Ngày tải lên :
21/02/2014, 12:20
...
Carbondioxide(CO
2
)isabsorbedby land andvegetationthroughtheprocessofphotosynthesis.The
netemissionsarenegative(sequestration)andsubstantial,offsettingapproximately884MMTCO
2
E,or
approximately13%oftotalemissionsin2006.
114
Thecarbonsequestrationandstorageprovidedby
land canbepreservedthough sustainable land management practices, andcanbeenhancedby
restorationof land, suchasreforestationofcontaminated land.
Theemissionsestimateforthe land basedcarbonsinkisgivenbytheInventory.Specifically,Chapter7,
Land Use, Land UseChange,andForestry,providesanassessmentofthenetGHGfluxresultingfrom
theusesandchangesin land typesandforestsintheU.S.,includingnetemissionsfromforestland
remainingforestland,croplandremainingcropland, land convertedtocropland,grasslandremaining
grassland, land convertedtograssland,settlementsremainingsettlements,landfillyardtrimmings,and
... T
on
=Timeperiodoftransition,defaultis1yearforcarbonlosses
AlthoughthisequationissimilartotheequationusedtoestimatecarbonlossesinDOM(seebelow),it
isnotinaccordancewiththe2006IPCCGuidelines.Theguidelinesrecommendagreaterdegreeof
disaggregationoflandusedatabyclimateandsoiltype.Theequationaboverepresentsa
simplificationofthevariabilityofcarboncontentsinsoilthatexistsonregionalandnationalscales.The
soilcarbonstockfortheoldlandusecategory(Cs
o
)wasbasedoninformationfordifferentecosystem
typespresentedinthe2000IPCCreportonLandUse,LanduseChange,andForestry.
117
Thesoil
carbonstockforthenewlandusecategoryofsettlements(Cs
n
)wasbasedonafractionofCs
o
.For
forestlandandgrassland,thefractionwas0.5andforcropland,thefractionwas0.8.GuoandGifford
(2002)observedthatlandusechangesofforestlandtocroplandandpasturelandtocroplandresulted
insoilcarbondecreasesof42%and59%,respectively.
118
Theestimateforthisprojectassumesthat
theconversionofforestlandorgrasslandtourbanlandisequivalenttoaconversiontocropland(bo
removeexistingvegetationandcausesignificantsoildisturbance);therefore,GuoandGiffordswork
supportsthiseffortsestimationofa50%lossassociatedwiththisconversion.Itisestimatedthatsoils
underforestsorgrasslandswillloseapproximately50%oftheoriginalorganiccarbonwhenthelandis
convertedtodevelopedland.Theselossesareaconsequenceofboththeremovalofsurfacesoils(to
providesuitablebuildingfoundation)andnaturaloxidationwhenthesoilisgradedfollowingremoval
ofthevegetativecover.Lossesfromcroplandsareonlyexpectedtobe20%becausethesesoilsalready
undergoperiodictillageandthemajorityofnaturaloxidationwillalreadyhaveoccurred.Aliterature
reviewforthisprojectdidnotidentifyotherstudiescomparabletoGuoandGifford(2002)that
estimatedsoilcarbonlossesassociatedwithconvertingcroplandtourbanland.Therefore,the20%soil
carbonlossestimatefordevelopmentofcroplandintourbanlandisbasedonbestprofessional
judgment.
th
...
Carbondioxide(CO
2
)isabsorbedby land andvegetationthroughtheprocessofphotosynthesis.The
netemissionsarenegative(sequestration)andsubstantial,offsettingapproximately884MMTCO
2
E,or
approximately13%oftotalemissionsin2006.
114
Thecarbonsequestrationandstorageprovidedby
land canbepreservedthough sustainable land management practices, andcanbeenhancedby
restorationof land, suchasreforestationofcontaminated land.
Theemissionsestimateforthe land basedcarbonsinkisgivenbytheInventory.Specifically,Chapter7,
Land Use, Land UseChange,andForestry,providesanassessmentofthenetGHGfluxresultingfrom
theusesandchangesin land typesandforestsintheU.S.,includingnetemissionsfromforestland
remainingforestland,croplandremainingcropland, land convertedtocropland,grasslandremaining
grassland, land convertedtograssland,settlementsremainingsettlements,landfillyardtrimmings,and
...