PA Water and Carbon Cycles

Question 1

What is an input?

Answer 1

Material or energy moving into the system from surroundings.

E.g. Precipitation (water cycle) or Precipitation with dissolved carbon (carbon cycle)

Question 2

What is an output?

Answer 2

Material or energy moving from the system to the surroundings.

E.g. Runoff (water cycle) or dissolved carbon with runoff (carbon cycle)

Question 3

What is energy?

Answer 3

Power or driving force.

E.g. latent heat associated with changes in the state of water (water cycle) or production of glucose through the process of photosynthesis (carbon cycle)

Question 4

What are stores?

Answer 4

The individual elements of parts of a system.

E.g. Trees, puddles, soil (water cycle) or Trees, soil, rocks (carbon cycle)

Question 5

What are flows/transfers?

Answer 5

The links or relationships between the stores.

E.g. Infiltration, groundwater flow, evaporation (water cycle) or burning, absorption (carbon cycle)

Question 6

What is a positive feedback loop?

Answer 6

A cyclical sequence of events that amplifies or increases change. These loops exacerbate the outputs of a system, promoting environmental instability.

Question 7

What is a negative feedback loop?

Answer 7

A cyclical sequence of events that damps down or neutralises the effects of a system, promoting stability and a state of dynamic equilibrium.

Question 8

What is dynamic equilibrium?

Answer 8

This represents a state of balance within a constantly changing system.

Question 9

What is an example of a positive feedback loop in the water cycle?

Answer 9

High surface temperatures result in the melting of freshwater ice. Reduced ice cover as a result of this, reduces the amount of solar reflection that occurs. This raises the surface temperatures resulting in more freshwater ice melting.

Question 10

What is an example of a positive feedback loop in the carbon cycle?

Answer 10

Increased temperatures due to climate change cause melting of permafrost. Organic matter then starts to decompose releasing CO₂ & CH₄. These gases then rise through the soil and release into the atmosphere, enhancing the greenhouse effect, raising temperatures further.

Question 11

What is an example of a negative feedback loop in the water cycle?

Answer 11

Increased surface temperatures lead to an increase in evaporation from the oceans. This leads to more cloud cover. Clouds reflect radiation from the sun, resulting in a slight cooling of surface temperatures.

Question 12

What is an example of a negative feedback loop in the carbon cycle?

Answer 12

High ocean temperatures promote the growth of phytoplankton. Phytoplankton absorb CO₂ from the atmosphere and release dimethyl sulphide (DMS). DMS helps cloud formation. Increased cloud cover results in more solar radiation being reflected resulting in global cooling.

Question 13

What are the main stores in the water cycle?

Answer 13

Lithosphere (land)
Hydrosphere (liquid water)
Cryosphere (frozen water - snow/ice)
Atmosphere (air)
Biosphere (living organisms)

Question 14

How long does water stay in different stores?

Answer 14

Ground water (deep): 10,000 years
Ground water (shallow): 100-200 years
Lakes: 50-100 years
Glaciers: 20-100 years
Seasonal snow cover: 2-6 months
Rivers: 2-6 months
Soil: 1-2 months

Question 15

What are the main flows/transfers in the water cycle?

Answer 15

Precipitation - Transfer of water from the atmosphere to the ground. This takes the form of rain, snow and hail.

Evaporation - Transfer of water from liquid state to gaseous state (water vapour). Also know as evapotranspiration if the water that is evaporated is water loss from plants.

Condensation - Transfer of water from a gaseous state to a liquid state, for example, the formation of clouds.

Sublimation - Transfer of water from a solid state (ice) to a gaseous state (water vapour) and vice versa.

Interception - Water intercepted and stored on the leaves of plants.

Overland flow - Transfer of water over the land surface.

Infiltration - Transfer of water from the ground surface into the soil where it may then percolate into the underlying rocks.

Throughflow - Water flowing through soil towards a river.

Percolation - Water soaking into rocks.

Groundwater flow - Transfer of water very slowly through rocks.

Question 16

What affect does deforestation have on the water cycle?

Answer 16

The removal of trees reduces interception and evapotranspiration as well as increasing infiltration & overland flow.

Question 17

What affect does urbanisation have on the water cycle?

Answer 17

Impermeable surfaces will be created reducing infiltration and increasing overland flow. If deforestation occurs to clear land for urban areas, rates of interception and evapotranspiration will also be reduced.

Question 18

What affect does farming have on the water cycle?

Answer 18

The creation of furrows encourages water to flow quickly towards rivers and lakes. The use of irrigation also increases the amount of water on the ground creating over saturated soils when rainfall occurs leading to increased overland flow.

Question 19

What affect do storms have on the water cycle?

Answer 19

Intense rainfall that is brought with storms increases the amount of rainfall that reaches the ground and therefore reduces the magnitude of water in the atmosphere whilst simultaneously increasing the magnitude of water in the other stores and the magnitude of transfers.

Question 20

What affect do seasonal changes have on the water cycle?

Answer 20

Summer - lower total rainfall, vegetation grows rapidly increasing interception and transpiration, high temperatures encourage evaporation, dry soils encourage infiltration and low flow conditions are more likely

Winter - Greater quantities of rainfall (including snow), vegetation dies reducing interception and transpiration, lower temperatures reduce evaporation, soil become saturated leading to overland flow and high flow conditions are more likely.

Question 21

What is a drainage basin?

Answer 21

An area of land that is drained by a river and its tributaries. The edge of a drainage basin is marked by a boundary called the watershed.

Question 22

What is the water balance?

Answer 22

An equation used to help hydrologists mitigate for future water supply and flood control.

The equation is:
P = O + E +/- S

P - Precipitation
O - Total runoff
E - Evapotranspiration
S - Storage

Question 23

What factors affect a flood hydrograph?

Answer 23

Drainage basin size
Drainage density
Rock type
Land use
Relief
Soil water
Rainfall intensity

Question 24

What is the difference between a flashy and a subdued hydrograph?

Answer 24

A flashy hydrograph has a short lag time and a high peak where as a subdued hydrograph has a long lag time and a low peak. This is due to variations within the different factors that affect a hydrograph.

Question 25

What causes a flashy hyrdograph?

Answer 25

Drainage basin size - Small
Drainage density - High density
Rock type - Impermeable
Land use - Urbanised
Relief - Steep slopes
Soil water - Saturated soils
Rainfall intensity - Heavy rainfall that exceeds the infiltration capacity

Question 26

What causes a subdued hydrograph?

Answer 26

Drainage basin size - Large
Drainage density - Low density
Rock type - Permeable
Land use - Forests (more interception)
Relief - Gentle slopes
Soil water - Dry soil
Rainfall intensity - Light rain

Question 27

How have human activities affected the water cycle?

Answer 27

Land use change:

• Urbanisation reduces infiltration as well as causing increased overland flow which makes flooding more likely and reduces soil and groundwater stores.
• Deforestation reduces evaporation and interception which increases surface runoff and the chance of soil erosion.

Farming practices:

• Farmers are able to control local water cycles through irrigation and land drainage.
• Soils covered with plants have higher infiltration and soil water rates and therefore bring reduced runoff.
• If desertification occurs, the capacity to retain water is much lower and is completely lost once the soil is sealed.

Water abstraction:

• Water is extracted from river or groundwater aquifers.
• Water that is abstracted is often used for irrigation, industrial and domestic purposes which can have a significant affect on the local water cycle.
• Aquifers can become depleted if over-abstracted. This can also lead to some aquifers becoming contaminated by inflowing salt water if the water table drops below sea level.

Question 28

What are the main stores in the carbon cycle? How much carbon do they store?

Answer 28

Marine sediments and sedimentary rock - 100,000 billion tonnes

Ocean - 38,000 billion tonnes

Fossil fuel deposits - 4,000 billion tonnes

Soil organic matter - 1,500 billion tonnes

Atmosphere - 750 billion tonnes

Terrestrial plants - 560 billion tonnes

Question 29

What are the main transfers in the carbon cycle?

Answer 29

Photosynthesis - Green plants absorb light energy from chlorophyll. The energy is then used to convert CO₂ from the air and water from the soil into glucose.

Respiration - Glucose is converted into energy releasing CO₂ and water into the air.

Decomposition - When organisms die, they are consumed by bacteria, fungi and earthworms. In this process, carbon is released to the atmosphere in the form of CO₂. Some organic matter passes into the soil where the carbon can be stored for hundreds of years.

Combustion - Organic matter which contains carbon is burned in a presence of oxygen. This forms energy, CO₂ and water. The CO₂ is then released into the atmosphere.

Question 30

What is burial & compaction?

Answer 30

Organic matter which contains carbon is buried and compacted. Over millions of years, these organic sediments may form hydrocarbons.

Question 31

What is carbon sequestration?

Answer 31

The transfer of carbon from the atmosphere to plants, rocks formations, soils and oceans which is both a human and natural process.

Question 32

What is Carbon Capture & Storage (CCS)?

Answer 32

A human process of carbon sequestration. Carbon that is released into the atmosphere from power stations (often due to combustion) is captured and transported to a storage area. This is often to empty oil reserves (e.g. underneath old oil rigs).

Question 33

What is weathering?

Answer 33

The breakdown or decay of rocks in their original place at or close to the surface. When CO₂ is absorbed by rainwater it forms a mildly acidic carbonic acid. Through a series of complex chemical reactions, rocks will slowly dissolve with the carbon being held in solution.

Question 34

What are some physical changes to the carbon cycle?

Answer 34

Natural climate change - The fluctuation between warm (interglacial) periods and cold (glacial) periods. In interglacial periods there was high ppmv (parts per million by volume) of carbon in the atmosphere as heat can be trapped.

Wildfires - In wildfires, the burning of trees result in the combustion of carbon that is stored which releases CO₂ into the atmosphere. This can turn carbon sinks into carbon sources.

Volcanic Activity - Carbon that has been stored in rocks deep within the Earth’s crust for millions of years is returned to the atmosphere during eruptions. The lava erupted contains silicates that slowly weather. Therefore, CO₂ in the air is converted into carbonates in solution, hence absorbing from the atmosphere very, very slowly.

Question 35

What impact do cold and warm conditions have in carbon stores and transfers?

Answer 35

Cold:

• Chemical weathering processes are more active as cold water can hold more carbon.
• Decomposers would be less effective so there would be reduced carbon transfer to soils.
• More water is stored in on-land ice & snow resulting in less water reaching the oceans. This reduces sediment transfer resulting in less sediment build up on the ocean floor. (sediment build up helps form sedimentary rock in which carbon can be stored e.g. limestone).

Warm:
- The melting of permafrost releases carbon from the soil into the atmosphere.

Question 36

What are some human changes to the carbon cycle?

Answer 36

Combustion of fossil fuels - Fossil fuels are important long-term carbon stores. When extracted and combusted, large amounts of energy is released alongside all the carbon that is stored.

Farming practices - Ploughing & harvesting, rearing livestock, using fossil fuel powered machinery and fertilisers that contain fossil fuels are practices that release carbon. For example, livestock (especially cattle) produces large quantities of CH₄ (around 20% of the US CH₄ emissions). The cultivation of rice also emits large quantities of rice, contributing up to 20% of global CH₄ emissions.

Deforestation - The removal of trees by burning of felling is often for commercial processes such as cattle rearing in the Amazon Rainforests or for growing palm oil in the Borneo Rainforest. Due to trees especially in dense rainforests being large carbon sinks, this process results in large quantities of CO₂ being released into the atmosphere.

Urbanisation - This has a significant impact to local carbon cycles due to important carbon stores e.g. vegetation and soils being replaced or covered up. The major sources of carbon in urban regions is transportation and industrial processes such as the making of concrete which produces CO₂ as a by-product.

Question 37

What is the carbon budget?

Answer 37

This is used to describe how much carbon is stored or transferred within the carbon cycle. The carbon budget can be global, national and local as well as for a certain object (e.g. the carbon budget of a tree).

Question 38

What is the unit of carbon in the carbon budget?

Answer 38

Pentagrams (Pg) - 1 Pg = 1 x 10 ¹⁵ g

Question 39

How does the carbon cycle affect the land?

Answer 39

• It is responsible for the formation and development of the soil as carbon in the form of organic matter introduces important nutrients and provides structure to the soil.
• Carbon stored in grass provides fodder for animals.
• Carbon provides a valuable source of energy in the form of wood and fossil fuels.
• Carbon in the form of organic matter is essential for plant growth and the production of food.

Question 40

How does the carbon cycle affect the ocean?

Answer 40

• Carbon can be converted into calcium carbonate, which is used by some marine organisms to build shells.
• The carbon cycle has an impact on the presence and proliferation (growth or production of cells) of phytoplankton which is a basic food for many marine organisms. Phytoplankton absorb CO₂ during photosynthesis which is passed along the food chain.

Question 41

How does the carbon cycle affect the atmosphere?

Answer 41

• CO₂ in the atmosphere helps to warm the Earth through the greenhouse effect. Without this, there would be no life on Earth.
• Increases in carbon emissions as a result of human activities (deforestation, combustion of fossil fuels) have led to the enhanced greenhouse effect, which threatens to have a profound impact on the world’s climate.
• Carbon stored by vegetation has a significant effect on the atmosphere, whether deforestation (carbon source) or afforestation (carbon sink).

Question 42

Amazon Rainforest - Water & Carbon cycle Case Study

Answer 42

Importance:

• Discharge of approx. 175,000 m3/s into the Atlantic Ocean
• Average rainfall of 2,300 mm annually. In some places it can reach 6,000 mm
• Estimated to store between 80-120 billion tonnes of carbon
• Above-ground biomass has been increasing by 0.3-0.5% annually
• Tropical rainforests around the world form a carbon sink of 1-3 GtC/year
• In the 1990s the Amazon could absorb 2 billion tonnes of CO2 per year but this has now halved
• Only 30% of rainfall reaches the sea

Impact of change:

• Any moisture that is evaporated from deforested areas form shallow cumulous clouds which do not usually produce rain
• Salt and organic fibres transpire with water. They help form clouds so when deforestation occurs less clouds are formed and therefore there is less rainfall
• Moisture content in the upper 1 metre of soil in pastures is 15% lower than that in nearby rainforests
• Forests roots help pump soil moisture to the surface producing 20-30% more air humidity and 5-20% more precipitation than pastures
• If destroyed, a vast carbon store will be released into the atmosphere
• Deforestation mainly occurs for agricultural processes such as the rearing of livestock which produce CH4 to the atmosphere. This replaces a sink to a source of carbon

Mitigation:

• National and International agreements:
• -> Amazon Cooperation Treaty Organisation (ACTO) to promote harmonious development
• ->The TARAPOTO process to help achieve harmonious forest development
• ->The Latin American Technical Cooperation Network on Watershed Management (REDLACH)
• The creation of national parks and forest reserves e.g. The Tumucumaque National Park (3.84 million hectares) and the Pará Rainforest Reserve (15 million hectares)
• Reforestation and the enrichment of degraded forests using native species
• Forest biofuel production could compete with ethanol production from sugar cane by 2030