The influence of alluvial gold mining on the natural complexes of river valleys of Amur River basin (Eastern Transbaikalia, Russia)

The article presents the qualitative and quantitative characteristics of violations of natural complexes of river valleys resulting from placer gold mining in the Shilka and Argun rivers basins, from the confluence of which the Amur River itself begins, obtained by analyzing satellite images and field studies. In the placer mining areas, which has been going on in Eastern Transbaikalia since the second half of the 19th century, the geomorphological structure of river valleys is completely transformed, new stream channels are formed, channel processes are activated, anthropogenic relief forms are formed, land and water vegetation is removed, aquatic biota is substantially changed and depleted, contaminated water environment. Two main types of technogenic landscapes are distinguished: a tape trench-dump landscape during dredging of placers and a practically disordered pitted-dump landscape when washing gold-bearing sands with water monitors. Spent dredged polygons in the Shilka river basin reach a size of 0.25 x 0.56 km2, and the length of the largest man-made lake is 1.3 km with a width of up to 0.55 km. In the Argun basin, the length of flooded pits is up to 1.3-1.8 km, and their width is up to 670-800 m. The length of individual sections of disturbed valleys in both basins reaches 58-60 km. The impact of alluvial gold mining on the natural environment extends downstream of the watercourses beyond the development area due to the transport of bot-tomset beds, finely dispersed suspended solids and dissolved substances by water flows. On example of river Srednyaya Borzya, whose valley is most disturbed by the exploitation of placers in the Argun river basin, including modern mining by both methods, shows the main components of water pollution. The most significant of them are suspended solids and iron, the content of which in water reached 278 and 6.5 mg / L respectively. Elevated concentrations also had (in μg / L) Cr (up to 28.3), Cu (24.3), Co (40.7), Ni (48.7). The reclamation of disturbed lands is been carried out in recent decades, mainly after the development of placers by hydromonitors, but is limited to the technical stage - the leveling of dumps. Vegetation is poorly restored, especially on the slopes of dumps devoid of soil cover and susceptible to water and wind erosion, and is represented by a limited number of mainly tree-shrub species. Due to the poor knowledge of the impact of placer gold mining on the environment in the region, the main directions of further research are proposed. They include the study of the influence of anthropogenic landscapes on the formation and regulation of water flow, assessment of pollution of the aquatic environment and its impact on the aquatic biota, primarily on the ichthyofauna, development of methods for the biological restoration of disturbed lands.

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