River Sediment Runoff in the Aldan River Basin and Mining Activities

Abstract—The article contains the results of a study of the features and causes of a sharp decrease of water turbidity and the suspended sediment discharges of rivers (1.5–5 times) in the Aldan River basin, which has been recorded since the second half of the 1980s and 1990s. The possible factors of this decrease are considered in detail. These are the runoff and temperature of water, economic activities, and the method of measurements at the gauging stations. It was found that water runoff, in general, increased in the average range of 5–30%. The maximum water discharges on the different stations had a multidirectional trends. The water temperature, as an important factor of thermal erosion, has increased. That is, hydrological factors could not have caused such a reduction in sediment runoff. Since the 1990s, the reliability of stationary data has decreased Main reason lies in the mining industry, its degradation in the 1990s, a new revival in the XXI century, but already under the pressure of strict environmental restrictions. Using numerous open sources, the author has built a map of exploited mineral deposits, identified the main stages of their development and the parameters of mining operation. All this information allowed us to substantiate the conclusion about the similarity of long-term fluctuations in river sediment runoff and the dynamics of mining, the stages of discovery and development of deposits, changes in the structure and localization, the implementation of measures to reduce the negative impact of mining on rivers. It was also found that the data of the stations from the very beginning of their collection did not reflect the natural regime of sediment discharges and water turbidity.