OCR A Level ELSS - 9 OCR A Level ELSS 4.3 How much change occurs over time in the water and carbon cycles Flashcards
Do the water and carbon cycles exist in dynamic equilibrium?
The Water and Carbon cycles exist in dynamic equilibrium at a variety of scales as long as they are unaffected by human activities.
What is an accurate definition of dynamic equilibrium in a system?
A system with continuous inputs, throughputs, outputs and variable stores that fluctuates from year to year but, in the long term retains stability.
What is an example of dynamic equilibrium at the drainage basin scale?
Intense rainfall means more water enters stores (infiltration to soil layer and percolation to groundwater, as well as directly into lakes etc.) These stores may overflow, resulting in flooding, however, when the rain stops, rivers discharge and floods recede, reverting back to its usual state.
What is an example of dynamic equilibrium at a global scale?
Some increase in atmospheric CO2 can increase rates of photosynthesis encouraging plant growth and increased storage of carbon in the biosphere. This reduces the concentration of atmospheric CO2 and brings the system back into equilibrium.
Define urbanisation
the conversion of land from a rural use (farmland and woodland) to urban use (housing/offices/roads etc.)
What impacts does urbanisation have on the water cycle?
- More impermeable surfaces therefore reduces infiltration 2. Urban drainage systems deliver rainwater to rivers more quickly, increasing flood risk 3. Urban development on floodplains reduces water storage capacity and leads to increased river flow and flooding
What impacts does urbanisation have on the carbon cycle?
- Urban areas reduce the amount of surface vegetation
- Increased CO2 emissions from energy consumption in urban areas as well as increased amount of transport and industry infrastructure
- Increased CO2 from cement manufacturing
What impacts does farming have on the water cycle?
- Irrigation diverts water from rivers and groundwater supplies to cultivated land. Some water is used by plants and then released by transpiration
- Interception, evaporation and transpiration are all lower in agroecosystems than in forest and grassland ecosystems
- Ploughing increases soil moisture loss and can lead to increased run-off and soil erosion
- Use of heavy machinery can compact the soil and lead to increased run-off
What impacts does farming have on the carbon cycle?
- Clearance of forest for farming reduces above and below-ground carbon stores
- Ploughing reduces soil carbon storage and exposes soil organic matter to oxidation
- Harvesting means only small amounts of organic matter are returned to the soil
- Rice paddies generate methane
- Livestock release methane
- Increased CO2 from emissions of farm machinery
What impacts does forestry have on the water cycle?
- Plantations of natural forest increase interception of rainfall
- Evaporation increases as leaf store water evaporates directly back to the atmosphere
- Run-off and stream discharge is reduced
- Lag times are long, peak flow low and total discharge low in plantation areas
- Transpiration in forested areas in higher than for farmland and moorland
- Localised deforestation means that evapotranspiration is lower, there is also less interception, consequently there is increased overland and throughflow with the lack of vegetation to slow these processes down. This could lead to increased risk of flooding.
What impacts does forestry have on the carbon cycle?
- Changing land use to forest increases carbon stores
- Forest trees extract CO2 from the atmosphere and sequester it for hundreds of years
- Forest trees are only an active carbon sink for the first 100 years. Therefore plantations usually have a rotation of 80-100 years
Define water extraction
the taking of water from surface and groundwater stores to meet public, industrial and agricultural demand. This direct human intervention changes the dynamics of river flow and groundwater storage.
What impacts does over-extraction have on the water cycle?
Over-extraction can lead to: Rivers drying up Damage to wetland ecosystems Sinking water tables (if extraction exceeds recharge) Empty wells In coastal areas intrusion of salt water from the sea degrades groundwater and leads to difficulties of usage for domestic and agricultural purposes
What impacts does over-extraction have on the carbon cycle?
No significant impacts
Where is the river Kennet and what are its characteristics?
The river drainage basin is mainly found on chalk, which is highly permeable. Therefore groundwater is essential for the river’s flow. The chalk naturally filters the water, providing very clear, highly oxygenated and fast flowing water - supporting a diverse habitat
Who extracts water from the River Kennet and for what purposes?
Thames Water abstracts water from upper catchment using boreholes to supply water for local industries, agriculture and public use (notably Swindon with 200,000 people)
What impacts has water extraction along the River Kennet had?
Water extraction has had significant impacts on the regional water cycle including:
- . Water Table has fallen, reducing flows by 10-14%
- During 2003 drought, flows fell by 20%
- There is a reduced amount of flooding that supports wetlands on the floodplain
- Springs have dried up and increased the amount of saturated overland flow
What is an aquifer?
underground stores of water
What is the water table?
The border between saturated and dry rock. This fluctuates according to the season and amount of water abstraction
What is an Artesian Basin and how do they form?
When sedimentary rocks form a basin shape or ‘syncline’. An aquifer forms that is trapped between impermeable layers. This means the water is stored under pressure. This allows for water to rise to the surface through a well or borehole under its own pressure. This is known as an artesian aquifer.
How is London an example of an Artesian basin?
Groundwater is found in the chalk layer, trapped between London Clay above and Gault Clay beneath. Rainwater from the North Downs and Chiltern hills recharges the chalk aquifer Over-abstraction in 19th and 20th Centuries led to a dramatic fall in the water table by 90m! Thames Water is now granted licenses to abstract certain amounts. The water table is now stable with this management approach
How many tonnes of CO2 are added to the atmosphere each year through the combustion of fossil fuels?
10 billion tonnes of CO2 per year
By how many parts per million does the combustion of fossil fuels increase the global concentration of CO2 in the atmosphere?
1 part per million
How many gigatonnes of CO2 have humans contributed to the atmosphere since 1750? What percentage are estimated to have come from fossil fuels?
Since 1750 humans are thought to have contributed 2000 Gigatonnes of CO2 to the atmosphere. 75% of these emissions are estimated to have come from burning fossil fuels.