Afixedlink(tunnelandbridge,intotal16km)wasconstructedbetweenSwedenandDenmarkduring1995-2000.Aspartofthework,approximately16milliontonnesofseabedmaterials(limestoneandclaytill)weredredged,andabout0.6milliontonnesofthesewerespilledinthewater.Modellingofthespreadingandsedimentationofthespilledsedimentstookplaceaspartoftheenvironmentalmonitoringoftheconstructionactivities.Inordertoverifytheresultsofthenumericalmodellingofsedimentspreadingandsedimentation,anewmethodwiththepurposeofdistinguishingbetweenthespilledsedimentsandthenaturallyoccurringsedimentswasdeveloped.Becausethespilledsedimentstendtoaccumulateattheseabedinareaswithnaturalsedimentsofthesamesize,itisdifficulttoseparatethesebasedpurelyonthephysicalproperties.Thenewmethodisbasedonthegeo-chemicaldifferencesbetweenthenaturalsedimentintheareaandthespill.ThebasicpropertiesusedarethehighercontentofcalciumcarbonatematerialinthespillascomparedtothenaturalsedimentsandthehigherCa/Srratiointhespillcomparedtoshellfragmentsdominatingthenaturalcalciumcarbonatedepositioninthearea.ThereasonforthesedifferencesisthatcarbonatederivedfromrecentshelldebriscanbediscriminatedfromDanienlimestone,whichisthematerialinwhichthemajorityofthedredgingtookplace,onthebasisoftheCa/Srratiobeing488inDanienLimestoneand237inshelldebris.Thegeochemicalrecognitionoftheoriginofthesedimentsprovedusefulinseparatingthespilledfromthenaturallyoccurringsediments.Withoutthisseparation,validationofthemodellingofaccumulationofspilledsedimentswouldnothavebeenpossible.Themethodhasgeneralvalidityandcanbeusedinmanysituationswheretheoriginoragivensedimentissought.
