Natural and Anthropogenic Changes in River Suspended Sediment Runoff in the Indigirka River Basin

The hydrometeorological conditions of river flow formation and the state of permafrost in the Indigirka River basin have changed since the 1990s. An increase of water runoff in the basin (by 20% or less) and water temperature (by 0.5–1°C) was a reaction to these changes. Therefore, an increase in sediment yield was to be expected. But that didn’t happen. It decreased by 6–33% in the 1990s and 2000s. But, subsequently, sediment yield increased by 50–220%. The reasons for the lack of positive dynamics could be negative processes in the mining industry since the 1990s, as well as changes in the monitoring system. Therefore, the objectives of the study were to analyze the gauge hydrological data, the long-term dynamics of water and sediment runoff, the stream temperature of rivers in the Indigirka River basin, the features of local mining, and the assessment of the contribution of anthropogenic and natural factors to the long-term variability of sediment runoff. Materials from 22 hydrological gauges in the Indigirka basin, satellite images, and various mining industry data were the information basis of this research. The rivers and areas in the Indigirka River basin affected by mining have been identified. The analytical links between the annual sediment runoff and its hydrological factors were substantiated. It was found that the negative processes in the mining industry at the turn of the 20th and 21st centuries explain less than 20–40% of the decrease of sediment runoff, the rest of the decrease in runoff is due to natural hydrological changes. After, a significant increase in sediment runoff was provided by both hydrometeorological and anthropogenic factors. For the first time, a comprehensive analysis of the reliability of stationary observation data has been carried out; a GIS of developed deposits and disturbed floodplain-channel complexes has been created.