ИСТИНА

The present research considers the unregulated Selenga River which contributes about 50 % of the total inflow into Lake Baikal. Elevated sediment-associated chemical concentrations reported for the area tend to fall into one of two categories: those associated with soil/petrologic anomalies or those associated with anthropogenic inputs. The latter is related to mining, industrial and agricultural activities within the Selenga drainage basin which affect sediment transport. At the same time, the region is reported to experience the water runoff decrease with acceleration since the 1970s. The key question for the understanding regional environmental change is to disentangle the influence of climate change from that of other changes in catchment. The study is based on novel screening campaigns were conducted in June–August 2011-2014. Discharge and suspended sediment concentration (SSC) data were combined to yield estimates of daily and monthly water discharges, suspended load averages at more than 150 locations. All samples (suspended and streambed sediments and filtered water) were analyzed for 62 elements by inductively-coupled plasma mass spectrometry ICP-MS (ICP-AES). Results indicate that high sediment loads were reported both for altered and natural rivers. Reported multi-decadal declines in sediment loads in the downstream part of Selenga River can be attributed to the abandonment of cultivated lands and changing hydroclimatic factors. Elemental composition of the mass flows mostly relate to the soil/petrologic conditions. With the exception of small impacted rivers where water quality impacts associated with mining were found, the formation of elemental compositions and sediment-associated chemical constituents generally reflects catchment characteristics.