Deep, Down and Dirty: The Science of Soil Page #4

---

to blow rock apart.

Well, you're expanding in a confined

space.

It only has one way to expand

and that's sideways.

That forces the rock apart and it's

the beginning

of the disintegration

to give us the soil.

This process is called

physical weathering.

It breaks down rock by sheer

brute force.

But we're still a long way

from soil.

Next comes a different process

entirely.

And it starts with rain.

We'll just drop some

hydrochloric acid onto limestone.

You can see it fizzing.

You can hear it fizzing.

It's really going at it.

What Stephen's showing me

is an exaggerated version of what

happens every time it rains.

Rain is slightly acidic

and, with limestone,

when this slightly acidic water

falls on the surface it weathers it.

And is that what we're seeing here,

on the surface of the rock?

That is exactly

what we're seeing here.

So rain reacts with the rock,

gradually dissolving it. This is

chemical weathering.

The second key step towards soil.

Using a stronger acid to speed

the process up,

we can see just how powerful it is.

Here, a piece of rock is almost

entirely dissolved. Leaving

behind nothing but insoluble,

sandy remains known as sediments.

And that's the beginning

of the soil.

It's a very small

amount of insoluble residue,

but that's where the soil

development starts.

But sediment isn't yet soil. There's

something fundamental missing.

Life. But look closely,

and this rock is not bare.

It's covered in this, lichen.

And this is what causes the final,

almost magical metamorphosis from

inert rock, to life-giving soil.

In this environment they are key

because the lichen will attack the

rock, very much like the chemical

weathering we saw, but it will break

it down, release nutrients.

Lichen is actually two organisms,

algae and fungus,

living in one body.

And though it seems almost

incredible, the fungus part is able

to break down the rock to release

nutrients that it can feed on.

Much as we saw the fungi do

with the wood in the forest.

Over time, generations of lichen

grow over one another,

the new on top of the dead.

The dead remains form

organic matter.

And when this mixes with sediment

the result is soil.

And so from an apparently barren

limestone pavement up here

we have the complete story

of the generation of our soils.

Bare rock through the various

weathering processes, the biological

processes and eventually the

formation of soil. It is all here.

Condensed into just a few

square metres.

Yeah, it's a wonderful example

of soil development in motion.

And what we've got is different areas

representing different timescales -

some it's just starting,

others it's been going on

for a few thousand years.

Soil is the place where the

relatively inert world of rock meets

the riot of life above.

It's a complex,

staggeringly complex ecosystem,

but it also offers

something of a conundrum

because the life creates soil,

breaking down organic matter and

forcing rocks apart, but that life

is also dependent upon the soil

for nutrients, moisture, habitat,

anchorage, somewhere to live.

That means there's a delicate

balance between the life

and the soil.

Challenge one and you inevitably

challenge the other.

And today that ancient balance

between rock and life

is being challenged

as never before in history.

A new force has entered the world

of the soil. Humankind.

In geological terms,

human civilisation is a mere

blink of the eye, at around about

9,000 years. And in that brief

moment in time we've arguably done

more to change our soils than

in the previous 400 million years.

We've mined it.

Built on it.

Farmed on it.

And, in places like this,

drained it.

And our actions have had

consequences we never imagined.

East Anglia is famed for its fenland

landscape. One of rivers,

marshes and streams.

But what we have left is just

a fraction of what was once here.

Largely because this is a habitat

that's prone to flooding

and since the 17th century

generation after generation have

been progressively draining it.

The great system of canals

and ditches have been dug.

To drain the unwanted water

into the sea.

Over the past 300 or so years,

the population of the UK has

grown rapidly.

This put huge pressure on places

like the fens.

To help feed all those extra mouths,

we needed to dry out

the waterlogged land to make way

for the business of agriculture.

Rivers and lakes were drained

and crops planted.

The few people who lived there were

thought rough and unfriendly.

Old ways of life and traditional

pastimes that had grown up

around the flooding

were swept aside.

But this progress came with

a sting in the tail.

As the rivers

and meres were drained,

something unexpected happened.

The land began to sink.

This is Holm Fen,

drained in the 1850s.

It was the home of Whittlesea Mere,

once thought to be the second

largest lake in England.

This is all that's left.

Previous experience had demonstrated

that if you drain the fens

the land would sink.

So a local landowner

here at Holme Fen, William Wells,

decided to measure that process.

He took a post

and pushed it into the ground

until the top was completely

covered. And that post today?

Well, here it is.

The top of the post was originally

ground level.

Since 1850 this whole tract of land

has sunk somewhere in

the region of four metres,

making this one of the lowest

places in Britain.

There can surely be no clearer

indication of the effect

of human interference on soil.

But why did it sink?

And what are the consequences?

'I'm joined by Dr Ian Homan.

'He and his colleagues at

'Cranfield University have

extensively studied the area.

'We're going to take a look

at a rather special type of soil

'found here in the fens.

'This is peat.'

Pretty good profile. It is indeed.

Peat forms in a wetland environment,

so the soils are waterlogged.

It's low in oxygen under the surface

and it's quite acidic.

So the combination of the

waterlogged nature,

the lack of oxygen and acidity slows

down the rate of decomposition.

The soil bacteria and

the microbiological

components of the soil aren't able to

decompose that organic material.

So it accumulates very slowly.

So in peat, instead of being broken

down, plant material builds up.

And this has an important effect.

Plants grow using carbon dioxide

from the air.

And if they're not broken down

when they die

they and the carbon they contain

become trapped within the soil.

This is what's

known as a carbon sink

and peat bogs are some of the best.

But remove the water,

and the balance changes.

Oxygen enters the soil, allowing

bacteria and fungi to breathe.

This is what happened

when the fens were drained

and it had profound consequences.

That allows the micro-organisms

to use the carbon within this peat

as an energy source, converting

the carbon into carbon dioxide

and energy.

Rate this script:3.0 / 2 votes