Environ Earth Sci (2017) 76:346 DOI 10.1007/s12665-017-6664-z ORIGINAL ARTICLE Impact of land uses on heavy metal distribution in the Selenga River system in Mongolia 1 1 2 Orgilbold Myangan • Masayuki Kawahigashi • Bolormaa Oyuntsetseg • Nobuhide Fujitake3 Received: 26 September 2016 / Accepted: 25 April 2017 / Published online: 9 May 2017 Ó Springer-Verlag Berlin Heidelberg 2017 Abstract The Selenga River contributes to 50% of the total heavy metals (Zn, Cu, and Cr) appeared in high concentrations inflow to Lake Baikal. Large tracts of the Selenga River Basin downstream of urban and mining areas (two- to sixfold have been developed for industry, urbanization, mining, and increases), indicating that these contaminants are carried by SS. agriculture, resulting in the release of suspended solids (SS) At two tributary junctions, the concentration of contaminants that affect downstream water quality and primary productivity. on the SS decreased due to a large influx of SS with low heavy This study addressed SS as the main factor controlling pollutant metal contents. Changes in electric conductivity and pH at transport and the primary indicator of land degradation in the downstream of tributary junctions enhanced the sedimentation Selenga River system. Tributaries with larger areas dedicated of SS and the removal of contaminants from the water phase to agricultural use had higher SS concentrations, reaching after aggregation of the SS. Land use changes in the tributary 862 mg L-1, especially during the high runoff and intensive watersheds are major controlling factors for the fate of con- cultivation season. Although the large SS flux was detected in taminants in the river system. the main river, the small tributaries were distinguished by high SS concentrations. The high SS concentration corresponded to Keywords Lake Baikal watershed Á Sorption Á widespread development in the watershed. Watersheds with Sedimentation Á Heavy metal contamination Á Land use high potential of SS release are sensitive to intensive land uses. change 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 minor Introduction Land cover and land use changes in developing countries & Masayuki Kawahigashi have been drastic in recent decades due to increased food [email protected] production and rapid urbanization (World Bank 2010; Orgilbold Myangan Lambin et al. 2003; Stevenson et al. 2013). Agriculturally [email protected] productive areas distributed in alluvial plains have been Bolormaa Oyuntsetseg replaced by urban areas, resulting in the use of sloping [email protected] virgin land for agriculture and intensive cultivation on low- Nobuhide Fujitake productivity soils using heavy machines (Ouedraogo et al. [email protected] 2010; Priess et al. 2015). Land development and mechan- ical cultivation can promote soil erosion, leading to the 1 Department of Geography, Graduate School of Urban Environmental Sciences, Tokyo Metropolitan University, release of suspended solids (SS) into rivers. Suspended Tokyo 1920397, Japan solids in a river affect water quality by carrying pollutants 2 Department of Chemistry, National University of Mongolia, and primary productivity by decreasing solar radiation Ulaanbaatar, Mongolia (Ryan 1991; Bilotta and Brazie 2008; Hartwig et al. 2012). 3 Graduate School of Agricultural Science, Kobe University, Basin-scale transport of pollutants results in elevated Kobe 6570013, Japan pollutant concentrations for downstream recipients. 123 346 Page 2 of 15 Environ Earth Sci (2017) 76:346 Understanding basin-scale pollutant loading and transport risk of becoming bioavailable if the pH decreases along requires research on SS as carriers in the water. Studies of their transport pathways due to changing land use. Previous SS dynamics are scarce because the focus has been on studies have mainly identified the release of pollutants monitoring dissolved pollutants due to their established from point sources, including urban and mining areas, in health risks. During transport along a river basin, pollutants the Selenga River Basin and compared dissolved heavy on carriers are influenced by transformation and retardation metals according to health-risk guideline values (Thorslund processes, ultimately resulting in attenuation of the pollu- et al. 2012; Dalai and Ishiga 2013; Itoh et al. 2011). tant loads (Thorslund et al. 2012; Chebykin et al. 2010). However, pollutants released from urban and industrial These processes include dispersion, sorption, dissolution– areas can be stably transported through sorption to the precipitation, and chemical reactions. Sediment resuspen- surface of SS (Rabodonirina et al. 2015; Chalov et al. sion and deposition patterns can cause spatial variations in 2012). Suspended solids that are largely released from non- sediment loads along a river (Chebykin et al. 2010; point sources such as intensive agricultural areas should be Dhanakumar et al. 2013; Chalov et al. 2012). Suspended addressed. A large agricultural area has been expanding in solids consist mainly of secondary minerals from terrestrial Northern Mongolia that accounts for over 60% of the total origins and particulate organic matter. These solids possess Mongolian agricultural productivity in the Selenga River extensive surface area, which strongly affects the parti- Basin (UNOPS 2013). Suspended solids released from the tioning of pollutants through sorption and co-precipitation. land surface to the Selenga River watersheds can be This reactivity enables the oxides in the particles to accu- affected by resuspension and deposition processes in the mulate heavy metals and organic pollutants. main river, especially at the confluence points between the The Selenga River, which is the largest tributary of Lake tributaries and the main river. Understanding this process is Baikal, passes through Mongolia to Russia. Historically, important for being able to evaluate the impact of land uses river basins in Mongolian territory have been minimally on downstream recipients. This study aimed to clarify the affected by anthropogenic activities. However, rapid and transportation and transformation of heavy metals in the intensive industrial development in Mongolia in the last Selenga River system by addressing carriers with different several decades has brought significant environmental sized fractions, and to investigate the influences of tribu- changes leading to land deterioration (Karthe et al. 2014; taries affected by different anthropogenic activities on the UNOPS 2013). In particular, recent increases in anthro- water quality and metal load to the main river. pogenic activity in Northern Mongolia have strongly affected land use, leading to a deterioration of the river water quality (Stubblefield et al. 2005). The river water Materials and method deterioration has occurred in the upper reaches of the watershed because of the low number of wastewater Selenga River Basin treatment systems (Brumbaugh et al. 2013). Heavy metals and organic pollutants doubled downstream of Ulaanbaatar The Selenga River is the largest and the most important compared to upstream of the Tuul River (Altansukh et al. tributary of Lake Baikal, occupying 82% (447,060 km2)of 2012; Itoh et al. 2011). Monitoring of toxic pollutants, such the watershed area (Potemkina and Potemkin 2014) as heavy metals, was recently begun at selected gauging (Fig. 1). The Selenga River contributes over 50% of the stations in the river system, especially in the Tuul and annual inflow to Lake Baikal (Lane et al. 2015; Tornqvist Orkhon River basins in Northern Mongolia (UNEP-NISD et al. 2014). It is a transboundary waterway originating in 2008; Theuring et al. 2013). the Khangai Mountains in Mongolia and flowing into Lake Mongolia gold production grew rapidly from 1993 to Baikal in Russia. The Yeruu, Kharaa, Shar, Tuul, Orkhon, 2000 (Grayson and Tumenbayar 2005). In particular, hasty Khanui, Chuluut, Ider, Delgermurun, and Eg Rivers flow gold mining boomed in the Selenga River Basin and along into the Selenga River in Mongolian territory. The three its tributaries. Thorslund et al. (2012) concluded that the largest tributaries of the Selenga River are the Orkhon, Zaamar Goldfield located in the Tuul River Valley could be Tuul, and Eg Rivers. making considerable contributions to high metal fluxes in The Selenga River Basin plays an important role in the the Selenga River system. However, heavy metal concen- socioeconomic life of Mongolia. The basin area covers trations in the area surrounding the Zaamar mining activ- 19.2% of the total land area of Mongolia (Dalai and Ishiga ities were below guideline values based on health risks 2013) and includes the capital city Ulaanbaatar, as well as (Thorslund et al. 2012). The high pH condition in the the second- and third-largest cities (Darkhan and Erdenet). Zaamar Goldfield could limit the dissolution of heavy Over 60 and 80% of agricultural and industrial products, metals. Most of the heavy metals (98%) are transported on respectively, are produced in the Selenga River Basin SS (Chalov et al. 2015). Heavy metals bound to SS are at (UNEP-NISD 2008). The water quality in the Selenga 123 Environ Earth Sci (2017) 76:346 Page 3 of 15 346 Fig. 1 Land use map of the Selenga River Basin in the Mongolian F Yeruu River, G Buir River, H Eg River, I Delgermurun River, territory. The alphabets indicate tributaries (A Selenga River, J Ider River, K