case study4 acid deposition impacts140307

8/9/2019 Case Study4 Acid Deposition Impacts140307

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Acid Deposition and Impacts

http://4.bp.blogspot.com/-fC4w1Bn-7YI/UA0sXP0bpPI/AAAAAAAAA7c/BBw6Tp0m37o/s1600/acid+rain.jpgCopyright: http://uksovannara.blogspot.co.uk/2012/07/harmful-effects-of-acid-rain.html


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Todays lecture

Sources of acidifying pollutants in air.Acid deposition and stages ofacidificationEffects of acid rain and their controlsTerrestrial ecosystemsAquatic ecosystems

UK Acid Water Monitoring Network(AWMN): Status, Recovery andFuture..

forest-acid-rain-bg


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What do we mean by Acid rain?

pH of unpolluted rain?Dissolution of CO2:Oxidation of N and S compounds in theatmosphere to form nitric and sulphuric acid:Other natural sources of acidity in rain.Thus rain with acids dissolved in it.

Dynamic equilibrium of carbonic acid with CO2 at pH 5.65


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Background acidification of soils by Nand S cycles

Freeman. 2007. Environmental Science: A Canadian Perspective,Peasons Inc.


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Marine originTerrestrial originPollutionSodiumSea saltSoil dustBiomass burningMagnesiumSea saltSoil dustBiomass burningPotassiumSea saltBiogenic aerosols, soildustBiomass burning,fertilizerCalciumSea saltSoil dustCement manufacture,Fuel burning, BiomassburningChlorideSea saltIndustrial hydrochloricacidSulphateSea salt, DMSDMS, H2S etc frombiological decay,volcanoes, soil dustFossil fuel burning,biomass burningNitrate/NitriteAtmosphericnitrogen, lighteningNOx from biologicaldecay, atmosphericnitrogen, lighteningVehicle emissions,fossil fuels, biomassbutrning, fertilizerAmmoniumAmmonia frombiological decayAmmonia frombiological decayAmmonia fertilizers,human, animal wastedecompositionAdapted from Heal, 2005, p360

SOURCES OF INDIVIDUAL IONS (Anions and cations) IN RAINWATER


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Anthropogenic sources of acidifyingpollutants: NOx

Sources of reactive N in theatmosphere:Ammonia released fromfertilizer and manureN2O, NO, NO2 from agriculture

FertilizerO2 + heat O + O

N2 + O NO + N

N + O2 NO + O


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Anthropogenic sources of acidifyingpollutants: SO2

SOx:Fossil fuel burning (particularly industrial fluegases

Fossil use in electric utilities (60-70 % SO2release source)Extraction of metal from ore (chalcopyrite-CuFeS2)


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NOx and SOx sources in New England by 2002

Source US EPA: http://www.epa.gov/region1/eco/acidrain/causes.html

Road engine as a sourcedominant hereIndustry as a source dominant here


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J. Galloway, 2008.A global increase in atmospheric reactive N deposition (Oxidized and reduced forms).


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History of acid rain research

Mid-nineteenth century, higherconcentrations of sulphuric acid inprecipitation near industrial towns(Manchester) identifiedAcid rain used for the first time in1870s1960s work by Ode declining fishpopulations in Scandinavia linkto acid rain

acid rainacid rain


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Trends in atmospheric pollutants

Sulphur traditionally been emitted in largerquantities than NCanadian Example (Schindler et al., 2005)NOx doubled 1970-1985, now remains constant17% decrease from regulations of vehicle emissions andsmelters ~balanced by 29% increase from electricalgeneration.NH3 increase due to increasing farming intensity SO42- in rain declined by 45-50% since 1980s due toreduced SOx emissions from smelters and coal-firedpower plants

UK (see Monteith and Evans, 2005, Kernan et al.2010)


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SO2 and NOx Oxidation in theatmosphere


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TRANSFER OF ATMOSPHERIC SOLUTES

Dry deposition: Occurs during dry periods betweenprecipitation events.Direct transfer of pollutant gases from the air (particularlySO2) onto vegetation, water or soil surfaceGravitational settling of larger particles.Subsequent oxidation to form H2SO4 and HNO3 takes placeon the surfaces when wetted with rain or dewGases may also pass into plant stomataAcid surge during initial runoffIncreased by afforested regions since plants scavenge drydeposits more than bare surface


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TRANSFER OF ATMOSPHERIC SOLUTES:2. Wet deposition

Wet deposition:Absorption of pollutant into droplets in or below cloudsand removal by precipitationWash out: removal of solutes by falling precipitationRain out: acid inputs which originate within the cloudsystem

Early part of rain often has highest solute concentrations

colonsay-rain


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TRANSFER OF ATMOSPHERIC SOLUTES: 3. Occult deposition

Occult deposition:Deposition of acidicpollutants (SO2 and NOx)onto surface by impactionof fog and cloud dropletsInfluenced by climaticfactors.Concentration of pollutantscan be much higher than inrain. Why?Important where lowrainfall but high relativehumidity.

imageEUGpine_needle_ice


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Dry vs wet deposition

In the UK averaged over a year the:

Dry deposition = wet deposition

Relative importance of wet or dry deposition varieswith geographic location and seasondifference in the amount of rainfall and emissions

Dry deposition dominates close to emission source -normally occurs in 2 or 3 daysIf pollutants stay in atmosphere for longer, thengets oxidised to acids followed by wet deposition.Wet deposition more important with distance fromthe source.


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Spatial trends.

Regional rather than global problem.Sulphur compounds in the atmosphere have a residencetime of a few days, therefore, they are not well mixedand have regional effectsAreas with high rainfall amounts may have higher acidloading even though less acidic precipitation.Rate and distance of movement also associated withheight of pollutant emissions i.e. tall stacks enhancelong-distance transferAtmospheric circulation patterns also important


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acid rainAcidprecipitation inEuropeElsom, 1992, p85

Sweden more acidityfrom wet deposition further from source general circulation


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Stages of acidification

3 stages ofacidification3 stages of acidification

1) natural buffering capacity provides resistance to pHchange

2) all buffering capacity utilized leading to variation inpH

3) New stable system with lower pH

H. Zhang. Oklahoma State University


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Natural buffering against acidification

If not well buffered, then catchments arehighly sensitive to acid inputsWhat is buffering?Capacity to assimilate a limited number of H+ions without an appreciable change in pH

Usually H+ absorbed by soils or freshwatersystems until a buffering threshold isexceeded, then have rapid decrease in pH


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Impacts of acidity on terrestrialand aquatic ecosystems


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effects of acid rainKemp, 2004, p353

Effects: Terrestrial and aquatic ecosystemsThe Impact Cascade


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acid rainEffects: Terrestrial ecosystems

See: Vrba, J. et al (2003) Long term studies (1871-2000) on acidification and recovery of lakesin the Bohemian Forest (central Europe). Science of the Total Environment, 310,73-85.

The effects of acid rain on aspruce forest in the CzechRepublic.

Suggested relationship to forestdecline (although possibly othereffects e.g. O3 in air).Direct acid deposition on leavesof plant can cause lesions, onlywhere pH 3.4 or belowLeaches Ca, Mg, K from leavesand needlesDepletion of Ca in needles affectssusceptibility to freezing


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acid conifers-Conifers areefficient

scavengers ofclouddroplets

Heal, 2005, p376

Acid inputs initially neutralized by exchange of H+ ions with Ca2+ and Mg2+ insoils at cation exchange sitesAcidification occurs if acid inputs continue faster than base cations releasedinto soil from mineral weathering


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Geological sensitivity

granite-xpl_pm18-23sandstone2_pm13-19Sandstone: grains of quartz, cementedtogether by calcium carbonate.

Granite: feldspars, quartz, mica,tourmaline.

limestone-xpl_pm14-09Limestone: fossils, and calcite crystals

http://www.earth.ox.ac.uk/~oesis/micro/index.htmlThe type of underlying bedrockwill control the catchmentssusceptibility to acidification asHCO3-concentrations influencedby catchment geologyThe type of underlying bedrock

will control the catchmentssusceptibility to acidification asHCO3- concentrations influencedby catchment geology


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Effects of acidifying water bodies

Acidification of lakesAcidification of lakes

Reduced bacterial activity insedimentsReduced bacterial activity insediments

Inhibits decomposition andnutrient generationInhibits decomposition andnutrient generation

Affects aquatic food websAffectsaquatic foodwebsDecline in invertebratepopulationsDecline in invertebratepopulations

Decline in fish depending oninvertebratesDecline in fish depending oninvertebrates

Decline in birds dependingon fishDecline in birds dependingon fish

Acidification of amphibianbreeding pools (esp. from

snowmelt)Acidification of amphibianbreeding pools (esp. fromsnowmelt)

Reduction in fertilisation ofeggsReduction in fertilisation ofeggs

Decline in amphibiannumbersDecline in amphibian

numbers

Loss of fish (Trout, Salmonetc.)


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acid rainGypsum highly soluble and occupies large volume (mechanical stress)Gypsum highly soluble and occupies large volume (mechanical stress)Effects: Calcareous building stone

1908

1969


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Summary of effects

Harm to terrestrial ecosystems (plants and soils)Harm to aquatic ecosystemsMobility of toxic metals (e.g. Al)Weathering of building materialEffects amplified where:Trees intercept clouds/fogHigh acid deposition (i.e. uplands with high rainfall)Base poor soils


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Solutions?

1.Technological:I.Desulphurization of flue gasesII.Liming of forests, soils and lakes

2.Prevention (see Schindler et al. 2006)3.International legislation - management of aciddeposition needs to be done internationally(i.e. EU, Canada/USA)


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Recovery of Lakes and Rivers from Acidification in the UK

UK government program tomonitor acidity trend at theAcid Waters MonitoringNetwork (AWMN) sitesProduce weekly or biweeklymonitoring dataTrends in pH, non-marineSO4 & NO3Key Q: Trends in bulkdeposition chemistry, UK (20years data trend)

Kernan et al. 2010, UKDEFRA Report

Visit the website here for relevant dataand papers.

http://awmn.defra.gov.uk/


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Trends in pH of Bulk Deposition: 1985-2005

Significant increase in pH in 11 out of 12 monitoring sites


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Non-marine SO4-2 deposition trends: 1985-2005

Red line: Significant decreasing trend


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Recovery of Aquatic Macrophytes: The scale of ecosystem impacts


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Current ANC status and reference levels toachieve in the UK

By 2007 actual ANC still lagged behind the referencetarget level


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pH recovery targets: Improving but in certainregions targets have yet to be achieved

By 2007 pH still lagged behind the reference target level


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So in case of the UK

Significant recovery in chemical and biologicalparameters of water bodies observed, but still lagsbehind the reference levels in most sites And (next page)


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SO4 reduction led to pH improvement in the UK water, but thefuture trends of NO3 could dampen this improvement


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RECAP

ACID deposition due to air pollutionImpacts on ecosystems and built environmentSignificant improvement in water bodies statusin the UKAtmospheric reactive N deposition may driveacidity in the current century.


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General References

Arnell, N. (2002) Hydrology and GlobalEnvironmental Change. Pearson.Elsom, D.M (1992) Atmospheric Pollution aGlobal Problem. Blackwell.Heal, K.V. (2005) Solutes. In: Holden, J. (Ed.)An Introduction to Physical Geography and theEnvironment. Pearson.Kemp, D.D. (2004) Exploring EnvironmentalIssues. An integrated approach. Routledge.


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case study4 acid deposition impacts140307

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