The case study is something that has been directly asked about in many past HSC examinations. In recent years, there has been a more indirect but a 7-8 mark question asked at the end of the core section. Part of the answer needs to discuss salinity in some detail and Wagga Wagga could be used as an example.
The initial act that culminated in Wagga Wagga having a salinity problem was the clearing of vegetation. In balanced systems where there existing salt, but no salinity problems, the amount of water in (recharge from rain) equals the amount of water out. The "out" that water can have in that area is by groundwater entering the the Murrumbidgee River or more importantly, by the removal of water by deep rooted native plants. In doing this, the water table is kept well away from the surface, and any salt that is in the soil remains solid. As a result, it cannot cause any harm.
By removing the vegetation, the balance is tipped so that recharge is greater than removal. Therefore, the water begins to build up in the soil and as the levels move closer to the surface, salt is dissolved.
There have also been additional water inputs into the soil which contributed to the salinity problem. These are:
1. Rubble pits for stormwater runoff from roofs.
2. Planting shallow rooted non-natives and grasses.
By the early 1990's Wagga Wagga council realised that they had to take steps to or face an annual bill of $6 million/year (1995 dollars) to maintain infrastructure damaged by salt.
This rising groundwater was not only damaging buildings and roads but was having other effects on the biotic (living) and abiotic (non-living) parts of the environment. You are expected to know and describe some of these.
They did this in a number of ways:
1. Groundwater pumping
2. Draining waterlogged areas into evaporation basins
3. Tree replanting.
You are also expected to know the scientific reasoning behind this and the success/failures of these strategies.
Wednesday, October 31, 2012
Saturday, October 27, 2012
Salinity - Types, Causes and Effects
In this section salinity will be discussed.
The single biggest cause of salinity in Australia is land clearing.
In the figure below, deep rooted native vegetation removes the water added to the system by rainfall, from the soil by transpiration. As a result, the salt cannot dissolve and is locked in the soil in a form that can cause no harm.
By removing the vegetation the water loss from the soil is reduced, as less evaporation/transpiration can take place. The water rises and salt contained in the soil is dissolved. The water being added by rain continues to also raise the water table. This is the cause of dryland salinity.
In the case where water is being added to the system by irrigation (such as on the left side of the bottom figure), this will be the cause of irrigation salinity.
Finally, when this salt affects built structures in residential areas, its called urban salinity.
Over time, as the water table rises, the salty water will reach the surface soil. The water will evaporate and the solid salt is left behind. When salt gets to the surface, very little can grow, and it is very time consuming and expensive to rehabilitate the land.
The single biggest cause of salinity in Australia is land clearing.
In the figure below, deep rooted native vegetation removes the water added to the system by rainfall, from the soil by transpiration. As a result, the salt cannot dissolve and is locked in the soil in a form that can cause no harm.
By removing the vegetation the water loss from the soil is reduced, as less evaporation/transpiration can take place. The water rises and salt contained in the soil is dissolved. The water being added by rain continues to also raise the water table. This is the cause of dryland salinity.
In the case where water is being added to the system by irrigation (such as on the left side of the bottom figure), this will be the cause of irrigation salinity.
Finally, when this salt affects built structures in residential areas, its called urban salinity.
Over time, as the water table rises, the salty water will reach the surface soil. The water will evaporate and the solid salt is left behind. When salt gets to the surface, very little can grow, and it is very time consuming and expensive to rehabilitate the land.
The best way that salinity can be dealt with is by lowering the groundwater level by either pumping the water out and discharging the water somewhere it cannot cause further harm or by replanting the vegetation so that the roots remove the water and any salt left being is re-solidified and again rendered harmless.
Friday, October 26, 2012
What's Due Next Week
There are plenty of things that need to be completed for next week.
1. Your experiment proposal Due Monday 29/10). I need to see the
following:
1. Your experiment proposal Due Monday 29/10). I need to see the
following:
- Aim
- Hypothesis
- Equipment
- Method
- Safety Precautions
- How you are going to record your results (desirable but not compulsory)
Please refer to your task notification, especially the section about best practice for writing reports. Remember, the more criteria you fulfil, the better your mark.
2. Your dot points for the first 2 sections of the syllabus. This is to do with:
- Australian soils (East vs West)
- Erosion (urban and rural)
This will be due in on Thursday 1/11. On that day a quiz will be done on the class to see your level of understanding and if I need to change what I am doing. There will be at least 1 past HSC question in this quiz.
Tuesday, October 23, 2012
Some more hints regarding the assessment task.
As discussed in class yesterday, there are a number of things you need to bear in mind. These include:
1. What is the variable that you are going to change?
2. What is the variable you are going to measure
- Time for water to enter the soil?
- Time it takes for water to leak out of the soil?
- Amount of water the soil can hold?
3. What variables need to be controlled?
4. What other pieces of information need to be collected and how are you going to present your results?
5. What were the faults in your experiment? Can these be improved?
Thursday, October 18, 2012
Assessment task - Compaction of soils
Task 1 - The effects of compaction of soils
The task notification can be viewed/downloaded from here
The handout notes can also be viewed/downloaded from here
You will need to perform the experiment and write it up. If you watch the movie that is on the network and note the key impacts it has on soil and its relationship with water, it should be fairly straightforward to design an experiment. The task notification gives you hints on equipment and how to write this up.
The task notification can be viewed/downloaded from here
The handout notes can also be viewed/downloaded from here
You will need to perform the experiment and write it up. If you watch the movie that is on the network and note the key impacts it has on soil and its relationship with water, it should be fairly straightforward to design an experiment. The task notification gives you hints on equipment and how to write this up.
Erosion in an Urban Setting
Building sites
Building sites are one region where erosion occurs in urban areas. This is because the vegetation is removed. As a result many building sites have to control the movement of sediments when rain washes the top layer of soil off.
Developed areas
In urban areas which are largely developed, the impermeable surfaces of roofs, paths and roads cause stormwater to be concentrated and fed into creeks and rivers. This causes a pulses of high and then low water flows between rain. During and immediately after rain when the water flows are high, they erode the sides of the creeks and rivers. This in turn means that sediment is picked up and deposited elsewhere.
With this in mind, we began looking at the Lake Macquarie area as a place where erosion and sedimentation was taking place. Not only is there erosion taking place in the creeks due to development, but the sediments were filling the main lake area. The council has been working with community groups to revegetate affected areas and constructing artificial wetlands. As schematic diagram is below:
Apart from acting as a sediment trap and removing nutrients from the water, artificial wetlands slow the flow rate of water and in doing so, they reduce the amount of erosion from the path that they travel. Various features of artificial wetlands are discussed in your handouts.
Apart from these wetlands, community groups have been heavily involved in revegetating areas around creeks etc that have been eroded to try and stabilise the situation. Once again the roots of the plants will hold the soil together and it should no longer wash away.
Finally, the council has adopted codes of practice that must be adhered to by building site managers. These include trapping sediment on site so that it is not washed away.
Building sites are one region where erosion occurs in urban areas. This is because the vegetation is removed. As a result many building sites have to control the movement of sediments when rain washes the top layer of soil off.
 |
| note the sediment fences to stop soil entering the storm water system and keep water quality high in nearby creeks/rivers |
Developed areas
In urban areas which are largely developed, the impermeable surfaces of roofs, paths and roads cause stormwater to be concentrated and fed into creeks and rivers. This causes a pulses of high and then low water flows between rain. During and immediately after rain when the water flows are high, they erode the sides of the creeks and rivers. This in turn means that sediment is picked up and deposited elsewhere.
With this in mind, we began looking at the Lake Macquarie area as a place where erosion and sedimentation was taking place. Not only is there erosion taking place in the creeks due to development, but the sediments were filling the main lake area. The council has been working with community groups to revegetate affected areas and constructing artificial wetlands. As schematic diagram is below:
Apart from acting as a sediment trap and removing nutrients from the water, artificial wetlands slow the flow rate of water and in doing so, they reduce the amount of erosion from the path that they travel. Various features of artificial wetlands are discussed in your handouts.
Apart from these wetlands, community groups have been heavily involved in revegetating areas around creeks etc that have been eroded to try and stabilise the situation. Once again the roots of the plants will hold the soil together and it should no longer wash away.
Finally, the council has adopted codes of practice that must be adhered to by building site managers. These include trapping sediment on site so that it is not washed away.
Tuesday, October 16, 2012
Erosion in a Rural Setting
Causes of Erosion and Possible Solutions in Rural Areas
The biggest cause of erosion is started by land clearing. By removing vegetation, there are no roots to hold or stabilise the soil and so it can be removed by wind or water. In the case of wind, the fine topsoil layer is lifted and carried away.
In the case of water, the lack of vegetation means the soil cannot hold as much water and it begins to flow over the surface. There are 3 main types of surface erosion:
1. Sheet erosion. As the name implies water moves over the surface in a large area. It removes the most productive layers of the soil (the A and O layers) and can remove seed from freshly planted fields.
2. Rill erosion. Once again, the upper layers of the soil are removed but now channels are starting to form. Rill erosion can lead to gully erosion.
3. Gully erosion. This is where channels over 0.5 m deep are dug out by the water. The channels are too deep to allow vehicles or animals to safely cross and so they effectively reduce the amount of usable land.
4. Streambank erosion. This is where rising water can wash out the sides of creeks and rivers. In our local area, the wash from boats can also contribute to this.
Erosion on rural land can be mitigated by:
1. Contour ploughing. This is where the land is ploughed at right angles to the slopes of hills. This means that water flow is greatly slowed by the furrows in the land and so it reduces the potential damage it can cause. Contour ploughing can only work on slight slopes and beyond that terracing may be required.
2. Seed drilling. Rather than pulling out the old crop or reploughing the land seed drilling involves slashing the old plants and leaving the roots still in the ground and a mulch cover on top. The mulch prevents drying and wind erosion while the roots stop water from carrying soil away. The new seed is planted by drilling it into the soil next to the slashed plant. As the new seed grows the old plant rots away adding organic material to the soil, and the growing plants roots begin to stabilise the soil This type of farming is called no-till farming and is increasing in popularity in Australia and around the world.
The biggest cause of erosion is started by land clearing. By removing vegetation, there are no roots to hold or stabilise the soil and so it can be removed by wind or water. In the case of wind, the fine topsoil layer is lifted and carried away.
In the case of water, the lack of vegetation means the soil cannot hold as much water and it begins to flow over the surface. There are 3 main types of surface erosion:
1. Sheet erosion. As the name implies water moves over the surface in a large area. It removes the most productive layers of the soil (the A and O layers) and can remove seed from freshly planted fields.
2. Rill erosion. Once again, the upper layers of the soil are removed but now channels are starting to form. Rill erosion can lead to gully erosion.
3. Gully erosion. This is where channels over 0.5 m deep are dug out by the water. The channels are too deep to allow vehicles or animals to safely cross and so they effectively reduce the amount of usable land.
4. Streambank erosion. This is where rising water can wash out the sides of creeks and rivers. In our local area, the wash from boats can also contribute to this.
Erosion on rural land can be mitigated by:
1. Contour ploughing. This is where the land is ploughed at right angles to the slopes of hills. This means that water flow is greatly slowed by the furrows in the land and so it reduces the potential damage it can cause. Contour ploughing can only work on slight slopes and beyond that terracing may be required.
2. Seed drilling. Rather than pulling out the old crop or reploughing the land seed drilling involves slashing the old plants and leaving the roots still in the ground and a mulch cover on top. The mulch prevents drying and wind erosion while the roots stop water from carrying soil away. The new seed is planted by drilling it into the soil next to the slashed plant. As the new seed grows the old plant rots away adding organic material to the soil, and the growing plants roots begin to stabilise the soil This type of farming is called no-till farming and is increasing in popularity in Australia and around the world.
12EES - Review of soils of Australia
Review of the soils of Australia.
In the first week of our new class format everyone should have completed the following:
1. The survey
2. The question sheets
3. The "dot point" questions/summaries.
The key points to be aware of are as follows:
1. Age
Western Australian soils come from rocks that are very old (over 2 billion years). Over time the minerals form the soil get leached from it by rainfall (the minerals that are dissolvable/soluble in water are removed and sink further away from access by plants). Eastern Australian soils have been formed from rocks that are only 10,000 to 30 million years old. Because of this they are far richer in minerals, and unsurprisingly make some of the most productive soils in this country. The reason the rock/soil in Eastern Australia is so young by comparison is due to the eastern region of Australia drifting over a hot spot which in turn led to a chain of volcanoes forming from QLD down to southern Victoria.
2. Rainfall.
Easter Australia is far wetter than most of Central Australia and WA. As a result vegetation is reduced. Vegetation is required to contribute to the organic content of the soil. In addition moist soil contains more micro-organisms which help break down the dead material into materials that can be absorbed by the soils and therefore accessible to plants planted by farmers.
3. Topography
You would notice that in the presented maps, that the only significant an rapid changes of height above sea level are on the Eastern coast. This means that when moist air is pushed up over these areas the moisture is more likely to condense and fall as rain. In Western Australia, the air passes over mostly flat terrain and so has less opportunity to form clouds and rain. The consequences of this is reduced rainfall (See 2.)
4. Lack of Glaciation
In recent history Australia has had no significant glaciation over the continent. When the last ice age ended 10000 years ago, the glaciers in Europe and North America had scoured away the old soils and replaced them with new ones made from the freshly ground rock that the glaciers had passed over. Because these soils are much newer they have a much greater mineral content compared to most Australian soils.
Differences between Easter and Western soils.
Eastern soils - red to brown due to higher mineral and organic content. Generally high in nitrates and phosphates. Some trace elements such as magnesium may be a bit low, but the soils are suitable for agriculture without the need for large scale fertiliser addition.
Western soils - Yellow to red soils with high silica content. This is a result of prolonged leaching causing minerals that are useful to plants being leached out. These soils tend to be low in nitrate and phosphate and for successful farming, repeated applications of fertiliser may be required.
In the first week of our new class format everyone should have completed the following:
1. The survey
2. The question sheets
3. The "dot point" questions/summaries.
The key points to be aware of are as follows:
1. Age
Western Australian soils come from rocks that are very old (over 2 billion years). Over time the minerals form the soil get leached from it by rainfall (the minerals that are dissolvable/soluble in water are removed and sink further away from access by plants). Eastern Australian soils have been formed from rocks that are only 10,000 to 30 million years old. Because of this they are far richer in minerals, and unsurprisingly make some of the most productive soils in this country. The reason the rock/soil in Eastern Australia is so young by comparison is due to the eastern region of Australia drifting over a hot spot which in turn led to a chain of volcanoes forming from QLD down to southern Victoria.
2. Rainfall.
Easter Australia is far wetter than most of Central Australia and WA. As a result vegetation is reduced. Vegetation is required to contribute to the organic content of the soil. In addition moist soil contains more micro-organisms which help break down the dead material into materials that can be absorbed by the soils and therefore accessible to plants planted by farmers.
3. Topography
You would notice that in the presented maps, that the only significant an rapid changes of height above sea level are on the Eastern coast. This means that when moist air is pushed up over these areas the moisture is more likely to condense and fall as rain. In Western Australia, the air passes over mostly flat terrain and so has less opportunity to form clouds and rain. The consequences of this is reduced rainfall (See 2.)
4. Lack of Glaciation
In recent history Australia has had no significant glaciation over the continent. When the last ice age ended 10000 years ago, the glaciers in Europe and North America had scoured away the old soils and replaced them with new ones made from the freshly ground rock that the glaciers had passed over. Because these soils are much newer they have a much greater mineral content compared to most Australian soils.
Differences between Easter and Western soils.
Eastern soils - red to brown due to higher mineral and organic content. Generally high in nitrates and phosphates. Some trace elements such as magnesium may be a bit low, but the soils are suitable for agriculture without the need for large scale fertiliser addition.
Western soils - Yellow to red soils with high silica content. This is a result of prolonged leaching causing minerals that are useful to plants being leached out. These soils tend to be low in nitrate and phosphate and for successful farming, repeated applications of fertiliser may be required.
Monday, October 15, 2012
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