Estuaries represent a crucial link between land and sea where river fluxes of trace elements are subjected to a variety of physical and biogeochemical processes. The boundary conditions are extremely variable in the estuarine mixing zone affecting trace element speciation and their partitioning among different phases. The Isonzo/Soča River represents the main source of Hg in the Gulf of Trieste due to past mining activity at the Idrija mercury mine (Slovenia). The aim of this work is to evaluate trace element occurrence, size partitioning and mixing behaviour at the mouth of the Isonzo/Soča River. For this purpose, large volume water samples were collected from surface, mixing and bottom layers under various seasonal conditions. Size fractionation was performed using vacuum filtration and cross-flow ultrafiltration to isolate the suspended particulate matter (SPM) and the colloidal retentate solution, respectively, from the truly dissolved. Trace elements appear to be mainly associated with the SPM and dilution effects between riverine and marine particles are responsible for the decrease in their concentration along the water column. As expected, Hg was notably present during winter in the surface freshwater, in particular under conditions of elevated river discharge. On the contrary, Mn was found to be higher at the bottom, particularly during summer, as a consequence of oxidation processes followed by the precipitation of Mn oxy-hydroxides promoted by high water temperature. The strong physico-chemical gradients, especially in terms of salinity, are often responsible for the non-conservative behaviour of several trace elements. Iron, Mn and Cu displayed a non-conservative behaviour during mixing and simultaneously showed the highest content of colloidal material. On the contrary, conservative behaviour was found for As and Cs which are often present under ionic dissolved forms in natural water systems

MIXING BEHAVIOUR OF TRACE ELEMENTS AT THE MOUTH OF THE ISONZO/SOČA RIVER (GULF OF TRIESTE, NORTHERN ADRIATIC SEA)

Elena Pavoni;Matteo Crosera;Gianpiero Adami;Elisa Petranich;Stefano Covelli;
2019

Abstract

Estuaries represent a crucial link between land and sea where river fluxes of trace elements are subjected to a variety of physical and biogeochemical processes. The boundary conditions are extremely variable in the estuarine mixing zone affecting trace element speciation and their partitioning among different phases. The Isonzo/Soča River represents the main source of Hg in the Gulf of Trieste due to past mining activity at the Idrija mercury mine (Slovenia). The aim of this work is to evaluate trace element occurrence, size partitioning and mixing behaviour at the mouth of the Isonzo/Soča River. For this purpose, large volume water samples were collected from surface, mixing and bottom layers under various seasonal conditions. Size fractionation was performed using vacuum filtration and cross-flow ultrafiltration to isolate the suspended particulate matter (SPM) and the colloidal retentate solution, respectively, from the truly dissolved. Trace elements appear to be mainly associated with the SPM and dilution effects between riverine and marine particles are responsible for the decrease in their concentration along the water column. As expected, Hg was notably present during winter in the surface freshwater, in particular under conditions of elevated river discharge. On the contrary, Mn was found to be higher at the bottom, particularly during summer, as a consequence of oxidation processes followed by the precipitation of Mn oxy-hydroxides promoted by high water temperature. The strong physico-chemical gradients, especially in terms of salinity, are often responsible for the non-conservative behaviour of several trace elements. Iron, Mn and Cu displayed a non-conservative behaviour during mixing and simultaneously showed the highest content of colloidal material. On the contrary, conservative behaviour was found for As and Cs which are often present under ionic dissolved forms in natural water systems
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11368/2948186
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