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Flashcards in Carbon and water cycles Deck (81):
1

How does water support life on Earth?

  • Water is the universal solvent, it allows organic molecules to mix, form more complex structures and be transported
  • Water acts as an essential habitat not only for fish but for microorganisms, plankton and various plant species such as corals that support animals
  • Water is essential for the survival of plants who use it to photosynthesis carbon dioxide and `water to form glucose. It is also essential in plants for structure and support as water is used to maintain turgor pressure in cells and prevent wilting.
  • Water is only present on Earth in its liquid form due to Earth falling in the Goldilocks zone at exactly the right distance from our sun.
  • Water is also essential to life on earth as it acts as a regulator for the movement of energy through the Earth’s climatic systems e.g. warm and cold ocean currents
    • Oceans moderate heat by absorbing it, storing it and releasing it slowly elsewhere, in this way heat can be redistributed more evenly across the earth reducing extremes in temperatures
    • They occupy 71% of the earth’s surface
  • Clouds reflect as much as ⅕ of incoming solar radiation ensuring lower, more productive surface temperatures
  • Water vapour acts as a potent greenhouse gas, absorbing long wave solar radiation from the earth and helping to maintain global temperatures around 15℃ higher than would otherwise be the case.

2

What potential uses are there for water on Earth by humans, fauna and flora?

  • Water makes up 65-95% of all living organisms and is crucial to their growth, reproduction and other metabolic functions
  • In plants, water is involved in many of the key processes including photosynthesis (which provides energy for higher up the food chain as well), respiration and transpiration
    • Photosynthesis takes place in the leaves of plants combining CO2, sunlight and water to make glucose and starches
    • Respiration in plants and animals converts glucose to energy through its reaction with oxygen, releasing water and CO2 in the process
    • Plants also require water to maintain their rigidity (plants wilt if they run out of water) and to transport mineral nutrients from the soil
    • Transpiration of water from leaf surfaces cools plants by evaporation
  • In people and animals water is the medium used for all chemical reactions in the body including the circulation of oxygen and nutrients
    • Water is used for cooling through sweating in humans
    • In fur-covered mammals, reptiles and birds, evaporative cooling is achieved by panting
  • Humans use water for economic activity, recreationally and as a service
    • Water is essential in farming as irrigation for crops, it is also used in the generation of electricity and as a coolant in other industrial processes
    • Water is also needed for sanitation and sewage
    • It is used in a huge range of industries including food manufacturing, brewing, paper making and steel making

3

Size and distribution of the major stores of the water cycle

  • Oceans contain 97% of the water on the planet and dominate the water cycle
    • They hold 1,370,000 km3x103 of water
  • Freshwater makes up only a tiny proportion of the water in store, three quarters of this freshwater is frozen in ice caps in Antarctica and Greenland
    • Polar ice and glaciers hold 2% of global water
    • Groundwater stores hold 0.7%
    • Lakes hold 0.01%
    • Soils hold 0.005%
    • The biosphere hold a negligible 0.0004%
  • Only a tiny proportion of water is stored in the atmosphere yet it plays a pivotal role, this can be explained as water in the atmosphere has the highest rate of flux, in average only being held there for 9 days
    • Only 0.0001% of water is held in the atmosphere, equivalent to 13 km3x103

4

Main inputs and outputs of the water cycle

  • The global water cycle budget circulates 505,000 km3 of water a year as inputs and outputs between principal sources.
  • Inputs of water to the atmosphere include water vapour evaporated from the oceans, soils, lakes and rivers as well as vapour transpired from leaves of plants
    • Together these processes are known as evapotranspiration.
  • Moisture leaves the atmosphere as precipitation (rain, snow, hail, etc.) and condensation (fog)
  • Ice sheets, glaciers and snowfields release water through ablation (melting and sublimation)
  • Precipitation and meltwater drain from the land surface into rivers by runoff
    • Most rivers flow to the oceans though some, in continental drylands like southwest USA, drain to inland basins
    • A large part of water falling as precipitation on the land only reaches rivers after infiltrating and flowing through the soil
  • Once infiltrated through the soil water under gravity may percolate into permeable rocks or aquifers
    • This groundwater will eventually find its way to the surface via springs and seepages and contribute to runoff

5

Water balance equation

The water balance equation summarises the flows of water in a drainage basin over time

  • It states that precipitation is equal to evapotranspiration and streamflow, plus or minus water entering or leaving storage

Precipitation (P) = Evapotranspiration (E) + Streamflow (Q) ± Storage

6

Precipitation (water cycle)

Precipitation - water and ice that falls from clouds to the ground

  • It takes several forms: most commonly rain and snow, but also hail, sleet and drizzle
  • Precipitation forms when vapour in the atmosphere cools to its dew point and condenses into tiny water droplets or ice particles to form clouds
    • Eventually these droplets or ice particles aggregate, reach a critical size and leave the cloud as precipitation
  • Precipitation also varies in terms of character and this impacts the water cycle at drainage basin scale
    • Most rain on reaching the ground flows quickly into streams and rivers, but in high latitudes and mountainous catchments, precipitation often falls as snow and may remain on the ground for several months
      • Thus there may be a considerable time lag between snowfall and runoff
    • Intensity is the amount of precipitation falling in a given time - high intensity precipitation of 10-15 mm per hour will move rapidly overland into rivers and streams
    • Duration is the length of time that a precipitation event lasts - prolonged events, linked to depressions and frontal systems, may deposit exceptional amounts of precipitation and cause river flooding
    • In some parts of the world precipitation is concentrated in one rainy period (e.g. the monsoon in India)
      • During this season river discharge is high and flooding is common, however in the dry season rivers may cease to flow altogether

7

Transpiration (water cycle)

Transpiration - the diffusion of water vapour to the atmosphere from the stomata of plants

  • It is responsible for around 10% of moisture in the atmosphere
  • Transpiration is influenced by temperature and wind speed, as well as water availability to plants
    • For example, deciduous trees shed their leaves in climates with either dry or cold seasons to reduce moisture loss through transpiration

8

Condensation (water cycle)

Condensation - the phase change of water vapour to its liquid form at the dew point

  • At this critical temperature air becomes saturated with vapour resulting in condensation
  • Clouds form through condensation in the atmosphere
    • Cumuliform clouds, with flat bases and considerable vertical development most often form when air is heated locally through contact with the Earth’s surface
      • This causes heated air parcels to rise freely through the atmosphere (convection), expand (due to the fall in pressure with altitude) and cool
      • As cooling reaches the dew point, condensation begins and clouds form
    • Stratiform or layer clouds develop where an air mass moves horizontally across a cooler surface (often the ocean)
      • This process, together with some mixing and turbulence, is known as advection
    • Wispy, cirrus clouds, which form at high altitude, consist of tiny ice crystals
      • Unlike cumuliform ands stratiform clouds they do not produce precipitation and therefore have little influence on the water cycle
  • Condensation at or near the ground produces dew and fog
    • Both types of condensation deposit large amounts of water on vegetation and other surfaces

9

Cloud formation (water cycle)

Cloud formation - clouds are visible aggregates of water or ice or both that float in the free air

  • Clouds form when water vapor is cooled to its dew point. Cooling occurs when:
    • Air is warmed by contact with the ground or sea surface and rises freely through the atmosphere
      • As the air rises and pressure falls it cools by adiabatic expansion
        • This vertical movement of air is known as convection
    • Air masses move horizontally across relatively cooler surfaces by advection
    • Air masses rise as they cross mountain barriers or as turbulence forces their ascent
    • A relatively warm air mass mixes with a cooler one
  • Clouds form by convection as the ground heated by the Sun warms the air in contact with the surface to 18℃
    • Because the air is warmer than its surroundings (13℃) it is less dense and therefore buoyant
    • This situation, known as atmospheric instability, results in air rising freely in a convection current
    • When its internal temperature reaches the dew point (8℃) condensation occurs and clouds start to form
    • The air continues to rise so long as its internal temperature is higher than the surrounding atmosphere
    • Above a cloud the atmosphere is stable - air cannot rise freely in this zone because it is cooler (and therefore heavier) than its surroundings

10

Lapse rates (water cycle)

Lapse rates - these describe the vertical distribution of temperature in the lower atmosphere, and the temperature changes that occur within an air parcel as it rises vertically away from the ground

  • There are three types of lapse rates - their interaction explains the formation of clouds
    • Environmental lapse rate (ELR) - the ELR is the vertical temperature profile of the lower atmosphere at any given time, on average the temperature falls by 6.5℃ for every kilometre of height gained
    • Dry adiabatic lapse rate (DALR) - the DALR is the rate at which a parcel of dry air (less than 100% humidity so that condensation is not taking places) cools, cooling caused by adiabatic expansion is approximately 10℃/km
    • Saturated adiabatic lapse rate (SALR) - the SALR is the rate at which a saturated parcel of air (one in which condensation is occuring) cools as it rises through the atmosphere. Because condensation releases latent heat, the SALR, at around 7℃/km, is lower than the DALR

11

Evaporation (water cycle)

Evaporation - the phase change change of liquid water to vapour and the main pathway by which water enters the atmosphere

  • Heat is needed to bring about evaporation and break the molecular bonds of water, but this energy does not produce a rise of temperature in the water
    • Instead the energy is absorbed as latent heat and released later in condensation
    • This process allows huge quantities of heat to be transferred around the planet: from the oceans to the continents; and from the tropics to the poles

12

Interception (water cycle)

Interception - vegetation intercepts a portion of precipitation, storing it temporarily on branches, leaves and stems

  • Eventually this moisture evaporates (interception loss) or falls to the ground
    • Rainfall that is briefly intercepted before hitting the ground is known as throughfall
    • During periods of prolonged or intense rainfall, intercepted rainwater may also flow to the ground along branches and stems, this is known as stem flow
  • Interception loss is affected by several factors
    • Interception storage capacity - when vegetation is dry its ability to retain water is at a maximum, however as it becomes saturated, output of water through stemflow and throughfall increases
    • Wind speed - rates of evaporation increase with wind speed, and turbulence increases with wind speed, causing additional throughfall
    • Vegetation type - interception losses are greater from grasses than from agricultural crops
      • Trees, which have a larger surface area and aerodynamic roughness, have higher interception losses than grasses
    • Tree species - interception losses are far greater from evergreen conifers than from broad-leaved, deciduous trees
      • This is because most conifers have leaves all year round and water adheres to the spaces between conifer needles

13

Catchment hydrology (water cycle)

Rain falling to the ground and not entering storage follows one of two flowpaths to streams and rivers

  • Infiltration by gravity into the soil and lateral movement or throughflow to stream and river channels
  • Overland flow across the ground surface either as a sheet or as trickles and rivulets to stream and river channels

Two conflicting ideas explain the flowpaths followed by rainwater:

  • One relates overland flow to the soil’s infiltration capacity
    • Thus, it is argued that when rainfall intensity exceeds infiltration capacity overland flow occurs
  • The second idea states that rainfall, regardless of its intensity, always infiltrates the soil
    • Overland flow only occurs when soil becomes saturated and the water table rises to the surface
    • This process is known as saturated overland flow

Where soils are underlain by permeable rocks, water seeps or percolates deep underground

  • This water then migrates slowly through the rock pores and joints as groundwater flow, eventually emerging at the surface as springs or seepages

Groundwater levels on the chalk in southern England follow a distinct seasonal pattern

  • By late October the water table is beginning to rise as temperatures and evapotranspiration fall
  • This recharge continues until late January
  • Groundwater levels then decline throughout the late winter, spring and summer, reaching their lowest point in early autumn

14

Ablation (water cycle)

Ablation - loss of ice from snow, ice sheets and glaciers due to a combination of melting, evaporation and sublimation

  • Meltwater is an important component of river flow in high latitudes and mountain catchments in spring and summer
  • Rapid thawing of snow in upland Britain in winter is a common cause of flooding in adjacent lowlands (e.g. Welsh uplands and the Lower Severn Valley, Pennines and the Vale of York)

15

Importance of carbon to the natural world and humans

  • Carbon is a common chemical element
    • It is stored in carbonate rocks such as limestone, sea floor sediments, ocean water (as dissolved CO2), the atmosphere (as CO2 gas), and in the biosphere
  • Life as we known it is carbon based: built on large molecules of carbon atoms such as proteins, carbohydrates and nucleic acids
    • It is the building block of life
  • Apart from its biological significance, carbon is used as an economic resource
    • Fossil fuels such as coal, oil and natural gas power the global economy
    • Oil is also used as a raw material in the manufacture of products ranging from plastics to paint and synthetic fabrics
  • Agricultural crops and forest trees also store large amounts of carbon available for human use as food, timber, paper, textiles and many other products

16

Size and distribution of the major stores in the carbon cycle

  • The global carbon cycle consists of a number of stores or sinks connected by flows of carbon
  • Carbonate rocks such as limestone and chalk, and deep-ocean sediments are by far the biggest carbon store
    • Sedimentary (carbonate rocks) store 60,000 - 100,000,000 Gt of carbon (residence time = 150 million years)
    • Fossil fuels contain 4,130 Gt of carbon
  • Most of the carbon that is not stored in rocks and sediments is found in the oceans as dissolved CO2
    • Oceans store 38,700 Gt of carbon (residence time = 25 years surface, 1250 years deep)
  • Carbon storage in the atmosphere, plants and soils is relatively small, however these stores play a crucial part in the carbon cycle and represent most of the carbon in circulation at any one time
    • Soils contain 2,300 Gt of carbon
    • The atmosphere contains 600 Gt of carbon (residence time = 6 years)
    • Land plants contain 560 Gt of carbon (residence time = 18 years)

17

Slow vs fast carbon cycles

  • There are two strands to the carbon cycle: a slow cycle and a fast cycle
    • Both are closed systems globally with no carbon actually being created.
  • The fast carbon cycle is 10 to 1000 times faster than the slow cycle which takes as long as 150 million years to complete a full loop

18

Characteristics of the Slow Carbon Cycle

  • Carbon stored in rocks, sea floor sediments and fossil fuels is locked away for millions of years
  • The total amount of carbon circulated by this slow cycle is between 10 and 100 million tonnes a year
  • CO2 diffuses from the atmosphere into the oceans where marine organisms such as coccolithophores make their shells and skeletons by fixing dissolved carbon together with calcium to form calcium carbonate (CaCO3)
    • These organisms die and sink to the ocean floor where they accumulate
    • Over millions of years, heat and pressure convert them to carbon-rich sedimentary rocks
  • Typical residence time for carbon held in rocks is 150 million years
  • Some carbon-rich sedimentary rocks, subducted into the upper mantle at tectonic plate boundaries, are vented to the atmosphere in volcanic eruptions
  • Others exposed at or near the surface by erosion and tectonic movements are attacked by chemical weathering
    • Chemical weathering processes such as carbonation are the result of precipitation charged with CO2 from the atmosphere, which forms a weak acid
    • The acid attacks carbonate minerals in rocks, releasing CO2 to the atmosphere, and in dissolved form to streams, rivers and oceans
  • On land partly decomposed organic material may be buried under younger sediments to form carbonaceous rocks such as coal, lignite, oil and natural gas
    • Like deep-ocean sediments, these fossil fuels act as carbon sinks that endure for millions of years

19

Characteristics of the Fast Carbon Cycle

  • Carbon circulates rapidly between the atmosphere, oceans, biosphere and soils
  • Land plants and microscopic phytoplankton absorb CO2 from the atmosphere through photosynthesis and combine it with water to make carbohydrates
    • Photosynthesis is a fundamental process and the foundation of the food chain
  • Respiration by plants and animals is the opposite process and results in the release of CO2
    • Decomposition of dead organic matter by microbial activity also returns CO2 to the atmosphere
  • In the fast cycle, carbon exchange also occurs between the atmosphere and oceans
    • Atmospheric CO2 dissolves in ocean surface waters while the oceans ventilate CO2 back to the atmosphere
    • Through this exchange individual carbon atoms are stored (by natural sequestration) in the oceans for, on average, about 350 years

20

Precipitation (carbon cycle)

Precipitation -  atmospheric CO2 dissolves in rainwater to form weak carbonic acids

  • This is a natural process, however due to anthropogenic emissions rising concentrations of CO2 in the atmosphere have increased the acidity of rainfall
  • This has contributed to increased acidity of ocean surface waters with potentially harmful effects on marine life

21

Photosynthesis (carbon cycle)

Photosynthesis - the flux of carbon from the atmosphere to land plants and phytoplankton

  • This flux averages 120 gigatons per year.
  • Using the Sun’s energy, CO2 from the atmosphere and water, green plants and marine phytoplankton convert light energy to chemical energy (glucose) through the process of photosynthesis
    • 6CO2 + 6H2O ----> C6H12O6 + 6O2
  • Plants use energy in the form of glucose to maintain growth, reproduction and other life processes
    • In doing so they release CO2 to the atmosphere in respiration

22

Weathering (carbon cycle)

Weathering - the in-situ breakdown of rocks at or near the Earth's surface by chemical, physical and biological processes

  • Most weathering involves rainwater containing dissolved CO2, derived from the soil as well as the atmosphere
  • Rainwater is a weak carbonic acid, which slowly dissolves limestone and chalk through carbonation.
    • Carbonation = CaCO3 + H2CO6 ---> Ca(HCO3)2
  • Carbonation releases carbon from limestones to streams, rivers, oceans and the atmosphere
    • The process is most effective beneath a soil cover because the higher concentration of CO2 in the soil makes rainwater highly acidic
    • It is estimated that chemical weathering transfers 0.3 Gt of carbon to the atmosphere and the oceans every year
    • The effectiveness of solution weathering on limestone can be seen at Norber Brow in the Yorkshire Dales, where the limestone surface has been lowered by nearly half a metre over the past 13,000 years
  • Physical weathering by freeze-thaw breaks rocks down into smaller particles but involves no chemical changes
    • However, it increases the surface area exposed to chemical attack
  • Biological weathering processes such as chelation also contribute to rock breakdown
    • Rainwater mixed with dead and decaying organic material in the soil forms humid acids which attack rock minerals
    • This process is important in humid tropical environments where decomposition is rapid and forest trees provide abundant leaf litter

23

Respiration (carbon cycle)

Respiration - the process in which carbohydrates (e.g. glucose) are converted into CO2 and water in order to release energy

  • Respiration = CH2O + O2 = CO2 + H2O + energy
  • Plants and animals absorb oxygen which ‘burns’ these carbohydrates and provides the energy needed for metabolism and growth
  • Respiration is the reverse of photosynthesis - whereas photosynthesis absorbs CO2 and emits oxygen, respiration absorbs oxygen and releases CO2
  • Respiration and photosynthesis are the two most important processes in the fast carbon cycle
    • The volume of carbon exchanged by photosynthesis and respiration each year is a thousand times greater than that moving through the slow cycle

24

Decomposition (carbon cycle)

Decomposition - decomposer organisms such as bacteria and fungi break down dead organic matter, extracting energy and releasing CO2 to the atmosphere and mineral nutrients to the soil

  • Rates of decomposition depend on climatic conditions
    • The fastest rates occur in warm, humid environments such as the tropical rainforest
    • In contrast, decomposition is slow in cold environments like the tundra or drylands such as tropical deserts

25

Combustion (carbon cycle)

Combustion - occurs when organic material burns in the presence of oxygen

  • The combustion process releases CO2  as well as other toxic gases such as sulfur dioxide and nitrous oxides
  • Combustion is a natural fuel in many ecosystems with
    • Forest fires caused by lightning strikes are essential to the health of some ecosystems such as the coniferous forests of the Rocky Mountains
    • Long, cold winters slow the decomposition of forest litter which builds up on the forest floor
  • Fire shifts this log jam, freeing carbon and nutrients previously inaccessible to forest trees
    • It also opens up the forest canopy, creating new habitats and increasing biodiversity
  • Combustion also results from human activities such as deliberate firing of forest and grassland in order to clear land for cultivation or improve the quality of grazing
    • More important is the combustion of fossil fuels - despite international efforts to curb CO2 emissions, oil, coal and natural gas power the global economy and their consumption continues to grow
    • Currently the burning of fossil fuels by humans transfers nearly 10 Gt of CO2  a year from geological stores to the atmosphere, oceans and biosphere

26

Physical (inorganic) pump (carbon cycle)

Physical (inorganic) pump - involves mixing of surface and deep ocean waters by vertical currents, creating a more even distribution of carbon - both geographically and vertically - in the oceans

  • Initially CO2 enters the oceans from the atmosphere by diffusion
  • Surface ocean currents then transport the water and its dissolved CO2 polewards where it cools, becomes more dense and sinks
    • This downwelling only occurs in a handful of places in the oceans
    • One of these places is the North Atlantic between Greenland and Iceland
  • Downwelling carries dissolved carbon to the ocean depths where individual carbon molecules may remain for centuries
  • Eventually deep ocean currents transport the carbon to areas of upwelling
    • There cold, carbon-rich water rises to the surface and CO2 diffuses back into the atmosphere

27

Biological (inorganic) pump (carbon cycle)

Biological (inorganic) pump - carbon is exchanged between the oceans and atmosphere through the action of marine organisms

  • Globally nearly half of all carbon fixation takes place in the oceans
    • Around 50 GT of carbon is drawn from the atmosphere by the biological pump every year
  • Marine organisms drive the biological pump
    • Phytoplankton, floating near the ocean surface combines sunlight, water and dissolved CO2 to produce organic material
  • Whether consumed by animals in the marine food chain, or through natural death, carbon locked in the phytoplankton either accumulates in sediments on the ocean floor or is decomposed and released into the ocean as CO2
  • Other marine organisms such as tiny coccolithophores, molluscs and crustaceans extract carbonate and calcium ions from sea water to manufacture plates, shells and skeletons of calcium carbonate
    • Most of this carbon-rich material eventually ends up in ocean sediments and is ultimately lithified to form chalk and limestone

28

Vegetation (carbon cycle)

Vegetation - land plants, especially trees in the rainforest and boreal forests, contain huge stores of carbon

  • Most of this carbon, extracted from atmospheric CO2 through photosynthesis, is locked away for decades

29

Water cycle - key flows

  • Precipitation - 111 km3 x 103 per year
  • Evaporation - 425 km3 x 103 per year
  • Precipitation - 386 km3 x 103 per year
  • Evapotranspiration - 71 km3 x 103 per year
  • Runoff/groundwater flow - 40 km3 x 103 per year

30

Carbon cycle - key flows

  • Photosynthesis - 120 Gt per year
  • Oxidation (combustion and decomposition) + respiration - 120 Gt per year
  • Weathering - 0.2 Gt per year
  • Oceans and atmosphere collectively exchange 182 Gt per year (92 to oceans, 90 to atmosphere)

31

The water and carbon cycles as open and closed systems

  • Systems are groups of objects and the relationships that bind the objects together
    • On a global scale the water and carbon cycles are closed systems driven by the Sun’s energy (which is external to the Earth)
    • Only energy (and not matter) cross the boundaries of the global water and carbon cycles - hence we refer to these systems as ‘closed’
  • At smaller scales (e.g. drainage basin or forest ecosystem), materials as well as the Sun’s energy cross system boundaries
    • These systems are therefore open systems
  • Stores are the amount of material held within a part of the system, they are expressed in units of mass
  • Fluxes are the measurement of the rate of flow of materials between stores, they are measured in mass per unit time
  • Processes are the physical mechanisms that drive the flux of material from one store to another, for example evaporation drives the flux of water between its store in the ocean to a store in the atmosphere

32

Dynamic equilibrium in the cycles

Dynamic equilibrium is defined as the balanced state of a system when its inputs and outputs are equal.

Systems are dynamic in the sense that they have continuous inputs, throughputs, outputs and variable stores of energy and materials.

  • In the short term: inputs, outputs and stores fluctuate year to year
  • In the long term: flows and stores usually maintain a balance

33

How urbanisation affects  the water cycle

  • Impermeable surfaces speed up surface runoff
  • Drainage systems (e.g. pitched roof, gutter) remove water more quickly
  • Reduction of trees stops interception and vegetation storage
  • Urban spaces encroach on floodplains, reducing water storage capacity
  • Shorter lag times, with higher peak flows

34

How farming affects the carbon and water cycles

  • Water
    • Reduced surface runoff
    • Increased infiltration
    • Greater stores of water
  • Carbon
    • Reduced photosynthesis
    • Reduced decomposition

35

How forestry affects the carbon and water cycles

  • Water
    • Reduced runoff and stream discharge due to high rates of interception, evaporation and absorption of water by the roots
    • Higher rates of interception in plantations
      • 60% higher for the Sitka Spruce in Eastern England
    • Increased evaporation - lots of rainfall on leaves
    • Transpiration is heightened
      • 350mm/year in the Pennines
    • Felling creates sudden but temporary changes in the local water cycle (increased runoff and stream discharge, lower evaporation and local rainfall)
    • Longer lag times, low peak flows
  • Carbon
    • Increased carbon storage
      • Mature forests hold 170-200 tonnes C/Ha, soil is an even larger store
    • Forest trees sequester CO2 from the atmosphere for hundreds of years, with most carbon stored in the wood or stem
    • Forest trees only absorb more carbon than they release for the first 100 years of their existence

36

Water extraction

Water is extracted from surface and groundwater to meet public, industrial and agricultural demand.

  • This intervention in the water cycle influences the groundwater storage and the river flow dynamics.
  • Water can be extracted from the surface of a basin, or alternatively below the surface.

37

River Kennet - background

  • The river flows 40km before entering the Thames at Reading; it has a 1200km2 drainage basin
  • The upper catchment is mainly composed as chalk (highly permeable), so groundwater contributes to the majority of its flow
  • As a chalk stream, the river supports a range of habitats and wildlife - its water is filtered through the chalk, giving it high oxygen levels and exceptional clarity
  • Among native fauna are Atlantic salmon, brown trout and water voles

38

River Kennet - extraction

  • Several urban areas rely on water from the Kennet basin to meet public supply, the largest being Swindon (population of 200,000)
  • Thames Water abstracts groundwater from the upper catchment from boreholes, none of this water is returned to the river as waste water

39

River Kennet - impact

  • Rates of groundwater extraction have exceeded rates of recharge, and the falling water table has reduced flows in the River Kennet by 10-14%
  • During the 2002 drought flows fell by 20% and in the dry conditions of the early 1990s by up to 40%
  • Lower flows have reduced flooding and temporary areas of standing water and wetlands on the Kennet’s floodplain
  • Lower groundwater levels have caused springs and seepages to dry up and reduced the incidence of saturated overland flow on the chalk
  • Assessment of the ecology has focused on water crowfoot, which requires swift-flowing water and has suffered during individual low flow years

40

River Kennet - future

  • Demand in the region is expected to rise by 11% by 2030

41

Aquifers

Aquifers are permeable or porous water-bearing rocks such as chalk and New Red Sandstone.

  • Groundwater is abstracted for public supply from aquifers by wells and boreholes
  • Emerging in springs and seepages, groundwater feeds rivers and makes a major contribution to their base flow
  • Within an aquifer the upper surface of saturation is known as the water table - its height fluctuates seasonally and is also affected by periods of exceptional rainfall, drought and abstraction
    • In normal years in southern England the water table falls between March and September as rising temperatures increase evapotranspiration losses
    • Recharge resumes in the late autumn.

42

Artesian basin

An artesian basin is a syncline or basin-like structure formed from sedimentary rocks which confines an aquifer between impermeable rock layers and keeps it under artesian pressure

  • If this groundwater is tapped by a well or borehole, water will flow to the surface under its own pressure - this is known as an artesian aquifer
  • The level to which the water will rise (the potentiometric surface) is determined by the height of the water table in areas of recharge on the edges of the basin

London is located at the centre of a synclinal structure which forms an artesian basin, with groundwater in the chalk aquifer trapped between impermeable London Clay and Gault Clay

  • Overexploitation of groundwater trapped in the chalk below London caused it to fall by nearly 90m, however with declining demand for water in industry and reduced abstraction it has recovered in the last 50 years

43

Fossil fuels as part of global energy consumption

Fossil fuels accounted for 87% of global energy consumption in 2013

  • Fossil fuel consumption releases 10 billion tonnes of CO2 every year, which increases atmospheric CO2 concentration by over 1ppm.

44

Carbon sources and sinks, 1750-2012

  • Sources
    • Coal - 673 Gt
    • Oil - 496 Gt
    • Gas - 202 Gt
    • Cement - 36 Gt
    • Land-use - 590 Gt
  • Sinks
    • Atmosphere - 879 Gt
    • Ocean - 590 Gt
    • Land - 528 Gt

45

CCS - theory

One solution to the problem of CO2 emissions is CCS (carbon capture and storage), a technology with the capability of catching ½ the world’s CO2 emissions by capturing carbon and transporting it far below the earth’s surface (in depleted oil and gas fields or deep saline aquifer formations)

  • There are three methods of CCS:
    • Pre-combustion capture - this system converts solid, liquid or gaseous fuel into a mixture of H2 and CO2  using processes like gasification or reforming
      • The CO2 is then stored and the H2 burned for electricity
    • Post-combustion capture - CO2 is captured from the exhaust of a combustion process by absorbing it into a suitable solvent
      • The absorbed CO2  is then liberated from the solvent and compressed for transportation and storage
    • Oxy-fuel combustion - fuel is burned in pure oxygen

46

CCS - examples

CCS is used around the globe, but far more projects are located in North America than anywhere else (15 vs 7 for the rest of the world)

  • Examples of these are the Alberta Carbon Trunk Line which has a capacity of 14.6 million tonnes of CO2 per annum, or the Century Plant in Texas with 8.4 million
  • The UK’s £1 billion competition for CCS projects has been cancelled by the Conservative government, limiting the development of CCS technology (the winning project was at Drax, backed by the White Rose Consortium)

47

Positive feedback loops

A positive feedback loop creates conditions that speed up a process and/or amplify the initial change or perturbation. This type of feedback can tend to push a system towards destabilization or even extreme states. The following are examples of positive feedback loops:

  • Water cycle - increased temperature -> increased evaporation and more vapour in the atmosphere -> increased cloud cover and precipitation -> increased absorption of the sun’s long-wave radiation ->
  • Carbon cycle - burning fossil fuels increases CO2 which increases absorption of the sun’s long-wave radiation -> increased temperature -> increased rates of decomposition and permafrost melting -> increased carbon in the atmosphere ->

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Negative feedback loops

A negative feedback loop creates conditions that slow down and/or dampen the initial change or perturbation. This tends to push a system towards stability, restoring balance. The following are examples of negative feedback loops:

  • Water cycle - heavy rainfall in a drainage basin -> increased river flow and evaporation -> increased infiltration to recharge aquifers -> increased throughflow and groundwater flow -> water flows into oceans -> increased evaporation as there is little cover and a greater surface area ->
  • Carbon cycle - increased CO2 levels in the atmosphere -> increased temperature -> increased rates of photosynthesis -> increased carbon storage in the biosphere -> over time, increased carbon storage in soils and ocean sediments -> equilibrium

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Wider implications of feedback loops

Feedback loops from each cycle can have an effect on the other (i.e. a positive feedback in the water cycle resulting in more water vapour in the atmosphere will accelerate melting of permafrost, but will also boost rates of photosynthesis).

Complex systems have multiple reinforcing (positive feedback) and balancing feedbacks (negative feedbacks) operating at the same time:

  • The influence of some feedbacks dominate the influence that other feedbacks have on the system (i.e. some feedbacks are stronger, some are weaker)
  • Some feedbacks cancel eachother out or change from one to another if environmental conditions change
  • Some feedbacks operate at different time scales (i.e days - centuries)
  • Some feedbacks operate at different spatial scales (i.e. local, regional, continental, global)

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Diurnal changes in the water cycle

Significant changes occur within a 24-hour period in the water cycle

  • Lower temperatures at night reduce evaporation and transpiration
  • Convectional precipitation, dependent on direct heating from the sun, is a daytime phenomenon often falling in the afternoon when temperatures reach a maximum
    • This is particularly significant in climatic regions in the tropics where the bulk of precipitation is from convectional storms
  • The tropics also will have a higher rate of flux on a diurnal scale due to greater extremes of temperature, whereas coastal regions will have far less variation as temperature is regulated by the sea
  • Areas remaining below 0℃ will retain ice and permafrost.

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Seasonal changes in the water cycle

Ultimately the seasons are controlled by variations in the intensity of solar radiation

  • In the UK, solar radiation intensity peaks in mid-June
    • A typical solar input in June in southern England is around 800 W/m2; in December the input falls to little more than 150 W/m2
  • As a result, evapotranspiration is highest in the summer and lowest in the winter
  • In the driest parts of England up to 80% of precipitation may be lost to evapotranspiration
    • Average monthly evapotranspiration in lowland England reaches 96 mm in July, compared to 49 mm in September
  • With large losses of precipitation to evapotranspiration and the exhaustion of soil moisture, river flows in England are normally at their lowest in late summer
  • There is also a planet-wide shift in ice stores every 6 months, with the albedo effect causing more evaporation in the summer

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Diurnal changes in the carbon cycle

Flows of carbon vary diurnally

  • During the daytime, CO2 flows from the atmosphere to vegetation
    • At night, the flux is reversed
  • Without sunlight, photosynthesis switches off, and vegetation loses CO2 to the atmosphere
  • The same diurnal pattern is observed with phytoplankton in the oceans.

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Seasonal changes in the carbon cycle

Seasonal variations in the carbon cycle are shown by month-to-month changes in the net primary productivity of vegetation (NPP)

  • In middle and high latitudes, day length (photoperiod), light intensity and temperature drive seasonal changes in NPP
    • Similar seasonal variations also occur in the tropics, though there the main cause is water availability
  • During the northern hemisphere summer, when trees are in full foliage, there is a net global flow of CO2 from the atmosphere to the biosphere, as boreal and temperate forests extract large amounts of CO2 from the atmosphere
    • This causes atmospheric CO2 levels to fall by 2 ppm, and across the globe there is a net intake of carbon (except for sub saharan Africa where slash and burn occurs)
  • At the end of summer, as photosynthesis is reduced, the flow is reversed with natural decomposition releasing CO2 back into the atmosphere and deciduous trees respiring more during the shorter days
  • Changes are more extreme in the northern hemisphere as it has a greater concentration of continental land masses and therefore more vegetation than the southern hemisphere
  • In the oceans phytoplankton are stimulated into photosynthetic activity by rising water temperatures, more intense sunlight and the lengthening photoperiod
    • Every year in the North Atlantic there is an explosion of microscopic oceanic plant life which starts in March and peaks in mid-summer
    • The resulting algal blooms are extensive

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Long term changes in the Earth's climate

The Earth’s climate has been highly unstable over the last million years, with large fluctuations in global temperatures at regular intervals

  • In the last 400,000 years there have been 4 major glacial cycles, each lasting around 100,000 years
  • At the height of the Last Glacial Maximum (18,000 years ago) temperatures in Britain were 5℃ lower and ice was up to 1 km thick in Scotland, Wales and northern England
  • During interglacials temperatures have been similar to today, but on longer timescales they have been more extreme e.g. 250 million years ago global average temperatures reached 22℃
  • These changes had a major impact on the water and carbon cycles

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Long term changes in the water cycle

During glacial periods the water cycle undergoes a number of changes:

  • Water is transferred from the ocean reservoir to storage in ice sheets, glaciers and permafrost
    • As a result, in glacials the sea level worldwide falls by 100-130 m
  • Ice sheets and glaciers expand to cover around one third of continental land mass
    • As ice sheets advance equatorwards they destroy extensive tracts of forest and grassland
    • The area covered by vegetation and water stored in the biosphere shrinks as a result
  • In the tropics, the climate becomes drier and deserts and grasslands displace large areas of rainforest
  • Lower rates of evapotranspiration during glacial phases reduce exchanges of water between the atmosphere and the oceans, biosphere and soils
    • This, combined with large levels of freshwater stored as snow and ice, slows the water cycle appreciably

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Long term changes in the carbon cycle

  • During glacial periods there is a dramatic reduction in atmospheric CO2
    • Temperature and atmospheric CO2 are closely related
    • At times of glacial maxima CO2 concentrations fall to around 180 ppm, while in warmer interglacial periods they are 100 ppm higher
  • These lower levels of CO2 may be caused by the atmospheric CO2 finding its way into the deep ocean
    • Changes in ocean circulation during glacials bring nutrients to the surface and stimulate phytoplankton growth, which fix large quantities of CO2 before dying and sinking into the deep ocean where the carbon is stored
    • Lower ocean temperatures also make CO2 more soluble in surface waters
  • Changes occur in the terrestrial biosphere
    • The carbon pool in vegetation shrinks during glacials as ice sheets advance and occupy large areas of the continents
    • In this process deserts expand, tundra replaces temperate forests and grasslands encroach on tropical rainforests
  • With much of the land surface buried by ice, carbon stored in soils will no longer be exchanged with the atmosphere
  • Expanses of tundra beyond the ice-limit sequester huge amounts of carbon in permafrost
  • With less vegetation cover, fewer forests, lower temperatures and lower precipitation, NPP and the total volume of carbon fixed in photosynthesis will decline
    • This means an overall slowing of the carbon flux and smaller amounts of CO2 returned to the atmosphere through decomposition

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Research and monitoring techniques

  • Ground-based measurements of environmental change at a global scale are impractical so monitoring relies heavily on satellite technology and remote sensing. Continuous monitoring allows changes to be observed over a variety of different timescales.

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Monitoring of Arctic sea ice

  • NASA’s Earth Observing System (EOS) satellites since 1978
  • Measures microwave energy radiated from earth’s surface. Comparison of time series images to show changes.
  • Shows how much water is stored as ice compared to atmosphere, as well as indication of global temperatures (and therefore atmospheric CO2).

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Monitoring of ice caps/glaciers

  • As well as ground-based estimates of mass, satellites like the ICESat-2
  • Measures surface height of ice sheet and glaciers using laser technology. Shows extent and volume of ice and changes.
  • Shows how much water is stored as ice compared to atmosphere, as well as indication of global temperatures (and therefore atmospheric CO2).

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Monitoring of sea surface temperatures (SSTs)

  • NOAA satellites
  • Radiometers measure the wave band of radiation emitted from the ocean surface. Changes in global SSTs and areas of upwelling and downwelling.
  • SSTs are good indicators of atmospheric temperature, as well as influencing how much carbon is absorbed into the ocean.

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Monitoring of water vapour

  • NOAA polar orbiters
  • Measures cloud liquid water, total precipitable water, etc. Long-term trends in cloud cover and water vapour in the atmosphere.
  • Shows level of water stored in the atmosphere, as well as giving an indication of the severity of the greenhouse effect (vapour is a greenhouse gas).

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Monitoring of deforestation

  • ESA albedo images from various satellites
  • Measurements of reflectivity of earth’s surface and land use changes.
  • Levels of deforestation affect how much carbon is stored in the atmosphere rather than the biosphere. Deforestation also affects the water cycle by decreasing evapotranspiration and increasing surface runoff.

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Monitoring of atmospheric CO2

  • NASA’s OCO-2
  • Global atmospheric CO2 as well as the effectiveness if absorption of CO2 by plants.
  • Important for determining how far humans have affected the carbon cycle. Also affects the water cycle by melting ice and creating more water vapour.

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Monitoring of primary production in oceans

  • NASA’s MODIS/AQUA
  • Measures net primary production in oceans and on land.
  • Linked to phytoplankton, which ar key in sequestering carbon in the oceans.

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Links between the cycles through the atmosphere

  • Atmospheric CO2 has a greenhouse effect and plays a vital role in photosynthesis by terrestrial plants and phytoplankton
  • Plants, which are important carbon stores, extract water from 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

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Links between the cycles through the oceans

  • Ocean acidity increases when exchanges of CO2 are not in balance
  • 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

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Links between the cycles through vegetation and soil

  • 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

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Links between the cycles through the cryosphere

  • CO2  levels in the atmosphere determine the intensity of the greenhouse effect and melting of ice sheets, glaciers, sea ice and permafrost
  • Malting 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
  • Runoff, river flow and evaporation respond to temperature change

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Human factors affecting the water and carbon cycles

Rapid population and economic growth, deforestation and urbanisation in the past 100 years have modified the size of water and carbon stores and rates of transfer between stores in the water and carbon cycles.

  • The impact of these changes is most apparent at regional and local scales.

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Effect of humans on 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 southwest, surface supplies have diminished as more water is abstracted from rivers, and huge amounts are evaporated from reservoirs like Lake Mead and Lake Powell
  • The quality of freshwater resources has declined elsewhere
    • Overpumping of aquifers in the coastal regions of Bangladesh has led to incursions of salt water, often making the water unfit for irrigation and drinking
  • Human activities such as deforestation and urbanisation reduce evapotranspiration and therefore precipitation, increase surface runoff, decrease throughflow and lower water tables
    • In Amazonia, 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
  • In numerical terms, humans have the following impacts (displayed as percentages of total water in the cycle)
    • Evapotranspiration reduced from 40-50% to 20-30%
    • Groundwater reduced from 10-40% to 10-20%
    • Surface runoff increased from under 1% to 20-30%

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Effect of humans on the carbon cycle

Human activity is also altering the carbon cycle, depleting some carbon stores and increasing others:

  • The world relies on fossil fuels for 87% of its primary energy consumption
    • The exploitation of coal, oil and natural gas has remover billions of tonnes of carbon from geological stores
    • This process 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 a 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 annually
  • Additional carbon is stored primarily as atmospheric CO2 where its concentration increases year-by-year
    • 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 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
    • Ultimately phytoplankton absorb more than half the CO2 from burning fossil fuels - significantly more than 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 stores in wetlands, drained for cultivation and urban development, have also been depleted as they dry out and oxidise

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Impact of climate change on the water cycle

  • Global warming has increased evaporation and therefore the amount of moisture circulating throughout the troposphere
    • More vapour, which is a natural greenhouse gas, has a feedback effect, helping to raise global temperatures, increase evaporation and precipitation
  • Warmer temperatures and increased rates of evaporation increase the atmosphere’s capacity to ‘hold’ water
    • Increased evaporation may dry out some areas and fall as excess precipitation on others
  • Increased precipitation will result in higher runoff in the water cycle and greater flood risks
    • There is increased frequency of intense precipitation events, mainly over land areas, and because of warmer temperatures this will increasingly fall as snow
    • Precipitation intensity will generally increase - the amount of rain falling during very heavy precipitation events in the USA over the last 50 years has increased greatly
      • In the Northeast, Midwest and upper Great Plains, tha amount of rain falling during the most intense 1% of storms has increased more than 30%
  • Water vapour is also a source of energy in the atmosphere, releasing latent heat on condensation
    • With more energy in the atmosphere, extreme weather events such as hurricanes and mid-latitude storms become more powerful and more frequent
  • Global warming is accelerating the melting of glaciers, ice sheets like Greenland and permafrost in the Arctic
    • Thus water storage in the cryosphere shrinks, as water is transferred to the oceans and the atmosphere
  • In parts of the Northern Hemisphere, an earlier arrival of spring-like conditions is leading to earlier peaks in snowmelt and resulting river flows
    • As a consequence, seasons with the highest water demand, typically summer and autumn, are being impacted by a reduced availability of freshwater
  • Warming winter temperatures cause more precipitation to fall as rain rather than snow
    • Furthermore, rising temperatures cause snow to begin melting earlier in the year, altering the timing of streamflow in rivers that have their sources in mountainous areas
  • Warmer temperatures have led to an increased drying of the land surface in some areas, with the effect of an increased incidence and severity of drought
    • The Palmer Drought Severity Index has shown that from 1900 to 2002, the Sahel region of Africa has been experiencing harsher drought conditions
    • This same index also indicates an opposite trend in South AMerica and the south central United States

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Impact of climate change on the carbon cycle

  • Impacts are complex, as they depend not just on rising temperatures, but also on geographical differences in rainfall amounts
  • Higher global temperatures will in general increase rates of decomposition and accelerate transfers of carbon from the biosphere and soil to the atmosphere
  • In the humid tropics climate change may increase aridity and threaten the extent of forests
    • As forests are replaced by grasslands the amount of carbon stored in tropical biomass will diminish
  • In contrast, in high latitudes global warming will allow the boreal forests of Siberia, Canada and Alaska to expand polewards
    • This increased growth is referred to as carbon fertilization, and models predict that plants might grow anywhere from 12 to 76 more if atmospheric carbon dioxide is doubled as long as nothing else limited their growth
  • Carbon frozen in the permafrost of the tundra is being released as temperatures rise above freezing anff allow oxidation and decomposition of vast peat stores
    • It is estimated that permafrost in the Northern Hemisphere holds 1,672 billion tonnes of organic carbon (just 10% of this being released would raise temperatures by 0.7℃ globally)
  • Acidification of the oceans through the absorption of excess CO2 from the atmosphere reduces photosynthesis by phytoplankton, limiting the capacity of the oceans to store carbon
  • The land may become a natural source of carbon to the atmosphere, with persistent drought causing dramatic forest fires and large losses in tropical forests
    • In 2008, deforestation accounted for about 12% of all human carbon dioxide emissions
    • Warmer temperatures also stress plants, making them more susceptible to fire and insects
  • Warming caused by rising greenhouse gases may also ‘bake’ the soil, accelerating the rate at which carbon seeps out in some places
  • Long-term climate change will probably see an increase in carbon stored in the atmosphere, a decrease in carbon stored in the biosphere and possibly a similar decrease in the ocean carbon stores
    • Movement of carbon into and out of the atmosphere will vary regionally depending on changes in rates of photosynthesis, decomposition and respiration

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Carbon cycle management - wetland restoration

  • Wetlands contain 35% of the terrestrial carbon pool while only covering 6-9% of the Earth’s land surfaces
  • Population growth, economic development and urbanisation have places huge pressure on wetland environments
    • In the lower 48 US states the wetland area has halved since 1600
    • Apart from loss of biodiversity and wildlife habitats, destruction of wetlands transfers huge amounts of CO2 and CH4 to the atmosphere
  • Climate change and the need to reduce CO2 emissions have led to a re-evaluation of the importance of wetlands as carbon sinks
    • In the twentieth century, Canada’s prairie provinces lost 70% of their wetlands, however restoration programmes in this area have shown that wetlands can store on average 3.25 tonnes C/ha/year
    • Now 112,000 ha have been targeted for restoration in the Canadian prairies which should eventually sequester 364,000 tonnes C/year
  • The need for protection of wetlands as wildlife habitats is reflected in management initiatives such as the International Convention on Wetlands and the European Union 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
  • Restoration focuses on raising local water tables to re-create waterlogged conditions
    • Wetlands on flood plains can be reconnected to rivers by the removal of flood embankments and controlled floods
    • Coastal areas of reclaimed marshland can be restored by breaching sea defences
    • Elsewhere water levels can be maintained at artificially high levels by blocking or diverting drainage ditches and installing sluice gates

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Carbon cycle management - afforestation

  • Afforestation is the establishment of forests on ground where there was previously no forest cover
  • Because trees are carbon sinks, afforestation can help boost carbon capture and sequestration, reducing atmospheric CO2 levels in the medium to long term
    • Secondary benefits include reducing flood risks (interception) and soil erosion, and increasing biodiversity
    • Afforestation also helps to maintain the nutrient cycle, enabling new trees to grow and keeping the NPP of a forested landscape at a healthy level
  • In China the massive government-sponsored Three North Forest project has been planting trees since 1978
    • It aims to afforest 400,000 km2 (an area roughly the size of Spain) by 2050 by using over 70 aircraft for aerial seeding
    • In the decade 2000-09, 30,000 km2 were successfully planted with non-native fast-growing species such as poplar and birch
    • This project aims no only to protect primary forests, but to combat desertification and land degradation in the vast, semi-arid expanses of northern China where the Gobi desert is likely to expand
    • Trees now cover 18% of northern China (target was 15%)
    • There have been unforeseen consequences for the local water cycle, with groundwater stores falling by up to 19m in Minqin

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Carbon cycle management - agricultural practices

  • Unsustainable agricultural practices such as overcultivation, overgrazing and excessive intensification often result in soil erosion and the release of large quantities of carbon into the atmosphere
    • Intensive livestock farming produces 100 million tonnes/year of CH4
    • Almost as important are CH4 emissions from flooded (padi) rice fields and from the uncontrolled decomposition of manure
  • Land and crop management
    • Zero tillage - growing crops without ploughing the soil, conserving its organic content and reducing oxidation
    • Polyculture - growing annual crops interspersed with trees to provide year-round ground cover and protect soils from erosion
    • Crop residues - leaving crop residues on fields after the harvest to provide ground cover and protection against soil erosion and drying out
    • Avoiding the use of heavy farm machinery on wet soils, which leads to compaction and the risk of erosion by surface runoff
    • Contour ploughing and terracing on slopes to reduce runoff and erosion
    • Introducing new strains of rice that grow in drier conditions and therefore produce less CH4
  • Livestock management
    • Improving the quality of animal feed to reduce enteric fermentation so that less feed is converted to CH4
    • Mixing methane inhibitors with livestock feed - seaweed causes a 98% reduction
  • Manure management
    • Controlling the way manure decomposes to reduce CH4 emissions
    • Storing manure in anaerobic containers and capturing CH4 as a source of renewable energy

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Carbon cycle management - international agreements

  • Climate change affects all countries and international cooperation is needed to solve the problem
  • Cooperation in the past was often patchy, with some of the world’s largest greenhouse gas emitters opting to pursue narrow self-interest
  • Under the Kyoto Protocol of 1997 most rich countries agreed to legally binding reductions of their CO2 emissions, however developing countries were not included
  • The 2015 Paris Agreement was significant, however targets are not legally binding and a timetable for implementing them has yet to be agreed
  • There is an obligation for rich countries to transfer funds and technologies to poor countries since
    • Countries such as China and India are still relatively poor
    • Historically, Europe and North America through their own industrialisation and economic development ate largely to blame for contemporary global warming

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Carbon cycle management - cap and trade agreements

  • Cap and trade offers an international, market-based approach to limit emissions
    • Under this scheme businesses are allocated an annual quota for their CO2 emissions
    • If companies emit less than their quota they receive carbon credits which can be traded on international market; if they exceed their quotas they must purchase additional credits or incur financial penalties
    • This gives companies a strong financial incentive to cut CO2 emissions
  • Examples include the EU’s Emissions Trading System, which has brought capped emissions down by 15% between 2005 and 2015

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Water cycle management - forestry

  • The crucial role of forests in the global water cycle is recognised by multilateral agencies such as the UN and WB
    • They, together with other organisations and governments, fund programmes to protect tropical forests
    • The UN’s REDD programme and the World Bank’s FCPF fund over 50 partner countries in Africa, Asia-Pacific 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 and the German Development Bank to protect its forests
    • The Amazon Regional Protected Areas (ARPA) programme now covers nearly 10% of the Amazon Basin - areas included in the programme are strictly protected, stabilizing the regional water cycle as well as supporting indigenous forest communities
  • The Parica Project is located in Rondonia in the western Amazon
    • It aims to develop a 1000 km2 commercial timber plantation on government-owned, deforested land
    • The plan is for 20 million fast growing, tropical hardwood seedlings to mature over a period of 25 years

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Water cycle management - water allocations

  • In countries of water scarcity, governments have to make difficult decisions on the allocation of water resources
  • Agriculture is by far the biggest consumer - accounting for 70% of global water withdrawals and 90% of consumption
    • Wastage of water occurs through evaporation and seepage through inefficient water management
    • Improved management techniques which minimise water losses to evaporation include mulching, zero soil disturbance and drip irrigation
    • Losses to runoff 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
  • Water allocation schemes protect the water cycle by reducing the amount of water that can be abstracted from streams and rivers, stopping a depletion of terrestrial storage of water and increased evaporation and runoff
  • The water markets of Chile were created in 1981
    • Here water sources are classified by the permanence and whether they are consumptive
      • To gain access to water, a permit must be obtained from the governments or shares can be bought from the current owners
    • In the Limari Valley, i share equals 4880 m3/year and is valued at $11,700
  • Water allocation schemes were introduced into Queensland, South Australia and New South Wales in the late 1980s
    • They allowed an allocated volume of water to be transferred to areas where it was needed
    • Most transfers were temporary to protect the water cycle as much as possible
    • In 1991, 140 million m3 of water was transferred in New South Wales, most of it temporarily

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Water cycle management - drainage basin planning

  • Drainage basin planning is the management of water resources within drainage basins to accommodate the conflicting demands of different water users as well as making water use sustainable
    • It works well on a local scale, allowing an individual drainage basin to be set targets for runoff, surface water storage and groundwater levels
  • Water users that affect a drainage basin include agriculture, industry, domestic use, wildlife, recreation and leisure
  • Rapid runoff is controlled by reforestation programmes in upland catchments, reducing artificial drainage and extending permeable surfaces in urban areas
  • Surface water storage is improved is improved by conserving and restoring wetlands, including temporary storage on floodplains
  • Groundwater levels are maintained by limiting abstraction and by artificial recharge, where water is injected into aquifers through boreholes
  • The EU’s Water Directive Framework was formed in October 2000 to help EU countries plan their drainage basins in order to protect the water cycle
    • In England and Wales, ten river basin districts have been defined which comprise major catchments such as the Severn, Thames and Humber
    • Each district has its own River Basin Management Plan published jointly by the Environment Agency and DEFRA
    • The plan sets targets in relation to, for example, water quality, abstraction rates, groundwater levels, flood control, floodplain development and the status of habitats and wildlife