Influence of particle-size on geochemical distribution of ...

BASE Biotechnol. Agron. Soc. Environ.201317(1),43-55

Influenceofparticle-sizeongeochemicaldistributionofstreamsedimentsintheLeserivercatchment,southernItalyIlariaGuagliardi(1),CarmineApollaro(2),FabioScarciglia(2),RosannaDeRosa(2)(1)CNR-InstituteforAgriculturalandForestSystemsintheMediterranean(ISAFOM).I-87036Rende(CS)(Italy).E-mail:[email protected](2)DepartmentofEarthSciences.UniversityofCalabria.PonteBucci15B.I-87036Rende(CS)(Italy).

ReceivedonJanuary17,2012;acceptedonOctober22,2012.

This study was carried out in a river catchment in southern Italy to determine some possible relationships between thedistributionofchemicalelementsandsizefractionsinstreamsediments.Throughthepresenceofvariationsinconcentrationofsomeelementsineachsizefraction,itwaspossibletoexaminetheinfluenceofparticle-sizeongeochemicaldistributionofstreamsediments.Fromthispointofview,itisveryusefultostudytheLeserivercatchmentbecauseitisrepresentativeofthewholeMediterraneanareagivenitscharacteristics,whicharecommontoothersimilarareas.Sedimentsampleswerecollectedfrom13stations in the catchment area.The chemical compositions of bulk samples coupledwith those of some selectedparticlesizefractionswereanalyzedfor25elementsbyusingX-rayfluorescencespectrometryandfortheirsedimentologicalcharacteristics.Particle-sizeanalysiswasfocusedontryingtounderstandhowsamplesfromthesamesiteshoweddifferentgeochemicaldistributioninthedifferentsizefractions.Streamsedimentsinthestudyareaconsistmostlyofsandparticles.Chemical analyseswere performed to determine towhat extent the stream sediments retain the geochemical signature oftheirparentrocks.Somesizefractions,andnotonlytherecommended<150µm,allowedtestingofthevalidityofFOREGSprocedures, which considers the <150µm to be the optimum fraction for chemical analysis. The elemental valueswereanalyzedaccordingtothevariousthresholdsimposedbyItalianlegislativeDecreeNo.152/2006.Thisstudysuggeststhatthegeochemistryofstreamsedimentsalsoneedstobecharacterizedinordertoevaluatethepotentialchemicalpollutionofanarea.Keywords.Sediment,particlesize,geochemistry,pollution,environment,Italy.

Influence de la dimension des particules sur la distribution géochimique des sédiments fluviaux dans le bassin du fleuve Lese, sud de l’Italie.CetteétudeaétéeffectuéedansunbassinduSuddel’Italieafindedéterminerlesrelationspossiblesentreladistributiondesélémentschimiquesetlesfractionsgranulométriquesdanslessédimentsfluviaux.Enconséquence,onapuexaminer,àtraverslaprésencedevariationsdecertainsélémentsdanschaquefraction,l’influencedelagranulométriesurladistributiongéochimiquedessédimentsfluviaux.Decepointdevue,l’étudedubassindufleuveLeseaététrèsutile,carreprésentativedel’ensembledelazoneméditerranéenne,poursescaractéristiquescommunesàd’autreszonessimilaires.Leséchantillonsdesédimentsontétérecueillisdans13sitesàl’intérieurdubassin.Lacompositionchimiquedelatotalitédeceséchantillons,aveccelledecertainesfractionsgranulométriquessélectionnées,ontétéanalyséespour25élémentsparlaméthodedelafluorescence-Xetpourleurscaractéristiquessédimentologiques.L’analysegranulométriques’estconcentréesur la détermination des conditions dans lesquelles les échantillons dumême site ont démontré différentes distributionsgéochimiquesdansplusieursfractions.Lessédimentsfluviauxdelazoneétudiéesontprincipalementconstituésdeparticulesdesable.Lesanalyseschimiquesontétéeffectuéesafindedéterminerdansquellemesurelessédimentsfluviauxgardentlasignaturegéochimiquedesrochesmères.Danscertainesfractionsgranulométriques,lestandard<150µmapermisdevérifierdesprocéduresimposéesparleFOREGS,quiconsidèrelafraction<150µmcommelafractionoptimalepourl’analyseselonleslimitesimposéesparleDécretItalienn°152/2006.Cetteétudesuggèrelanécessitédecaractériseraussilagéochimiedessédimentsfluviaux,afind’évaluerl’éventuellepollutionchimiqued’unezone.Mots-clés.Sédiment,grosseurdesparticules,géochimie,pollution,environnement,Italie.

1. INTRODUCTION

Streamsedimentsarecommonlyusedasanexplorationtool for regional geochemical surveys (Cohen et al.,

1999;Cannon et al., 2004).Active stream sedimentsrepresentthefine–tomedium—grainedsolidmaterial(clayey-silty-sandy),whichconsistsoffragmentsthatarederived from theerosionofweathered rocksand

44 Biotechnol. Agron. Soc. Environ. 201317(1),43-55 GuagliardiI.,ApollaroC.,ScarcigliaF.etal.

soilbystreamorriverwaterand,dependingontheirparticlesizeandstreamwatervelocity,aretransportedin suspension, by saltation or by creeping along thestreambed.Thustheyrepresentthesourcecatchmentareaofthestreamdrainagenetwork(Ranasingheetal.,2008).

The mineralogy, particle-size and geochemistryof stream sediment in rivers have commonly beenexplainedasreflectingthecompositionofsourcerocks,mechanical and chemical weathering, hydrologicalandmorphological features of the basin, winnowingand sorting, and climate, as well as several other,possibly less important, factors (Pratt et al., 2007;Grunskyetal.,2009;Ranasingheetal.,2009;Singh,2010). Identifying the impact of natural factorsmaycontributetotheidentificationoftheimpactofhumanactivities, e.g., agriculture, mining, and industry, onstreamsedimentgeochemistry(Piperetal.,2006).

It is important to consider the influence ofgeochemical and mineralogical controls on particle-size distribution of stream sediments (Ranasingheetal.,2002).

Many research results reveal that the chemicalcompositionofsedimentvarieswithgrainsizedueto:– multiple sources contributing mineralogically and texturallydistinctgrainsizes;– mechanicalweatheringofrockfragmentsintofiner components;– chemicalweatheringofweakgrainsintoproductsof alteration.

Thestudyofthesizefractionsinastreamsedimentsampleprovides thebestopportunity for recognizingdifferentgeologicalprocesses.Theycanhaveastronginfluence on how the geochemistry of an area maybe interpreted (Grunsky et al., 2009). Indeed, someelements have a strong affinity for particles, andtheirsubsequentfateisstronglyinfluencedbyfluvialprocesses.

Studies of the distribution of trace elements inrelationtothesizefractionofstreamsedimentsgenerallyshowthatseveralelements,includingMo,Cu,Zn,MnandFe,areconcentratedin thefinestfractionsof thesediment (Horowitz et al., 1987;Moore et al., 1989;Stoneet al., 1996;Singhet al., 1999).Therefore themajorityofstreamsedimentsurveyshavebeenbasedonthecollectionof<200μmmaterial.

The FOREGS (Forum of European GeologicalSurvey) standardsievemesh is<150μm: this isnotonlyfineenoughtoincludetheveryfinesand,silt,clayand colloidal fractions, but it is also coarse enoughto yield sufficient fine material in the majority ofsituations(Salminenetal.,1998).

Thereforethe<150μmsizefractionisparticularlyuseful for regionalgeochemistrysampling.However,inthissurvey,othersizefractionswerealsomeasured

to test the possibility that some elements of interestmaybetendentiallyboundtocoarserones.

Itisalsoimportanttounderstandthedistributionandvariabilityofelementswithinfluvialsystemsinordertoevaluateriskandpotentialenvironmentalremediationoptions(Reneauetal.,2004).Indeedparticlesizeplaysasignificantroleintheaccumulationofheavymetalsandotherpotentiallyharmfulelements,andmanagingtheterritoryrationallymeansdeterminingthesetoxicelements. Moreover, heavy metal accumulation caninfluencetheimpactthatenvironmentalpollutioncanhaveonman,animalsandvegetation.Forthisreason,inrecentyears,theinterestthegeochemicalmappingofstreamsedimentsholdsfortheinternationalscientificcommunityhas increasedconsiderably.Basedon theabove considerations, we decided to carry out thisstudyinacatchment,whichissuitableforthestudyofthesephenomena.InfacttheLeserivercatchmentcanbe considered representative of the whole Calabrianterritory, as well asMediterranean zones in general,becauseofitsgeological,geomorphological,climatic,andhumanpressurecharacteristicsthatarecommontotheseareasandmaketheLesecatchmentofsouthernItalyanareaofscientificinterest.Thepurposesofthispaperwere:– to compare the geochemistry of stream sediments withlocalparentrocksintheLeserivercatchment (southernItaly),inordertoinvestigatetheinfluence ofparticle size and the lithological featuresof the source area on the concentration of chemical elements;– to quantify potentially harmful element concentrations in different particle size fractions in relation to Italian legislative Decree No.152 of 03/04/2006 by approximating the sediments to thesoils.Thiswasbecause theItaliangovernment established intervention values for some selected toxic elements in soil, stream water and marine sediments,butnotforstreamsediments;– to show that the particle size fraction <150μm, asimposedbyFOREGS,iseffectiveinrepresenting theentirestreamsedimentintermsofgeochemical composition.

2. MATERIALS AND METHODS

2.1. Geological and geomorphological setting

TheLeserivercatchmentislocatedintheSilaMassifinthecentral-easternsectorofCalabriaandisincludedin theCrotonesedimentarybasin.TheCrotonebasinis considered to be amember of the Ionian ForearcBasin (Amodio-Morelli et al., 1976), located alongthe southern border of the Calabrian Arc (Zecchinetal.,2004).ItisboundedbytwoNW-SEfaultzones,

Streamsedimentgrainsizeandgeochemicalcomposition 45

Rossano-SanNicola to the north andPetilia-Sosti tothe south (Tortorici, 1982;Meulenkampet al., 1986;VanDijk,1990;VanDijk,1991;VanDijketal.,1991;VanDijketal.,2000).

The study area consists of middle-high- to low-grade metamorphic rocks, Palaeozoic plutonic rocksandasedimentary turbiditicsuccession thatoccurredbetween the Miocene and the Pleistocene (Messinaetal.,1991;Messinaetal.,1994)(Figure 1a).

Lithologicaloutcropsinthestudyareaaremainlyformedofacomplexofintrusiveacidrocksofvaryingcomposition (quartz-diorite, quartz-monzonite,granodiorites, granite) and low- to medium-grademetamorphites(shale,clayey-schist,phyllite)affectedby cleavage (Lorenzoni et al., 1983). These rocksinclude elements relating to oceanic and continentalalpineunitsandaregenerallyaffectedbyveryintensecleavageandfractures.Inaddition,sedimentarydetriticterrains, mainly pelitic with subordinate evaporiteintervals, occur widely in the southernmost part ofthecatchment.TheseincludeupperMiocenedeposits,withbothevaporiticanddetritic facies,andPliocenesandy,clayeyandmarlydeposits(Sorriso-Valvoetal.,1996). The most elevated portion of the catchmentis the result of tectonic uplift,whichoccurred at thebeginningof thePleistocene,and ischaracterizedbyawidespreadregolith,whichhasnotyetbeenerodedandoftenreachesathicknessofseveraltensofmeters(LePeraetal.,2001).Athickmantleofalteredproducts

(regolith+soil)covers thecrystallinebedrockof theLesebasin.Thedifferentstagesofweatheringof thebasement rocks that initiated in the lowerCenozoic-Quaternary, are characterized by different colors,mineralogicalalterationandtexturalchange(LePeraetal.,2000).Theweatheringprofileusuallyconsistsoforganicsoilhorizonsonthickerlayersofgrus,whichhave been completely removed by erosion in placesleavingfreshbedrockoutcrops.

TheLeseriverdrainagebasinisalefttributaryofthe Neto river. The Neto river basin covers an areaof 1,073.29 km2 and, along its length, the principalchannelgraduallyflowsacrossplutonic,metamorphicandsedimentaryrocks.Numerousstreamswithin thecatchment tend to emplace alluvial fans toward thelowestreachesoftheSilaMassif,producingdifferentnatural(wildandsuggestive)landscapes.

2.2. Sampling and chemical analyses

AswasrecommendedbyFOREGS,theForumoftheEuropeanGeologicalSurvey (Plant et al., 1997), theactivestreamsedimentswerecollectedfromthesmall,second order, drainage basin at a suitable site abovethepointofitsconfluencewiththemain,thirdorder,channelofthelargedrainagebasin.

Thirteen stream sediment sampleswere collectedfromthestudyarea(Figure 1b)andsamplelocationsweremarkedoncompilationmapsanddigitized.Each

Figure 1. a: GeologicalsketchmapofLeserivercatchmentthatconsistsofmetamorphicrocksandasedimentaryturbiditicsuccession— Schéma géologique du bassin du fleuve Lese qui est constitué de roches métamorphosiques et de roches sédimentaires torbiditique en série;b:Samplingmapofstudyareawiththeindicationsofthe13investigatedsites—Plan de l’échantillonnage de la zone d’étude avec l’indication des 13 sites étudiés.

Sea and continental sedimentary deposits (Plio-Pleistocene)Sedimentary detritic deposits (Miocene-Pliocene)Sedimentary detritic rocks of sea origin (Miocene)Metamorphic rocks of low degree (Paleozoic)Acid and metamorphic intrusive rocks of middle-high degree (Paleozoic)

Sampling points

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stream sediment sample includes material collectedfrom5-10pointsoverastreamsegmentof250-500m.Theentiresetofsampleswerecollectedwithaplasticspatula and kept in PVC packages. Then, followingFOREGS procedures, part of these samples wasinitiallysievedin situtoagrainsizeof<2,000μmsoastoremovecoarsesandandafterthrougha150μmsievetopickupmud,clayandcolloidalparticles.Metalfreenylonsieve-meshhousedininertwoodwasused.

All thesamplesweremovedontoasheetoffilterpaperinthelaboratoryandplacedintoanovenat50°Cforavaryingperiodofthreetofivedaysonthebasisofthegreaterorlesserpresenceofwaterinthesediments.

The bulk stream sediment samples were sievedthroughanunifiedseriesofsievesfrom>2,000μmto<63μm (ASTMcodes) by usingmechanical sieves.Quantitativeassessmentofthepercentageofdifferentgrainsizeinstreamsedimentswasperformedandthedistributionofdifferentsizefractionswasdeterminedbyweighingthecontentsofeachsieve.

Eachsizefractioninthesampleswasgroundupintopowderwithin amechanical agatemortar and boric-acidbackedpelletswerepreparedwiththepowderforX-rayfluorescencespectrometry(XRF).

Elemental analyses for major and some traceelements were obtained by Philips PW 1480X-rayfluorescence spectrometry in theX-ray laboratory oftheUniversityofCalabria(Italy).

Tenoxidesofmajorelements(NaO,MgO,Al2O3,SiO2,P2O5,K2O,CaO,TiO2,MnO,Fe2O3)andfifteentraceelements(Ni,Cr,V,La,Ce,Co,Ba,As,Pb,Zn,Nb,Zr,Y, Sr,Rb)were determined on bulk sample,on seven size fractions (>2,000μm, 2,000-500μm,500-250μm, 250-125μm, 125-63μm, <63μm) andparticularlyon the size fraction<150μm.Total losson ignition (L.O.I.)wasdeterminedafterheating thesamplesfor3hat900°C.

Tounderstandthesignificanceofthegeochemicalcompositionofstreamsediments,fivesamplesofthemainrockspresentinthestudyarea(evaporites,clays,schists,quartzitesandgranodiorites)werecollectedonoutcrops.Portionsoftherocksamplesweregroundtofineparticles,usingamechanicalagategrinder,beforebeing analyzed. The analyses of the rock samples,onpressedpowderdisks,werealsocarriedoutattheX-raylaboratoryof theUniversityofCalabria(Italy)by using the same X-ray fluorescence spectrometryutilizedforstreamsedimentsamples.

Accuracy of the data was determined as <3%through analysis of the U.S. Geological SurveystandardsAGV-1,BCR-1,BR,DR-N,GA,GSP-1,andNIM-G,attherateof1pereachbatchof10samples.The precision (<5%) was determined by analysisof duplicate samples. During the analyses, testedmethodologiesofqualityguaranteewereappliedforagoodlevelofdatareliability.

3. RESULTS AND DISCUSSION

3.1. Grain-size distribution

The study of the pattern of grain-size distribution inriver-transportedsedimentsisimportantbecauseitisasource-rock-specificprimaryfeature.

Thecurvesofcumulativefrequencyforalmostallof the samples show a high degree of homogeneity:indeed the sandy fraction, with about 83% of totalpercentagesinweightofallsamplesonaverage,wasmostpresent,whiletheothers,gravellyandsilty-clayeyfractions,showedlowerpercentagesinweight.Theseresultsaredisplayedintable 1.

3.2. Geochemistry

Comparisonofmajorandtraceelementconcentrationsin the different size fractions of stream sediments inthe studied river catchment is shown in table 2.Thestream sediment composition is strongly affected bytherockchemistryofthearea.

It is useful to examine the availabledata throughsomebinarydiagramsinwhichthebulkcompositionsof the 13samples are compared with the averagecompositions of local evaporites, clays, schists,quartzites and granodiorites. The trends identifiedinclude variations that almost always lie within thecompositional ranges (mean values) of outcroppinglithologies as well as some rare anomalies of someelementsthatareoutsidetheseranges.

In the diagrams for these trends, silica wasselected as a reference variable because it is one ofthe largestcomponentsofall rock types in thestudyarea, although there are strong differences betweenevaporites(6,55%inweight),granodiorites(70,85%)andquartzites(75,35%).Almostallsamplesfallwithinthecompositionalfielddefinedbytheaveragecontentsoflocalclays,granodioritiesandquartzitessuggestingthatstreamsedimentsarestronglyinfluencedbylocalgeology.Infigure 2somerepresentativeelementsareshown.

The influence of local rock chemistry was alsoconfirmed in some diagrams, shown in figure 3,on the particle size fraction >2,000μm, where twopopulations of samples can be easily separated, incomparisontotheconsideredelements.

Table 1. Particle size distribution of Lese sediments—Distribution granulométrique des sédiments du fleuve Lese.

Min (%) Max (%) Mean (%) St. Dev.Gravel 0 29.93 13.14 9.59Sand 65.85 97.47 83.51 9.70Silt-clayey 0.70 10.55 3.34 2.92


An initial group, including the samples C2, C7,C9,C10,C11andC12,ischaracterizedbylowvaluesof FME (Fe2O3, Ni, Cr, Co) and TiO2, suggesting aderivation of the sediments by lithological intrusiveacidoutcrops.Asecondgroup,lesshomogeneousthanthefirstone,includesthesamplesC1,C3,C4,CZ,LE1,C8.1andC8.2thatshowedawiderrangeinvaluesofalltheconsideredelements,althoughtheyarealwayshigherthanthoserelatingtothefirstgroup.Theoriginofthesediment,inthiscase,canprobablybeascribedtoschistsandgneiss.

Duetotheircommonorigin,geochemicallysimilarsedimentswouldbeexpectedtohavethesamebehavior,but there are two different main populations due tosourcevariationsorphysicaland/orchemicalprocessesthatsystematicallymodifysedimentcomposition.

From an environmental perspective, trendsrepresentelementalnaturalbackgroundbehavior.

The study of the chemical composition of thestream sediments allowed us not only to assess howitisinfluencedbythegeologicalsubstrate,butalsotoevaluatethechemicaleffectsduetohydraulicsorting.In fact these effects, together with the particle-sizeof the stream sands, notably influence the chemicalcomposition of samples according to parent rockmineralogy.

The compositional changes among just threeparticle-size fractions, >2,000μm, 500-250μm and<63μm,were represented by using spider diagramsnormalized to the bulk composition of each sampleso that rateshigheror lower than1 indicate elementenrichmentordepletion,respectively,intheconsidered

Table 2.StatisticalanalysisandcomparisonofmajorandtraceelementconcentrationsinthedifferentsizefractionsofLesesediments—Analyse statistique et comparaison des concentrations en éléments majeurs et en eléments traces dans les différentes fractions granulométriques des sédiments du fleuve Lese.

Unit > 2,000 µm 2,000-500 µm 500-250 µm

Min Max Mean St. Dev. Min Max Mean St. Dev. Min Max Mean St. Dev.NaO %wt 0.7 3.5 2.4 0.9 1.0 2.4 2.0 0.5 0.8 2.4 2.0 0.5MgO %wt 1.2 3.8 1.7 0.7 0.7 3.1 2.1 0.8 0.7 3.8 2.1 0.9Al2O3 %wt 5.9 15.9 13.3 3.5 5.6 15.3 12.7 3.2 5.9 16.0 12.6 3.2SiO2 %wt 36.4 72.2 64.7 11.6 46.2 74.5 67.2 6.9 40.3 74.1 67.0 8.4P2O5 %wt 0.1 0.1 0.1 0.0 0.1 0.1 0.1 0.0 0.1 0.1 0.1 0.0K2O %wt 1.2 4.2 3.2 0.9 1.8 4.4 3.7 0.8 1.5 4.2 3.6 0.8CaO %wt 0.8 27.3 5.3 8.8 1.0 20.0 3.9 6.0 0.9 23.6 4.2 6.6TiO2 %wt 0.2 0.5 0.3 0.1 0.1 0.7 0.4 0.2 0.1 0.8 0.4 0.2MnO %wt 0.0 0.1 0.1 0.0 0.0 0.1 0.1 0.0 0.0 0.2 0.1 0.0Fe2O3 %wt 2.0 4.1 2.9 0.8 1.2 5.0 3.3 1.1 1.2 5.2 3.4 1.1Ni ppm 5.0 36.0 15.2 9.6 5.0 39.0 11.7 8.9 5.0 56.0 13.2 13.3Cr ppm 11.0 51.0 29.0 15.3 12.0 31.0 19.0 6.6 13.0 39.0 21.4 7.9V ppm 27.0 80.0 47.0 14.7 14.0 84.0 51.7 22.4 14.0 93.0 52.5 22.3La ppm 18.0 31.0 22.5 4.7 6.0 32.0 19.2 8.2 10.0 42.0 24.0 8.8Ce ppm 30.0 58.0 42.5 10.2 13.0 60.0 31.2 12.6 15.0 72.0 44.2 15.9Co ppm 5.0 11.0 7.5 2.3 4.0 12.0 8.2 2.2 4.0 14.0 8.6 2.6Ba ppm 502.0 990.0 728.8 132.1 541.0 1265.0 801.5 159.8 484.0 2390.0 853.6 478.5As ppm 2.0 10.0 5.1 2.7 2.0 9.0 5.8 2.2 3.0 12.0 6.7 3.3Pb ppm 8.0 54.0 17.8 12.7 10.0 26.0 19.1 4.1 7.0 35.0 19.2 6.2Zn ppm 24.0 86.0 45.5 21.7 8.0 101.0 50.3 24.3 5.0 86.0 53.2 23.4Nb ppm 4.0 12.0 7.1 3.0 0.0 16.0 8.0 4.8 0.0 13.0 8.1 4.3Zr ppm 87.0 176.0 125.5 29.4 72.0 215.0 120.2 37.5 64.0 237.0 117.6 41.7Y ppm 2.0 25.0 14.8 7.4 0.0 17.0 11.1 6.1 1.0 17.0 11.7 5.4Sr ppm 100.0 5319.0 754.8 1461.8 125.0 6641.0 778.7 1856.6 118.0 7323.0 768.9 1976.5Rb ppm 52.0 147.0 110.8 27.1 62.0 142.0 116.3 24.5 58.0 133.0 112.6 20.8


fraction.Intheserepresentations,itwasobservedthatthe particle-size fraction that was compositionallymostdifferentfromthebulkcompositionwasthatof<63μm(Figure 4).

The effects of particle-size and grain shape areresponsible for the concentration of clayminerals inconcomitancewith adecreaseof quartz and feldsparin the finest fraction. In the <63μm particle-size,thisproducesadecreaseinSiO2andacorrespondingincrease in the content of other elements, such asAl2O3,K2OandTiO2,andmanytraceelementsthatareprobablyrelatedtoclaymineralsand/orironoxides.Inparticular,theseelementsmayenterthecrystallatticeofthesemineralphasesorbeadsorbedontheirchargedsurfaces as a consequence of pedogenetic processes(Nesbitt,1979;Patinoetal.,2003;Casparietal.,2006).

Argast et al. (1987) suggest that, in the silty-clayeyfraction (<63μm), potassium is transported in theformofdetritalorneogenicilliteinwhichtheprincipalinter-layercationispotassium.Thepositivecorrelationbetween Al2O3 and K2O existing in the <63μmfractionconfirmedthatthefinestfractioncontainsthemost detrital or neogenic illite and that, in contrast,the coarse fraction (>2,000μm) contained the mostquartz.Ifthesiliciclasticcomponentisconsideredtobethesourceofquartzinthebedsediment,theregressionforSiO2versusAl2O3canbeinterpretedastracingthechangeincompositionofthistwo-componentsystemastheAl-silicatemineralsareselectivelyremovedbysedimentwinnowingorchemicalleaching.

Fe2O3, Co and Cr show higher values ofconcentration in the silty-clayey fractions than in

Table 2 (continued).Statisticalanalysisandcomparisonofmajorand traceelementconcentrations in thedifferent sizefractionsofLesesediments—Analyse statistique et comparaison des concentrations en éléments majeurs et en eléments trace dans les différentes fractions granulométriques des sédiments du fleuve Lese.

Unit 250-125 µm 125-63 µm <63 µmMin Max Mean St. Dev. Min Max Mean St.Dev. Min Max Mean St.Dev.

NaO %wt 0.8 2.7 2.1 0.5 0.6 2.5 1.7 0.5 0.6 2.5 1.5 0.5MgO %wt 0.9 2.9 1.9 0.6 1.9 4.4 2.8 0.7 2.5 5.0 3.3 0.8Al2O3 %wt 5.9 14.8 12.3 2.9 8.6 17.7 14.1 2.8 8.8 18.6 15.2 3.4SiO2 %wt 36.3 72.2 65.5 9.4 38.4 67.1 59.3 8.3 37.2 61.0 53.6 6.6P2O5 %wt 0.1 0.2 0.1 0.0 0.1 0.2 0.2 0.0 0.2 0.4 0.2 0.1K2O %wt 1.3 3.8 3.2 0.7 1.5 3.4 2.9 0.6 1.4 3.6 2.7 0.6CaO %wt 0.9 25.2 5.0 7.0 1.4 21.8 6.6 6.6 1.9 19.9 6.9 6.0TiO2 %wt 0.2 0.6 0.4 0.1 0.4 0.9 0.6 0.2 0.4 1.0 0.7 0.2MnO %wt 0.0 0.2 0.1 0.0 0.1 0.2 0.1 0.0 0.1 0.1 0.1 0.0Fe2O3 %wt 1.5 6.0 3.7 1.1 3.0 5.9 4.4 0.7 3.9 6.7 5.1 0.8Ni ppm 4.0 68.0 16.4 16.8 8.0 58.0 21.5 13.8 12.0 61.0 34.2 14.8Cr ppm 16.0 44.0 26.4 7.7 26.0 69.0 45.3 12.6 38.0 135.0 79.7 25.8V ppm 21.0 117.0 59.8 24.1 57.0 103.0 76.8 13.5 81.0 125.0 96.2 13.3La ppm 14.0 48.0 32.2 10.9 25.0 53.0 36.6 9.5 24.0 73.0 46.9 16.1Ce ppm 14.0 100.0 64.4 24.1 31.0 114.0 67.8 23.9 53.0 140.0 94.1 30.8Co ppm 6.0 17.0 10.2 3.1 9.0 18.0 11.2 2.6 13.0 18.0 14.7 1.7Ba ppm 441.0 1993.0 820.2 408.3 372.0 848.0 625.6 118.3 360.0 695.0 590.8 95.8As ppm 3.0 19.0 8.6 5.0 3.0 27.0 9.8 7.2 5.0 24.0 10.7 6.9Pb ppm 12.0 38.0 21.4 7.0 9.0 39.0 24.1 8.4 12.0 49.0 27.4 10.0Zn ppm 14.0 107.0 59.7 25.3 29.0 137.0 70.6 32.1 54.0 147.0 96.2 28.8Nb ppm 1.0 11.0 8.2 3.3 5.0 14.0 10.9 3.1 6.0 18.0 13.0 3.4Zr ppm 72.0 179.0 129.0 30.8 167.0 662.0 339.9 167.9 258.0 1454.0 754.3 459.6Y ppm 3.0 24.0 16.9 6.2 8.0 50.0 30.8 12.6 12.0 86.0 50.8 24.0Sr ppm 118.0 5335.0 627.8 1423.1 122.0 4902.0 665.4 1297.4 127.0 6123.0 819.6 1630.4Rb ppm 54.0 120.0 105.0 18.6 65.0 137.0 107.6 18.0 67.0 141.0 114.1 22.6


Figure 2. Correlationdiagrams—Diagrammes de corrélation.

Bulkcompositionsofsamplesarecomparedwiththelocalaveragecompositionsoflocalrocktypesforsomerepresentativeelements— Les compositions de la masse des échantillons sont comparées avec les compositions moyennes des roches locales pour certains éléments représentatifs. : lithologicaloutcropscomposition— composition lithologique des affleurements;: streamsedimentscomposition— composition des sédiments fluviaux.

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4

0

0.16

0.14

0.12

0.10

0.08

0.06

0.24

0.20

0.16

0.12

0.08

0.04

0

MnO

(%w

t)P

2O5

(%w

t)A

s (p

pm

)Z

r (p

pm

)

0 20 40 60 80

0 20 40 60 80

0 20 40 60 80

0 20 40 60 80

SiO2 (%wt)


the coarseones (Figure 4).Thismaybe related to agreaterconcentrationofbiotite,chlorite,andmagnetitecrystals in the silty-clayey fraction of the sediment(Cullers,1988).

Dataonthestudyareashowcorrelationsbetweentheseelementsandcertainminerals.Theseassociationsare described by some authors, such as Deer et al.(1992)whoreportedthatsphene,zirconandrutileareassociatedwithmagnetiteandprobablyaccountforthestrongrelationsbetweenmagnetiteandFe,CoandCr.ThisisalsotrueforLesesedimentswhere,furthermore,Ca,Mg,TiandVareassociatedtoo.

In the silty-clayey fractions, more elevatedconcentrationsofZrandYwere found.Thepositivecorrelation (R2=0.851) between these two elements(Figure 5) suggests the presence of zircon crystals.Indeed, zircon is an accessory residual mineral thatis common in many sediments, in which it is oftenresistanttomorethanonecycleofalteration(Wuet al.,2004).Thusgrain-sizeeffectsmaycontributetoahighzirconconcentrationinthe<63µmfraction.

The positive correlation between Fe2O3 and V(R2=0.665) (Figure 5) clearly suggests that theirabundanceisrelatedtothepresenceofiron-richchloriteinthefinestfractions.Indeed,chloriteoftenoccursinclaymineralsinfineiron-richsediments,becausethedeficit of negative charge left in it by aluminium isbalancedbytheFe3+ion(LePeraetal.,2000).

Thecontentsof some traceelements, suchasLa,Ce, Zr andY, were very low in the sandy fraction,due to its being particularly depleted in transitionelements, in comparisonwith theother fractions andthebulksample.Thetransitionelementsarelocatedintheoctahedrallayersand/oradsorbedontonegativelycharged surfaces of clay minerals. In the <63μmfraction,anenrichmentoftheseelementswasnoticedtogether with an increase ofAl2O3, which indicatesa dominant influence on element fractionation byweathering and pedogenetic processes (Mongelli,1993;Laveufetal.,2009;Scarcigliaetal.,2011).

Forthebulkcomposition,thelackofanysignificantrelationshipbetweenSiO2andSrwasnoticedtogether

Figure 3. Elemental concentration in the particle size fraction> 2,000μm— Concentration des éléments de la fraction granulométrique > 2 000 µm.

Twopopulationsofsamplescanbeeasilyseparated,suchasrepresentedwithellipses— Les deux populations d’échantillons peuvent être facilement séparées, comme représenté par les ellipses.

69 70 71 72 73 74 75

69 70 71 72 73 74 75

0.6

0.5

0.4

0.3

0.2

60

50

40

30

20

10

TiO

2 (%

wt)

Cr

(pp

m)

SiO2 (%wt)

69 70 71 72 73 74 75

69 70 71 72 73 74 75

4.5

4

3.5

3

2.5

2

20

16

12

8

4

Fe2O

3 (%

wt)

Ni (

pp

m)

SiO2 (%wt)


Figure 4. Bulk normalized plots of data from three size fractions (> 2,000 μm, 500-250 μm and <63 μm) of the samesamples—Diagrammes normalisés à la totalité des échantillons de trois des fractions granulométriques (> 2 000 µm, 500-250 µm et < 63 µm ) des mêmes échantillons. Thecompositionalchangesarerepresentedwithspiderdiagramsnormalizedtothebulkcompositionofeachsample—Les changements de composition sont représentés par des diagrammes spider normalisés à la composition totale de chaque échantillon.

Sample C1 Sample C2

Sample C3 Sample C4

Sample C8.1 Sample C8.2

Sample C12 Sample C10

>2,000μm.bulk-1500-250μm.bulk-1< 63 μm.bulk-1

43.5

32.5

21.5

10.5

0

54.5

43.5

32.5

21.5

10.5

0

876543210

109876543210

876543210

76543210

12

10

8

6

4

2

0

141210

86420

LOINaO

CaOM

nOFe 2

O 3Ni Cr V La Ce Co Ba As Pb NbZn Zr Sr RbYTiO2

MgOAl 2

O 3

SiO 2

P 2O 5

K 2O

LOINaO

CaOM

nOFe 2


MgOAl 2

O 3

SiO 2

P 2O 5

K 2O

LOINaO

CaOM

nOFe 2


MgOAl 2

O 3

SiO 2

P 2O 5

K 2O

LOINaO

CaOM

nOFe 2


MgOAl 2

O 3

SiO 2

P 2O 5

K 2O

LOINaO

CaOM

nOFe 2


MgOAl 2

O 3

SiO 2

P 2O 5

K 2O

LOINaO

CaOM

nOFe 2


MgOAl 2

O 3

SiO 2

P 2O 5

K 2O

LOINaO

CaOM

nOFe 2


MgOAl 2

O 3

SiO 2

P 2O 5

K 2OLO

INaO

CaOM

nOFe 2


MgOAl 2

O 3

SiO 2

P 2O 5

K 2O

Sam

ple

/bul

kS

amp

le/b

ulk

Sam

ple

/bul

kS

amp

le/b

ulk


with a high correlation (R2=0.867) between Sr andCaO:thisbehaviorsuggeststhatstrontiummayreplacecalciumincalciteoraragonite(Reimannetal.,2003).

3.3. Is < 150 µm the optimum fraction for chemical analysis?

Recommendations in the FOREGS GeochemicalMapping Field Manual (Salminen et al., 1998)regarding the optimum fraction indicate <150µmas being the most appropriate fraction for chemicalanalysis,becauseitisnotonlyfineenoughtoincludetheveryfinesand,silt,clayandcolloidalfractions,butitisalsocoarseenoughtoyieldsufficientfinematerialinthemajorityofsituations.Inthisstudy,wetestedthisassumptionbycomparingsevenparticle-sizefractions,as well as the <150µm, in order to corroborate orcontradicttherecommendationsofFOREGS.Themainresultsofthiscomparisonaredisplayedinsomebinarydiagrams (Figure 6), which show that the <150µmfractionencapsulates theentire streamsedimentwell

and reproduces its dominant geochemical behavior.ThisconfirmsthevalidityoftheFOREGSassumptionthatconsidersthe<150µmfractiontobetheoptimumfractionforchemicalanalysis.

3.4. Evaluation of the regulatory thresholds of element contamination

The Italian government has established interventionvaluesforsomeselectedtoxicelements(As,Cd,Co,Cr,Cu,Hg,Ni,Pb,Sb,Se,Tl,VandZn)insoilandstreamwater(Ministerodell’Ambiente,2006),butnotforstreamsediment.Byadoptingthesamethresholdsfor sediments as for soils, it was noticed that twoelements exceeded the regulatory thresholds whichareconsideredacceptableinsitesdestinedforpublic,private and residential green use (LimitA of ItalianLegislativeDecreeNo.152of03/04/2006).

More precisely, arsenic exceeded the regulatorythreshold (20ppm) of concentration for 18% ofthe analyzed sediments in the <150μm fraction of

Figure 5. Elemental concentration in the particle size fraction < 63 μm—Concentration des éléments dans la fraction granulométrique < 63 µm. Inthesegraphsareshowedthepositivecorrelationsbetweentheconsideredelements—Ces graphiques montrent les relations positives entre les éléments étudiés.

0 400 800 1200 1600

100

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120

100

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1600

1200

800

400

0

Zr (ppm)

Zr

(pp

m)

Y (p

pm

)

Y (p

pm

)

V (p

pm

)

La (p

pm

)

Ce

(pp

m)

Fe2O3 (%wt) Al2O3 (%wt)

Al2O3 (%wt) Al2O3 (%wt)Al2O3 (%wt)

12 14 16 18 20 12 14 16 18 20 12 14 16 18 20

12 14 16 18 205 5.5 6 6.5 7 7.5


the CZ and C8.1 samples. Vanadium exceeded theregulatorythreshold(90ppm)in50%oftheanalyzedsamples, particularly in the<150μm fraction of the

C1,C4,LE1,C8.1,C8.2,C9andC10samples.Inalltheanalyzedsamples, thevaluesofcobalt, chrome,nickel,leadandzincconcentrationfellbelowLimitA

Figure 6.Comparisonofelementalconcentrationinallsizefractionsandin<150µm—Comparaison de la concentration des éléments dans chaque fraction granulométrique et dans la fraction < 150 µm.

Inthesegraphsitisclearlydisplayedthatthe<150µmfractioniswellabletorepresentthewholestreamsedimentsuchasindicatedinFOREGS—Ces graphiques montrent clairement que la fraction < 150 µm est parfaitement capable de représenter la totalité des sédiments fluviaux, comme le FOREGS l’indique.

50 55 60 65 70 75 80

50 55 60 65 70 75 80 50 55 60 65 70 75 80

50 55 60 65 70 75 80 50 55 60 65 70 75 80

50 55 60 65 70 75 80

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As

(pp

m)

Co

(pp

m)

Cr

(pp

m)

Pb

(pp

m)

V (p

pm

)

Ni (

pp

m)

SiO2 (%wt) SiO2 (%wt) SiO2 (%wt)

SiO2 (%wt)SiO2 (%wt)SiO2 (%wt)

50 55 60 65 70 75 80

160

120

80

40

0

Zn

(pp

m)

bulk> 2,000 μm2,000-500 μm500-250 μm250-125 μm125-63 μm< 63 μm

SiO2 (%wt)

< 150 μm


andwere,therefore,withinthelimitsofacceptabilityimposedbytheDecree.

4. CONCLUSION

The elemental distribution in different grain sizefractions of stream sediments is a very importantaspect that needs special emphasis in geochemicalexploration.

The Lese catchment provided an excellentopportunityforevaluatinghowparticle-sizeinfluencesthe geochemical distribution of stream sedimentsand for formulating some considerations on theirrelationshipswithmineralogicalassemblagesofparentrocks. This study proved that element concentrationlevelsvarysignificantlywithgrainsize.

Allthestreamsedimentsamplesanalyzeddisplayedone prevailing particle size fraction, i.e. the sand-grainedfraction,whichisfarmoreevident thanboththefinerandcoarserfractions.

Analysis of element concentrations in the bulkcompositions suggests that local lithologies arethe main factor in their distributions. The chemicalanalysesofsomemajorandtraceelementsshowedaclear geochemical imprint that allowed the possiblemineralogicalcompositiontobehypothesized.

Thecomparisonofthepatternsrelatingtothethreefractions, chosen as representatives of thewhole setofsamples,underlinedthebehaviorofsomeelementswithinthefractions.Amongotherthings,thedecreaseinSiO2andthecorrespondingincreaseinthecontentofotherelements,suchasAl2O3,K2O,TiO2andmosttraceelements, suggest that theyareprobablyboundin the clay mineral or iron oxide crystal lattices oradsorbed on their charged surfaces, in the <63μmfraction.Duetotheirsizeandmorphology,aswellasmechanicalsortingorpedogenesis,thephyllosilicatesusuallydominatethefinestsedimentaryfraction,whilequartzandfeldspardominatethecoarsest.

Thestudyofalltheparticlesizefractions,andnotonlythe<150μmfractionusedinstandardprocedure,allowedbetterdetailingoftheconcentrationbehaviorwithin the sampled sediments. Indeed, thanks to thismoredetailedanalysis,itwaspossibletogetresultsonelementdistributions,withinsinglesamples,intermsof their particle size distribution and the presumedmineralogyoftheirparentrocks.

Althoughthe<150μmfractionappearstocapturethe entire stream sediment composition well, onlythe complete set of particle size fractions permitsthe tracingandcorrect interpretationof their specificgeochemicaldistributionandbehavior.

Therefore, this paper allows optimization of theanalytical procedure for the determination of thechemicalelementsinstreamsediments.

Inaddition,itemergedfromthechemicalanalysisthat two elements, arsenic and vanadium, exceededthe threshold imposed by Italian Legislative DecreeNo.152/2006.This result suggests that, given that itrepresentsanimportanttooltopreservehumanhealth,thegeochemistryofstreamsedimentsalsoneedstobecharacterized in order to evaluate potential chemicalpollutionofanarea.

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