Abstract
Assessing the environmental quality of coastal systems is important not only for the management and protection of such areas, but also for improving the quality of water resources. Since sediment itself can often be a source of certain toxic elements, in addition to information on the distribution of metals in the water column and in the sediment itself, it is useful to determine the bioavailable forms of individual elements, particularly toxic ones. In this study, water and sediment geochemical data were supplemented with oxyanion mobility in sediments estimated by diffusion gradients in thin film (DGTs). The data obtained indicate that the chemical composition of the water in the Raša River estuary primarily reflects the high input of suspended sediment from the catchment, the mixing of freshwater and seawater, and to a lesser extent the effects of anthropogenic activities. Although sediment composition is primarily determined by geological and hydrodynamic conditions in the catchment, it also indicates moderate enrichment in Co, Cr, Mo and Ni. In contrast, the distribution of oxyanions in sediment pore water indicates the influence of sediment as a source of some elements in the bottom water; e.g., sediment contributes to 40% of the arsenic bottom water budget. The obtained depth profiles of the oxyanion distribution in the sediment pore water indicate an early onset of suboxic to anoxic conditions in Raša Bay, which is prone to rapid sedimentation. All this demonstrates the need to consider the bioavailable forms of elements when assessing environmental quality, as the lack of such information can lead to an incomplete assessment, especially in dynamic coastal systems such as estuaries.
Highlights
The Adriatic Sea is part of the Mediterranean Sea
ReFsiunltes-grained particles predominate in the samples studied (Table 1), with a p2r.o1.pGorratiinoSniszeoDficstlraibyu,tsioinltinanSeddismaenndts of 20%, 51% and 29%, respectively
Information on the geochemistry and mineralogy of Raša coal and the impact of its combustion products on the local soil, biota and water system is beyond the scope of this article and can be found elsewhere [2,3,35,36,37]
Summary
The Adriatic Sea is part of the Mediterranean Sea. Separated by the Italian Peninsula and the Balkan Peninsula, it extends from the Gulf of Venice southward to the Strait of Otranto. A comparison of concentrations of detergents, oils, phenols, heavy metals and other pollutants has shown that the input to the Adriatic Sea is the lowest compared to the Black Sea and the Baltic Sea. The most sensitive area, is the northwestern coast, where the polluted waters of the Po cause eutrophication and promote algal blooms [1]. The northeastern coast of the Adriatic (Istrian peninsula) is less affected, but the influences of the centuries-old tradition of Raša coal mining in this area cannot be overlooked. The entire region is marked by the remnants of coal mining and its decades-long use in nearby thermal power plants and factories. The negative impacts of Raša coal mining and its use in the local industrial sector are reflected in the elevated levels of various inorganic and organic pollutants in local watercourses, soils, sediments and biota [2,3]. Since near-shore marine systems are vulnerable to pollution by numerous pollutants carried into them by rivers, the focus of this study is on the estuary of the Raša River, whose catchment area coincides with the area of the aforementioned activities
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