Assessment of riverine loads of nitrogen and phosphorus to the Dniester Estuary and the Black Sea over 2010–2019

Summary Purpose of the work was to quantify riverine nitrogen (N) and phosphorus (P) loads to the Dniester Estuary and estimate their contributions to the Black Sea over 2010–2019. Methodology. The data on monthly water discharge and monthly N and P compounds concentrations in surface water monitored in-situ were used. Results and Discussion. Mean annual riverine water discharge to the estuary was 7.9±0.2 km3 (range: 5.6–14.2 km3). Higher variation of water discharges was found in the Turunchuk River (variation coefficient of 38%), 1.7 times higher than in the Dniester River before confluence. Annual TN loads to the estuary varied from 10.8 GgN (2016) to 74.6 GgN (2010), the mean was 25.7±5.8 GgN/year. Mean annual TP load was of 1.16±0.08 GgP/year (range: 0.95–1.66 GgP/year). On average, the shares of organic N and P were 48% and 43% respectively. Nitrates dominated in DIN contributing 84±2%. Conclusions. Dniester water discharge and thus water supply for its deltaic area are strongly dependent on climatic and anthropogenic factors, both affected by climate change. We have found that 25.7±5.8 GgN/year and 1.16±0.08 GgP/year are entering the Dniester Estuary annually. Mean riverine total N and total P loads to the Black Sea made 23.1±5.2 GgN/year and 1.04±0.07 GgP/year.