Ngày tải lên :
21/02/2014, 12:20
...
Carbondioxide(CO
2
)isabsorbedby land and vegetationthroughtheprocessofphotosynthesis.The
netemissionsarenegative(sequestration) and substantial,offsettingapproximately884MMTCO
2
E,or
approximately13%oftotalemissionsin2006.
114
Thecarbonsequestration and storageprovidedby
land canbepreservedthough sustainable land management practices, 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
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 %and5 9%,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 describeshowwemanage and use land toprovideopenspace and habitat,food,
naturalresources, and placesforpeopletolive,work, and recreate.EPApromotesintegrated land
management strategiesthatuse land asproductively and sustainablyaspossiblebypromotingsmart
growth,preventing and minimizingtheoccurrenceofcontamination and bycleaningup,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
cleaneduptolevelsprotectiveofhumanhealth and the
environment.
Land...