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Carbondioxide(CO
2
)isabsorbedby land and vegetationthroughtheprocessofphotosynthesis.The
netemissionsarenegative(sequestration) and substantial,offsettingapproximately884MMTCO
2
E,or
approximately13%oftotalemissionsin2006.
114
Thecarbonsequestration and storageprovidedby
land canbepreservedthoughsustainable land managementpractices, and canbeenhancedby
restorationof land, suchasreforestationofcontaminated land.
Theemissionsestimateforthe land basedcarbonsinkisgivenbytheInventory.Specifically,Chapter7,
Land Use, Land UseChange, and Forestry,providesanassessmentofthenetGHGfluxresultingfrom
theuses and changesin land types and forestsintheU.S.,includingnetemissionsfromforestland
remainingforestland,croplandremainingcropland, land convertedtocropland,grasslandremaining
grassland, land convertedtograssland,settlementsremainingsettlements,landfillyardtrimmings, and
... T
on
=Timeperiodoftransition,defaultis1yearforcarbonlosses
AlthoughthisequationissimilartotheequationusedtoestimatecarbonlossesinDOM(seebelow),it
isnotinaccordancewiththe2006IPCCGuidelines.Theguidelinesrecommendagreaterdegreeof
disaggregationof land usedatabyclimate and soiltype.Theequationaboverepresentsa
simplificationofthevariabilityofcarboncontentsinsoilthatexistsonregional and nationalscales.The
soilcarbonstockfortheold land usecategory(Cs
o
)wasbasedoninformationfordifferentecosystem
typespresentedinthe2000IPCCreporton Land Use, Land useChange, and Forestry.
117
Thesoil
carbonstockforthenew land usecategoryofsettlements(Cs
n
)wasbasedonafractionofCs
o
.For
forestland and grassland,thefractionwas0.5 and forcropland,thefractionwas0.8.Guo and Gifford
(2002)observedthat land usechangesofforestlandtocropland and pasturelandtocroplandresulted
insoilcarbondecreasesof42% and 59%,respectively.
118
Theestimateforthisprojectassumesthat
theconversionofforestlandorgrasslandtourban land isequivalenttoaconversiontocropland(bo
removeexistingvegetation and causesignificantsoildisturbance);therefore,Guo and Gifford’swork
supportsthiseffort’sestimationofa50%lossassociatedwiththisconversion.Itisestimatedthatsoils
underforestsorgrasslandswillloseapproximately50%oftheoriginalorganiccarbonwhenthe land is
convertedtodeveloped land. Theselossesareaconsequenceofboththeremovalofsurfacesoils(to
providesuitablebuildingfoundation) and naturaloxidationwhenthesoilisgradedfollowingremoval
ofthevegetativecover.Lossesfromcroplandsareonlyexpectedtobe20%becausethesesoilsalready
undergoperiodictillage and themajorityofnaturaloxidationwillalreadyhaveoccurred.Aliterature
reviewforthisprojectdidnotidentifyotherstudiescomparabletoGuo and Gifford(2002)that
estimatedsoilcarbonlossesassociatedwithconvertingcroplandtourban land. Therefore,the20%soil
carbonlossestimatefordevelopmentofcroplandintourban land isbasedonbestprofessional
judgment.
th
...
REDUCINGORAVOIDINGGHGEMISSIONSTHROUGH LAND MANAGEMENTPRACTICES
Land managementdescribeshowwemanage and use land toprovideopenspace and habitat,food,
naturalresources, and placesforpeopletolive,work, and recreate.EPApromotesintegrated land
managementstrategiesthatuse land asproductively and sustainablyaspossiblebypromotingsmart
growth,preventing and minimizingtheoccurrenceofcontamination and bycleaningup,reusing, and
restoringcontaminated land forbeneficialreusebycommunities.
67
AsdescribedinBox7, land managementhasthreekeycomponents: land protection,sustainable land
use, and land revitalization.Similartothematerialsmanagementapproachesthatcanbeusedinthe
materialflow, land managementapproachescanbeusedtoreduceGHGemissionsbyimproving
practiceswithinoracrosseachofthesecomponents. Land protectionpracticeslimithowmuch land is
contaminatedeachyear.When land iscontaminated,itshouldbe
cleaneduptolevelsprotectiveofhumanhealth and the
environment.
Land...