The article is devoted to the study of vanadium, a metal capable of stimulating the growth of phytoplankton in situ and has the greatest biological activity in dissolved form. The pattern of an increase in the concentration of vanadium dissolved forms in the mixing zones during the transition from river waters to seawaters is known. In this article, we examine the behavior, ratio and change in the concentrations of vanadium dissolved and suspended forms during the passage of geochemical barriers. The estuarine zone of the Razdolnaya River–Amur Bay (Sea of Japan) is considered as "river-sea" mixing zone. Modelling of physicochemical processes was carried out using the Selector-S and MINTEQA2/PRODEFA2 software systems. Ion-associative models of sea and river water were built and the modelling of the process of their mixing was carried out using the Selector-S software package. The sorption process was simulated using the MINTEQA2/PRODEFA2 software package. The results of modelling physicochemical processes occurring at geochemical barriers help to understand the reasons for changes in concentrations, both total vanadium and biologically active dissolved vanadium forms, during the passage of geochemical barriers in the "river-sea" mixing zones. The results showed that there is a change in the dissolved forms of vanadium migration, their transformation and an increase in the concentration of dissolved forms of vanadium at the geochemical barrier