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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
...
REDUCINGORAVOIDINGGHGEMISSIONSTHROUGH LAND MANAGEMENT PRACTICES
Land management describeshowwemanageanduse land toprovideopenspaceandhabitat,food,
naturalresources,andplacesforpeopletolive,work,andrecreate.EPApromotesintegrated land
management strategiesthatuse land asproductivelyandsustainablyaspossiblebypromotingsmart
growth,preventingandminimizingtheoccurrenceofcontaminationandbycleaningup,reusing,and
restoringcontaminated land forbeneficialreusebycommunities.
67
AsdescribedinBox7, land management hasthreekeycomponents: land protection, sustainable land
use,and land revitalization.Similartothematerials management approachesthatcanbeusedinthe
materialflow, land management approachescanbeusedtoreduceGHGemissionsbyimproving
practiceswithinoracrosseachofthesecomponents. Land protectionpracticeslimithowmuch land is
contaminatedeachyear.When land iscontaminated,itshouldbe
cleaneduptolevelsprotectiveofhumanhealthandthe
environment.
Land...