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ContentslistsavailableatScienceDirect

Ecological

Engineering

j o u r n a l ho me p ag e :w w w . e l s e v i e r . c o m / l o c a t e / e c o l e n g

Effects

of

flooding

on

the

seed

bank

and

soil

properties

in

a

conservation

area

on

the

Han

River,

South

Korea

Hyohyemi

Lee

a,c,∗

,

Josu

G.

Alday

b

,

Kang-Hyun

Cho

d

,

Eun

Ju

Lee

c

,

Rob

H.

Marrs

b,∗

aBureauofEcologicalConservationResearch,NationalInstituteofEcology,Seocheon325-813,SouthKorea bSchoolofEnvironmentalSciences,UniversityofLiverpool,LiverpoolL693GP,UK

cSchoolofBiologicalSciences,SeoulNationalUniversity,Seoul151-742,SouthKorea dDepartmentofBiologicalScience,InhaUniversity,Incheon,402-751,SouthKorea

a

r

t

i

c

l

e

i

n

f

o

Articlehistory:

Received30October2013

Receivedinrevisedform20March2014 Accepted19April2014

Keywords:

Soilphysico-chemicalproperties Seedbank

Flooding

Multivariateanalysis Conservation Restoration

a

b

s

t

r

a

c

t

Floodingcanhaveamajorimpactonriversideplantcommunities,andthisislikelytobeespecially

importantinmonsoonalclimates,wherelargefloodsoccurafterheavyrain.Inurbanareaswhere

ripar-ianvegetationremnantsaretheonlyvegetationofconservationinterestremaining,understandingthe

impactsthatfloodshaveontheseecosystemsisneededtoinformtheirfutureconservation.Accordingly,

weassessedtheimpactofafloodcausedbyTyphoon“Ewiniar”onthesoilseedbankoffiveplant

com-munitiesoftheonlyremainingfragmentofhigh-qualityriverinehabitatwithintheSeoulcitystretchof

theHanRiver(SouthKorea).Wesurveyedtheseedbankcompositionofthefivedominantplant

com-munitiesbeforeandaftertheflood.Wealsomeasuredselectedsoilphysico-chemicalpropertiesineach

community.Weusedunivariateandmultivariatemethodstoexaminetheeffectofthefloodonbothseed

bankandsoilphysico-chemicalproperties.Floodingresultedinvariabledepositionofsedimentwithin

theplantcommunities;fourcommunitiesvariedfrom14.6to18.8cmbutthefifth(dominatedby

Mis-canthussacchariflorus)hadmuchlesssediment(4.8cm).Thephysico-chemicalpropertiesofthesurface soilalsochangedaftertheflood,withthesedimentparticlesizebeingthemostaffected.Thespecies richnessandcompositionoftheseedbanksufferedsignificantchangesaftertheflood.Inbothcasesthere

wasahomogenizationprocess,withwasalsoimpingedonspecieswithdifferentlife-forms(annualsand

perennials).Ourresultssuggestthatanextremefloodcanaffecttheriparianvegetationseedbankby

removingwetlandplantspeciesandallowingcommonandruderalspeciestoestablish.Theremayalso

bedifferentinteractionsbetweenthedifferentplantcommunitiesintermsofsedimentcaptureandthis translatesintoalteredsoilconditionsandseedbanks.Theseresultsareofusetoconservation policy-makersaimingtoconserveanativeflorawithinseverelymodifiedurbanrivers,andtheseremnantareas canprovideanimportantseedsourceofwetlandplantstoaidrestorationofriparianecosystems.

©2014ElsevierB.V.Allrightsreserved.

1. Introduction

Naturalriverlandscapesofthetemperateregionscanharboura highbiodiversityduetotheirhighhabitatheterogeneityandboth lateralandlongitudinalriverconnectivity(Naimanetal.,1993;Van Looyetal.,2009).Thelongitudinalexchangeviawaterflow,creates areasofgeo-diversitywithinriverlandscapesthroughtheerosion, transportationanddepositionofsediment(Strombergetal.,2011).

Correspondingauthorat:UniversityofLiverpool,LiverpoolL693GP,UK.Tel.: +44979108321/+441517955172;fax:+44979108440.

E-mailaddresses:ejlee@snu.ac.kr(H.Lee),calluna@liverpool.ac.uk(R.H.Marrs).

Floodingisalsoamajorfactorincontrollingbiologicalcommunity structure(AlvesPagottoetal.,2011),oftenmoderatingthe relation-shipsbetweenthehydrologicalregime,soilstructure(sediment), floraandfauna.

Riverinesystemsusuallyincludethelandwithinawater catch-ment,a network of streamswhich drain it, and itscomponent floraandfauna(FISRWG,1998).Riverinesystemsare,therefore, importantlandscapecomponentsfromaholisticconservation per-spective,beingundergreat threat,especiallythose partsofthe riverflowingthroughurbanareas(Gergeletal.,2002;Karrand Chu,2000;PaulandMeyer,2008).Theremnantvegetationwithin urbanriversystemsisusuallyhighly-fragmented,degradedand susceptibletohumandisturbance.Manypartsoftheriverine sys-temaresubjecttoenvironmentalpressureswhichaffectboththe chemicalandphysicalenvironment,beingsomepartsdisturbed

http://dx.doi.org/10.1016/j.ecoleng.2014.04.014

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H.Leeetal./EcologicalEngineering70(2014)102–113 103

onaregularbasisbyfloodingwhichvariesinextentandduration (AbernethyandWillby,1999;AmiaudandTouzard,2004;Capon andBrock,2006;ChoandCho,2005;HölzelandOtte,2001;Jutila, 2001).Whenfloodingoccursthereisalargeflowofwater,usually resultingfromheavyrainwithintheupstreamcatchment,andthe effectscanbesevere,changingtherivertopography(AlvesPagotto etal., 2011;Schmidt etal., 2001;Stromberg etal.,2011; Yarie etal.,1998).However,inlessseverecases,thereisoftensediment transportwithinthewaterflowwhichisdepositeddownstream (Hayashi et al.,2012).In thesecases, theflood-deposited sedi-mentprovidesanincomingsourceofboth mineraland organic material,eachcontainingnutrients,and ofcourseplant propag-ules,i.e.seedsandvegetativefragments(CockelandGurnell,2012; RiisandBaattrup-Pedersen,2011).Theroleofseedbanksin river-inerestorationhasrecentlybeenemphasizedbyCuietal.(2013) whodescribedspeciesdensitiesvariationsbetweenriverpositions, sedimentdepthandpollutantloads.Floodingcanhavedirect neg-ativeeffectsthroughboththeerosionofplantsandsoils(Capon andBrock,2006;EldridgeandLunt,2010),andthroughthe physi-caldepositionofflood-bornesediments(Chang,2005;vanderValk etal.,1983);thelatterkillingnewly-emergentseedlingsand pre-ventingseedlingemergenceasthesurfacesoilisburied.Recovery after flooding can alsobe affected by thesediment deposition asitimpingesonbothsoilphysico-chemicalcharacteristicsand theseedbank,bothof whichcouldalter successionalrecovery. Here,therefore,weexaminetheimpactofdepositedsedimenton thevegetationandsoilseedbankinthefloodplainofarefugeof semi-naturalvegetationofconservationinterestwithina highly-modifiedriver.

Inthispaper,westudiedthefloodingimpactswithinarefuge ofsemi-naturalvegetationonthebanksoftheHanRiverwithin SeoulCity(SouthKorea).TheHanRiverissubjecttoannual flood-ingduringtheheavymonsoonal rainfallwithexceptional peaks every3–5years.Tominimizethisflooding,waterflowsare man-agedintwoways:first,therearethreelargedamsupstreamfrom Seoul(Soyang,ChungjuandPaldangdams;Kim,2008),andsecond in Seoul,theriver waschannelized andembanked in the mid-1960s,providingpublicparks,roads,andcarparksalongtheriver banks(Woo,2010).Asaresult,thepreviousecologicalfunctions derivedfromthenaturalriparianvegetationhavebeenlostwithin theurbanreachesoftheHanRiver.However,therearefourrefuge areaswithintheconfinesoftheSeoulcitywherenatural vegeta-tionremains.Leeetal.(2011)describedtheplantcommunitiesand seedbanksofthesefourrefuges;though,threeofthesehad suf-feredrecentdisturbance,andone,theAmsawetlandwasshown tobetheonlyremainingfragmentofrelatively-undisturbed, semi-naturalriverinevegetationwithinthecityreaches.Therefore,the Amsa refuge areais extremely important from a conservation viewpoint as it retains somevegetation along witha bank of propagulesinthesoilwhichcouldassistinfutureriver restora-tion strategies (Jeon et al., 2008; Kim and Ju, 2005; Lee et al., 2011).

Moreprecisely,westudiedtheimpactofthesevere2006flood ontheseedbanksandsoilsoffiveplantcommunitiestypesalong atransectfromtheriverthroughtothelandwardendwithinthe Amsawetland.Thisfloodwasgeneratedasaresultofexceptionally heavy,seasonalrainfall(typhoon‘Ewiniar’)whichproducedoneof thehighestfloodsinthelast25years.Theeffectofthisfloodonthe riverinecommunitieswithintheAmsawetlandwasanalyzedby measuringchangebeforeandafterthefloodin(1)arangeofsoil physico-chemicalvariables,and(2)thesoilseedbanksofthefive dominantplantcommunities(Lee,2010;Leeetal.,2011).Itwas hopedthatthisinformationwouldprovideapreliminary assess-menttohelpinformconservationplanningofriverbankvegetation inprotectedareas.

2. Methods

2.1. Studysiteandfloodevent

TheHanRiverisamajorriverinSouthKorea;itis470kmlong withawatershedareaof26,200km2andflowsthroughthe

capi-talSeoulthroughtotheYellowSea(Fig.1).Withinthecatchment, theaverageannualprecipitationis1294mm,with65%occurring betweenJulyandSeptember.TheHanRiverissubjecttoannual flooding during the heavy monsoonal rainfall withexceptional peaksevery3–5years.Thestudiedfloodwasgeneratedasaresult ofexceptionallyheavy,seasonalrainfall(typhoon‘Ewiniar’)which producedoneofthehighestfloodsinthelast25years(Fig.2).Since 1984,theSouthKoreanfloodforecastingsystemhasissued13flood alertsundertwocategories(‘Floodadvisory’and‘Floodwarning’). The2006eventwasclassifiedas“Floodadvisory”,andproduced the9thhighestrecordedwaterlevelattheHangRiverBridge mon-itoringstationsince1920;indeedthemonitoringstationwasitself floodedfor24h.

Lee et al. (2011)described the plantcommunities and seed banksof thefourrefugesontheHanRiver; threeof thesehad sufferedrecentdisturbance,andone,theAmsawetland(0.1km2,

N3733′ 5.72′′,W127715.3′′,Fig.1),wasshowntobetheonly remainingfragmentofrelatively-undisturbed,semi-natural river-inevegetationwithinthecityreaches.Thissite wasdesignated an“EcologicalLandscapeProtectedArea”toconservethis habi-tatin2002,andhasbeenfencedtopreventhumanaccess.Five plantcommunitiesweredescribedatthissite(Lee,2010;Leeetal., 2011)formingazonationfromtheriverbanksidetotheland-side as follows(Fig. 1;Nomenclaturefollows Lee,1999), i.e. Water-front (Wf),Bankside(Bn),and communitiesdominated bySalix sp.(Ss),Phragmitesaustralis(Pa),andMiscanthussaccariflorus(Ms). TheAmsawetland,therefore,containsamosaicofhabitatswhich wouldotherwisebeabsentfromtheurbanreachesoftheHanRiver, providing aestheticand educationalservicesaswellas a semi-natural habitatmuch valuedformigratorybirds(YooandChoi, 2007).

2.2. Soil/sedimentsamplingforseedbankassessmentand chemicalanalysis

Thepre-floodsoilphysico-chemicalconditionsandseedbank characteristics were assessed in spring (March) of 2005 and 2006, respectively; there was a small flood in 2005. On both sampling occasions, five replicate 1m2 quadrats were located

randomly within each of the five plant communities. At each of these quadrats,five soil cores weretaken usinga soil corer (Eijkelkamp BV, Netherlands; corer dimensions=5cm diame-ter, 5cm deep,500ml volume in total per sample).Seed bank assessment was performed in March because at this time all

seeds available for germination over the summer would be

present.

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Fig.1. (a)LocationoftheAmsaecologicalconservationareaontheHanRiver,Seoul,SouthKorea;(b)elevationalprofileofthefivecommunitiesattheAmsawetland:WF: Waterfront;Bn:Bank;Ss:Salixsp.;Pa:Phragmitesaustralis;Ms:Miscanthussaccariflorus.

2.3. Assessmentofsoilphysico-chemicalproperties

Soil/sedimentpHand electrical conductivityweremeasured in a 1:2 mixture of fresh soil in distilled water. Moisture contentwasthenmeasuredbyweighingbefore,andafter,drying

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H.Leeetal./EcologicalEngineering70(2014)102–113 105

Fig.2.ThedailymaximumwatertablerecordfromJune1995toAugust2010attheHangangBridgeinHanRiver,Seoul,Koreaindicatingfloodevents.

at60rpmdensitymeasurementsweremadeusingaBouyoucos soilhydrometer(USA/ASTM151H)after40sand7h.Dropsof Iso-amylalcoholwereaddedtoremovebubblesifnecessary(Sheldrick andWang,1993).Totalnitrogenwasanalyzedusing aKjeldahl Protein/Nitrogen Analyzer (Automatic; Kjeltec Auto 1035/1038 System).Extractablephosphorus(EP) andexchangeable cations (Na,Mg,K,Ca)wereextractedusingMehlichIIIsolution(Simsetal., 2002);EPwasanalyzedusingtheascorbicacidmethod(APHA, 1992)andexchangeablecationsusinganinducedcoupledplasma (ICP)emissionspectrometer(Shimadzu/ICPS-7510).

2.4. Assessmentofspeciesintheseedbank

Allsoil/sedimentsamplesforseedbankassessmentwerestored at4◦Cuntilthestartoftheseedlingemergenceexperiment follow-ingLooneyand Gibson(1995).Allsamplesweretheninspected andanyrootsorplantstemspresentwereremovedbyhand;the sampleswerethenplacedinindividualseedtrays(44×30×7cm) and transferred toa glasshouse where thetrays werewatered daily. Seedling emergence was observed for 16 weeks, during

whichtimetheminimumandmaximumtemperaturesrecorded

in theglasshouse were 10.4◦C and 35.8C, respectively. Emer-gent seedlingswereidentified usingAsano(2005)and counted everytwoweeks for4 months;mostseedlings emergedin the firsttenweeks(Lee,2010).Whereidentificationwasnot possi-bletheseedlingwastransferredtoaseparatepotandgrownon untilidentificationwaspossible.Theseednumbersemergingwere convertedtoseeddensitiesonanareabasis(m−2).

Speciesdetectedin theseedbank wereclassifiedintothree life-form groups (annuals, perennials and biannual) using the database of “Koreabiodiversity information system (NATURE)” (KoreaNationalArboretum,2012).

2.5. Statisticalanalysis

All analyses were performed using the packages “nlme”

(Pinheiroetal.,2013)and“vegan”(Oksanenetal.,2011)within theRstatisticalenvironment(version2.15.2.,RCoreTeam,2013). Principalcomponentanalysis(PCA)wasusedtoprovidean inte-gratedanalysisofthepatternsofvariationforsoilphysico-chemical

variables.PCAwascarriedoutoverthecorrelationmatrixofsoil data considering13 variables (seeTable 2for detailed list).All variableswerestandardizedbeforeanalysistocorrectfordifferent scalesofmeasuringunits.Differencesbetweenpre-andpost-flood valuesweretestingusingat-test.

Linearmixedmodels(LMMs)wereusedtoevaluatethechanges (size,diversity)insoilseedbankbetweenfloodeventsandfive veg-etationcommunities.Inthisanalysis,flood(pre-andpost-flood) andvegetationcommunities(5levels)weretreatedascategorical fixedfactors,andplotnestedwithinsiteswereincludedas ran-domfactorstoaccountforspatialautocorrelation(Pinheiroand Bates,2000).Allvariableswerelog-transformed(log(x+1))before analysis.

Theeffectoffloodeventsandvegetationcommunitiesonseed bankcompositionwerealsotestedusingpermutational multivari-ateanalysisofvariance(PMAV,‘adonis’function;Oksanenetal., 2011).These analyseswere performedfirst for allseedsfound andthendiscerningbetweenthethreelife-formsconsidered(i.e. annuals,biennialsandperennials).Thespecies-abundancematrix waslog-transformed(log (x+1)) toreducetheinfluence ofthe most abundantspecies.In theseanalyses, thefive sub-samples fromthesamevegetationcommunitywerepooledtoreducethe spatialheterogeneityoftheseedbanks.Bray–Curtisdistancewas usedwith999permutations.Finally,detrendedcorrespondence analysis(DCA,‘decorana’function;Oksanenetal.,2011)wasused toidentifyinordinationspacetheseedbankcompositional dif-ferences betweenfloodeventsand vegetationcommunities. To helptheinterpretationstandarddeviationalellipsesofeachflood eventandvegetationcommunitywereused(‘ordiellipse’function; Oksanenetal.,2011).Finally,therelationshipbetweenthespecies complementofthevegetationandtheseedbankspre-and post-floodwereestimatedusingSørensen’ssimilarityindex(‘vegdist’ function;Oksanenetal.,2011).

3. Results

3.1. Sedimentdepositionbytheflood

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Table1

ThedepthandmassofsedimentsdepositedonthefivecommunitiesattheAmsawetlandontheHanRiverfloodplain,Seoul(SouthKorea)duringthe2006flood(n=5).

Sedimentmeasure Sites

Waterfront Bank Salixsp. Phragmitesaustralis Miscanthussacchariflorus

Depth(cm) 14.6±0.9 18.8±2.7 15.6±1.5 17.5±0.5 4.8±0.2

Weight(kg/m2) 135±23 262±59 169±36 254±11 55±1

the Miscanthus sacchariflorus community (Ms) where sediment

depthwaslower(4.8cm,Table1).Themassofsedimentdeposited

showedthesamerankorderasthesedimentdepthbutwithgreater variation;greatestmasswasfoundintheBank(Bn)andP. aus-traliscommunities(Pa),intermediatevaluesintheWaterfront(Wf) andSalixsp.communities(Ss)andtheleastintheM.sacchariflorus community(Ms)(Table1).

3.2. Changeinsoilphysico-chemicalpropertiesbeforeandafter theflood

Most of the soil physico-chemicalproperties showed a sig-nificant differencebetween the pre- and post-flood conditions (Table 2).Five variables showed a consistent pattern after the flood event onallcommunities; soilmoisture content,pHand extractablePconcentrationeitherstayed thesameorincreased aftertheflood,andextractableNaconcentrationandelectrical con-ductivity decreasedaftertheflood. Theothervariables showed aninconsistentpatternbetweencommunities;forexample,the organicmatterincreasedinthreecommunities(Wf,PaandMs) anddecreasedintwoothers(BnandSs).

ThePCAordinationofthesoilphysico-chemicalvariables pro-videdaclearerinterpretationofthechangescausedbytheflood; thefirsttwoPCAaxesproducedeigenvectorsof7.123and3.982 whichexplained51%and28%ofthevariance(Fig.3).Aclear gra-dientwasfoundonaxis1basedonparticlesize,withincreased clayandsiltatthepositiveend ofaxis1andincreasedsandat thenegativeend(Fig.3).Theclayandsiltendofthisgradientwas correlatedwithexchangeableCaandMgandthesandendwas cor-relatedwithincreasingpH.Thegradientonaxis2showedahigh moisturecontentandextractablePatthenegativeendand electri-calconductivity,exchangeableKandNaandtotalNatthepositive end.Thepre-floodcommunitieswereorderedalongaxis1inorder (clay/silttosand)Ms,Ss,BnandPawhichwereveryclosetogether andthentheWfHowever,allofthesecommunitieshadpositive valuesonaxis2.Afterthefloodallofthecommunitiesmoveddown axis2indicatinganincreaseinmoisturecontentandavailableP (Fig.3).Therankorderofcommunitiesalongaxis1alsochanged to:Ms,WfandPawhichwereveryclosetogetherandthenSsand Bn.MsandPamovedmoreorlessverticallydownwardsshowing littleshiftontheclay-siltgradientbutwaterfrontsoilsincreased insilt/clayandbothBnandSsincreasedinsandcontent.

3.3. Changeinsoilseedbanksbeforeandaftertheflood

3.3.1. Sizeanddiversity

Overall, thepre-flood seed banksize contained seedsof 86 speciescorrespondingtoanoverallseeddensityof37,308±9508 seedsm−2.Incontrast,afterthepost-floodseedbankwasreduced

significantlyto4702±538seedsm−2(t-value=3.92,P=0.001)of

57 species.Seeddensities variedconsiderablybetweenthefive communities(Table3).Thereductioninoverallseednumberafter thefloodwasonlyconsistentforbienniallife-formseeds (reduc-tion=7190±1946,t-value=3.70,P=0.011,Table3),althoughin the case of annual and perennial seeds there was a signifi-cantflood×plantcommunityinteraction(annualsF-value=9.90, P<0.001;PerennialsF-value=3.20,P=0.034).Densityofseedbank

was significantly or slightly reduced in annuals, biennials and perennialsinallcommunities(Table3,Fig.4aandb).

Speciesnumberinseedbankwasreducedfrom86to57species aftertheflood(Appendix1).Thirty-nine speciespresent inthe pre-floodsoilseedbankswereabsentpost-flood,10newspecies weredetected,and47specieswerepresentbeforeandafterthe flood. Seed bank richness was influenced by the flood×plant community interaction(F-value=4.70, P=0.008,Fig. 4c), show-ingasignificantreductioninrichnesswithintheWf,Bn,Paand Mscommunitiesaftertheflood(averagereductionof10species percommunity),but therewasnoeffect onthe Sscommunity seedbankrichness.Thesamepatternswereobservedanalyzing fortherichnessofthethreelife-formsconsidered.Ontheother hand,thefloodproducedasignificantincreaseinseedbank even-nessin fourcommunities(flood×plantcommunityinteraction, F-value=47.74,P<0.001,Fig.4d);onlythePacommunity main-tainedidenticalevennessvaluesbeforeandaftertheflood.

3.3.2. Compositionalchanges

TheDCAofseedbankcompositionproducedeigenvalues()of 0.32,0.25,0.19and0.12,andgradientlengths(GL)of2.61,2.75, 3.15and1.90forthefirstfouraxes,respectively.Thesitesbiplot showedsignificantdifferencesintheseedbankcompositionbefore andaftertheflood(r2=0.43,P=0.008;Fig.5aandb);thepre-flood

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H.Leeetal./EcologicalEngineering70(2014)102–113 107

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Fig.5.DCAordinationofthesoilseedbankofpre-andpost-floodsitesontheHanRiverfloodplain,Seoul,SouthKorea.(a)Samplesandfloodevents(pre-floodandpost-flood) expressedasbivariate-deviationalellipses(95%confidenceintervals);(b)mostfrequentspeciesbiplot;and(c)siteinteractiveeffectsbetweenpre-(N)andpost-flood(F) plotsexpressedasbivariate-deviationalellipses.Keytospecies:Bifr:Bidensfrondosa,Brja:Bromusjaponicas,Chal:Chenopodiumalbumvar.centrorubrum,Chfi:Chenopodium ficifolium,Cyfl:Cyperusflaccidus,Elac:Eleocharisacicularisfor.longiseta,Lipr:Linderniaprocumbens,Maja:Mazusjaponicas,Padi:Panicumdichotomiflorum,Pepe:Persicaria perfoliata,Pool:Portulacaoleracea,Rois:Rotalaindica,Sevi:Setariaviridis,Alae:Alopecurusaequalisvar.amurensis,Arse:Arenariaserpyllifolia,Eran:Erigeronannuus,Erca:

Erigeroncanadensis,Leap:Lepidiumapetalum,Stal:Stellariaalsinevar.undulate,Staq:Stellariaaquatica,Vepe:Veronicaperegrine,Cadi:Carexdimorpholepis,Casp:Carexsp., Erhi:Erechtiteshieracifolia,Ixch:Ixerischinensisvar.strigosa,Jual:Juncusalatus,Jute:Juncustenuis,Lepa:Lemnapaucicostata,Phau:Phragmitesaustralis,Popr:Poapratensis, Posp:Poasphondylodes,Pokl:Potentillakleiniana,Rucr:Rumexcrispus,Trja:Triadenumjaponicum,Veam:Veronicaamericana.

sampleswerelocatedinthecentralrightsideoftheordinationand werecorrelatedwithspeciessuchasPersicariaperfoliata,Eleocharis acicularisvar.longiseta,Cyperusflaccidus,Ecliptaprostrate,Mazus japonicus.Incontrast,thepost-floodsampleswerelocatedatthe negativeendofaxis1andwerecorrelatedwithspeciessuchas Arenariaserpyllifolia,Portulacaoleracea,Panicumdichotomiflorum, Bromusjaponicas,andCarexdimorpholepis.Atthesametime,there wasaninteractionbetweenpre/post-floodandvegetation commu-nitiesonseedbankcommunities(r2=0.93,P<0.010,Fig.5c).Inthe

pre-floodsamples,thereweresignificantdifferencesinseedbank compositionbetweenthefivecommunities(r2=0.70,P<0.001).

However,afterthefloodtheseedbankcompositionaldifferences wereexclusivelybetweenMsandtheothercommunities(r2=0.40,

P=0.010,Fig.5c).Thesesignificantchangesinseedbank compo-sitionproducedbythefloodweremaintainedifthelife-formof theseedswasconsidered(Annualsr2=0.21,P=0.013;Biennials

r2=0.26,P=0.026;Perennialsr2=0.27,P=0.010).

Therelationshipbetweenindividualspeciesintheseedbank wereinvestigatedfurtherbycalculatingaratiofromthe differ-enceinseeddensitiesinthepre-andpost-floodsamplesandthen dividingbythepre-flooddensities(Fig.6).Thisshowedaclear sep-arationintospeciesthatincreasedafterflooding,andthosethat

declined.Thespecies wereclassifiedonthebasisof this analy-sisintothreegroups;thosethatshowed(a)alargeincrease,(b) asmallincrease,and(c)asmalldecrease(Table4).Ofthe com-monspecies,allexceptsixwereeitherclassifiedasalienorruderal species.Onlysixperennialspecieswereclassifiedasnativewetland species(Table4),two(Scirpusradicans,Typhaangustifolia)showed anincreaseafterfloodingandfourdecreased(Juncusalatus,Juncus effususvar.decipiens,Penthorumchinense,P.australis)intheseed bankaftertheflood.

Thesimilaritybetweenthevegetationandpre-floodsoilseed bankrangedfrom21to60%(Wf=32%,Bn=52%,Ss=60%,Pa=42%, Ms=21%),whereasthesimilarityafterfloodrangedfrom9to50%, decreasinginalltheareasexceptinWfwheresimilarityincreased 18%(Wf=50%,Bn=43%,Ss=47%,Pa=33%,Ms=9%).

4. Discussion

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H.Leeetal./EcologicalEngineering70(2014)102–113 109

Fig.6. Changeofseedlingsdensitiesofcommonspeciesofpreandpost-floodsoilwithinfivecommunitiesattheAmsawetlandontheHanRiver,Seoul,SouthKorea. Theratiowasthechangeinmeanseednumberaftertheflood(post-pre)overthenumberinthepre-floodsoilexpressedasapercentage.Keytospecies:Afi=Androsace filiformis,Apr=Artemisiaprincepsvar.orientalis,Ase=Arenariaserpyllifolia,Bfr=Bidensfrondosa,Cbu=Capsellabursa-pastoris,Cdf=Cyperusdifformis,Cfe=Cardamine flex-uosa, Cfi=Chenopodiumficifolium,Cmi=Centipedaminima,Cor=Cyperusorthostachyus,Csa=Cyperussanguinolentus, Dsa=Digitariasanguinalis, Ean=Erigeronannuus, Ecr=Echinochloacrus-galli,Emu=Eragrostismulticaulis,Gci=Galinsogaciliate,Gsp=Galiumspurium,Ich=Ixerischinensisvar.strigosa,Jal=Juncusalatus,Jef=Juncuseffusus

var.decipiens,Lap=Lepidiumapetalum,Lat=Linderniaattenuate,Lmi=Linderniamicrantha,Lpr=Linderniaprocumbens,Lup=Ludwigiaprostrate,Mja=Mazusjaponicas, Ood=Oenotheraodorata,Pau=Phragmitesaustralis,Pch=Penthorumchinense,Pdi=Panicumdichotomiflorum,Pno=Persicarianodosa,Pol=Portulacaoleracea,Ppa=Potentilla paradoxa,Ppr=Poapratensis,Psp=Poasphondylodes,Rcr=Rumexcrispus,Rgl=Rorippaglobosa,Ris=Rorippaislandica,Rsc=Ranunculussceleratus,Sal=Stellariaalsinevar.

undulate,Saq=Stellariaaquatic,Spl=Salviaplebeian,Sra=Scirpusradicans,Tan=Typhaangustifolia,Tpe=Trigonotispeduncularis,Vam=Veronicaamericana,Vun=Veronica undulata.

(Leeetal.,2011).Inspiteofthis,theriverisstillsubjecttoperiodic floods,especiallyduringtheTyphoonseasonandherewe investi-gatedtheimpactsofafloodinducedbyTyphoon“Ewiniar”atthe AmsaconservationwetlandontheHanRiver;thissiteisthelast remainingrefugeofsemi-natural,riverinevegetationof conserva-tioninterestwithinSeoul(Leeetal.,2011).Assuchitprovidesa rangeofculturalecosystemservices(MEA,2005)withintheSeoul citylandscape;aswellasanaestheticvaluetherearepotential educationalopportunitiesaswellasitsintrinsicconservationvalue (Jeonetal.,2008).Accordinglyinformationonhowitrespondsto environmentalpressures,suchasflooding,issorelyneeded.

Animportantresultwasthedifferencesinthedepthof sed-imentdeposited inthe communitiesduring theflood;thefour communitiesnearesttheriverhadsedimentdepositedtobetween

14 and 19cm depth, but even the landwardcommunity had a

4.8cmdeposition.Thus,floodeventsduringtheTyphoonseason canproduceverylarge,albeitvariable,sedimentinputstothese riverinecommunitiesashasbeendemonstratedelsewhere(Yang, 1999;Yamamoto andChiba, 1994).Given thatseedrichness in thesedimentbankhasbeenshowntoreducefromtheriveredge tomid-channel,anddownthesoilprofile(Cuietal.,2013), the additionof sedimentin suchlargequantitiesduringflood, will inevitablychangeboththephysico-chemicalconditionsofthe sur-faceandthesurfaceseedbankprofile.Thelattercanbebrought aboutintwoways,throughtheimportationofnewspecies( Barrat-Segretainetal.,1998;Barrat-SegretainandBornette, 2000)and throughtheburialofexistingseedspresentinthesurfacesoil lay-ers.Moreover,theactionofthesedimentdepositionmayalsocause physicaldamagetoexistingvegetationthuscreatingdisturbance andbaregroundsuitablefornewspeciescolonization(Amiaudand Touzard,2004;KalameesandZobel,2002).Takentogether,there

are,thereforearangeofprocessesthroughwhichextremeflooding canaffectriverinecommunitiesandtheirseedbanks,andhence theirrestorationpotentialandsubsequentsuccessional trajecto-ries.

4.1. Effectsofthefloodonsoilphysico-chemicalproperties

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Table2

Physico-chemicalpropertiesofpre-floodandpost-floodsoiloffivecommunitiesattheAmsawetlandontheHanRiverfloodplain,Seoul(SouthKorea).Thesoilpropertiesarecoded:WC:moisturecontent;OM:organicmatter; EC:electricalconductivity;TN:totalnitrogen;AP:extractablephosphorous;Na:exchangeablesodium;Mg:exchangeablemagnesium;K:exchangeablepotassium;Ca:exchangeablecalcium(n=5,mean±S.E.).Significance level:***=P<0.001,**=P<0.01;BonferronicorrectionwasusedtoadjustforTypeIerrorratewithineachsoilvariable,henceP<0.01wastakenastheminimumsignificantdifference(SokalandRohlf,1995).

Variable unit

Waterfront Bank Salixsp. Phragmitesaustralis M.sacchariflorus

Pre Post t-Val Pre Post t-val Pre Post t-val Pre Post t-val Pre Post t-val

Sand % 85±2 52±5 5.1** 57±4 87±2 5.5*** 46±2 69±4 4.2** 50±6 50±1 0.0 32±3 18±1 3.9** Silt 12±1 36±4 5.1** 33±3 10±1 6.0*** 41±1 20±3 5.4** 38±4 35±0 0.7 50±2 57±1 2.1 Clay 2±0 11±1 4.5** 9±1 2±1 3.9** 11±0 10±1 0.5 11±2 15±0 1.5 17±1 25±0 7.7*** WC 29±1 75±2 21.0*** 32±1 47±2 6.1** 30±0.4 52±4 6.0** 30±2 70±2 14.2*** 34±0.4 107±8 9.3*** OM 2.9±0.4 6.8±0 9.3*** 5.8±0.3 3±0.3 6.3*** 5.9±0.2 4.2±0.5 3.0 6±0.5 6.4±0.2 0.6 8.2±0.3 9.5±1.2 1.0 pH 6.7±0.1 6.7±0.02 0.2 6.7±0.02 7.0±0.1 4.3** 6.9±0.02 6.8±0.04 1.7 6.9±0.02 7.0±0.04 2.4 6.7±0.1 6.7±0.01 0.6 EC mS/m 13.6±1.5 2.2±0.1 7.1*** 25.6±1.2 1.2±0.1 19.4*** 23.2±1.6 1.8±0.1 12.6*** 16.8±2.3 2±0 6.4*** 14.3±0.6 2.1±0.1 18.6*** TN Mg/g 0.5±0 0.8±0 3.6 1.2±0.1 0.5±0 4.7** 1.8±0 0.7±0 9.4*** 1.5±0.1 0.9±0 3.0 1.8±0.1 1.1±0 6.2*** AP ␮g/g 16.7±1.4 31.5±5 2.8 18.5±0.5 44.4±3.6 6.9** 16.9±1 29.6±1 8.8*** 18.8±1.3 31.1±2.7 3.9** 21.3±1.5 22.5±0.7 0.6 Na 367±3 148±2 52.5*** 363±1 145±2 74.4*** 386±10 158±1 20.4*** 370±3 161±1 54.9*** 411±11 171±6 17.9*** Mg 100±11 224±13 7.0*** 227±12 121±1 8.4*** 252±18 207±9 2.2 185±25 250±3 2.5 289±23 315±4 1.0 K 62±6 127±12 4.7** 233±14 56±2 12.0*** 388±33 100±10 8.3*** 334±41 125±4 4.9** 307±24 191±4 4.6** Ca 662±82 1544±81 7.5*** 1475±59 686±70 8.5*** 1887±68 1378±62 5.4** 1533±171 1779±102 1.2 1925±89 2095±172 0.8

Table3

Pre-andpost-floodseedsnumberfoundintheseedbankoffivecommunities(July2006)attheAmsawetlandontheHanRiverfloodplain,Seoul(SouthKorea).Resultsforthetotalnumberofspeciesfoundandthenumber inthreelife-historycategories(annual,biennialandperennialspecies)arepresented.

Life-history category

Unit Site

flood

Waterfront Bank Salixspp. P.australis M.sacchariflorus Grandtotal

Pre Post Pre Post Pre Post Pre Post Pre Post Pre Post

Total No.ofseeds/m2 105300±31498 5188±386 18360±1479 6401±741 16620±6708 7945±673 4020±524 2630±291 42240±6062 1347±368 37308±9508 4702±537

No.ofspecies 59 38 54 39 46 36 27 26 32 18 86 57

Annuals No.ofseeds/m2 81900±24315 1267±271 3800±694 2181±506 2620±526 1667±465 860±147 601±139 37220±5804 291±229 25280±7865 1201±201

No.ofSpecies (%) 30(51) 14(37) 22(41) 17(44) 21(46) 17(47) 13(48) 11(42) 13(41) 6(33) 40(47) 24(42)

Biennials No.ofseeds/m2 18040±6962 2261±331 11380±1696 2460±253 11560±5888 4094±486 1600±243 1301±123 4360±556 878±183 9388±2072 2199±259

No.ofspecies (%) 17(29) 10(26) 18(33) 13(33) 14(30) 8(22) 5(19) 8(31) 11(34) 7(39) 23(27) 14(25)

Perennials Noofseeds/m2 5360±1263 1660±265 3180±373 1760±316 2440±1079 2184±343 1560±463 729±214 660±166 178±52 2640±460 1302±184

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H.Leeetal./EcologicalEngineering70(2014)102–113 111

Table4

Changeinseedlingdensitiesofcommonspeciesbetweenofpreandpost-floodsoilwithinfivecommunitiesattheAmsawetlandontheHanRiverfloodplain,Seoul, SouthKorea(n=5).A:Alien,W:Wetland,R:Ruderal(weed),M:Monocotyledon,D:Dicototyledon.

Lifehistorycategory (a)Largeincreaseratio>100 (b)Smallincreaseratio<100 (c)Smalldecrease(negativeratios)ratio≤100

Annuals Bidensfrondosa(ARW)D Androsacefiliformis(RW)D Capsellabursa-pastoris(R)D

Digitariasanguinalis(R)M Centipedaminima(R)D Chenopodiumficifolium(AR)D Echinochloacrus-galli(RW)M Cyperusorthostachyus(RW)M Cyperusdifformis(RW)M

Eragrostismulticaulis(R)M Cyperussanguinolentus(RW)M

Panicumdichotomiflorum(AR)M Linderniaattenuata(AR)D

Persicarianodosa(RW)D Linderniamicrantha(RW)D

Portulacaoleracea(R)D Linderniaprocumbens(RW)D

Ludwigiaprostrata(RW)D Mazusjaponicus(R)D Ranunculussceleratus(RW)D

Biennials Arenariaserpyllifolia(R)D Cardamineflexuosa(RW)D Galiumspurium(R)D

Lepidiumapetalum(AR)D Erigeronannuus(AR)D Rorippaislandica(R)D Oenotheraodorata(AR)D Galinsogaciliata(AR)D Salviaplebeia(R)D

Veronicaundulata(RW)D Stellariaálsinevar.undulata(RW)D

Stellariaaquatica(RW)D Trigonotispeduncularis(R)D

Perennials Poapratensis(AR)M Ixerischinensisvar.strigosa(R)D Artemisiaprincepsvar.orientalis(R)D

Poasphondylodes(AR)M Juncusalatus(W)M

Scirpusradicans(W)M Juncuseffususvar.decipiens(W)M

Typhaangustifolia(W)M Penthorumchinense(W)D

Phragmitesaustralis(W)M Potentillaparadoxa(AR)D Rorippaglobosa(RW)D Rumexcrispus(ARW)D Veronicaamericana(ARW)D

floodchangedthesoilpropertieswhichmaylimitvegetation

ger-minationanddevelopmentintheseareas.Theimportanceofthese

changeforvegetationhasbeenshowninsimilarfloodingstudies

(RobertsandMarston,2011),wherechangesinpHandelectrical conductivitywerelimitingfactorsforvegetation.Atthesametime, thesesoilchangesmayreflectmerelyphysicalforceswithrespect ofsedimentdeposition,whichisknowntooccurinfloodplainsat arangeofspatialscales(WallingandHe,1998).However,itmay alsoreflectaninteractionwiththevegetationstructure(Corenblit etal.,2009;Gurnelletal.,2006),assedimentdepositiondiffered betweenthecommunities.Wesuggestthatsomeofthisvariation wouldresultfromdifferentialinterceptioninducedbythe differ-entvegetationtypes;i.e.fromsparseplantcoverattheWaterfront, throughdensegrassstands(M.sacchariflorusandP.australis)tothe shrub-dominatedSalixsp.communities(Leeetal.,2011).

4.2. Impactsofthefloodonseedbanks

Theimmediate impactof floodingwasto reducethe differ-encesinspeciesdiversitybetweentheplantcommunities(Asaeda etal.,2011;HölzelandOtte,2004;Uchidaetal.,2012),aswell astoproduceacompositionalhomogenizationinpost-floodseed bankincomparisonwithpre-floodseedbank.Inparticular,the seedbanks ofthe pre-flood soilsshoweda heterogeneous dis-tributionpattern,probablybecauseatleastsomeseedinputsto thesoilresultedfromlocaldispersalfromnearbyparentplants (HölzelandOtte,2001;WillemsandBik,1998).Beforethefloodthe mostdiversecommunitiesweretheonesnearesttheriver,whereas afterthefloodtheyappearedmoresimilar,essentiallytheysuffer abiotichomogenization (Smartetal.,2006).Thus,immediately afterthefloodthedifferencesbetweenthecommunitiesin diver-sityandcompositionwerereduced.Thefloodalsoimpingedon species withdifferentlife-historystrategies, similar resultshas beenshowninflow-meadowsinEuropesubjectedtofloodregimes (HölzelandOtte,2004).Alllife-historycategorieswerereducedon theriverbank;bothannualsandperennialswereaffectedinthe

intermediateSalixwoodlandandtheP.australiscommunities,but annualsweremostaffectedintheM.saccharifloruscommunity.

Overall,theSørensensimilaritybetweenstandingvegetation andthepre-andpost-floodseedbankwasrelativelylow,andthis appearstypicalinwetlandstudies(CaponandBrock,2006). How-ever,itisimportanttohighlightthatthesimilaritybetweenthe standingvegetationandseedbankwasreducedafterfloodevent (10%inaverage),exceptintheWfareawheresimilarityincreased 10% by an increase of perennialspecies. Theresult of discrep-ancybetweenabove-groundvegetationandseedbankarecommon inrepeatedlydisturbedenvironmentsuchaswetlandecosystem (CaponandBrock,2006).

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mighthaveanegativeeffectonfuturesuccessionaltrajectoriesof thesecommunities,iftheinterestspeciesseedbankisnotproperly restored.

TheseedbankoftheAmsariverreservoircanbeconsideredas theonlypotentialsourceofseedsforrestorationofthisand sim-ilarwetlandcommunities.However,afterextremefloodsevents

the sediments deep can compromise the seed bank

regenera-tionpotential(i.e.deeppreventedseedlingemergence),beingthe extantvegetationofinterestthemainsourceoftheseedsforthe seedbankregeneration(González-Aldayetal.,2009).Thus, conser-vationactionsafterextremefloodingmustfocuson(1)therecovery ofvegetationstructureand(2)onthereductionofsedimentsdeep facilitatingpreviousseedbankseedlingemergence,beingbothof themvitalforthemaintenanceoftheseareas.Inanycase,thelackof goodamountsofinterestspeciesinfloodsedimentslimitstheuse ofthesedimentsfoundinthisareaforfuturerestorationprojects ofvegetationrefugeesinHanRiver.

5. Conclusions

Floodingisthemajordisturbanceoftheseriparianecosystems, inducingchangetothetopographyofriverchannel.Inurbanareas where riparianvegetation remnantsare theonly vegetation of conservationinterestremaining,understandingtheimpactsthat floodshaveontheseecosystemsisneededtoinformtheirfuture conservation.Ourresultsshowedthatimmediatelyaftertheflood, thespeciesrichnesswerereducedinboththeabove-ground vege-tation(1–10species;Lee,2010)andseedbanks(1–21species).In addition,thefloodtransportedalargeamountofsediment contain-ingsomeseedsoverthefloodplain,withanoverallhomogenizing effect(speciescompositionanddiversity);indeedaftertheflood therewasa9–50%similarity(Lee,2010).Furthermore,theflood sediment(4.8–18.8cmdepth)hadalowseeddensityandthis pre-ventedgerminationfromtheunderlyingpre-floodsoillaterand henceencouragingthosespecieswithvegetativepropagation.Our resultssuggestthatextremefloodscanimpingeontheriparian veg-etationbyremovingwetlandplantspeciesandallowingcommon, ruderalorperennialwetlandspecies topersist, mainlybecause thereproductivepatternsoftheseperennialsoccurbyvegetative propagationratherthanseeds.Theseresults,therefore,inform con-servation management policiesfor maintainingof semi-natural areasinreachesofurbanriverssuchastheHan RiverinSouth Koreathataresubjecttosubstantialflooding.

Acknowledgements

WethankJ.S.ParkandK.LeefromthePlantEcology Labora-tory,SeoulNationalUniversityfortechnicalsupport.Thisstudywas supportedbytheCAER(CenterforAquaticEcosystemRestoration) ofEco-STARprojectfromtheMinistryofEnvironment,Republic of Korea and basic science researchprogram through the NRF (NationalResearchFoundationofKorea)fundedbytheMinistry ofEducation(NRF-2013R1A1A2058596),RepublicofKorea.

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