Using 137Cs and 210Pbex measurements and

Using

137

Cs

and

210

Pb

ex

measurements

and

conventional

surveys

to

investigate

the

relative

contributions

of

interrill/rill

and

gully

erosion

to

soil

loss

from

a

small

cultivated

catchment

in

Sicily

Paolo

Porto

a,b,

_*

_,

_Desmond

_E.

_Walling

a

_,

_Antonina

_Capra

b a_{Geography,CollegeofLifeandEnvironmentalSciences,UniversityofExeter,Exeter,UK}

b_{DipartimentodiAgraria,Universita` degliStudiMediterraneadiReggioCalabria,Agro-ForestandEnvironmentalSciencesandTechnologies,ContradaFeodi}

Vito,ReggioCalabria89122,Italy

1. Introduction

Inrecentdecades,landdegradationandsoilerosionhavebeen increasingly recognised as a serious environmental problem in semiarid Mediterranean regions. Recent studies carried out in southernItalyhavedocumentedratesofsoilerosionrangingfrom 10–85tha1_yr1_{,oncultivatedland(PortoandWalling,2012a,b)}

andfrom100–150tha1_yr1_{,inareascoveredbyforests(Portoet}

al.,2011).Thesehigherosionratesreflectboththenatureofthe environment and the long-termimpact of humanactivity. The rainfallregimeofMediterraneanareas,whichischaracterisedby events of extremely short duration and very high intensity followedbylongdryperiods,isparticularlyconducivetoerosion. Human activity further increases the erosion risk through, for example, creatingbare surfaces on cultivated land after tillage operationsandlandabandonmentinmarginalandimproductive areas.InSicily,soillossfromcultivatedlandsreflectsthegeneral situationinSouthernItaly,butratesofsoillossdifferaccordingto erosion type and land degradation processes. Erosion due to

ARTICLE INFO

Articlehistory:

Received19March2013

Receivedinrevisedform21August2013 Accepted31August2013

Keywords: 137_Cs;210_Pbex

Interrillandrillerosion Ephemeralgullyerosion Sedimentredistribution Sicily

ABSTRACT

InmanycultivatedareasinsemiaridMediterraneanregions,soilerosionisresponsibleforproblems

relatedtobothon-siteandoff-siteimpacts,includingreducedcropproductivity,waterquality,and

degradationoffreshwaterecosystems.InsomeareasofSicily,whereintenseshortdurationrainfall

eventsarecommon,soilerosionisaveryseriousproblem,especiallyonlandsubjectedtocontinuous

tillageoperations.Theratesofsoillossintheseareasandtheirimpactdifferaccordingtothedominant

typeoferosion.Severalexistingstudieshavefocusedontheimpactsofeitherlinear(gully-orephemeral

gully-erosion)orinterrill–rillerosion,buttodatetherelativemagnitudeofthesetwodifferenttypesof

erosion,hasrarelybeenassessed.Thispaperreportstheresultsofastudyaimedatcomparingthe

relativecontributionof interrill–rillerosion andgullyerosion to soil lossfromasmall cultivated

catchmentlocatedinSicily(Italy).Surveysofephemeralgullies(EG)inthestudycatchmentcarriedout

attheeventscalesince1999areusedtoquantifysoillossattributabletoEGerosion.137_Csand210_Pb

ex

measurementsareusedtoquantifythenetsoillossfromthecatchmentattributabletointerrill–rill(IRR)

erosion.ThestudydemonstratesthatEGformationoccurred7yearsoutof10,withameansoilloss

averagedovera10-yearperiodequalto26.5tha1_yr1_{.TheratesofIRRerosionestimatedusing}137_Cs

and 210_Pb

ex measurements provided values of mean annual net soil loss of 38.8tha1yr1 and

34.2tha1_yr1_{, respectively. Theresulting ratios ofsoil loss attributable to EG to total soil loss}

(IRR+EG)were0.41and0.44forthe137_Csand210_Pb

exmeasurements,respectively.Theresultssuggest

thatthecontributionsofEGandIRRerosionareofasimilarmagnitudeinsemiaridregionsofSicily,

althoughtheprecisevalueoftheratioislikelytovarybothspatiallyandtemporallyinresponseto

catchmentmorphology,soilerodibilityandlanduseandinter-annualvariabilityofrainfallmagnitude

anderosivity.Thefindingsareconsistentwiththoseofotherstudiesthathaveattemptedtocomparethe

relativeefficacyofthetwoerosiontypes.Theuseof137_Csand210_Pb

exmeasurementsinthestudyarea

providedimportantinsightsintotherelativeimportanceofIRRandEGerosionandthesameapproach

couldbeemployedinotherlocationswherebothformsoferosionoccurandthereisaneedtoquantify

theirrelativeimportance.

ß_{2013ElsevierB.V.Allrightsreserved.}

* Correspondingauthor.Tel.:+39096557481.

E-mailaddresses:P.Porto@exeter.ac.uk,paolo.porto@unirc.it(P.Porto), D.E.Walling@exeter.ac.uk(D.E.Walling),acapra@unirc.it(A.Capra).

ContentslistsavailableatScienceDirect

Soil

&

Tillage

Research

j o urn a l hom e pa g e : ww w . e l se v i e r. c om / l oca t e / st i l l

concentratedflowisverysevereonmanyunprotectedfarmfields andthepresenceofvariousgullytypescanbeobservedinmany areasoftheregion.Theinitiationanddevelopmentof channels routinely obliterated by tillage and other farm operations, commonly referred to as ephemeral gullies(EG), constitutes a severeproblem(Capra,2013).Growingcropscanberemovedby scourasthesesmallgulliesdevelop,thecropsatthelowerendof the gully can be buried by the sediment discharged from the ephemeral gullyand deposited in analluvial fan. Furthermore, filling operations reduce the long-term productivity of the farmland. Although the importance of EG erosion is well recognised,even at thelocal scale (Capra and Scicolone,2002; Capraetal.,2005)littleresearchhasfocusedonthiserosiontype andmostsoilerosionpredictionstudieshavereliedongeneralised empirical models (Capra et al., 2005; Capra et al., 2009a,b; Di Stefanoet al.,2013).

Incontrast,IRRerosionratesarebetterunderstoodinSicilyand over the last 50 years many different approaches have been employedtopredictIRRerosion,inordertoassesssoilerosionrisk anddevelopeffectivestrategiestocontrolerosionand sedimen-tationin theseareas.Thesedifferentapproaches are basedon differenttypesofmodelsthatrangefromempirical-parametric approachessuchasSEDD(Ferro,1997;FerroandPorto,2000), throughconceptualmodels,whichcorrelatesoillosstophysical parametersdependingonsoilerodibilityandlanduse(Novaraet al.,2011),topography(Bagarelloetal.,2011)orrainfallerosivity (Agneseetal.,2006),torecentphysically-basedmodels,suchas WEPP (Nearing et al.,1989),whichaim tosimulateboththe detachmentandtransportofsoilparticles(Amoreet al.,2004). The results provided by these studies demonstrate that IRR erosionisalsoanimportantprobleminSicily,althoughthereisa need for further calibration and validation of the models employedfor local conditions, in order toincrease confidence intheiroutput.

Theuseoffalloutradionuclidesandmoreparticularly caesium-137(137_{Cs)andexcesslead-210(}210_Pb

ex)todocumentratesofsoil

and sediment redistribution in the landscape has attracted increasingattentionin recentyears (Mabitet al.,2008; Ritchie andRitchie,2007;Walling,2010;Zapata,2002)andtheapproach isnowbeingsuccessfullyemployedinMediterraneanareas(e.g.

Benmansour et al., 2013; Estrany et al., 2010; Gaspar et al., 2013a,b;Navasetal.,2013;Portoetal.,2006,2013).Thisapproach isabletoovercomeseveralofthelimitationsassociatedwithmore traditionalmethodsofdocumentingerosionandsoil redistribu-tion.Ofparticularimportanceisitspotentialtoprovide retrospec-tive information on medium-term average rates of soil redistributiononthebasisofasinglesitevisitandrepresentative distributeddataforfieldsandlargerareas,withouttheneedto disturbthesystembyinstallingmeasuringequipment.Forsome applications, particularly those requiring spatially distributed information on soil redistribution rates, fallout radionuclides arguably provide an essentially unique means of assembling data thatcannotbeobtainedusingalternativeapproaches.By virtueoftheirdifferenthalf-livesandfalloutorigins,137_Csand 210_Pb

exprovideinformationrelatingtodifferentperiodsoftime. 137

Csmeasurementsareprimarilyusedtogenerateinformation onmean annual erosion rates overthe past ca.50 years and

210_Pb

exmeasurementsare abletoprovideinformationrelating

to a longer period of up to ca. 100 years (Walling and He, 1999a,b).

ThestudyreportedhereaimstoquantifyEGandIRRerosion ratesin asmallcultivatedcatchmentlocatedinSicily(Italy),to comparetheirrelativecontributiontothetotalsoillossfromthe catchment and thereby provide important information on soil erosionratesinthestudyregion.Anempiricalapproach,basedon field measurements was used to quantify the erosion rates associated with EG erosion, while the rates IRR erosion were estimatedusing137_Csand210_Pb

exmeasurements.Totheauthors’

knowledgethisisthefirstattempttoundertakesuchacomparison inItaly.

2. Thestudyarea

Thestudyarea(Fig. 1)comprisesasmall0.86hacatchment locatedinSicily,Italy.Thiscatchmentispartofalargerdrainage area (80ha in size) belonging to a national network of experimentalcatchmentsforerosionstudies.Thedata-setofEG measurements in thestudy area extendsover 18years (from 1995 to 2013). The study catchment is characterised by an altitudinalrangeof325to355mabovesealevel,ameanslopeof 28%andasinglemaindrainagelinewithaNW–SE orientation (Capra andScicolone,2005)(seeTable 1).Thecatchmentisa tributary(W-side)ofthemiddlereachesoftheSimetoriver,and isdevelopedontheoldestallochthonousunitsoftheApennines– MaghrebianChain(ImereseUnit,UpperTrias–MiddleMiocene), whichunderliethesyn-andpost-orogenicunits(Burdigalianand lowerTortonian)(LonghitanoandColella,2007).Thedominant soiltype is Vertic Xerocrept, which is verycommon in Sicily. Particle size analysis carriedout for 10soilsamplescollected withinthecatchment,indicatedthepresenceofsiltyclayloam and silt loam textural classes (see Table 1 for details) with negligiblestonecontent.

Thecatchmenthasbeencultivatedsincetheearly1950s.The maincropisdurumwheatthatrequirestwotillageoperationsin summer or early autumn with a cultivator and one ploughing operationcarriedouteveryfewyears(generallyaminimumof3 years).Theclimateofthestudyareais typicallyMediterranean withamildwetwinterandawarmdrysummer.Themeanannual rainfallfortheperiod1971–2007isca.500mm,withacoefficient ofvariationofca.40%.Morethan80%oftherainfalloccursduring theperiodextendingfromOctobertoMay.

Anactiveephemeralgully(EG)developsalongthemainswale in thecentreof thecatchmentduringtherainyseasoninmost years(Fig. 1).Asisusuallythecaseforcultivatedland,theEGis obliteratedbyinfillingwithsoilfromareasimmediatelyadjacent tothechannel,usingordinarytillageequipment.However,theEG frequentlyrecursinthesameplaceduringthenextrainyseason. TheextentanddevelopmentoftheEGsysteminthecatchmenthas beendocumentedsince1995,butmeasurementsattheeventlevel didnotcommenceuntil1999(CapraandScicolone,2002,2005). Until1998,rainfalldatawerecollectedusinganautographicrain gaugeequippedwithachartrecorder,locatedabout600maway fromthestudyarea.In1999,adigitalrecordingraingaugewas installedinthebasin.Acomparisonoftherainfallmeasuredby bothgaugesoveraperiodof4monthsshowedgoodagreement betweenthetwogauges(Capraet al.,2009b).

Table1

Characteristicsofthestudycatchment.

Drainagearea(ha) Minaltitude (masl)

3. Themeasurementprogramme

3.1. Theephemeralgullysystem

Themeasurementprogrammefortheephemeralgullysystem involvedfieldsurveysundertakenaftereacherosiveevent.When thetimeintervalbetweentwoerosiveeventswastooshorttovisit thesite,asinglemeasurementsubsumedbothevents.Thesurveys involvedsurveyingthemainbranchoftheEG(seeFig. 1)andits tributaries(ifpresent).ApostprocessingdifferentialGPSwitha planimetricaccuracy of12cm(CapraandScicolone,2002)was usedtoestablishthespatialco-ordinatesofpointslocatedalongthe channelatabout5mintervalsinthelongitudinaldirection. Cross sectionsweremeasuredataboutevery5mofchannel,orwhenevera change in the EG cross section or the entry of tributaries was observed.AsitwaspossibletotreatthecrosssectionoftheEGasa trapezium(orarectangle)(Capraet al.,2011),thechannelwidths (upper andlower) anddepths were measured with a steel tape graduatedevery 5mm.Allthemeasures were madebythesame expertoperator.

ThelengthoftheEGwascomputedfromtheco-ordinatesofthe survey points.The volumesof material removedby erosion to createeachchannelsegmentwerecalculatedusingtheendarea method(i.e.theproductofthemeanareaoftwosuccessivecross sectionsandthedistancebetweenthem).Thetotalvolumeofsoil erodedfromtheEGwascalculatedas:

V¼X n

i¼1

Vi¼

Xn

i¼1

A_i1þAi

2 Li (1)

whereVisthetotalvolumeofsoilerodedfromtheEG(m3_);nisthe

numberofsegments;Viisthevolumeoferodedsoilfromeach

segment(m3_);A

i1isthedownstreamcrosssectionalareaofthe

segment (m2_{); A}

i is the upstream cross sectional area of the

segment (m2_{); and L}

i is the distance between adjacent cross

sections(m).Thedatarelatingtothevolumeofsoilremovedfrom the gulley system were converted to values of mass using representative values of in situ bulk density for the material removed.

3.2. Soilsamplingof137Csand210Pbex

Inordertouse137_Csand210_Pb

exmeasurementtoestimaterates

ofinterrill–rillerosionwithinthestudycatchment,twoseparate soilsamplingprogrammeswereundertaken.The firstaimedto establishthemagnitudeandspatialdistributionofsoil redistribu-tion rates within the catchment and involved two sampling campaigns. During the first campaign, undertaken in 2009, replicate bulk soil cores were collected at 30 sites, using an 11cm diameter steel core tube inserted to depth of 45cm. Deeper cores were collected from sites where there was the possibilityofdeposition.Thesesoilcores,whichwerecollectedat the intersections of an approximate 20m20m grid, were supplementedby afurther 52 bulkcores collectedin thesame wayfromsitesselectedtoimprovethecoverageoftopographic variability, during a second sampling campaign in 2010 (see

Fig. 1).Inallcasesthesamplingpointswereselectedtoavoidthe zoneoccupiedbytheEGandthezonefromwhichsoilwasmoved forinfillingthegully,andarethereforeseenasbeing representa-tive of the soil redistribution occurring on the slopes of the catchment beyond the EG. The second sampling programme, undertaken in 2010,aimed to obtain information on the local referenceinventoryandthedepthdistributionof137_Csand210_Pb

ex

bothatthereferencesiteandinthecultivatedsoilprofileofthe

catchment.Sinceitwasnotpossibletoidentifyasitethatwasboth undisturbedandunaffectedbysoilredistributionwithinthestudy catchment,thesamplesusedtoestablishthereferenceinventory werecollectedfromanareaofpermanentpasturewithminimal slopeadjacenttothestudycatchment.Inthiscase,eightseparate coreswerecollected fromanarea of ca. 25m2 _usingan11cm

diametersteelcoretubeinsertedtodepthof60cm,inordertotake accountofmicro-scalevariabilityinthereferenceinventory(cf.

OwensandWalling,1996).Eachcorewassectionedusingthesame depthincrements,whichrangedfrom1to4cm,andtheindividual depthincrementsfromtheeightcoreswerebulked.Bulkingwas undertaken to reduce the mass of material that needed to be transportedtothelaboratoryintheUK,wherethesampleswere assayedfor137Csand 210Pbex,andbecauseoflimitationson the

total number of samples that could be assayed. Additional sectioned cores were also obtained from two sampling sites withinthecatchmentselectedtoberepresentativeofaneroding andadepositionalsite(seeFig. 1),usingthesameprocedureas employedatthereferencesite.

3.3. Laboratoryanalysesfor137_Csand210_Pb ex

Allbulkcoreanddepthincrementalsamplescollectedfromthe catchmentandfromthereferenceareawereovendriedat105₈C for 48h, disaggregated and dry sieved toseparate the <2mm fraction.Arepresentativesub-sampleofthisfractionwaspacked intoa330cm3_{cylindricalplasticpotfordeterminationofits}137_Cs

and 210_Pb

ex activity by gammaspectroscopy in theradiometry

laboratoryoftheDepartmentofGeographyattheUniversityof Exeter.Thesamplesweresealedfor21dayspriortoassay,inorder to achieve equilibrium between 226_{Ra and its daughter} 214_Pb.

Activitiesofboth137_Csand210_{Pbinthesoilandsedimentsamples}

were measured simultaneously by gamma-ray spectrometry, usingahigh-resolutionlowenergyLOAXcoaxialHPGedetector (relativeefficiency30%)coupledtoanamplifierand PC-based datacollectionsystem.Count timesweretypically ca. 90000s, providingresultswithananalyticalprecisionof10%atthe95% levelofconfidence.Detectionlimitsfor137_Csand210_Pbwereca.0.5

and 5.0Bqkg1_{, respectively. The efficiency of the detection}

systemwascalibratedusingstandardsamplespreparedbyadding known amounts of certified 137_Cs, 210_{Pb and multi-element}

standards to a soil/sediment matrix representative of the samplestobeanalysed.The137Csactivitiesinthesampleswere obtainedfromthecountsat662keV.Thetotal210_Pbactivityof

thesampleswasmeasuredat46.5keV,andthe226_{Raactivitywas}

obtained by measuring the activity of 214_{Pb, a short-lived}

daughterof 226_{Ra, at 351.9keV. No self absorption correction}

wasappliedtothe210_{Pbmeasurements,sincethedetectorwas}

calibratedwithrepresentativesoil/sedimentstandards.The in

situ 226_Ra-supported 210_{Pb concentration, associated with}

individual soil and sediment samples, was derived from the measured226_{Raconcentration.Inmostterrestrialenvironments,}

thesupported210_{Pbwill notbein equilibriumwiththe}226_Ra,

sincesome222_{Rnwilldiffuseupwardsthroughthesoilorrock}

andescapetotheoverlyingatmosphere.Thislossiscommonly accountedusingareductionfactorbasedontheaverageratioof themeasuredtotal210_Pband226_{Raconcentrationsforsamples}

collectedfrom thelowerpart ofthe soilprofile, wherefallout

210_Pbor210_Pb

excanbeassumedtobeabsent(cf.Grausteinand

Turekian,1986;WallbrinkandMurray,1996).Avalueof0.8was obtained for the study site. Excess 210_{Pb concentrations}

associated with the samples were calculated by subtracting the 226Ra-supported 210Pb concentrationsfrom thetotal 210Pb concentrations(cf.Joshi,1987).

4. Results

4.1. Soillossfromtheephemeralgullysystem

The event-based monitoring of the ephemeral gullysystem spanned 9years and extendedfromAugust 1999toNovember 2008(seeTable 2fordetails).Asobservedinmanyotherstudies, EGformationandexpansioncommonlyoccursasaresultofonlya verylimitednumberofprecipitationeventsduringagivenyear (e.g.Casalı´ et al.,1999,2008).Inthestudyarea,themeannumber of rainy days per year is about 50, but EG formation and developmentgenerallyoccursduringonlyasingleerosiveevent. Inthestudyreported,theimpactof13erosiveeventsresponsible forEGformationanddevelopmentweredocumentedandthese represent effectively all of the erosive events resulting in EG development that occurred during the period covered by the detailedEGsurveys(1999–2008).

Therainfalltotalsassociatedwiththedifferenterosiveevents rangedfromaminimumof17.7mmtoamaximumof193.4mm, withameanof66.6mm.TheminimumEGerosionwasassociated withtheeventsof29/8/1999and3/9/1999,whenthesoillossfrom the catchment was only 0.03tha1 _{and the maximum was}

associatedwiththelast eventthatoccurred inNovember2008, whenasoillossof82.1tha1_{wasobserved.Basedonthe18years}

of observation of EG development in thestudy catchment, EG formation occurred in 7 years out of 10, with a frequency corresponding to70% of theyears covered by the survey. The cumulative soil loss for the periodcovered by the detailed EG surveys that commenced in 1999 was calculated, in order to quantifythetotalEGerosionfortheperiod.Themeanannualsoil lossfromthecatchmentfromtheEG,forthesevenyearswhenthe EGwasactive,was37.9tha1_yr1_{.Averagingtheresultsoverthe}

nine years, including the years during which no EG erosion

Table2

CharacteristicsoftheerosiveeventsresponsibleforEGformationanddevelopmentduringthestudyperiod(H=precipitationdepth;Imax=maximum30minintensityforthe precipitationevent;R=R-factor;A=meanEGcross-sectionalarea;D=meanEGdepth).

Date H(mm) Imax(mmh1) R(MJmm1ha1h1) A(m2) D(m) EGerosion(tha1)

29/08/1999 24.6 20.0 111.7 0.01 0.06 0.03

03/09/1999 17.7 13.2 46.2 0.01 0.05 0.03

07/09/1999 34.9 20.9 157.1 0.02 0.07 5.34

09/09–13/11/1999 80.5 20.1 302.4 0.16 0.47 18.97

28/11–1/12/99 193.4 19.9 663.6 0.03 0.06 4.35

12–14/1/2000 75.3 12.3 376.8 0.37 0.35 16.19

15/10/2003 104.2 43.0 1130.5 0.18 0.54 21.47

03/03/2005 65.6 8.6 536.4 0.11 0.17 10.82

22/10/2005 60.4 60.4 1701.2 0.05 0.28 15.86

25/12/2006 82.2 16.0 876.0 0.16 0.29 67.15

3–4/11/2007 51.6 33.2 3372.2 0.10 0.24 19.38

13/11/2008 34.0 9.6 410.8 0.04 0.15 5.56

occurred,themeanannualsoillossfromthecatchmentassociated withthedevelopmentoftheEGwasca.26.5tha1_yr1_.

4.2. 137_Csand210_Pb

exinventoriesanddepthdistributionsat

thereferencesite

Theestimatesofthe137_Csand210_Pb

exreferenceinventoriesfor

thestudyareaarebasedonassayofthecompositedsectionsfrom eightcores.Theseareseenasprovidingrepresentativevaluesfor the local reference inventories, although their precision or uncertaintyisnotexplicitlyquantified,duetothebulkingofthe samples.The uncertaintyintroducedbymeasurement precision (i.e.ca.10%)canbeexpectedtobeconsiderablyreduced,relativeto that associated with an individual measurement of a bulk core, becausethevaluerepresentsthesumofthevaluesofarealactivity densityobtainedfortheindividualslicesandpositiveandnegative precisionerrorsassociatedwiththosevaluesarelikelytocancelout tosomedegree.Equally,theaveragingoftheresultsfrom8cores throughtheuseofcompositesamplesmeansthattheuncertainty associatedwithmicro-scale,andsamplingvariabilityaswellaslocal variability of the reference inventory will also be significantly reduced. Based on previous experience in the wider region, an uncertaintyof10%atthe95%levelofconfidencehasbeenassumed for the estimates of the 137_{Cs and} 210_Pb

ex reference inventories

obtained(Portoet al.,2011).

The representative depth distributions of 137_{Cs and} 210_Pb ex

documentedforthereferencesitebasedonthecompositedslices fromtheeightcoresarepresentedinFig. 2.Thesearetypicalofan undisturbedsite (Wallingand Quine, 1992;Porto et al., 2001, 2003),withawelldefinedexponentialreductioninactivitywith depthand with90%of thetotalinventoryexisting inthetop

15–20cm.Valuesof432and2800Bqm2_{wereobtainedforthe} 137_Csand210_Pb

exreferenceinventories.

The reference inventoryvalues obtained for both 137_{Cs and} 210_Pb

ex must be seen as relatively low when compared with

correspondinginventories foundat othersitesin southernItaly (seePortoet al.,2001,2006).However,theycanbeaccountedfor by the lower mean annual rainfall (ca. 500mm) in this area. Similarlylow valuesforthe137_{Csreferenceinventoryhavealso}

been documented for another area of Sicily, where the mean annualrainfallisca.700mm(DiStefanoetal.,2000).Inthiscase,a referencevalue of944Bqm2 _{wasreported (DiStefanoet al.,}

1999). Correction of this value to the same year as the measurements made in the current study provides a value of 717Bqm2,and this canbe seen as consistentwiththe value reportedforthecurrentstudysite.

4.3. 137_Csand210_Pb

exinventoriesontheslopesofthestudycatchment

Thevaluesof137_{Csinventoryassociatedwiththe82sampling}

pointsinthestudycatchmentrangedfrom0.25to1192Bqm2_,

withameanvalueof255Bqm2_{(seeTable 3fordetails).Inthe}

caseof210_Pb

ex,theequivalentinventoryvaluesobtainedforthe

samesamplingpointsrangedfrom0.6to14443Bqm2_,witha

meanvalueof2285Bqm2_.

Taking account of the 10% uncertainty associated with the referenceinventoriesindicatedabove,comparisonoftheinventory valuesfortheindividualsamplingpointswiththereferencevalues indicatedthat67%ofthe137_{Csinventoriesweresignificantlylower}

than the reference value, indicating erosion, and 18% were significantlygreater,indicatingdeposition.Theresultsindicatedalso that15%ofthe137_{Csinventoryvalueswerenotsignificantlydifferent}

Fig.2.Thedepthdistributionof137_Cs(a)and210_{Pbex(b)atthereferencesite.}

Table3

Therangeof137_Csand210_{Pbexinventoriesassociatedwiththesamplingpointsinthestudycatchmentandthenumberofpointsshowingevidenceoferosion,depositionor} stableconditions.

Min(Bqm2_{) Max(Bqm}2_{) Mean(Bqm}2_{) SD(Bqm}2_{) Referencevalue(Bqm}2_{) N}

erod Ndep Nstable

137_{Cs 0.25 1192 255 294 432 55 15 12}

210_Pb

fromthereferencevalue,indicatingthatthesamplingpointswere essentially stable, experiencing neither erosion nor deposition. Similarresultswereobtainedfor210Pbexinventories,where76%of

the measured values provide evidence of erosion, 19% indicated depositionand5%experiencedneithererosionnordeposition.Itis clearthat considerablesoilredistribution hasoccurredwithinthe studybasin since thecommencement of137_{Csfallout inthe mid}

1950s, but erosion has dominated soil redistribution within the catchment.Inthecaseof210_Pb

ex,theperiodreflectedbythereduced

andincreasedinventoriesislesseasytodefine,since,unlike137_Cs,the

falloutisessentiallycontinuousfromyeartoyear.However,although

210_Pb

exinventoriesmaybesensitivetoerosionoccurringduringthe

past ca. 100 years, they will be particularly sensitive to soil

redistributionoccurring inthepast20years,duetotherelatively shorthalf-lifeof210_Pb(22years).

Fig.3presentsdepthprofilesofthetworadionuclidestypicalof anerodingsite.Thetotalinventoriesof349Bqm2_for137_Csand

1823Bqm2_for210_Pb

ex,areconsiderablylowerthanthereference

inventories.Thissamplingsiteislocatedintheupperpartofthe catchmentwhereerosionprocessesareexpectedtodominate(see

Fig. 1). ThedepthprofilesshowninFig. 4arecharacterisedby inventoryvalues of4219Bqm2 _for137_{Cs and 7792Bqm}2 _for 210_Pb

ex,whichareconsiderablyhigherthanthereferencevalues.

Thesearetypicalofadepositionalsite.Inthiscase,thesectioned coreswerecollectedinthemiddlepartofthecatchmentcloseto theconfluenceofthemainEGandoneofitstributaries(seeFig.1).

Fig.3.The137_Cs(a)and210_{Pbex(b)depthdistributionsdocumentedforarepresentativeerodingsitewithinthestudycatchment.}

Fig.4.The137_Cs(a)and210_Pb

4.4. Using137_Csand210_Pb

extoestimatesoilredistributionbyinterrill–

rillerosiononthecatchmentslopes

Estimationofratesoferosionand depositionfrom137_Csand 210_Pb

ex measurements is generally based on the degree of

reductionorincreaseofthemeasured inventory,relativetothe local reference inventory. For cultivated soils, the calibration relationship (or conversion model) required to convert the magnitudeofthereductionin theradionuclideinventorytoan estimateoftherateofsoillosscommonlyemploysamassbalance model (e.g. Kachanoski and de Jong, 1984; Walling and He,

1999a,b). Such models are based on the assumption that a

samplingpointwithatotalradionuclideinventoryA(Bqm2_)less

than the local reference inventory Aref (Bqm2) represents an

erodingsite,whereasapointwithatotalradionuclideinventory greater than the local reference inventory is assumed to be a depositionalsite.

FollowingWallingandHe(1999a,b),theactivityof accumulat-ed210_Pb

exor137CsA(t)(Bqm2)perunitareawithtimet(yr)atan

erodingsitecanberepresentedas:

AðtÞ¼Aðt0Þe depthrepresentingtheaverageploughdepth(kgm2_);

l

is the decayconstantfor137_Csor210_Pb

ex(yr1);I(t)istheannual137Csor 210_Pb

exdepositionflux(Bqm2yr1);

G

isthepercentageofthe

freshly deposited 137_{Cs or} 210_Pb

ex fallout removed by erosion

beforebeingmixedinto theplough layer;Pis theparticle size correctionfactor;t0(yr)istheyearwhencultivationstarted;A(t0) (Bqm2₎₌210_Pb

exor137Csinventoryatt0;A(t)isgreaterthanthe

localreferenceinventoryArefatasamplingpoint,depositionmay

beassumed.Inthiscase,themeansoildepositionrateR0_canbe

calculatedfromthefollowingequation:

R0

where H is the relaxation mass depth of the initial depth distribution of the fallout input. This represents the depth to whichthefreshfalloutinputpenetratesthesoil.Assumingthatthe depthdistributionisexponential,Hisdefinedasthemassdepth (kgm2_{)atwhichtheradionuclideconcentrationreducesto1/eof}

thesurfaceconcentration(seeHeandWalling,1997).

Cd(t0)reflectstheradionuclidecontentofsedimentmobilised

fromalltheerodingareasthatconvergeontheaggradingpoint. Generally,Cd(t0)canbeassumedtoberepresentedbytheweighted

mean137_Csor210_Pb

exactivityofthesedimentmobilisedfromthe

upslope contributing area S (m2_{); P}0 _{is a further particle size}

correctionfactorreflectingdifferencesingrainsizecomposition betweenmobilisedanddepositedsediment;

g

istheproportionof theannualfalloutsusceptibletoberemovedbyerosionpriorto incorporationintothesoilprofilebytillage.

4.5. Soilredistributionratesonthecatchmentslopes

The conversion model described above was used to derive estimatesoferosionanddepositionratesforthesamplingpoints withinthestudycatchmentthatshowedinventoriessignificantly differentfromthereferenceinventory(67and78,respectivelyfor

137_Csand210_Pb ex).

Acomputer-basedroutinewhichconvertsthepercentageloss or gain in the 137_{Cs or} 210_Pb

ex inventory, relative to the local

referencevalue,toanequivalentrateofsoillossordepositionwas used to solve Eqs. (2) and (3), and to estimatethe erosion or deposition ratesassociated withtheindividualsamplingpoints withinthestudycatchment.AnaverageploughdepthDof200 (kgm2_{)wasselectedasbeingrepresentativeofcultivationinthe}

catchment,andanaveragevalueof4(kgm2_{)wasusedtodescribe}

therelaxationmassdepthHoftheinitialfalloutinput.Avalueof1 wasassumed bothfor

g

,basedontherelationshipbetweenthe timingofcultivationandtherainfallregime,andfortheparticle size correction factor P, based on the lack of an appreciable differencebetweenthegrainsizecompositionofthesoilandof samplesoftransportedsedimentcollectedduringthestudyperiod. The magnitude and spatial variability of the erosion and deposition rates estimated for the individual sampling points withinthestudycatchmentarepresentedinFig. 5a,for137_Csand

inFig. 5bfor210_Pb ex.

5. Discussion

5.1. Interrill/rillerosionontheslopesofthecatchment

TheresultspresentedinFig.5emphasisethattheslopesofthe study catchment are characterised by appreciable rates of soil redistribution,withacleardominanceoferodingsites.Estimates ofthegrosserosionrate(tha1_yr1_{)forthecatchmentassociated}

withthe82samplingpointsidentifiedinFig. 5havebeenderived astheproductofthemeanerosionrateforthepointsindicatedby the137_Csor210_Pb

exmeasurementstobecharacterisedbyerosion

and the proportion of the catchment subject to erosion, as represented by the proportion of the sampled points that documentederosion.Thesameapproachwasappliedtoestimate the total deposition on the slopes of the catchment that was derived as the product of the mean deposition rate for the sampledpointsinthecatchmentdemonstratingdepositionand theproportionofthecatchmentsubjecttodeposition. Subtrac-tionofthetotaldepositionwithinthecatchmentfromthegross erosionprovides anestimateofthe neterosion,whichis here interpretedtorepresentthesedimentdeliveredtothechannel system.

Basedon the82 samplingpoints,thegrosserosionfromthe slopeswasestimatedtobe49and 60tha1_yr1_{,basedon the} 137_{Cs and} 210_Pb

ex measurements, respectively. Thenetsoil loss

fromtheslopesofthestudycatchmentestimatedfromthe137Cs and210_Pb

exmeasurementswas38.8and34.2tha1yr1,

respec-tively.Thesevalues provideasedimentdeliveryratioofca.79% and57%for137_Csand210_Pb

ex,respectively.Netsoillossratesofthis

magnitude, althoughvery highwhen compared tothose docu-mentedforotherregionsofItaly,arerelativelycommoninSicily. Forexample,Bagarelloetal.(2010)workingonexperimentalplots ranginginlengthfrom11to44m,documentedvaluesofmeansoil lossrangingfromca.22to57tha1_yr1_{inasimilarlocation.}

Thereare,however,anumberofimportantdifferencesbetween theestimatesofsoilredistributionrateprovidedbythe137_Csand 210_Pb

ex measurements. The first is that the estimates of gross

erosionrateprovidedbythe210_Pb

exmeasurementsarehigherthan

those provided by the 137Cs measurements. Secondly, the net erosion rateestimatedfromthe137_{Csmeasurementsis slightly}

higherthanthat obtained fromthe210_Pb

exmeasurements.This

latter contrast reflectsthe higherestimates of deposition rates provided by the 210_Pb

ex measurements and the associated

reductionin thesedimentdelivery ratio.Althoughitis difficult toprovideadefinitiveexplanationforthedifferentvaluesofgross andneterosionprovidedbythetworadionuclides,itisimportant torecognisetheirdifferenttemporalsensitivities.In thecase of

137_{Cs, themeasurements providea time-integratedestimate of}

commencementof137_{Csfalloutinthemid1950stothepresent.}

Falloutwasminimalduringmuchofthisperiod(i.e.sincethemid 1970s)andthe137_{Csinventoriesprimarilyreflectthelonger-term}

influenceofsoilredistributionprocessesonarelativelyshort-term inputoffalloutinthelate1950sand1960s,whichhasremainedin thesoil.Incontrast,theannualfalloutof210_Pb

excanbeseenas

essentiallyconstantand,inviewofitsshorterhalflife(22.3yr), currentinventoriesarelikelytobemoresensitivetoerosionand soil redistribution occurring during the past 20 years. Where erosionanddepositionratesderivedusingthe210_Pb

ex

measure-mentsarehigherthanthoseobtainedusing137_{Csmeasurements,}

this could reflect increased erosion in recent years, due, for example, to an increased incidence of high magnitude events duringthis shorter time window,than duringthelonger time-windowreflectedbythe137_{Csmeasurements.Thiswasthecasefor}

theareasinCalabria(southernItaly)investigatedbyPortoet al. (2009), Porto and Walling (2012a,b). However, D’Asaro et al. (2007)investigatedtrendsinannualrainfallerosivityinSicilyand foundthatingeneraltherainfallerosivityfactorR(Wischmeier andSmith,1978)hasnot showna significantincreasein Sicily duringthetwentiethcentury.Afurtherdifferencerelatestothe spatialpatterns of soilredistribution demonstrated by thetwo radionuclides(seeFig. 5).Thisisnotunexpectedconsideringthe differenttemporalsensitivityofthetworadionuclidesnotedabove andboththisandthereducedsedimentdeliveryratioassociated withthe210_Pb

exmeasurementsmayreflectprogressivechangesin

soilpropertiescausedbythehighratesofsoillossfromthefield.A gross erosion rate of 50–60tha1 _{year equates to an average}

surfaceloweringofca.20–25cmoverthe50yearperiod.Therate of surface lowering in themain eroding areas within thefield wouldbesignificantlygreater.Thisprogressivelossofsurfacesoil causedbyerosionandtheassociatedincorporationintotheplough horizon of soil from beneath the original plough depth, char-acterisedby differenttexture,can be expectedto have caused changesinthetextureandorganicmattercontentofthesurface

soil.Suchchangesarelikelytobereflectedbychangesinboththe magnitudeandspatialdistributionofrunoffanderosion.

5.2. Therelativeefficacyofinterrill/rillerosionandgullyerosion

Theestimatesofnetsoillossprovidedbythe137_Csand210_Pb ex

measurementscanbecomparedwiththoseobtainedfortheEG. Thedifferenttime windowsrepresentedbythedifferentsetsof measurements necessarily introduce some uncertainty, but the comparisonis,nevertheless, seenasmeaningful. Combiningthe

137_{Cs and} 210_Pb

ex estimates (IRR) with the EG measurements

reported above,provides estimatesof thetotalannual soilloss (TSL=EG+IRR)of65.3tha1_yr1_,and60.7tha1_yr1_andofthe

ratioEG/TSLequalto0.41and0.44basedontheestimatesifIRR derived fromthe137_Csand210_Pb

exmeasurements,respectively.

Theestimateofsoillossprovidedbythe210_Pb

exmeasurementsis

arguably more representative of the 9 year period 1999–2008 covered by the gully surveys than that provided by the 137_Cs

measurements,whichrelatesmoreclearlytotheperiodextending from the mid 1950s to the time of sampling. Therefore, the estimatesofTSLof60.7tha1_yr1_{andoftheratioEG/TSLof0.44}

couldbeseenasmorereliable.Theseresultssuggestthatinthe studycatchmentthecontributionsofEGand IRRerosiontothe total net soil loss are of similar magnitude. However, the magnitude of the EG/TSL ratio can be expected to vary both throughtime,inresponsetochanginglanduseand hydrometeo-rological conditions, and between different catchments in re-sponsetovariationsincatchmentmorphology,soilpropertiesand landuse.Furtherworkisclearlyrequiredtoestablishifthevalue for the EG/TSL ratio obtained for the study catchment is representativeof thelocal region inSicily.However, studies in otherpartsofEuropehavereportedsimilarresults.Forexample,

Casalı´ etal. (1999),investigated someactivelyerodingareas in Navarra(Spain),andreportedthatEGtypicallycontributesabout 30%tothetotalsoilloss,althoughitcanreachashighas100%.

Vandaele et al. (1996) working in central Belgium document valuesoftheEG/TSLratiorangingfrom0.29to0.7.Cerdanet al. (2002), following two extreme rainfall events that occurred in Normandy(France),calculatedthattheEG/TSLratiosforthetwo eventswere0.21and0.56.Lookingmoregenerally,Poesenetal. (2003)recognisedthattheratesofsoillossratesassociatedwith differentkindsofgullycouldvaryconsiderably,resultingingully contributions to the total sediment export from a catchment rangingfrom10%toup94%(i.e.aG/TSLratioof0.1–0.94).

6. Conclusions

Prediction of soil erosion is an important requirement for managinglanddegradationprocessesinsemiaridMediterranean areas. However, most prediction techniquesrequire calibration and/orvalidation,iftheyaretoproducereliableresults.Thestudy reported here has provided empirical confirmation of the magnitudeof both EGand IRR erosion froma small cultivated catchmentlocatedinSicily.Theresultsobtainedhavepermitted the relative contribution of EG and IRR erosion to the total sedimentoutputfromthecatchmenttobequantifiedandhave shownthatthetwoerosionprocessesareofsimilarimportance. Thelatterfindingisconsistentwithresultsofotherstudiesthat haveattemptedtoestablishtherelativeimportanceofEGandIRR erosion and emphasises that both forms oferosion needtobe consideredwhenplanningcatchmentscalesoilconservationand sedimentcontrolmeasureswithinthestudyregion.

Thestudyalsodemonstratesthepotentialforusing137_Csand 210_Pb

exmeasurementstoobtaininformationonmedium-termsoil

erosionandsoilredistributionrateswithinsmallcatchments.By virtueof their differenthalf-lives andfallout origins, 137_{Cs and} 210_Pb

ex can provideinformation on land degradationprocesses

relatingtodifferenttimewindows.Inthisstudytheinformationon IRRerosionratesgeneratedbythe137_Csand210_Pb

exmeasurements

wascombinedwiththeresultsofamoretraditionalmeasurement programmeaimedatassessingsoillossassociatedwithEGerosion toassesstherelativeimportanceofthetwoerosiontypestothe totalsoillossfromthestudycatchment.Assuch137_Csand210_Pb

ex

measurements should be seen as potentially providing an importantcomplementtomoretraditionalmeasurements,rather thananalternative.

Acknowledgements

Thestudyreportedinthispaperwassupportedbygrantsfrom MIURPRIN2010–2011,andtheIAEA(TechnicalContract15478). TheassistanceofSueRouillardinproducingthefiguresandofJim Grapesin undertakingthegammaspectrometrymeasurements aregratefullyacknowledged.

References

Agnese,C.,Bagarello,V.,Corrao,C.,D’Agostino,L.,D’Asaro,F.,2006.Influenceofthe rainfallmeasurementintervalontheerosivitydeterminationsinthe Mediter-raneanarea.JournalofHydrology329,39–48.

Amore,E.,Modica,C.,Nearing,M.A.,Santoro,V.C.,2004.ScaleeffectinUSLEand WEPPapplication forsoilerosioncomputationfrom threeSicilian basins. JournalofHydrology293,100–114.

Bagarello,V.,Ferro,V.,Giordano,G.,2010.Misuradell’erodibilita` delsuolonelle parcellesperimentalidiSparacia,inSicilia.In:XXXIIConvegnoNazionaledi IdraulicaeCostruzioniIdrauliche. Palermo,(inItalian),pp.1–10.

Bagarello,V.,DiStefano,C.,Ferro,V.,Kinnel,P.I.A.,Pampalone,V.,Porto,P.,Todisco, F.,2011.Predictingsoillossonmoderateslopesusinganempiricalmodelfor sedimentconcentration.Journalofhydrology400,267–273.

Benmansour,M.,Mabit,L.,Nouira,A.,Moussadek,R.,Bouksirate,H.,Duchemin,M., Benkdad,A.,2013.Assessmentofsoilerosionanddepositionratesina Mor-occanagriculturalfieldusingfallout137_Csand210_{Pbex.JournalofEnvironmental} Radioactivity115,97–106.

Capra,A.,Scicolone,B.,2002.Ephemeralgullyerosioninawheat-cultivatedareain Sicily(Italy).BiosystemsEngineering83(1) 119–126.

Capra,A.,Scicolone,B.,2005.Monitoraggiodell’erosioneephemeralgullyinun piccolobacinosiciliano.In:AttidelConvegnodell’AssociazioneItaliana di IngegneriaAgraria(AIIA)2005. Cataniacod.6010,(inItalian),pp.1–12. Capra,A.,Mazzara,L.M.,Scicolone,B.,2005.ApplicationoftheEGEMmodelto

predictephemeralgullyerosioninSicily(Italy).Catena59,133–146. Capra,A.,DiStefano,C.,Ferro,V.,Scicolone,B.,2009.Similaritybetween

morpho-logicalcharacteristicsofrillsandephemeralgulliesinSicily,Italy.Hydrological Processes23,3334–3341.

Capra,A.,Porto,P.,Scicolone,B.,2009.Relationshipsbetweenrainfall character-isticsandephemeralgullyerosioninacultivatedcatchmentinSicily(Italy).Soil &TillageResearch105,77–87.

Capra,A.,DiStefano,C.,Ferro,V.,Scicolone,B.,2011.Morphologicalcharacteristics ofephemeralgulliesinSicily,SouthItaly.LandformAnalysis17,27–32. Capra,A.,2013.Ephemeralgullyandgullyerosionincultivatedland:areview.In:

Lannon,E.C.(Ed.),DrainageBasinsandCatchmentManagement:Classification, Modellingand EnvironmentalAssessment. NovaSciencePublishers, Haup-pauge,NY.

Casalı´,J.,Gastesi,R.,A´lvarez-Mozos,J.,DeSantisteban,L.M.,Lersundi,J.,DelVallede Lersundi,R.,Gime´nez,A.,Larranˇaga,M.,Gonˇi,U.,Agirre,M.A.,Campo,J.J., Lo`pez,M.,Done´zar,M.,2008.Runoff,erosion,andwaterqualityof agricul-turalwatershedsincentralNavarra(Spain).AgriculturalWaterManagement 95,1111–1128.

Casalı´,J.,Lo´pez, J.J.,Gira´ldez,J.V.,1999.Ephemeralgully erosioninSouthern Navarra(Spain).Catena36,65–84.

Cerdan,O.,LeBissonnais,Y.,Couturier,A.,Bourennane,H.,Souche`re,V.,2002.Rill erosiononcultivatedhillslopesduringtwoextremerainfalleventsin Nor-mandy,France.Soil&TillageResearch67,99–108.

D’Asaro,F.,D’Agostino,L.,Bagarello,V.,2007.Assessingchangesinrainfallerosivity inSicilyduringthetwentiethcentury.HydrologicalProcesses21,2862–2871. DiStefano,C.,Ferro,V.,Porto,P.,1999.Linkingsedimentyieldandcaesium-137 spatialdistributionatbasinscale.JournalofAgriculturalEngineeringResearch 74(1) 41–62.

DiStefano,C.,Ferro,V.,Porto,P.,2000.Lengthslopefactorsforapplyingtherevised universalsoillossequationatbasinscaleinsouthernItaly.Journalof Agricul-turalEngineeringResearch75(4) 349–364.

DiStefano,C.,Ferro,V.,Pampalone,V.,Sanzone,F.,2013.Fieldinvestigationofrill andephemeralgullyerosionintheSparaciaexperimentalarea,SouthItaly. Catena101,226–234.

Estrany,J.,Garcia, C.,Walling,D.E.,2010.Aninvestigationofsoilerosionand redistributioninaMediterraneanlowlandagriculturalcatchmentusing caesi-um-137.InternationalJournalofSedimentResearch25,1–16.

Ferro,V.,1997.Furtherremarksonadistributedapproachtosedimentdelivery. HydrologicalSciencesJournal42(5) 633–648.

Ferro,V.,Porto,P.,2000.SedimentDeliveryDistributed(SEDD)Model.Journalof HydrologicEngineering5(4) 411–422.

Gaspar,L.,Navas,A.,Walling,D.E.,Machı´n,J.,Go´mezArozamena,J.,2013.Using 137_Csand210_{Pbextoassesssoilredistributiononslopesatdifferenttemporal}

scales.Catena102,46–54.

Gaspar,L.,Navas,A.,Machı´n,J.,Walling,D.E.,2013.Using210_{Pbexmeasurementsto} quantifysoilredistributionalongtwocomplextoposequencesin Mediterra-neanagroecosystems,northernSpain.Soil&TillageResearch130,81–90. Graustein,W.C.,Turekian,K.K.,1986.210_Pband137_{Csinairandsoilsmeasurethe}

rateandverticalprofileofaerosolscavenging.JournalofGeophysicalResearch 91(D13) 14355–14366.

He,Q.,Walling,D.E.,1997.Thedistributionoffallout137_Csand210_{Pbinundisturbed} andcultivatedsoils.AppliedRadiationandIsotopes48,677–690.

Joshi,S.R.,1987.NondestructivedeterminationofLead-210andRadium-226in sedimentsbydirectphotonanalysis.JournalofRadioanalyticalandNuclear Chemistry116,169–212.

Kachanoski,R.J.,deJong,E.,1984.Predictingthetemporalrelationshipbetween soilcesium-137 and erosionrate. Journal of EnvironmentalQuality 13, 301–304.

Longhitano,S.,Colella,A.,2007.Geomorphology,sedimentologyandrecent evolu-tionoftheanthropogenicallymodifiedSimetoRiverdeltasystem(eastern Sicily,Italy).SedimentaryGeology194,195–221.

Mabit,L.,Benmansour,M.,Walling,D.E.,2008.Comparativeadvantagesand limita-tionsofthefalloutradionuclides137_Cs,210_Pbexand7_{Beforassessingsoilerosion} andsedimentation.JournalofEnvironmentalRadioactivity99,1799–1807. Nearing,M.A.,Foster,G.R.,Lane,L.J.,Finkner,S.C.,1989.Aprocessbasedsoilerosion

modelforUSDA-watererosionpredictionprojecttechnology.Transactionsof theASAE32(5) 1587–1593.

Navas,A.,Lo´pez-Vicente,M.,Gaspar,L.,Machı´n,J.,2013.Assessingsoil redistribu-tioninacomplexkarstcatchmentusingfallout137_{CsandGIS.Geomorphology} 196,231–241.

Novara,A.,Gristina,L.,Saladino,S.S.,Santoro,A.C.,Cerda`,A.,2011.Soilerosion assessmentontillageandalternativesoilmanagementsinaSicilianvineyard. Soil&TillageResearch117,140–147.

Owens,P.N.,Walling,D.E.,1996.Spatialvariabilityofcaesium-137inventoriesat reference sites: an example from two contrasting sites in England and Zimbabwe.AppliedRadiationandIsotopes47,699–707.

Poesen, J.,Nachtergaele,J., Verstraeten,G.,Valentin, C.,2003.Gully erosion andenvironmentalchange:importanceandresearchneeds.Catena50(2– 4) 91–133.

Porto,P.,Walling,D.E.,2012b.Usingplotexperimentstotestthevalidityof mass balance models employed to estimate soil redistribution rates from137_Csand210_{Pbexmeasurements.AppliedRadiationandIsotopes70,} 2451–2459.

Porto,P.,Walling,D.E.,Callegari,G.,2011.Using137_{Csmeasurementstoestablish} catchmentsedimentbudgetsandexplorescaleeffects.HydrologicalProcesses 25,886–900.

Porto,P.,Walling,D.E.,Callegari,G.,2013.Using137_Csand210_Pb

exmeasurementsto investigatethesedimentbudgetofasmallforestedcatchmentinsouthernItaly. HydrologicalProcesses27,795–806.

Porto,P., Walling,D.E., Callegari,G., Capra,A.,2009. Using caesium-137and unsupportedlead-210measurementsto explore therelationship between sedimentmobilisation,sedimentdeliveryandsedimentyieldforaCalabrian catchment.MarineandFreshwaterResearch60,680–689.

Porto,P., Walling, D.E.,Callegari, G., Catona,F., 2006. Usingfallout lead-210 measurementstoestimatesoilerosioninthreesmallcatchmentsinsouthern Italy.Water,Air,&SoilPollution:Focus6,657–667.

Porto,P.,Walling,D.E.,Ferro,V.,2001.Validatingtheuseofcaesium-137 measure-mentstoestimatesoilerosionratesinasmalldrainagebasininCalabria, southernItaly.JournalofHydrology248,93–108.

Porto, P., Walling, D.E., Ferro, V., Di Stefano, C., 2003. Validating erosion rateestimatesbycaesium-137measurementsfortwosmallforested catch-mentsinCalabria,SouthernItaly.LandDegradationandDevelopment14, 389–408.

Ritchie,J.C.,Ritchie,C.A.,2007.Bibliographyofpublicationsof137_{Csstudiesrelated} toerosionandsedimentdeposition.AgriculturalResearchService.USDept. Agriculture,Washington,DC.

Vandaele,K.,Poesen,J.,MarquesdeSilva,J.R.,Desmet,P.,1996.Ratesand predict-abilityofephemeralgullyerosionintwocontrastingenvironments. Ge´omor-phologie:Relief,ProcessesEnvironment2(2) 83–95.

Wallbrink,P.J.,Murray,A.S.,1996.Determiningsoillossusingtheinventoryratioof excesslead-210tocesium-137.SoilScienceSocietyofAmericaJournal60, 1201–1208.

Walling,D.E.,2010.Usingfalloutradionuclidestoinvestigateerosionandsediment delivery:somerecentadvances.In:IAHSPubl.337.IAHSPress,Wallingford,pp. 3–16.

Walling,D.E.,He,Q.,1999a.Improvedmodelsforestimatingsoilerosionratesfrom cesium-137measurements.JournalofEnvironmentalQuality28(2)611–622. Walling,D.E.,He,Q.,1999b.Usingfalloutlead-210measurementstoestimatesoil erosiononcultivatedland.SoilScienceSocietyofAmericaJournal63,1404–1412. Walling,D.E.,Quine,T.A.,1992.Theuseofcaesium-137measurementsinsoil

erosionsurveys.In:IAHSPubl210.IAHSPress,Wallingford,pp.143–152. Wischmeier,W.H.,Smith,D.D.,1978.Predictingrainfallerosionlosses:aguideto

conservationplanning.In:AgriculturalResearchServiceHandbook537.US Dept.Agriculture,Washington,DC.