4.a. The two cycles are linked and interdependent

Question 1

How does human activity cause changes in the water cycle?

Answer 1

• Most evident in rivers and aquifers - rising demand for water for irrigation, agriculture and public supply, especially in arid and semi-arid environments has created acute shortages
• In the Colorado Basin in the south-west USA, surface supplies have finished as more water is abstracted from rivers and huge amounts are evaporated from reservoirs like Lake Mead
• Elsewhere the quality of fresh water resources has declined, over-pumping of aquifers in the coastal regions of Bangladesh has led to incursions of salt water, often making the water unfit for irrigation and drinking water
• Compared to natural ecosystems, human activities such as deforestation and urbanisation reduce evapotranspiration and therefore precipitation, increase surface runoff-off, decrease through flow and lower water tables
• In the Amazon, forest trees are a key component of the water cycle, transferring water to the atmosphere by evapotranspiration which is then returned through precipitation - in places extensive deforestation has broken this cycle, causing climates to dry out and preventing regeneration of the forest

Question 2

How does human activity cause changes in the carbon cycle?

Answer 2

• World relies on fossil fuels for 87% of its primary energy consumption, the exploitation of coal, oil and natural gas has removed billions of tonnes of carbon from the geological store, a process that has gathered momentum in the past 30 years with the rapid industrialisation of the Chinese and Indian economies
• Currently around 8 billion tonnes of carbon per year are transferred to the atmosphere by burning fossil fuels
• In addition, land use change (mainly deforestation) transfers approximately 1 billion tonnes of carbon to the atmosphere every year, the additional carbon is stored primarily as CO2 in the atmosphere where the concentration increases yearly
• Around 2.5 million tonnes is absorbed by the oceans and a similar amount by the biosphere
• Massive deforestation has reduced the planet’s forest cover in historic times by nearly 50%, thus the amount of carbon stored in the biosphere and fixed by photosynthesis has declined steeply
• Even more significant is photosynthesis by phytoplankton in the oceans, they absorb more than half the CO2 from burning fossil duels, significantly more than the tropical forests
• Acidification of the oceans threatens this vital biological carbon store as well as adversely affecting marine life
• Soil is another important carbon store which is being degraded by erosion caused by deforestation and agricultural mismanagement
• Carbon storms in wetlands, drained for cultivation and urban development have also been depleted as they dry out and are oxidised

Question 3

How are the water and carbon cycles linked within the atmosphere?

Answer 3

• Atmospheric CO2 has a greenhouse effect, CO2 plays a vital role in photosynthesis by terrestrial plants and phytoplankton
• Plans, which are important carbon stores, extract water form the soil and transpire it as part of the water cycle
• Water is evaporated from the oceans to the atmosphere and CO2 is exchanged between the two stores

Question 4

How are the water and carbon cycles linked within the oceans?

Answer 4

• Ocean acidity increases when exchanges of CO2 are not in balance (ie. inputs to the oceans from the atmosphere exceed outputs)
• The solubility of CO2 in the oceans increases with lower SSTs
• Atmospheric CO2 levels influence SSTs and the thermal expansion of the oceans, air temperatures, the melting of ice sheets and glaciers and sea level

Question 5

How are the water and carbon cycles linked within the vegetation and soil?

Answer 5

• Water availability influences rates of photosynthesis, NPP, inputs of organic litter to soils and transpiration
• The water-storage capacity of soils increases with organic content
• Temperatures and rainfall affect decomposition rates and the release of CO2 to the atmosphere

Question 6

How are the water and carbon cycles linked within the cyrosphere?

Answer 6

• CO2 levels in the atmosphere determine the intensity of the greenhouse effect and melting of ice sheets, glaciers, sea ice and permafrost
• Melting exposes land and sea surfaces which absorb more solar radiation and raise temperatures further
• Permafrost melting exposes organic material to oxidation and decomposition which releases CO2 and CH4
• Run-off, river flow and evaporation respond to temperature change

Question 7

How does long-term climate change impact on the water cycle?

Question 8

How does long-term climate change impact on the carbon cycle?

Question 9

What kind of management strategies can be implemented to protect the global carbon cycle?

Answer 9

Wetland restoration
Afforestation
Agricultural practices
International agreements to reduce carbon emissions
Cap and trade

Question 10

What is wetland restoration?

Answer 10

• Wetlands: include freshwater marshes, salt marshes, peatlands, floodplains and mangroves
• Wetlands are important in the carbon cycle, they occupy 6-9% of the Earth’s land surface and contain 35% of the terrestrial carbon pool
• Population growth, economic development and urbanisation have placed huge pressure on wetland environments, in the 20th century, Canada’s prairie provinces lost 70% of their wetlands
• Restoration programmes in this area have shown that wetlands can store on average 3.25 tonnesC/ha/yr^-1, now 112,000 ha have been targeted for restoration in the Canadian prairies which should eventually sequester 364,000 tonnes C/year^-1
• Need for protection of wetlands as wildlife habitats as well as carbon stores is reflected in management initiatives such as EU Habitats Directive
• In the UK, up to 400 ha of grade 1 farmland in East Cambridgeshire is currently being converted back to wetland, this project will assist the UK Government to meet its target to restore 500 ha of wetland by 2020, a similar scheme is underway in Somerset
• Restoration focuses on raising local water tables to re-create waterlogged conditions
• Wetlands on floodplains for instance can be reconnected to rivers by the removal of flood embankments and controlled floods
• Coastal areas of reclaimed marshland used for farming can be restored by breaching sea defences
• Elsewhere, water levels can be maintained at artificially high levels by diverting or blocking drainage ditches and installing sluice gates

Question 11

What is afforestation?

Answer 11

• Involves planting trees in deforested areas or in areas that have never been forested
• Because trees are carbon sinks, afforestation can help reduce atmospheric CO2 levels in the medium to long term and combat climate change
• It also has other benefits, such as reducing flood risks and soil erosion
• Protecting tropical forests from loggers, farmers and miners is an inexpensive way of curbing GHG emissions, the UN’s Reducing Emissions from Deforestation and Forest Degradation (REDD) scheme incentivises developing countries to conserve their rainforests by placing a monetary value on forest conservation
• In China, a massive government-sponsored afforestation project began in 1978, it sims to afforest 400,000km^2 by 2050 - project also functions to combat desertification and land degradation in the vast semi-arid expanses of northern China

Question 12

What are agricultural practices?

Answer 12

• Unsustainable, agricultural practices such as over-cultivation, overgrazing and excessive intensification often result in soil erosion and the release of large quantities of carbon to the atmosphere
• Intensive livestock farming produces 100 million tonnes/yr^-1 of CH4, a potent greenhouse gas
• Almost as important are CH4 emissions from flooded rice fields and from the uncontrolled decomposition of manure

Question 13

What international agreements to reduce carbon emissions are there?

Answer 13

Kyoto Protocol (1997) - under Kyoto, most rich countries agreed to legally binding restrictions in their CO2 emissions, though controversially, developing countries, and some of the biggest polluters (eg. China and India), were exempted, also several rich countries, eg. USA, refused to ratify the treaty as all countries were not bound by the same terms
Paris Agreement (2015) - aims to reduce CO2 emissions below 60% of 2010 levels by 2050 and keep global warming below 2 degrees, ideally below 1.5 (although we are currently at this figure), countries set their own voluntary targets and these are not legally binding
These are limited because reaching a significantly impactful agreement that still appeases all nations is essentially impossible - also countries such as India and China argue that since they are still undergoing industrialisation which is essential to raise living standards to levels comparable to those in ACs and Europe and North America, through their own economic development, are largely to blame for contemporary global warming and climate change

Question 14

What is cap and trade?

Answer 14

• Offers an alternative, international market-based approach to limit CO2 emissions
• Under this scheme, businesses are allocated an annual quota for their CO2 emissions, if they emit less than their quota they receive carbon credits which can be traded on international markets
• Businesses that exceed their quotas must purchase additional credits or incur financial penalties
• Carbon offsets are credits awarded to countries and companies for schemes such as afforestation, renewable energy and wetland restoration, they can be bought to compensate for excessive emissions elsewhere

Question 15

What kind of management strategies can be implemented to protect the global water cycle?

Answer 15

Forestry
Water allocations
Drainage basin planning

Question 16

What forestry strategies have been put in place?

Answer 16

• UN’s Reducing Emissions from Deforestation and Forest Degradation (REDD) programme and the World Bank’s Forest Carbon Partnership Facility (FCPF) fund over 50 partners counties in Africa, Asia and South America
• Financial incentives to protect and restore forests are a combination of carbon offsets and direct funding
• Brazil has received support from the UN, World Bank, World Wildlife Fund (WWF) and German Development Bank to protect its forests
• Amazon Regional Protected Areas (ARPA) programme now covers nearly 10% of the Amazon Basin
• Areas included in the programme are strictly protected, this stabilises the regional water cycle, supports indigenous forest communities and promotes ecotourism

Question 17

What water allocation strategies have been implemented?

Answer 17

• In countries of water scarcity governments have to make difficult decisions on the allocation of water resources
• Agriculture is by far the biggest consumer - globally it accounts for 70% of water withdrawals and 90% of consumption
• Wastage of water occurs through evaporation and seepage through inefficient water management (eg. over-irrigating crops)
• Improved management techniques which minimise water losses to evaporation include drip irrigation
• Losses to run-off on slopes can be reduced by terracing, contour ploughing and the insertion of vegetative strips
• Better water harvesting, with storage in ponds and reservoirs, provides farmers with extra water resources
• Recovery and recycling of waste water from agriculture, industry and urban populations is technically feasible, but as yet little used outside the developed world

Question 18

What drainage basin planning strategies have been implemented?

Answer 18

• Management of water resources is most effective at the drainage basin scale, at this scale it is feasible to adopt an integrated or holistic management approach to accommodate the often conflicting demands of different water users
• Agriculture, industry, domestic use, wildlife and recreation and leisure generate demands that impact on water quality, river flow, groundwater levels, wildlife habitats, biodiversity and so on
• In England and Wales, drainage basin management is well advanced, under the EU’s Water Directive Framework, ten river basin districts have been defined
• The district comprise major catchments, such as as the Severn, Thames and Humber - each district has its own River Basin Management Plan published jointly by the Environment Agency and DEFRA (Department for Environment, Food and Rural Affairs)
• The plan sets targets in relation to, for example, water quality, groundwater levels, flood control and the status of habitats and wildlife