Major ion geochemistry of the Nansihu Lake basin rivers, North China: chemical weathering and anthropogenic load under intensive industrialization

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1 Environ Earth Sci (2016) 75:453 DOI /s ORIGINAL ARTICLE Major ion geochemistry of the Nansihu Lake basin rivers, North China: chemical weathering and anthropogenic load under intensive industrialization Jun Li 1 Guo-Li Yuan 1,2 Xian-Rui Deng 3 Xiu-Ming Jing 1 Tian-He Sun 1 Xin-Xin Lang 1 Gen-Hou Wang 1 Received: 12 April 2015 / Accepted: 23 November 2015 / Published online: 10 March 2016 Springer-Verlag Berlin Heidelberg 2016 Abstract To explore the chemical weathering processes and the anthropogenic disturbance of weathering, 20 water samples were collected from the tributaries in the Nansihu Lake basin, a growing industrial area. The major ions in river waters were analyzed to identify and quantify the contributions of the different reservoirs. Based on stoichiometric analyses and end-member determination, the contributions of individual reservoirs were calculated for each tributary. In the study region, the averaged contributions of atmospheric inputs, anthropogenic inputs, evaporite weathering, carbonate weathering and silicate weathering were 2, 37, 28, 25 and 8 %, respectively. Combined with information regarding runoff and drainage area, the annual average contribution of TDS to waters was estimated to be 1.90 ± 0.95 ton/km 2 from silicate weathering, 5.68 ± 2.84 ton/km 2 from carbonate weathering. Furthermore, the associated consumption of CO 2 was calculated to be approximately mol/a. The industrial and mining activities were the main sources for anthropogenic inputs, and they produced non-co 2 acids (NCA). Of all protons involved in chemical weathering, Electronic supplementary material The online version of this article (doi: /s ) contains supplementary material, which is available to authorized users. & Guo-Li Yuan yuangl@cugb.edu.cn School of the Earth Sciences and Resources, China University of Geosciences, Beijing , China State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Beijing , China Shandong Provincial Institute of Land Surveying and Mapping, Jinan , China 34 % was presumed to be originated from NCA, causing mol/a of CO 2 degassing. Moreover, industrial inputs could play a major role in the modification of the chemicals in the water system, and they could even change the carbonate weathering rate in such an intensively industrializing region. In North China, the chemical weathering associated with NCA was found to be significant for the first time. Keywords Water geochemistry Major ions Rock weathering CO 2 consumption Long term CO 2 degassing Introduction The major chemical compositions of river waters can reveal the natural weathering processes and anthropogenic activities on a basin-wide scale (Gibbs 1970; Stallard and Edmond 1983; Sarin et al. 1989; Brennan and Lowenstein 2002; Moquet et al. 2011). At the global scale, large rivers have been studied to estimate the weathering rates of different rock types and CO 2 consumption (Gaillardet et al. 1999; Roy et al. 1999; Moon et al. 2007, 2014; Noh et al. 2009; Moquet et al. 2011; Pattanaik et al. 2013). However, the small-scale studies have been considered to be better for understanding specific weathering and anthropogenic processes under certain conditions (Barnes and Raymond 2009; Gurumurthy et al. 2012; Price et al. 2013; Wu et al. 2013). In China, most researchers have focused on the Yangtze River (Hu et al. 1982; Zhang et al. 1990; Chen et al. 2002; Li and Zhang 2005; Chetelat et al. 2008), the Yellow River (Hu et al. 1982; Zhang et al. 1990, 1995; Li and Zhang 2005; Wu et al. 2005; Fan et al. 2014), and the Pearl River (Chen and He 1999; Zhang 1999; Zhang et al. 2007b). The historical data of these three large rivers had

2 453 Page 2 of 16 Environ Earth Sci (2016) 75:453 shown the increases in major ion concentrations during the past years, such as chloride increasing around two times. Since the wastewater discharged into the Yangtze River basin and the Yellow River basin climbed from *10 billion and 2.2 billion tons in 1980 to 34 billion and 4.2 billion tons in 2010, respectively (Wang 2015), human activities were possible responsible for the elevated concentrations. Recently, some studies have focused on the major chemical composition of river water in the upper Han River basin (Li et al. 2009) and the Huai River basin (Zhang et al. 2011), because these two river basins are associated with China s South to North Water Transfer Project (SNWTP). Nansihu Lake is the largest freshwater lake in North China. The east line of the SNWTP will flow through this lake, which serves not only as an important water transportation channel for the SNWTP but also as a storage lake for the SNWTP. It is therefore important to identify and quantify the chemical compositions of river waters flowing into Nansihu Lake. On the other hand, the modification by anthropogenic inputs of the chemical compositions of waters should be paid more attention, as human activities are becoming increasingly extensive in the region. Zhang et al. (2011) has emphasized the anthropogenic influence in this region. Therefore, it is necessary to differentiate the industrial and agricultural inputs for major ions at a regional scale and then individually estimate the contributions of weathering of different parent rocks (e.g., carbonates, evaporites and silicates) and the associated CO 2 consumption. In addition to carbonic acid, other acids (such as H 2 SO 4 and HCl) have recently been recognized as protons involved in rock weathering (Calmels et al. 2007; Xu and Liu 2007; Chetelat et al. 2008; Beaulieu et al. 2011; Lang et al. 2011). If these others acids contribute to chemical action, then carbonate weathering may lead to CO 2 production instead of CO 2 sequestration (Li et al. 2008). Several studies of small and moderate water systems indicate the importance of non-co 2 acids (NCA) in chemical weathering (Han and Liu 2004; Xu and Liu 2007; Li et al. 2008; Meyer et al. 2009). In a heavily industrialized basin, the study of rock weathering by NCA helps us to estimate the associated CO 2 production and to observe the influence of NCA on carbonate weathering rate (CWR). Then, the balance between CO 2 production and consumption could be well understood at a basin scale. In this study, the major chemical compositions of 20 sites were determined for the rivers flowing into the Nansihu Lake basin. The main goals are (1) to identify their sources and quantify the contributions of the various reservoirs to the dissolved load, especially the anthropogenic contributions including industrial and agricultural inputs; (2) to calculate chemical weathering rates and the associated CO 2 consumption; (3) to study the anthropogenic influence on CWR; and (4) to estimate the contribution of NCA to rock weathering at a basin scale. Materials and methods Geography and geology The Nansihu Lake basin (NLB) ( N, E), as one sub-basin of Huai River basin, is situated in the North China Plain between the Yellow River and the Huai River (the second- and third-largest rivers in China) (Fig. 1a). The total drainage area is 31,700 km 2, covering 32 counties with a population of 22 million in Jiangsu, Shandong, Henan and Anhui Provinces. Geologically, the NLB consists of various source rocks (Fig. 1b). The major lithologies exposed in the study region are Cambrian and Ordovician carbonate rocks (limestones and dolomites) and Jurassic detrital sedimentary rocks (siltstones and sandstones), which are widely distributed in the basin and cover 35 and 30 % of the basin area, respectively. The Precambrian outcrops covering about 12 % of the area, are mainly granite gneiss which occurs in the eastern hills and mountainous areas. Carbonic and Permian coal deposits are interbedded in shale strata and are separately distributed in the eastern and western sections with approximately 4 % of the area. The Tertiary rocks covering 5 % of the whole area, are mainly detrital rocks (shale and sandstone) and evaporites. The Quaternary fluvial sediments occupying 14 % of the basin area, are distributed over the whole plain. Climate, hydrology and land cover This basin is subject to temperate monsoon climate, and the annual mean temperatures is 12 C in Jining City which occupies the north section of the basin and 15 C in Zaozhuang City for the south section. Average annual precipitation and evaporation vary from 685 and 900 mm on the drier part to 900 and 1050 mm around the lake, and more than 80 % of annual precipitation falls during the flood season from May to September (Wu et al. 2010). In this basin, there are 13 tributaries encompassing a wide range of lithologies and land uses (Table S1 in supplementary materials, abbreviated as SM), including the Guangfu, Si, Baima, Guo, Xinxue, Dongyu, Zhuzhaoxin, Dayun, Beijie, Beisha, Hanzhuang, Hui and Wanfu Rivers, with the former eight tributaries being the major ones. The average annual discharge input to the lake is m 3 (Wu et al. 2010). In addition, Li et al. (2011) reported that there were no thermal sources in the NLB, and the groundwater did not have significant

3 Environ Earth Sci (2016) 75:453 Page 3 of Fig. 1 a Map showing the rivers and sampling sites of the drainage basin of Nansihu Lake, China and b map showing the geology of the Nansihu Lake basin influence on the major ions in river waters, even though the alluvial aquifer recharges the river water that is flowing across the plain. Cultivated land, used for growing wheat, corn and cotton, represents approximately 53 % of the NLB (Huang et al. 2012). Heavy forests are mostly distributed in the eastern mountainous areas, and vegetation covers approximately 33 % of the surface area. The building area covers 14 % of the basin, including more than 100 large manufacturing and mining companies. Sampling and analysis In the NLB, about 80 % of the runoff occurs in the flood season (Wu et al. 2010). The lower water flowing in winter may cause more Ca2? precipitation than Na? (Li et al. 2011). Thus, the waters in summer are considered more representative of the flowing conditions in the study region. And the sampling was performed in the high-flow season during June Water samples were collected from 20 sites along the rivers flowing into Nansihu Lake (Fig. 1a). Although each site was sampled only once, the sampling locations in 13 river estuaries provided a comprehensive understanding of the water chemistry of the entire basin. At each site, water samples from the surface, middle and bottom of the river were mixed together and then filtered (0.45-lm Millipore nitrocellulose filter) in the field. The first portion of the filtrate was discarded to clean the membrane. The sampled waters were stored in pre-cleaned HDPE bottles. Filtered solutions for cation analysis were acidified to ph \2 with ultra-purified 6 M HNO3-. Cleaning of plastic bottles and plastic bags was performed by soaking in 15 % (v/v) HNO3- for 24 h and then rinsing with Millipore water. Water temperature, ph, electrical conductivity (EC) and total dissolved solids (TDS) were measured in situ using a YSI 6920 (Ohio, USA) after calibration. The HCO3- was determined by titration with HCl on the sampling day. Major cations (Na?, K?, Ca2? and Mg2?) and Si were measured using inductively coupled plasma atomic emission spectrometry (ICP-AES) (IRIS Intrepid II XSP, USA) with a precision better than 5 %. Anions (F-, Cl-, NO3and SO42-) were measured by ion chromatography (IC) (Shimadzu HIC-SP, Japan) with a precision better than 5 %. Reagent and procedural blanks were tested in parallel with the sample treatment, using identical procedures. Each calibration curve was evaluated by analysis of quality control standards before, during and after the analysis of every eight samples. In addition, the MapGis 6.7 software was used to produce the sampling location map (Fig. 1a) and the geology map (Fig. 1b), and the Grapher 9 software was used to produce the ternary diagram, scatter diagram and histogram (Figs. 2, 3, 4, 5, 6, 7).

4 453 Page 4 of 16 Environ Earth Sci (2016) 75:453 Fig. 2 Ternary diagrams showing the cationic and anionic variation of the rivers of the Nansihu Lake basin. The round represents up-mid-stream samples and the triangle represents downstream samples Fig. 3 a Plots of Cl - versus Na?, b HCO 3 - versus Ca 2?? Mg 2?, c Cl -? SO 4 2- versus Na?, and d SO 4 2-? HCO 3 - versus Ca 2?? Mg 2? for the rivers of the Nansihu Lake basin. The cross represents up-mid-stream samples and the triangle represents downstream samples

5 Environ Earth Sci (2016) 75:453 Page 5 of Fig. 4 Scatter diagram of (Ca 2?? Mg 2? )/HCO 3 - versus SO 4 2- / HCO 3 - for the rivers of the Nansihu Lake basin Results and discussion Major ions The chemical composition and physico-chemical parameters of the sampled water are reported in Table 1. The ph values of the river waters were slightly alkaline, in the range of The water temperatures varied from 17.3 to 23.6 C. As introduced above, the NLB is one sub-basin of the Huai River basin. Its TDS value ( mg/l) was higher than that of the whole Huai River basin (Zhang et al. 2011). The total cationic charge (TZ? ) and total anionic charge (TZ - ) varied from 5467 to 40,933 leq/l and from 5932 to 43,131 leq/l, respectively. This result was consistent with that of the previous study (Zhang et al. 2011) and indicated the enrichment of dissolved solids in the study region. Because the Nansihu Lake provided enough water for the convenience of the domestic, industrial and irrigational usage, massive human activities occurred in the downstream section around the lake. The cations and anions concentrations displayed a similarly spatial variability, with the higher concentration in the lower reaches and the lower concentration in upper reaches as shown in Table 1. Na? was the dominant cation, with concentrations in the range of ,642 lm/l. The concentrations of Ca 2? and Mg 2? were and lm/l, respectively. With the exception of the Hui River, the samples collected in the lower reaches exhibited a Na? contribution of % of TZ? and a (Ca 2?? Mg 2? ) contribution of % of TZ?. When concerning the upper and middle basin, Na? contributed to % of TZ?, and Ca 2? and Mg 2? collectively contributed to % of TZ?. K? only contributed to 1 3 % of the total cation charge. Among the anions, Cl - was the most abundant anion, in the range of lm/l with a mean of 4637 lm/l, followed by SO 4 2- and HCO 3 -, which were in the ranges of ,677 and lm/l with means of 3449 and 3264 lm/l, respectively. Moreover, Cl - accounted for % of TZ -, and SO 4 2- and HCO 3 - accounted for % and 6 50 %, respectively. To illustrate the major ion variations, cation and anion-silica ternary diagrams were employed. As shown in Fig. 2a, samples were spread widely in the ternary diagrams for cations, indicating the multiple solute sources. In the case of anions, the samples fell far away from the silica point (Fig. 2b), and there was no strong correlation between SiO 2 and other ions (Table S2 in SM). Both ternary plots implied that silicate weathering had little influence on major ions for the basin Fig. 5 Calculated contributions (in %) of the different sources to the cationic TDS (mg/l) for the rivers of the Nansihu Lake basin, and their average values

6 453 Page 6 of 16 Environ Earth Sci (2016) 75:453 as a whole. On the other hand, the high levels of (Cl -? SO 2-4 ) with the high correlation coefficient of 0.98 between (Cl -? SO 2-4 ) and TDS suggested that evaporites might contribute more than carbonates for solutes in rivers. As mentioned in Climate, hydrology and land cover, the samples were collected along each river, including the upper, middle and lower reaches. For the samples of the upper and middle reaches, the average ratio of Cl - /Na? (0.84) was close to 1, as shown in Fig. 3a. This result indicates that the two ions may mainly originate from the weathering of evaporites, where halite is responsible for the approximately equivalent charges of Na? and Cl -. On the other hand, the most downstream samples fell below the isometric line of Cl - /Na? (Fig. 3a), suggestive of an important source of Na?. The extra Na? could be interpreted as originating from the weathering of silicates or anthropogenic sources rather than weathering of chloride evaporites (Zhang et al. 2007b; Xu and Liu 2010). In the plot of (Ca 2?? Mg 2? ) versus HCO - 3 (Fig. 3b), all samples fell under the isometric line of HCO - 3 /(Ca 2?? - Mg 2? ), indicating that the cations of Ca 2? and Mg 2? originated not only from carbonate weathering but also from evaporite weathering in the study region. Comparison with Chinese and world rivers Fig. 6 a Evolution of the cationic carbonates as a function of the runoff in the Nansihu Lake basin with lower anthropogenic influence, and b with higher anthropogenic influence Compared with large rivers worldwide (Table 2), the average TDS concentration of the rivers of the NLB was more than 10-fold that of the global median (Meybeck and Helmer 1989) but was similar to that of the Tarim River basin, which is located in an extremely arid region with poor irrigation practices (Xiao et al. 2012). Although Li et al. (2011) reported that the river sediments and alluvial aquifers in the NLB were controlled by the Yellow River basin, the TDS of the NLB was approximately 1.5 times that of the Yellow River (Fan et al. 2014). The reasons might be the influence of intensive human activities on the water systems in the NLB (Wang and Ongley 2004; Cheng et al. 2005). Contributions of different reservoirs Fig. 7 The variations of the sum of the cations derived from silicate and carbonate weathering versus HCO 3 - To assess the contribution of rock weathering and the associated CO 2 consumption, it is necessary to first quantity the contributions of individual reservoirs to major ions at the level of the whole basin. The outline of the calculating process is shown in Fig. S1 (in SM), and all of the equations corresponding to the calculation are listed under Calculation methods in Appendix. The following is a detailed explanation and discussion of the results of the calculation.

7 Environ Earth Sci (2016) 75:453 Page 7 of Table 1 Chemical compositions of rivers in the Nansihu Lake basin rivers, China Sample number Rivers T ( C) ph EC (ls/ cm) K? Na? Ca 2? Mg 2? - HCO 3 Cl - 2- SO 4 - NO 3 F - SiO 2 TDS (mg/l) TZ? (leq) TZ - (leq) NICB (%) S01 Guangfu Lower , S02 Guangfu Upper S03 Si Lower , S04 Si Upper S05 Baima Lower , ,635 17, S06 Beijie Lower , ,704 16, S07 Beijie Upper ,009 10, S08 Beisha Lower , ,556 22, S09 Beisha Middle ,686 13, S10 Beisha Upper S11 Guo Lower ,555 20, S12 Guo Upper ,317 16, S13 Xinxue Lower ,845 14, S14 Xinxue Upper S15 Hanzhuang Lower ,611 15, S16 Dongyu Lower , ,418 17, S17 Hui Lower S18 Wanfu Lower , ,772 19, S19 Zhuzhaoxin Lower , , ,934 43, S20 Dayun Lower , ,695 18, Average of upper-middle reaches Average of lower reaches , ,462 18, Average ,592 15,

8 453 Page 8 of 16 Environ Earth Sci (2016) 75:453 Table 2 Major ion concentrations (mg/l) in the present study and with other rivers from the literature River Sample date Ca 2? Mg 2? Na? K? HCO 3 - Cl - SO 4 2- NO 3 - TDS References Nansihu Lake Jun This study tributaries Huai River basin Jul Zhang et al. (2011) Han River basin Li et al. (2008) Yangtze River Aug Chetelat et al. (2008) Yangtze River Hu et al. (1982) Yellow River Aug Fan et al. (2014) Yellow River Oct Hu et al. (1982) Pearl River Zhang et al. (2007b) Pearl River Chen and He. (1999) Tarim River basin Aug Xiao et al. (2012) Amazon Stallard and Edmond (1983) Orinoco Lewis and Saunders (1989) St. Lawrence Tremblay and Rivard (1985) Ganges Sarin et al. (1989) Seine Roy et al. (1999) Global median / Meybeck and Helmer (1989) Global median / Levinson (1974) Atmospheric inputs The NLB is located in the North China Plain, which is subject to substantial air pollution (Huo et al. 2010). Thus, the chemical compositions of the atmospheric inputs in this region were proposed to be associated with not only sea salt and continental dust but also anthropogenic dust, which was supported by the relatively high concentrations of SO 2-4 and NO - 3 in rainfall (Zhang et al. 2007a). Traditionally, chloride has been applied as an index to calculate atmospheric inputs to rivers because it was assumed to have originated entirely from the atmosphere in pristine areas where there were no salt rocks or hydrothermal inputs (Stallard and Edmond 1981; Liu et al. 2013). Unfortunately, such an assumption cannot be applied in our case because of the mixed evaporite and/or anthropogenic sources of Cl -, as discussed in Major ions and Comparison with Chinese and world rivers. Nevertheless, the composition of F can be used to evaluate the atmospheric contribution (Chetelat et al. 2008; Fan et al. 2014) by a simple method using ratios of ions in rain water. The measured concentrations of F in the NLB tributaries varied little, from 9.5 to 36.4 lm/l (Table 1), which was in the range of F concentration in rainwater ( lm/l) (Wang et al. 2006). Even at site S19, which had the highest TDS value, the F concentration (17.3 lm/l) was lower than the mean level of the basin (19.3 lm/l). This result illustrated that the anthropogenic inputs exerted less influence on the F concentration in the river waters (F riv ). Thus, it can be proposed that atmospheric deposition contributed all of F riv. Based on monitoring data from rainfall samples in the study region (Huo et al. 2010), the equivalent ratios of chemicals in rainwater are listed in Table S3 (in SM). Then, the contribution of major ion concentrations from the atmosphere to river waters can be obtained by Eq. 1) (in Appendix). According to this method, the atmospheric contributions to river waters were negligible for Na?,Mg 2? and Cl - ( , , % respectively), can be significant for K?, Ca 2? and Cl - (5 25, 4 13 and 3 32 % respectively) and can be predominant for NO - 3 (16 99 %). Anthropogenic inputs The NLB drains several cities, as well as coalfields with approximately 12.7 billion tons of explored coal. Many plants and mining factories in the downstream area generated large quantities of wastewater, which was discharged into the rivers. Moreover, the widespread agricultural activities, including fertilizer application and animal waste, caused additional contamination. In this case, the anthropogenic inputs tentatively contained the agricultural and industrial inputs. The industrial influences on major ions in the Yellow and Yangtze Rivers have been reported by Fan et al. (2014) and Chetelat et al. (2008), respectively. Their studies also

9 Environ Earth Sci (2016) 75:453 Page 9 of exhibited an increase in concentrations of Na?,SO 2-4 and Cl - from 1978 (Hu et al. 1982) to 2012 (Fan et al. 2014) and from 1978 (Hu et al. 1982) to 2006 (Chetelat et al. 2008), respectively (Table 2). The temporal variation trend was even more readily discernable in the Pearl River (Zhang et al. 2007b), where concentrations of Na? increased by 262 %, SO 2-4 by 70 % and Cl - by 108 % from 1984 to 2002 (Table 2). In the NLB, the industrial activities, such as the transfer of wastes and the pumping of deep saline waters to the surface in mining projects, were considered to be responsible for high concentrations of Na?,SO 2-4 and Cl - in surface waters (Palmer et al. 2010; Moquet et al. 2014). This was evidenced by the concentrations being significantly higher in the lower reaches (Table 1), as the lithology does not vary substantially from the upper section to the lower section. As shown in Fig. 3c, samples fell above as well as close to the 1:1 line, suggesting that industrial activities contributed Na? in proportion to (Cl -? SO 2-4 ) to some extent. In the NLB, a large quantity of Na 2 SO 4 was generated by recovering phenol from coal tar, producing chemical fibers, and dyeing textiles by dozens of factories located in the downstream area. Consequently, the industrial inputs of Na? and SO 2-4 to the downstream samples resulted in the apparent excess of Na? over Cl - (Fig. 3a) and (SO 2-4? HCO - 3 )over(ca 2?? Mg 2? )(Fig.3d), respectively. A similar evolution of these ions was also found in the Seine due to factory effluents (Roy et al. 1999). To assess the industrial end-member, water samples S02 and S01 in the Guangfu River were chosen. S02 was collected from the upstream mountain area, and S01 was collected from downstream where the river flows through the coalfield and industrial district. As shown in Table 1, there were almost no differences in the concentrations of HCO - 3, K?,Ca 2? and Mg 2? between S01 and S02, but the concentrations of Na?, Cl -, and SO 2-4 were substantially higher in S01. In this case, it can be assumed that the industrial emissions mainly contributed Na?, SO 2-4 and Cl -. Thus, the equivalent ratio of (Cl -? SO 2-4 )/Na? in the industrial end-member could be calculated to be 1.1 according to Eq. 2 (in Appendix). This value was lower than the range of reported previously (Meybeck 1998; Roy et al. 1999; Chetelat et al. 2008). In their study, Ca 2? was defined partially from industrial inputs accompanied by SO 2-4 and/or Cl - (Chetelat et al. 2008), which was excluded from our case as discussed above. As another possible reason, the contribution of (Cl -? SO 2-4 )fromgypsumand halite might be underestimated in previous studies. On the other hand, NO - 3 concentrations in the 20 water samples were at least eight times higher than 1.0 mg/l as the average values for rivers worldwide (Levinson 1974; Meybeck and Helmer 1989). In addition to atmospheric inputs, anthropogenic inputs, including agricultural fertilizers and industrial wastewaters, also contributed NO 3 - to river waters (Roy et al. 1999). The natural NO 3 - from rock weathering was negligible in the case. By the same calculating method as that for (Cl -? SO 4 2- )/Na?, the value for NO 3 - /Na? from industrial inputs was estimated to be 0.05, very close to the results for the Wujiang and Yangtze Rivers (Lang et al. 2006; Chetelat et al. 2008). At the same time, the average equivalent ratio of NO 3 - / Na? from anthropogenic inputs was calculated to be 0.15 with a maximum at 1.86 (Eqs. 11 and 14). In addition to industrial sources, the excess NO 3 - mainly originated from farming practices (Roy et al. 1999; Chetelat et al. 2008). Agricultural NO 3 - (NO 3 - agr ) can be calculated according to Eq. 3. Based on the agricultural end-member values combined by Roy et al. (1999), the concentrations of other ions from agricultural inputs can also be estimated, and they were found to be one to two orders of magnitude lower than those from industrial inputs. Thus, the anthropogenic inputs of Na?,SO 4 2- and Cl - are considered to be equal to their industrial inputs. As a result, the contribution of industrial inputs to TDS was about 13 %, significantly higher than 2 % from agricultural inputs. Evaporites In the Nansihu Lake area, the crystallized salt layers in the Quaternary fluvial sediments drain relatively large areas (Fig. 1b) and contribute Na?,Ca 2?,Mg 2?,Cl - and SO4 2- to surface waters. In addition, Tertiary evaporites (covering approximately 9 % of the whole basin) are readily weathered to release these ions (Meybeck 1987). Herein, the contribution of evaporites to surface waters includes the weathering of the evaporites and the dissolution of the remaining crystallized salt in sediments. As shown in Fig. 4, half of the samples plotted near the unity line of (Ca 2?? Mg 2? )/SO 4 2-, indicating that gypsum and kieserite dissolution significantly contributed Ca 2?,Mg 2? and SO 4 2- to riverine solutes. The dominant contribution of evaporites was also found in the Yellow River (Wu et al. 2005). Such a result was due to the analogous terrain structures and fluvial sediments in these two watersheds (Shao et al. 1989; Liu 1999). In contrast, some other drainage areas in North China were quite different due to their carbonate dominance, such as the Beiyuanhe River basin (Jiang et al. 2012) and Hongzehu Lake (Zhang et al. 2011). The proportion of area covered by evaporites in North China is 1 % (Mei and Li 1994), which is one-tenth of that in the NLB. Because of the highly variable evaporite compositions from halite to gypsum (kieserite), the evaporite endmember value from the literature cannot be applied in this case. Moreover, a geochemical survey of evaporite layers in the NLB is lacking. To achieve the end-member value,

10 453 Page 10 of 16 Environ Earth Sci (2016) 75:453 the equivalent ratio of SO 4 2- /Cl - was determined using the samples with the lowest TDS values (319 mg/l in S14 and 360 mg/l in S17), which represented the least anthropogenic influence on SO 4 2- and Cl -. The ratios of SO 4 2- / Cl - (by subtracting the atmospheric inputs) were 1.59 in S14 and 1.60 in S17, respectively. The two values were almost the same and were distributed in the range of evaporite end-members reported in the Yangtze River (Chetelat et al. 2008). In theory, the ratio of (Ca 2?? - Mg 2? )/SO 4 2- is 1 in gypsum (kieserite) and Na? /Cl - is 1 in halite. Therefore, the evaporite end-member value of (Ca 2?? Mg 2? )/Na? was equal to that of SO 4 2- /Cl - and was determined to be 1.60 by using sample S17. On the other hand, the ratio of Mg 2? /Ca 2? in waters was in the range of , with a mean at 0.75, which is clearly higher than the ratio in the carbonate end-member in the study region, as discussed below, illustrating the enrichment of magnesium evaporites in the NLB. This result was also supported by a stronger correlation between Mg 2? and SO 4 2- (0.58) than that between Ca 2? and SO 4 2- (0.40, Table S2). Carbonates Carbonate rocks are widely dispersed in the study region and are mainly covered by Cambrian Ordovician strata. Previous study of carbonate-dominated watersheds suggested that the limestone and dolomite end-members had Mg 2? /Ca 2? equivalent ratios of 0.1 and 1.1, respectively (Han and Liu 2004). Therefore, the ratio of Mg 2? /Ca 2? in the carbonate end-member should be determined by the mixture of limestone and dolomite. Li and Mei (1990) reported that the weight ratios of limestone to dolomite in the study region were 3.10 in Cambrian strata and 3.07 in Ordovician strata, respectively. According to these ratios, the equivalent ratio of Mg 2? /Ca 2? in Cambrian-Ordovician strata was calculated to be 0.25, which was applied as the carbonate end-member value in this case. Evidently, this value was close to the ratio of Mg 2? /Ca 2? at site S02, which is covered by carbonate. In areas of carbonate dominance, dissolution of CO 2 in water will contribute protons to chemical weathering. Because of the industrial and coal mining activities in the NLB, NCA was likely to be another source of protons. Unlike weathering by carbonic acid, no CO 2 is consumed in carbonate weathering by NCA. Silicates Commonly, the contributions of silicates are estimated on the basis of Na? concentrations in waters and the ratios of other ions to Na? in a silicate end-member (Galy and France-Lanord 1999; Wu et al. 2013). However, Na? may not be a suitable proxy in this case because of its anthropogenic sources, as discussed above. Herein, K? was proposed to be supplied entirely from silicate weathering in the NLB. In addition, it was also assumed that the cations were released to waters in the same ratio as their abundances in silicates. Based on the above two assumptions, K? was used as an index (Gupta et al. 2011) for calculating the cations in waters from silicate weathering according to Eqs. 4 7 (in Appendix). In the east of the NLB, the silicate rocks mainly consist of Precambrian granite gneiss, in which the average equivalent ratios of Ca 2? /K?,Mg 2? /K? and Na? /K? were reported to be 1.75, 1.10 and 2.30, respectively (Zhang 1991). These ratios were applied as the silicate end-member values in the east of the NLB. Although K? can also be released into the water by evaporites weathering or vegetation inputs, the uncertainty caused by the assumption that K? was all from silicates would be very limited because K? constituted only 2 % of the total cations in waters in the study. In contrast, silicate rocks seldom crop out in the west of the NLB. The silicate sediments of this area are mainly from the Yellow River basin (Li et al. 2011). Furthermore, the rivers draining the west of the NLB are connected to the Yellow River (Zhang et al. 2011). Thus, the silicate end-member values compiled for the Yellow River were used for the west of the NLB, where the Ca 2? /K?,Mg 2? /K? and Na? /K? equivalent ratios were 1.00, 0.62 and 1.90, respectively (Wu et al. 2005; Fan et al. 2014). These silicate end-member values are summarized in Table S4 in SM. The values of (Ca 2? /K? ) sil (Mg 2? /K? ) sil and (Na? / K? ) sil estimated for granite gneiss were all higher than those observed in the Yellow River. This was likely because the formation of smectite clay during gneiss weathering would limit the mobility of K? rather than Ca 2?,Mg 2? or Na? (Gupta et al. 2011). On the other hand, the value of (Ca 2? /Na? ) gg was lower compared with the silicate end-member composition of global rivers (Gaillardet et al. 1999). This was either because of the regional variability of cations in silicates or because of the significantly enhanced release of Ca 2? over Na? during gneiss weathering (Dalai et al. 2002). Meybeck (1986) reported (Na? /K? ) sil = 6 by studying rivers draining silicates. This value was close to that deduced by Millot et al. (2003), but was appreciably higher than that used in this case. For Mg 2? /K?, the ratio of 1.1 in granite gneiss was compatible with that deduced for silicate terrain by Galy and France- Lanord (1999) and discussed by Han and Liu (2004). Chemical budget and estimation of chemical weathering rate Stoichiometric analysis provides some qualitative information for tracing sources of major ions dissolved in river

11 Environ Earth Sci (2016) 75:453 Page 11 of waters. To quantify the relative contributions of atmosphere, anthropogenic inputs and rock weathering to the tributaries of the NLB, the mass balance equation was applied as Eq. 8. Based on the above discussion, the outline of the calculation process shown in Fig. S1 (in SM) should be understandable. The detailed calculations for each ion can be expressed as Eqs. 9 16), and the end-member values of individual reservoirs used in these calculations are also summarized (Tables S3 S4 in SM). Thus, the contributions of atmospheric deposition, anthropogenic inputs and weathering of three types of rocks (evaporite, carbonate and silicate) to the total cationic TDS in each tributary were individually calculated, and the results are shown in Fig. 5. In all 13 tributaries, the atmospheric contribution was in the range of 1 3 %. The anthropogenic contribution was %, which was much higher than the values for Yangtze and Xijiang (Chetelat et al. 2008; Xu and Liu 2010), indicating a significant anthropogenic influence on the cationic TDS in the NLB. The general trend was an increase from upstream (a mean of 20 %) to downstream (a mean of 46 %), with a maximum at the Zhuzhaoxin River (S19). Rock weathering dominated the dissolved loading, with contributions in the range of %, included 7 51 % from evaporites, 6 46 % from carbonates and 2 13 % from silicates. Because an uncertainty of ±50 % was assumed in calculating silicate contributions (Galy and France-Lanord 1999; Dalai et al. 2002; Moon et al. 2007), an uncertainty for carbonate was also prospected to be ±50 % in the case. This was because the average uncertainties for the carbonate end-member were calculated to be very close to those for silicate one in China and world-wide (Moon et al. 2007; Chetelat et al. 2008; Rai et al. 2010). Thus, the carbonate contribution and silicate contribution would account for and 5 16 % in the Guangfu River, 3 9 and 6 17 % in the Si River, 9 28 and 2 6 % in the Baima River, 5 16 and 4 13 % in the Guo River, 8 23 and 2 7 % in the Xinxue River, 7 21 and 3 8 % in the Dongyu River, 3 10 and 1 3 % in the Zhuzhaoxin River and and 2 5 % in the Dayun River, respectively. The contributions of rock weathering were similar to those of some stations in the upper Yellow River in a semi-arid environment (Wu et al. 2005). However, this result was different from those dominated by carbonates (Chetelat et al. 2008; Xu and Liu 2010) or by silicates (Pattanaik et al. 2013; Wu et al. 2013). Combining the runoff data (Xu and Liu 2010), the weathering rates (or cationic TDS) of evaporites, carbonates and silicates of the eight major tributaries can be estimated on the basis of their weathering contributions, and the results are shown in Table 3. The detailed calculation is expressed as Eqs Thus, the estimation for the entire area of the NLB was also available. In the case of CWR, it should be linearly correlated with runoff under natural conditions, which has been confirmed either at the global scale (Gaillardet et al. 1999) or at the regional scale (Eiriksdottir et al. 2011). Among the tributaries of the NLB, such a CWR-runoff relationship was also observed for the less polluted water samples (with anthropogenic contributions of less than 1/3 of the total) (Fig. 6a), three of which are covered by carbonate. However, the samples in the highly polluted environment (with anthropogenic contributions of more than 1/3) did not follow the CWR-runoff trend (Fig. 6b), even if half of them are covered by carbonate. In the Yangtze River basin, Table 3 Chemical weathering rates and CO 2 consumption for the Nansihu Lake basin and its main rivers River name Discharge (10 8 m 3 /a) Surface area (10 3 km 2 ) Silicate Carbonate Evaporites Total rocks weathering Cationic TDS (ton/km 2 /a) CO 2 (10 9 mol/a) Cationic TDS (ton/km 2 /a) CO 2 (10 9 mol/a) Cationic TDS (ton/km 2 /a) Cationic TDS (ton/km 2 /a) Guangfu a ± ± ± ± Si b ± ± ± ± Baima b ± ± ± ± Guo b ± ± ± ± Xinxue a ± ± ± ± Dongyu b ± ± ± ± Zhuzhaoxin b ± ± ± ± Dayun a ± ± ± ± Nansihu Lake basin b ± ± ± ± The discharge is the average values a The data of discharge and surface area from b The data of discharge and surface area from

12 453 Page 12 of 16 Environ Earth Sci (2016) 75:453 Chetelat et al. (2008) also found that the sample dominated by anthropogenic inputs was isolated in the plots of CWRrunoff. In other words, the CWR could be influenced by massive anthropogenic activities, especially the intensive industrialization in this case. As analyzed in Anthropogenic inputs, the value of (Cl -? SO 4 2- )/Na? was 1.1 in the industrial end-member. The excess (Cl -? SO 4 2- ) over Na? can be attributed to NCA (HCl/H 2 SO 4 ), which would participate to some degree in rock weathering, as discussed in Contribution of NCA to chemical weathering. Although the involvement of NCA could increase the weathering rates (Chetelat et al. 2008), the NLB only has approximately 1/5 of the runoff relative to the large Chinese rivers, resulted in a much lower CWR in the NLB (5.68 ± 2.84 ton/km 2 /a) compared with the Yangtze (17 56 ton/km 2 /a), Xijiang (29 38 ton/km 2 /a) and Wujiang (97 ton/km 2 /a) Rivers (Han and Liu 2004; Chetelat et al. 2008; Xu and Liu 2010). In contrast with CWR, silicate weathering rate (SWR) showed a strong relationship with runoff at the scale of the NLB (Fig. S2 in SM). The control of runoff on SWR was observed in both small rivers and large rivers world-wide (Gaillardet et al. 1999; Gurumurthy et al. 2012; Wu et al. 2013). The high runoff in Xishui, the Alps and Puerto Rico resulted in the high SWRs (Millot et al. 2002; West et al. 2005; Wu et al. 2013), which were several times higher than that in the NLB. In addition to runoff, the influence of temperature was also proposed (Millot et al. 2002). The SWRs in Siberia, Canada and Norway were relatively low, which were attributed to the cold climates (Millot et al. 2002; West et al. 2005). However, SWR was more variable and was influenced by multiple factors in the warm climates (Millot et al. 2002; West et al. 2005; Gurumurthy et al. 2012). For example, SWR was closely linked to river gradient in the NLB (Fig. S3 in SM). The higher rates were observed in the tributaries with higher slope gradients, such as the Guo River, where steeper slopes lead to higher physical erosion in the watershed. Together with the distribution of silicates as mentioned in Silicates, the rivers in the east of the NLB, which drain mountainous landforms, had SWRs varying from 1.81 ± 0.90 to ± 7.76 ton/km 2 /a, several times to one order of magnitude higher than those in the west of the NLB, which drain floodplains (Table 3). Subsequently, the CO 2 consumptions associated with the weathering of silicates and carbonates by carbonic acid were calculated on the basis of the cationic charge budget, and the detailed methods are listed as Eqs ) (in Appendix). On the other hand, the participation of NCA in rock weathering caused cation release to waters without consuming CO 2. Therefore, the estimated CO 2 consumption (Table 3) was the upper limit value without the contribution of NCA (Beaulieu et al. 2011). Contribution of NCA to chemical weathering Weathering of carbonates and silicates by H 2 CO 3 produces HCO - 3, and the equivalent charge of cations in solution resulting from carbonate and silicate weathering should be equal to that of HCO - 3. Nevertheless, the equivalent charges of cations (carb? sil) were higher than those for HCO - 3 in this case (Fig. 7). In addition (Ca 2?? Mg 2? )/ HCO - 3 was positively correlated with SO /HCO 3 (Fig. 4). Both of them suggested that NCA was involved in rock weathering. A similar occurrence was observed in South and Southwest China, where NCA was from acid rain (Han and Liu 2004; Xu and Liu 2007, 2010), but this is the first time that weathering by NCA has been noted in North China. The equivalent charges of protons provided by NCA can be calculated by (TZ þ carbþsil HCO 3 ), and they ranged from 206 (S02) to 2554 leq/l (S08), with a mean of 924 leq/l. In this case, NCA could be released by natural pyrite oxidation and/or it could be of industrial origin. Differentiating them helped to better understand the industrial influence on weathering (Li et al. 2008). Site S12 was collected from the upstream of the Guo River, which flows through the Tengbei Coalfield without factories nearby (the anthropogenic contribution was 11 % in S12). To separate industrial NCA from natural NCA (H 2 SO 4 ) produced by pyrite oxidation, one reasonable assumption was to use the NCA concentration at site S12 as the concentration of natural NCA in the NLB, although this value may be overestimated or underestimated in this case. Accordingly, the equivalent charge of natural NCA was determined to be 201 leq/l, which was close to that assumed in Southwest China (Li et al. 2008) and lower than that in the Yangtze River (Chetelat et al. 2008). Then, the industrial NCA could be calculated by (NCA - NCA S12 ) with a mean of 723 leq/l. This result clearly showed that NCA was mainly of industrial origin in the study region. The large scale industry in the study region emerged after 1970s, suggesting that the NCA might participate in the rock weathering on short timescales. NCA participating in carbonate and silicate weathering might reduce the consumption of CO 2 derived acid (H 2 CO 3 ) in weathering. This part of CO 2 which should have involved in the weathering as H 2 CO 3, was thought as the degassed CO 2. Thus, the equivalent charges of NCA in the NLB tributaries represented the amount of degassed CO 2.Using the runoff data, the fluxes of degassed CO 2 by NCA and industrial NCA could be calculated individually (Table S5 in SM). In detail, the degassing of CO 2 was mol/a for the Xinxue River and mol/a for the Zhuzhaoxin River. The flux of degassed CO 2 in the Guangfu River was the lowest, at mol/a. For the Nansihu Lake drainage basin, the fluxes of degassed CO 2 associated

13 Environ Earth Sci (2016) 75:453 Page 13 of with NCA and industrial NCA were and mol/a, respectively. The area of the whole basin is approximately km 2, and the annual rates of CO 2 degassing were approximately 3.80 and 2.98 ton/km 2, respectively. Moreover, of all protons involved in the weathering of silicate and carbonate rocks, the proportions of NCA ranged from 12 % (Dongyu River) to 72 % (Xinxue River) in the 13 tributaries (Table S5). The average was 34 % in the area of the NLB. The contribution of NCA to weathering of silicate and carbonate rocks was approximately three times higher than that in the Xijiang drainage basin (Xu and Liu 2010). The maximum value (72 %) in this case was also higher than that of the Wujiang River (55 %, Han and Liu 2004). Nevertheless, the action of NCA participating in rock weathering is not a direct source of CO 2. In term of CO 2 transfers, silicate weathering by NCA is neutral (neither a source nor a sink), while carbonate weathering by NCA is neutral over short term timescales and constitutes a net source of CO 2 at long timescales (taking into account the - oceanic C cycle). In other words, for 2 mol of HCO 3 released by carbonate weathering, 1 mol of calcite precipitate into the oceans and 1 mol of CO 2 is released to the atmosphere over long term timescales (Calmels et al. 2007; Beaulieu et al. 2011). By consequence, if carbonate weathering was associated with NCA, NCA would act as a net source of CO 2 only when it contributes to carbonate weathering over long term timescale ( ,000 years). If carbonate weathering was due to protons derived from CO 2, carbonate weathering would be neutral over long term timescales. Conclusions The sampling of waters in 13 tributaries in the NLB and the analysis of major ions allowed the identification and quantification of the contributions of the reservoirs. The dominant anions were Cl - and SO4 2-, but the distribution of cations was notably complex due to the dominance of evaporite weathering and the anthropogenic supply of Na? in the basin. Through detailed calculation, the contributions of different reservoirs were determined for each tributary, including atmospheric inputs ( %), anthropogenic inputs ( %) and weathering of rocks (31 97 %). The average contribution from weathering of rocks in the basin was approximately 61 %, including 28 % from evaporites, 25 % from carbonates and 8 % from silicates. Moreover, their weathering rates in the Nansihu Lake drainage area were estimated based on the runoff data. The annual contributions of cationic TDS to waters were 1.90 ± 0.95 ton/ km 2 from silicates, 5.68 ± 2.84 ton/km 2 from carbonates and 7.32 ton/km 2 from evaporites. Based on the weathering of silicates and carbonates, the consumption of CO 2 was approximately mol/a for the whole basin. The proton contribution of NCA involved in weathering of rocks was identified as being in the range % for the major tributaries and 34 % on average for the whole basin. In the area of the Nansihu Lake drainage basin, the flux of degassed CO 2 was mol/a, and the annual rate of CO 2 degassing was approximately 3.80 ton/km 2. Acknowledgments This research was financially supported by the National Nature Science Foundation of China ( ), the Fundamental Research Funds for the Central Universities ( ), the State Key Laboratory of BGEG (GBL2135, GBL201405) and the fund for advantage discipline of geochemistry in CUGB. It was also supported by the Shandong Provincial Department of Land and Resources with the project Assessment of ecological and geological environment influenced by Coal mining in the area of Nansihu-Lake (LUKANZI ). We thank the project members of the Shandong Provincial Institute of Land Surveying and Mapping for their help with the field work. Appendix: Calculation methods (Eqs. 1 21) Calculation methods Contributions of various reservoirs Atmospheric inputs X atm ¼ F atm ½X=F rain ð1þ Anthropogenic inputs Cl þ SO 2 h 4 =Na þ anth ¼ Cl þ SO 2 4 S01 ð2þ Cl þ SO 2 4 S02 i = Na þ S01 Naþ S02 NO 3 agr ¼ NO 3 riv NO 3 atm NO 3 ind Silicates Ksil þ ¼ Kþ riv Kþ atm Ca 2þ sil ¼ K þ sil Ca2þ =K þ Mg 2þ sil ¼ K þ sil Mg2þ =K þ gg gg ð3þ ð4þ ð5þ ð6þ Na þ sil ¼ Kþ sil ½ Naþ =K þ gg ð7þ Chemical budget and chemical weathering rate estimation X riv ¼ X atm þ X anth þ X eva þ X carb þ X sil ð8þ F riv ¼ F atm ð9þ K þ riv ¼ Kþ atm þ Kþ sil ð10þ NO 3 riv ¼ NO 3 atm þ NO 3 anth ð11þ Cl riv ¼ Cl atm þ Cl anth þ Cl eva ð12þ SO 2 4 riv ¼ SO2 4 atm þ SO2 4 anth þ SO2 4 eva þ SO2 4 pyr ð13þ