Chapter 10 BIOGEOCHEMISTRY.docx
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Chapter 10 BIOGEOCHEMISTRY.docx
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Chapter10BIOGEOCHEMISTRY
Chapter10BIOGEOCHEMISTRY:
NUTRIENTCYCLING
Thelifeoftheecosystemdependsontheflowofenergyandtherecyclingofmatterthroughtheecosystem.
Energyandmatterflowtogetherthroughtheecosystemasorganicmatter.
Thelinkbetweenenergyandmatterbeginswithphotosynthesis.
TYPESOFNUTRIENTCYCLES
Nutrientsmovethroughtheecosysteminbiogeochemicalcycles.
Thecyclesinvolvetheexchangeofelementsbetweentheatmosphere,rocks,waterandorganisms.
Therearetwotypesofbiogeochemicalcycles:
gaseousandsedimentary.
Ingaseouscycles,thenutrientsaccumulateintheatmosphereandtheoceans
∙Theyhaveaglobalinfluence.
∙Nitrogen,oxygenandcarbondioxide.
Insedimentarycycles,themainreservoirsarerockandsoil.
∙Availableformsofthenutrientsoccurasdissolvedsaltsinsoilwater,lakes,ocean,etc.
∙Thecycleconsistsofsalt-solutionphaseandarockphase.
MODELOFNUTRIENTCYCLES
Allbiogeochemicalcyclesinvolveinputs,internalcyclingandoutputs.
INPUTS
Theinputofnutrientstotheecosystemdependsonthetypeofbiogeochemicalcycle:
∙Nutrientswithgaseouscycleentertheecosystemviatheatmosphere.
∙Nutrientswithasedimentarycycleentertheecosystemaftertheweatheringofrocks.
Air,snow,rainandanimalssupplementthenutrientsinthesoil.
∙Wetfallreferstonutrientscarriedbyprecipitation.
∙Dryfallbringsnutrientsintheformofairborneparticlesandaerosols.
Watertricklingdowntheforestcanopyandstemscarriesdustparticlesthathadsettledontheleaves.
Epiphyticlichensremovenutrientsasthewaterflows
Waterdrainageisthemajorinputforaquaticecosystems.
INTERNALCYCLING
Nutrientsarestoredinlivingtissues.
Asoldtissuesdie,nutrientsarereturnedtothesoil.
Mineralizationisthereleaseoforganicallyboundnutrientsintoaninorganicformavailableforplantsandmicrobes.Detritivoresoxidizeorganiccompoundsintosmallerandsimplerproducts.
Thesenutrientsareonceagainavailabletoplantsforuptakeandincorporationintonewtissues.
Nutrientsstoredintrunk,limbs,barkandrootsisremovedfromshort-termcycling.
Nutrientsaccumulatedinsoilorganicmatterpreventrapidlossesfromthesystem.
Nutrientstightlyboundtoorganicmatterhavetobereleasedthroughtheactivityofdecomposers.
Ecosystemprocessesinfluencingtherateofnutrientcycling.
Therateatwhichnutrientscyclethroughtheecosystemisdirectlyrelatedtotheratesatwhichprimaryproductivityanddecompositionoccur.
∙Primaryproductivitydeterminestherateatwhichnutrientsaretransferredfrominorganictoorganicform(nutrientuptake).
∙Decompositiondeterminestherateoftransformationoforganicnutrientsintoinorganicform(nutrientrelease).
Thesetwoprocessesareinterdependent.
∙Reducednutrientavailabilitycanhavethecombinedeffectorreducingboththenutrientconcentrationofplanttissues(primarilyleaftissues)andnetprimaryproductivity.
∙Thisreductionlowersthetotalamountofnutrientsretunedtothesoilindeadorganicmatter.
∙Reducedquantityandconcentrationoforganicmatterenteringthedecomposerfoodchainincreasesimmobilizationandreducestheavailabilityofnutrientsforuptakebyplants.
∙Conversely,highnutrientavailabilityencourageshighplanttissueconcentrationsandhighnetprimaryproductivity.
Climate
Temperatureandmoistureinfluencetherateofmicrobialactivity.
Lowtemperatureanddryconditionsinhibitmicrobialactivity.
Rateoflitterdecaydependsonthechemicalcompositionofthelitter,temperature,humidityandpH.
∙Decompositionrateisfastestformaterialcontaininglittlelignin,inwarmandmoistconditions.
∙LowpHslowsdecay.
Tropicalrainforestsarecharacterizedbyhaving
∙ahighrateofnetprimaryproductivity
∙higherannualratesoflitterinputtotheforestfloor
∙verylowmassoflitterontheforestfloor
∙highrateofdecomposition
∙organicmatterisbeingconsumedbydecomposersataboutthesamerateatwhichitisfallingtotheforestfloor.
Borealforests,whicharefoundincoolernorthernlatitudes,have…
∙lowrateofnetprimaryproductivity
∙lowratesoflitterinput
∙extremelylowratesofdecomposition
∙highaccumulationoflitterontheforestfloor.
Movinginlatitudefromsouthtonorth,therateofdecompositiondecreases,theaccumulationoflitterincreases,andtheinputofforestlitterdecreases.
Thereisaninverserelationshipbetweenthebiomassoforestfloorandbiomassofthelitterinput,e.g.intropicalrainforest,theinputintotheforestfloorishighbuttheaccumulationisverylowifany.
Therateofdecompositionaffectstheamountoflitterthataccumulatesontheforestfloor.
Morenutrientsaretiedupindeadorganicmatterinthecooler,morenorthernforestecosystems,resultinginaslowerrateofinternalnutrientcycling.
Speciescharacteristicsaffectthenutrientcycling.
Zooplanktonandphytoplanktonabsorbnutrientsquickly,areshort-lived,growrapidlyandreturnthenutrientstotheavailablenutrientpool.Recyclingisfast.
Foresttreesarelarge,growslowly,andstorelargequantitiesofnutrientsintheirbiomassforlongerperiods.Thesenutrientsareremovedfromshort-termcycling.
Treesandshrubsstorenutrientsinlongandshorttermstructures,e.g.bark,trunks,leaves,flowers,fruits,etc.
Speciesdifferintheirconcentrationofnutrientsandtheirabilitytorecyclethem.
OUTPUTS
Theexportofnutrientsfromtheecosystemmustbeupsetbyinputsifanetdeclineisnottooccur.
∙CarbonisexportedtotheatmosphereasCO2viatheprocessofrespiration.
∙Organicmattercanberemovedbyrunoffwaterintostreamsandrivers.
∙Herbivorescantransportnutrientsfromoneecosystemtoanother.
Largequantitiesofnutrientsareboundtightlyinorganicmatter;theyarenotavailableuntilreleasedbyactivitiesofdecomposers.
Farmingandloggingcarryasubstantialamountofnutrientsouttheecosystem.Theselossesmustbereplacedbytheapplicationoffertilizers.
Clear-cutloggingalterstheinternalcyclingcausingtheleachingofnutrients:
∙Clear-cutloggingincreasestheamountofradiationincludingdirectsunlight,reachingtheground.Thisresultsinanincreaseinsoiltemperaturethatpromotesdecompositionresultinginanincreaseinnetmineralizationrate.
∙Thishappensatthetimewhenthedemandislowduetotheremovalofvegetation.Thiscausesanincreaseinleachingofnutrientsfromtheecosysteminsurfacewaters.
∙Thisistheresultofuncouplingnutrientdecompositionandnutrientuptakeinnetprimaryproductivity.
Fireincreasesthelossofnutrientsvolatilizationandairborneparticulate.
Nitratesinasharequicklymineralized.Surfacerunoffincreasesafterfireandleachesnutrientsfromthesoil.
CONTRASTINGNUTRIENTCYCLINGINTERRESTRIALANDAQUATICECOSYSTEMS.
Nutrientcycling,thelinkbetweenprimaryproductivityanddecomposition,areanessentialfeatureofallecosystems.
Thereisaseparationbetweenthezoneofdecompositionandthezoneofproductivity.
Interrestrialecosystems,plantsexitinbothzones:
rootsinthesoil,canopyexposedtolight.
Indeepaquaticecosystems,decompositionoccursinthebenthiczoneandisseparatedfromthephoticzonewhereproductivityiscarriedoutbyphytoplankton.
Epilimnion:
∙Ratherwarmduetosolarradiation.
∙Dissolvedoxygenishigh.
∙Lowerdensitywater.
Hypolimnion:
∙Cold.
∙Lowinoxygen.
∙Higherdensitywater.
Metalimnionistheregionofthefastdropintemperature,thermocline.
Thecolderdeepwaterisrelativelynutrientrich;thesurface,warmerwaterisnutrientpoor.
Inautumnandwinter,thesurfacewaterscoolandapproachthetemperatureofthehypolimnion;thesurfacewaterbecomedenserandsinkandthethermoclinebreaksdown;thedisplaceddeepwatermovestothesurface:
thisiscalledtheturnover.
Winterturnoverbringsnutrientstothesurface.
Nutrientsareusedupasthespringandsummerprogressandproductivitydeclines.
Therearetwopartstothecarboncycle,theatmosphereandthewatercycles.
MAJORBIOGEOCHEMICALCYCLES
CARBONCYCLE
ThemainreservoirofcarbonisintheformofCO2intheatmosphere,butthereisaconsiderableamountofcarbontiedupinthebiosphere.
Carbonisintimatelytiedtotheenergyflowthroughtheecosystem:
justasenergypassesthroughthefoodchainsodoescarbon.
TheconcentrationofCO2fluctuatesthroughouttheday.Indaytimeislowandincreasesatnighttime.
ThereisaseasonalchangeintheproductionandutilizationofCO2.DuringthespringgrowingseasonthereisanincreaseinrespirationandproductionofCO2.intheautumnthereisadeclineinCO2production.
Inaquaticenvironments,atpH<4.3,mostCO2isfoundasdissolvedgas,atpHbetween4.3and8.3,mostlyasHCO3‾,andatpH>than8.3asCO32-.
CarbonatesdepositedassedimentonthebottomoftheoceansaretakenintothelowerlayersoftheearthcrustandeventuallyreleasedasCO2duringvolcanicactivity.
Carbondioxideisagreen-housegasthattendstokeeptheearthsurfacewarm,e.g.waterremainsliquid.
NITROGENCYCLE
Thecyclehasfourstages:
1.Nitrogenhastobefixed,convertedtoausableform(NH3,NO31-),beforeitcanbeusedbyorganisms.
2.Mineralizationorammonificationthatistheconversionofaminoacidstoammonia.
3.Nitrification:
theconversion(oxidation)ofammoniatonitritesandnitrates.
4.Denitrification,theconversionofnitratestoatmosphericnitrogen,N2.
Nitrogenfixationcanoccurthrough
∙lightningintheatmosphere:
10%ofthefixednitrogen;~35mg
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