomy.
Now, the soils contain three phases.
So, they have solid phase, this two,
they have liquid phase of water,
and they have a gas phase in them or soil air.
Now, solid phase include both mineral particles and also organic matter in them.
Now, if you think about it each of these phases in addition, has multiple components.
So, if you think about the soil air as I knew there
are multiple gases that are present in the soil air.
If you think about water from multiple solids that are dissolved in this water.
There are many different minerals present in the soil.
And in addition, the organic matter that are shown here,
can have some living matter,
and can have dead and decaying material or
can be some completely transformed broke humidified material.
So as a result of this,
the soils are extremely heterogeneous.
Space between soil particles.
The mineral and the organic matters that I showed before is called soil porosity,
and can be filled either with air or with water.
So, if the soil is saturated completely like after the rainfall,
then all the pores are going to be filled with water,
or if you dry the soil,
and remove all the water then it's going to be filled with the air.
The spaces between the particles are going to be filled with the air.
Now, it's really difficult to dry soil when there is no water present at all.
Most of the time what happens is,
it's conditional like that,
where you have some of the pores are empty,
all the water, so they contain air and some of them contain water.
There is a larger pores that drain fast,
then what they do is they transmit water through the soil,
and also they allow gasses to transmit when the soil is drained.
Now, the smaller pores, things like that,
they hold water longer and that provide the pool for the plants and microorganisms.
Midwinter rains. As soils are formed through several mechanism,
and one of these is weathering of the rock.
Another one is addition of organic material from the biota,
either plants of microorganisms.
And then there is a translocation of the material in solution up and down the profile,
or also in the gas space,
and sometimes even in the solid phase through the soil.
Now, weathering is this very important factor in the soil formation.
So, the weathering overall is a change from
the primary minerals that are formed in high temperatures and pressures,
from the magma to the second minerals,
that happens through physical and chemical processes,
and here I'm showing the chemical process that allows weathering.
The CO2 in the atmosphere when combined with water will form carbonic acid.
It is a weak acid but an acid nonetheless.
And so, the pH of the rain water is about 5.4.
So, it is acidic.
Now, if this water said trackted with this CO2,
then is weathering with the rock.
And this is an example of the primary mineral, potassium feldspar.
What will happen is,
you'll have formation of a new secondary mineral,
you'll have release of some elements into a solution,
and then you'll have also caption some of
this carbonic acid as bicarbonate dicarbonate in solution.
Now, all of these are significant for the functioning of the soil.
Formation and the secondary minerals allows for the storage of the nutrients in the soil.
So, when these elements which are plant nutrients,
or some of them plant nutrients are released.
They would be flushed out of the soil with
the rain unless they have something to attach to.
And these secondary minerals,
some of them are seriously Kaolinite,
they have charges on the surfaces that allow these nutrients to attach to.
So, they are present so they are not leaching.
Yet, if they're needed for the plants,
they can be easily dissolved from those place.
Now, this is important because this provides a mechanism,
also the removal of the CO2 from the atmosphere.
Remember we started here was a CO2 in
the atmosphere which combines with the water and rainfall.
Now, this here when it is leaching through the soil,
if it goes further out of the soil and into the rivers and eventually in the ocean.
What will happen is, it will be stored in the ocean for a very long time.
And so, this provides a good mechanism of the removal of the CO2 from the atmosphere.
Now, after these processes happened,
what the soil would be is,
it will have finer textured than the parent material.
It will contain organic matter so those additions from the plants and microorganisms.
It will be able to hold nutrients in it.
And it will be heterogenous.
One of the parts of this hierarchy need is formation of soil profile.
So, this soil changes in composition and texture from the surface downward.
If you're looking at this plot.
And on the very surface you can see how very dark it is.
So, this is due to the organic matter present there.
And as you can see, plants here are depositing organic matter under the surface.
That's why it's dark under the surface.
And if you go down, then it becomes lighter and then it
has different patterns developing over the belt.
Now, different soils will form different types of profiles.
They are extremely variable and when classified by the soil taxonomy,
there are 12 different soil orders.
And these are examples of the soil orders from NRCS,
Natural Resources Conservation Service.
So, you can see how different soils would be in the different regions.
The factors that are influencing the soil formation or also called pedogenesis
are plants and animals that provide organic matter that is added to the soil.
Climates such as temperature and precipitation.
There's that parent material depending on what you have to start with,
of course your soil is going to be different.
So, the composition of the parent material or particle size of that material is going to
matter in terms of what is going to be in the soil that has been formed.
Topography. Topography influences water flow and the temperature,
so it influences soil formation as well, and time.
All of these processes are connected and they happen over time.
So, the longer time you have,
the more soil formation will happen.
Now, this is a plot that describes what is the effect of climate
and associated other processes to this whole formation.
So, if you look at this plot,
this is a cross section.
We are going from here from the polar region to the equator here.
And if you look at the red line here,
so red line is for the temperature.
So, there is increase in the temperature of course from the polar regions to the equator.
If you look at the blue line,
the blue line is where there is precipitation.
So, there is very little precipitation here in the polar regions,
there is very little here in the deserts.
But then in between, you have increasing precipitation.
Now, in the agreement with the temperature and with the rainfall,
you will see that you'll have more vegetation here in the temperate regions,
then you'll have more vegetation here in
the tropical regions and equatorial regions but you'll have very little in the deserts
here because of so little rainfall is happening here and
very little here in the Arctic region because again,
it's cold and there is very little water.
So, what does it mean in terms of the soil formation?
So if you look here in the temperate regions,
you'll have soil formation happening because there is quite a bit of
vegetation and there is rainfall.
Source of water comes in,
it weathers the rocks,
the plants deposit organic matter.
So, you'll have deeper soils here.
Then, if you look at the deserts here,
there is very little soil formation because there is very little rain,
there's very little biological activity.
And then, you go here to tropical regions and again,
we have very deep soils.
So, these soils tend to be deeper than the ones here in
temperature regions because there is more rainfall and the temperatures are higher,
so there's more vegetation.
So, all of these factors contribute to deeper soil.
Now, interestingly, you would not necessarily find that
these soils are also more productive than these soils.
Because it was the amount of rains that you'll get here and with high temperatures,
the weather can proceed quite far,
and most of the nutrients can overtime be leached out.
So, the tropical rainforest soils are often
less rich in nutrients than the one you'll find in temperate regions.
And in addition, you also find
less organic matter here surprisingly than you'll find here.
Because here you would think that with all the precipitation that you have from
the tropical rainforest you would have lots of deposition of the organic matter.
But something to be considered first that here you have an annual turnover.
So every year over the winter,
there are leaves and they
process die and they fall in the ground and they become part of the soil organic matter.
But at the same time,
what's happening or more importantly,
what's not happening is microbial activity because during winter,
it's too cold for microbes to transform these organic compounds into the CO2.
Now, if you look at this region,
since it's warm the whole year,
then the deposition of the organic matter from
the plants is going to be transformed by the microorganisms into the CO2.
And so, the storage of derogating water is smaller than you'll find here.
Now, there are several ways that we can examine soils.
Soils are very heterogeneous,
it's very difficult to observe soil formation
in nature and environment because they form very slowly.
And in addition, there are multiple interactions between biological,
physical, and chemical processes that are happening the same time.
So there are multiple feedbacks between them.
So, what we have developed is this experiment which is
called Landscape Evolution Observatory or LEO for short.
It contains three instrumented model landscapes.
What it allows to do is examine
soil formation from the very beginning, from initial stages.
And it does not simulate any particular natural environment.
It uses ground basalt as a starting point for the soil formation.
But what it allows to do is to examine
soil formation process under controlled conditions.
And what we see here in the LEO is that even over a very short timescales,
maybe several years worse,
we all already see this formation of heterogeneity on the slopes.
We can see formation of the soil profiles.
We do not have plants yet on the slopes but plants will
add another level of complexity to the soil formation.
And so, in order to examine impact of
the plant's own soil formation processes and microorganisms,
what we did is we submitted a grant to National Science Foundation.
And we had a project where we looked at
the effect of plants and microorganisms of soil weathering.
And then, the loss of mineral-forming elements from the soil.
We looked at four different rocks.
So, we looked at the basalt, granite, schist,
and rhyolite and we had different biological treatment.
So, there was a control when there was no microbe or plant,
there were microbes only,
then there were plants,
and those elusive pine, and the grass.
And then, there were plants with mycorrhiza.
The mycorrhiza is a fringy which leads into a symbiosis from
the plants and it helps them obtain water and nutrients.
So, these are the experiments that we show,
so you can see that we have to keep it very clean.
We want to make sure that we don't have
any inputs of nutrients from the outside of the system.
So, all the neutrons have to come from the weathering of
the rock that was present there in this Metha cosmos.
But what we've found is that there was increasing
the weathering with increasing the complexity of the biological system.
So, if we went from control,
to the microbes only, to the plants,
and to plants with the mycorrhiza,
with each of these steps, we'll see increase in weathering.
But interestingly, we didn't see necessarily increase in the element loss.
So, export in the reverse would not be increasing the set
of all of these elements whilst weather is increasing.
And we often look for the indications of biological effect weathering in the rivers.
So, it shows us that we see plant effect
but we do not necessarily see plant effect on the export.
And this is important and also central to the soil formation
because if you have these elements released and then lost from the system,
then what is the benefit for the plant that are living in there.
So, if they're recycled with in the system
that is a further step into the soil formation.
In the last experiment that I wanted to mention to
you is an Ecotron experiments that we did in France.
And there, we validated that we wanted additional control over the system.
We wanted to be able to simulate the effect of
elevated temperature and the CO2 from
the climate change on biological and abiotic weathering.
And the reason we wanted to do it is we were interested,
is there a negative feedback that is provided by increase in
the plant growth or increase in weathering as
a result of these elevated temperatures or the CO2?
So what we did, we had two different treatments for the CO2,
400 and 800 ppm,
and this was in the atmosphere.
And then, we had two different temperatures,
ambient temperature and elevated temperature,
four degrees higher than this,
and four biological treatments.
So, there is the treatment result plant and then there was alfalfa,
velvet mesquite, and green sprangletop.
So, what we observed was that there was observed increase in
the plant growth and weathering with increase in CO2 and temperature.
And so, we do expect there has going to be a negative feedback in
response to the climate change according to this experiment.
So, we have information about these experiments available online for you.
And with this, I would like to finish this part of the module.
Thank you very much and goodbye.
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