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 River system in

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 . 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 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 , K , and L Khanui River) B Orkhon River, C Tuul River, D Kharaa River, E Shar River,

River has deteriorated due to increased agricultural area, of suspended solids at 6 gauging stations located on 6 rapid urbanization, scarce wastewater treatment systems, tributaries in the Mongolian Selenga River watershed and hasty mining development in Mongolia (Karthe et al. (Fig. 2). Suspended solids are collected once a month. 2014). Since the Mongolian economy transitioned from a Monitor data between 2009 and 2013 were obtained from planned economy to a market economy, many sub-basins the institute to evaluate SS release in each river. of the river are now used for the intensive mining of gold, silver, and coal. Other issues include inefficiently operated Water and sediment sampling and field wastewater treatment systems and increased non-point measurements pollution sources (Grayson and Tumenbayar 2005). Major pollutants in the gold mining area are not gold itself, but Sampling sites were selected at tributary junctions. Sam- rather Zn, Cu, and Fe (Kratz et al. 2010; Byambaa and pling points were set both the up- and downstream from the Todo 2011). Governmental monitoring has found higher junction. Tributary water and sediment samples were col- concentrations of these pollutants in the river (Ministry of lected during August 14–20, 2013, at each sampling station Environment and Green Development 2012a, b). (Fig. 2). However, the main stream between sites 5 and 6 was not sampled because an approach could not be found Data analysis of national gauging network by car using available roads (Fig. 2). One of the largest Mongolian gold mining areas, the Zaamar Goldfield, is The Mongolian Institute for Meteorology and Hydrology located on the upper stream of the study field. The river (MIMH) monitors river water discharge and concentrations water samples were collected into pre-rinsed

123 346 Page 4 of 15 Environ Earth Sci (2017) 76:346

Fig. 2 Elevation map of the Selenga River Basin with locations of sampling stations (green solid circle) and 6 national gauging stations of the 6 tributaries (yellow solid triangle). Yellow arrows indicate flow direction

polypropylene bottles (2 L). The river bottom sediments transported to Japan for further analyses. In the field, basic were also collected using polyethylene bags at the same physicochemical parameters were measured using a Hanna sites. The water samples were taken directly using plastic Instruments HI 9828. bottles or the Bandon water sampler (Rigo-sha, Tokyo Japan), and sediments were taken using a sediment sampler Laboratory analysis (Rigo-sha, Tokyo Japan) or directly by shovel. Water and sediment samples were collected without spatial replicates Detectable elements in water samples were qualitatively because the targeted tributaries have different widths and searched by a direct scanning method operated by ICP- water depths. It is difficult to collect spatial replicates in a AES (ICPE-9000, Shimadzu, Kyoto, Japan). The detected small tributary with narrow width and shallow depth. After elements (Al, Fe, Cu, Cr, Ni, Na, B, Mn, Zn, Zr, Ca, K, Mg, the confirmation of uniform water properties, including and Si) were quantitatively determined in the GF-F filtrated turbidity, in a tributary (Hanna Instruments HI 9828), water water and the acidified water using the ICP-AES in high samples were collected. Stone samples were avoided for sensitivity mode, which has a detection limit of less than use as sediment samples. 10 mg m-3. The total carbon (TC) and total nitrogen (TN) The collected water samples were immediately filtered in the acidified and filtered water samples were determined through glass fiber filters (GF-F, Advantec, Tokyo Japan) using a total carbon and nitrogen analyzer (Shimadzu 2- at the sampling site using a vacuum filter system to collect TOC-L, Shimadzu, Kyoto, Japan). Major anions (SO4 , 3- - - - - the SS. The filtered water samples were divided evenly into PO4 ,Cl ,F ,NO3 , and NO2 ) in the GF-F filtered two subsamples. One set of subsamples were acidified with water were determined using ion chromatography (Shi- concentrated nitric acid (HNO3) for determination of the madzu LC solutions, Shimadzu Kyoto Japan) after pre- total metal concentration. The other set of subsamples were filtration with a 0.2 lm syringe filter (Dismic 25-AS, kept in plastic tubes for further determination of the dis- Advantec, Tokyo, Japan). Non-acidified water samples solved heavy metals, total basic metals (Na, Ca, K, and from the field were further filtered through a 0.025-lm Mg), total Si, total carbon, total nitrogen, and anion con- membrane filter (polysulfonate filter, Millipore LTD, centrations. The water and bottom sediment samples were Tokyo Japan) and analyzed for elemental composition, in

123 Environ Earth Sci (2017) 76:346 Page 5 of 15 346 the same manner as the GF-F filtered and acidified water April to October) for 5 years, as collected by MIMH. A samples, to determine concentrations of dissolved scatterplot with linear regression analyses and evaluation elements. of the significance was also made using Sigma plot 13 The elemental concentrations in colloidal fractions were (SYSTAT Software Inc.). calculated as the difference in concentrations found in the acidified and 0.025 lm filtered water samples. The col- loidal Si and basic cations were estimated as the difference Results and discussion in the measured concentrations of Na?,K?,Ca2?,Mg2?, and Si from the GF-F filtered water samples and the con- Changes in SS concentrations in the Selenga River centrations of 0.025 lm filtered water samples. system The suspended solids on the GF-F filters were dried at 105 °C in a dry oven. Dry weights of the SS were deter- SS concentrations at each sampling station in the Selenga mined by gravimetric analysis. The filters with SS were River system are presented in Fig. 3. The highest concen- combusted in a muffle furnace at 550 °C for 4 h. The tration of SS was detected in the lower reaches of the Shar organic matter content was estimated as the loss of weight River (Shar 8), at 862 mg L-1. Concentrations of the SS on ignition (LOI) using the difference between the dry and fractions are related to the land use in a given catchment. combusted weights of the SS. The concentration of SS in Intensive agricultural land use is widely distributed in the each river was estimated from the combusted weights of SS Shar watersheds (Fig. 1), with the primary land use being and the volume of filtered water. Preparation and estima- agriculture with irrigated systems (UNDP 2011). The area tion of SS and LOI followed the Environmental Science of agricultural land use in the Shar River watershed con- Section (ESS) method (Wisconsin State Lab of Hygiene sisting of potato (1300 ha) and vegetable (800 ha) pro- 1993). The combusted SS samples were thoroughly duction in 2013 has increased from just 65 ha of wheat digested using a mixture of concentrated nitric acid and production in 1968. The Kharaa River has the secondary perchloric acid in an aluminum block heater at 155 °C for highest SS concentration, at over 200 mg L-1. Cropland more than 12 h. The digested solutions were analyzed for covers over 11% of the Kharaa River Basin, which pro- elemental concentrations (the same elements as for the motes the release of SS as a result of the higher erosion rate acidified water) using the ICP-AES instrument. (7.2 Mg ha-1 year-1) for croplands as compared to that of River bottom sediments were freeze-dried. The dried grassland (2.0 Mg ha-1 year-1) (Priess et al. 2015). samples were homogenized and sieved through a 2-mm Surface soil erosion due to cultivation on agricultural sieve. The sieved sediments were powdered using a cera- lands directly releases soil particles during the denuded mic mortar. The amounts of total carbon and total nitrogen period. Soil particles released in tributaries can affect water of the powdered samples were determined by an NC ana- quality with pollutants that are carried on the SS surfaces. lyzer (Sumica NC-80, Sumitomo Kagaku, Osaka, Japan). Potato and vegetable cultivation in irrigated agricultural Bottom sediment samples were digested using a mixture of areas greatly affects the surface soil erosion because soil is nitric acid and perchloric acid following the method described by Twyman (2005). Approximately 500 mg of 1000 powdered samples were digested in the same manner as the Main River SS samples, and the elements were analyzed using the ICP- -1 Tributaries AES. 800

Data evaluation and statistical analysis 200

Between three and six replicates were performed to account for experimental errors during sample analysis. 100

The number of replicates depended on the SS concentration Concentration of SS mg L in the water samples. A higher SS concentration required more filtration to completely collect the SS. Relationships 0 between the determined elements in the SS were evaluated using the correlation function in the Excel analytical Buir (5) Shar (8) Tuul (16) Tuul (15) Tuul (14) package (Microsoft Excel 2016). Sigma plot 13 (SYSTAT Yeruu (6) Orkhon (4) Orkhon (3) Orkhon (9) Orkhon (7) Selenga (1) Selenga (2) Kharaa (10) Software Inc.) was used to make scatterplots of the average Orkhon (13) Orkhon (12) Orkhon (11) values with standard deviations of the SS concentrations Fig. 3 Suspended solid concentrations at each station. Flow direction and river discharges during the active flow season (from is from 16 to 1 123 346 Page 6 of 15 Environ Earth Sci (2017) 76:346 dry in these semi-arid regions (UNDP 2011). Modern 9. On the other hand, SS concentrations decreased at irrigated cultivation usually requires deeper cultivation Selenga 1, Orkhon 4, and Tuul 14, as compared to compared to traditional croplands, promoting surface ero- upstream values, due to a dilution effect by the effluent sion and excessive release of surface soils to the river. from tributaries and the removal of SS through Severe erosion from agricultural land use (for potatoes and sedimentation. vegetables) is an important environmental issue facing water management in Mongolia. Flux and release rate of suspended solids in the river The most of tributary watersheds in the Selenga River system system are consisting of Kastanozems in the plain areas and Phaeozems in the mountainous areas (Theuring et al. The SS flux was estimated using a combination of the river 2015; Hartwig et al. 2012). Kastanozems are mainly used water discharge and SS concentrations from the data set of for crop production and rangeland for grazing because of MIMH between 2009 and 2013. Results of the averaged SS its fertility. However, high susceptibility of Kastanozems fluxes indicate a rather high SS flux in the larger tributaries to cultivation promotes surface soil erosion, especially due of the Selenga (1612 ton day-1) and Orkhon (1119 to mechanical intensive cultivation in the present agricul- ton day-1) Rivers, as compared to the smaller Tuul (71 ture from 2008 (Priess et al. 2011). This promotion of ton day-1), Shar (145 ton day-1), Kharaa (211 ton day-1), agricultural production enhances SS release into the and Yeruu (294 ton day-1) Rivers, during the active flow Selenga River system. season (from April to October). Watersheds with a larger Greater SS release due to placer gold mining has been area have a higher potential for SS release, resulting in reported by Chalov et al. (2015). However, based on the larger SS fluxes in those tributaries. Since main streams Mongolian Human Development Report of 2011 (UNDP collect all effluents from any connecting tributaries, the SS 2011), the area of land degradation caused by mining and fluxes are high in the Selenga and Orkhon Rivers. Land fires is not large. Rather, agricultural lands and grasslands surface disturbances in tributaries with a small watershed account for the bulk of the area. Forest and steppe fires as area cause a rapid response. On the other hand, even large along with mining accounted for the smallest share of all development areas in a large watershed produce a small land degradation in 2012 (UNDP-GEF 2012). Furthermore, effect on the SS. The effect of a land disturbance can be excavated soils and rocks in mining areas have typically promptly detected in small tributaries by changes in the SS been stock piled in separate fields after the extraction or flux and concentration. purification processes (Farrington 2000, 2005; Karpoff and Higher discharges usually accompanied a larger release Roscoe 2005). Soil eroded from the excavated land surface of SS. A positive linear correlation between river discharge includes deposited soils and slag in the bottom sediments and SS load has been previously confirmed (Walling 2006; of excavated ponds, resulting in a lower release of soil and Walling and Fang 2003). Larger SS loads can generally be mineral particles from mining areas to tributaries. attributed to intense land use change, such as land clear- The lowest concentration of suspended solids was ance for agriculture, catchment disturbances by industri- detected in the lower reaches of the Buir River (Buir 5), alization, and increased runoff from increased which is a relatively small branch tributary of the precipitation. Both river water discharge and SS concen- Orkhon River (Fig. 2). Relatively low concentrations of tration should be characteristic for tributaries and their SS were detected related to the landscape of the river watershed. The relationship between river water discharge watershed, which is a wetland on a flat plain and and SS concentration in each tributary is shown in Fig. 4. includes the large city of Sukhbaatar. The transportation The Shar River is characterized as a turbid river with high potentials of suspended solid fractions in a river system SS concentrations despite low water discharge. The are mainly affected by the river current velocity (Tansel Selenga and Orkhon Rivers are characterized by higher SS and Rafiuddin 2016). The low flow rate of the tributary fluxes and low SS concentrations with larger water dis- over flat land results in the precipitation of SS to the charges. Both the Tuul and Yeruu Rivers have low SS bottom sediments. Moreover, a small development area concentrations. A higher rate of impervious surface area in on the plain watershed probably protects the land surface the Tuul River watershed could be the cause of decreased from soil erosion, resulting in relatively low SS at Buir SS release. The lower exploited area found in the Yeruu 5. Vegetation cover in the wetland is also effective River watershed is also a possible reason for its lower SS against soil erosion. concentration. The Shar and Kharaa Rivers are presumably Changes in the concentrations of SS in the main stream sensitive to SS releases by land use changes since they throughout the research area reflect the influence of con- have relatively small watersheds. Increased mechanical necting tributaries. A large flux of SS from connecting agriculture within a watershed promotes SS release due to tributaries increases the SS concentrations at Orkhon 7 and land degradation. 123 Environ Earth Sci (2017) 76:346 Page 7 of 15 346

) 1000 can change into bioavailable forms in alkaline conditions. -1 Shar River Kharaa River Their partitioning between the colloidal and dissolved Yeruu River fractions depends on the water condition, indicating that Tuul River Orkhon River variations in water condition found in the present river Selenga River environment can increase the bioavailable fraction of heavy metals. 100 A constant composition of solid Al and Fe was found in the SS, as confirmed by the positive liner correlation between the concentrations of SS fractions and the Al and Fe contents (Fig. 5). This relationship indicates that the source of the SS fractions was surface soil in the tributary watersheds. The

Suspended solid concentration (mg L 10 concentrations of Al and Fe in the SS fractions were also 1 10 100 1000 highly correlated to other elements (Table 4), indicating that 3 -1 River discharge (m s ) the measured elements are primarily carried by SS particles Fig. 4 Relationships between suspended solids and river discharges in the Selenga River system, or occur naturally in the SS at the 6 gauging stations during active discharge seasons from April to structure with a high stability in river water. However, sev- October, including 5-year data from 2009 to 2013. Concentration of eral elements (Cr, Cu, and Zn) were not significantly corre- suspended solids and river discharge data were provided by the lated to the concentrations of Al and Fe in the SS fractions Mongolian Institute for Meteorology and Hydrology (MIMH). Error bars are standard errors (Table 4). Those three elements Cr, Cu, and Zn are irregu- larly distributed with SS in the Selenga River system and can deteriorate the main river water quality. These spatial Elemental composition of suspended solids occurrences of heavy metal contaminants with SS along the Selenga River system, and their releases through different Terrigenous elements consisting of Fe and Al were major land uses, can be explained by changes in the weight basis constituents in the SS (Table 5). Secondary minerals as concentrations of heavy metals. oxides contribute to SS constituents released from soil. Basic metals (Ca, Mg, and K) were also major elements in Transformation of metals during in-stream the SS fractions (Table 4). At Orkhon 13, the rate of Ca processes and K was higher than that of Fe and Al, indicating that primary minerals from sedimentary rocks, including lime- Concentrations (weight basis) of Cr, Cu, and Zn in the SS stone, were the major constituents in the SS fraction. Basic were high in the upper reaches of the Tuul (Tuul 16) and elements were mainly detected in the dissolved and col- Orkhon (Orkhon 13) Rivers (Fig. 6). The main upstream loidal fractions (Tables 2, 3). On the other hand, the major pollution source in the Tuul River is the capital city of metals found in terrigenous sediments (Fe and Al) and Ulaanbaatar (Nadmitov et al. 2015; Itoh et al. 2011). The heavy metals were detected at higher concentrations in the mass flows of dissolved heavy metals in the downstream SS fractions than in the dissolved and colloidal fractions. Although the ratio of heavy metals in the SS was small, their spatial distribution was consistent with the elemental 50 Al dynamics of the river system. Heavy metal transport on ) 2

-1 R = 0.9304 suspended particles accounted for 98% of the total trans- 40 y = 0.0469x + 0.7783 port in the Selenga River Basin (Chalov et al. 2015). Thorslund et al. (2012) studied the impact of gold mining 30 on riverine heavy metal transport in the upper Selenga River Basin. The results suggest that the prevailing alkaline 20 conditions in the vicinity of gold mining can limit the dissolution of heavy metals and maintain heavy metal concentrations below health-risk guideline values. Down- 10 Fe R2 = 0.9284 stream tributary water with a relatively low pH value Concentration of metals (mg L y = 0.0465x + 0.3934 allows for the dissolution of large heavy metal concentra- 0 tions transported on SS (Plyusnin et al. 2008). These heavy 0 200 400 600 800 1000 -1 metals, after dissolving from the suspended particles, can Concentration of SS (mg L ) undergo phase transformations that enhance their Fig. 5 Relationship between concentration of suspended solids and bioavailability. Some dissolvable heavy metals, such as Zn, concentration of Al and Fe in the suspended solids 123 346 Page 8 of 15 Environ Earth Sci (2017) 76:346

7 anthropogenic sources. Suspended solids carry heavy Zn Main River metals by adsorption on their surface during long distance 6 Tirbutaries transport. Heavy metals released from urban and mining 5 areas can be transported downstream with gradual dilution )

-1 caused by mixing with high concentrations of SS that have 4 lower heavy metal concentration and come from intensive 3 agricultural watersheds along the Shar and Kharaa tribu- taries (Fig. 6). Suspended solids coated with organic matter 2 were a major component of the SS, which was confirmed 1 with a significant positive correlation (p \ 0.95) between the loss on ignition (LOI) and weight of SS fractions 0 (Fig. 7). Suspended solids consisting of an organo-mineral 4 Cu complex can adsorb dissolved heavy metals during trans- port from a river source all the way downstream. 3 The elemental compositions of SS in tributaries were Concentration of metals in SS (mg g different at the various river junctions. Suspended solids affected by anthropogenic pollution sources can influence 2 water quality and the fate of heavy metals due to the SS transformation processes (including dilution, adsorption, desorption, resuspension, and deposition processes). 1 Increases in SS concentrations from Tuul 16 to Tuul 15 (Fig. 3) accompanied decreased concentrations of Cr, Cu,

0 and Zn in the SS (Fig. 6). The increase in SS concentra- 350 tions from Tuul 16 to Tuul 15 was related to dilution Cr caused by mixing with SS having low heavy metal sorption

) 300

-1 that originated from upstream of the Tuul River to the

g Zaamar mining area. At Tuul 14, the weight-based con-

µ 250 centrations of Cr, Cu, and Zn in the SS sharply increased 200 (Fig. 6), indicating that the heavy metals had accumulated

150 onto the surface of the SS during transport between Tuul 15 and 14. The concentrations of major anions, DOC 100 (Table 1), and dissolved metals (Table 2) increased downstream of the Zaamar Gold field (Tuul 15 and 14). At 50 Concentration of Cr ( the mining pit, ore excavation likely increases dissolved Fe 0 and counter anions. The high concentrations of dissolved Buir (5)

Shar (8) 12 Tuul (15) Tuul (14) Tuul (16) 2 Yeruu (6) R =0.895 Orkhon (9) Orkhon (4) Orkhon (7) Orkhon (3) Kharaa (10) Selenga (1) Selenga (2) Orkhon (12) Orkhon (13) Orkhon (11) Y=9.6173x-4.0014 10 Fig. 6 Weight-based concentrations of Zn, Cu, and Cr in suspended solids at each sampling station 8

Tuul River near the capital area were twice as high as those 6 upstream of the city center (Altansukh et al. 2012; Itoh et al. 2011). On the other hand, the largest Cu and Mo 4

mining companies in Mongolia, as well as some small gold (mg) Loss on ignition mining areas, are located in the upper reaches of the 2 Orkhon River (Chebykin et al. 2012). High concentrations of suspended particulate matter and dissolved heavy metals 0 are released from the mining areas (Ministry of Environ- 0 20406080100120 Suspended solid fractions (mg) ment and Green Development 2012a, b). These heavy metals show an irregular distribution irrespective of the Fe Fig. 7 Relationship between loss on ignition and weight of sus- and Al distribution, indicating that they are from pended solids 123 Environ Earth Sci (2017) 76:346 Page 9 of 15 346

Table 1 General properties, major anions, and dissolved organic carbon (DOC) in the river water samples

2- 3- - - - River name pH EC SO4 PO4 F Cl NO3 DOC (sample ID) (lSm-1) (mmol L-1) (mmol L-1) (mmol L-1) (mmol L-1) (mmol L-1) (mg L-1)

Selenga (1) 7.80 0.2 140 35 27 60 20 8.5 Selenga (2) 7.81 0.2 140 34 23 20 10 11.6 Orkhon (3) 7.82 0.2 130 28 33 100 40 7.7 Orkhon (4) 7.93 0.2 110 32 26 80 34 7.4 Buir (5) 7.91 1.0 170 230 100 220 3 26.4 Yeruu (6) 7.66 0.1 50 16 22 14 6 8.3 Orkhon (7) 8.17 0.3 170 50 40 180 44 6.1 Shar (8) 8.35 0.3 220 52 44 110 30 9.3 Orkhon (9) 8.47 0.3 190 44 37 180 50 6.2 Kharaa (10) 8.39 0.3 190 59 42 150 30 7.6 Orkhon (11) 8.07 0.3 200 52 37 190 20 4.1 Orkhon (12) 8.39 0.3 170 50 35 180 20 6.8 Orkhon (13) 7.95 0.2 140 53 36 70 30 5.2 Tuul (14) 8.19 0.4 270 71 39 410 20 11.8 Tuul (15) 8.03 0.3 270 74 39 470 20 10.2 Tuul (16) 7.85 0.2 130 46 23 330 70 5.9

Table 2 Concentration of dissolved metals in river water from the Selenga River and its tributaries River name (sample ID) Al (lgL-1)Fe(lgL-1) Ca (mg L-1) K (mg L-1) Mg (mg L-1) Na (mg L-1) Si (mg L-1)Zn(lgL-1)

Selenga (1) – 20 23.2 1.0 10.8 3.2 6.0 7 Selenga (2) – 30 30.5 0.7 12.2 4.9 5.5 4 Orkhon (3) 10 30 23.9 0.9 11.8 4.4 6.4 4 Orkhon (4) 100 100 22.2 0.7 10.2 3.7 6.1 7 Buir (5) – 30 84.2 1.1 112.0 76.4 11.4 20 Yeruu (6) 100 100 8.4 0.4 6.6 2.6 5.8 10 Orkhon (7) – – 28.1 0.9 16.2 16.0 6.0 6 Shar (8) – – 36.4 1.3 22.9 18.1 7.0 7 Orkhon (9) – 20 30.0 0.9 16.5 18.3 6.2 8 Kharaa (10) – – 32.7 0.9 18.2 17.2 6.1 1 Orkhon (11) – – 30.1 1.0 16.7 21.6 6.5 8 Orkhon (12) 10 30 28.8 1.0 16.2 24.7 6.2 20 Orkhon (13) – – 29.9 0.7 15.5 15.4 6.5 4 Tuul (14) 25 51 27.6 1.3 18.0 35.8 5.9 20 Tuul (15) – 30 26.6 1.2 17.1 33.6 5.8 6 Tuul (16) – – 21.5 0.6 7.2 13.3 4.4 9 (–) indicates below the detection limit

Fe were accompanied by a larger colloidal Fe concentra- solubility of heavy metals in the river water near the tion at Tuul 15 and a further increase at Tuul 14 (Table 3). Zaamar mining area, resulting in the high accumulation of Diffuse flows through groundwater can convey dissolved heavy metals on the SS mineral surfaces. and colloidal metals from the excavated mining site to a A second point of interest was the junction of two main downstream site (Thorslund et al. 2012). Water pumped tributaries, the Tuul and Orkhon Rivers, at Orkhon 12. from the river is stored in ponds after the gold purification Highly concentrated Zn, Cu, and Cr on SS surfaces process and can infiltrate to groundwater as diffuse flows or upstream of Orkhon 13 also sharply declined downstream be released into the main river. An increase in the EC value of the junction due to dilution with SS particles carrying accompanied by salt concentrations promotes low lower concentrations of heavy metals from the Tuul River

123 346 Page 10 of 15 Environ Earth Sci (2017) 76:346

Table 3 Concentrations of colloidal metals in river waters from the Selenga River and its tributaries River name (sample ID) Al (mg L-1)Fe(lgL-1) Ca (mg L-1) K (mg L-1) Mg (mg L-1) Si (mg L-1)Zn(lgL-1)

Selenga (1) 0.17 90 0.2 0.0 0.0 0.0 12 Selenga (2) 0.14 80 8.2 0.5 3.9 1.8 14 Orkhon (3) 0.15 190 6.4 0.5 5.1 1.8 15 Orkhon (4) 0.02 – 4.5 0.8 4.9 2.3 9 Buir (5) 0.12 40 13.1 0.8 60 4.1 6 Yeruu (6) 0.08 10 5.1 0.4 0.0 2.2 19 Orkhon (7) 0.11 60 10.1 0.9 6.9 2.8 8 Shar (8) 0.24 100 10.5 1.2 8.5 2.6 12 Orkhon (9) 0.17 100 7.5 0.9 7.0 2.4 12 Kharaa (10) 0.11 70 9.7 0.9 8.7 2.3 14 Orkhon (11) 0.12 90 6.2 0.7 6.8 1.9 4 Orkhon (12) 0.18 90 1.4 0.5 3.4 0.9 5 Orkhon (13) 0.12 60 6.9 0.5 6.8 2.1 11 Tuul (14) 0.33 200 4.2 0.9 6.0 1.5 24 Tuul (15) 0.22 100 6.0 1.1 8.1 2.0 19 Tuul (16) 0.15 70 5.6 0.5 3.3 2.3 19 (–) indicates below the detection limit

Table 4 Concentrations of metals in suspended solid fractions from the Selenga River and its tributaries with correlations data River name Al Fe Ca K Mg Zn Mn Cu Ni Cr Zr (sample ID) (mg L-1) (mg L-1) (mg L-1) (mg L-1) (mg L-1) (lgL-1) (lgL-1) (lgL-1) (lgL-1) (lgL-1) (lgL-1)

Selenga (1) 2.9 2.8 1.7 2.5 1.1 100 90 50 13 12 12 Selenga (2) 4.8 5.6 4.4 2.6 2.3 130 150 30 18 14 6 Orkhon (3) 9.3 8.5 4.9 4.3 3.3 180 220 – 20 14 6 Orkhon (4) 4.3 3.9 2.4 3.1 1.5 130 110 60 14 11 4 Buir (5) 0.2 0.1 0.5 0.7 0.2 180 12 – 10 9 2 Yeruu (6) 0.9 0.8 0.3 0.2 0.2 60 20 – 17 3 8 Orkhon (7) 19.6 19.6 9.6 3.3 6.0 390 460 – 23 14 1 Shar (8) 40.1 39.6 27.7 16.9 15.6 530 810 160 74 46 15 Orkhon (9) 7.3 6.8 3.8 1.3 2.3 220 190 – 6 7 2 Kharaa (10) 10.4 8.4 5.3 3.7 3.3 120 250 – 2 11 8 Orkhon (11) 7.2 6.3 5.1 5.3 2.9 290 180 170 24 18 11 Orkhon (12) 5.8 5.5 3.9 4.1 2.5 200 170 180 20 17 10 Orkhon (13) 2.2 1.7 1.7 2.2 0.8 190 50 100 12 9 6 Tuul (14) 4.7 4.2 2.7 3.6 1.8 180 160 190 19 16 9 Tuul (15) 6.7 5.5 2.7 3.4 2.3 160 170 4 14 12 8 Tuul (16) 1.7 1.5 0.8 1.5 0.6 130 60 120 11 10 5 Al 1 0.99 0.98 0.91 0.99 0.89 0.99 0.29 0.92 0.88 0.61 Fe 1 0.99 0.90 0.99 0.89 0.99 0.28 0.92 0.88 0.61 Ca 1 0.95 0.99 0.88 0.97 0.31 0.96 0.93 0.62 K 1 0.95 0.80 0.89 0.37 0.97 0.98 0.68 Mg 1 0.88 0.98 0.30 0.95 0.92 0.63 Zn 1 0.89 0.51 0.79 0.81 0.51 Mn 1 0.31 0.89 0.87 0.62 Cu 1 0.39 0.42 0.42 Ni 1 0.95 0.71 Cr 1 0.68 Zr 1 (–) indicates below the detection limit

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Table 5 Weight-based concentrations of metals in suspended solid fraction from the Selenga River and its tributaries with correlations data River name Al Fe Ca K Mg Zn Mn Cu Ni Cr Zr (sample ID) (mg g-1) (mg g-1) (mg g-1) (mg g-1) (mg g-1) (mg g-1) (mg g-1) (mg g-1) (lgg-1) (lgg-1) (lgg-1)

Selenga (1) 52.6 52.2 31.2 46.7 20.3 1.9 1.6 0.9 250 220 210 Selenga (2) 32.8 37.6 29.0 19.3 15.1 0.9 1.0 0.1 120 100 40 Orkhon (3) 50.3 46.1 26.4 23.2 17.8 1.0 1.2 - 110 80 30 Orkhon (4) 61.2 53.6 34.5 53.1 21.1 2.8 1.6 3.0 340 300 120 Buir (5) – – – – – – – – – – – Yeruu (6) – – – – – – – – – – – Orkhon (7) 72.0 71.8 35.6 12.3 22.2 1.4 1.7 80 50 40 Shar (8) 46.8 45.8 32.1 19.4 18.1 0.6 0.9 0.2 90 60 20 Orkhon (9) 46.7 43.4 24.3 8.3 14.8 1.4 1.2 - 40 40 10 Kharaa (10) 50.9 41.3 26.1 18.2 16.3 0.6 1.2 - 100 50 40 Orkhon (11) 60.2 51.9 43.1 48.6 23.7 2.8 1.6 1.7 230 180 100 Orkhon (12) 44.5 42.4 29.7 30.9 19.0 1.5 1.3 1.3 160 130 70 Orkhon (13) 65.7 52.2 51.6 67.2 24.9 5.7 1.6 3.1 370 260 170 Tuul (14) 57.8 51.6 32.8 44.7 22.3 2.3 1.9 2.3 240 190 110 Tuul (15) 50.8 42.2 20.8 26.3 17.6 1.2 1.3 - 110 90 60 Tuul (16) 49.5 45.6 24.4 45.8 16.5 3.9 1.9 3.5 340 300 150 Al 1 0.88 0.61 0.41 0.82 0.49 0.66 0.35 0.38 0.31 0.34 Fe 1 0.50 0.18 0.70 0.27 0.57 0.17 0.20 0.16 0.23 Ca 1 0.63 0.86 0.67 0.32 0.47 0.54 0.41 0.41 K 1 0.69 0.85 0.62 0.87 0.96 0.92 0.88 Mg 1 0.61 0.60 0.50 0.57 0.47 0.52 Zn 1 0.65 0.87 0.87 0.81 0.73 Mn 1 0.71 0.67 0.67 0.67 Cu 1 0.94 0.94 0.74 Ni 1 0.98 0.87 Cr 1 0.88 Zr 1 (–) indicates below the detection limit

(Fig. 6). Additionally, SS in the Orkhon River would be transformed due to the different conditions from those in 40 )

-1 Main River the Tuul River water. Mixing water from two tributaries Tributaries can cause physicochemical changes in the river water. The water properties of tributaries can therefore control ele- 30 mental dynamics and water properties in the main stream. Concentrations of solutes, DOC, and EC were all higher in 20 the Tuul River water at Tuul 14 than those in the Orkhon River water at Orkhon 13 (Tables 1, 2). The concentrations of solutes and EC decreased at Orkhon 12 after the mixing 10 of the tributaries. The change in water quality can trans- form SS and solutes in the river. During the transformation process, sizes of the suspended particulate matter increased Amount of Fe in the sediment (mg g 0 through aggregation and sorption of dissolved metals and DOC on the surface of SS. Aggregation and sorption Buir (5) Shar (8) Tuul (15) resulted in increased SS concentrations at Orkhon 12 Tuul (16) Tuul (14) Yeruu (6) Orkhon (9) Orkhon (7) Orkhon (4) Orkhon (3) Kharaa (10) Selenga (1) Selenga (2) Orkhon (11) (Fig. 3). Main indicators of this transformation process Orkhon (13) Orkhon (12) include a change in elemental compositions in the sedi- Fig. 8 Distribution of Fe concentration in bottom sediments at each ments and changes in dissolved and colloidal metal station. Flow direction is from 16 to 1 123 346 123 ae1 f15 of 12 Page

Table 6 Concentrations of metals in river bottom sediment from the Selenga River and its tributaries River name (sample Al Fe Ca Mg K Mn Zn Cu Cr Ni Zr C N ID) (mg g-1 ) (mg g-1 ) (mg g-1 ) (mg g-1 ) (mg g-1 ) (mg g-1 ) (lgg-1 ) (lgg-1 ) (lgg-1 ) (lgg-1 ) (lgg-1 ) (mg g-1 ) (mg g-1 )

Selenga (1) 8.0 18.7 12.8 2.3 0.3 0.19 30 – 11 13 – 0.88 0.08 Selenga (2) 23.7 24.9 17.1 5.1 0.8 0.56 60 70 39 39 16 2.32 0.21 Orkhon (3) 11.7 18.9 11.6 3.1 0.6 0.25 40 – 13 16 1.6 1.39 0.14 Orkhon (4) 47.4 38.6 16.3 7.7 2.2 0.93 110 80 55 49 25 3.15 0.30 Buir (5) 22.9 19.7 23.0 5.1 1.5 0.47 60 – – 25 16 2.24 0.17 Yeruu (6) 20.3 17.6 6.1 3.6 1.2 0.42 50 – 18 19 11 0.55 0.06 Orkhon (7) 11.2 11.5 9.2 2.0 0.6 0.22 20 – 6 9 5 0.09 0.009 Shar (8) 12.5 11.4 11.0 2.3 0.7 0.22 30 – 13 10 10 0.16 0.013 Orkhon (9) 7.8 7.0 6.1 1.3 0.4 0.23 20 – – 5 1 0.03 0.003 Kharaa (10) 23.5 19.4 40.6 4.6 1.6 0.60 60 – 28 26 14 1.04 0.097 Orkhon (11) 23.0 19.2 7.5 4.8 1.4 0.46 60 2 23 25 14 0.93 0.09 Orkhon (12) 29.7 26.4 13.8 7.0 1.9 0.58 70 30 36 34 16 0.78 0.07 Orkhon (13) 20.7 17.3 9.4 4.2 1.1 0.36 50 – 19 21 13 0.71 0.06 Tuul (14) 23.0 19.7 9.6 4.5 0.9 0.46 50 – 19 22 11 0.32 0.03 Tuul (15) 20.3 15.7 10.8 4.4 1.1 0.39 40 15 21 21 11 0.26 0.02 Tuul (16) 19.6 12.7 4.7 2.8 1.2 0.43 40 14 16 14 12 0.56 0.06 (–) indicates below the detection limit nio at c 21)76:346 (2017) Sci Earth Environ Environ Earth Sci (2017) 76:346 Page 13 of 15 346 concentrations. The amount of Fe in the sediment sample Production of SS in watersheds was high at Orkhon 12 downstream of the Orkhon–Tuul River junction (Fig. 8; Table 6). After the two tributaries Agricultural land use has a high impact on soil erosion, mix, the SS particles were easily deposited at Orkhon 12 resulting in large mass flows of soil particles to tributaries. due to aggregation. The concentrations of dissolved Fe The suspended solid concentrations in small tributaries (Table 2), major anions (sulfate and chloride), and DOC (Shar and Kharaa) during the high discharge seasons (Table 1) decreased at Orkhon 12. The aggregation effect reached 1 kg m-3, indicating that high soil erosion was also confirmed by a decrease in the concentration of occurred in their watersheds due to agricultural cultivation colloidal Fe from 0.21 mg L-1 at Tuul 14 to 0.093 mg L-1 before high rainfall events. Surface erosion of the bare land at Orkhon 12 (Table 3). Deposition of colloidal and SS promoted high SS discharges in the rainy seasons, when the particles consisting of Fe oxides was probably the main tributary had a high flow rate. Even during base flow sea- cause of increased Fe concentrations in sediments at sons, the small tributaries had large SS concentrations and Orkhon 12. Transformation of the Fe from colloids to fluxes due to land surface disturbance after land develop- suspended solids or river bottom sediments was also ment during the past two decades. Since the tributaries speculated as an aggregation process caused by changes in provide SS to the main stream, land use and land cover the salt concentration or pH (Table 1). changes in the watersheds can affect the total transport of A strong transformation process was also observed SS in the main stream. downstream of the junction between the Orkhon and Buir Rivers (Orkhon 4). The very low concentrations of colloidal Fate of contaminants during in-stream processes Fe (Table 3) were probably due to removal of Fe colloids through co-precipitation caused by the high concentrations The fate of contaminants with differently sized fractions of dissolved basic and heavy metals (Table 2) and organic depended on the transformation processes, including matter (Table 1) in the wetland tributary water (Buir 5), adsorption of dissolved metals onto particulate matter, where concentrations of dissolved organic carbon (DOC), aggregation of particulate matter with metals and organic dissolved metals and EC were the highest. This indicates that matter, dilution of SS, and resuspension of sediments. Such Fe colloids were completely removed from the liquid phase transformation processes mainly exist at the junctions of at Orkhon 4 by co-precipitation with organic matter and two tributaries. Concurrently, the elemental composition of adsorbed metals, primarily due to an aggregation of colloidal SS in tributaries changes at these junctions through the particles by organic compounds that then precipitated to the dilution of highly contaminated SS with less contaminated river bottom as sediments, changing the colloidal fractions SS from agricultural areas. Changes in the physicochemical into suspended solids. The main indicator of this precipita- properties of tributaries affect the transformation and tion process was the Fe concentration in the sediment sam- transportation of contaminants sorbed to the SS in the main ples. The highest Fe concentration (38.6 g kg-1) was river. The physicochemical properties are in turn strongly detected downstream of the junction between the Orkhon influenced by land use and land cover changes in tributary and Buir Rivers (Fig. 8; Table 6). watersheds. Extensive land development in Northern Mongolia will further control the transport and fate of contaminants released from developing urban, industrial, Conclusion mining, and agricultural areas.

Sources and carriers of contaminants Acknowledgements This study was supported by Grant-in-Aid for Scientific Research (B), Grant No. 25304001 from Japan Society for the Promotion of Science. The authors also thank to Ms. Batdulam B., Heavy metals, mainly released from urban and mining Mr. Galdmaa, D., Ms. Bolormaa T. National University of Mongolia areas in the Selenga River system, adsorb to and flow with is appreciated by the research support. SS. Colloidal and dissolved heavy metals are scarce in the tributary system. Cr, Cu, and Zn accumulated heavily on References SS downstream of the urban and mining areas as solid contaminants, differing from the other heavy metals. Altansukh O, Whitehead P, Bromley J (2012) Spatial patterns and Release of SS was highest at the agricultural field where temporal trends in the water quality of the Tuul River in the concentration of heavy metals (including Cr, Cu, and Mongolia. Energy Environ Res 2:62–78 Zn) decreased due to larger uncontaminated SS concen- Bilotta GS, Brazie RE (2008) Understanding the influence of SS on water quality and aquatic biota. Water Res 42:2849–2861 trations in the tributary water. Suspended solids are a major Brumbaugh WG, Tillitt DE, May TW, Javzan Ch, Komov VT (2013) controlling factor for heavy metal concentrations through Environmental survey in the Tuul and Orkhon River basins of the processes of adsorption, desorption, and sedimentation. north-central Mongolia, 2010: metals and other elements in 123 346 Page 14 of 15 Environ Earth Sci (2017) 76:346

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