geography aqa alevel carbon and water cycle - paper 1

WATER CYCLE: what is a system

a set of interconnected components that interact to form a functioning whole

key charas:

- linked by flows of energy or matter

- systems can be opened or closed

- they often operate in dynamic equilibrium

example: the global hydrological cycle is a system where water moves between stores

what are inputs, outputs, stores and flows in a system

inputs:

- matter or energy entering a system

e.g. precipitation entering a drainage basin

outputs:

- matter or energy leaving a system

e.g. river discharge flowing into the sea

stores:

- location where matter is held within a system

e.g. soil moisture of groundwater

flows (transfers):

- the movement between stores

e.g. infiltration or runoff

difference between open and closed system

closed:

- exchange energy but not matter with surroundings.

- self contained

e.g. the global hydrological cycle (water remains constant)

open:

- exchanges both energy and matter with surroundings

e.g. a drainage basin, where water enters as precipitation and leaves as discharge

what is dynamic equilibrium

the idea that natural systems try to maintain a balance between different parts of their system

occurs when:

- inputs and outputs are balanced over time

- the system changes constantly, but overall conditions remain stable

e.g. in a drainage basin, rainfall inputs may equal river discharge outputs over time

what are positive and negative feedback loops in a system

positive:

- a change that amplifies or increases the original change

e.g. melting ice reduces albedo - more heat absorbed - more melting

negative:

- a change that reduces or stabilises the original change

e.g. increased vegetation growth absorbs more CO2 reducing atmospheric carbon

THE GLOBAL HYDROLOGICAL CYCLE - where is water stored in the global water cycle

water is stored in several major global stores:

- hydrosphere - oceans, lakes, rivers

- cryosphere - glaciers, ice sheets, and sea ice

- lithosphere - groundwater and aquifers

- atmosphere - water vapour and clouds

the oceans contain the largest water store on earth

approximately how much water is stored in each global store

oceans - 97%

ice sheets and glaciers - 2%

groundwater - - 0.6-1%

surface water - 0.01%

atmosphere - 0.001%

only a tiny portion of earths water is easily available freshwater

how is water stored in the lithosphere through aquifers

an aquifer is a layer of permeable rock that stores and transmits groundwater

unconfined aquifer - water enters directly from precipitation

confined aquifer - trapped between impermeable rock layers

water moves through aquifers via percolation and groundwater flow

what is evaporation and what factors affect its rate

evaporation is when liquid water changes into water vapour and enters the atmosphere

factors affecting evap:

- temp - high temps increase evap

- wind speed - removes moist air

- humidity - lower humidity increases evap

- surface area of water

- solar radiation

what is condensation and what conditions are required

condensation occurs when water vapour cools and changes back into liquid droplets

conditions:

- air must cool to its dew point

- condensation occurs around condensation nuclei (dust particles)

this leads to cloud formation

types of rainfall

convectional:

surface of the earth is heated by sun - warm surface heats air above it - hot air rises - air cools & begins to condensate - rain forms - rainfall (lots)

relief/orographic:

when warm, moist air is forced to rise over high land, such as mountains or hills. As the air ascends, it cools and condenses, forming clouds and precipitation on the windward side. The air then descends the leeward side, warming and drying, creating a "rain shadow"

frontal:

two air masses meet (cold and warm) - the lighter, less dense WARM air is forced to rise over the denser cold air - warm air cools & condenses - rain is formed - variety clouds - rainfall

how does the cryoshpere change during ice ages and interglacial periods

ice ages (glacial periods)

- expansion of ice sheet and glaciers

- more water stored as ice

- lower sea levels

interglacial periods

- ice melts and water returns to oceans and rivers

- sea levels rise

these changes affect global sea level and climate patterns

cryosphere can increase via:

- snowfall - blown by wind - avalanches - ACCUMULATIOIN

loose water via:

- melting/evap - ice falls into hydrosphere - ABLATION

THE DRAINAGE BASIN HYDROLOGICAL CYCLE - what are the main stores and flows in a drainage basin

stores:

- interception store

- surface storage

- soil moisture storage

- groundwater storage

- channel storage

flows:

- interception

- stemflow

- through flow

- infiltration

- percolation

- through flow

- surface runoff

- groundwater flow

what factors affect water stores and flow speeds in a drainage basin

climate:

- rainfall intensity and temperature

geology:

- permeable rocks allow infiltration

slope:

- steeper slopes increase runoff

vegetation;

- more vegetation increases interception

soil type:

- clay soils reduce infiltration

human activity

- urbanisation increases surface runoff

what is the water balance equation

water balance shows the relationship between:

- precipitation (P)

- evapotranspiration (E)

- runoff (Q)

- changes in storage (S)

simplified equation:

P = E + Q +/- S

it shows whether a drainage basin has a water surplus or deficit

What is potential evapotranspiration?

PET is the maximum possible evaporation and transpiration if sufficient water is available

PET depends on:

- temperature

- solar radiation

- wind

when PET exceeds precipitation, a water deficit occurs

what are the stages of a soil moisture budget graph

field capacity:

- maximum water soil can hold

utilisation:

- plants use stored soil moisture

deficit

- soil moisture is depleted

recharge

- rainfall replenishes soil moisture

surplus:

- soil becomes satruated and excess water becomes runoff

RIVER REGIMES - what is river discharge and how is it measured

discharge is the volume of water flowing in a river channel per second

measured in cubic meters per second (m3/s)

calculated using:

- discharge = cross-sectional area x velocity

- velocity can be measured using flow meters or floats

what is a river regime

a river regime is the annual pattern of river discharge over a year

it shows:

- seasonal variations

- periods of high and low flow

often displayed using a river regime graph

how do climate and geology affect river regimes

climate:

- rainfall patterns determine peak flows

- snowmelt can cause seasonal peaks

geology:

- permeable rock stores water and releases it slowly

- impermeable rock causes rapid runoff and higher flood risk

FLOOD HYDROGRAPHS - what are the key features of a flood hydrograph

key components:

- peak rainfall - highest rainfall during a storm

- rising limb - rapid increase in river discharge

- lag time - time between peak rainfall and peak discharge

- peak discharge - maximum river flow

- falling limb - discharge decreases after storm

what is the difference between flashy and delayed hydrographs

flashy hydrograph

- short lag time

- steep rising limb

- high peak discharge

delayed hydrograph

- long lag time

- gentle rising limb

- lower peak discharge

what factors affect lag time in a drainage basin

factors that shorten lag time: (flashy)

- impermeable geology

- steep slopes

- high drainage density

- urbanisation

- deforestation

- compacted agricultural soils

factors that lengthen lag time: (delayed)

- permeable geology

- dense vegetation

- gentle slopes

HUMAN IMPACTS ON WATER CYCLE - how does deforestation in the Amazon affect the water cycle

in the amazon rainforest:

- reduced interception

- reduced evapotranspiration

- increased runoff

- reduced regional rainfall

this can lead to drier climates and increased flooding

how does soil drainage affect the water cycle

artificial drainage systems:

- removes water from soils faster

- increased surface runoff

- reduced soil moisture storage

- increases river discharge after rainfall

what is water abstraction and how does it affect the water cycle

water abstraction is the removal of water from rivers, lakes or aquifers for human use

impacts include:

- reduced river discharge

- lower groundwater levels, water table - dig deeper = more £. less baseflow to rivers - may dry out - dead habitats

- reduced wetland habitats

- causes subsidence - soil shrinks in size as it dries causing a change in surface level

- for coastal areas it means salt water infiltrates - cant drink water

over abstraction:

- too much removal

groundwater abstraction:

- pumping water from wells in aquifers

water abstraction in SE england

due to periods of low rainfall the demand for water meant there was an increase in groundwater usage

- 50% of chalk rivers dried up

- increase in pollution

- salt water intrusion in Brighton

- groundwater levels dropped significantly in south London

humans impact on soil drainage

soil drainage - removal of water from soil

- improves land for farming

advantages:

- improves soil structure

- less chance of compaction from heavy farmery

- soil can warm quicker

disadvantages:

- causes flooding

- top soil may become too dry

- fertilisers may go into rivers

- more CO2 emmitted

impact on water cycle:

- increase in through flow/groundwater

- decrease in surface storage

- decrease in evaporation rates

- flashy hydrographs

CASE STUDY: RIVER EXE - what physical and human factors affect the water cycle in the river exe drainage basin

location: devon, SW england, exmoor

physical factors:

- impermeable rocks on Exmoor increase runoff - more flooding

- high rainfall in upland areas

- steep slopes increase flow speed

human factors:

- urban areas (Exeter) increase runoff

- farming compacts soil and reduces infiltration

these factors affect flood risk and river discharge patterns

(rest of river exe on sheet)

CARBON - what are the main forms of carbon

CO2 - a gas found in the atmosphere, soils and oceans

methane - a gas found in atmosphere, soils, oceans and sedimentary rock

calcium carbonate - a solid compound found in calcareous rocks, oceans & the skeletons/shells of ocean creatures

hydro-carbons - solids, liquids, gas in sedimentry rick e.g coal

how is carbon stored in the lithosphere

the largest store of carbon

carbon is stored in rocks and sediments such as limestone and chalk (calcium carbonate)

also stored in fossil fuels like coal, oil & natural gas formed from ancient organic matter

can remain stored for millions of years

how is carbon stored in the hydrosphere

carbon stored mainly as dissolved carbon dioxide and bicarbonate ions in seawater

oceans also store carbon in marine organisms (shells and skeletons made of calcium carbonate)

the deep ocean is a very large longterm carbon store

how is carbon stored in the biosphere

carbon stored in plants through photosynthesis

stored in animals through food chains

also stored in soils, peat and decomposing organic matter

how is carbon stored in the atmosphere

carbon stored mainly as carbon dioxide and small amounts of methane

this store changes quickly due to photosynthesis, respiration, combustion and decomposition

how does carbon move into, around and out of the lithosphere

weathering of rocks - carbon in the atmosphere dissolves in rainwater forming carbonic acids, which chemically weathers rocks and transfers carbon into sediments and oceans.

sedimentation and burial - marine organisms with calcium carbonate shells sink and become limestone/chalk, storing carbon in rock.

formation of fossil fuels - dead organic matter buried under pressure forms coal, oil and natural gas over millions of years.

volcanic activity - carbon stored in rocks is released as CO2 during volcanic eruptions and tectonic activity

- these processes are part of the SLOW carbon cycle, operating over millions of years

how does carbon move into, around and out of the biosphere

photosynthesis - plants absorb CO2 from the atmosphere and convert into organic carbon (biomass)

respiration - plants, animals and microbes release CO2 BACK INTO the atmosphere during respiration

decomposition - dead organic matter is broken down by microbes, releasing CO2 and methane

food chains - carbon moves through ecosystems as animals consume plants and other animals

- these floes are part of the FAST carbon cycle, happening over days to decades

how does carbon move into, around and out of the hydrosphere

air-sea gas exchange - CO2 dissolves into oceans from the atmosphere through diffusion

biological pump - phytoplankton photosynthesis, absorbing CO2. When organisms die carbon sinks into the deep ocean

shell formation - marine organisms (e.g. shellfish, corals) use carbon to form calcium carbonate shells

ocean circulation - ocean currents move carbon between surface waters and the deep ocean

- oceans act as a major carbon SINK, storing large amounts of carbon LONG term

how does carbon move into, out of and around the atmosphere

diffusion - CO2 moves between the atmosphere and hydrosphere through gas exchange

photosynthesis - plants remove CO2 from the atmosphere

respiration and combustion - release CO2 back into the atmosphere

condensation and precipitation - CO2 dissolves rainwater forming carbonic acid, transferring carbon to land and oceans through weathering (chemical)

- the atmosphere is a small but highly active carbon store

how can the speed of carbon flows vary (slow vs fast carbon cycles)

fast cycles:

- occurs over days to years

- includes photosynthesis, respiration, decomposition and ocean diffusion

slow cycles:

- occurs over thousands to millions of years

- includes rock formation, fossil fuel creation, sedimentation and tectonic processes

- human activities are rapidly transferring carbon from slow stores (fossil fuels) into the fast cycle (atmosphere)

how do carbon stores and flows change over time in vegetation

seasonal changes:

- in summer, photosynthesis increases - vegetation acts as a carbon sink

- in winter, photosynthesis decreases while respiration continues - less carbon stored

ecological succession:

- early stages (grassland) store little carbon

- later stages (mature forests) store large amounts in biomass and soils

- as ecosystems mature, carbon storage increases significantly

how do carbon stores and flows vary locally and globally

local variation - depends on vegetation type, climate, soil and land use

global variation - major stores include oceans, forests and the lithosphere

what is the carbon budget

the balance between carbon sources and carbon sinks

carbon store - a reservoir holding carbon e.g. oceans, forests

carbon sink - absorbs more carbon than it releases

carbon source - releases more carbon than it absorbs

Changes in the carbon cycle: how do natural processes change the carbon cycle

forest fires:

- releases carbon through combustion

- dead material decomposes, releasing more CO2

- regrowing vegetation later absorbs carbon again

volcanoes:

- releases CO2 stored in the lithosphere into the atmosphere

- emit sulphur dioxide which can influence climate temporarily - global warming or cooling

- natural changes occur but usually over long time scales

how do human activities chnage the carbon cycle

burning hydrocarbons:

- fossil fuel combustion releases large amounts of CO2

agriculture:

- rice paddies and cattle produce methane

- nitrate fertilisers increase greenhouse gas emissions

urbanisation:

- cement production releases CO2

- urban expansion reduces vegetation carbon sinks

deforestation:

- trees removed - less photosynthesis

- burning/decay releases stored carbon

- forests change from carbon sink to carbon source

what are the impacts of carbon cycle changes on the oceans

ocean acidification:

- more atmospheric CO2 dissolves in oceans forming carbonic acid

- this lowers pH and damages shell-forming organisms (corals, shellfish, plankton)

salinity changes:

- melting ice and increased rainfall reduce ocean salinity (by introducing large volumes of fresh water into the ocean, which dilutes the existing salt concentration.)

- this can weaken thermohaline circulation, including the North Atlantic currents

. Freshwater from melting ice reduces ocean salinity in the North Atlantic, making water less dense so it sinks less easily, weakening thermohaline circulation and slowing heat transport by currents such as the Gulf Stream.

temperature increase:

- warmer oceans cause coral bleaching, where corals expel symbiotic algae and may die

sea level rise:

- caused by thermal expansion of seawater and melting glaciers/ice sheets

thermohaline circulation and the north atlantic

1. What is Thermohaline Circulation?

Thermohaline circulation is the global ocean circulation system driven by differences in:

- Temperature ("thermo")

- Salinity or salt content ("haline")

Cold and salty water is denser, so it sinks, while warmer, less salty water stays near the surface.

This movement creates a global conveyor belt of ocean currents that transports heat around the planet.

2. The Role of the North Atlantic

In the North Atlantic Ocean, surface water moves northwards as part of currents like the Gulf Stream and North Atlantic Drift.

When this warm water reaches higher latitudes:

- It cools due to cold Arctic air.

- It becomes saltier because ice formation leaves salt in the water.

- The water becomes dense and sinks.

- This sinking water drives the deep ocean circulation and keeps the whole system moving.

3. How Climate Change Affects It

Climate change adds large amounts of freshwater to the North Atlantic from:

- melting glaciers

- melting Arctic sea ice

- increased rainfall

Freshwater reduces salinity, which means the water becomes less dense.

Because it is less dense:

- it does not sink as easily

- the circulation slows down

4. Why This Weakens Thermohaline Circulation

If the water doesn't sink properly, the global conveyor belt slows.

This weakens thermohaline circulation, including the North Atlantic currents that transport warm water.

5. Why It Matters

A weaker circulation could lead to:

- less heat transported to Europe

- cooler conditions in the North Atlantic region

- changes in weather patterns and rainfall

- impacts on marine ecosystems

This is why salinity changes from melting ice are an important feedback in the climate and carbon cycle.

what are the impacts of carbon cycle changes on land systems

melting permafrost:

- rising temperatures thaw frozen soils

- this releases stored carbon dioxide and methane, accelerating warming

carbon fertilisation:

- higher CO2 levels can increase plant growth and photosynthesis

- this may temporarily increase carbon storage in vegetation

changing growing seasons:

- warmer temperatures lengthen growing seasons in some regions

- this alters ecosystems productivity and carbon storage patterns

what are the impacts of carbon cycle changes on the atmosphere

enhanced greenhouse effect:

- increased greenhouse gases trap more heat in the atmosphere

- this increases global temperatures

radiative forcing:

- the change in the balance between incoming solar radiation and outgoing heat energy

FEEDBACK LOOPS

positive feedback:

- changes that amplify warming (e.g. increased plant growth absorbing CO2)

negative feedback:

- change's that reduce warming (e.g. increased plant growth absorbing CO2)

what are positive and negative feedback loops in the carbon cycle: examples

Positive (amplify climate change)

- permafrost thaw - rising temps melt permafrost, releasing CO2 and methane, causing further warming...

- forest fires - hotter, drier conditions increase forest fires, releasing stored carbon and reducing vegetation that absorbs CO2, leads to increased temps...

- reduced ocean absorption - warmer oceans absorb less CO2, leaving more carbon in the atmosphere...

Negative (reduce climate change)

- carbon fertilisation - higher atmospheric CO2 increases photosynthesis, so plants absorb more carbon

- increased vegetation growth in warmer regions - longer growing seasons allow more carbon to be stored in biomass

- enhanced weathering - more rainfall increases chemical weathering of rocks, removing CO2 from the atmosphere

how are the water and carbon cycles linked

- rainwater absorbs CO2 forming carbonic acid

- this causes chemical weathering of carbon rich rocks such as limestone

- carbon is transported by rivers into oceans and sediments

- water also enables photosynthesis, linking the two cycles through plant growth

the water cycle helps transport and dissolve carbon, connecting major carbon stores

Managing increased atmo carbon: What is carbon mitigation

mitigation refers to actions taken to reduce greenhouse gas emissions or increase carbon sinks

examples:

- renewable energy

- carbon capture technology

- reforestation

- reducing fossil fuel use

goal: slow or prevent further climate change

what is carbon capture and storage (CCS)

- CO2 is captured from power stations or industrial processes

- the carbon is compressed and transported

- it is stored deep underground in geological formations, such as depleted oil and gas fields

purpose:

- prevent CO2 from entering the atmosphere

what is carbon offsetting

- individuals or companies compensate for emissions by funding carbon reduction projects

these include:

- tree planting projects

- renewable energy developments

- conservation programmes

key issues:

offsets may not always fully compensate for emissions

how can transport changes reduce atmospheric carbon

cars:

- electric vehicles reduce emissions from fossil fuels

- improved public transport reduces car use

aviation:

- development of sustainable aviation fuels

- improving aircraft efficiency

goal: reduce emissions from one of the fastest growing sources of CO2

how can changes in farming and forestry reduce atmospheric carbon

farming:

- reducing livestock methane emissions

- improved fertiliser use to reduce greenhouse gases

forestry:

- afforestation and reforestation increases carbon sinks

- protecting existing forests prevents carbon release

What is the Paris Agreement and its role in managing atmospheric carbon

The Paris Agreement (2015) is an international climate treaty

key goals:

- limit global warming to well below 2 degrees, ideally 1.5

- countries set nationally determined contributions to reduce emissions

importance:

encourages global cooperation to reduce carbon emissions.

CASE STUDY: TROPICAL RAINFORESTS

how does the water cycle operate in the amazon rainforest

high rainfall (often 2000+ mm annually)

dense canopy intercepts large amounts of rainfall before it reaches the ground

evapotranspiration:

- trees release large amounts of water vapour through transpiration

- around 50-70% of rainfall is recycled within the rainforest

infiltration and through fall:

- water infiltrates soil quickly due to deep root system and permeable soils

key idea:

rainforests recycle a large proportion of its own rainfall, maintaining a stable regional climate

how does the carbo cycle operate in the amazon

major carbon sink:

- the amazon rainforest stores about 90-140 billion tonnes of carbon in vegetation and soils

photosynthesis:

- trees absorb large amounts of CO2 from the atmosphere, storing carbon in biomass

rapid nutrient cycling:

- warm and wet conditions cause fast decomposition, returning carbon to the soil and atmosphere

large biomass store - most carbon is stored in living vegetation rather than soils.

key idea:

the amazon plays a crucial role in regulating global atmospheric carbon levels

how does deforestation affect the amazons carbon and water cycle

carbon cycle impacts:

- cutting and burning trees releases large amounts of CO2

- loss of vegetation reduces photosynthesis and carbon storage

- parts of the amazon rainforest are shifting from carbon sink to carbon source

water cycle impacts:

- reduced evapotranspiration, meaning less atmospheric moisture

- lower regional rainfall and increased drought risk

- increased surface runoff and soil erosion

overall impact:

deforestation disrupts both the regional climate and global carbon balance

what are the main causes of deforestation in the amazon rainforest

cattle ranching:

- responsible for about 70-80% of deforestation

- land is cleared to create grazing areas

commercial farming:

- large scale soybean production for global food markets

logging:

- trees removed for timber exports

infrastructure:

- roads such as the trans-amazon highway open remote areas to development

mining and energy:

- extraction of gold, iron ore and bauxite

key idea:

economic development and global demand for resources drive most forest loss

how does the amazon rainforest link the carbon and water cycles

through vegetation

- photosynthesis - trees absorb CO2 from the atmosphere, storing carbon in biomass

- evapotranspiration - water released from leaves enters the atmosphere, contributing to cloud formation and rainfall

- vegetation growth - water availability supports dense forest growth, which increases carbon storage

- moisture recycling - around 50-70% of rainfall is recycled through evapotranspiration

key idea - the amazon acts as both a major carbon sink and a key driver of the regional water cycle

what is the amazons tipping point and why is it important

the amazon may reach a tipping point where deforestation and climate change cause irreversible damage

how it happens:

- large scale deforestation reduced evaportranspiration

- this lowers regional rainfall

- forest areas may shift towards savanna like ecosystems

Carbon impacts

- Massive amounts of stored carbon could be released into the atmosphere.

Global importance:

- The Amazon stores around 90-140 billion tonnes of carbon.

Key idea: If the tipping point is reached, the Amazon could change from a global carbon sink to a major carbon source.

what are the global impacts of deforestation in the amazon

Climate change:

- Burning forests releases large amounts of CO₂, increasing atmospheric carbon.

Reduced carbon sink:

- Fewer trees means less CO₂ removed from the atmosphere.

Changes to global weather:

- Reduced evapotranspiration may alter regional and global rainfall patterns.

Biodiversity loss:

- The Amazon contains around 10% of the world's known species.

Key idea: Because of its size and carbon storage, changes in the Amazon affect the global carbon cycle and climate system.