Impact of open-cast placer mining on sediment transport across Far Eastern rivers of Russia

Abstract

This study examines patterns of sediment transport in Far Eastern rivers of Russia affected by open-cast placer mining—mostly for gold, rarely for silver, and in a few cases for platinum and diamonds. Long-term monitoring and remote-sensing data are used to determine the location of mining landscapes and to detect sediment concentrations and plumes originating from the mining sites. The current study suggests that catchments of the Amur, Kolyma, and Lena rivers are global mining hot spots accommodating up to 1.1%–3.8% of total mining-related vegetation losses. Here, ∼20,100 km of river valleys (0.48% of the river network length) are currently disturbed by mining, with the maximum density of disturbed river valleys being up to 200–300 m/km2 in the basins of the tributaries of the Upper Kolyma and Zeya rivers. To explore the potential mining impact on sediment load, these data were linked with the long-term sediment trends. Concentrations and discharges of mean annual, monthly, and daily suspended sediment decreased from the 1970s and 1980s to the present day at more than 40% of the 40 stream gauge sites assessed across the contiguous Far East. Increasing sediment trends were widespread across 20% of the sites localized in the cluster of greatest mining-related land disturbances. Up to 30% of the sites are characterized by sediment load growth up to the end of the 1980s and a subsequent decline due to the recent abandonment of mining activities. The current study highlights the non-linear relations between mining-related vegetation losses and sediment release into the river network, which is explained by diverse sources of sediment generation within mining areas and other drivers of sediment transport that interact and may attenuate or intensify the signal of mining impact.