life cycle of oil and gas fields 1 in 1 the 1 mississippi 1 river 1 delta: 1 a 1 review 1 ·...

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Waterȱ2020,ȱ12,ȱ1492;ȱdoi:10.3390/w12051492ȱ www.mdpi.com/journal/waterȱ

Reviewȱ

LifeȱCycleȱofȱOilȱandȱGasȱFieldsȱinȱtheȱMississippiȱRiverȱDelta:ȱAȱReviewȱJohnȱW.ȱDayȱ1,*,ȱH.ȱC.ȱClarkȱ2,ȱChandongȱChangȱ3,ȱRachaelȱHunterȱ4,*ȱandȱCharlesȱR.ȱNormanȱ5ȱ1ȱ DepartmentȱofȱOceanographyȱandȱCoastalȱSciences,ȱLouisianaȱStateȱUniversity,ȱBatonȱRouge,ȱ ȱ

LAȱ70803,ȱUSAȱ2ȱ DepartmentȱofȱEarth,ȱEnvironmentalȱandȱPlanetaryȱScience,ȱRiceȱUniversity,ȱHouston,ȱTXȱ77005,ȱUSA;ȱ

[email protected]ȱ3ȱ DepartmentȱofȱGeologicalȱSciences,ȱChungnamȱNationalȱUniversity,ȱDaejeonȱ34134,ȱKorea;ȱ

[email protected]ȱ4ȱ ComiteȱResources,ȱInc.,ȱP.O.ȱBoxȱ66596,ȱBatonȱRouge,ȱLAȱ70896,ȱUSAȱ5ȱ CharlesȱNormanȱ&ȱAssociates,ȱP.O.ȱBoxȱ5715,ȱLakeȱCharlesȱLAȱ70606,ȱUSA;ȱ[email protected]ȱ*ȱ Correspondence:ȱ[email protected]ȱ(J.W.D.);ȱ[email protected]ȱ(R.H.)ȱ

Received:ȱ20ȱAprilȱ2020;ȱAccepted:ȱ20ȱMayȱ2020;ȱPublished:ȱ23ȱMayȱ2020ȱ

Abstract:ȱOilȱandȱgasȱ(O&G)ȱactivityȱhasȱbeenȱpervasiveȱinȱtheȱMississippiȱRiverȱDeltaȱ(MRD).ȱHereȱweȱreviewȱtheȱlifeȱcycleȱofȱO&GȱfieldsȱinȱtheȱMRDȱfocusingȱonȱtheȱproductionȱhistoryȱandȱresultingȱenvironmentalȱ impactsȱandȱ showȱhowȱcumulativeȱ impactsȱaffectȱcoastalȱecosystems.ȱ Individualȱfieldsȱcanȱlastȱ40–60ȱyearsȱandȱmostȱwellsȱareȱinȱtheȱfinalȱstagesȱofȱproduction.ȱProductionȱincreasedȱrapidlyȱ reachingȱaȱpeakȱaroundȱ1970ȱandȱ thenȱdeclined.ȱProducedȱwaterȱ laggedȱO&GȱandȱwasȱgenerallyȱhigherȱduringȱdecliningȱO&Gȱproduction,ȱmakingȱupȱaboutȱ70%ȱofȱtotalȱliquids.ȱMuchȱofȱtheȱwetlandȱlossȱinȱtheȱdeltaȱisȱassociatedȱwithȱO&Gȱactivities.ȱTheseȱhaveȱcontributedȱinȱthreeȱmajorȱwaysȱtoȱwetlandȱlossȱincludingȱalterationȱofȱsurfaceȱhydrology,ȱinducedȱsubsidenceȱdueȱtoȱfluidsȱremovalȱandȱfaultȱactivation,ȱandȱtoxicȱstressȱdueȱtoȱspilledȱoilȱandȱproducedȱwater.ȱChangesȱ inȱsurfaceȱhydrologyȱareȱrelatedȱtoȱcanalȱdredgingȱandȱspoilȱplacement.ȱAsȱcanalȱdensityȱincreases,ȱtheȱdensityȱ ofȱ naturalȱ channelsȱ decreases.ȱ Interconnectedȱ canalȱ networksȱ oftenȱ leadȱ toȱ saltwaterȱintrusion.ȱ Spoilȱ banksȱ blockȱ naturalȱ overlandȱ flowȱ affectingȱ exchangeȱ ofȱ water,ȱ sediments,ȱchemicals,ȱ andȱ organisms.ȱ Lowerȱ wetlandȱ productivityȱ andȱ reducedȱ sedimentȱ inputȱ leadsȱ toȱenhancedȱsurficialȱsubsidence.ȱSpoilȱbanksȱareȱnotȱpermanentȱbutȱsubsideȱandȱcompactȱoverȱtimeȱandȱmanyȱspoilȱbanksȱnoȱlongerȱhaveȱsubaerialȱexpression.ȱFluidȱwithdrawalȱfromȱO&Gȱformationsȱleadsȱtoȱinducedȱsubsidenceȱandȱfaultȱactivation.ȱFormationȱporeȱpressureȱdecreases,ȱwhichȱlowersȱtheȱ lateralȱ confiningȱ stressȱ actingȱ inȱ theȱ formationȱ dueȱ toȱ poroelasticȱ couplingȱ betweenȱ poreȱpressureȱandȱstress.ȱThisȱpromotesȱnormalȱfaultingȱinȱanȱextensionalȱgeologicalȱenvironmentȱlikeȱtheȱ MRD,ȱ whichȱ causesȱ surfaceȱ subsidenceȱ inȱ theȱ vicinityȱ ofȱ theȱ faults.ȱ Inducedȱ reservoirȱcompactionȱresultsȱinȱaȱreductionȱofȱreservoirȱthickness.ȱInducedȱsubsidenceȱoccursȱinȱtwoȱphasesȱespeciallyȱwhenȱproductionȱrateȱisȱhigh.ȱTheȱfirstȱphaseȱisȱcompactionȱofȱtheȱreservoirȱitselfȱwhileȱtheȱsecondȱphaseȱ isȱcausedȱbyȱaȱslowȱdrainageȱofȱporeȱpressureȱinȱboundingȱshalesȱthatȱ inducesȱtimeȬdelayedȱ subsidenceȱassociatedȱwithȱ shaleȱ compaction.ȱThisȱ secondȱphaseȱ canȱ continueȱ forȱdecades,ȱevenȱafterȱmostȱO&Gȱhasȱbeenȱproduced,ȱresultingȱinȱsubsidenceȱoverȱmuchȱofȱanȱoilȱfieldȱthatȱ canȱbeȱgreaterȱ thanȱ surfaceȱ subsidenceȱdueȱ toȱalteredȱhydrology.ȱProducedȱwaterȱ isȱwaterȱbroughtȱ toȱ theȱ surfaceȱduringȱO&Gȱextractionȱandȱanȱestimatedȱ2ȱmillionȱbarrelsȱperȱdayȱwereȱdischargedȱintoȱLouisianaȱcoastalȱwetlandsȱandȱwatersȱfromȱnearlyȱ700ȱsites.ȱThisȱwaterȱisȱaȱmixtureȱofȱ eitherȱ liquidȱ orȱ gaseousȱ hydrocarbons,ȱ highȱ salinityȱ (upȱ toȱ 300ȱ ppt)ȱwater,ȱ dissolvedȱ andȱsuspendedȱsolidsȱsuchȱasȱsandȱorȱsilt,ȱandȱinjectedȱfluidsȱandȱadditivesȱassociatedȱwithȱexplorationȱandȱproductionȱ activitiesȱ andȱ itȱ isȱ toxicȱ toȱmanyȱ estuarineȱorganismsȱ includingȱvegetationȱ andȱfauna.ȱSpilledȱoilȱhasȱ lethalȱandȱ subȬlethalȱ effectsȱonȱ aȱwideȱ rangeȱofȱ estuarineȱorganisms.ȱTheȱcumulativeȱeffectȱofȱalterationsȱinȱsurfaceȱhydrology,ȱinducedȱsubsidence,ȱandȱtoxinsȱinteractȱsuchȱthatȱoverallȱ impactsȱ areȱ enhanced.ȱRestorationȱofȱ coastalȱwetlandsȱdegradedȱbyȱO&Gȱ activitiesȱshouldȱbeȱinformedȱbyȱtheseȱimpacts.ȱ

Waterȱ2020,ȱ12,ȱ1492ȱ 2ȱ ofȱ 30ȱ

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Keywords:ȱ oilȱ andȱ gasȱ production;ȱ producedȱ water;ȱ oilȱ andȱ gasȱ wetlandȱ impacts;ȱ inducedȱsubsidence;ȱwetlandȱrestorationȱ�

1.ȱIntroductionȱ

TheȱfirstȱsuccessfulȱoilȱwellȱwasȱdrilledȱinȱLouisianaȱinȱ1901ȱinȱsouthwesternȱLouisiana,ȱinȱtheȱJenningsȱfieldȱandȱmarkedȱtheȱbeginningȱofȱoilȱandȱgasȱ(O&G)ȱproductionȱinȱLouisianaȱthat,ȱbyȱtheȱmidȬ20thȱcentury,ȱwasȱtheȱstate’sȱprimaryȱindustryȱ[1].ȱProductionȱofȱpetroleumȱhasȱbeenȱwidespreadȱinȱ theȱMississippiȱRiverȱDeltaȱ (MRD)ȱandȱ thereȱ isȱaȱdenseȱnetworkȱofȱpipelinesȱbothȱ inshoreȱandȱoffshoreȱ(Figureȱ1).ȱHydrocarbonȱextractionȱinȱtheȱMRDȱnecessitatedȱtheȱdredgingȱofȱcanalsȱthroughȱwetlandsȱandȱwaterbodiesȱforȱnavigation,ȱpipelines,ȱandȱO&Gȱextraction.ȱAsȱcanalsȱwereȱdredged,ȱspoilȱmaterialȱfromȱcanalsȱwasȱplacedȱonȱtheȱsideȱofȱcanalsȱpartiallyȱimpoundingȱwetlands;ȱalteringȱnaturalȱ hydrologyȱ andȱ salinity;ȱ decreasingȱ nutrient,ȱ organicȱ matter,ȱ andȱ sedimentȱ exchange;ȱchangingȱvegetationȱcompositionȱandȱreducingȱvegetationȱproductivityȱ(e.g.,ȱ[2–5]).ȱ

ToȱunderstandȱtheȱimpactsȱofȱO&GȱactivityȱonȱMRDȱwetlands,ȱitȱisȱimportantȱtoȱrecognizeȱthatȱwetlandȱdegradationȱinȱO&Gȱfieldsȱoccurredȱmuchȱmoreȱrapidlyȱ(decades)ȱthanȱtheȱnaturalȱdeltaicȱcycle,ȱwhichȱ tookȱplaceȱoverȱ centuriesȱ toȱmillenniaȱ [5–10].ȱNaturallyȬoccurringȱgeologicȱ faulting,ȱsedimentȱcompaction,ȱtheȱdeltaȱlobeȱcycle,ȱvariabilityȱinȱriverȱdischarge,ȱglobalȱseaȬlevelȱchange,ȱtidalȱexchange,ȱwaveȱerosion,ȱandȱstormsȱsuchȱasȱhurricanesȱandȱfrontalȱpassagesȱhaveȱshapedȱtheȱMRDȱlandscapeȱforȱthousandsȱofȱyearsȱ[5–15].ȱHowever,ȱ inȱ lessȱthanȱaȱcentury,ȱmoreȱthanȱ30,000ȱkmȱofȱcanalsȱwereȱdredgedȱinȱtheȱMRDȱ[16–18],ȱcausingȱdramaticȱwetlandȱlossȱ(e.g.,ȱ[9])ȱdueȱtoȱcumulativeȱeffectsȱ[4,19]ȱofȱalteredȱsurfaceȱhydrology,ȱinducedȱsubsidenceȱandȱfaultȱactivationȱ[20],ȱandȱtoxicityȱofȱproducedȱwaterȱandȱspilledȱoilȱ[21–23].ȱ ȱ

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Figureȱ 1.ȱ (a)ȱ Mapȱ ofȱ oilȱ andȱ gasȱ pipelinesȱ inȱ coastalȱ Louisianaȱ(http://www.dnr.louisiana.gov/assets/docs/oilgas/data/SLA_Pipelines.pdf)ȱandȱ(b)ȱtheȱdistributionȱofȱoilȱandȱgasȱwellȱpermitsȱissuedȱbetweenȱ1900ȱandȱ2017ȱthatȱwereȱ‘plugged’ȱorȱ‘abandoned’ȱasȱofȱ2017ȱinȱtheȱ14ȱcoastalȱparishesȱ[18].ȱ


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OurȱobjectiveȱinȱthisȱpaperȱisȱtoȱreviewȱtheȱliteratureȱonȱtheȱlifeȱcycleȱofȱO&GȱfieldsȱinȱtheȱMRDȱbyȱ(1)ȱdescribingȱtheȱproductionȱhistoryȱofȱhydrocarbonsȱandȱproducedȱwaterȱandȱ(2)ȱreviewingȱtheȱimpactsȱofȱsurfaceȱalterations,ȱinducedȱsubsidence,ȱandȱtoxicȱmaterials.ȱAlthough,ȱtheseȱimpactsȱhaveȱbeenȱwellȱdocumented,ȱtheirȱinteractingȱaffectsȱhaveȱbeenȱlessȱwellȱaddressed.ȱThus,ȱanȱimportantȱobjectiveȱ isȱ toȱ considerȱ theirȱ cumulativeȱ andȱ indirectȱ impactsȱ onȱ coastalȱ ecosystems,ȱ especiallyȱwetlands,ȱinȱtheȱMRDȱandȱtoȱshowȱhowȱthisȱinformationȱinformsȱrestoration.ȱ ȱ

2.ȱProductionȱHistoryȱofȱOilȱandȱGasȱFieldsȱ

Hydrocarbonȱ extractionȱ hasȱ occurredȱ inȱ theȱMRDȱ forȱ overȱ aȱ century.ȱProductionȱ increasedȱrapidlyȱandȱthenȱdeclinedȱasȱreservesȱwereȱdepletedȱandȱfluidȱoutputȱwasȱdominatedȱbyȱproducedȱwaterȱ(Figuresȱ2ȱandȱ3).ȱThisȱisȱtrueȱforȱtheȱoverallȱproductionȱhistoryȱandȱforȱindividualȱfieldsȱthatȱwereȱactiveȱforȱ30–50ȱyearsȱorȱmore.ȱ

ȱFigureȱ2.ȱAnnualȱoilȱandȱgasȱproductionȱinȱsouthernȱLouisianaȱbetweenȱ1945ȱandȱ2019.ȱDataȱsource:ȱ(http://www.dnr.louisiana.gov/assets/TAD/OGTables/Table03.pdf).ȱ

WetlandȱlossȱinȱcoastalȱLouisianaȱhasȱbeenȱquantifiedȱ[19,24,25].ȱResearchersȱhaveȱusedȱdifferentȱproxiesȱofȱfieldȱdevelopmentȱtoȱcorrelateȱthisȱlandȱlossȱwithȱspecificȱoilȱandȱgasȱactivitiesȱ[26–29].ȱTheȱauthorsȱ ofȱ [30]ȱ reportedȱ theȱ highestȱ ratesȱ ofȱ wetlandȱ lossȱ inȱ theȱ MRDȱ correlatedȱ withȱ peakȱhydrocarbonȱproductionȱ(Figureȱ3).ȱInȱ[18]ȱitȱwasȱreportedȱthatȱtheȱannualȱnumberȱofȱwellȱdrillingȱpermits,ȱ aȱproxyȱ forȱproduction,ȱ correlatedȱwithȱwetlandȱ lossȱ ratesȱ (Figureȱ 4).ȱ Inȱ thisȱpaperȱweȱinvestigateȱtheȱfactorsȱcontributingȱtoȱtheseȱrelationships.ȱ


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ȱFigureȱ3.ȱCompositeȱhistoriesȱofȱfluidȱproductionȱfromȱoilȱandȱgasȱfieldsȱandȱwetlandȱlossȱinȱsouthȱLouisiana.ȱProductionȱdataȱfromȱtheȱLouisianaȱDepartmentȱofȱNaturalȱResourcesȱandȱtheȱPI/DwightsȱPLUSȱdatabaseȱ [31].ȱWetlandȱ lossȱvaluesȱwereȱdeterminedȱbyȱ [32]ȱ andȱ JohnȱBarrasȱ (unpublishedȱdata).ȱ Theseȱ historicalȱ data,ȱ integratedȱ acrossȱ theȱ deltaȱ plain,ȱ showȱ closeȱ temporalȱ andȱ spatialȱcorrelationsȱbetweenȱratesȱofȱwetlandȱlossȱandȱratesȱofȱfluidȱproductionȱ[30].ȱNoteȱthatȱ“water”ȱinȱtheȱlegendȱrefersȱtoȱproducedȱwater.ȱ

ȱFigureȱ4.ȱTheȱnumberȱofȱoilȱandȱgasȱpermitsȱissuedȱannuallyȱandȱlandȱlossȱratesȱ[18].ȱ

Althoughȱindividualȱfieldsȱshowȱaȱsimilarȱpatternȱofȱproductionȱhistoryȱandȱwetlandȱloss,ȱtheyȱdifferȱinȱsomeȱdetailsȱasȱillustratedȱforȱfourȱdifferentȱfieldȱcomplexesȱ(Figureȱ5)ȱthatȱproducedȱO&Gȱoverȱ 4–6ȱ decades.ȱ Theȱ Bullyȱ Campȱ andȱ Madisonȱ Bayȱ areaȱ hadȱ increasedȱ producedȱ waterȱdevelopmentȱ inȱ theȱ secondȱhalfȱofȱ theirȱproductionȱhistory.ȱPeakȱwaterȱproductionȱ inȱ theȱBayouȱRambioȱandȱDuLargeȱfieldsȱcoincidedȱwithȱpeakȱgasȱinȱthisȱregionȱthatȱhadȱrelativelyȱlowȱoilȱcapture.ȱWaterȱproductionȱwasȱalsoȱhighȱinȱtheȱsecondȱhalfȱofȱtheȱproductionȱhistoryȱofȱthisȱarea.ȱTheȱpatternȱofȱwaterȱproductionȱinȱtheȱPointeȱauȱChienȱstudyȱareaȱwasȱsimilarȱtoȱgasȱproductionȱinȱtheȱsecondȱhalfȱofȱtheȱoilȱfieldȱlife.ȱInȱeachȱexampleȱthough,ȱtheȱproductionȱofȱoil,ȱgas,ȱandȱproducedȱwaterȱvariedȱoverȱtheȱfieldȱlifeȬcycle,ȱeachȱfieldȱbegan,ȱpeaked,ȱthenȱgraduallyȱdepletedȱoverȱdecades.ȱAllȱfieldsȱcombineȱtoȱyieldȱtheȱoverallȱhistoryȱofȱtheȱcoastalȱzoneȱ(Figuresȱ2ȱandȱ3).ȱAllȱfourȱfieldsȱillustrateȱtheȱconceptȱofȱaȱdevelopmentȱcycleȱ thatȱ includesȱaȱrunȬupȱ toȱpeakȱproductionȱ followedȱbyȱaȱgradualȱdecreaseȱtoȱtotalȱabandonment.ȱIndividualȱfieldsȱandȱtheȱaggregateȱofȱallȱfieldsȱfollowȱaȱsimilarȱlifeȱ


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cycle.ȱ Theseȱ patternsȱ haveȱ importantȱ implicationsȱ forȱ theȱ impactsȱ ofȱ hydrocarbonȱ extractionȱ onȱcoastalȱecosystems,ȱespeciallyȱwetlands,ȱ forȱ threeȱmainȱ reasons.ȱFirst,ȱdredgingȱofȱcanalsȱ leadsȱ toȱsevereȱalterationȱofȱsurfaceȱhydrologyȱthatȱimpactsȱcoastalȱwetlands.ȱSecond,ȱextractionȱofȱfluidsȱ(oil,ȱgas,ȱ andȱwater)ȱ leadsȱ toȱ changesȱ inȱ poreȱ pressureȱ thatȱ resultȱ inȱ inducedȱ subsidenceȱ andȱ faultȱactivation.ȱThird,ȱaccidentalȱspillsȱandȱintentionalȱreleasesȱofȱoilȱandȱproducedȱwaterȱcauseȱtoxicityȱstressesȱ thatȱdegradeȱ coastalȱ ecosystems.ȱTheseȱ factorsȱ areȱdiscussedȱ inȱmoreȱdetailȱbelow,ȱ afterȱwhichȱweȱshowȱhowȱcumulativeȱandȱinteractingȱimpactsȱmultiplyȱtheȱindividualȱimpacts.ȱ ȱ

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Figureȱ5.ȱProductionȱhistoryȱofȱselectedȱoilȱandȱgasȱfieldsȱinȱtheȱMississippiȱdelta.ȱUpperȱleft—BullyȱCamp;ȱupperȱright—BayouȱRambioȱandȱDeLargeȱfields;ȱ lowerȱ left—MadisonȱBayȱfieldȱarea;ȱlowerȱright—PointeȱauȱChienȱstudyȱareaȱ[30].ȱNoteȱthatȱ“water”ȱinȱtheȱlegendsȱrefersȱtoȱproducedȱwater.ȱ

3.ȱPatternsȱofȱWetlandȱLossȱandȱOilȱandȱGasȱActivitiesȱ

Fromȱ1930ȱtoȱ2010ȱaboutȱaȱquarterȱ(aboutȱ5000ȱkm2)ȱofȱMRDȱcoastalȱmarshesȱwereȱlost,ȱmostlyȱbyȱ conversionȱ toȱopenȱwaterȱ [33,34]ȱwithȱ twoȱgeneralȱpatternsȱ (Figureȱ6).ȱWetlandȱ lossȱhasȱbeenȱpervasiveȱacrossȱtheȱcoastȱwithȱhighȱlossȱnearȱtheȱmouthȱofȱtheȱMississippiȱRiver,ȱinȱtheȱBaratariaȱandȱTerrebonneȱbasins,ȱandȱ inȱtheȱChenierȱPlain.ȱTwoȱareasȱstandȱoutȱwithȱmuchȱ lessȱ loss.ȱOneȱ isȱtheȱcentralȱ coastȱ thatȱ receivesȱ inputȱ fromȱ theȱAtchafalayaȱRiver,ȱwhichȱ carriesȱaboutȱaȱ thirdȱofȱ totalȱMississippiȱRiverȱdischarge,ȱthatȱflowsȱ intoȱshallowȱbaysȱandȱwetlandsȱoverȱaȱwideȱarcȱalongȱtheȱcentralȱLouisianaȱcoast.ȱTheȱotherȱzoneȱisȱonȱtheȱnortheasternȱflankȱofȱtheȱdeltaȱinȱtheȱseawardȱreachesȱofȱtheȱPontchartrainȱestuary.ȱ ȱ


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ȱ ȱFigureȱ6.ȱWetlandȱlossȱinȱcoastalȱLouisianaȱfromȱ1932ȱtoȱ2016.ȱRedȱandȱyellowȱareasȱhaveȱhighȱlandȱlossȱrates.ȱNoteȱthatȱlandȱlossȱisȱlowȱinȱtheȱcentralȱcoastȱandȱinȱtheȱnortheasternȱflankȱofȱtheȱdelta.ȱ(Source:ȱ [33,34]ȱ Theȱmapȱ canȱ beȱ downloadedȱ atȱ https://pubs.usgs.gov/sim/3381/sim3381.pdfȱ forȱdetailedȱ examinationȱ ofȱ specificȱ areasȱ ofȱ change.ȱ Seeȱ alsoȱhttps://pubs.er.usgs.gov/publication/sim3381).ȱ

AȱnumberȱofȱstudiesȱhaveȱdiscussedȱtheȱcausesȱofȱwetlandȱlossȱandȱaddressedȱtheȱroleȱofȱO&Gȱactivitiesȱinȱthisȱlossȱ(Tableȱ1).ȱO&Gȱactivitiesȱreduceȱforcesȱleadingȱtoȱwetlandȱsustainabilityȱ(e.g.,ȱsedimentation,ȱaccretion,ȱvegetationȱbiomassȱproduction)ȱandȱenhanceȱforcesȱleadingȱtoȱdeteriorationȱ(e.g.,ȱincreasedȱsubsidence,ȱsaltwaterȱintrusion,ȱvegetationȱdecline,ȱtoxicityȱstresses).ȱO&Gȱimpactsȱonȱwetlandsȱ areȱ bothȱ directȱ andȱ indirect.ȱ Directȱ lossȱ isȱ dueȱ bothȱ toȱ canalȱ dredgingȱ andȱ spoilȱplacement,ȱwhileȱindirectȱimpactsȱincludeȱalterationȱofȱsurfaceȱhydrology,ȱinducedȱsubsidence,ȱandȱintroductionȱofȱtoxicȱsubstances.ȱDirectȱimpactsȱareȱreportedȱtoȱhaveȱcausedȱbetweenȱ6%ȱandȱ70%ȱorȱmoreȱlandȱlossȱwhileȱindirectȱimpactsȱhaveȱcausedȱbetweenȱ20%ȱandȱ80%ȱorȱmoreȱofȱwetlandȱlossȱ(Tableȱ1).ȱ ȱ

Tableȱ1.ȱEstimatesȱofȱtheȱpercentageȱofȱwetlandȱlossȱcausedȱbyȱallȱoilȱandȱgasȱactivitiesȱ(overall)ȱorȱbyȱdirectȱorȱindirectȱimpactsȱofȱoilȱandȱgasȱactivities.ȱ

LocationȱTimeȱPeriodȱ

OverallȱImpactsȱ(%ȱWetlandȱLoss)ȱ

DirectȱImpactsȱ(%ȱWetlandȱLoss)ȱ

IndirectȱImpactsȱ(%ȱWetlandȱLoss)ȱ

Sourceȱ

CoastalȱLouisianaȱ

1931–1967ȱ ȱ 69ȱ ȱ [35]ȱ


ȱ 45ȱ ȱ ȱ [36]ȱ


ȱ ȱ 10–69ȱ ȱ [37]ȱ


ȱ ȱ 10ȱ upȱtoȱ80ȱ [38]ȱ


1955–1978ȱ ȱ 10ȱ 48–97ȱ [39]ȱ

MississippiȱRiverȱDeltaicȱPlainȱ

1955/56–1978ȱ

ȱ 25–39ȱ ȱ [40]ȱ


1932–1990ȱMajorityȱofȱlossesȱdueȱtoȱ

canalsȱȱ ȱ [18,26,27]ȱ ȱ


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1955–1978ȱ 20–60ȱ 14–16ȱ 20–60ȱ [16]ȱ


1955–1978ȱ ȱ 16ȱ ȱ [41]ȱ


1955–1978ȱ ȱ 6.6ȱ ȱ [42]ȱ


1955–1978ȱ ȱ 16ȱ 30–59ȱ [43]ȱ

BretonȱSoundȱ

1933–1990ȱ 68ȱ ȱ ȱ [9]ȱ

BaratariaȱBasinȱ

1933–1990ȱ 72ȱ ȱ ȱ [9]ȱ

MermentauȱBasinȱ

1933–1990ȱ 35ȱ ȱ ȱ [9]ȱ

MississippiȱRiverȱDeltaicȱPlainȱ

1930–1990ȱ 33.2ȱ 10.8ȱ 22.4ȱ [24,25]ȱ

Wetlandȱlossȱpatternsȱareȱgenerallyȱsimilarȱtoȱtemporalȱpatternsȱofȱproductionȱ(Figureȱ7).ȱTheȱdifferentȱstudiesȱwereȱdoneȱusingȱdifferentȱmethodsȱandȱrepresentȱdifferentȱconceptualizationsȱofȱtheȱdeltaȱandȱsubȬareasȱsampled.ȱRegardlessȱofȱtheȱproxyȱusedȱtoȱdescribeȱtheȱoilȱandȱgasȱlifeȬcycle,ȱtheȱrelationȱtoȱlandȱlossȱisȱunmistakable.ȱTheȱratesȱofȱlandȱlossȱdifferȱbecauseȱtheyȱareȱforȱdifferentȱareasȱ(e.g.,ȱtotalȱcoastȱvs.ȱdeltaicȱandȱChenierȱplains)ȱandȱforȱdifferentȱtimeȱperiodsȱandȱtheȱstudyȱmethods,ȱthoughȱsimilar,ȱareȱnotȱtheȱsameȱ[32,34,44].ȱPeakȱlossȱoccurredȱgenerallyȱbetweenȱ1960ȱandȱ1980.ȱTheȱcurveȱforȱtotalȱO&GȱproductionȱisȱsharperȱthanȱthatȱofȱlandȱlossȱlikelyȱbecauseȱofȱdelayedȱimpactsȱofȱO&Gȱasȱwellȱasȱotherȱcausesȱofȱlandȱlossȱ(e.g.,ȱisolationȱfromȱriverineȱinput,ȱedgeȱerosion,ȱhurricaneȱimpacts).ȱ ȱ

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Figureȱ7.ȱOilȱandȱgasȱproductionȱandȱ landȱ lossȱstudiesȱforȱcoastalȱLouisiana.ȱLossȱvaluesȱareȱfromȱ[32,34,44]ȱwhereȱrateȱvaluesȱrepresentȱanȱaverageȱoverȱtheȱtimeȱintervalȱshown.ȱProductionȱdataȱareȱfromȱLouisianaȱDepartmentȱofȱNaturalȱResources.ȱTheseȱhistoricalȱdataȱ showȱ closeȱ temporalȱandȱspatialȱcorrelationsȱbetweenȱratesȱofȱwetlandȱlossȱandȱratesȱofȱhydrocarbonȱproduction.ȱ

4.ȱIndirectȱImpactsȱofȱOilȱandȱGasȱExplorationȱandȱProductionȱonȱCoastalȱLouisianaȱWetlandsȱ

4.1.ȱAlterationȱofȱSurfaceȱHydrologyȱDueȱtoȱCanalȱDredgingȱandȱSpoilȱPlacementȱ

MRDȱwetlandsȱareȱdependentȱonȱsheetȱflowȱforȱexchangeȱofȱwater,ȱsediments,ȱandȱnutrientsȱtoȱsustainȱwetlandȱhealth.ȱUnimpededȱwetlandȱhydrologyȱfacilitatesȱalternatingȱfloodingȱandȱdrainingȱofȱwetlands.ȱCanalsȱ andȱ spoilȱ banksȱ areȱ linearȱ andȱ intersecting,ȱ andȱ spoilȱ banksȱ areȱ higherȱ inȱelevationȱthanȱsurroundingȱwetlandsȱandȱnormalȱhighȱtidesȱ[4,9,15,45].ȱPlacementȱofȱdredgeȱspoilȱimpoundsȱwetlands,ȱreducingȱorȱeliminatingȱsurfaceȱwaterȱexchangeȱandȱtidalȱinfluence,ȱreducingȱsedimentȱdepositionȱontoȱwetlands,ȱimpedingȱtheȱexchangeȱofȱmaterialsȱ(e.g.,ȱnutrients,ȱsediments,ȱorganisms)ȱ betweenȱ semiȬimpoundedȱ marshesȱ andȱ theȱ surroundingȱ marsh,ȱ andȱ increasingȱinundationȱdurationȱwhileȱdecreasingȱinundationȱfrequencyȱ[2,4,16,46–50].ȱSpoilȱbanksȱtrapȱwater,ȱincreasingȱwaterȱloggingȱandȱdecreasingȱdrainage,ȱsedimentȱaccretion,ȱandȱvegetationȱproductivityȱ(Figureȱ8)ȱ[4,15,16,19,46,48,51–63].ȱAsȱsurfaceȱflowȱisȱminimizedȱbyȱspoilȱbanks,ȱwaterȱmayȱonlyȱbeȱintroducedȱ intoȱ impoundedȱwetlandsȱwhenȱwaterȱ levelsȱareȱ elevatedȱduringȱ frontalȱpassagesȱorȱmajorȱstorms.ȱ ȱ

ȱFigureȱ8.ȱTotalȱhoursȱflooded,ȱforȱoneȱmonth,ȱatȱaȱreferenceȱmarshȱwithȱaȱnaturalȱbermȱandȱaȱpartiallyȱimpoundedȱareaȱwhereȱaboutȱ75%ȱofȱtheȱnaturalȱbermȱhadȱbeenȱreplacedȱbyȱaȱdredgedȱcanalȱspoilȱbank,ȱGoldenȱMeadowȱoilȱandȱgasȱfieldȱsouthȱofȱNewȱOrleans,ȱLAȱ[52].ȱTheȱdashedȱlineȱshowsȱwhatȱtheȱrelationshipȱwouldȱbeȱifȱthereȱwereȱnoȱpartialȱimpoundment.ȱ

Dueȱtoȱspoilȱbanks,ȱaccretionȱinȱunȬimpoundedȱmarshesȱmayȱbeȱupȱtoȱfiveȱtimesȱhigherȱthanȱthatȱinȱ impoundedȱ marshesȱ [3,57,61,64–67].ȱ Canalsȱ alsoȱ promoteȱ saltwaterȱ intrusionȱ intoȱ wetlandsȱpreviouslyȱisolatedȱfromȱdirectȱexchangeȱwithȱhigherȱsalinityȱwatersȱ[2,4,27,47,48,68–71].ȱIncreasesȱinȱsalinityȱcauseȱchangesȱinȱvegetationȱcompositionȱandȱreducedȱproductivityȱand/orȱdeathȱofȱfreshȱandȱlowȱsalinityȱmarshȱspeciesȱandȱleadȱtoȱformationȱofȱopenȱwaterȱ[53,71–73].ȱIntroductionȱofȱsaltwaterȱincreasesȱsulfateȱconcentrations,ȱwhichȱcanȱbeȱreducedȱtoȱsulfidesȱinȱanaerobicȱsoils,ȱthatȱstressesȱandȱcausesȱmortalityȱtoȱlowȱsalinityȱwetlandȱvegetationȱ[73]ȱandȱrapidȱdecompositionȱandȱcollapseȱofȱsoilȱorganicȱmatterȱandȱsoilȱstructureȱpeatsȱ[74].ȱReducedȱvegetationȱproductivityȱandȱvegetationȱdeathȱexacerbateȱ landȱ lossȱbecauseȱplantȱrootsȱbindȱsoilsȱandȱ increaseȱsoilȱstrength.ȱWhenȱrootsȱdie,ȱtheȱwetlandȱrapidlyȱlosesȱelevationȱandȱisȱmoreȱvulnerableȱtoȱerosionȱ[74,75].ȱ

Overȱtime,ȱcanalsȱwidenȱasȱaȱresultȱofȱspoilȱbankȱundercutting,ȱerosion,ȱandȱcollapseȱcausingȱadditionalȱwetlandȱlossȱ[45,46].ȱLocalizedȱsubsidenceȱalongȱpipelineȱcanalsȱoccursȱalongȱtheȱflanksȱofȱspoilȱbanksȱwhenȱtheȱweightȱofȱtheȱspoilȱdepressesȱtheȱsurfaceȱofȱtheȱmarshȱandȱleadsȱtoȱtheȱformationȱ


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ofȱlinearȱpondsȱbehindȱtheȱspoilȱbanksȱdueȱtoȱsubsidenceȱfromȱtheȱweightȱofȱtheȱspoil,ȱtrappingȱofȱwaterȱatȱtheȱbaseȱofȱspoilȱbanksȱandȱblockingȱofȱsedimentȱinputȱ[76].ȱTheȱauthorsȱofȱ[77]ȱdocumentedȱsoilȱ compactionȱbeneathȱ spoilȱbanksȱ createdȱmoreȱ impenetrableȱ soilsȱ thatȱ reducedȱgroundȱwaterȱmovement.ȱ Theseȱ processesȱ isolateȱ theȱ wetlandȱ behindȱ theȱ spoilȱ bankȱ fromȱ bothȱ aboveȬȱ andȱbelowgroundȱwaterȱexchange.ȱ

O&Gȱ canalsȱareȱdeep,ȱ straightȱ channelsȱwhileȱnaturalȱwaterwaysȱareȱprimarilyȱ shallowȱandȱsinuousȱ tidalȱ channelsȱ [4].ȱAsȱ canalȱdensityȱ increasesȱ inȱanȱarea,ȱ theȱdensityȱofȱnaturalȱ channelsȱdecreasesȱbecauseȱcanalsȱpreferentiallyȱcaptureȱwaterȱflowȱfromȱnaturalȱchannelsȱ(Figureȱ9)ȱ[37,52]ȱinȱaȱprocessȱ termedȱ ‘channelȱ theft’,ȱbecauseȱdeep,ȱstraightȱcanalsȱ transportȱwaterȱmoreȱefficientlyȱthanȱnaturalȱshallowȱandȱsinuousȱchannelsȱ[50].ȱ ȱ

ȱFigureȱ9.ȱTheȱrelationshipȱbetweenȱcanalȱdensityȱandȱtheȱdensityȱofȱnaturalȱchannels.ȱTheȱdataȱareȱaveragesȱofȱreplicateȱ1Ȭkm2ȱgridsȱ(numbersȱshownȱbyȱsymbol)ȱinȱtheȱregionȱofȱLeeville,ȱLA,ȱaȱsalineȱmarshȱareaȱ[37].ȱ

Onceȱdredged,ȱspoilȱbanksȱareȱnotȱpermanentȱfeaturesȱandȱhaveȱaȱlifeȱcycleȱofȱtheirȱown.ȱTheyȱdisappearȱoverȱtimeȱdueȱtoȱcompaction,ȱsubsidence,ȱseaȬlevelȱrise,ȱandȱerosion.ȱSpoilȱbanksȱprotectȱremnantȱmarshȱfromȱwaveȱerosionȱandȱasȱspoilȱbanksȱdisappearȱremnantȱmarshȱcanȱbeȱlostȱdueȱtoȱwaveȱattack,ȱleadingȱtoȱfurtherȱwetlandsȱloss.ȱInȱFigureȱ10,ȱsubaerialȱlandȱthatȱdisappearedȱbetweenȱtheȱtwoȱmappingȱdatesȱ(centerȱpanelȱinȱFigureȱ10)ȱinȱtheȱLeevilleȱFieldȱincludesȱbothȱspoilȱbanksȱandȱmarsh.ȱ


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ȱFigureȱ10.ȱAerialȱimageryȱofȱaȱportionȱofȱtheȱLeevilleȱoilȱandȱgasȱfieldȱinȱsouthernȱLouisianaȱshowingȱtheȱdisappearanceȱofȱspoilȱbanksȱandȱmarshȱbetweenȱ1998ȱandȱ2017.ȱBayouȱLafourcheȱisȱinȱtheȱupperȱleftȱinȱeachȱofȱtheȱimagesȱ[5].ȱAreasȱdepictedȱinȱredȱinȱimageȱBȱdisappearedȱbetweenȱtheȱtwoȱdates.ȱRedȱlinearȱstripsȱareȱspoilȱbanksȱthatȱdisappeared.ȱGreenȱshowsȱsubaerialȱland,ȱbothȱspoilȱbanksȱandȱmarsh,ȱ thatȱwasȱ stillȱpresentȱ inȱ 2017.ȱTheȱSouthwestȱLouisianaȱCanalȱ atȱ theȱ topȱofȱ imageȱAȱwasȱdredgedȱinȱtheȱlateȱ19thȱcentury.ȱInȱ1998,ȱsomeȱspoilȱbanksȱalongȱtheȱcanalȱwereȱstillȱpresent,ȱbutȱbyȱ2017ȱtheyȱhadȱdisappeared.ȱLouisianaȱhighwayȱ1ȱisȱshownȱatȱtheȱupperȱleftȱinȱimageȱA.ȱByȱ2017,ȱaȱnew,ȱ elevatedȱ highwayȱ wasȱ constructedȱ (whiteȱ linesȱ inȱ Imageȱ C).ȱ Theȱ widthȱ ofȱ imagesȱ isȱapproximatelyȱ2.8ȱkm.ȱ

AsȱO&Gȱcanalsȱareȱsoȱpervasive,ȱitȱhasȱbeenȱsuggestedȱthatȱcanalsȱareȱresponsibleȱforȱpracticallyȱallȱwetlandsȱ loss.ȱForȱ example,ȱ theȱauthorsȱofȱ [18,27]ȱplottedȱ landȱ lossȱ fromȱ15Ȭminȱquadranglesȱagainstȱcanalȱdensityȱandȱconcludedȱthatȱlandȱ lossȱwasȱdirectlyȱrelatedȱtoȱtheȱpercentȱofȱcanalsȱinȱeachȱmap,ȱindicatingȱthatȱalmostȱallȱlandȱlossȱwasȱrelatedȱtoȱcanalsȱ(Figureȱ11).ȱHowever,ȱinȱ[5]ȱandȱ[9]ȱtheȱauthorsȱshowedȱthatȱthisȱapproachȱisȱflawedȱbecauseȱitȱstatisticallyȱrelatesȱallȱlandȱlossȱinȱ15Ȭminȱquadranglesȱ(whichȱcoverȱaboutȱ66,000ȱha)ȱtoȱcanalȱdensityȱinȱtheȱquadrangleȱevenȱwhenȱitȱisȱneitherȱ spatiallyȱorȱ functionallyȱ relatedȱ toȱ landȱ lossȱpatterns.ȱAdditionally,ȱasȱweȱdiscussȱbelow,ȱinducedȱ subsidenceȱ causesȱ landȱ lossȱ butȱ isȱ notȱ functionallyȱ relatedȱ toȱ surfaceȱ alterationsȱ inȱhydrology.ȱInȱaddition,ȱtoxicȱstressȱdueȱtoȱspilledȱoilȱandȱproducedȱwaterȱcauseȱvegetationȱstressȱandȱmortality.ȱ However,ȱ alteredȱ hydrology,ȱ inducedȱ subsidence,ȱ andȱ toxicȱ compoundsȱ interactȱsynergisticallyȱandȱcauseȱwetlandȱlossȱasȱindicatedȱbyȱtheȱinteractionsȱdemonstratedȱinȱtheȱLeevilleȱfieldȱ(Figureȱ10).ȱ ȱ


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ȱFigureȱ11.ȱTheȱlandȱlossȱrateȱfromȱtheȱ1930sȱtoȱ1990ȱandȱcanalȱdensityȱinȱ15Ȭminȱquadrangleȱmaps.ȱTheȱauthorsȱofȱ[18]ȱconcludedȱthatȱthisȱdemonstratesȱthatȱmostȱwetlandsȱlossȱisȱdueȱtoȱcanals.ȱThisȱisȱincorrect,ȱhowever,ȱbecauseȱofȱtheȱlargeȱsizeȱofȱ15Ȭminȱquadrangleȱmapsȱandȱotherȱcausesȱofȱlandȱlossȱdueȱtoȱinducedȱsubsidenceȱandȱtoxicȱstress.ȱ

4.2.ȱOilȱandȱGasȱProductionȱInducedȱSubsidenceȱ

Oil,ȱgas,ȱandȱbrineȱextractionȱdepletesȱtheȱhydrocarbonȱreservoir,ȱoftenȱprecipitously,ȱresultingȱinȱpressureȱdrop,ȱcompaction,ȱandȱfaultȱactivationȱ(usuallyȱreactivation);ȱandȱthisȱchangeȱatȱdepthȱtranslatesȱupward,ȱmanifestingȱatȱtheȱsurfaceȱasȱsubsidenceȱandȱfaulting.ȱThatȱis,ȱwithoutȱpressureȱsupportȱtheȱdepletedȱreservoirȱcollapses,ȱandȱtheȱpressureȱdifferenceȱatȱtheȱnearbyȱassociatedȱfaultȱplaneȱnucleatesȱslippageȱthereȱ[4,20,28,30],ȱ leadingȱtoȱaȱsubtle,ȱandȱsometimesȱdramatic,ȱoverprintȱintegratedȱ withȱ otherȱ O&Gȱ relatedȱ processes.ȱ Observationsȱ generallyȱ confirmȱ theȱ relationshipȱbetweenȱfluidȱproductionȱandȱsubsidenceȱinȱcoastalȱLouisiana:ȱforȱexample,ȱwetlandȱlossȱisȱtypicallyȱhigherȱinȱtheȱvicinityȱofȱoilȱandȱgasȱfieldsȱ[9,20,29,78–83].ȱOnȱtheȱcoastalȱChenierȱPlain,ȱtheȱauthorsȱofȱ[83]ȱsuggestedȱthatȱpaleoȬseaȱlevelȱelevations,ȱverticallyȱoffsetȱbyȱ0.5–1ȱmȱonȱaȱtransectȱnearȱtheȱareaȱofȱmaximumȱoilȱandȱgasȱproduction,ȱwereȱinfluencedȱbyȱthisȱproduction.ȱLocalȱratesȱofȱmeasuredȱsubsidenceȱinȱoilȱandȱgasȱfieldsȱinȱsouthȱcentralȱLouisianaȱ(oftenȱmoreȱthanȱ20ȱmm/year)ȱwereȱmuchȱhigherȱthanȱregionalȱratesȱinȱtheȱMississippiȱRiverȱDeltaȱ(aboutȱ10ȱmm/year)ȱ[84].ȱInȱ[30]ȱtheȱauthorsȱanalyzedȱ relevelingȱ surveys,ȱ remoteȱ images,ȱ subsurfaceȱ maps,ȱ stratigraphicȱ sections,ȱ andȱhydrocarbonȱproductionȱdataȱ inȱrelationȱtoȱwetlandȱlossȱforȱtheȱTerrebonneȬLafourcheȱbasinsȱandȱfoundȱthatȱtheȱhighestȱratesȱofȱsubsidenceȱcoincidedȱwithȱtheȱlocationȱofȱoilȱandȱgasȱfieldsȱ(Figureȱ12)ȱ[30].ȱThisȱstudyȱalsoȱshowedȱthatȱsubsidenceȱratesȱwereȱgreaterȱinȱtheȱlaterȱepochȱ(1982–1993)ȱthanȱtheȱ earlierȱ (1965–1982);ȱ thatȱ is,ȱ subsidenceȱ acceleratedȱ lateȱ inȱ theȱ cycleȱ ofȱO&Gȱ production.ȱ Inȱ[20,30,84]ȱitȱwasȱconcludedȱthatȱtheseȱrapidȱchangesȱwereȱlikelyȱcausedȱbyȱinducedȱsubsidenceȱandȱfaultȱreactivationȱdueȱtoȱoilȱandȱgasȱactivity.ȱ


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�Figureȱ12.ȱMapȱshowingȱaverageȱsubsidenceȱratesȱbetweenȱ1965ȱandȱ1993ȱinȱsouthȱLouisiana.ȱAreasȱofȱhighestȱsubsidenceȱratesȱ(>12ȱmm/year;ȱhatchedȱpattern)ȱcorrelateȱcloselyȱwithȱlocationsȱofȱoilȱandȱgasȱfields.ȱLowestȱaverageȱsubsidenceȱratesȱareȱlocatedȱbetweenȱmajorȱproducingȱfieldsȱ[30].ȱ

ElevationȱchangeȱrelatedȱtoȱfaultingȱinȱtheȱMRDȱisȱoftenȱmarkedȱbyȱanȱarcuateȱscarpȱseparatingȱmarshȱandȱwaterȱ[85],ȱwhileȱsubsidenceȱrelatedȱtoȱaȱreservoir’sȱcompactionȱisȱspreadȱoverȱandȱbeyondȱtheȱproductionȱareaȱ(upȱtoȱkilometersȱawayȱfromȱtheȱproducingȱwells)ȱ[20].ȱSubsidenceȱinvolvedȱwithȱO&Gȱfieldsȱtypicallyȱbeginsȱaroundȱtheȱtimeȱofȱpeakȱproductionȱ[84],ȱandȱcontinuesȱforȱanȱextendedȱtimeȱasȱtheȱfieldȱisȱdepleted,ȱoftenȱdecadesȱafterȱpeakȱproductionȱ[29,79,86],ȱthoughȱitȱtooȱreachesȱanȱultimateȱlimitȱ[79,84].ȱ ȱ

Theȱ Mississippiȱ Deltaȱ isȱ particularlyȱ susceptibleȱ toȱ subsidenceȱ andȱ faultingȱ sinceȱ rapidȱdepositionȱofȱsandsȱandȱclaysȱhasȱcreatedȱaȱweak,ȱmetastableȱsituationȱthatȱrespondedȱfromȱearlyȱinȱitsȱgeologicȱhistoryȱwithȱ“landslideȬlike”ȱfaultingȱ(downȱtoȱtheȱcoastȱlistricȱnormalȱfaulting)ȱparallelȱtoȱ theȱ coast,ȱ andȱ thatȱ faultingȱ hasȱ progressedȱupwardȱ asȱdepositionȱ continued—thatȱ is,ȱ growthȱfaultingȱ [14,87–89].ȱ Theȱ sedimentaryȱ sectionȱ developedȱ soȱ rapidlyȱ thatȱ thereȱwasȱ littleȱ timeȱ forȱconsolidation,ȱcementation,ȱorȱinȱmanyȱcases,ȱnormalȱpressureȱequilibration.ȱAtȱtheȱsameȱtime,ȱtheseȱfaultsȱandȱrelatedȱrolloverȱanticlinesȱonȱtheirȱdownthrownȱside,ȱformedȱhydrocarbonȱtraps,ȱtheȱbasisȱforȱmanyȱofȱtheȱpresentȬdayȱO&Gȱfieldsȱonȱtheȱdeltaȱ(Figureȱ13).ȱToȱaddȱcomplexity,ȱtheȱlowȱdensity,ȱeasilyȱdeformedȱLouannȱsaltȱlayerȱthatȱbeganȱnearȱtheȱbaseȱofȱtheȱgeologicȱsectionȱflowedȱupwardȱinȱvariousȱgeometries,ȱcreatingȱsaltȱdomesȱdraggingȱupȱsteeplyȱtiltedȱbeds,ȱfaults,ȱandȱanticlinalȱfeaturesȱthatȱ becameȱhydrocarbonȱ trapsȱ asȱwell.ȱGrowthȱ faultsȱ inȱ theȱdeltaȱmoveȱ episodicallyȱ overȱ theirȱlifetime,ȱandȱalongȱsegmentsȱaȱfewȱkilometersȱinȱlengthȱ(e.g.,ȱ[90]).ȱOverȱtheȱcycleȱofȱMRDȱpetroleumȱdevelopment,ȱaȱnumberȱofȱtheseȱgrowthȱfaultsȱrelatedȱtoȱoilȱandȱgasȱfieldsȱhaveȱbeenȱreactivated,ȱwithȱconsequentȱdisplacementȱandȱsurfaceȱsubsidenceȱonȱtheȱfaultȱdownthrownȱside.ȱTheȱmechanismȱofȱ reactivationȱ alongȱ theseȱ growthȱ faultsȱ isȱ expeditedȱ byȱ aȱ poroelasticȱ reductionȱ ofȱ horizontalȱconfiningȱ stress,ȱwhichȱoccursȱ asȱ aȱ resultȱofȱ theȱ fluidȱwithdrawalȱ andȱ consequentȱporeȱpressureȱdecreaseȱ[91,92].ȱThatȱis,ȱfaultsȱrelatedȱtoȱMRDȱO&Gȱfieldsȱthatȱbreakȱtheȱsurfaceȱtodayȱareȱmostlyȱ


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reactivatedȱgrowthȱfaultsȱinvolvedȱwithȱtheȱreservoirsȱbelow—reservoirsȱthatȱtheseȱfaultsȱcreatedȱinȱtheȱfirstȱplace.ȱ ȱ

�Figureȱ 13.ȱ Typicalȱ Mississippiȱ Riverȱ Deltaȱ oilȱ andȱ gasȱ reservoir,ȱ aȱ rolloverȱ anticlineȱ onȱ theȱdownthrownȱ sideȱofȱaȱdownȬtoȬtheȬcoastȱnormalȱ fault.ȱOil,ȱgas,ȱandȱwaterȱproductionȱaffectsȱ theȱsubsurfaceȱinȱandȱaroundȱtheȱproducingȱreservoir.ȱTheȱdepletionȱprocessȱleadsȱtoȱproductionȱinducedȱfaultȱactivation,ȱreservoirȱcompactionȱwithȱadditionalȱcompactionȱofȱboundingȱshalesȱasȱshownȱinȱtheȱsubsurface.ȱTheȱsurfaceȱmanifestationȱofȱtheseȱsubsurfaceȱchangesȱisȱshownȱasȱaȱcompositeȱofȱlandȱlossȱonȱ theȱdownthrownȱsideȱ theȱactivatedȱ faultȱplusȱsubsidenceȱoverȱtheȱcompactedȱoil,ȱgas,ȱandȱwaterȱproducingȱreservoir.ȱ

Theȱ mechanismȱ ofȱ O&Gȱ subsidenceȱ isȱ involvedȱ withȱ theȱ collapseȱ ofȱ theȱ reservoirȱ itself.ȱSubsidenceȱhappensȱwhenȱproductionȱofȱoil,ȱgas,ȱandȱwaterȱ(andȱsometimesȱsand)ȱreducesȱreservoirȱsandȱporeȱpressureȱtoȱtheȱpointȱwhereȱitȱcanȱnoȱlongerȱsupportȱtheȱoverburdenȱ[93].ȱThus,ȱtheȱdelta’sȱyoung,ȱ oftenȱ poorlyȱ consolidatedȱ reservoirȱ sands,ȱ sandwichedȱ betweenȱ shales,ȱ oftenȱ undergoȱcompactionȱ withȱ productionȱ drainageȱ andȱ thisȱ deformationȱ isȱ transferredȱ toȱ theȱ surfaceȱ asȱ aȱsubsidenceȱ bowlȱ form.ȱ Theȱ authorsȱ ofȱ [94]ȱ modeledȱ thisȱ reservoirȱ compactionȱ andȱ surfaceȱdeformationȱprocessȱusingȱtheȱconceptȱofȱaȱnucleusȬofȬstrainȱ(theȱimpactedȱreservoir),ȱtogetherȱwithȱanȱelasticallyȱdeformingȱhalfȬspaceȱ(theȱgeologicȱsectionȱabove),ȱspreadingȱtheȱeffectȱandȱreducingȱtheȱdisplacementȱtoȱproduceȱaȱhaloȬlikeȱeffectȱinȱandȱaroundȱtheȱO&Gȱfield.ȱInȱ[79]ȱtheȱauthorsȱusedȱthisȱconceptȱalongȱwithȱ1982–1993ȱepochȱrelevelingȱatȱtheȱLeeville,ȱGoldenȱMeadow,ȱCutȱOff,ȱandȱValentineȱfieldsȱandȱtheȱauthorsȱofȱ[95]ȱmodeledȱtheȱLapeyrouseȱfieldȱ(Figureȱ12).ȱAtȱLapeyrouse,ȱmodelingȱmatchedȱtheȱmeasuredȱrelevelingȱwhenȱaȱreactivatedȱdownȬtoȬtheȬcoastȱgrowthȱfaultȱwasȱaddedȱtoȱtheȱdeformationȱofȱtheȱcompactedȱdiscȱreservoirȱsand.ȱThisȱreservoirȱcompactionȱsubsidenceȱprocessȱisȱfoundȱinȱfieldsȱalongȱtheȱLouisianaȱcoastȱandȱoftenȱactsȱinȱconcertȱwithȱO&Gȱfieldȱrelatedȱfaulting.ȱ ȱ

Inȱ[29]ȱtheȱauthorsȱconsideredȱtheȱextendedȱtimeframeȱofȱsubsidenceȱwhereȱdisplacementȱrelatedȱtoȱdepletedȱO&Gȱfieldsȱdidȱnotȱstopȱasȱtheȱproductionȱcycleȱended,ȱbutȱacceleratedȱsignificantlyȱforȱdecades.ȱAsȱshownȱinȱFigureȱ14,ȱthisȱstudyȱindicatesȱ(a)ȱgreaterȱsubsidenceȱoverȱtraversedȱO&Gȱfieldsȱ


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forȱeachȱepochȱ(panelsȱAȱandȱB),ȱ(b)ȱincreasedȱsubsidenceȱratesȱ(acceleratedȱsubsidence)ȱinȱtheȱlaterȱepochȱ(panelȱC),ȱandȱ(c)ȱareasȱofȱgreatestȱsubsidenceȱandȱratesȱlikelyȱrelatedȱtoȱfaultȱdisplacement.ȱ ȱ

�Figureȱ14.ȱElevationȱchangesȱduringȱepochȱ1ȱ(1965–1982;ȱA)ȱandȱepochȱ2ȱ(1983Ȭ1993;ȱB),ȱandȱtheȱratesȱofȱsubsidenceȱinȱtheȱtwoȱepochsȱ(C).ȱOverȱtheȱentireȱtransect,ȱsubsidenceȱratesȱwereȱgreaterȱinȱepochȱ2ȱthanȱinȱepochȱ1.ȱTheȱyellowȱsquaresȱinȱ(A)ȱandȱ(B)ȱindicateȱanȱarbitrarilyȱselectedȱreferenceȱstationȱapproximatelyȱ 8ȱ kmȱ southȱ andȱ outsideȱ ofȱ theȱ projectedȱ Leevilleȱ (seeȱ Figureȱ 10)ȱ toȱ estimateȱ theȱmagnitudesȱofȱlocalȱproductionȬrelatedȱsubsidenceȱsignalsȱ[29].ȱ

WhileȱpostȱproductionȱtimeȬdependentȱsubsidenceȱisȱintuitivelyȱexpectedȱdueȱtoȱfactorsȱsuchȱasȱslowȱ dissipationȱ ofȱ poreȱ pressureȱ inȱ theȱ reservoirȱ (e.g.,ȱ [96]),ȱ andȱ timeȬdependentȱ creepȱ inȱ theȱreservoirȱ[97],ȱthisȱsubsidenceȱtypicallyȱhappensȱoverȱonlyȱaȱfewȱyears,ȱnotȱdecadesȱafterȱandȱnotȱwithȱacceleration.ȱTheȱauthorsȱofȱ[29]ȱconsideredȱtheȱroleȱofȱtheȱboundingȱshaleȱaboveȱandȱbelowȱtheȱsandȱreservoirȱitselfȱ(Figureȱ15),ȱandȱmodeledȱcompactionȱinȱtheȱValentineȱfieldȱ(Figuresȱ12ȱandȱ14)ȱinȱtwoȱstages,ȱtheȱfirstȱbeingȱporoelasticȱcompactionȱofȱtheȱreservoirȱsandȱduringȱactiveȱproduction,ȱfollowedȱbyȱtheȱtimeȬdelayedȱcompactionȱresultingȱfromȱslowȱporoelasticȱandȱviscoplasticȱcompactionȱofȱtheȱlowȬpermeableȱboundingȱshaleȱasȱincludedȱporeȱwaterȱslowlyȱdrainedȱintoȱtheȱdepletedȱsand.ȱ ȱ


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�Figureȱ15.ȱAȱ simpleȱcompactionȱmodelȱofȱ sandȱ reservoirȱembeddedȱwithȱ surroundingȱ shale.ȱ Itȱ isȱassumedȱthatȱduringȱproductionȱstage,ȱporeȱpressureȱdepletionȱinȱaȱsandȱreservoirȱinducesȱporoelasticȱcompaction,ȱandȱafterȱdepletion,ȱaȱslowȱdecreaseȱinȱporeȱpressureȱinȱtheȱboundingȱshaleȱinducesȱshaleȱcompactionȱ inȱ twoȱ independentȱ rheologicalȱmodesȱ (poroelasticȱ andȱ viscoplastic)ȱ (modifiedȱ fromȱ[29]).ȱ

CompactionȱthatȱoccursȱinȱreservoirȬboundingȱshalesȱisȱoftenȱevidencedȱbyȱwellboreȱproblemsȱinȱoverburdenȱformationsȱduringȱandȱafterȱproduction,ȱsuchȱasȱcasingȱdamageȱandȱevenȱshearȱ(e.g.,ȱ[98]).ȱTheseȱstudiesȱandȱothersȱmatchingȱdisplacementȱmeasurementsȱandȱmathematicalȱmodelingȱofȱcausalityȱmechanisms,ȱconfirmȱtheȱimportanceȱofȱoilȱandȱgasȱfieldȱinducedȱsubsidenceȱandȱfaulting.ȱInȱsummary,ȱfaultȱreactivationȱandȱreservoirȱcompactionȱleadȱtoȱinducedȱsubsidenceȱatȱtheȱsurfaceȱthatȱ reflectsȱ both.ȱ Theȱ interactionȱ ofȱ theseȱ elevationȱ changeȱmechanismsȱwithȱ oilȱ andȱ gasȱ fieldȱdevelopmentȱisȱanȱimportantȱpartȱofȱlandȱlossȱinȱtheȱMRD.ȱ ȱ

5.ȱToxicȱImpactsȱofȱProducedȱWaterȱandȱSpilledȱOilȱ ȱ

Producedȱwaterȱ fromȱO&Gȱ fieldsȱ isȱbroughtȱ toȱ theȱsurfaceȱduringȱcrudeȱoilȱandȱnaturalȱgasȱextractionȱ and,ȱ priorȱ toȱ theȱ USEPAȱ banningȱ surfaceȱ dischargeȱ ofȱ producedȱ waterȱ inȱ 1992,ȱ anȱestimatedȱ2ȱmillionȱbarrelsȱperȱdayȱwereȱdischargedȱintoȱLouisianaȱcoastalȱwetlandsȱfromȱnearlyȱ700ȱsitesȱ[99].ȱItȱisȱbyȱfarȱtheȱlargestȱvolumeȱbyproductȱorȱwasteȱstreamȱassociatedȱwithȱO&Gȱextractionȱandȱisȱaboutȱ10ȱtimesȱmoreȱtoxicȱthanȱoilȱ[100].ȱTheȱfluidȱgenerallyȱincludesȱaȱmixtureȱofȱeitherȱliquidȱorȱgaseousȱhydrocarbons,ȱhighȱsalinityȱwater,ȱradioactiveȱmaterials,ȱdissolvedȱorȱsuspendedȱsolids,ȱsolidsȱsuchȱasȱsandȱorȱsilt,ȱandȱinjectedȱfluidsȱandȱadditivesȱassociatedȱwithȱexploration,ȱdrilling,ȱandȱproductionȱactivitiesȱ(Tableȱ2)ȱ[101,102].ȱ

Tableȱ2.ȱCommonȱcomponentsȱofȱproducedȱwaterȱresultingȱfromȱoilȱandȱgasȱproductionȱ[103].ȱ

Categoryȱ Constituentȱ

MetalsȱAluminum,ȱantimony,ȱarsenic,ȱbarium,ȱboron,ȱcadmium,ȱgold,ȱiron,ȱmercury,ȱchromium,ȱcopper,ȱlead,ȱzinc,ȱnickel,ȱplatinum,ȱsilver,ȱ

strontium,ȱtin,ȱmagnesium,ȱmolybdenum,ȱtitanium,ȱthallium,ȱvanadiumȱNaturallyȱoccurringȱradioactiveȱmaterialsȱ

RadiumȬ226,ȱradiumȬ228ȱ

Monocyclicȱaromaticȱhydrocarbonsȱ

Benzene,ȱbenzoicȱacid,ȱchlorobenzene,ȱdiȬnȬbutylȱphthalate,ȱtoluene,ȱethlybenzene,ȱisopropylbenzene,ȱnȬPropylbenzene,ȱpȬchloroȬmȬcresol,ȱ

xylenesȱPolycyclicȱaromaticȱ

hydrocarbonsȱAcenaphthene,ȱanthracene,ȱbenzo(a)anthracene,ȱcyrsene,ȱ

dibenzothiophenes,ȱfluoranthene,ȱflourene,ȱnapthalene,ȱbenzo(a)pyreneȱ


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Miscellaneousȱorganicȱchemicalsȱ

Phenols,ȱbis(2Ȭethylhexyl)phthalate,ȱoilȱandȱgreaseȱ

Miscellaneousȱotherȱcomponentsȱ

Calcium,ȱpotassium,ȱradon,ȱsodiumȱchloride,ȱtotalȱdissolvedȱsolids,ȱammonia,ȱbromides,ȱsulfates,ȱsulfidesȱ

Severalȱ factorsȱ determineȱ theȱ fateȱ andȱ effectsȱ ofȱ producedȱwatersȱ inȱ coastalȱ environmentsȱincludingȱ theȱ volumeȱ andȱ compositionȱ ofȱ theȱ dischargeȱ andȱ theȱ hydrologicȱ andȱ physicalȱcharacteristicsȱofȱtheȱreceivingȱenvironmentȱ[22,104].ȱInȱmanyȱcases,ȱoilȱfieldȱbrineȱwasȱdischargedȱdirectlyȱtoȱwetlandsȱandȱsurfaceȱwatersȱ[105].ȱEnergeticȱstormsȱcanȱmixȱtheȱwaterȱcolumnȱandȱadvectȱproducedȱwaterȱintoȱmarshesȱwhereȱitȱcanȱsignificantlyȱdamageȱvegetation.ȱSpillsȱmayȱalsoȱimpactȱwetlands.ȱInȱ[106]ȱaccidentalȱbrineȱspillsȱbetweenȱ1990ȱandȱ1998ȱwereȱstudied,ȱandȱaȱtotalȱofȱ567ȱbrineȱspillsȱwereȱreportedȱtoȱLDEQ.ȱInȱsitesȱwhereȱproducedȱwaterȱwasȱspilled,ȱacuteȱandȱchronicȱexposureȱaffectedȱ theȱ vegetation.ȱ Theȱ studyȱ authorȱ documentedȱ ecologicalȱ impactsȱ rangingȱ fromȱminorȱvegetationȱdamageȱtoȱtheȱdestructionȱofȱhundredsȱofȱhaȱofȱwetlands.ȱManyȱwetlandsȱwhereȱaȱsingleȱspillȱhadȱoccurredȱhadȱnotȱrecoveredȱupȱ toȱ10ȱyearsȱ laterȱandȱmostȱofȱ theȱwetlandsȱwithȱchronicȱexposureȱwereȱnoȱlongerȱvegetatedȱandȱsomeȱhadȱconvertedȱtoȱopenȱwater.ȱInȱ[105]ȱtheȱformationȱofȱnewȱpondsȱwhereȱproducedȱwaterȱwasȱbeingȱdischargedȱwasȱdocumentedȱandȱtheȱauthorsȱofȱ[23]ȱreportedȱthatȱhalfȱofȱtheȱSpartinaȱalternifloraȱexposedȱtoȱ120ȱmg/Lȱofȱoilȱandȱgrease,ȱwhichȱisȱtheȱnormȱforȱproducedȱwater,ȱdiedȱwithinȱ30ȱdays.ȱ

Salinityȱofȱproducedȱwaterȱrangesȱfromȱaȱfewȱpsuȱtoȱupȱtoȱ300ȱpsuȱ[21,22,102,103].ȱHighȱsalinityȱleadsȱ toȱ theȱdeathȱofȱmostȱplantsȱandȱhasȱbeenȱ linkedȱ toȱwetlandȱ lossȱ [105].ȱ InȱCameronȱParish,ȱLouisiana,ȱnorthȱofȱBlackȱLakeȱandȱtheȱHackberryȱO&Gȱfields,ȱthousandsȱofȱhaȱofȱsawgrassȱmarshȱwereȱkilledȱdueȱtoȱdischargeȱofȱproducedȱwaterȱandȱtheȱareaȱsubsequentlyȱconvertedȱtoȱopenȱwaterȱ[107,108].ȱNaturallyȱoccurringȱradioactiveȱmaterialȱ(NORM),ȱprimarilyȱradiumȬ226ȱandȱradiumȬ228,ȱisȱpresentȱ inȱmuchȱ ofȱ theȱproducedȱwaterȱ inȱ theȱGulfȱ ofȱMexicoȱ [109,110].ȱTheȱ authorsȱ ofȱ [104]ȱreportedȱtotalȱradiumȱactivitiesȱrangedȱfromȱ304ȱtoȱ2312ȱdpm/L.ȱ ȱ

Hydrocarbonsȱareȱalsoȱpresentȱinȱproducedȱwater,ȱbothȱinȱdissolvedȱandȱdispersedȱ(oilȱdroplets)ȱformȱthatȱcanȱinteractȱwithȱtheȱbenthicȱcommunityȱ[103].ȱDispersedȱoilsȱcanȱalsoȱriseȱtoȱtheȱsurfaceȱandȱinterfereȱwithȱtheȱtransferȱofȱoxygenȱfromȱtheȱatmosphereȱintoȱtheȱwater,ȱcoatȱmarineȱmammals,ȱbirdsȱ andȱ fish,ȱ andȱ haveȱ directȱ toxicȱ actionȱ onȱ someȱ organismsȱ [111].ȱWholeȱ effluentȱ toxicityȱassessmentsȱhaveȱreportedȱhighȱtoxicityȱlevelsȱofȱproducedȱwaterȱ[21,112].ȱProducedȱwaterȱhasȱbeenȱshownȱtoȱreduceȱabundanceȱofȱbenthicȱmacroinfaunalȱcommunitiesȱinȱwetlandsȱreceivingȱdischargeȱ[21,99,104,112]ȱoftenȱatȱdistancesȱofȱhundredsȱofȱmȱfromȱdischargeȱsources.ȱ[112].ȱTheȱpresenceȱofȱhighȱ concentrationsȱ ofȱ hydrocarbonsȱ inȱ sedimentsȱ nearȱ dischargeȱ sitesȱ indicatesȱ longȬtermȱaccumulationȱandȱresistanceȱtoȱdegradationȱ[21,22].ȱ

Inȱ[4]ȱtheȱauthorsȱreviewedȱtheȱecologicalȱimpactsȱofȱO&GȱdevelopmentȱonȱcoastalȱecosystemsȱinȱtheȱMississippiȱdelta.ȱOilȱspillsȱhaveȱgeneratedȱsignificantȱimpactsȱdueȱtoȱtheȱtoxicityȱofȱspilledȱoil.ȱEffectsȱonȱplantȱcommunitiesȱincludeȱdisruptionȱofȱplant–waterȱrelationships,ȱdirectȱimpactsȱtoȱplantȱmetabolism,ȱtoxicityȱtoȱlivingȱcells,ȱandȱreducedȱoxygenȱexchangeȱbetweenȱtheȱatmosphereȱandȱtheȱsoil.ȱEffectsȱonȱconsumersȱincludeȱgrowthȱinhibition,ȱreducedȱproduction,ȱalteredȱmetabolicȱsystems,ȱandȱbiomagnificationȱofȱhydrocarbonȱcompounds.ȱTheȱcombinationȱofȱtheseȱfactorsȱincreasesȱplantȱstressȱandȱplantȱdeath.ȱ

6.ȱInteractive,ȱCumulative,ȱandȱIndirectȱImpactsȱofȱOilȱandȱGasȱImpactsȱ

Eachȱ ofȱ theȱ threeȱ typesȱ ofȱ oilȱ andȱ gasȱ activityȱ (alterationȱ ofȱ surfaceȱ hydrology,ȱ inducedȱsubsidence,ȱandȱproductionȱofȱtoxicȱcontaminants)ȱcausesȱsignificantȱimpacts.ȱHowever,ȱwhenȱtheȱeffectsȱofȱallȱthreeȱactivitiesȱinteractȱinȱcumulativeȱandȱindirectȱways,ȱtheȱimpactsȱareȱmuchȱgreater.ȱ

InȱFigureȱ 16,ȱ theȱ impactsȱofȱ eachȱ typeȱofȱ activityȱ areȱ shownȱ separately.ȱTheȱdirectȱ effectȱofȱinducedȱsubsidenceȱisȱaȱlossȱofȱsurfaceȱelevationȱdueȱfaultȱactivationȱand/orȱcompactionȱofȱsubsurfaceȱsedimentsȱdueȱtoȱfluidȱremoval.ȱLossȱofȱsurfaceȱelevationȱleadsȱinȱturnȱtoȱstressedȱwetlandȱvegetation,ȱlowerȱproductivity,ȱandȱultimatelyȱvegetationȱdeathȱandȱwetlandȱloss.ȱ ȱ


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Surfaceȱ hydrologicȱ alterationȱ dueȱ toȱ canalsȱ andȱ spoilȱ banksȱ alsoȱ leadsȱ toȱ aȱ lossȱ ofȱ surfaceȱelevationȱdueȱ toȱ aȱ cascadingȱ seriesȱofȱ impactsȱ asȱ shownȱbyȱ theȱ relationshipsȱ inȱFigureȱ 16.ȱDeepȱstraightȱcanalsȱcauseȱtheȱdeteriorationȱofȱnaturalȱtidalȱchannelsȱandȱchangesȱinȱregionalȱhydrologyȱandȱsaltwaterȱintrusion.ȱSpoilȱbanksȱblockȱtidalȱfloodingȱofȱmarshesȱandȱleadȱtoȱincreasedȱinundationȱofȱmarshesȱasȱwellȱasȱreducedȱsedimentȱandȱnutrientȱinputȱtoȱmarshes.ȱTheseȱimpactsȱstressȱmarshesȱsoȱ thatȱ productivityȱ isȱ lowerȱ andȱ organicȱ soilȱ formationȱ isȱ reduced.ȱ Theȱ combinationȱ ofȱ lowerȱsedimentȱinputȱandȱlowerȱorganicȱsoilȱformationȱcausesȱhigherȱshallowȱsubsidenceȱandȱultimatelyȱtoȱvegetationȱdeath.ȱSaltwaterȱintrusionȱandȱvegetationȱdeathȱleadȱtoȱcollapseȱofȱtheȱsoilȱcolumnȱdueȱtoȱrapidȱdecompositionȱofȱsoilȱorganicȱmatter.ȱ ȱ

Toxicȱ impactsȱ areȱdueȱ toȱoilȱ spillsȱandȱproducedȱwaterȱdischargeȱwhichȱ containsȱveryȱhighȱsalinityȱbrinesȱandȱaȱvarietyȱofȱtoxicȱmaterials.ȱTheseȱstressȱvegetationȱandȱcauseȱwetlandȱmortalityȱandȱcollapseȱofȱmarshȱsoilsȱleadingȱtoȱlossȱofȱelevation.ȱ

Thus,ȱ allȱ threeȱ typesȱ ofȱ impactsȱ leadȱ toȱ stressedȱwetlandȱ vegetation,ȱ lossȱ ofȱ elevation,ȱ andȱvegetationȱdeath.ȱTheȱcumulativeȱandȱindirectȱimpactsȱareȱmuchȱgreaterȱthanȱforȱindividualȱimpactsȱactingȱindependently.ȱTheseȱinteractȱwithȱaȱrangeȱofȱenvironmentalȱforcingsȱsuchȱasȱlackȱofȱriverineȱinput,ȱseaȬlevelȱrise,ȱandȱhurricanesȱtoȱexacerbateȱwetlandȱlossȱevenȱfurther.ȱForȱexample,ȱwetlandȱlossȱinȱtheȱregionȱofȱtheȱcentralȱcoastȱimpactedȱbyȱAtchafalayaȱRiverȱdischargeȱisȱmuchȱlowerȱthanȱmostȱofȱtheȱrestȱofȱtheȱcoastȱevenȱinȱareasȱimpactedȱbyȱO&Gȱactivityȱ[74,113].ȱTheȱnetȱeffectȱisȱthatȱO&Gȱactivitiesȱmakeȱwetlandsȱmoreȱsusceptibleȱtoȱotherȱforcingsȱthatȱnegativelyȱaffectȱwetlands.ȱ


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Figureȱ16.ȱDiagramȱshowingȱ theȱ threeȱgeneralȱ typesȱofȱ impactsȱ fromȱoilȱandȱgasȱactivityȬinducedȱsubsidence,ȱtoxicityȱeffects,ȱandȱalteredȱsurfaceȱhydrologyȱdueȱtoȱcanalsȱandȱspoilȱbanks.ȱTheȱimpactsȱofȱtheseȱactivitiesȱareȱshownȱseparately,ȱandȱimpactsȱshownȱinȱredȱareȱcommonȱtoȱallȱthreeȱactivities.ȱAsȱreducedȱvegetationȱproductivity,ȱlossȱofȱelevation,ȱandȱvegetationȱdeathȱcanȱresultȱfromȱallȱthreeȱactivities,ȱthereȱareȱpervasiveȱcumulativeȱandȱindirectȱimpactsȱthatȱresultȱinȱoverallȱgreaterȱimpactsȱonȱcoastalȱecosystems,ȱespecially,ȱthatȱwouldȱresultȱfromȱtheȱimpactsȱactingȱseparately.ȱ

SuchȱcumulativeȱandȱindirectȱimpactsȱdueȱtoȱO&Gȱproductionȱareȱevidentȱwhenȱimagesȱofȱoilȱfieldsȱareȱviewedȱoverȱtime.ȱTheȱVeniceȱSaltȱDomeȱinȱPlaqueminesȱParishȱandȱtheȱBullyȱCampȱoilȱfieldȱinȱTerrebonneȱParishȱareȱjustȱtwoȱofȱhundredsȱofȱexamplesȱofȱwetlandȱdisappearanceȱoverȱtimeȱinȱcoastalȱLouisianaȱ(Figuresȱ17ȱandȱ18).ȱInȱtheseȱtwoȱfields,ȱpreȬoilȱandȱgasȱactivityȱmapsȱshowȱtheȱpresenceȱofȱsmallȱnaturalȱleveeȱridgesȱandȱextensiveȱunbrokenȱmarsh.ȱInȱbothȱfields,ȱtheȱ1950sȱmapsȱshowȱcanalsȱandȱspoilȱbanksȱbutȱwithoutȱsignificantȱmarshȱloss.ȱOverȱtime,ȱmarshȱlossȱexpandsȱtoȱcoverȱalmostȱtheȱentireȱareaȱofȱtheȱfieldȱandȱspoilȱbanksȱbeginȱtoȱdisappearȱasȱtheyȱsubsideȱbelowȱ


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waterȱ level.ȱTheȱwidespreadȱ lossȱofȱwetlandsȱ isȱdueȱ toȱsuchȱcumulativeȱandȱ interactingȱeffectsȱofȱsurfaceȱalterationsȱinȱhydrology,ȱinducedȱsubsidence,ȱandȱtoxicȱeffects.ȱ ȱ

ȱ

Figureȱ17.ȱImagesȱofȱhydrologicȱchangesȱandȱwetlandȱlossȱinȱtheȱVeniceȱfield,ȱPlaqueminesȱParish,ȱLouisianaȱoverȱtime.ȱThisȱoilȱandȱgasȱfieldȱhasȱbeenȱtermedȱtheȱ“wagonȱwheel”ȱbecauseȱofȱtheȱcircularȱcanalsȱandȱspoilȱbanksȱthatȱoutlineȱtheȱsaltȱdomeȱaroundȱwhichȱoilȱandȱgasȱcontainingȱformationsȱwereȱlocated.ȱNoteȱthatȱwetlandȱlossȱoccursȱbothȱinȱtheȱvicinityȱofȱtheȱcanalsȱasȱwellȱasȱthroughoutȱtheȱareaȱofȱtheȱfield.ȱInȱadditionȱtoȱwetlandȱloss,ȱmanyȱofȱtheȱspoilȱbanksȱhaveȱsubsidedȱbelowȱwaterȱlevelȱandȱareȱnoȱlongerȱvisible.ȱTheȱgreenȱhighlightedȱchannelsȱinȱtheȱ1940sȱareȱminorȱdistributaryȱridgesȱthatȱbothȱconveyedȱwaterȱandȱwereȱaȱbarrierȱtoȱhorizontalȱflowȱperpendicularȱtoȱtheseȱridges.ȱ(ImagesȱfromȱUSGSȱtopographicȱmapsȱ(lateȱ1940s)ȱandȱGoogleȱEarth).ȱ


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ȱFigureȱ18.ȱImagesȱofȱtheȱBullyȱCampȱoilȱandȱgasȱfieldȱoverȱtime.ȱTheȱyellowȱlineȱdenotesȱanȱownershipȱtractȱ inȱ theȱ fieldȱ andȱ redȱdotsȱ showȱ locationsȱofȱoilȱ andȱgasȱwells.ȱNoteȱ thatȱ landȱ lossȱhasȱbeenȱpervasiveȱoverȱtheȱgeneralȱareaȱofȱtheȱfield.ȱTheȱcentralȱwaterȱbodyȱinȱtheȱ1989ȱimageȱisȱoverȱanȱareaȱofȱsulfurȱproductionȱonȱtheȱtopȱofȱtheȱsaltȱdomeȱunderlyingȱthisȱfield.ȱTheȱnarrowȱblueȱlinesȱinȱtheȱ1935ȱmapȱareȱabandonedȱminorȱdistributaryȱridgesȱthatȱwereȱbreachedȱbyȱcanalsȱ(imagesȱfromȱ[76]).ȱ

7.ȱRestorationȱ

AȱwellȬdesignedȱrestorationȱplanȱshouldȱbeȱbasedȱonȱinformationȱaboutȱtheȱimpactsȱduringȱtheȱlifeȱcycleȱofȱO&Gȱfields.ȱRestorationȱofȱwetlandsȱlostȱdueȱtoȱO&GȱactivitiesȱwillȱinvolveȱaȱsynergisticȱapproachȱthatȱdealsȱwithȱtheȱdamageȱofȱO&Gȱimpactsȱandȱrebuildsȱaȱfunctioningȱcoastalȱwetlandȱsystem.ȱAȱ centralȱ objectiveȱ inȱ restorationȱ isȱ rebuildingȱ elevationȱdueȱ toȱ bothȱ surfaceȱ subsidenceȱcausedȱbyȱalteredȱhydrologyȱandȱ subsurfaceȱ inducedȱ subsidence.ȱSubsurfaceȱ inducedȱ subsidenceȱcannotȱbeȱreversed,ȱsoȱsedimentȱmustȱbeȱaddedȱatȱtheȱsurfaceȱtoȱoffsetȱbothȱsubsurfaceȱandȱsurfaceȱsubsidence.ȱ Optionsȱ forȱ restorationȱ includeȱ (1)ȱ marshȱ creationȱ andȱ restorationȱ usingȱ dredgedȱsedimentsȱ [114–117];ȱ (2)ȱ fullȱuseȱ ofȱ allȱ availableȱ sedimentȱ resourcesȱ includingȱMississippiȱRiver,ȱGIWW,ȱandȱsedimentsȱresuspendedȱduringȱstormsȱ[118,119];ȱandȱ(3)ȱhydrologicȱrestorationȱsuchȱasȱbackfillingȱcanalsȱandȱspoilȱbankȱmanagement,ȱandȱrestorationȱofȱhydrologicȱnetworksȱ [119–123].ȱRebuildingȱnaturalȱleveeȱridgesȱthatȱhaveȱbeenȱseveredȱbyȱcanalsȱcanȱhelpȱrestoreȱnaturalȱhydrologyȱtoȱ preventȱ saltwaterȱ intrusionȱ andȱ reduceȱ increasedȱ hydrologicȱ energyȱ causedȱ byȱmoreȱ directȱconnectionsȱbetweenȱinteriorȱpartsȱofȱtheȱdeltaȱandȱtheȱGulfȱofȱMexico.ȱ

Elevationȱcanȱbeȱbuiltȱupȱbyȱaddingȱdredgedȱmaterialȱtoȱshallowȱwaterȱbodies,ȱsomeȱthatȱwereȱpreviouslyȱwetlands,ȱtoȱanȱelevationȱthatȱwillȱsupportȱmarshȱvegetationȱ[115,124,125].ȱRestorationȱofȱopenȱwaterȱ andȱdegradedȱwetlandȱ areasȱ toȱ sustainableȱmarshȱ areȱ ofȱ tremendousȱ importanceȱ inȱcoastalȱ Louisiana.ȱ Theȱ 2017ȱ CoastalȱMasterȱ Planȱ (CMP)ȱ forȱ restorationȱ ofȱ theȱMississippiȱ deltaȱdedicatesȱnearlyȱ$18ȱbillionȱtoȱmarshȱcreationȱ(theȱlargestȱinvestmentȱinȱaȱsingleȱtypeȱofȱrestorationȱ


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project)ȱandȱmanyȱofȱthoseȱprojectsȱincludeȱbothȱaȱshortȬtermȱandȱaȱlongȬtermȱphaseȱ[126].ȱTheȱshortȬtermȱphaseȱfocusesȱonȱimmediateȱactionsȱneededȱtoȱprotectȱvulnerableȱmarshesȱfromȱtheȱproximalȱcausesȱ ofȱ lossȱ (saltwaterȱ intrusion,ȱ erosion,ȱ andȱ otherȱ consequencesȱ ofȱ significantȱ hydrologicȱmodifications)ȱusingȱaȱcombinationȱofȱrestorationȱtechniquesȱ(especiallyȱhydrologicȱrestorationȱandȱmarshȱ creationȱ usingȱ dredgedȱ sediments).ȱ Successfulȱ implementationȱ ofȱ shortȬtermȱ strategiesȱreducesȱratesȱofȱwetlandsȱlossȱandȱprovidesȱtheȱfoundationȱforȱlongerȬtermȱstrategies.ȱTheȱlongȬtermȱphaseȱ focusesȱ onȱwetlandsȱ gainsȱ throughȱMississippiȱRiverȱ sedimentȱ diversionsȱ andȱ captureȱ ofȱsedimentsȱ advectedȱ overȱ theȱmarshȱ surface,ȱwithȱ theȱ intentȱ ofȱ encouragingȱ developmentȱ ofȱ aȱsustainableȱwetlandȱecosystemȱ(https://www.lacoast.gov/new/about/Basin_data/te/Default.aspx).ȱ

Introductionȱ ofȱ sediments,ȱ throughȱ placementȱ ofȱ fillȱmaterialȱ and/orȱ sprayȱ dredging,ȱ isȱ aȱnecessaryȱcomponentȱofȱmarshȱrestorationȱ inȱdegradedȱO&Gȱfieldsȱandȱsedimentȱcanȱbeȱpumpedȱlongȱdistances,ȱasȱisȱtheȱcaseȱforȱmanyȱ2017ȱCMPȱprojectsȱ[127–132].ȱContainmentȱdikesȱareȱutilizedȱtoȱ confineȱ unconsolidatedȱmaterialȱ untilȱ itȱ settlesȱ andȱ dewatersȱ [120].ȱ Thenȱ theseȱ dikesȱ canȱ beȱdegradedȱorȱgappedȱtoȱtheȱsameȱelevationȱasȱtheȱmarshȱplatformȱinȱorderȱtoȱallowȱwaterȱexchangeȱandȱmarshȱ drainage,ȱ toȱ improveȱ productivityȱ andȱ aeration,ȱ andȱ increaseȱ captureȱ ofȱ suspendedȱsedimentsȱthatȱareȱadvectedȱoverȱtheȱmarshȱsurface.ȱ ȱ

Sedimentȱadditionȱ increasesȱmarshȱ surfaceȱelevation,ȱ thusȱ reducingȱ floodȱ stressȱ toȱ theȱplantȱcommunity.ȱTheȱauthorsȱofȱ[114]ȱshowedȱthatȱraisingȱtheȱsurfaceȱofȱaȱdeterioratingȱSpartinaȱalternifloraȱsaltȱmarshȱ byȱ 10ȱ cmȱusingȱdredgeȱ spoilȱ resultedȱ inȱ aȱ twofoldȱ increaseȱ inȱ abovegroundȱ biomassȱproductionȱafterȱtheȱsecondȱgrowingȱseason.ȱInȱ[115]ȱitȱwasȱfoundȱthatȱincreasedȱelevationȱthroughȱtheȱdepositionȱ ofȱ aȱ 2ȱ cmȱ layerȱ ofȱdredgedȱmaterialȱ inȱ aȱdeterioratedȱLouisianaȱmarshȱ increasedȱpercentȱcoverȱofȱS.ȱalternifloraȱthreeȬfoldȱwithinȱoneȱyear.ȱTheȱauthorsȱofȱ[125]ȱstudiedȱdeadȱmarshesȱnearȱLeevilleȱ thatȱwereȱ restoredȱusingȱdredgedȱmaterialȱandȱ foundȱ thatȱsedimentȬslurryȱadditionȱincreasedȱ theȱ elevationȱ ofȱ theȱ marshȱ surfaceȱ andȱ alleviatedȱ stressȱ associatedȱ withȱ excessiveȱinundationȱandȱhighȱsalinity.ȱPrimaryȱproductionȱwasȱhighestȱatȱelevationsȱrangingȱfromȱ29ȱtoȱ36ȱcmȱNAVDȱ88ȱ (12–20ȱcmȱaboveȱambientȱmarsh),ȱandȱdecreasedȱatȱelevationsȱaboveȱ36ȱcmȱNAVDȱ88,ȱwhereȱ primaryȱ productionȱ wasȱ limitedȱ byȱ insufficientȱ floodingȱ andȱ lowȱ nutrientȱ availability.ȱSedimentȱ subsidyȱ increasesȱ soilȱmineralȱmatter,ȱ soilȱ fertility,ȱ andȱmarshȱ elevation,ȱ andȱ therebyȱreducesȱnutrientȱdeficiency,ȱflooding,ȱandȱ interstitialȱsulfideȱstresses,ȱgeneratingȱaȱmoreȱfavorableȱenvironmentȱforȱplantȱgrowthȱandȱpotentially,ȱmarshȱsustainabilityȱ[116,117].ȱ ȱ

Afterȱcontainmentȱdikesȱareȱgapped,ȱrestoredȱmarshȱwillȱhaveȱconnectivityȱwithȱsurroundingȱecosystemȱandȱplantsȱwillȱnaturallyȱrecruitȱtoȱtheȱareaȱorȱtheyȱcanȱbeȱplanted.ȱAlthoughȱtheȱcreatedȱmarshȱwillȱbeȱinitiallyȱhigherȱthanȱsurroundingȱmarshes,ȱitȱwillȱsettleȱandȱhaveȱaȱhigherȱbulkȱdensity.ȱItȱ isȱ likelyȱ thatȱ theseȱ createdȱmarshesȱwillȱhaveȱaȱhigherȱproductivityȱandȱproductionȱofȱorganicȱmatterȱ thanȱ surroundingȱmarshes.ȱ Theȱ plantȱ speciesȱ richnessȱ shouldȱ theȱ sameȱ asȱ surroundingȱmarshes,ȱwhichȱisȱnotȱveryȱhighȱinȱbrackishȱandȱsaltȱmarshesȱofȱcoastalȱLouisianaȱcomparedȱtoȱfreshȱmarshes.ȱPlantȱdiversityȱandȱsoilȱorganicȱmatterȱcontentȱareȱhigherȱ inȱbrackishȱmarshȱthanȱ inȱsaltȱmarsh.ȱ Brackishȱ marshȱ isȱ typicallyȱ dominatedȱ byȱ Spartinaȱ patensȱ (marshhayȱ cordgrass).ȱ Otherȱsignificantȱ associatedȱ speciesȱ includeȱ Distichlisȱ spicataȱ (saltȱ grass),ȱ Schoenoplectusȱ olneyiȱ (threeȬcorneredȱ grass),ȱ S.ȱ robustusȱ (saltȱ marshȱ bulrush),ȱ Eleocharisȱ parvulaȱ (dwarfȱ spikesedge),ȱ Ruppiaȱmaritimaȱ(widgeonȱgrass),ȱPaspalumȱvaginatumȱ(seashoreȱpaspalum),ȱJuncusȱroemerianusȱ(blackȱrush),ȱBacopaȱmonnieriȱ (coastalȱwaterȱhyssop),ȱS.ȱ alternifloraȱ (smoothȱ cordgrass),ȱandȱS.ȱ cynosuroidesȱ (bigȱcordgrass)ȱ[130].ȱSaltȱmarshȱhasȱtheȱleastȱplantȱdiversityȱofȱanyȱmarshȱtype.ȱTheȱcommunityȱisȱoftenȱtotallyȱdominatedȱbyȱsmoothȱcordgrass.ȱSignificantȱassociateȱspeciesȱincludesȱmarshhayȱcordgrass,ȱsaltȱgrass,ȱblackȱrush,ȱandȱBatisȱmaritimaȱ(saltȱwort).ȱ

Aȱtidalȱnetworkȱneedsȱtoȱdevelopȱinȱtheȱrestoredȱmarsh.ȱAllȱrestorationȱplansȱneedȱaȱcomponentȱthatȱfocusesȱonȱnaturalȱhydrologicalȱfunctioning.ȱAȱlargeȬscaleȱrestorationȱprojectȱonȱDelawareȱBayȱindicatedȱthatȱifȱaȱfewȱprimaryȱchannelsȱwereȱdredged,ȱtheȱsystemȱwouldȱnaturallyȱthenȱdevelopȱaȱfullȱtidalȱchannelȱnetworkȱ[130,131].ȱTheȱprojectȱinvolvedȱrestorationȱofȱtidalȱfloodingȱbyȱbreechingȱdikesȱ aroundȱ formerlyȱdikedȱ saltȬhayȱ farmȱ andȱ reȬexcavationȱ ofȱ tidalȱ creeks.ȱHydrologicȱdesignȱoccurredȱ inȱ aȱ “selfȬdesign”ȱ fashionȱ afterȱ onlyȱ initialȱ cutsȱ byȱ constructionȱ ofȱ theȱ largestȱ (classȱ 1)ȱchannels.ȱ ȱ


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Spoilȱbankȱandȱcanalȱmanagementȱshouldȱbeȱpartȱofȱaȱrestorationȱplan.ȱSomeȱcanalsȱshouldȱbeȱbackfilledȱasȱmuchȱasȱpossibleȱbyȱpushingȱspoilȱbanksȱbackȱintoȱcanals.ȱAsȱspoilȱbanksȱhaveȱsettledȱandȱorganicȱmatterȱhasȱdecomposed,ȱcanalsȱcannotȱbeȱfullyȱfilledȱinȱusingȱmaterialȱfromȱspoilȱbanks.ȱThus,ȱdredgedȱmaterialȱwillȱhaveȱtoȱbeȱusedȱtoȱfullyȱfillȱcanals.ȱInȱsomeȱcases,ȱspoilȱbanksȱshouldȱbeȱleftȱinȱplaceȱtoȱprotectȱremainingȱmarshesȱfromȱwaveȱattackȱ(seeȱFigureȱ13).ȱ

Afterȱ theȱmarshȱ isȱ restoredȱ andȱ naturalȱ hydrologyȱ hasȱ beenȱ reȬestablished,ȱ fullȱ useȱ ofȱ allȱavailableȱ sedimentsȱ shouldȱ beȱ incorporatedȱ intoȱ theȱ restorationȱ design.ȱ Importantȱ sourcesȱ ofȱsedimentsȱincludeȱMississippi/AtchafalayaȱRiversȱasȱwellȱasȱsmallerȱrivers,ȱsedimentȱdiversions,ȱtheȱGulfȱ IntracoastalȱWaterway,ȱ andȱ sedimentsȱ resuspendedȱ byȱ stormsȱ [118].ȱWaterȱ sourcesȱ withȱappreciableȱlevelsȱofȱnutrientsȱshouldȱbeȱusedȱwhereȱpossibleȱtoȱenhanceȱmarshȱproductionȱincludingȱuplandȱrunoff,ȱagriculturalȱdrainage,ȱandȱtreatedȱmunicipalȱeffluentȱ[133,134].ȱ

Whenȱ planningȱ restorationȱ priorities,ȱ considerationȱ shouldȱ beȱ givenȱ toȱ theȱ moreȱ stableȱunderlyingȱgeologicȱframeworkȱchoices,ȱandȱavoidanceȱofȱthoseȱareasȱstillȱinȱtheȱactivelyȱdegradingȱpartȱofȱtheȱcycle.ȱExamplesȱincludeȱmarshȱconstructionȱonȱtheȱmoreȱstableȱupthrownȱsideȱofȱaȱfault,ȱratherȱthanȱtheȱsubsidenceȱcompactionȱandȱfaultȱaffectedȱO&Gȱfieldȱonȱtheȱdownthrownȱside.ȱTheȱauthorsȱofȱ [14]ȱdiscussedȱ theȱroleȱofȱ faultingȱ inȱwetlandȱ lossȱ inȱ theȱMississippiȱdelta.ȱ Inȱ [135]ȱ theȱauthorsȱpointedȱtoȱfailedȱrestorationȱprojectsȱwhereȱfaultingȱhasȱnotȱbeenȱconsidered.ȱThus,ȱtakingȱintoȱconsiderationȱunderlyingȱgeologyȱcanȱleadȱtoȱmoreȱsuccessfulȱandȱsustainableȱrestoration.ȱ ȱ

Decontaminationȱofȱrestoredȱsitesȱisȱanȱintegralȱpartȱofȱrestoration.ȱInȱmanyȱcases,ȱtoxinsȱcanȱbeȱburiedȱ inȱ placeȱ butȱ inȱ someȱ instancesȱ theȱ contaminantsȱ haveȱ toȱ beȱ removedȱ [4].ȱ Inȱ additionȱ toȱenvironmentalȱ impactsȱassociatedȱwithȱ landȱ lossȱ fromȱO&Gȱproductionȱoperations,ȱ thereȱoftenȱ isȱenvironmentalȱdamageȱtoȱsoilȱandȱgroundwaterȱcontaminationȱthatȱmayȱhaveȱoccurredȱfromȱtheseȱsameȱtypesȱofȱO&Gȱoperations.ȱTheseȱdamagesȱincludeȱcontaminationȱtoȱsoils,ȱgroundwater,ȱandȱinȱsomeȱcasesȱundergroundȱsourcesȱofȱdrinkingȱwater.ȱTheseȱtypesȱofȱdamagesȱrequireȱextensiveȱtestingȱandȱtheȱrestorationȱincludesȱsoilȱtreatmentȱorȱremovalȱandȱtheȱcleanupȱofȱcontaminatedȱfreshwaterȱzones.ȱDealingȱwithȱcontaminationȱcanȱinvolveȱremovalȱofȱtheȱsurfaceȱwaste,ȱexcavationȱofȱ‘hotȱspots’ȱofȱ concentratedȱpollutionȱ (chemicalsȱ ofȱ concern,ȱCOC)ȱ followedȱ byȱ treatmentȱ andȱdisposal,ȱ andȱpumpingȱandȱtreatmentȱofȱcontaminatedȱgroundwaterȱfollowedȱbyȱtreatmentȱorȱsubsurfaceȱinjection.ȱTheȱgoalȱofȱtheȱremediationȱeffortȱisȱtoȱreturnȱtheȱsoilȱandȱgroundwaterȱtoȱagreedȬuponȱstandardsȱsuchȱasȱbackgroundȱ soilȱ standardsȱ containedȱ inȱ theȱLa.ȱDNR/OCȱ regulationsȱknownȱasȱ29Bȱ (theȱsectionȱofȱtheȱrules)ȱandȱtheȱLa.ȱDEQȱRECAPȱ(RiskȱEvaluation/CorrectiveȱActionȱProgram)ȱforȱbothȱsoilȱandȱgroundwater.ȱAȱmixȱofȱtheȱstandardsȱisȱsometimesȱused.ȱTheȱtermȱ ‘agreedȱupon’ȱ isȱusedȱbecauseȱ cleanupȱ isȱ usuallyȱ doneȱ inȱ theȱ contextȱ ofȱ aȱ legalȱ actionȱ withȱ theȱ involvementȱ ofȱ theȱlandownerȬplaintiff,ȱtheȱoilȱcompanies(s),ȱDNR,ȱDEQ,ȱandȱtheȱCourt.ȱTheȱDNRȱ29Bȱ(Titleȱ43,ȱPartȱXIX,ȱstatewideȱorderȱ29B)ȱstandardsȱwere/areȱheavilyȱinfluencedȱbyȱtheȱoilȱandȱgasȱexplorationȱandȱproductionȱindustryȱ(E&P)ȱwhileȱtheȱDEQȱRECAPȱstandardsȱareȱbasedȱonȱriskȱscienceȱ(LACȱ33,ȱ2003;ȱhttps://www.deq.louisiana.gov/assets/docs/Land/RECAP/RECAPfinal.pdf).ȱ RECAPȱ providesȱnumericalȱscreeningȱstandardsȱforȱmanyȱchemicalsȱinȱsoilȱandȱgroundwaterȱandȱthreeȱmanagementȱoptions.ȱInȱmanyȱcases,ȱaddressingȱlandȱlossȱandȱenvironmentalȱcleanupȱmustȱbeȱdoneȱatȱtheȱsameȱtimeȱtoȱfullyȱrestoreȱtheȱland.ȱ

InȱplanningȱforȱrestorationȱofȱdegradedȱwetlandsȱinȱO&Gȱfields,ȱthereȱshouldȱbeȱcoordinationȱwithȱotherȱprojects.ȱForȱexample,ȱbeneficialȱuseȱofȱdredgedȱsediments,ȱwhereȱavailable,ȱcanȱbeȱusedȱtoȱraiseȱelevation.ȱThereȱareȱnumerousȱwetlandȱrestorationȱprojectsȱtakingȱplaceȱinȱtheȱMississippiȱDelta.ȱ Theseȱ includeȱ marshȱ creation,ȱ riverȱ diversions,ȱ hydrologicȱ restoration,ȱ barrierȱ islandȱrestoration,ȱrebuildingȱofȱdistributaryȱridges,ȱandȱshorelineȱprotectionȱ[126,136].ȱRestorationȱofȱtheȱimpactsȱofȱO&Gȱactivitiesȱinvolvesȱtoȱaȱlessorȱorȱgreaterȱdegreeȱallȱofȱtheseȱactivities.ȱForȱexample,ȱwhereȱ sedimentȱ diversionsȱ areȱ plannedȱ inȱ theȱ vicinityȱ ofȱ anȱO&Gȱ fieldȱ thatȱ isȱ beingȱ restored,ȱmaximumȱuseȱofȱdivertedȱsedimentsȱshouldȱbeȱaȱgoalȱofȱtheȱproject.ȱAsȱnotedȱabove,ȱbeneficialȱuseȱofȱsedimentsȱdredgedȱforȱotherȱactivitiesȱsuchȱasȱnavigationȱcanalȱmaintenanceȱshouldȱbeȱconsideredȱforȱmarshȱcreationȱ inȱrestoringȱwetlandsȱdegradedȱbyȱO&Gȱactivities.ȱHydrologicȱrestorationȱandȱnaturalȱleveeȱrestorationȱinȱtheȱvicinityȱofȱaȱrestorationȱprojectȱinȱanȱO&Gȱfieldȱshouldȱbeȱdoneȱinȱaȱ


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wayȱthatȱcomplimentsȱtheȱlargerȱefforts.ȱInȱthisȱway,ȱtheȱrestorationȱofȱandȱO&Gȱfieldȱcanȱbeȱdoneȱtoȱincreaseȱbenefitsȱoverȱaȱlargerȱarea.ȱ

8.ȱSummaryȱandȱConclusionsȱ

Oilȱ andȱ gasȱ activityȱ hasȱ beenȱ pervasiveȱ inȱ theȱMississippiȱ deltaȱ andȱ bothȱ productionȱ andȱenvironmentalȱimpactsȱfollowȱaȱpredictableȱlifeȱcycle.ȱThereȱareȱhundredsȱofȱO&GȱfieldsȱinȱcoastalȱLouisiana,ȱ asȱwellȱ asȱ aȱdenseȱ networkȱ ofȱ canalsȱ associatedȱwithȱdrillingȱ access,ȱ navigation,ȱ andȱpipelines.ȱTheȱproductionȱhistoryȱforȱindividualȱfieldsȱcanȱ lastȱ40–60ȱyearsȱwithȱproductionȱrisingȱrapidlyȱtoȱaȱpeakȱaroundȱ1970ȱandȱthenȱdeclining.ȱSinceȱmostȱdrillingȱstartedȱinȱtheȱ1940sȱandȱ1950s,ȱmostȱwellsȱareȱnoȱlongerȱproducingȱorȱareȱinȱtheȱfinalȱstagesȱofȱproductionȱandȱthisȱcycleȱconclusionȱholdsȱtrueȱforȱaggregateȱMRDȱproduction.ȱMostȱfieldsȱhadȱveryȱlowȱlevelsȱofȱproductionȱbyȱtheȱ2000s.ȱProducedȱwaterȱgenerallyȱlaggedȱO&GȱproductionȱandȱwasȱgenerallyȱhigherȱduringȱdecliningȱO&Gȱproduction.ȱ

Oilȱandȱgasȱactivitiesȱhaveȱcontributedȱinȱthreeȱmajorȱwaysȱtoȱenvironmentalȱimpactsȱonȱcoastalȱecosystemsȱandȱspecificallyȱ toȱwetlandȱ loss.ȱTheseȱ includeȱalterationȱofȱsurfaceȱhydrologyȱdueȱ toȱcanalȱ dredgingȱ andȱ spoilȱ placement,ȱ inducedȱ subsidenceȱ andȱ faultȱ reȬactivationȱ dueȱ toȱ fluidsȱwithdrawal,ȱandȱtoxicȱstressȱdueȱtoȱpollutionȱbyȱspilledȱoilȱandȱproducedȱwater.ȱWetlandȱlossȱdueȱtoȱO&Gȱgasȱactivityȱisȱinitiallyȱdueȱmainlyȱtoȱdirectȱimpactsȱofȱcanalȱdredgingȱandȱspoilȱplacement,ȱbutȱgrowsȱoverȱtimeȱdueȱtoȱcumulativeȱandȱinteractiveȱeffects.ȱThisȱwetlandȱlossȱthenȱgrowsȱoverȱtimeȱtoȱencompassȱmuchȱ ofȱ theȱ fieldȱ andȱ adjacentȱ areas.ȱNetworksȱ ofȱ interconnectedȱ canalsȱ formȱ newȱpatternsȱ ofȱwaterȱ flowȱ andȱ oftenȱ leadȱ toȱ saltwaterȱ intrusion.ȱ Interestingly,ȱ spoilȱ banksȱ areȱ notȱnecessarilyȱ aȱpermanentȱ landscapeȱ featureȱ andȱhaveȱ aȱ lifeȱ cycleȱofȱ theirȱown.ȱTheyȱ subsideȱ andȱcompactȱoverȱtimeȱandȱaȱquarterȱtoȱaȱthirdȱofȱspoilȱbanksȱlikelyȱhaveȱnoȱsubaerialȱexpression.ȱ

FluidȱwithdrawalȱfromȱO&Gȱformationsȱleadsȱtoȱinducedȱsubsidenceȱandȱfaultȱactivationȱ[91].ȱInducedȱsubsidenceȱoccursȱinȱtwoȱphases.ȱWithdrawalȱofȱO&Gȱandȱproducedȱwaterȱinduceȱreservoirȱcompactionȱresultingȱinȱaȱreductionȱofȱreservoirȱthickness.ȱAȱslowȱdrainageȱofȱporeȱpressureȱinȱtheȱboundingȱ shaleȱ mainlyȱ dueȱ toȱ waterȱ pumpingȱ inducesȱ timeȬdelayedȱ shaleȱ compactionȱ andȱsubsidenceȱcanȱcontinueȱforȱdecadesȱafterȱmostȱO&Gȱhasȱbeenȱproduced.ȱThisȱresultsȱinȱsubsidenceȱoverȱmuchȱofȱtheȱoilȱfieldsȱthatȱcanȱbeȱgreaterȱthanȱsurfaceȱsubsidenceȱdueȱtoȱalteredȱhydrology.ȱ

ProducedȱwaterȱfromȱO&GȱfieldsȱisȱwaterȱbroughtȱtoȱtheȱsurfaceȱduringȱO&Gȱextractionȱandȱgenerallyȱincludesȱaȱmixtureȱofȱeitherȱliquidȱorȱgaseousȱhydrocarbons,ȱhighȱsalinityȱproducedȱwater,ȱdissolvedȱorȱsuspendedȱsolids,ȱproducedȱsolidsȱsuchȱasȱsandȱorȱsilt,ȱandȱinjectedȱfluidsȱandȱadditivesȱassociatedȱwithȱexplorationȱandȱproductionȱactivities.ȱProducedȱwaterȱhasȱbeenȱshownȱtoȱbeȱtoxicȱtoȱmanyȱestuarineȱorganismsȱincludingȱvegetationȱandȱconsumers.ȱSpilledȱoilȱhasȱbeenȱshownȱtoȱhaveȱlethalȱandȱsubȬlethalȱeffectsȱofȱaȱwideȱrangeȱofȱestuarineȱorganisms.ȱTheȱthreeȱmainȱtypesȱofȱimpactȱofȱO&Gȱactivitiesȱactȱinȱcumulative,ȱsynergistic,ȱandȱindirectȱwaysȱthatȱleadȱtoȱgreaterȱoverallȱimpact.ȱRestorationȱofȱwetlandsȱlostȱdueȱtoȱO&GȱactivitiesȱwillȱinvolveȱaȱsynergisticȱapproachȱthatȱdealsȱwithȱtheȱdamageȱofȱO&Gȱimpactsȱandȱrebuildsȱaȱfunctioningȱcoastalȱwetlandȱsystem.ȱ

Restorationȱ shouldȱ beȱ theȱ finalȱ stageȱ inȱ theȱ lifeȱ cycleȱ ofȱO&Gȱ fields.ȱAȱ centralȱ objectiveȱ ofȱrestorationȱisȱrestoringȱlostȱelevation.ȱOptionsȱforȱrestorationȱincludeȱmarshȱcreationȱandȱrestorationȱusingȱdredgedȱsediments,ȱfullȱuseȱofȱallȱavailableȱsedimentȱresources,ȱandȱhydrologicȱrestoration.ȱDecontaminationȱofȱrestoredȱsitesȱisȱanȱintegralȱpartȱofȱrestoration.ȱ ȱ

AuthorȱContributions:ȱAllȱauthorsȱcontributedȱtoȱtheȱwritingȱofȱthisȱreviewȱmanuscript.ȱAllȱauthorsȱhaveȱreadȱandȱagreedȱtoȱtheȱpublishedȱversionȱofȱtheȱmanuscript.ȱ

Funding:ȱThisȱresearchȱdidȱnotȱreceiveȱanyȱspecificȱgrantȱfromȱfundingȱagenciesȱinȱtheȱpublic,ȱcommercial,ȱorȱnotȬforȬprofitȱsectors.ȱ

Conflictȱ ofȱ Interest:ȱ J.W.D.,ȱH.C.C.,ȱR.G.H.,ȱ andȱC.R.N.ȱ stateȱ thatȱ theyȱ areȱ engagedȱ asȱ expertsȱ inȱ lawsuitsȱregardingȱ theȱ environmentalȱ impactsȱofȱoilȱ andȱgasȱ activityȱonȱ coastalȱ ecosystems.ȱNoȱ fundingȱ fromȱ theseȱactivitiesȱwasȱusedȱforȱtheȱpreparationȱofȱthisȱpaper.ȱ� ȱ


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