soil biology - joshtabor.comjoshtabor.com/docs/classes/secondyear/contaminanthydro/notes.pdf · §...

ThefocusisonsoilecologywhichconsidersPopulationdynamicsoHowdifferentorganismtypesrelate toeachotherandtheirenvironmento

Definitions

Community:Agroupofinteractingpopulations•Population:Anassemblageofanorganismtypeinanarea•Habitat:Placeoccupiedbyanorganismtype,populationorcommunity•

EachorganismtypeoccupiesaparticularecologicalnicheTheroleanorganismtypeplaysinitsenvironmentoie.:itsfunctionandplaceintheecosystemo

Anicheisaspecificsetofcircumstancesforanorganismtypeandisdefinedby:ThetypeoffooditconsumesoItspredatorsoPhysicalconstraints

Temperature,light,moisture§o

ChemicalconstraintspH,redoxconditions,nutrientrequirements,toxiceffects§

Anoverlappingofconditionsresultsincompetition•

GroupsofSoilOrganisms•

HigherPlants(PlantKingdom)Provideareserveoffood(nutrients)andenergyforotherorganismsbyphotosynthesis

CO2+H2O→CH2O+O2§

EnergyforthereactionisprovidedbylightLight+2H2O→Energy+4H++O2§

ChlorophyllcatalyzestheconversionoflightenergytochemicalenergyoPhotosynthesisisthebasisoflifeonearthasweknowit

Mostorganismsdependonitdirectlyorindirectly○Responsibleforaerobicconditions(atmosphericO2@21%)andlowatmosphericCO2

http://www.geocraft.com/WVFossils/Carboniferous_climate.html○

GreenplantsareautotrophsOrganismsthatdonotneedorganicenergysubstrates○

ie.:theydonotoxidizeorganicmatterfortheirenergyrequirements○ProduceorganictissuesfromCO2andionsusinglightastheenergysource○

PlantsprovideorganicmattertosoilsintheformofrootsandlitterIntegralpartofthecarboncycle○

SmallAnimals(AnimalKingdom)Helminths,annelids,mollusks,arthropods(pp.143)oAnimalsareheterotrophs

Carbonandnutrientsareassimilatedandenergyrequirementsaremetbyrespiration

Aerobicrespirationisrepresentedby:○CH2O+O2→CO2+H2O+Energy○

CarbonCycleThisisthecyclingofcarbonfromorganictoinorganicformsandbackagainoInvolvesautotrophsandheterotrophs(animalsandmicrobes)alongwithchangingenvironmentalconditions

PhotosynthesisCO2+H2O→CH2O+O2§

(Aerobic)RespirationCH2O+O2→CO2+H2O§

TheCO2canbe:Returnedtotheatmosphere§Incorporatedintosoilmoistureandgroundwater§

CO2+H2O→H2CO3§H2CO3→H++HCO3–§HCO3-→H++CO3=

HCO3–andCO3=canbeprecipitatedasmineralsØ~99%ofallcarbononearthisboundincarbonateminerals

SomeasfossilfuelsoØ

MicrobesProtozoa,somealgae,somefungi,bacteria

Includes:§KingdomProtista§KingdomMonera§

KingdomProtistaGroupintowhichallunicellulareukaryotescanbeplacedoProtozoa,unicellularalgae,unicellularfungioEukaryotes:

Organismshavingadistinctnuclearmembrane§o

Protozoa:Unicellular(oracellular)@~8µm§Foundinmoistsoilsandaquaticenvironments

DormantotherwiseascystsandsporesØ§

Waterisneededfortheirmobilityandforthatoftheirfood§Reproducebybinaryfission§Lifestyles

ActivepredatorsOfbacteriao

ScavengersOfparticulateorganicmattero

SaprophytesAbsorbdeadorganicmatterinthedissolvedformo

ParasitesNobenefittohosto

ExamplesAmoebaØCiliatesØFlagellatesØ(Giardia)Ø(Cryptosporidium)Ø

AlgaeSimpleplantsthatcontainchlorophyll§Liveonmoistsoil(andaquaticenvironments)§

FungiHeterotrophs

DestroyorganicmatterØDeriveenergybyoxidationoforganicmatterØ

Singlecelledormulticellular§Enjoymoistconditionsonland§Lifestyles

AllaresaprophytesØSomeparasiticØSomesymbioticØ

ExamplesMushroomsØMoldØYeastØ

MicorrhizaeSymbioticrelationshipbetweenplantrootsandfungi

PlantProvidesfoodforthefunguso

FungusProvidesplantwithinorganicnutrientsbyextendingtheirhyphae(filamants)anddeliveringnutrientstotheplant

KingdomMonera(Bacteria)Allaresinglecelledprokaryotes

5– 5µm§Canbe~100million/gramoffertiletopsoil§

FoundeverywhereinthebiosphereoExtremelydiversephysiologicallyoVeryprolific

Candividebybinaryfissioneveryfewhours§o

Veryadaptabletochangingphysical,chemicalandnutrientconditionsasfarastheirtypesandnumbersareconcerned

Godormantascystsorsporesinbadtimes§Opportunistic

TakeadvantageoffavourableconditionsØ§

Spreadquicklybydust,waterandotherorganismso

BacteriacanbeidentifiedbyvariouswaysGram’sstainoShape

Rod,spirillum,coccus,filiments§o

BygrowthusingspecificnutrientbrothsandtemperatureoWhattheyuseasanenergysource

Organicmatter§Inorganicmatter§Light§

WhetherornottheyrequirefreemolecularoxygenforrespirationAerobic§Anaerobic§Facultative§

RespirationOrganicsubstancesarebrokendown(oxidized)intosimplerproductswithreleaseofenergy

Thisenergyisincorporatedintoenergycarryingmolecules(ATP)usedformetabolicpurposes

ATPhashighenergyphosphatebonds§Incells/musclesitishydrolyzedtoADPtoreleaseenergy§

AerobicrespirationOrganicsareoxidizedusingfreeO2

Carbohydrate+O2→ CO2+H2O+Energy§o

AnaerobicrespirtaionNO3-,SO4=andCH2Ocanbeusedasoxidantscorrespondingto:

Increasinglyreducingconditions§Changeinpopulationtypes§Slowerratesofdecay§

FermentationSpecialcaseofanaerobicrespirationoSomeoftheorganicsubstrateitselfisusedastheoxidizingagentandisreducedtoacids,alcoholandmethane

Carbohydrate→ CO2+Acids/Alcohol/Methane+EnergyØ

RoleofBacteriainSoils

Largelyresponsiblefordecompositionoforganicmatter(incombowithfungi)Absorbdissolvedorganics§Canuseenzymestofacilitatedissolution§

MostlyheterotrophsAerobic,anaerobic,facultativeanaerobic§

SomeareautotrophsBlue-greenalgae§

Somearechemautotrophs(lithotrophs)Importantrewaterchemistry§

ImportantrenutrientcyclingoContributetohumusproductionoImportantinbioremediation

Converttoxicmaterialstonon-toxicbyproducts§o

SomeareparasitesoSomearesymbiotic

Nfixers§Assistindigestioninthegutofotherorganisms§

DecompositionofOrganicMatter•

AfunctionofheterotrophsoMostimportantgroupsaremicrobes

Especiallybacteriaandfungi§LikeDOM§Useenzymestohelpdissolveorganicsolids§

Deadanddyingorganicmaterialisrapidlycolonizedbyfastgrowing,opportunisticbacteria

Soluble,easilydegradedcellularconstituentsareattackedfirst§

Moreresistant,complex,insolublematerial takesmoretimeBreakdownofthismaterialishelpedbyanimalssuchasinsects,bugsandworms

Theychewitupandpartiallydigestitresultinginprogressivelysimplercompoundsthatcanbeusedbysimplerorganisms

BacteriaintheirguthelpØ

Wood(celluloseandlignin)isattackedbyaveryspecializedseriesoffungiUsespecificenzymestodissolvematter§

Eventuallyablack,amorphous,resistanthumusformsandtheprocessslowsoHeatisreleasedcorrespondingtoalargereductioninmass

ConvertedtoCO2§Someorganicelementsareconvertedtonewbiomass§Somereleasedintosolutionasorganicandinorganicsolutes§

Ratesofdecay(andorganismsinvolved)atanypointdependonThenatureofthematerial§Stageofdecay§Environmentalfactors§Nutrientsupply§

NatureofmaterialDecayisretardedifthematerialis:

InlargepiecesLowersurfaceareaØHardertoingestØ

DenseandnonporousLessaccessibletomicrobes,water,nutrientsandO2Ø

ResistantNon-soluble,complex,highmolecularweightØ

Itistheroleofanimalstochewandpartiallydigestmaterialtomakeitmoreporousandsimpler

StageofDecayDecayisrapidatfirstanddiminisheswithtimeoSolublecell constituentsareattackedfirst

Resultsinaresidueofinsoluble,resistantmaterial§o

EnvironmentalFactorsPhysical

TemperatureCanchangewidelyatsurfaceØOptimum@35oC

35oCtendstokill•Ø

Temperaturesclosetofreezingwill~stopgrowthbutnotkillØ

MoisturecontentLowerlevels

Reducesmobilityofmicrobes,foodandnutrientsoLeadstoinsolubilityoCaninitiatedormancyo

DesiccationmaybeavoidedbyOsmoticregulationØHidinginsideaggregatesØ

SaturationResultofpoordrainageandcompactionØLeadstoanaerobicconditionsandslowdecayratesØAnaerobicformslurkinsideaggregatesreadytotakeoverØ

ChemicalEnvironmentpHtoohigh/toolow

DirecteffectonmetabolismØResultsintoxiclevelsofsomeelementsØ

HighersalinityCancausedesiccationØ

RedoxconditionsAffectsdominantpopulationsandspeedofdecayØ

NutritionalConstraintsCandNaremostcommonlylimitingforbacteria§Deficiencyoftensuchthattheelementsarepresentinthewrongform

Tendtobeboundupinlarge,organicmoleculesØSoluble,inorganicformsareneeded

NH4+andNO3-arefavouredformsofNoCdeficiency

Lackofreadilydecomposableorganicmatter§o

Animalsfacilitatebreakdownofresistantmattermakingnutrientsmoreaccessible

SoilBiologyJanuary6,2016 10:26PM

Definitions

CO2+H2O→CH2O+O2§

FungiHeterotrophs

Definitions

CO2+H2O→CH2O+O2§

FungiHeterotrophs

Definitions

CO2+H2O→CH2O+O2§

FungiHeterotrophs

Definitions

CO2+H2O→CH2O+O2§

FungiHeterotrophs

Definitions

CO2+H2O→CH2O+O2§

FungiHeterotrophs

Definitions

CO2+H2O→CH2O+O2§

FungiHeterotrophs

Definitions

CO2+H2O→CH2O+O2§

FungiHeterotrophs

Definitions

CO2+H2O→CH2O+O2§

FungiHeterotrophs

Definitions

CO2+H2O→CH2O+O2§

FungiHeterotrophs

Definitions

CO2+H2O→CH2O+O2§

FungiHeterotrophs

Definitions

CO2+H2O→CH2O+O2§

FungiHeterotrophs

Definitions

CO2+H2O→CH2O+O2§

FungiHeterotrophs

Definitions

CO2+H2O→CH2O+O2§

FungiHeterotrophs

Definitions

CO2+H2O→CH2O+O2§

FungiHeterotrophs

Definitions

CO2+H2O→CH2O+O2§

FungiHeterotrophs

Definitions

CO2+H2O→CH2O+O2§

FungiHeterotrophs

Definitions

CO2+H2O→CH2O+O2§

FungiHeterotrophs

Definitions

CO2+H2O→CH2O+O2§

FungiHeterotrophs

Definitions

CO2+H2O→CH2O+O2§

FungiHeterotrophs

Definitions

CO2+H2O→CH2O+O2§

FungiHeterotrophs

Definitions

CO2+H2O→CH2O+O2§

FungiHeterotrophs

Definitions

CO2+H2O→CH2O+O2§

FungiHeterotrophs

Definitions

CO2+H2O→CH2O+O2§

FungiHeterotrophs

Mostgroundwaterstartsasrainorsnowthatinfiltratessoilandmakesitswayintotheunderlyingearthmaterial

Soilzoneprocessescanhavealargeeffectonwaterchemicalquality•Manyprocessesmaycontinuetoaffectgroundwaterasitmakesitswayfromrechargetodischargeareasindifferenthydrogeologicsettings

AtmosphericEffects•

RainwaterisaverydilutesolutionbutitisnotpureRaincontainsmanydissolvedgasesandsolids§

AtmosphericaerosolsContributedissolvedsolidstorain§Smallparticlesofsolidsorliquidsranginginsizefromafewmoleculesupto~40μ

Mostendupinrainsincetheyactascloudcondensationnuclei(CCN)§

AtmosphericwatervapouralwayscondensesonaparticleornucleusoCondensationoccurspreferentiallyon

Largeparticles§Solubleparticles§

Dropletsgrowinsizebycollisionandcohesiontothepointwheretheyfalloutasrain

Particlesintheatmospherereturntotheearth’ssurfacebyRainout

ThoseservingasCCNandaffectingrainchemistry•§

WashoutTheflushingoutofparticlesbyfallingraindrops•

(Dry)FalloutParticles>~40μ•

OriginandCompositionofAtmosphericAerosols•

Twomaintypes:Primaryparticles§Secondaryparticles§

PrimaryparticlesEmitteddirectlyintotheatmosphereassolids§Tendtobelarger (>1μ)§

Examples:oSeasaltcrystals

Fromwaterdropletspropelledintotheairbyburstingbubblesattheoceansurface

2– 20μ diameter§Reflectthechemicalcompositionofseawaterwith~55%Cl- and~28%Na+

DustSilica,mica,clays,ironoxides§ContributeAl,Fe,Si,Ca,K,Na,Mg§

SmokeFineparticlesoforganiccarbonwithaccessoryelements§Biomassburning§

FuelcombustionAsh§Soot§

VolcanismSilicatemineralparticles§

SecondaryparticlesFormedfromgaseousemissionsthatsubsequentlycondenseintheatmosphere

Oxidationofgaseslessensvolatilitycontributingtoaerosoldevelopment§Tendtoformsmalleraerosols<1μ§

Examples:Volatileorganiccompounds(VOC’s)

Metabolicby-productsofvegetation•Organicmatterdecomposition•

SulfateaerosolsfromgaseousprecursorsSO2

Fuel(coal)combustionoVolcanismo

BiogenicDMS(di-methylsulfide,S(CH3)2)Fromplanktonmetabolismandbiologicaldecay•

Resultinsulfate(SO4=)aerosolsbyoxidationintheatmosphere2SO2 +O2+2H2O→4H+ +2SO4=•

RainWaterChemistry•

TDSVerydilute§Lowerinremote,continentalareas§Higherinmaritimeareasandareasaffectedbyindustrial/urbanactivity§

pHAslowas4- 5fromacidraineffects

SulfuricacidfromburningofpyriticcoalandcrudeoilS+O2→SO2o2SO2 +O2+2H2O→4H+ +2SO4=o

Nitricacidfromvehicleemissions4NO2+O2+2H2O→4H++4NO3-o

[email protected]– 5.7forraininequilibriumwithatmosphericCO2 andintheabsenceofacidraineffects

H2O+CO2→H2CO3o

SummaryofRainSolutionChemistry•

Rainwateris:Verydilute§Slightlytomoderatelyacidic§Oxidizing§

Hence:chemicallyactiveinpromotionofsoilzoneprocesses

SoilZoneEffects

AlmostallwaterthatentersagroundwaterzonepassesthroughasoillayerThiscanexertalargeinfluenceonwaterchemistry§

Significantly:LargeamountsofacidcanbegeneratedaffectingpH§Concurrently,allormuchofthedissolvedoxygenmaybeconsumedaffectingtheoxidation-reductionpotential(ORP)

TypesofAcidsGeneratedinSoils

CarbonicAcidAresultofoxidativeprocessesinvolvingrespirationandconsequentcarbonationofwater

Importantly:microbesandrootsCH2O+O2→CO2 +H2O□CO2 +H2O→H2CO3□

BiologicallyactivesoilsresultinmuchhigherCO2 contentinporespacesCanbe10– 100’softimesatmosphericconcentrationswitharangeinpartialpressuresfrom10-3 to10-1bar

SoilmoisturepHcandropsignificantlyAPCO2of10-1 canresultinapHof~4.5dependingontemperature

CO2 concentrationsarevariableinspaceandtimeandareaffectedby:Temperature

AffectsbiologicalactivityandCO2 dissolution□§

MoisturecontentAffects:

Biologicalactivity□GenerationofH2CO3□CO2 diffusionoutofthesoil□

SoilproductivityAffectstypeandamountoforganicmatter,plantgrowthandmicrobialactivity

SoilPermeabilityAffectedbysoiltextureandstructure§Affectsgasdiffusion

O2 intosoil□CO2 outofsoil□

IntermittentpulsesofH2CO3 aregeneratedatrainfallevents○H2CO3 encountersmineralsthatreactwiththeacidcontributingtoweatheringreactions,theformationofnewmineralsandsolutiondevelopment

H2CO3canbeconsumedwhileatthesametimebereplenishedbyongoingrespiration

MineralAcidsMineralacidsarearesultaerobicbacteria-drivenoxidationofinorganicmaterial

SulfuricAcidOxidationofsulfideinsulfide-bearingmineralssuchaspyrite(FeS2),arsenopyrite,chalcopyrite,sphalerite,pyrrhotite(FeS)

Calledacidrockdrainage§FeS2 +15/4O2+7/2H2O→ Fe(OH)3+4H++2SO4=

eg.:ByThiobacillusferrooxidans□§

NitricAcidAmmoniumfromorganicmatterdecay,fertilizersetc.isoxidized

NH4++2O2→2H++NO3-+H2O□§

Referredtoasnitrification§

OrganicAcidsDerivedfromdecayoforganicmatter§eg.:humicandfulvicacids§

Weakacids○

ElectrochemicalEvolutionSequence•

Thisrelatestothetendencyfortheredoxpotentialtodecreaseaswatermovesalongitsflowpathfromtherechargearea

Thiscanbeasignificantsoilzoneeffect§

Raininitiallyhasahighredoxpotentialof~750mVduetoexposuretoatmosphericoxygen

OxidationoforganicandinorganicmatterinthesoilzonecanremovemuchoftheDOandtheORPdrops

ByhowmuchtheORPdeclinesbeforewaterreachesthewatertabledependsonanumberoffactors

SoilproductivityTypeandamountoforganicmatter•Plantgrowth•Microbialactivity•

PresenceofoxidizableinorganicmatteroSoilpermeability

AffectsContacttimeofwater•Oxygendiffusionintosoil•

SoilthicknessoDepthtowatertableoTemperature

AffectsBiologicalactivity(respiration)•Oxygendissolution•

SoilmoisturecontentAffects:

Respirationrates•Oxygendiffusionintosoil•

ExamplesRechargeareaisclayey/silty

ShallowgroundwatermaynothavedetectableDO(<0.1mg/L)

Rechargeareaissandy/gravellyShallowgroundwaterwillhavedetectableDOo

RechargeareahaslittleornosoilcoveroverfracturedbedrockDOisdetectablefaroutintothegroundwaterflowsystem

Little/noconsumption§Fastinfiltration§

EvenatDOlevelsatorbelowdetectablelimits(~0.1mg/L)canbesufficienttodrivemanyimportantoxidationreactions

Importantconsequencesrethechemicalevolutionofgroundwater•

ImportantInorganicOxidation(andReduction)ReactionsinSoils

MajorAnionEvolutionSequence•

Salinityandmajorionconcentrationstendtoincreasealongagroundwaterflowpath

Thechemical characterofgroundwatertrendstowardthatofseawaterwithincreasing:

Distanceoftraveland/or§Contacttimewithgeologicmaterial§

ThistrendcanbereflectedintermsofthedominantanionpresentoWithconcentrationsinmeq/L:

HCO3-→SO4=→Cl-§o

TheanionevolutionsequencecanbecorrelatedwithIncreasingage(contacttime)anddistanceoftravel○IncreasingTDS○Flowfromrechargetodischargeareas○Increasingdepth○

WorksbestinthicksedimentarybasinsoHCO3- Stage

Representsyoungwaterneartherechargearea○Azoneofactiveflushing○HCO3- isderivedfromatmosphericandsoilzoneCO2

H2CO3→H++HCO3-§○

VeryfreshwaterwithlowTDSoTDSislimitedby:

Shortcontacttimeandtraveldistance○PCO2○PresenceofmineralssusceptibletoH2CO3○

SO4= StageoImportant~solublemineralsthatreleaseSO4=oGypsum(CaSO4 .2H2O)

K=10-4.6○o

Anhydrite(CaSO4)K=10-4.5○

GypsumandanhydriteareoftenpresentintraceamountssuchthatwaterhastotravelasignificantdistanceforSO4= todominate

Activeflushingintheshallowsubsurfacemayhavealreadyremovedthesemineralsbypriordissolution

Watermaybebrackisho

Lessactivecirculationinthiszoneo

Cl- StageoIndicatesoldwaterthathashadalongcontacttimeanddistanceoftravel

Cl-ispresentintraceamountsonlyintherockformingsilicateminerals○o

EvaporitedepositsarecommonatthebaseofdeepsedimentarybasinsHalite(NaCl)andsylvite(KCl)arecommonandverysoluble○Khalite =101.6○Ksylvite =100.9○

Maybedealingwithconnateorfossilwatero

CanbehighTDS(saline)watero

Verysluggishflowo

TheanionevolutionsequencecanhelpinterprettheflowhistoryofawaterPiperplotsareuseful○

Majorcontrolsontheanionevolutionsequenceare:Mineralavailability○Mineralsolubility○Scaleoftheflowsystem○Sequenceofcontactwithdifferentmineraltypes○

Theanionevolutionsequencemay:Occurasaslow,gradualchange○Occurindistinctsteps○Beshortcircuited○NotevolvebeyondtheHCO3- orSO4= stage○

AsimilarschemeforacationevolutionsequenceisnotfeasibleCationexchangecancauseabruptchangesorreversalsinanyprescribedsequence

GroundwaterinCarbonateTerrain•

Thisisasummaryof:Howwaterchemistrychangesasitflowsthrough§rocksandsedimentscontainingcarbonateminerals§

ThecontrolsinvolvedoImportantmineralsinvolved

Calcite(CaCO3)§Dolomite(Ca,Mg(CO3)2)§

CarbonatesareverysusceptibletodissolutionbyacidsoCarbonatemineralsarewidespread:

Sedimentarysystems:Tills•Cementingagentinsedimentaryrock•Limestonebeds•

MetamorphicrockMarble•

IgneousrocksFracturefilling•

Importanceofcarbonatesinwaterchemistry:ControlspHandalkalinity§Contributesinorganiccarbon§

Thereare2carbonatedissolutionmodels:Opensystem§Closedsystem§

OpenSystemDissolution•

OccursabovethewatertableintheunsaturatedzoneCO2isabundantintheunsaturatedporespaces○PCO2 isconstantthroughout

Ongoingrespiration§Diffusionintheopenporespaces§

Hence,H2CO3 remainsconstantevenasitisbeingconsumed

"#$% = (∝ )%#$*+#$%

⎯⎯⎯⎯⎯⎯⎯⎯)○o

WaterquicklyequilibrateswiththeCO2 atrechargeeventsanddissolutionofcarbonatesproceedstoequilibrium

CO2 +H2O→H2CO3§H2CO3+CaCO3→Ca++ +2HCO3-§

ThefollowingpredictionscanbemadeastowaterchemistryatequilibriumforagivenpCO2

pH○HCO3-○Ca+○CaCO3 neededforsaturation○Alkalinity○TIC○

pHrisesbecauseoftheadditionoftheconjugatebasepHof7– 8typical○

CarbonatesprovideanothersourceofHCO3- whenreactedwithH2CO3o

ClosedSystemDissolution•

NocarbonatesoccurintheunsaturatedzoneoCO2– chargedwaterentersthesaturatedzonewherecarbonatesdissolvetoequilibriumunderclosedconditions

pCO2willnotremainconstantItwilldecreaseasH2CO3isconsumed:

NodiffusionofCO2 throughthesaturatedporespaces§Sluggishgroundwaterflow§

Consequently,atequilibrium:pHwillbesignificantlyhighercomparedtotheopensystemcaseforagiveninitialPCO2

H2CO3isconsumedwithoutreplenishment§Additionoftheconjugatebase§

LessCa++ andHCO3-○Loweralkalinity○LessCaCO3dissolvedforsaturation○LowerTIC○

RealworldconditionscanbeanywherebetweentheopenandclosedcaseoTypicalpHrangeintheshallowsaturatedzoneincarbonateterrainis7– 8oImpliestheopensystemmodelisatworkoThesaturatedzoneinthedeepsubsurfacemimicstheclosedsystemdissolutioncase

SomeControlsandInterferencesontheCarbonateSystem

Openvs.ClosedSystemDissolutionoInitialPCO2oCarbonatemineralavailabliityoIncompletediffusionofCO2intheunsaturatedzone

InitiallyhighPCO2dissolvescalcitetoequilibriumintheunsaturatedzone○ThewatermigratestoalowerpartoftheunsaturatedzonehavingalowerPCO2becauseofincompletediffusion

Result:DegassingofCO2§RiseinpH§PrecipitationofCaCO3§

TemperatureAffectsequilibriumconstants○CO2solubility○

CationexchangeoCommonioneffect

Calcite,Dolomite,Gypsum,Anhydrite○o

Ionicstrengtho

GroundwaterinCrystallineRocks

AKAsilicateterrainIgneousandmetamorphicrock○

Theserocksarecomprisedoftheprimaryrockformingsilicateminerals•Thesemineralsandrocksformedunderconditionsofhightemperatureand/orpressure

Theybecomeunstablewhenexposedtotheweatheringeffectsoftheatmosphere

ie:acidic,oxidizingconditions○

Theytherebytendtodissolveoralterintomorestableproducts•DiluterainwaterchargedwithCO2andO2 encounterssilicateminerals•Thesemineralsareaffectedbyhydrolysisandoxidationreactions•SiandaccessoryelementsareleachedwhileAltendstostaybehindresultinginformationofclayminerals

Incongruentdissolution=mineralalterationreaction○

DissolutionandalterationofsilicatesinvolvesconsumptionofacidResultsinariseinsolutionpHalongthegroundwaterflowpath○pH@6– 7typical○

AdiagnosticconstituentinthissettingisSianditsdifferentformsAtpH6– 7thestableformofSiisSi(OH)4§Typicalconcentrations@10– 30mg/LasSiO2§

SummaryofGroundwaterChemistryinSilicateTerrain

Asgroundwatertravelsalongitsflowpath:IncreasingpHasH+isconsumedbyhydrolysis

pH6– 7typical•pH7– 8ifreactionsgofarenough•

IncreasingCa++,Mg++,K+ andNa+Cationsreleasedinresponsetohydrolysistomaintainelectricalneutrality§

IncreasingHCO3- (alkalinity)oIncreasingSioIncreasingTIC(asHCO3-)intheunsaturatedzone

FromreactionwithH2CO3§OpensystemdissolutionwithaconstantPCO2§CO2 isconstantlyreplenishedtoformH2CO3 evenasH2CO3isconsumed§

TICremainsconstantinthesaturatedzoneClosedsystemconditions§ItsformmaychangefromH2CO3 toHCO3-§

LowTDSoHCO3- isthedominantanionoCl- andSO4= arepresentinminor/traceamountsoSi(asSiO2)ispresentinmajoramountsrelativetoothercationso

GroundwaterinSedimentarySystems

Sedimentaryrocksandunconsolidatedsedimentarydepositsarecomplicatedsincetheyarecomprisedofmixedassemblagesofminerals

Bothbetweenbedsandwithinindividualbeds§

Therearelargedifferencesinwaterchemistryandthechemistrycanbehardtointerpret

Majorcontrols:Typeandamountofdifferentmineralsencountered§Mineralsolubility

Amountandrateofmineraldissolution•§

Orderofencounterofdifferentmineraltypes§

Thiscanbeillustratedbylookingattwosimplified,hypotheticalhydrogeologicsystems

Theremaybeothercontrolsongroundwaterchemistry:oSulfatereduction

2CH2O+SO4=→ HCO3-+HS-+CO2+H2O§HS- canbefurtherreducedtoH2S§

Coalificationoflignite:Underheatandpressure§CnH2O→n/2CO2+½CnH2n+2§

GroundwaterinGlacialDeposits

Thisincludesshallowgroundwateraffectedbydepositsoftill,glaciofluvialoutwashanddrumlinsupto~100feetthick

Lowcontacttime○Shorttraveldistance○Therealmofdugwaterwells○

IllustratedontheSurficialGeologyMapofNovaScotiaoChemicalcompositionofwaterinthissettingisveryvariableoControlsandprocessesaresimilartothoseinsedimentarysystemsingeneral

Mineralavailability○Mineralsolubility○

ThreecategorieshavebeenestablishedastogeneralcompositionReflecttheoriginoftheglacialmaterialinvolved○

Type1o

Glacialmaterialderivedfromsilicateterrain○Composition

Affectedby:Lowsolubilityofsilicateminerals□Shortcontacttime□LittleconsumptionofH2CO3□

Slightlyacidic@pH6– 7○Veryfresh@TDS<100mg/L○Na+ andCa++ aredominantcations○HCO3- isthedominantanion

DissociationofH2CO3§MineralreactionwithH2CO3§

Softwater○CorrosivewaterwithanegativeLangelier Index

LowpH§Lowalkalinity§LowTDS§LowCa++ hardness§

Type11o

Showsinfluenceofcarbonateterrain:Slightlyalkaline

pH@7– 8□HCO3- derivedfromreactionwithH2CO3□

Fresh○Hard○Ca++ (andMg++)dominantcations○Ca++– HCO3- – typewatertypical○Cationexchangemaybeimportant○

Type111o

Reflectstheinfluenceofevaporitedeposits○Moderatelytoverysolubleminerals○WindsorGroupinN.S.

Halite(NaCl)§Sylvite(KCl)§Gypsum(CaSO4 .2H2O)§Calcite(CaCO3)§

Slightlyalkaline○Poorquality

Hard§Brackish§

Highconcentrationsofthemajorions○

TheHydrogeologicSetting•

ThehydrogeologicsettingisimportanttoestablishincontaminantstudiesoFactorsthatrelatetosoilandgroundwaterflow

Flowdirection§Flowvelocity§Flowpattern§KandaquiferT§

Factorsthatmayaffectsoilwaterandgroundwaterchemistryandthechemicalenvironment

Byestablishingthenaturalbackgroundchemistry,(monitoringwells,springs)subsequentchangesinchemistrymayindicatetheonsetofcontamination

Aswell,themigrationandfateofcontaminantsinthesubsurfaceareaffectedbythesamephysical,chemicalandbiologicalprocessesaffectingnaturalwaterchemistry

ChemicalEvolutionofGroundwaterSunday,January17,2016 3:51PM

H2O+CO2→H2CO3o

SoilZoneEffects

NH4++2O2→2H++NO3-+H2O□§

Weakacids○

K=10-4.6○o

Watermaybebrackisho

Verysluggishflowo

"#$% = (∝ )%#$*+#$%

⎯⎯⎯⎯⎯⎯⎯⎯)○o

Ionicstrengtho

Type1o

Type11o

Type111o

Hard§Brackish§

H2O+CO2→H2CO3o

SoilZoneEffects

NH4++2O2→2H++NO3-+H2O□§

Weakacids○

K=10-4.6○o

Watermaybebrackisho

Verysluggishflowo

"#$% = (∝ )%#$*+#$%

⎯⎯⎯⎯⎯⎯⎯⎯)○o

Ionicstrengtho

Type1o

Type11o

Type111o

Hard§Brackish§

H2O+CO2→H2CO3o

SoilZoneEffects

NH4++2O2→2H++NO3-+H2O□§

Weakacids○

K=10-4.6○o

Watermaybebrackisho

Verysluggishflowo

"#$% = (∝ )%#$*+#$%

⎯⎯⎯⎯⎯⎯⎯⎯)○o

Ionicstrengtho

Type1o

Type11o

Type111o

Hard§Brackish§

H2O+CO2→H2CO3o

SoilZoneEffects

NH4++2O2→2H++NO3-+H2O□§

Weakacids○

K=10-4.6○o

Watermaybebrackisho

Verysluggishflowo

"#$% = (∝ )%#$*+#$%

⎯⎯⎯⎯⎯⎯⎯⎯)○o

Ionicstrengtho

Type1o

Type11o

Type111o

Hard§Brackish§

H2O+CO2→H2CO3o

SoilZoneEffects

NH4++2O2→2H++NO3-+H2O□§

Weakacids○

K=10-4.6○o

Watermaybebrackisho

Verysluggishflowo

"#$% = (∝ )%#$*+#$%

⎯⎯⎯⎯⎯⎯⎯⎯)○o

Ionicstrengtho

Type1o

Type11o

Type111o

Hard§Brackish§

H2O+CO2→H2CO3o

SoilZoneEffects

NH4++2O2→2H++NO3-+H2O□§

Weakacids○

K=10-4.6○o

Watermaybebrackisho

Verysluggishflowo

"#$% = (∝ )%#$*+#$%

⎯⎯⎯⎯⎯⎯⎯⎯)○o

Ionicstrengtho

Type1o

Type11o

Type111o

Hard§Brackish§

H2O+CO2→H2CO3o

SoilZoneEffects

NH4++2O2→2H++NO3-+H2O□§

Weakacids○

K=10-4.6○o

Watermaybebrackisho

Verysluggishflowo

"#$% = (∝ )%#$*+#$%

⎯⎯⎯⎯⎯⎯⎯⎯)○o

Ionicstrengtho

Type1o

Type11o

Type111o

Hard§Brackish§

H2O+CO2→H2CO3o

SoilZoneEffects

NH4++2O2→2H++NO3-+H2O□§

Weakacids○

K=10-4.6○o

Watermaybebrackisho

Verysluggishflowo

"#$% = (∝ )%#$*+#$%

⎯⎯⎯⎯⎯⎯⎯⎯)○o

Ionicstrengtho

Type1o

Type11o

Type111o

Hard§Brackish§

H2O+CO2→H2CO3o

SoilZoneEffects

NH4++2O2→2H++NO3-+H2O□§

Weakacids○

K=10-4.6○o

Watermaybebrackisho

Verysluggishflowo

"#$% = (∝ )%#$*+#$%

⎯⎯⎯⎯⎯⎯⎯⎯)○o

Ionicstrengtho

Type1o

Type11o

Type111o

Hard§Brackish§

H2O+CO2→H2CO3o

SoilZoneEffects

NH4++2O2→2H++NO3-+H2O□§

Weakacids○

K=10-4.6○o

Watermaybebrackisho

Verysluggishflowo

"#$% = (∝ )%#$*+#$%

⎯⎯⎯⎯⎯⎯⎯⎯)○o

Ionicstrengtho

Type1o

Type11o

Type111o

Hard§Brackish§

H2O+CO2→H2CO3o

SoilZoneEffects

NH4++2O2→2H++NO3-+H2O□§

Weakacids○

K=10-4.6○o

Watermaybebrackisho

Verysluggishflowo

"#$% = (∝ )%#$*+#$%

⎯⎯⎯⎯⎯⎯⎯⎯)○o

Ionicstrengtho

Type1o

Type11o

Type111o

Hard§Brackish§

H2O+CO2→H2CO3o

SoilZoneEffects

NH4++2O2→2H++NO3-+H2O□§

Weakacids○

K=10-4.6○o

Watermaybebrackisho

Verysluggishflowo

"#$% = (∝ )%#$*+#$%

⎯⎯⎯⎯⎯⎯⎯⎯)○o

Ionicstrengtho

Type1o

Type11o

Type111o

Hard§Brackish§

H2O+CO2→H2CO3o

SoilZoneEffects

NH4++2O2→2H++NO3-+H2O□§

Weakacids○

K=10-4.6○o

Watermaybebrackisho

Verysluggishflowo

"#$% = (∝ )%#$*+#$%

⎯⎯⎯⎯⎯⎯⎯⎯)○o

Ionicstrengtho

Type1o

Type11o

Type111o

Hard§Brackish§

H2O+CO2→H2CO3o

SoilZoneEffects

NH4++2O2→2H++NO3-+H2O□§

Weakacids○

K=10-4.6○o

Watermaybebrackisho

Verysluggishflowo

"#$% = (∝ )%#$*+#$%

⎯⎯⎯⎯⎯⎯⎯⎯)○o

Ionicstrengtho

Type1o

Type11o

Type111o

Hard§Brackish§

H2O+CO2→H2CO3o

SoilZoneEffects

NH4++2O2→2H++NO3-+H2O□§

Weakacids○

K=10-4.6○o

Watermaybebrackisho

Verysluggishflowo

"#$% = (∝ )%#$*+#$%

⎯⎯⎯⎯⎯⎯⎯⎯)○o

Ionicstrengtho

Type1o

Type11o

Type111o

Hard§Brackish§

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