Soil erosion (Types and Causes)

Go to page 180 of Edexcel Geography book, I've adapted the page here, and have added some explanations where I thought they were needed. :)

Soil erosion is the washing away or blowing away of top soil. Basically the wearing away and loss of exposed top soil, mainly by the action of wind and rain (as surface run-off). 

Soil erosion can result in reduce soil fertility. It is a natural process, but it is made worse by people.

There are three main types of soil erosion:

• sheet erosion: occurs in parts of the world where there is moderate rainfall. When this falls on bare soil, the top of the soil will be removed down slope. 
• gully erosion: where there is intense rainfall, as during tropical storms, the force of the water can cut gullies in slopes. This is most likely to happen where there is little vegetation cover. 
• wind erosion: in dry parts of the world, loose dry soil is readily blown away by the wind

Thus, areas most at risk of soil erosion:
-mountainous areas with steep slopes (e.g. Himalaya slopes in Nepal), so the topsoil is removed as rain flows downslope. One quarter of a million tonnes of topsoil are washed off the deforested mountain slopes of Nepal and northern India each year only to be deposited into the Bay of Bengal.
-areas with unreliable rainfall, as the soil dries and becomes really light so the wind can carry it away quickly

Also keep in mind that exposed soil doesn't just get washed downhill by water, it can move downwards slowly under gravity too. Soil erosion can be particularly bad during wet seasons as it is washed away by the storms and it is blown away during dry season..

Soil erosion is made more rapid and severe where there is misuse of the land.
Activities that cause problems include:

• removing vegetation by cutting down trees and bushes for fuel or to make way for more farmland. This exposes the soil to the wind and rain.
• overgrazing by animals-rearing too many animals in relation to amount of grass available. Result: ditto above.
• overcultivating the soil by failing to 'feed' it with fertilisers or by growing the same crop  in the same field year after year. This monoculture weakens the soil structure and removes vital minerals from the soil. (The same crop uses up the same nutrients until it is all depleted.) The net result is that crops will fail and the soil will be left exposed to the forces of erosion. 
• compacting the soil by the use of heavy machinery. (e.g. if a tractor went over a patch of soil, the weight of it would increase pressure on the soil, squashing it together and making it more compact.) This reduces the rate at which rainwater is able to infiltrate the soil. So much of the rainwater flows across the soil surface and erodes the soil as it does so. 
• ploughing fields in the same direction as the slope. This readily encourages gullying. (Ploughing up and down hill creates channels down which rain water can flow. Increases amount and speed of surface run-off.)

In general, you can say that the threat of soil erosion increases with the sparseness (lack of) of vegetation. It also does so where population numbers are so great that they put pressure on the land. (E.g. increase in population means more food is needed, so farmers try to grow more crops but on the same piece of land..growing crops so intensively to feed a growing population can only result in decreasing fertility of the soil, especially when fertilisers are not added to replenish nutrients taken up by the crop!)

Fragile environments and sustainability

Our living standards and health may depend on the quality of the Earth's physical environment, but we are destroying it. There's a delicate balance between non-living (climate, rocks, soils) and living (plants, animals) parts. 

And natural environments are fragile. That means these places are sensitive to the presence of people, and are easily abused and harmed by us. 

Though natural hazards like forest fires and volcanic eruptions have always disturbed environments, these places have always managed to recover. 

But now, the growth of the world's human population is what threatens the fragile balance of the environments the most. 

We have disturbed 90% of the Earth to some degree or another. It's hard to find truly wild and natural areas that are untouched by human activity. 

There are three important processes that are responsible for making environments more fragile:

• soil erosion
• desertification
• deforestation 

They not only damage natural environments, but are linked to global warming and climate change too. In fact, they are both causes and consequences of climate change. 

I will discuss them in later posts. But keep in mind they are not the only ways in which natural environments are being upset, but for this course, they are the 3 processes focused on.

Understand that most processes that upset the natural environment relate to us humans exploiting the land. We cause a lot of land, air and water pollution.

Two terms you must know when studying fragile environments: ecological footprint and sustainability. 

Ecological footprint: this is a measure of the mark we humans make on the world.

It considers how much land and sea are needed to provide us with the water, energy and food we need to support our lifestyles. 

If the Earth's resources were shared equally among everyone, we would each have a little less than 2 hectares of the globe! However, the UK has an ecological footprint of about 5.5 global hectares per person. This means that if everyone in the world consumed resources at the rate people in UK do, we would need 2 more planets to sustain our present population. 

Sustainability: 'actions and forms of progress that meet the needs of the present without reducing the ability of future generations to meet their needs'. 

That's the textbook definition, but I like to think of it as the following just so I understand it better:

"The ability to meet the needs of the present while preserving the environment so future generations can meet their needs too. 

Try explaining 'sustainability' to someone else in your own words, to see if you truly understand it. 

Global variations in the ecological footprint

So if we are to continue using the natural resources in the global range of different environments, we need:

• to do so with much more moderation
• to be aware of how easily the balances of those environments are upset
• to reduce our ecological footprint to a minimum

It's very idealistic, and may be what we need to do, but in fact it'll be very hard to do so.

It could mean that some places cannot have economic development. Which really should be the case in the few remaining truly wilderness areas, like Antarctica, the tundra of Siberia and the Amazon rainforest. 

It's vital that the biodiversity and pristine nature of such environments are protected for the general 'health' of the Earth and its people. If not, our present abuse of the planet promises an unsustainable future. :/ 

The link between ecological footprint and sustainability is that the ecological footprint theory helps us to judge how sustainable our lives are now. It helps us to make judgement about the future too.

We know that global population will continue to grow for at least the next 50 years. It warns us of the extent to which the world's environments will become even more fragile. It advises us as to what is sustainable. 

UK Water Demand & Supply Case Study

Somebody asked for this, but it's not the case study I'm doing so this is just me copying what's in my book, it's all I've got since I know nothing about this.. :S Hope it helps anyway. 

I'll add some posts about water supply and demand that hopefully you can apply to this case study. :) 

Meeting the rising demand for water in England and Wales

Daily water consumption in England and Wales is about 120 litres per person per day. This is not a particularly high figure compared to 309 litres for France and 185 litres for Germany.

Water consumption in Britain has been rising along with the growth of population.

However, over the last 200 years, it has been given a number of pushes.

1. The growth in manufacturing in the early 19^th century. With deindustrialization in the second half of the 20^th century, manufacturing uses less water (now 14%). Other consumers now account for more water use. Most notable is the use of water in the generation of electricity. More water is being used today to irrigate crops (14%) to feed a growing population and British citizens are using more water in their homes (20%). More homes today have washing machines, dishwashers and swimming pools.

Water is important in making electricity in two ways:

·   It is used to turn the turbines that generate the electricity, as in HEP (hydroelectric power).

·   It is converted into steam by the burning of fossil fuels and the steam turns the turbines.

The problem that faces England and Wales is that the distribution pattern of water demand is different from that of water supply (Figure 1.27). The highest water demand is in SE England which happens to be the driest part of the country. Water is most readily available (the rainfall is highest) in upland areas that are mainly located in Wales and the north of England. The mismatch between demand and supply creates different levels of water stress (Figure 1.28). Clearly the greatest water stress lies in the south-east of England. It is being tackled as follows:

·         Extracting as much water as possible from the aquifers of SE England

·         Constructing reservoirs in the north and west of the country to collect as much rainfall as possible. Famous reservoir schemes include Lake Vyrnwy in Wales and Kielder in NE England

·         Transferring this collected water by pipeline to the main reas of water deficit, i.e. the major cities of the Midlands and South

There is no doubt that meeting the rising demand for water is a challenge for the UK. Attempts are being made to reduce water consumption by encouraging a much more efficient use of the available water and to eliminate water wastage.