Hydrochemical Regime of the Kiliya Delta of the Danube River in Retrospective and Modern Conditions: I. Main Indicators of Water Chemical Composition

Abstract

—The article focuses on the changes in the hydrochemical regime of the Kiliya delta of the Danube River, which have occurred during many years of research. It is established that after damming of the Danube River, supersaturation of the river water with dissolved oxygen is observed in the upper and middle river course, which results from an increase in the photosynthetic activity of the algae, a reduction in the content of suspended solids, and pollution of the water with inorganic nitrogen and phosphorus compounds. It is shown that since the 1970s the water mineralization level has increased by approximately 30%. The concentration of Na⁺, K⁺, SO₄^2–, and Cl^– ions has increased. Cases of saltwater penetration into the waters of the Prorva, the Gneushev, and the Bystryi branches have been observed. In modern conditions, the concentrations of nitrate ions and inorganic phosphorus remain high, whereas the concentration of ammonium nitrogen, on the contrary, has decreased almost thrice. It is found that there is an increase in the concentration of dissolved organic substances, especially in spring and summer, which is due to the intensification of bioproduction processes. Among dissolved organic substances in the water of the Kiliya delta of the Danube River, the dominating position is occupied by humic substances, the relative content of which reaches 54.8–85.6%.