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.
What are the CO2 levels currently?
Today, CO2 levels are the highest for at least 800,000years at around 400ppm (from 280ppm in 1750).
What would the concentration of CO2 be in the atmosphere if oceans and the biosphere had not absorbed large amounts of anthropogenic carbon?
above 500 parts per million
What is carbon sequestration?
the process by which carbon dioxide is removed from the atmosphere and held in solid or liquid form.
What are the steps of artificial carbon sequestration (Carbon Capture and Storage - CCS)?
- CO2 is separated from power station, 2. CO2 compressed and transported 3. CO2 is injected into porous rocks deep underground
Why has artificial carbon sequestration (Carbon Capture and Storage - CCS) not become viable?
High capital costs (e.g. Drax and Peterhead projects in the UK would have cost £1 billion) Uses large amounts of energy Requires specific geological conditions to store
What are the diurnal changes in the water cycle?
During the day Evaporation and Transpiration are HIGH Rainfall high in tropical areas due to convection At night Evaporation and transpiration are LOW No convectional precipitation
What are the diurnal changes in the carbon cycle?
During the day CO2 flows from atmosphere to vegetation At night CO2 flows from vegetation to atmosphere. This also happens in the oceans with phytoplankton Electricity production in power stations increases in late afternoon/early evening
What are the seasonal changes
The further north or south from the equator the greater the seasonal change. Seasons are caused by Earth’s axial tilt, which varies the amount of light received from the sun. Changes in temperature directly affect processes such as: Evaporation (greater in summer) Precipitation (less in summer, although often comes in short, heavy bursts due to convectional rainfall) Plants are seasonal - in mid-latitudes deciduous trees shed leaves in Autumn and grow new ones in Spring. Transpiration is reduced in winter and greatest in summer. Photosynthesis is greatest in summer.
What are the seasonal changes in sunlight and its impact on the water cycle?
Evapotranspiration highest in summer, lowest in winter. This can reduce soil moisture and reduce river flow. Example - Southern England solar input in June is 800 W/m2 meanwhile in December it is 150 W/m2. This leads to high evapotranspiration and so river flows are lowest in late summer Monsoon rainfall patterns are seasonal (SE Asia) Snowmelt in Tundra increases discharge of rivers in spring
What are the seasonal changes in vegetation and its impact on the carbon cycle?
Changes in Net Primary Productivity (NPP)* between seasons shows when ecosystems act as carbon sinks and CO2 flows from the Atmosphere to the Biosphere
This is all year round in rainforests * NPP = the amount of organic matter that is available to humans and animals to harvest and consume On land
Mid-High latitude environments will experience month-to-month changes in the net primary productivity of vegetation (NPP) depending on the number of sunlight hours (photoperiod). The more available sunlight, the greater amount of photosynthesis and therefore the greater flow of carbon from atmosphere to plants (in the rainforests, this is all year round with no monthly variation).
During Northern Hemisphere Summer (because of the large land masses here) Trees are at full foliage THEREFORE Net Global flow of CO2 from Atmosphere to Biosphere reduces global CO2 concentrations by 2 ppm In the Oceans Phytoplankton are stimulated into activity by higher temperatures THEREFORE there is an explosion of microscopic ocean plant life in March, peaking in mid-summer (algal blooms are visible from space)
What are the long term changes in the water cycle?
Key changes in the Water Cycle over the long term are around the cycle of glacial (ice advance) and inter-glacial (ice retreat) periods
Over the last 400,000 years there have been 4 major glacial cycles
Cold GLACIALS - e.g during the height of last glacial (20,000 yrs ago) average temperatures in UK were 5oC lower with large parts of the UK under 1km of ice
Warmer INTER-GLACIALS - some had similar temperatures to today, however 250million yrs ago average global temperatures were 7-8oC warmer than today. Each cycle lasts around 100,000 years
What are the long term changes in the carbon cycle?
Carbon that is locked up in carbonate rocks can be stored for millions of years Carbon is released into the atmosphere from active volcanoes Carbon flows change during glacial periods More CO2 is absorbed by cooler oceans. This increases the amount of phytoplankton, which then die and deposit carbon in ocean sediments On land, more carbon was sequestered into the permafrost During inter-glacials, atmospheric CO2 levels increase and NPP increases as photsynthesis increases
What are the expected long term impacts of climate change on the water cycle?
- In glacials sea levels fall worldwide by 100-130m as water is stored in ice sheets, glaciers and permafrost
- Ice sheets and glaciers expand to cover 1/3 continental land mass
- The area covered by vegetation and water stored in the biosphere shrinks
- Tropics- climate become drier In inter-glacials - there is is increased evapotranspiration as temps are higher, more water is moved through the cycle, there is increased run off into rivers.
- Glaciers and ice sheets shrink increasing infiltration and ground water stores
- A water storage due to global warming in the cryosphere shrinks it makes its way to rivers and oceans
- Water vapour being created in the atmosphere releases latent heat which could explain why there are more hurricanes and extreme weather events
What are the expected long term impacts of climate change on the carbon cycle?
Dramatic reduction in CO2 in the atmosphere during the glacials.
As temperature increases, so does the amount of atmospheric CO2
In glacials 180ppm meanwhile in interglacials- 280ppm
Possible reasons
- Phytoplankton growth at the surface of the ocean- absorbs CO2 and then sinks and dies- storing it
- Lower ocean temps also absorb more CO2
- Carbon pools in vegetation shrink in glacials- much is destroyed in the path of advancing ice sheets and glaciers
- Ice also covers soil which prevents the exchange of carbon between the soil and the atmosphere
- As temperatures continue to increase, vegetation changes and in tropical areas the ability for vegetation to store carbon diminishes and in high latitudes it increases (but not as much as in TRF)
- Carbon is released as permafrost melts and vast peat stores decompose
- Excess CO2 is absorbed by the oceans- leading to acidification and reduction in photosynthesis by phytoplankton
What is the name of NASA’s remote sensing satellite for monitoring amounts of ice?
ICESat-2
What are the objectives of ICESat-2?
- Measure melting ice sheets and investigate how this affects sea level rise,
- Measure and investigate changes in the mass of ice sheets and glaciers,
- Estimate and study sea ice thickness, 4. Measure the height of vegetation in forests and other ecosystems worldwide.
What is the name of the instrument attached to the International Space Station to monitor atmospheric carbon
Orbiting Carbon Observatory 3 (OCO-3)
What are the objectives of the Orbiting Carbon Observatory 3 (OCO-3)?
It will investigate CO2 levels related to growing urban centers and increased fossil fuel combustion. It will also explore, for the first time, daily variations in the release and uptake of CO2 by the world’s rainforests.
Approximately how many tonnes of Carbon Dioxide are emitted into the earth’s atmosphere each year?
Nearly 40 billion tons of CO2
Approximately how much of the total amounts of CO2 emitted each year are absorbed by the oceans and vegetation?
About half
What is Net Primary Productivity (NPP)?
it is the rate at which all plants in an ecosystem produce net useful chemical energy. NPP is equal to the difference between the rate at which plants in an ecosystem produce useful chemical energy (or GPP), and the rate at which they expend some of that energy for respiration.
