Geochemical characterization of changes in the chemical composition of river sediments under the continuous anthropogenic influence of Yerevan, Armenia.

The long-term study of the chemical composition of river sediments within urban areas and the establishment of baseline values of major and trace elements is an important task. Therefore, this study aims to provide a geochemical characterization of the sediments, establish a local geochemical baseline, unveil geochemical associations of elements, study the trend of changes in element pollution levels and the associated ecological risks. The results indicate that the change of the local physical characteristics across the river flow (canyon-flat relief surrounded by buildings-reservoir-flat relief under the influence of contamination sources) and locations of contamination sources conditioned the formation of positive extreme values detected for the majority of the studied elements. An analogous variation pattern of major and trace elements median values (2019-2023) was observed for Cr, V, Cu, Fe, Co, Zr Mn, Zn, K, Ba over 5 years representing the geochemical signature of the local geological composition (basalt, andesibasalts, andesite, tuff, K-feldspar). The pollution level and the ecological risk assessment showed that during the study period moderately and highly hazardous levels of multi-element pollution were detected in the southwestern part of the river located near the industrial enterprises. In the meantime, moderate (in 2020) and considerable (in 2021) ecological risk levels were observed at the site near the artificial reservoir. A hierarchical clustering combined with the geochemical ratio analysis reveals three groups of geochemical associations that have a natural (Fe, Mn, Co, V, Ti, Zr, K, Rb, Ba); anthropogenic (Cu, Zn, Pb, Mo) and mixed (Ca, Sr, Cr) origin. Moreover, the anthropogenic association shows affinity to Ca hence denominating the dominant role of carbonates in the fixation and coprecipitation of Cu, Pb, Mo, Zn ions. The comparison of the baseline values of the studied elements with the upper continental crust values confirmed their applicability for differentiation of their origin.