The Influence of Water Sources onto the Pokhabikha River and onto the Adjacent littoral of Lake Baikal

The geochemical method has established the degree of influence of water sources on the Pokhabikha River and the adjacent littoral of Lake Baikal in 2022 and 2024. The water contributions (WC), geochemical contributions (GCC) and summary geochemical contributions (SGCC) of water sources (clean riverine water, wastewater and Baikalian waters) into mixing objects (Pokhabikha River at the mouth, littoral of Lake Baikal) have been determined. The lower WC from Slyudyanka City wastewater into the Pokhabikha River in 2024 (0.98 %) compared to 2022 (1.75 %) are probably due to the greater water content of the river. The highest GCC of wastewater into riverine waters (>10 %) is typical for (in %) P (56-75), Cl (41-43), Na (28-36), Zr (11-25), K (16-24), Cs (13-22), Ga (10-21) and Ni (11-20), as well as for Sb (39), As (19), Rb (16), Br (10) and Ti (10) in 2022 and for I (20) in 2024. For all informative elements, the SGCC into river waters in 2022 was 440 %, which is 1.4 times more than in 2024 (311 %). In 2024, the influence of polluted waters of the Pokhabikha River in Lake Baikal littoral was traced at all depths within a radius of ~ 100 m from the mouth, and frontally along the surface reached 200 m. Subaquatic discharge of polluted riverine waters was detected at a distance of 65-80 m from the mouth. In 2022, surface water was studied in the sector ~ 50 m from the mouth and in the coastal zone up to 90 m from the mouth, where the influence of polluted riverine waters was also detected. The littoral waters of Lake Baikal in the zone of influence of the Pokhabikha River are formed mainly due to the mixing of two main sources – Baikalian and pure riverine waters. WC of wastewater are 56-101 times less than WC of riverine water and up to three orders of magnitude less than WC of Baikalian water. Geochemical contributions of wastewater to Lake Baikal littoral are more significant than their water contributions. The main effect of wastewater here can be traced to the same elements as for the Pokhabikha River, but with lower GCC (%): P (3.7-64), Cl (2.9-35), Na (0.5-17), Zr (1.0-20), K (0.5-13), Cs (1.0-16), Ga (1.0-16), Rb (0.6-12), I (0.3-7.0), Ni (0.3-5.6), as well as some other elements: Mn (3.9-8.9), Fe (0.7-3.8), Cr (0.5-4.8), Pb (0.5-2.9), Si (0.4-2.5) Ge (0.6-4.3) and B (0.3-4.6). The main contribution to the formation of the geochemical composition of the littoral waters of Lake Baikal is made by clean riverine and Baikalian waters. With the exception of P, the GSS of clean riverine waters in the Baikal littoral were in all cases higher than the GSS of wastewater (1.3-116 times). The main influence of clean riverine waters (GCC %) was by Mn (61-94), Fe (18-91), Si (16-94), Ga (30-85), REE (15-92), Pb (14-86), Y (17-87), Ge (11-80), Ti, Cr, Ba and Al (10-80). For the remaining elements, themaximal GSS were less than 80 %, and the minimal GSS were less than 10%. The SGCC of pure riverine waters varied in the range of 189-3158 %, at all stations they were 6-12 times higher than the corresponding SGCC of wastewater. With the exception of P, Cl, Mn and Ga, the GSS of Baikal waters were in all cases higher than the GSS of wastewater (1.03-5760 times). The maximal effect of Baikalian waters was by As, Sb, Mo, W, Ni, I, Li, U, Br, Zn and Na (GSS = 53-~100%). High GSS (12-98%) were also found for most other elements: K, B, Sr, S, V, Al, Ti, Ca, Cs, Ga, Ge, Cu, Rb, Mg, Co, Ba, P, Zr, Cl, and Cr. GSS of FREE, Pb, Si, Fe, Si, and Mn ranged from 0.3 to 85 %. The GSS of Baikalian waters varied in the range of 1058-3092 %, at all stations they were higher (5-106 times) than the corresponding GSS of wastewater. In the interannual dynamics of 2022/2024, the geochemical differences in the clean waters of the Pokhabikha River, as well as the wastewater from the Slyudyanka City water treatment facilities (WTF), are small in most chemical elements (<50 %). The stronger differences (in times) by Cr (2.4), Ti (1.9), Ga (1.7), and Zr (1.7) in wastewater are most likely due to variations in fine suspension. Significant differences in riverine waters by Sb (6.1), Ni (3.2), P (2.4), Mn (2.1), Ga (1.8) and Al (1.6) are probably related to changes in river water content and the influence of other factors (suspended matter, physico-chemical and biogeochemical processes). In WTF waste waters from Severobaikalsk town, exceeding of regulations by P (45-96 MPC), Mn (4.7-5.6 MPC), Fe (2.9 PC) and V (2.0-2.5 MPC) was detected.