The respective environments in two ancient rivers were studied using geochemical methods with paleogeographic
reconstructions of fossil material represented by shells of freshwater bivalve mollusks. The studied
outcrops are located in the basins of the Dniester and Prut rivers. Materials were collected from two Pliocene
(Brînza, Giurgiuleşti) outcrops and the ages of the second group of localities (Sucleia, Slobozia Mare, Gura
Bîcului) are from Middle to Late Pleistocene. The determination of the taxonomic position was carried out
using standard malacological methods. Geochemical data were used for the environmental reconstruction
and included stable isotope ratio and trace element compositions in subfossil freshwater bivalve shell (Bivalvia:
Unionoida). Key indicators of paleoenvironments show changes in water temperature. Changes in the
taxonomic composition of bivalve mollusk assemblages also occurred. In the present study, increasing the
water temperature caused a change of stenobiont species of bivalve mollusks to eurybiont species. Eutrophication
of watercourses, caused by anthropogenic pollution and climate change in the direction of warming,
has led to the replacement of pearl mussels of the family Margaritiferidae by more eurybiont species of the
family Unionidae in the benthic communities of European oligotrophic rivers. These processes are similar to
those deduced for the Neogene-Quaternary watercourses of the Prut and Dniester basins, but they proceed
at a much faster pace. They are processes of eutrophication of watercourses – the main factor leading to the
catastrophically rapid modern reduction of the ranges of pearl mussel.