The water and carbon cycles

system definition

a set of interrelated stores and processes coming together to form a working unit

the global hydrological cycle

it is a closed system (fixed amount of water on Earth)

largest water store

ocean - 97%

residence time of water

longest residence - ice (15k years), shortest residence - atmosphere (10 days) / short residence causes regional weather patterns, long residence moderates temperatures and climates in oceans/glaciers

general water stats (ice caps + glaciers, freshwater in the ground, countries + freshwater supply)

ice caps + glaciers cover 10% of the Earth’s surface / 20% of freshwater is in the ground / less than 10 countries possess 60% of freshwater supply

water and moderating temperatures/climates (oceans, clouds, water vapour)

oceans have a high specific heat capacity = areas near coasts are warmer / clouds have a high albedo = reflects sun’s energy / water vapour = greenhouse gas

precipitation process

water vapour in the atmosphere cools to its dew point and condenses to form clouds, eventually these droplets aggregate - they reach a critical size to leave the cloud

intensity

the amount of precipitation falling measured in mm/hr (high = 10-15mm/hr, low = 2mm/hr)

ablation

the loss of of water from snow, ice, and glaciers due to melting, evaporation, and sublimation

evapotranspiration

responsible for 10% of water in the atmosphere = fundamental process / combination of evaporation and transpiration (explain both in an exam)

seeder-feeder effect (orographic and frontal rain)

combined effect of orographic and frontal rain / orographic rainfall occurs in mountainous areas close to prevailing winds / frontal rainfall occurs in mid-latitude regions

convectional rainfall - how it’s produced (connective clouds, unstable = bubbles, cools and condenses, cauliflower)

produced by connective clouds (e.g.: cumulonimbus) / forms in an unstable atmosphere by ‘bubbles’ of buoyant, heated air - air cools and condenses into distinctive, cauliflower-top clouds

convectional rainfall - characteristics

falls as showers with rapidly changing intensity over a much smaller area, often lasts 20-60mins while frontal lain lasts for hours

drainage basin (throughfall, stemflow, interception)

throughfall - water that’s intercepted by leaves but falls to the ground / stemflow - prolonged rainfall = water flows along branches to the ground / interception loss - intercepted water that’s evaporated

factors affecting interception loss (tree species, vegetation type, wind, temps)

tree species - evergreen trees (e.g.: oak and pine) intercept all year long / vegetation type - trees have a bigger SFA than grasslands = greater interception / wind - higher wind / temp - higher temps

infiltration vs percolation

I - the vertical, downward movement of water into the soil surface / P - the downward transfer of water from the surface/soil into the bedrock below

overland flow, throughflow, and groundwater flow

O = excess stormwater flows over the Earth’s surface, results in soil erosion, fastest speed / T - lateral transfer of water downslope through the soil, medium speed / GW - transfer of percolated water through permeable/porous rocks, slowest speed

3 main cloud types

cumuliform clouds - flat bases, vertical development, heated air rises and expands / stratiform clouds - air mass moves horizontally across a cooler surface / wispy cirrus clouds - high altitude, consists of tiny ice crystals

importance of carbon

ubiquitous, forms the basis for 95% of known compounds

global carbon cycle

global scale - closed system, local - open system

main stores of carbon

largest store - sedimentary rocks (99.9% of carbon)

precipitation and photosynthesis in the carbon cycle

carbonic acid in rainfall - increased due to anthropogenic emissions (harmful to marine life) / phytoplankton sequesters 10GT of carbon per year

weathering in the carbon cycle (transfer, Yorkshire Dales)

carbonic acid = chemical weathering, CW estimated to transfer 0.3bn tonnes of CO2 per year / Yorkshire Dales - limestone surface has been lowered by >1/2 a meter (evidence of CW)

combustion in the carbon cycle (Rocky Mountains)

combustion transfers 10bn tonnes of CO2 per year - harmful to ecosystems (e.g.: coniferous forests in the Rocky Mountains)

the physical pump (diffuses into oceans - poles - currents to upwelling - rises and diffuses)

CO2 diffuses from the atmos. to the ocean - dissolves and is transported to the poles (cools and sinks) - currents transport CO2 to areas of upwelling, CO2 water rises and diffuses back to the atmos.

biological pump - phytoplankton (fast carbon cycle)

ocean phytoplankton (50% of all photosynthesised CO2 comes from the oceans) - phytoplankton consumed and transferred along the food chain - dead organisms sink to ocean flow - organic carbon accumulates as FFs or is decomposed

biological pump - carbonates (slow carbon cycle) - weathering releases, rivers into oceans, crustaceans/molluscs, sedimentation, accumulate, sedimentary rock

weathering releases calcium bicarbonate - discharged by rivers into oceans - crustaceans/molluscs fix carbon in their shells - shells and skeletons fall to floor where sedimentation occurs - sediment layers accumulate and CO2 becomes stored as sedimentary rock

water extraction + global water use

extracted from surface and groundwater - direct human intervention / avg. person in the US uses 156 gallons per day, agriculture accounts for 70% of water use

River Kennet (covers, supplies water to, extraction reduced flows, droughts, has disturbed)

covers an area of 1,200km² / supplies water to urban areas (e.g.: Swindon has a pop. of 200K) / extraction reduced flows by 10-14%, 2003 droughts saw flows fall by 20% / abstraction has disturbed the natural dynamics of the water cycle

aquifers (what they are, what they’re made up of, freshwater storage, human reliance)

great reservoirs of water and a natural regulator of the water cycle, made up of permeable/porous rocks (chalk/sandstone) / GW stored in aquifers accounts for 30% of all freshwater storage - 1,500mn ppl rely on aquifers for water

human impact on aquifers (excessive pumping, ldn, GW levels, recharge + urbanisation)

excessive pumping lowers the water table = no more water / ldn water table rising by 2m/yr = flooding / abstraction also lowers GW levels (key - 1,500mn people rely on this) / recharge levels are prevented by urbanisation

artesian basin

a pumpless water source - pressure builds up between rock layers and gets relieved when it reaches open air

abstraction in London

past over-abstraction has slowed since deindustrialisation / water table is still rising by 2m per year = flooding

combustion of FFs

87% of all energy comes from FFs - releases 10bn tonnes of CO2 annually (increases the CO2 concentration by >1ppm p.a.)

changes to the atmospheric CO2 store (change, cause, US vs Africa)

pre industrial = 280ppm, now there’s 420ppm / 2/3s of this was caused by FF combustion / US contributes 25% to global cumulative emissions while Africa only contributes 3% (spatial variation)

sequestration of CO2 - carbon capture

CO2 is captured and compressed, it’s then transported by pipeline to storage areas, finally it’s injected into porous rocks to be stored permanently

carbon capture advantages (US coal emissions + CC, Drax Project set to)

40% of the US’s emissions are from coal - CC can reduce these emissions by 80-90% / Drax Project in North Yorkshire set to capture 2mn tonnes of CO2 per year

carbon capture disadvantages (difficult - Drax costs + energy use, specific)

difficult to do: Drax Project was axed in 2016 - was going to cost £1bn, would use 20% of a power plant’s energy, requires specific storage reservoirs

short term water cycle changes - diurnal/seasonal

D - low temps at night = less evapotranspiration, convectional rain increases during the day / S - evapotranspiration is highest in summer (UK solar radiation is 800W//m² in June vs 150W//m² in winter), summer - 80% of precipitation is lost to evapotranspiration

short term carbon cycle changes - diurnal/seasonal

D - CO2 flows from atmosphere to vegetation in the day / S - summer = more photosynthesis, atmospheric CO2 levels fall by 2ppm, winter = increased decomposition

quaternary period (began, D, H)

began 2.6mn years ago / the last ice age was the Devensian (ended 11,700 years ago) - temps were 5*C lower and sea levels were 100-150m lower / currently in the interglacial, Holocene age

glacial vs interglacial periods

G - water stored in ice = thermal contraction = eustatic sea level fall, 1/3 of the NH is covered in ice / IG - land ice melts = thermal expansion of water = eustatic sea level rise, CO2 concentrations increase from 100ppm to 280ppm

monitoring techniques (NASA - OES, OCO-2, importance)

NASA’s OES satellites have monitored sea ice since 1978 and their OCO-2 has measured atmospheric CO2 since 1958 / importance - measuring the W&C cycles help devise solutions

W&C links

they are inextricably linked and interdependent - but they are linked asymmetrically (C relies more on W)

biosphere interdependence - carbon on water (photosynthesis, decomposition)

photosynthesis - relies on water to function (NPP varies with water - e.g.: Arctic = low NPP + low rainfall), decomposition - decomposers need warm and wet conditions

biosphere interdependence - water on carbon (evapotranspiration, vegetation, soil moisture)

evapotranspiration (key = 71,000 km³ of water goes through evapotranspiration per yr), vegetation needs C to grow, organic carbon content of soil is important for soil moisture

hydrosphere interdependence

97% of water is stored in the ocean + oceans also store 38,700bn tonnes of CO2 and 50% of combusted FF is absorbed by oceans

atmosphere interdependence (smallest, carbonation, increased CO2)

smallest store for both water and carbon / water evaporates into the atmosphere and mixes with carbonic acid = carbonation / increased CO2 in the atmos. has an impact on the water cycle

cryosphere interdependence (freshwater and CO2, human)

68% of freshwater is stored in the cryosphere and 1600GT of CO2 is stored in permafrost / also linked through human change (ablation releases water and CO2)

carbon cycle management - wetland restoration (land occupation + carbon storage, Cambridgeshire, Canada + will sequester, enhances, BUT - revenue, urbanisation + agriculture, US wetlands )

occupies 9% of land surface and contains 30% of carbon / UK - 400ha in Cambridgeshire is becoming wetland / Canada - 112,000ha targeted for restoration (will sequester 364,000 tonnes per year) / enhances sinks / BUT they don’t generate revenue - urbanisation and agriculture often takes precedence (so wetlands in the USA have halved since 1600)

carbon cycle management - afforestation (UNREDD, China’s project, carbon sinks, BUT - legal, secondary forest, sustained will + Gloucester)

UN’s REDD / China’s afforestation project since 1978, aims to afforest 400,000km² by 2050 / trees are carbon sinks / BUT not legally binding, takes 25 years to become secondary forest, needs sustained will and maintenance (Gloucester 2022, 12,800 saplings but 95% died due to a lack of water)

carbon cycle management - agricultural practices (zero tillage, polyculture, crop residues, what they do, BUT - revenue, lower yield, sustained political will)

zero tillage - no ploughing / polyculture / crop residues / reduces carbon emissions while enhancing sinks / BUT - doesn’t create revenue, lower crop yield, needs sustained political will (ELMS UK was rejected under Liz Truss)

carbon cycle management - international agreements (Kyoto, Paris, BUT - ACs, Brazil + sinks)

1997 Kyoto Protocol - EU emissions were 22% lower by 2012 / Paris Climate Convention 2015 - aims to reduce CO2 emissions by 2050, richer countries to aid poorer ones ($100bn/yr) / BUT - Kyoto only involved ACs so global CO2 emissions grew to 65% (driven by China and India’s growth) / some countries (Brazil) use their sinks to offset their emissions so they’re not doing much to tackle their emissions

water cycle management - forestry (UNREDD + World Bank, ARPA, water cycle + offsetting, BUT only targets, mono + UNREDD funding and the ecnom

UN REDD and the World Bank fund >50 countries to protect TRFs / ARPA now protects>10% of the Amazon Basin / stabilises the regional water cycle while offsetting 430mn tonnes of CO2 / BUT - only targets specific places, monoculture, UNREDD funding from rich countries drops with the economy (0.7%-0.5% in 2022)

water cycle management - water allocations (agriculture %, % Indus’ flow, Colorado Basin, Israel, BUT)

agriculture accounts for 70% of water extraction and 90% of water consumption / 92% of the Indus’ flow is given to the Punjab and Sindh in Pakistan / Colorado Basin water is allocated to neighbouring states (semi-arid regions) / 55% of Israel’s water comes desalinated water / BUT - strategies only accessible to richer countries, raises domestic water prices

water cycle management - drainage basin planning (major catchments in the UK, runoff + GW, local scale, BUT - transboundary, e.g.: Nile + Grand Renaissance Dam)

each major catchment in the UK (e.g.: Severn, Thames) has its own River Basin Management Plan) / controls rapid runoff, improves GW store / effective on a local scale / BUT - difficult when the drainage basin is transboundary, e.g.: Nile (Grand Renaissance Dam in Ethiopia flooded 1,680m² of forest and 10% of water from reservoirs evaporates every year)

use of water - humans (paramount - made up of it, agriculture, industry, US use)

paramount importance - humans are 60% water, 70% of water abstracted is for agriculture, 20% of water is used for industry, US person uses 156 gallons per day

use of water - habitable earth (surface, water vapour, ice albedo)

water makes up 70% of earth’s surface, water vapour is the most abundant GG (would be 33*C cooler without it), ice has an albedo of 97% (helps maintain radiative equilibrium)

use of water - carbon cycle (movement of C, ocean stores etc.)

water helps the movement of C (biological pump), 38,700GT is stored in oceans and 1600GT in the ice, water is required for photosynthesis