Assessing the impact of right tributaries on the ecological state of the Dniester river in the Republic of Moldova under the seasonal aspect

The aim of the work is to investigate under the seasonal aspect some physico-chemical parameters of the water quality of the Dniester River, before and after the confluence of the rivers Raut, Bâc and Botna, from the point of view of the functioning of the lotic ecosystem. In situ hydrochemical investigations and water sampling were carried out during the hydrological seasons 2024 and 2025 (summer, autumn, winter and spring) in the lower sector of the Dniester River Basin on the territory of the Republic of Moldova. The influence of the tributaries on the Dniester water temperature is pronounced in the period of Spring High Waters and practically absent in the period of hydrological drought. The pH values of the Dniester and the tributaries water vary within the quality classes I and II. The seasonal dynamics is not pronounced. According to the oxygen regime parameters, the WQC ranges from I to V, and the critical values of the oxygen regime are stably recorded for the Bâc River. The recovery of the oxygen regime by the Dniester River ecosystem is more effective during good flows and low water temperatures (winter and spring) and less effective during periods of high water temperatures and hydrological droughts.