Geoecology – Three Essays in Section – Choose One – Each essay 80 marks Sample Geography Paper


Climate a Characteristic of Desert Regions



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Climate a Characteristic of Desert Regions


  • Rainfall is usually v low and unpredictable. Short bursts of rain that are not easily absorbed into the ground. This is due to the high rate of evaporation. Rainfall has therefore a minimal effect on vegetation growth.

  • Annual rainfall in the hot desert regions varies between 150mm and 300 mm per year. The Cold Desert receives 300mm of precipitation throughout the year. This falls as snow during the winter months.

  • The temperature range in the deserts is extreme. Diurnal range is often greater than 30˚C. Annual temperature range is between 20˚C and 30˚C. ‘Night is the winter of the desert’.

  • Due to the latitudes, by day the sun is high in the sky, shining vertically on the barren region. With little vegetation and cloud cover very little heat is lost and most is absorbed by the stony surfaces. The temperature can climb to 45˚C.

  • Night time, temperatures plummet due to the absence of cloud cover and vegetation. The temperature can fall below freezing point.


Soil - A Characteristic of Desert Regions


  • Dominant soil is Aridsols in this region. Aridsols range from sand and fine textured to gravelly and coarse textured. Soils have been eroded and washed down from mountainous areas during repeated downpours over 1,000’s of years.

  • Lower slopes have coarse textured soils. These are well drained due to their texture. There is a deep soil cover of fine soil but this cover is susceptible to erosion if winds are strong as fine particles can be borne in the wind.

  • Composition Aridsols have a low percentage of organic matter due to the sparse vegetation cover. There is very little humus in the upper horizon of the soil which means that the soil does not have a visible A horizon. The soil tend to have a light grey colour also due to the absence of dark coloured humus.

  • Nutrients Due to the mineral content of the soil the soil has many nutrients. This is evident when plants grow rapidly after a downpour. However, due to lack of vegetation and humus in the soil, the soil cannot retain the moisture it receives from as a result of precipitation and it is lost through intense evaporation.

  • Salinisation occurs as a result of the arid conditions. Moisture moves up through the soil by capillary action. Dissolved salts are brought back to the surface creating saltpans on the surface. These poison the soil and totally restrict growth.

  • Calcification can also occur as a result of the vertical movement of moisture. A hardpan layer of calcite builds up in the lower soil horizons. This prevents roots from penetrating the soil and creates hard areas within the soil.



Adaptation of Plant Life to Soil and Climatic Conditions


  • Fast growing plants are supported due to the availability of moisture in the soil for short periods of time. These ephemerals complete their life cycle in a short 2-3 week period. This occurs following heavy showers of rain. The seeds have a waxy coating which ensures that the seeds can survive many years if necessary. Examples of these include the Desert Paintbrush and Creosote Bush.

  • Succulent plants store water for long periods. They store water during wet periods in their structure, this can include tap roots, stems or spines. The plants swell up when they absorb water and appear to shrink as water is lost. Examples include the Joshua Tree and varieties of the Yucca plant.

  • Large root systems provide plants with the opportunity to absorb large amounts of water when it rains. The roots are close to the surface and spread outwards. The Giant Saguaro Cactus has a shallow root system.

  • The Mesquite has long taproots reaching up to 50 ms which allows the plant reach deep underground in search of moisture.

  • Defensive systems such as unpleasant smells and tastes are another way that plants have adapted to the harsh soil and climatic conditions. The Creosote bush produces toxins if an animal attacks it.

  • The spiky leaves and spines found on a cactus stop creatures eating its succulent flesh and hence its water supply. These also reduce evaporation in the intense heat.


Adaptation of Animal Life to Soil and Climatic Conditions


  • Animals are nocturnal. Animals such as the rattle snake and elf owl are only active in the morning or evening.

  • Animals burrow into the ground to escape the heat. Tarantulas hide in the ground during the hottest parts of the day and come out to hunt and feed when the desert is cooler.

  • Insects use the shade of twigs to stay out of the direct glare of the sun. The Jackrabbit shades under the larger Joshua Tree and moves with the shadow to keep out of the sun.

  • Many desert animals have paler skin/fur than other varieties of their species. This makes the animal less obvious to predators and assists the animal in absorbing less heat.

  • Animals such as the jackrabbit have developed long body parts to lose some of their body heat. The jackrabbit has extremely long ears.

  • Animals such as the squirrel hibernate during the extremely hot summer season.

  • The road runner, a bird typical of the North American desert, runs instead of flying, thus preserving most of its energy. (and keeping ahead of the coyote)

Answer this question-. Describe how plant and animal life adapt to soil and climatic conditions in a biome which you have studied. Throughout the answer keep on referring back to the question. Use linking statements such as – ‘In order to best describe how the vegetation and fauna have adapted to the North American Desert, it is essential to describe the soil and climatic conditions of the region.’ Or ‘This is another example of how plant life in this biome has adapted to the soil conditions’.


The Impact of Human Activity on a Biome
A biome that has been greatly impacted by Human Activity is the Desert Biome of California.
Prior to the gold rush of the 1850's this area was not densely populated. It was home to Native Americans and those descendents of Spanish expedititions. However since the Gold Rush of the 1850's the tide of immigration continues into the state of California. The motto of the State of California is Eureka, meaning we found it referring to the discovery of Gold in the State. It is also known as the Gold State.
Deforestation


  • California's forests of Giant Redwood Trees have been decimated since the Goldrush. There is only 4% of the original stock of forests remaining. The Giant Redwood was seen as the most hard wearing and were used before the forests of oaks and pines.

  • Lumber from the trees was the first building material to be produced industrially in Northern California.

  • Sawmills were established throughout the region to process the wood from forests.

  • Wood was originally used to support mines, used as pit props.

  • Wood was used to build mining towns, agricultural towns and commercial centres.

  • The building of railways meant that lumber could be transported as far south as San Francisco. Forests were cleared for railway lines and farmland.

  • The forested areas were replaced by towns and cities built by the wood that once naturally grew there.

  • Where hillside areas were deforested, grassland and scrub woodlands grew.

  • Presently the remaining forests have been brought under the control and ownership of the State and logging has been banned.

  • The remaining forests of trees that are in some cases over 100m tall and over 2000 years old continue to provide a habitat for many species of animals and plants that were also endangered with deforestation.


Permanent Settlement


  • Every year over 500 km2 of natural habitat continues to be taken over by human settlement. This land has been taken over by residential and commercial use.

  • The population of California has increased at a high rate since the 1850's. At that time the population was 100k, it is projected to be 50 m by the year 2050.

  • The original residents of the biome were Native American Indians who built temporary settlements that did not permanently impact on the environment.

  • Settlements were built to provide centres for those who came to California during the Gold Rush. These settlements were often left abandoned after the Gold Rush (Neil Young)

  • With a growing population, the vast urban area of LA sprawls over an area greater in area of county Dublin.

  • Las Vegas founded in the Mojave desert in 1905, now has a population of over 560,000

  • Species of animals such as the Desert Tortoise are under threat of extinction as a result of urban growth in to natural habitats.

  • California's residents are car and road users and these drivers pose a threat to wildlife as many animals are killed by cars as well as being affected by pollution from California's cities.


Intensive Agriculture


  • Intensive cattle and sheep grazing in California has led to the destruction of native vegetation.

  • Attempts were made to introducing fast-growing varieties of grasses from Europe. These plants were not suitable to the local conditions and did not survive. As a result weeds such as Tumbleweeds took over native grass of the region.

  • California is the main food producing state in the United States. One in 10 of its population is employed in Agriculture.

  • In order to produce such a large amount of food in such an arid area many artificial methods including irrigation are used.

  • Several thousand hectares of desert and wetland areas are converted every year to agriculture. Resulting in the loss of habitat for native plant and animal species.

  • Overuse of ground water led to drop in water table level. This has led to salinisation in the soil rendering it unusable and the loss of vegetation cover.

  • Dams have been constructed which have changed the natural flow of rivers this has resulted in the loss of water source to plant and animals.

  • Due to intensive farming practices, pesticides and fertiliser including nitrogen and phosphorous are found in the run off from irrigated land. These chemicals cause the growth of algae. Water in rivers and lakes has less oxygen and is unable to support as much fish life as previously.



Soil Composition and Characteristics
Introduction

  • Soils are a fertile, natural resource

  • Soils develop from the weathering of rocks in one place and from redeposited weathered materials

Composition

Soil is made up of


  1. Mineral particles –

Pieces of weathered or eroded rock from the soil’s parent (original) rocks over a long period of time

Mineral particles make up approx 45% of soil

Example of mineral particles – calcium from limestone rock


  1. Air

Air is found in spaces or pores between soil particles. Air supplies oxygen and nitrogen that help plants grow.

Air makes up approx 25% of a soil.



  1. Water

Water is found is spaces between soil particles.

Water dissolves soluble minerals and moves fertile minerals to roots in the plants

Water therefore nourishes plants

Water makes up approx 25% of soil. This is not the case in deserts



  1. Humus

Humus is organic matter, the remains of dead plants and animals

Dead plants are broken down into humus be microorgansisms (earthworms and fungi)

Humus darkens soil and increases fertility

It is found near the surface



Organic matter is approx 5% of soil


Refer to the graph - Match 1,2,3,4

with the four elements of soil.

Note the title of the graph

Note the data labels.

Using the information that we have studied today, write a short piece no more than 12 sentences long on the four elements of soil.



Soil Characteristics
There are 6 major characteristics (qualities) of soils


  • Colour

  • Structure

  • Texture

  • Organic Content (Humus)

  • PH Value (Acidity)

  • Water (Content and Retention)

We will study and learn three in detail – Texture, Structure, Water Content and Retention.


Texture of Soils


  • The texture refers to the smoothness of coarseness (roughness) of soil. The texture depends on the size of the soil particles, which effects the pore space or gaps between the soil particles.

  • The different pore spaces mean that soils will have different

    • Aerations (Amount of Air)

    • Drainage (water passing through)

There are three main textures –

Sandy Soils


  • Rough/coarse and loose textures

  • Large pores between particles so air and water can pass through them

  • Little waterlogging so the particles don’t stick together

  • Leaching of nutrients can occur and during a dry spell there may be a shortage of water

Clay Soils

  • Smooth with small soil particles and are packed closely together (tight fitting)

  • Very tiny pores so they prevent water and air passing through them

  • Waterlogged in winter due to heavy rain (heavy/sticky) and hard, dry cracked surfaces in summer

  • High in nutrients as leaching does not happen easily

Loam Soils

  • Form from roughly equal amounts of sand and clay particles

  • Moderate pore sizes allow enough air and drainage

  • They usually don’t become waterlogged in winter or too dry in summer

  • Light soils and high in nutrients so ideal for agriculture.


Structure of Soils

  • Soil structure describes how soil grains are lumped or cemented together by Humus and Water

  • The grains of soild are in small lumps called PEDS.

  • The structure of the soil depends on the shape of the peds

  • The spaces (pores) between the peds allow the soils to hold air and water or let air and water through

  • The main soild structure are – Crumb (granular) allow air and water to pass through – Platy where the peds are flat and overlap and prevent water from passing through (waterlogging occurs)


Water Content and Retention

  • The amount of water in a soil or the amount of water a oil can retain depends mainly on:

  • Texture

    • Coarse sandy soils have large pores so they allow to pass through (little retention)

    • Small grained clay soils don’t allow water to pass through so they are poorly drained




  • Structure

    • Crumb structures allow water to pass through, so they can dry up quickly

    • Platy structures restrict water movement so they have a large amount of water

  • Humus – Soils rich in humus can hold more water than those with a low humus content




So far we have learnt a lot about soil and the questions that are asked in this Elective.

How many essay questions are on the paper? ________________ How many do you answer?_______

How many marks are there for each essay?____________________

Name four components of soil._______________________________________________________

Name four characteristics of soil _____________________________________________________

Which soil has the most desirable texture ______________. Why is this__________________________ _______________________________________________


Today we are going to learn two things 1 Factors Affecting Soil Formation. 2 The Factors that influence the characteristics of soil




1 Factors Affecting Soil Formation
Soil is produced by the interaction of six major factors –

  1. Parent Material

  2. Climate

  3. Relief

  4. Organisms

  5. Time

  6. Human Influence (study later)

1 Parent Material



  • The first stage in the formation of soils is the physical weathering of parent rock to give a layer of loose, broken rock called regolith.

  • Parent material can come from a number of sources. These include River Alluvium, Glacial deposits including boulder clay, sand and gravel and volcanic material such as lava and ash.

  • Parent material supplies minerals for the development of soil.

  • Soils retain features of the original parent material therefore producing soils of different mineral content, depth, quality, acidity and texture.

    • Sandstone soils – Sandy and free draining

    • Shale – High clay content – badly drained

    • Limestone – Alkaline and have high PH

2 Climate



  • The two components of climate temperature and rainfall have a major influence of the formation of soil on a global scale.

  • Climate affects the rate of parent rock weathering and the most rapid breakdown of parent rock into minerals occurs in the hot, wet and humid equatorial and tropical regios where chemical weathering is very rapid.

  • Mechanical weathering as more prevalent in regions of colder climates.

  • Colder regions can be frozen for long periods of the year thus reducing the amount of vegetation on the soil and the rate of breakdown of organic matter into humus.

  • Rainfall amounts influence the type of vegetation that grows – influences creation of humus

  • Regions where there is heavy rainfall have most leaching causing acidic soils.

  • A combination of rainfall and hot climates speeds up the decay of vegetation.

3 Relief


  • Height of the land determines clouds and rain, temperature and growing season.

  • Flat upland areas get waterlogged due to the slow rate of movement of water

  • Peat soils develop due to the non conversion of dead organic matter into humus caused by low temperatures.

  • Sloping land is usually well drained and dry.

  • Risk on sloping land of soil creep as soils are thin.

  • Lowlying flat areas have deeper soil. The area is warmer so that humification can take place and the soils are richer and more fertile.

  • Sometimes lowlying areas can be waterlogged and boggy due to rainwater collecting at the bottom of slopes



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