GEOCHEMICAL CHARACTERIZATION OF ORGANIC-RICH LACUSTRINE SEDIMENTS FROM ROSULET, ROSU AND PUIU LAKES, DANUBE DELTA, ROMANIA.

Several geochemical analyses (bulk parameters, particle size, loss on ignition, major, minor and trace elements) were performed on 51 recent sediment samples collected in May 2022 from Rosulet, Rosu and Puiu lakes which are located in the fluvio-marine delta plain of the Danube Delta, Romania. The aim of this study was to decipher the potential origin of anthropogenic and/or natural sources, weathering, sedimentary processes and the local geochemical fingerprint on the distribution of specific chemical elements in lacustrine sediments. The resulting compositional dataset showed an interesting spatial variation of the investigated variables. Loss on ignition identified higher concentration of sedimentary organic matter (TOM%) suggesting the autochthonous input derived largely from macro-and micro-phytoplankton, remnants of the biota etc. Similarly, the higher concentrations of total carbonates (CAR%) are attributed to autochthonous input being associated with biogenic debris. Generally, the particle size results exhibited that the lacustrine samples belong to the textural categories as sandy silt and silt. The spatial distribution of major (CaCO₃%, TOC%, Fe₂O₃%), minor (MnO%) and trace components (Rb, Sr, Zr mg/kg) is considerably influenced by the sediment catchment basin lithology. Technophilic elements results (As, Cr, Cu, Hg, Ni, Pb, V and Zn) were related to the maximum allowable limits (MAL) and/or to the natural background reference values stipulated by the national environmental references. Based on the results of contamination analysis, most of the heavy metals (Cr, Cu Pb and Zn) were below the limits (MAL), implying that they have insignificant environmental risk. Instead, the obtained results implied a relatively high concentration of As, Hg, Ni and V, which exceed the corresponding reference standards in some samples. This may be attributed to the presence of allochthonous elevated concentrations of metals transported by the main and secondary hydrographic network waterways up to the interdistributary depressions, or as a consequence of autochthonous input, reflecting a local signature of the natural geochemical fingerprint. The findings from this study provide useful information for the environmental risk assessment relating to the current environmental conditions within deltaic ecosystems as an integral part of the Danube Delta Biosphere Reserve, one of the world's most important and vulnerable areas in terms of pollution, Danube River water levels, extreme weather conditions (floods and droughts), and other factors exacerbated by the climate change. [ABSTRACT FROM AUTHOR]