The growing concern for most European rivers is due to pollution with potentially toxic elements (PTEs) and is of course a priority challenge for the Danube, a river that interconnects fresh water with the marine environment. The accumulation of PTEs from the Lower Danube River sediments and the potential negative effects of these chemicals on the water quality during and after the hydro-construction works carried out in the area to improve the navigation conditions have been studied in the present work. For seven years period (2011-2017), sampling campaigns from 10 monitoring sites were carried out. Sediment samples were taken from the Lower Danube River (km 375 - km 175) from the left and right banks, monthly during the construction period (2011 - 2015) and quarterly in the post-construction period (2015 - 2017). A total approximately of 1200 samples were analyzed and Cd, Cr, Cu, Pb, Zn and Ni content was determined to obtain the assessment of sediments that can influence water quality. Multivariate statistical analysis was applied to the complex data set obtained, the degree of accumulation and the distribution of these metals on the studied section was calculated. Also, the quality indicators of sediments were evaluated according to the legislation in force. The results showed that all concentrations of the monitored PTEs have recorded values over the normal values from the current legislation. On the whole, Zn has the highest concentration, while Cd has the smallest one. The order of the absolute average concentrations values found in this study is Zn ] Cu ] Cr ] Ni ] Pb ] Cd. For the Zn and Cu elements, slightly higher values were recorded compared to other heavy metals (Pb and Cd), which means that historically contaminated deposits in sediments can be remobilized and transported to the upper layers of the sediment or even be diffused in water. Generally, due to different sediment types and input levels, there is a variable contamination throughout the Danube aquatic ecosystem. The statistical analysis applied to analytic data highlighted the action of anthropogenic sources on the Danube aquatic ecosystem, showing the interdependencies between monitored indicators and seasonal influence.
Modeling water quality in the Anthropocene: directions for the next-generation aquatic ecosystem models
