Multi-Model Approach to Quantify Future Sediment and Pollutant Loads and Ecosystem Change in Selenga River System

The Selenga River, which originates in Mongolia, contributes about 50% of the total inflow into Lake Baikal. Hydroclimatic development and abrupt landscape evolution due to mining, industrial, and agricultural activities within the Selenga drainage basin affect the pollutant influx and transport along the course of the river and its tributaries and influence the riverine ecosystem, including fish habitats. This paper presents a process-based distributed modeling approach for the assessment of water, sediment, and contaminants dynamics and its environmental consequences at river basin scale by integrating various tools at multiple spatial scales. Different water quantity and quality processes were considered and modelled, e.g., the hydrology in the river basin, the erosion and sediment transport and budget, and fish migration. A set of regression models and a climate-driven hydrological model (ECOMAG) were applied to create projections of possible changes to the sediment and pollutants transport regime of the Selenga River and its delta that may occur in response to the projected variations of climate of the XXI century. Climate change may reduce the mean flow in the Selenga River at Kabansk by an average of 3-5% in the 2020s-2030s and 4-25% in the 2080s-2090s, depending on climate projections. The future increase in temperatures with permafrost thaw and the expansion of agricultural and mining activities along with urbanizaiton processes may induce up to 6% increase in the particulate modes and 3%, in the dissolved modes of some metals in the river system. Water runoff decline will dramatically decrease suspended sediment retention in the delta. Depending on the climate change scenario, in the 2080-2099, the suspended sediment load will change in the delta by -0.8% (retention) or by +1% (increase), which is much less than the recent observed average of sediment retention rates -33%. The reduction of runoff will induce a decrease in the migration distance of Baikal omul (Coregonus migratorius)) in the XXI century from 185 to 320 km, with a tendency to an increase towards the end of the century.