Ngày tải lên :
21/02/2014, 12:20
...
Carbondioxide(CO
2
)isabsorbedbyland and vegetationthroughtheprocessofphotosynthesis.The
netemissionsarenegative(sequestration) and substantial,offsettingapproximately884MMTCO
2
E,or
approximately13%oftotalemissionsin2006.
114
Thecarbonsequestration and storageprovidedby
landcanbepreservedthoughsustainablelandmanagementpractices, and canbeenhancedby
restorationofland,suchasreforestationofcontaminatedland.
Theemissionsestimatefortheland‐basedcarbonsinkisgivenbytheInventory.Specifically,Chapter7,
LandUse,Land‐UseChange, and Forestry,providesanassessmentofthenetGHGfluxresultingfrom
theuses and changesinlandtypes and forestsintheU.S.,includingnetemissionsfromforestland
remainingforestland,croplandremainingcropland,landconvertedtocropland,grasslandremaining
grassland,landconvertedtograssland,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
... September2009
UsingmaterialsmanagementapproachestohelpreduceoravoidGHGemissionsisconsistentwith
EPA’svision and manyofthestrategiestoincreasetheefficient and sustainableuseofresources and
reducewastegenerationaredescribedinBeyondRCRA:Waste and MaterialsManagementintheYear
2020.Someofthestrategiesincludereducingtheamountofmaterialsusedtomakeproductsor
performservices and influencingproductdesign,use, and reusecapabilitiestominimizerawmaterial
inputs,extendproductlifespans, and maximizetheease and frequencyofsubsequentproduct
disassembly,recycling, and/ ortransformationforfurtherproductiveuse.
27
Inadditiontoincreasing
materialefficiency and reducingwaste,materialsmanagementactivitieshavethepotentialto
significantlyreduceGHGemissions,asdescribedinthefollowingsections.
Landmanagementisatermusedtodescribeseparateorintegratedstrategiesthatinfluencehowwe
manage and uselandtoprovideopenspace and habitat,food,naturalresources, and placesforpeople
tolive,work, and recreate.Forexample,landmanagementincludesthepracticesofdevelopingland
and managinglandforagricultural and forestrypurposes.Thewaywemanageourlanddirectly
influencesGHGemissionsrelatedtoagriculture,thebuiltenvironment(e.g.,residential and
commercialemissions),electricityuse, and transportation.
TheconceptoflandmanagementlinksdirectlytoEPA’svisionofpreventinglandcontamination,in
part,byencouragingsmartgrowth,
28
improvingchemical and wastemanagementtoprevent
contamination,restoringcontaminated and potentiallycontaminatedlandforreusebysociety, and
encouragingthesustainablereuseofproperty.SomelandmanagementapproachescanalsoyieldGHG
emissionreductionsorcanprotectthecarbonsinkprovidedbyU.S.land,whichisfurtherdescribedin
Section2.
Bytakingadvantageofopportunitiespresentedbymaterials and landmanagement,EPA and its
partnerscancontributetoareductionoravoidanceofGHGemissionsaswellasimprovementto
publichealth and theenvironment.
LeveragingOSWERprogramstoachievemeasurableclimatechangebenefitsinnowayreplacesor
supersedesotherOSWERprogramgoals.Rather,thisdocumentpromotestherecognitionthat
materials and landmanagementprogramshavesignificantclimatebenefitswhileyieldingpositive
environmental,economic, and societalco‐benefitsincommunitiesacrossthecountry.
Inthecaseofmaterialsmanagement,themajorityofGHGreductionbenefitsfromrecyclingorwaste
preventioncomefromtheenergysavingsfromavoidedresourceextraction and materials
processing.
29
Thisenergysavingscarriesco‐benefitsofimprovementsinlocalairquality.Similarly,the
conservationofrawmaterialreducesenvironmentaldegradation and waterpollutionfrommining,
logging, and oilextraction.
...