Raffaella Piani

The role of a spring river as a source of 137Cs in a lagoon environment: the case of the Stella river (Marano lagoon, Northern Adriatic Sea)

Abstract The results from some cruises made in order to determine the influence of the Stella river as a source of 137 Cs within the Lignano basin (Marano Lagoon, Northern Adriatic Sea) are presented. The suspended solid transport of this spring river is previously estimated. Furthermore, particle size and composition features of the Stella river particulate suspended matter are used to discuss the 137 Cs in situ K d measured in suspended matter. The pattern of salinity of water bodies in the lagoon, nearby the Stella mouth, confirm the distribution of radiocaesium in the bottom sediments.

Suspended particulate mercury associated with tidal fluxes in a lagoon environment impacted by cinnabar mining activity (northern Adriatic Sea)

The Isonzo River has been demonstrated to be a continuing point source of mercury (Hg) in the Gulf of Trieste although the Idrija mine was last active in 1996. The present study aims to investigate the role of the suspended particulate matter (SPM) associated with tidal fluxes to disperse particulate Hg (PHg) into the Grado coastal lagoon system. PHg concentrations (avg. 3.11±2.62μg/g, d.w.), notwithstanding the ebb or flood tides, were significantly higher than the local sediment background (0.13μg/g). The relative affinity of Hg for the particulate phase in surface waters was confirmed by higher average distribution coefficient (Kd) values (5.6-6.7). PHg contents showed the highest values in ebb tide conditions, thus suggesting their origin from the erosion of tidal flats and saltmarshes of the lagoon. When compared to river discharge, high PHg surface concentrations in flood tide are related to rainfall events occurring within the river basin. Results can be used to make an indicative assessment of the amount of Hg bound to SPM which is transported in and out of the lagoon basin following the action of tidal fluxes. A simple estimation provides a negative budget for the Grado lagoon sub-basin which loses between 0.14 and 1.16kg of PHg during a tidal semi-cycle. This conclusion is in agreement with the evidence of morphological deterioration which has emerged from recent studies on the lagoon environment, and which testifies to a current sedimentary loss from the lagoon into the northern Adriatic Sea.