A preliminary study of particle dynamics in the water column of Saronikos Gulf, Greece, by using Th-234/U-238 disequilibrium approach

In the present study the particle export flux in the water column of 3 sampling stations (one of them near the pipeline outfall of the Waste Water Treatment Plant—WWTP of Psitalia) in the Eastern Saronikos gulf, Central Greece, is investigated based on the disequilibrium ratio of 234 Th with its parent 238 U. This approach is based on direct measurements of the activity concentrations of 234 Th and calculated ones of 238 U from the respective salinity measurements. From the derived results, the values of the activity concentrations of particulate and dissolved fraction of 234 Th in the surface layer of the studied area range from 2.7 ± 1.4 to 3.8 ± 1.8 Bq m -3 and 13.2 ± 1.4 to 28.2 ± 1.9 Bq m -3 respectively, which educe fluctuation according to the station environmental features. Regarding the vertical distribution of radionuclides, the observed profile curves from the 3 sampling stations follow the same pattern of dispersion in the water column. However, the calculated export flux (sinking rate) of particles associated with 234 Th results to a wide range of values depending on the sampling station. From the calculated residence times in the 3 stations, the station near the WWTP shows the longer residence time for the dissolved fraction, which is attributed to the sewage outflow. Besides, total suspended matter (TSM) and dissolved organic carbon (DOC) have been analyzed in the samples and the correlation coefficients with the particulate and dissolved 234 Th have been calculated on the basis of the relation of 234 Th cycling with particulate matter and organic substances.

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