Estimates of the surge phenomena effects on the potential for heavy metal compounds accumulation in the Don Delta soil during the low water period (2007–2020)
Authors:   Southern Scientific Centre of the Russian Academy of Sciences (SSC RAS), Berdnikov S. V. , Gerasyuk V. S. ,   Southern Scientific Centre of the Russian Academy of Sciences (SSC RAS), Kleshchenkov A. V. ,   Southern Scientific Centre of the Russian Academy of Sciences (SSC RAS), Kulygin V. V. ,   Southern Scientific Centre of the Russian Academy of Sciences (SSC RAS), Likhtanskaya N. V. ,   Southern Scientific Centre of the Russian Academy of Sciences (SSC RAS), Sheverdyaev I. V. ,   Southern Scientific Centre of the Russian Academy of Sciences (SSC RAS)
Published: December 2024

Background. The contamination of the Lower Don floodplain soil by potentially toxic elements (PTE), which include heavy metal (HM) compounds, is associated with the introduction of these substances with river water during high water periods, when the delta is flooded by flood water and suspended sediments and various chemical compounds migrating within them accumulate on its territory. During the current prolonged period of low water, spring floods are absent, and flooding occurs mainly by surge sea water from Taganrog Bay. Relevance. A multidisciplinary approach based on the data collected during field studies and observations conducted at hydrological stations, as well as on the results of mathematical modeling makes it possible to reveal how PTEs migrating as part of suspended sediments can contaminate the Don Delta soils and how this is related to surge phenomena. The aim of this work is to describe the conditions of the Don Delta pollution with PTEs, primarily HM compounds, in the context of low water and decreasing solid runoff of the Don River and the surge phenomena influence. Methods. To describe the transport and transformation of suspended solids, we used an approach based on the joint application of the detailed hydrological model HEC-RAS adapted to the conditions of the Don River estuary (DonDeltaHECRAS) and the dynamic model of the balance of water and substances transported by water masses (DonDeltaBalanceModel). Results. Estimates of HM introduction with runoff to the Don River estuary and its contribution to the “filtration” of chemical compounds on the paths of their migration with river water to the Azov Sea have been obtained. Calculations of suspended sediment dynamics for six types of surges have been carried out, and estimates of suspended sediment accumulation in the Don Delta have been obtained. Estimates of HM input into the upper soil layer of the Don Delta during surges have also been obtained. Conclusion. The source of pollution of the delta with PTEs is their anthropogenic runoff. While during high water and floods the accumulation of PTEs occurs due to the river contribution, during low water and surges, anthropogenic riverine PTEs, after their biogeochemical transformation on the estuarial seashore, in Taganrog Bay, and the Azov Sea, return to the delta via surges. The role of the delta and the estuary as a “filter” on the migration path of dissolved and suspended forms of PTEs from the river to the sea has been transformed.