Peatland Restoration Guide Site Preparation and Rewetting

Peatland Restoration Guide Site Preparation and Rewetting

François Quinty, Marie-Claire LeBlanc and Line Rochefort

2 Site Preparation and Rewetting

Photo credits

Marie-Claire LeBlanc: Cover image, Fig. 1, Fig. 3, Fig. 5, Fig. 6, Fig. 8; François Quinty: Fig. 2; Flor Salvador: Fig. 9; Pete Whittington : Back cover.

This document should be cited as followsQuinty, F., M.-C. LeBlanc and L. Rochefort. 2020. Peatland Restoration Guide – Site Preparation and Rewetting. PERG, CSPMA and APTHQ. Québec, Québec.

Published jointly by

With the financial assistance of


TABLE OF CONTENTS Introduction 4

Moss Layer Transfer Technique 4

Site Preparation 5

RefreshingandReprofilingtheSurface 6

WhyRefreshandReprofile 6

HowtoRefreshandReprofile 6

WhenNottoRefreshandReprofile 7

ShouldDrainageDitchesBeFilled? 7

ControllingRunoffandImprovingWaterDistribution 8

TypesofDikes 8

DikeConstruction 10

Re-establishingConnectivitybetweentheRestoredPeatland andtheAdjacentEnvironment 12

ReducingForestDensity 13

RemovingtheEmbankment 14

RestructuringtheSlope 14

SituationstoAvoidandProblemsEncounteredduring Site Preparation 15

Synthesis of the Site Preparation Options 16

DrainageDitchBlocking 18

BuildingDams 18

SecondaryDitches 18

PrimaryDitches 20

FillingDitches 21

WhentoBlockDrainage 22

Resources,TimeandCosts 22

Summary 23


INTRODUCTIONThisbookletinthePeatlandRestorationGuideserieshasbeenpreparedtomakeavailablenew approaches to site preparation and rewetting1thathavebeendevelopedsincethe2003publicationofthePeatland Restoration Guide, Second Edition.2Itisintendedmainly forthehorticulturalpeatindustry,butmayalsobeusefulforthoseinterestedinrestoringpeatlandsthathavebeendrainedandwherethesurfaceislargelybarepeat.Itisanupdateofthe2003guidesectioncoveringsitepreparationanddrainageditchblocking(pp.25to35andpp.60to62oftheEnglishversion).

ThisbookletbeginswithabriefreviewoftheMossLayerTransferTechnique.Itthen describeshowtopreparethesite,managewaterflowandretentionbybuildingdikes(alsoknownasberms),makesuretherestoredsectorisconnectedtoadjacentlandandrewetthesitethroughditchblocking.Thetimeandresourcesrequiredforeachsteparealsodescribed.

Rewettingisacriticalsuccessfactorinpeatlandrestoration,andre-establishingan appropriatehydrologicalregimeisoneofthemainobjectivestoreachovertheshortterm.RewettingtechniqueshaveevolvedgreatlysincethepublicationofthePeatland Restoration Guide, Second Edition.ThePeatlandEcologyResearchGroup(PERG,UniversitéLaval)alsopublishedin2011aguide3thatdescribesindetailthevarioustechniquesusedtoblockditches,basedontheirsize,aswellastofilldrainageditchesandcuttrees,twoothermeasuresthatsupportrewetting.

MOSS LAYER TRANSFER TECHNIQUETheMossLayerTransferTechnique(MLTT)developedbythePERGfortherestorationofpeatlands(bogs,poorfensandmoderate-richfens)isbasedonactivereintroductionofpeatlandplantspeciescombinedwithrewettingthroughhydrologicalmanagement.ThistechniquehasbeenusedinoveronehundredrestorationprojectsinCanadaaswellasinmanyothercountries.Itmakesitpossibletobringbacktotherestoredsiteover80%ofthespeciespresentintheplantmaterialcollectedfromadonorsite,anditlimitsnon-peatlandplantspeciestoonly3to6%.Inaddition,long-termmonitoringofthevegetation(morethan10years)showsaprogressivedecreaseintheseatypicalspeciesasthemosscarpetdeve-lops.AstudybyPERGincollaborationwithresearchers

1 For the purposes of this document, “rewetting” means the actions taken to re-establish the original hydrological conditions, which are characterized by a water table located near the surface, with limited variations in level. 2 Quinty, F. and L. Rochefort. 2003. PeatlandRestorationGuide,2nd edition. Canadian Sphagnum Peat Moss Association and New Brunswick Department of Natural Resources and Energy. Québec, Québec.3 Landry, J. and L. Rochefort. 2012. The Drainage of Peatlands: Impacts and Rewetting Techniques. Peatland Ecology Research Group, Université Laval, Québec, Québec.


atMcGillUniversitydemonstratedbeyondalldoubtthatapeatlandwasonceagainabletocaptureandsequestercarbon15yearsafterrestoration.4

ThesuccessoftheMossLayerTransferTechniqueislargelyrelatedtohowwelltherestora-tionworkisdone,aswellasthemeteorologicalandhydrologicalconditionsprevailingwhiletheworkiscarriedout.TheMLTTinvolvesthefollowingsteps:

• Planning;• Preparingthesectortoberestored;• Collectingplantmaterialfromadonorsite;• Spreadingtheplantmaterial;• Spreadingmulch;• Fertilizing;• Rewettingbyblockingthedrainagesystem;and• Monitoring the restored sectors.

Thisbookletfocusesprimarilyonthestepsinvolvedinsitepreparationandinrewetting byblockingthedrainagesystem,aspartoftherestorationofSphagnum-dominated peatlands.

SITE PREPARATION Thegoalofpreparingasite5istocreateconditionsthatwillallowtheestablishmentandgrowthofplantfragmentsoriginatingfromtheplantmaterialthatwillbespreadoverthesurface.Thisstephasfivemaingoals:

• Refreshingthesurface;• Reprofilingthesector;• Controllingrunoffandimprovingwaterdistribution;• Decreasingevapotranspiration;• Re-establishingconnectivitywiththeadjacentecosystem.

Selectingthemeasurestoapplyandplanningtheworkdependonthesite’shistoryandthepostextractionresidualconditions.Thisinformationshouldhavebeengatheredduringtherestorationplanningstep(seethebookletfromthisseriesonthattopic).

4 Nugent, K., I.B. Strachan, M. Strack, N.T. Roulet and L. Rochefort. 2018. Multi-year net ecosystem carbon balance of a restored peatland reveals a return to carbon sink. Global Change Biology 24(12): 5751-5768. 2018. 5 The term "site" refers to a peat production site, i.e. a peat bog. The term "sector" describes a homoge-neous area affected by the same drainage network. It is the scale at which restoration is planned. A sector includes a number of peat fields, which are separated by secondary drainage ditches. However, for ease of reading, the terms "site" and "sector" are both used in this document to designate areas undergoing restoration.


Refreshing and Reprofiling the Surface

Why Refresh and Reprofile Fieldswherepeatextractionisnolongertakingplacearegenerallycoveredwithalooselayerofpeatremainingfromthelastharrowing.Thepeatfieldsmaybeaffectedbyfrostheaving,windorpeatoxidationanddecomposition.Thesurfacemayalsobecoveredbyathin“biologicalcrust,”madeupofamixtureofcyanobacteria,lichens,algae,mossesandliverworts.Allofthesecannegativelyimpactplantestablishmentbycreatingabarrierbetweentheplantfragmentsandthecompactedpeatsubstrates.Thesurfaceofthesectorstoberestoredshouldthereforebecompletelyreworked.Theoxidizedsurfacelayerofloosepeat,wooddebrisandthebiologicalcrustmustberemovedtoexposeafreshpeatsurface.Thisfacilitatescontactbetweenthesubstrateandtheintroducedplantfragments, enablingthemtogetwaterthroughcapillaryactionaswellasfromprecipitation.

Thereareseveralotherreasonstorefreshthesurface.Thisoperationremovesanyvegeta-tionthathasestablishedspontaneouslysincepeatextractionendedandthatcanpreventtheintroducedplantfragmentsfromestablishingcontactwiththesoil.Also,somefieldsthathadbeengivenaconvexprofiletoallowthedrainageanddryingneededforpeatextractionneedtobeflattened.Andfinally,itenablesanyothersurfaceirregularitiesto belevelled.

Thepeatsurfacethatwillreceivetheplantfragmentsandmulchmustbeflattened.Anexperimentcomparingflatsurfacestotopographiescreatedbyploughing,harrowingorwithacrawlertractorshowedthatflatsurfacesprovidethebestconditionsforplantestablishment.Theothertypesofmicrotopographyofferfavourableconditionsinlow-lyingareas,but,consideredoverall,nottotheextentofflatsurfaces.Infact,thehighestareastend to dry out faster and to erode.

Reprofilingdomedfieldsisimportantbecauseitcreatesuniformlyhumidconditionsovertheentiresurface.However,thegoalofreprofilingthetopographyshouldbetocreatea flatprofileratherthanaconcaveone.WhileexperiencehasshownthataconcaveprofileimprovesSphagnumestablishmentinthelowerslopes,italsoleadstodryconditionsintheupperslopesandtotheerosionofpeat,plantsandmulchbyrunoffwater.Inaddition,someplantfragmentsinthedepressiongetburiedundererodedmaterialcomingdownslope.

How to Refresh and ReprofileTheloosepeatandeverythingelsefoundatthesurfacemustberemoved,usingagrader,screwlevellerorbulldozer,untilalayerofundegradedpeatisreached.Reprofilingmayrequiretheremovalofathickerlayerofpeattoobtainaflatsurface.Thepeatremovedinthisoperationcanbeusedtofilldrainageditchesortoconstructdikesasdiscussedlateron in the text.


When Not to Refresh and ReprofileInsomecases,theareatoberestoredmayalreadycontainspontaneouslyestablishedvegetationmadeoftypicalpeatlandspecies.Thisisgenerallyseeninsiteswherehydrolo-gicalconditionsre-establishontheirownaftertheditcheshavecollapsed.Inthesecasesitispossibletokeepthisvegetationandnotrefreshthesurface.However,carefulattentionmustbegiventotheplantcommunitiesinplace.Forinstance,denseSphagnum carpets or well-establishedsedgesshouldbekept,butinvasiveorverycommonspecies,suchascattailsorcottongrass,shouldnot.Asageneralrule,preservingthevegetationinplaceshouldbeanexceptionanddoneonlytosavepeatlandplantcommunities.Inallothercases,thesurfaceshouldberefreshed,asitisessentialforsuccessfulSphagnum reintro-duction.

Should Drainage Ditches Be Filled? Therearebenefitsanddrawbackstofillingditches.Thedecisionofwhetherornottodoitshouldbebasedonthesiteconditions.

Filled ditches:Whenrefreshingorreprofilingthesitesurface,alargeportionofthesurfacepeatcanbeputintheditches,therebyfillingthem,atleastpartly.Eveniftheyarenotcompletelyblocked,itwillmaketheblockingofditcheseasierlateron.Fillingditchesallowsmachinerytomovearoundthesiteinalldirections,whichthenfacilitatesotherrestorationwork,especiallyinsectorsthathaveshortfieldsordikes.

Open ditches: Leavingdrainageditchesopen(i.e.,notfilledwithpeat)canhelpcreatediversehabitatsandtherebyincreasebiodiversityonthesite.Insuchcases,theditches areblockedattheends,atregularintervals,duringtherewettingstep.Theaccumulation ofwatercreateselongatedpoolsbetweendams.Thesepoolsaresoonusedbyavarietyofinsectsandwetlandplantspecieswillestablishthereovertime.Theseditchescanalso helpcollectexcesswater,potentiallydecreasingtheriskoffloodsandsurfacerunoffin thepeatland.Furthermore,thewaterstoredintheformerditchescanhelprewetthepeatsubstrateindryperiods.

WHICH TO CHOOSE?Combiningbothstrategiesonasinglesitecanprovidethebenefitsofbothoptions.Forinstance,afewdrainageditchescanbekeptopen,whiletheothersarefilledduringthesurfacereprofiling.Ditchescanalsobefilledoverafewmetresoneithersideofthedikestofacilitatethemovementofheavyequipment.


Controlling Runoff and Improving Water Distribution Whilemostsiteshavegentleslopes,thiscanstillcreatedryconditionsupstreamandverywetconditionsdownstreamifnocorrectivemeasuresaretaken.Aftertheditcheshavebeenblocked,theseslopescanalsocausesurfacerunoffthatislikelytoerodethesoilanddisplacethepreviouslyspreadplantsandmulch.

Itwouldbepainstakingtocorrectthissituationsolelybyreprofilingthesurfaceunlessthepeatfieldsareshort,withaverygentleslope.Buildingdikes6isaneffectivemeansofcontrollingrunoffandretainingwaterontherestorationsite.

DIKES

Inpeatlandrestoration,a“dike”isalow,linearpeatconstruction(30to75cmhigh)usedtoretainandcontrolwaterrunoffandtoensurethatwaterisuniformlydistributedwithinarestoredsector.Severaltypesofdikescanbebuilt,dependingonthesite’sconditionsandwhatneedstobecorrected.Theterm“berm”isalsosometimesused.

Types of Dikes

Peripheral dikesPeripheraldikesaremainlyusedtokeepwaterwithinasite.Astheirnamesuggests,theyarebuiltaroundthesectorstoberestored.Theyareneededwhenthesectorsareborderedbydrainageditchesthatcannotbeblockedorareadjacenttosurfacestowardwhichthewatercouldflowout.Thatsituationisnotideal,anditispreferabletoblocktheditchifpossible.Themainditchcanalsobemovedtoallowthesectortoberewettedandconnec-tedtothesurroundingenvironments.

Dependingonthesizeofthesectorstheysurround,peripheraldikesmayneedtoholdbacklargeamountsofwater.Theythereforehavetoberesistantandcompactedenoughtowithstandconsiderablepressure.Inthespring,dikescanbegoodalliesinpreservingthesnowmeltbecausepeat’sinsulatingqualitieshelpmaintainanicecorethatstrengthensthedikesandhelpsthemactasabarrier.Evenso,itisstronglyrecommendedthatthedikes’conditionandstabilitybemonitoredforthefirstfouryearsfollowingtherestoration,untilthevegetationisestablished.Oncestabilized,peripheraldikescanbetterwithstandthelargeamountofwaterreleasedduringthespringthaw.

Dikes perpendicular to the slopeDikesthatarebuiltperpendiculartotheslope(Figures1and2)aimtoimprovewaterdistri-bution.Thistechniquecreatesasuccessionofterracesseparatedbydikes(liketerracedricepaddies)thatretainthewaterandslowitsflow.Itisrecommendedthatatopographicsurveyofthesitebeconductedduringtheworkplanningstagetodeterminethenumberofdikesrequiredandtheirlocation.Asageneralrule,aperpendiculardikeisneededforevery30-centimetredropinelevation.Forexample,a100-metre-longpeatfieldwhosechangeinelevationisonemetrefromoneendtotheotherwillneedthreetofourdikes.Thetopogra-phicsurveywillalsohelpdeterminethelayoutofdikesthatneedtobebuiltalonglinesof

6 Underlined words refer the reader to the boxes.


thesameelevation.ThedikesattheInkermanFerrysiteinNewBrunswickwerepositionedinthisway,whichhelpedensurebetterwaterdistributionthaniftheyhadbeenbuiltwithouttakingtheslope’scomplexityintoaccount(Figure2).Giventheireffectivenessandeaseofconstruction,dikesperpendiculartotheslopeshouldbeerectedonnearlyallpeatlandrestoration sites.

Checkerboard-pattern dikesSomesituationscallforcheckerboard-patterndikes,whichcreatesmallcellsthattrap thewater.Thisisusefulwhenlargesurfacesneedtoberestoredonaflatsite,becausethecellskeepthepeat,plantfragmentsandmulchfrombeingdisplacedbywaterandwind.Checkerboard-typedikesareanalternativetodikesbuiltperpendiculartotheslope.Asanexample,theChemin-du-LacsiteinQuébecischaracterizedbycomplexslopesandshortfields.Toensureuniformwaterdistribution,agrader(leveller)wasusedtoformacheckerboardpattern.Thecellsareapproximately30metreswide,andthedikeswere30centimetreshighaftercompacting.Themachinerycirculatingonthedikesduringthespreadingoftheplantmaterialandstrawdidnotcausedamagetothepointofreducingthedikes’effectiveness.

TheElmasiteinManitoba(Figure3)wascoveredwithcheckerboard-patterndikestocountertheeffectsofstrongwindsandthespringsnowmelt,whichcouldcauseerosionanddisplacetheplantmaterialandmulch.Thedikesretainthewateranddistributeitthroughouttheentiresite.Thecellsofthecheckerboardweremadewithabulldozer. Theyareapproximately10metreswide,andthedikeswere30centimetreshighafter compacting.Thiswasdoneatthesametimethesitewaslevelled.

Figure 1. Dike perpendicular to the slope at the Saint-Fabien-sur-Mer peatland in Québec, two years after restoration.

Figure 2. Aerial photo of the Inkerman Ferry restoration site in New Brunswick. The dikes were erected along contour lines obtained from a topographic survey.


Thebulldozeroperatorpushedtheexcesspeatovera10-metredistancewiththeblade,thenbuiltadikewiththegatheredmaterial.Theoperatorthencompactedthedikewiththebulldozer’stracks,beforebuildinganewdikeparalleltothefirst,10metresfartheraway.Uponreachingtheendofthesite,theoperatorstartedtheprocessanew,buildingdikesperpendiculartotheonesjustcreated,takingcaretoliftthebladeateachdikeencoun-tered.Finally,atractorwasusedtocompacttheperpendiculardikeswithoutdamagingthefirstones.

Dike ConstructionDikesareerectedusingthepeatfromtherefreshmentoftherestorationsite’ssurface.Anyequipmentthatcanmovepeatcanbeusedtobuilddikes.Gradersandbulldozersaremostcommonlyused.

Adike’swidthmakesadifferenceinitserosionresistance.Theheightofthewaterthatwillberetainedbythedikedeterminesthewaterpressurethatwillbeexertedonit.Dikescanbereinforcedorbroadenedwherewaterpressurewillbestrongest.Withtheexceptionofperipheraldikes,dikesdonotneedtobeveryhigh.Aheightof30centimetresaftercom-pactingissufficientunlessalargeamountofwaterneedstoberetained.Whendikesareusedtocountertheeffectsofwindortocontainalargeamountofwater,aheightofupto75centimetresmaybeneeded.

Herearesomerecommendationstofollowtobuilddikesthataremoreresistantandwatertightandtoreducetheriskofhavingtomakecorrectionslater:

1. Build broader dikesforgreaterresistancewhenasectioncouldbesubjectedtostrongwater pressure.

Figure 3. Checkerboard-pattern dikes in Elma, Manitoba.


2. Firmly compact the peatonceithasbeenpushedintoamound,tomakeitwatertightandmoreresistanttowindandwatererosion.Dikescanbecompactedbydrivingoverthetopwithatractor.Thetractor’srepeatedtripsoverthefieldwhenspreadingtheplantmaterialandmulchcanbeusedasanopportunitytocompactthedikes.

3. Itisimportanttoremove any wood, branches or other debrisfromthepeatastheycanweakenthedikeandcauseleaks.

4. Clean the soil surface before building the diketoensurebettercontactbetweenthedikeandthegroundsurface.Thiswillreducetheriskofwaterinfiltrationandleaks. Also,allvegetationmustberemovedfromwherethedikewillbeerected.Scrapingthesurfacewillremovethevegetationwhileensuringgoodcontact.

5. Whenbuildingperipheraldikesanddikesperpendiculartotheslope,avoid 90-degree anglesastheywillweakenthedike.Roundeddikesarepreferable.

6. Dikebreachisarathercommonproblembecausepeatcanerodeeasily,evenwhencompacted.Installing devices to remove excess waterhelpspreventdikeerosion.Manycommercialwaterevacuationsystemsexist.Thesimplestinvolvesinstallingapipethatcrossesthedikeandevacuateswaterouttheotherside.Theheightoftheintakecaneitherbefixedoradjustable.Theoutletshouldincludeaprotectivestructure(e.g.,abedoflargestonesorlogs)todissipatethewater’senergyandpreventerosion.

7. Whenthereisamarkeddifferenceinelevation,itisimportanttopush the peat upslope whenbuildingdikesratherthandowntheslope.Pushingitdownwillsteepentheslope(Figure4)whilepushingitupwillhelpcreateflatterraces.

Recommendations1,3,5and6donotapplytocheckerboard-patterndikesbecausetheyarenotsubjectedtoasmuchpressureasperipheraldikesanddikesperpendiculartotheslopegiventhenumberofcellsanddikescreated.

Figure 4. Illustration showing the topography obtained when dikes are built by pushing the peat down the slope (A) and up the slope (B). Pushing the peat up creates terraces, while pushing it down makes the slope steeper.

A Incorrect

B Correct


Re-establishing Connectivity between the Restored Peatland and the Adjacent Environment Themaindrainageditchesonasite’speripheryaffecttheadjacentnaturalenvironments byloweringthewatertable.Evenaftertheperipheralditchesarefilled,theireffectcan stillextendupto25metresintotheadjacentnaturalpeatland.Theseadjacentareasare frequentlypeatlandsectorswhosepeatisnotthickenoughordoesnothavethepropertiesrequiredforhorticulturaluse.Theycanalsobetransitionareasbetweenthepeatlandandothersurroundingenvironments.

Alowerwatertablefostersandacceleratesthegrowthoftreesandvascularplants.Thetreestakeadvantageofthedrierconditionstoestablishand,inturn,lowerthewatertablethroughevapotranspiration.Thiscycleleadstoforestdensification.Thiseffectofdrainageisespeciallypronouncedinthefirsteightmetresadjacenttothepeatland.

Peatextractionalsocausesachangein,andevenareversalof,theslopeprofilebetweenthenaturalpeatlandandtheonetoberestored.Asthepeatisextracted,thepeatland’soriginallydome-shapedsurfaceisloweredtothepointofcreatingadifferenceinelevationofuptoseveralmetresbetweenthetwo(Figure5).

Buildingandmaintainingthedrainagenetworkaroundthepeatlandalsochangesthesurroundingenvironmentwhentheexcavatedmaterial(organicandmineralmatterfromthebottomoftheditches)isplacedattheedgeoftheadjacentenvironment.Insomeplaces,theyformlargeterracesofcompactedsubstratethatareusedtoallowmachinerytomovearoundthepeatland.Similarly,moundsofdebris,suchasbranchesandrootsfromharrowingandcleaningthefieldsinoperation,canalsocreateembankmentsaroundthepeatland.Thesecanformtheidealenvironmentforundesirablespecies(oftenruderalorinvasive)and,inversely,createabarrierkeepingdiasporesoftypicalpeatlandspeciesfromreachingthesitetoberestored.

Figure 5. Significant difference in elevation between the restored sector and the adjacent environment at Moss Spur 2 in Manitoba.


Givenallthesefactors,thepeatlandinrestorationandtheadjacentnaturalecosystemshowdifferentconditionsoncepeatextractionhasbeencompleted.Duringtherestorationprocess,reducingforestdensity,removingtheembankmentandrestructuringtheslopehelprestorethesiteclosertoitsinitialconditionsandre-establishtheconnectionbetweenthetwoenvironments.

Reducing Forest Density Reducingforestdensitybytree cuttingshouldbedoneimmediatelyafterceasingpeatextractionactivities,toreducethetrees’negativeimpactsonthehydrologyassoonaspossible.Inpractice,alltreeswithineightmetresoftheperipheraldrainageditchshouldbecut.Promptcuttingalsomakesitpossibletoclearthelandforthesubsequentactivitiesthatneedtobecarriedouttore-establishconnectivityandrestorethesite.

Coniferoustreescanbecutaccordingtotheusualforestrypractices,butspecialcaremustbetakenwithbirchandpoplartrees,whichestablishquicklyalongdrainedpeatland.Birchestendtogrowmanystumpshootswhencutneartheground.Tophysiologicallyweakenthetree,therecommendationistocutthemdowninfullsummer,beforecoldhardening(accumulationofreservesforwinter)beginsandtodosoataheightofonemetre.

Anotherstrategytoreduceforestdensityistopullthetreesoutwithanexcavator.Thismakesitpossibletoselectexactlywhichundesirabletreestoremove,evenbeyondtheeight-metrestrip.Sincethetreesareoftenuprooted,theriskofstumpsproutingisminimal.Thisoperationcanbecarriedoutwhilerestructuringtheslopeatthejunctionbetweenthepeatlandtoberestoredandtheadjacentenvironment.

TREE CUTTING

Treecuttingcontributestorewettingbecausetreesplayaroleindryingouttheareabyevaporatinglargeamountsofwater.Treecuttingcanbedoneinthefollowinglocations:

• Sitesthathavebeenclosedforalongtime.• Naturalpeatlandareasadjacenttorestorationsites,wheredrainagehasfosteredtree

growth.• Formerblock-cutsites.• RestoredareaswheretreesarecompetingwiththeSphagnum.


Removing the EmbankmentMoundsofmaterialontheperipheryoftheextractionsitekeepdiasporesfromthe naturalenvironmentfromreachingthepeatlandandareconducivetotheestablishment ofinvasiveorundesirablespecies.Thismaterialcanbecompletelyremoveddowntotheunderlyingorganicsoilandusedtofilltheperipheraldrainageditches,toppedwithalayerofatleast40centimetresofpeat.

Restructuring the SlopeInordertore-establishecologicalandhydrologicalconnectivity,itisrecommendedthat agradualtransitionberecreatedbetweenthesitetoberestoredandtheundisturbedadjacentenvironment.Thisoperationhastwoobjectives:tofilltheperipheraldrainageditchandtocreateagentle,regularslope.

Peripheralditchesneedtobecompletelyfilled,unlikesecondarydrainageditchesbetweenformerpeatextractionfields,whichcansimplybeblocked.Themostefficientwaytofilltheseditchesistousethematerialfromtheembankmentandfromdiggingtheditch,beingsuretoplacethemineralmaterial(ifpresent)atthebottomoftheditchandthepeatontop,asthefinallayer(Figure6).

Thereareafewrulestofollowtocreateagentle,regularslope.Theslopeshouldextendatminimumovertheentirepreviouslyclearedeight-metrestripandshouldbeasgentleaspossible.Heretoo,itisimportanttorespecttheruleofbuildingonedikeperpendiculartotheslopeforevery30-centimetrechangeinelevation.Tobesuretocreateagradual,regularslope,anybigpiecesofwoodmustberemovedfromthepeatwhenworkingthesurface.Forthisreason,itispreferabletoavoidcarryingoutthisstepduringwinter,asathicksnowcoverandfrozenpiecesofpeatwillmakeitdifficulttobuildaregularslope.

Whentheslopeisverygentle,itcanundergothesamerestorationoperationsastherest ofthepeatland(introductionofplantfragments,mulch,fertilizer,etc.).Whentheslopeissteeperandthetopislikelytostaydrier,seedingoraddingmulchcanhelpstabilizethesurface.

Restructuringtheslopethereforemakesitpossibletoextendtherestoredareaallthewaytotheedgeoftheadjacentenvironmentratherthanbeinglimitedstrictlytothesurface occupiedbytheextractionfields.

Figure 6. Removing the embankment and filling the ditch at Elma in Manitoba.


Situations to Avoid and Problems Encountered during Site Preparation

• Rapid rise in water level:Sitepreparationinvolvesreconfiguringthesite(refreshingthesurfaces,levelling,etc.)ratherthanrestoringthepeatlands’typicalhydrologicalcondi-tions.However,sincesomeoftheoperationscarriedoutduringthisstepwillinevitablyleadtoatleastpartialblockingofthedrainageditchesandpartialrewetting,itisimpor-tanttomakesurethatthenextrestorationstepsbeaccomplishedassoonaspossible.Otherwise,thispartialrewettingcouldmakemachinerycirculationdifficultandcompro-misethesubsequentrestorationsteps.Whendikebuildingrequiresthatthedrainageditchesbeblocked, shortsectionscanbeleftopenandonlybeblockedattheveryendoftheworktoavoidsaturatingthesoil,whichcancausethemachinerytogetstuck.

• Flooding:TheidealconditionsforSphagnum’sestablishmentisawaterlevelrightbelowthesoil’ssurface(0to10cm).NorthAmerica’sclimateischaracterizedbylongwintersduringwhichprecipitationfallsintheformofsnowandaccumulatesontheground.Allthissnowusuallymeltswithinashortperiodoftime,releasinglargequantitiesofwaterthatcanfloodthesites.Whileresearchshowsthatshort-termfloodingwillnotkillSphagnum,prolonged(>1month)ormoresevereflooding(>20cmofwaterabovethesurface)hasnegativeeffects.Sphagnumthatiscompletelysubmergedcannolongeraccessthecarbondioxide(CO2)itneedsforphotosynthesis,whichaffectsitsgrowth.Also,floodingcandisplacetheplantfragmentsandmulchcausingthemtofloatawayduringtheestablishmentphase.Theactionofwavesoverlargesurfacesandmeltwaterrunoffcancausethedikestoerodeandfail.Theseproblemsaretemporary,however.Oncewellestablished,thenewvegetationcarpetsareresistanttotheexcesswater’seffects.

• Itisverydifficulttoremodelpeatfieldsorbuilddikesinthespringbecausepeat stays frozen a long timeandgetswaterloggedwhenitthaws.Itisthereforepreferabletowaituntilsummerorfalltopreparethesite.

• Itisimportanttonever expose the mineral substrate,nomatterwhichoperationisbeingcarriedout.Doingsoenrichesthesurfacepeatwithnutrientsandfavourstheestablish-mentofundesirablespecies.Thebestwaytoavoidthisistoleaveasufficientlythicklayerofpeatinplaceafterextractiontopreservetheacidicnatureofthepeatsubstratetoberestored(pH<5.5–5.8).

• Carryingouttheworkwhenthesoilissaturatedwithwaterwillleadtoanirregular microtopography.CarryingouttheworkcreatinganirregularmicrotopographydoesnotimprovetheestablishmentofSphagnumandothermosses.Aflat topographyispreferable.

• Dikesaresubjecttobreaches,notablyduetoerosioncausedbyrunoff.Good compaction ofthepeatandtheinstallationofanexcess water evacuation systemcanpreventthistypeofproblem.


Synthesis of the Site Preparation Options

OPERATION APPLICATION CONDITIONS ADVANTAGES

Refreshing the surface of the site

• Allsites • Removestheloosepeat,biologicalcrustandvegetationtofacilitatecontactbetweentheplantfragmentsandthesubs-trate

Removing the vegetation • Allsites,especiallysectorsinvadedbytreesandundesirablespecies (e.g.,birchtrees)

• Facilitatescontactbetweentheplantfrag-mentsandthesubstrate

• Preventsundesirablespeciesfromestablishing

• Reducesevapotranspi-ration when trees are present

Keeping the vegetation in place

• Very wet, restricted areas colonizedbytypicalpeatlandspecies

• Preservestheestablishedvegetation

• Preventsthemachineryfromgettingstuck

Reprofiling the peat fields • Allfieldswithaconvexprofile(dome-shaped)

• Siteswithanirregulartopography

• Favoursbetterwaterdistribution

• Flattensthesurface

Filling the secondary drainage ditches

• Shortfields• Allsites,asdesired

• Facilitatesthecirculationofmachinery

• Makesitpossibletodisposeofthepeatresult-ingfromthesurfacepreparation

Filling the peripheral drainage ditches

• Allsiteswhereitwillnotaffect the sectors in operation

• Improvesthehydrologicalconditions

• Contributestotheeco-hydrologicalconnectivitywiththeadjacentenviron-ment


Building peripheral dikes • Sectors in which the primaryditchcannotbeblocked

• Sectors in which the adjacentenvironmentislowerorstillinoperation

• Keeps the water within the site

Building dikes perpendicular to the slope

• Everytimethereisa30cmdifferenceinelevation

• Longfields(>100m)• Siteswithariskofthematerialormulchbeingmovedbythewindorwater

• Favoursbetterwaterretentionanddistribution

• Preventsfloodingoflargesurface areas

• Actsaswindbreaks

Building checkerboard- pattern dikes

• Siteswithcomplexslopes• Vastorflatsites• Siteswithariskofthematerialormulchbeingmovedbythewindorwater

• Favoursbetterwaterretentionanddistribution

• Preventsfloodingoflargesurface areas and the impactofwaves

• Actsaswindbreaks

Reducing the tree density • Sites with a dense forest border

• Reducesevapotranspira-tion and the interception of surface runoff

• Clearstheborderandfacilitatesrestructuring

Removing the embankment • Siteswithamoundofplantdebris,mineralmaterialand peat separat ing the sectorbeingrestoredfromtheadjacentenvironment

• Facilitateswateranddiasporescirculationbetweenthetwoenviron-ments

• Permitsamorenaturaltransition

Restructuring the slope at the edge of the restoration site

• Siteswithalargediffer-enceinelevationbetweenthe restoration sector and the adjacent area

• Facilitateswateranddiasporescirculationbetweenthetwoenviron-ments

• Permitsamorenaturaltransition


DRAINAGE DITCH BLOCKINGTherearethreetypesofditches:secondary ditches,whichrunalongsideandseparatetheextractionfieldsbeforespillingintotheprimary ditches, which carry the drainage water into the peripheral ditches,whichdivertallthedrainagewateroutofthepeatland.

Thissectionfocusesspecificallyonblockingsecondaryditchesandprimaryditches,whichconstitutethebasisofthepeatlanddrainagenetworkusedforpeatextraction.ThissectionsummarizestheblockingmethodspresentedindetailinthePERGtechnicalguidepubli-shed in 2011.7

Blockingdrainageditches:

• reduceswaterlossbyupto85%;• raisesthewatertableclosertothesurfaceandreduceswaterlevelfluctuations,whichfosterstheestablishmentofpeatlandplants,includingSphagnum,whilelimitingtreesandnon-peatlandspeciesestablishmentandgrowth;and

• increasesbiologicaldiversityintherestoredsitebycreatingdiversehabitats.

Building Dams

Secondary DitchesPeatdamsaretypicallyusedtoblocksecondaryditcheswithonlyaslightslopeandlowwaterpressure.Blockingditchesmayappearquitesimple,buttherearecertainrulestofollowtoconstructeffective,long-lastingdams(Figure7).

• Clean the ditch bottom and sides.Freshwetsurfacesprovideabettercontactsurfacefortheblockingmaterialandbetterwatertightness.Cleaningremovesanyvegetationandwooddebristhatwouldenablewatertoflowbelowthedamandcauseerosion.

• Compact the dam after every addition of peat.Damsaresoliderandmoreeffectivewhenpeatiscompactedeverytimeitisadded.Atemporarydamcanbeinstalledupstreamtodrythearea,whichimprovescompaction.

• Dams must be two to five metres longtolimiterosionandenablemachinerytopass.• Dams must be approximately 50 centimetres higher than the field surface and extend

two to five metres on each side.Thisallowsextrawatertodisperseonthesurfacesincaseofoverflowratherthanpoolingandformingachannelthatcoulderodethedam.

7 Landry, J. and L. Rochefort. 2011, op. cit.


• Use wet, decomposed peat.Simplyfillingaditchwithsurfacepeatandthencompactingitcancauseleaksordamfailure.Digupstreamfromthedamsitetoreachthedecom-posedpeatthatislocateddeeper.Peatfromdiggingandcleaningtheditchcanbeusedtofillintheholefromwhichthewetpeatwasremoved.Theholecanalsobeleftunfilledtocreateasmallpoolhabitat.Inthiscase,itshouldhaveagentleslopesoanimalsthatventureintothepoolcangetouteasily.

• Do not dig into the mineral substrateduringditchwork,asthiscancausewaterlossif thewaterproofbarrierispiercedandresultinaninfluxofnutrientsandcolonizationbyundesirablespecies.

Figure 7. Illustration of a dam in a secondary drainage ditch, in cross-section (A) and from the top (B).

2 to 5 m dam extension

A) Cross-sectional view

B) Top view

2 to 5 m damextension

Material other than peat (optional)

Mound

50 cm

Mound

WaterGentle slope Gentle slope Ditch bottom

Field surface

Water


Iftheslopeistoosteeportherewilllikelybehighwaterpressureagainstthedam,forinstanceagainstthelastdamdownstreamadrainageditch,thedamscanbeconstructedfromothermaterialsasisdoneinprimaryditches(seebelow).Ingeneral,however,thisisnot necessary in secondary ditches.

Inmostcases,severaldamsareneededinasecondaryditchtoensureadequaterewetting.Thenumberofdamsdependsontheslopeoftheterrain:thegreaterthedifferenceinelevationbetweentheendsoftheditch,themoredamsareneeded.Thespacingbetweenthedamsfollowsthesamelogicasforthosethatareperpendiculartotheslope.Spacingshouldbedeterminedsothatthedifferenceinelevationbetweenonedamandthenextdoesnotexceed30centimetres.Damscouldbecombinedwithdikesperpendiculartotheslope.

Abackhoeisthebesttypeofequipmentfordamconstructionbecauseitcaneffectivelycleanthesidesandbottomofditches,especiallywhenovergrownwithvegetation(Figure8).Sincetheequipmentisstationary,itdoesn’tdamagelargeareasincasesditchesareblockedafterplacingtheplantsandmulch.Incomparison,atractorwithafrontloaderpushesthesurfacepeatintotheditchusingabackandforthmovement,whichdamagesalargeareaaroundthedam.

Forallsites,itisbesttobeginworkinginthehighersections,becauseblockingthedamsinupperareaswillcreatebetter(dry)workingconditionswhenputtinginthelowerdams.

Primary DitchesPrimaryditchescollectwaterrunningoutofthesecondaryditchesanddirectittotheperipheralditches,whichdischargethedrainagewateroutofthepeatland.Primaryditchesexperiencegreaterwaterpressureandarelargerthanthesecondaryditches.Likethelatter,thedamsmustbeabout50centimetreshigherthanthefieldsurfaceandextendouttwotofivemetresoneitherside.Suchmeasuresallowanyexcesswaterduetooverflowtodisperseoverthenearbysurfaces,ratherthangatheringandformingapool,whichcoulderodethedam.

Figure 8. Blocking a secondary drainage ditch with peat, at the South Julius peatland in Manitoba.

Figure 9. Blocking a peripheral drainage ditch using a wooden dam covered with geotextile on the upstream side and peat, at the Bic-Saint- Fabien peatland in Québec.


Materialsotherthanpeatmaybeusedtoincreaseresistancetoerosion.Suchmaterialsincludewoodpanels,boardsorlogs;strawbales;orpanelsmadeofothermaterials(Figure9).Thesecomponentsmustbeburiedintothesoildeeperthanthebottomoftheditchandintobothsidesoftheditchtoensurethedamisstrongandwatertight.Addingageotextileoramembraneontheupstreamsideofthedamwillalsoimprovewatertightnessandresistance to erosion.

Aswithsecondaryditches,thebottomandsidesmustbecleanedofwooddebrisandvegetation.Inallcases,werecommendcreatingagentleslopebothupstreamanddownstreamofthedamtomitigatewaterpressure.

Weadviseplacingtheremovedclumpsofvegetationontonearbysurfaces(Figure7)tohelpthedamstabilizefaster.Tobuildthesedamsandlargerones,asneededinperipheralditches,refertothePERGguidetitledThe Drainage of Peatlands: Impacts and Rewetting Techniques,whichexplainsindetailwhenandhowtoconstructthem.

Filling DitchesDitchesareoftenfilledwhenrestoringpeatlands,andtheadvantagesanddisadvantagesofthistechniquearediscussedatthebeginningofthisbooklet.Ditchescanbefilledwhentheresidualpeatisthickenough.Agraderorotherpieceofmachineryisusedtomovethepeatandfilltheditch.Thistechniquerequireshandlingmuchlargeramountsofpeatandthusinvolvesmoreworkthansimplyblockingaditch.Ontheotherhand,fillingditchesisagoodstrategyforusingthepeatremovedduringsurfacepreparation.Peatusedasfillmustbecompactedtoallowpassageofthemachineryoverformerfilledditchesduringthesubse-quentwork.Werecommendaddingenoughpeattocreateamound,aftercompacting,tocompensateforthesettlingthatwilloccurovertime.

Fillingditchesisnotareplacementforblockingditches;rather,itisusedtofillsegmentsbetweentwodams.Itisimportantto:

• beginwiththeupstreamsection.• compactthepeatintheditches;and• createamoundapproximately30centimetresabovethefieldsurfacetoaccommodate subsequentsettling.


When to Block DrainageBlockingdrainageditcheswillinevitablyraisethewatertableandreducegroundsupport,whichcouldrestricttheabilityofmachinerytomovearoundduringotherphasesofresto-ration.Evenwithoutblockingdrainage,someinterventionsduringthesitepreparationstagewillcertainlyblockthedrainageditches,atleastpartly,causingthewaterleveltorise.Assuch,itisimportanttoaccomplishthepost-restorationstepswithinashortperiodoftimeandtodo the final ditch blocking at the right time, generally after all the other work is completed.

Developaworkscheduleinformedbystaffexperience,informationaboutthesiteandtheassessmentofrewettingpotentialconductedduringtheplanningstage.Aschedulewillensurethattheworkisdoneunderthebestconditionspossible.Forexample,planningshouldtakeintoaccountthatanadjacentnaturalsitewilllikelybeasignificantsourceofwater.

RESOURCES, TIME AND COSTS Thetimeneededtoprepare the sitevariesconsiderably,duetothediversityofspecificconditions.Preparingfieldsthathavebeenclosedtoproductionforashortperiodwillrequirelesstimeandeffortintermsofrefreshingsurfaces.Fieldsthathavebeenclosedforalongertimeandhaveloosepeat,abiologicalcrustordensesurfacevegetationrequiremoreplanningandresources.Theaveragetimeneededtoprepareasiteiscalculatedatapproximatelyfourhoursperhectare.Agraderisthemostsuitableandpopulartypeofmachineryforsurfacepreparation.Itcanleveloffconvexfields,moveandrefreshsurfacepeat,fillditchesandbuilddikes.Itisalsobestforcreatingflat,evenpeatsurfaces.Afrontloaderorabulldozercanbeusedtofillditchesandbuilddikes,buttheirback-and-forthmotioncandamagewideareasunlesstheyareusedonfrozenordrysurfaces.

Blocking drainage ditches,however,doesnottakemuchtimeorresources.Weestimatethatitwouldtakeasingleoperatorusingtherightequipment,forexampleabackhoe,onehourperhectaretoblockditches.Ifwetakeintoconsiderationtheapproximatesizeofafield(30mx330m),itwouldtakeonehourtoblockseverallocationsinasecondaryditchalongsideafield.Siteswithaflatsurfacerequirefewerblockagesthanthosewithaslope,especiallyknowingthattheidealplacementofdamsisateach30-centimetreelevationdifference.


SUMMARY• Refreshandreprofilefieldsurfacestocreateaclean,even,regularsurface.• Ensureanevenwaterdistributionacrossthesitebybuildingdikesinstrategiclocations.• Broaderdikesaremoreresistanttoerosionbuttheirheightcanbelimitedto30centimetresoncecompacted.

• Restoretheecohydrologicalconnectionbetweentherestoredsiteandtheadjacentareasbyreducingforestdensity,removingtheembankment,restructuringtheslopeandfillingtheperipheraldrainageditch.

• Retainasmuchwateraspossibleontherestorationsite,aimingtoraisethewatertableascloseaspossibletothesurfacewithoutcreatingfloodedareas.

• Preventfloodingoflargeareasforlongperiods(morethanonemonth).• Cleanthesidesandbottomofditchesbeforeblocking.• Blockditcheswithwetpeatoveralengthoftwotofivemetres,compactingafterevery

addition. • Builddams50centimetresabovethepeatlandsurfaceandwithextensionsoneithersideoftheditch,sowatercandisperseacrossthesurroundingsurfacesincaseofoverflow.

• Neverdigdowntoorexposethemineralsubstrate.• Secondaryditchescanbefilledwithsurfacepeatbutmuststillbeblockedatregular intervals.

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With the financial assistance of

Peatland Restoration Guide Site Preparation and Rewetting

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