Orgilbold Myangan1 • Masayuki Kawahigashi1 • Bolormaa Oyuntsetseg2 • Nobuhide Fujitake3
Environ Earth Sci
Lake Baikal watershed Sorption Sedimentation Heavy metal contamination Land use change
The Selenga River contributes to 50% of the total inﬂow to Lake Baikal. Large tracts of the Selenga River Basin have been developed for industry, urbanization, mining, and agriculture, resulting in the release of suspended solids (SS) thataffectdownstreamwaterqualityandprimaryproductivity. ThisstudyaddressedSSasthemainfactorcontrollingpollutant transport and the primary indicator of land degradation in the Selenga River system. Tributaries with larger areas dedicated to agricultural use had higher SS concentrations, reaching 862 mg L-1, especially during the high runoff and intensive cultivation season. Although the large SS ﬂux was detected in the main river, the small tributaries were distinguished by high SS concentrations. The high SS concentration corresponded to widespread development in the watershed. Watersheds with highpotentialofSSreleasearesensitivetointensivelanduses. SS in the river system had a constant elemental composition consisting mainly of Fe and Al oxides, indicating that surface soils were major constituents of the tributary SS. Three minorheavymetals(Zn,Cu,andCr)appearedinhighconcentrations downstream of urban and mining areas (two- to sixfold increases),indicatingthatthesecontaminantsarecarriedbySS. At two tributary junctions, the concentration of contaminants on the SS decreased due to a large inﬂux of SS with low heavy metal contents. Changes in electric conductivity and pH at downstream of tributary junctions enhanced the sedimentation of SS and the removal of contaminants from the water phase after aggregation of the SS. Land use changes in the tributary watersheds are major controlling factors for the fate of contaminants in the river system.