Environ Earth Sci (2016) 75:453 DOI 10.1007/s12665-016-5305-2

ORIGINAL ARTICLE

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

1 1,2 3 1 1 Jun Li • Guo-Li Yuan • Xian-Rui Deng • Xiu-Ming Jing • Tian-He Sun • 1 1 Xin-Xin Lang • Gen-Hou Wang

Received: 12 April 2015 / Accepted: 23 November 2015 / Published online: 10 March 2016 Ó Springer-Verlag Berlin Heidelberg 2016

Abstract To explore the chemical weathering processes 34 % was presumed to be originated from NCA, causing 9 and the anthropogenic disturbance of weathering, 20 water 2.74 9 10 mol/a of CO2 degassing. Moreover, industrial samples were collected from the tributaries in the Nansihu inputs could play a major role in the modification of the Lake basin, a growing industrial area. The major ions in chemicals in the water system, and they could even change river waters were analyzed to identify and quantify the the carbonate weathering rate in such an intensively contributions of the different reservoirs. Based on stoi- industrializing region. In North China, the chemical chiometric analyses and end-member determination, the weathering associated with NCA was found to be signifi- contributions of individual reservoirs were calculated for cant for the first time. each tributary. In the study region, the averaged contribu- tions of atmospheric inputs, anthropogenic inputs, evap- Keywords Water geochemistry Á Major ions Á Rock orite weathering, carbonate weathering and silicate weathering Á CO2 consumption Á Long term CO2 degassing 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 Introduction estimated to be 1.90 ± 0.95 ton/km2 from silicate weath- ering, 5.68 ± 2.84 ton/km2 from carbonate weathering. The major chemical compositions of river waters can

Furthermore, the associated consumption of CO2 was cal- reveal the natural weathering processes and anthropogenic culated to be approximately 7.50 9 109 mol/a. The activities on a basin-wide scale (Gibbs 1970; Stallard and industrial and mining activities were the main sources for Edmond 1983; Sarin et al. 1989; Brennan and Lowenstein anthropogenic inputs, and they produced non-CO2 acids 2002; Moquet et al. 2011). At the global scale, large rivers (NCA). Of all protons involved in chemical weathering, have been studied to estimate the weathering rates of dif-

ferent rock types and CO2 consumption (Gaillardet et al. 1999; Roy et al. 1999; Moon et al. 2007, 2014; Noh et al. Electronic supplementary material The online version of this 2009; Moquet et al. 2011; Pattanaik et al. 2013). However, article (doi:10.1007/s12665-016-5305-2) contains supplementary material, which is available to authorized users. the small-scale studies have been considered to be better for understanding specific weathering and anthropogenic & Guo-Li Yuan processes under certain conditions (Barnes and Raymond [email protected] 2009; Gurumurthy et al. 2012; Price et al. 2013; Wu et al. 2013). In China, most researchers have focused on the 1 School of the Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China River (Hu et al. 1982; Zhang et al. 1990; Chen et al. 2002; Li and Zhang 2005; Chetelat et al. 2008), the 2 State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Beijing 100083, (Hu et al. 1982; Zhang et al. 1990, 1995;Li China and Zhang 2005; Wu et al. 2005; Fan et al. 2014), and the 3 Shandong Provincial Institute of Land Surveying and (Chen and He 1999; Zhang 1999; Zhang et al. Mapping, Jinan 250013, China 2007b). The historical data of these three large rivers had 123 453 Page 2 of 16 Environ Earth Sci (2016) 75:453

shown the increases in major ion concentrations during the associated CO2 consumption; (3) to study the anthro- past 20-30 years, such as chloride increasing around two pogenic influence on CWR; and (4) to estimate the con- times. Since the wastewater discharged into the Yangtze tribution of NCA to rock weathering at a basin scale. 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 Materials and methods activities were possible responsible for the elevated con- centrations. Recently, some studies have focused on the Geography and geology major chemical composition of river water in the upper basin (Li et al. 2009) and the basin The Nansihu Lake basin (NLB) (34°240–36°190N, 114°520– (Zhang et al. 2011), because these two river basins are 117°420E), as one sub-basin of Huai River basin, is situated associated with China’s South to North Water Transfer in the North China Plain between the Yellow River and the Project (SNWTP). Huai River (the second- and third-largest rivers in China) Nansihu Lake is the largest freshwater lake in North (Fig. 1a). The total drainage area is 31,700 km2, covering China. The east line of the SNWTP will flow through this 32 counties with a population of 22 million in Jiangsu, lake, which serves not only as an important water trans- Shandong, and Provinces. portation channel for the SNWTP but also as a storage lake Geologically, the NLB consists of various source rocks for the SNWTP. It is therefore important to identify and (Fig. 1b). The major lithologies exposed in the study quantify the chemical compositions of river waters flowing region are Cambrian and Ordovician carbonate rocks into Nansihu Lake. On the other hand, the modification by (limestones and dolomites) and Jurassic detrital sedimen- anthropogenic inputs of the chemical compositions of tary rocks (siltstones and sandstones), which are widely waters should be paid more attention, as human activities distributed in the basin and cover 35 and 30 % of the basin are becoming increasingly extensive in the region. Zhang area, respectively. The Precambrian outcrops covering et al. (2011) has emphasized the anthropogenic influence in about 12 % of the area, are mainly granite gneiss which this region. Therefore, it is necessary to differentiate the occurs in the eastern hills and mountainous areas. Carbonic industrial and agricultural inputs for major ions at a and Permian coal deposits are interbedded in shale strata regional scale and then individually estimate the contri- and are separately distributed in the eastern and western butions of weathering of different parent rocks (e.g., car- sections with approximately 4 % of the area. The Tertiary bonates, evaporites and silicates) and the associated CO2 rocks covering 5 % of the whole area, are mainly detrital consumption. rocks (shale and sandstone) and evaporites. The Quaternary

In addition to carbonic acid, other acids (such as H2SO4 fluvial sediments occupying 14 % of the basin area, are and HCl) have recently been recognized as protons distributed over the whole plain. involved in rock weathering (Calmels et al. 2007; Xu and Liu 2007; Chetelat et al. 2008; Beaulieu et al. 2011; Lang Climate, hydrology and land cover et al. 2011). If these others acids contribute to chemical action, then carbonate weathering may lead to CO2 pro- This basin is subject to temperate monsoon climate, and the duction instead of CO2 sequestration (Li et al. 2008). annual mean temperatures is 12 °C in Jining City which Several studies of small and moderate water systems occupies the north section of the basin and 15 °Cin indicate the importance of non-CO2 acids (NCA) in Zaozhuang City for the south section. Average annual chemical weathering (Han and Liu 2004; Xu and Liu 2007; precipitation and evaporation vary from 685 and 900 mm Li et al. 2008; Meyer et al. 2009). In a heavily industrial- on the drier part to 900 and 1050 mm around the lake, and ized basin, the study of rock weathering by NCA helps us more than 80 % of annual precipitation falls during the to estimate the associated CO2 production and to observe flood season from May to September (Wu et al. 2010). In the influence of NCA on carbonate weathering rate (CWR). this basin, there are 13 tributaries encompassing a wide

Then, the balance between CO2 production and consump- range of lithologies and land uses (Table S1 in supple- tion could be well understood at a basin scale. mentary materials, abbreviated as SM), including the In this study, the major chemical compositions of 20 Guangfu, Si, Baima, Guo, Xinxue, Dongyu, Zhuzhaoxin, sites were determined for the rivers flowing into the Nan- Dayun, Beijie, Beisha, Hanzhuang, Hui and Wanfu Rivers, sihu Lake basin. The main goals are (1) to identify their with the former eight tributaries being the major ones. The sources and quantify the contributions of the various average annual discharge input to the lake is reservoirs to the dissolved load, especially the anthro- 29.60 9 108 m3 (Wu et al. 2010). In addition, Li et al. pogenic contributions including industrial and agricultural (2011) reported that there were no thermal sources in the inputs; (2) to calculate chemical weathering rates and the NLB, and the groundwater did not have significant 123 Environ Earth Sci (2016) 75:453 Page 3 of 16 453

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 first portion of the filtrate was discarded to clean the alluvial aquifer recharges the river water that is flowing membrane. The sampled waters were stored in pre-cleaned across the plain. HDPE bottles. Filtered solutions for cation analysis were - Cultivated land, used for growing wheat, corn and cot- acidified to pH \2 with ultra-purified 6 M HNO3 . ton, represents approximately 53 % of the NLB (Huang Cleaning of plastic bottles and plastic bags was performed - et al. 2012). Heavy forests are mostly distributed in the by soaking in 15 % (v/v) HNO3 for 24 h and then rinsing eastern mountainous areas, and vegetation covers approx- with Millipore water. imately 33 % of the surface area. The building area covers Water temperature, pH, electrical conductivity (EC) and 14 % of the basin, including more than 100 large manu- total dissolved solids (TDS) were measured in situ using a - facturing and mining companies. YSI 6920 (Ohio, USA) after calibration. The HCO3 was determined by titration with HCl on the sampling day. Sampling and analysis Major cations (Na?,K?,Ca2? and Mg2?) and Si were measured using inductively coupled plasma atomic emis- In the NLB, about 80 % of the runoff occurs in the flood sion spectrometry (ICP-AES) (IRIS Intrepid II XSP, USA) - - - season (Wu et al. 2010). The lower water flowing in winter with a precision better than 5 %. Anions (F ,Cl ,NO3 2? ? 2- may cause more Ca precipitation than Na (Li et al. and SO4 ) were measured by ion chromatography (IC) 2011). Thus, the waters in summer are considered more (Shimadzu HIC-SP, Japan) with a precision better than representative of the flowing conditions in the study region. 5 %. Reagent and procedural blanks were tested in parallel And the sampling was performed in the high-flow season with the sample treatment, using identical procedures. Each during June 2013. Water samples were collected from 20 calibration curve was evaluated by analysis of quality sites along the rivers flowing into Nansihu Lake (Fig. 1a). control standards before, during and after the analysis of Although each site was sampled only once, the sampling every eight samples. locations in 13 river estuaries provided a comprehensive In addition, the MapGis 6.7 software was used to pro- understanding of the water chemistry of the entire basin. At duce the sampling location map (Fig. 1a) and the geology each site, water samples from the surface, middle and map (Fig. 1b), and the Grapher 9 software was used to bottom of the river were mixed together and then filtered produce the ternary diagram, scatter diagram and histogram (0.45-lm Millipore nitrocellulose filter) in the field. The (Figs. 2, 3, 4, 5, 6, 7).

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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

- ? - 2? 2? - 2- ? 2- - 2? 2? Fig. 3 a Plots of Cl versus Na , b HCO3 versus Ca ? Mg , c Cl ? SO4 versus Na , and d SO4 ? HCO3 versus Ca ? Mg for the rivers of the Nansihu Lake basin. The cross represents up-mid-stream samples and the triangle represents downstream samples

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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 down- stream 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 1192–30,642 lM/L. The concentrations of Ca2? and Mg2? were 988–3804 and 374–2442 lM/L, respec- tively. With the exception of the , the samples collected in the lower reaches exhibited a Na? contribution of 49–75 % of TZ? and a (Ca2? ? Mg2?) contribution of 25–50 % of TZ?. When concerning the upper and middle 2? 2? - 2- Fig. 4 Scatter diagram of (Ca ? Mg )/HCO3 versus SO4 / basin, Na? contributed to 24–37 % of TZ?, and Ca2? and HCO - for the rivers of the Nansihu Lake basin 3 Mg2? collectively contributed to 62–74 % of TZ?.K? only contributed to 1–3 % of the total cation charge. Results and discussion Among the anions, Cl- was the most abundant anion, in the range of 919–8979 lM/L with a mean of 4637 lM/L, 2- - Major ions followed by SO4 and HCO3 , which were in the ranges of 760–15,677 and 1541–5949 lM/L with means of 3449 The chemical composition and physico-chemical parame- and 3264 lM/L, respectively. Moreover, Cl- accounted for - 2- - ters of the sampled water are reported in Table 1. The pH 18–45 % of TZ , and SO4 and HCO3 accounted for values of the river waters were slightly alkaline, in the 24–72 % and 6–50 %, respectively. To illustrate the major range of 7.2–8.8. The water temperatures varied from 17.3 ion variations, cation and anion-silica ternary diagrams to 23.6 °C. As introduced above, the NLB is one sub-basin were employed. As shown in Fig. 2a, samples were spread of the Huai River basin. Its TDS value (339–2787 mg/L) widely in the ternary diagrams for cations, indicating the was higher than that of the whole Huai River basin (Zhang multiple solute sources. In the case of anions, the samples et al. 2011). The total cationic charge (TZ?) and total fell far away from the silica point (Fig. 2b), and there was - anionic charge (TZ ) varied from 5467 to 40,933 leq/L no strong correlation between SiO2 and other ions and from 5932 to 43,131 leq/L, respectively. This result (Table S2 in SM). Both ternary plots implied that silicate was consistent with that of the previous study (Zhang et al. 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

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as a whole. On the other hand, the high levels of - 2- (Cl ? SO4 ) with the high correlation coefficient of 0.98 - 2- between (Cl ? SO4 ) and TDS suggested that evapor- ites 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 inter- preted 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 2? 2? - plot of (Ca ? Mg ) versus HCO3 (Fig. 3b), all sam- - 2? ples fell under the isometric line of HCO3 /(Ca ? - Mg2?), indicating that the cations of Ca2? and Mg2? 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, Compared with large rivers worldwide (Table 2), the and b with higher anthropogenic influence 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 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

To assess the contribution of rock weathering and the

associated CO2 consumption, it is necessary to first quan- tity the contributions of individual reservoirs to major ions at the level of the whole basin. The outline of the calcu- lating 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 Fig. 7 The variations of the sum of the cations derived from silicate detailed explanation and discussion of the results of the - and carbonate weathering versus HCO3 calculation.

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Table 1 Chemical compositions of rivers in the Nansihu Lake basin rivers, China ? ? 2? 2? - - 2- - - ? - Sample Rivers T pH EC K Na Ca Mg HCO3 Cl SO4 NO3 F SiO2 TDS TZ TZ NICB number (°C) (lS/ (lM) (lM) (lM) (lM) (lM) (lM) (lM) (lM) (lM) (lM) (mg/L) (leq) (leq) (%) cm)

S01 Guangfu Lower 22.1 7.52 953 216 6466 1638 480 3140 4758 1741 348 13.2 126 622 10,918 11742 -7.54 S02 Guangfu Upper 21.5 7.91 621 83 2567 1744 374 3253 2150 897 148 13.6 101 407 6886 7359 -6.87 S03 Si Lower 22.1 7.98 915 229 6128 1406 609 1541 4963 2111 348 13.8 95 652 10,387 11088 -6.75 S04 Si Upper 21.3 7.94 736 222 2423 1818 406 3371 1672 760 166 12.9 61 400 7093 6742 4.95 S05 Baima Lower 22.6 8.11 1460 142 10,129 2029 1153 3381 5941 4010 350 21.1 71 1058 16,635 17,713 -6.48 S06 Beijie Lower 23.6 7.94 1249 155 10,435 1955 1602 3659 5289 3831 263 18.9 234 1041 17,704 16,892 4.58 S07 Beijie Upper 21.3 8.17 509 134 3313 1807 1474 4323 2596 1657 143 15.5 65 572 10,009 10,391 -3.82 S08 Beisha Lower 21.8 7.82 1661 189 12,837 3804 961 5949 5096 5508 516 36.4 50 1434 22,556 22,614 -0.26 S09 Beisha Middle 22.8 8.26 966 175 4969 3181 1090 4216 4311 2533 237 29.2 57 808 13,686 13,859 -1.27 S10 Beisha Upper 21.3 7.22 613 128 2153 1310 1239 2375 1920 1055 387 15.6 354 454 7379 6808 7.74 S11 Guo Lower 22.9 7.29 1495 321 9524 3530 1325 3488 6533 5044 658 22.6 233 1268 19,555 20,790 -6.31 S12 Guo Upper 23.1 8.34 1120 296 4803 3199 1410 3595 5265 3292 894 25.3 110 961 14,317 16,363 -14.29 S13 Xinxue Lower 23.1 8.82 1026 155 8944 1057 1816 1919 5676 3482 198 21.8 185 908 14,845 14,778 0.45 S14 Xinxue Upper 20.9 7.54 425 109 1286 1396 640 2332 919 954 656 12.9 91 319 5467 5828 -6.60 S15 Hanzhuang Lower 21.9 8.11 1024 216 7205 1480 2115 2996 5072 3461 340 18.9 76 893 14,611 15,349 -5.05 S16 Dongyu Lower 21.5 8.15 1196 185 10,067 988 2095 3124 6627 3807 299 18.1 113 1032 16,418 17,682 -7.70 S17 Hui Lower 22.2 7.70 498 83 1192 1632 716 2418 1035 995 150 9.5 459 360 5971 5602 6.18 S18 Wanfu Lower 20.9 8.12 1329 171 10,173 1772 2442 4130 7105 4150 305 21.0 30 1160 18,772 19,861 -5.80 S19 Zhuzhaoxin Lower 23.5 8.06 1871 214 30,642 2738 2301 2568 8979 15,677 548 17.3 78 2787 40,934 43,471 -6.20 S20 Dayun Lower 21.8 8.13 1249 143 10,106 2019 1704 3510 6830 4021 495 27.4 56 1108 17,695 18,905 -6.84 Average of upper-middle reaches 21.7 7.91 713 164 3073 2065 948 3352 2690 1593 376 17.9 120 560 9263 9622 -3.88 Average of lower reaches 22.3 7.98 1225 186 10,296 2004 1486 3217 5685 4449 371 20.0 139 1102 17,462 18,191 -4.17 Average 22.1 7.96 1046 178 7768 2050 1298 3264 4637 3449 372 19.3 132 912 14,592 15,192 -4.11 ae7o 16 of 7 Page 123 453 453 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

2? 2? ? ? - - 2- - River Sample date Ca Mg Na K HCO3 Cl SO4 NO3 TDS References

Nansihu Lake Jun. 2013 82.0 31.1 178.6 6.9 199.1 164.6 331.3 23.1 912.0 This study tributaries Huai River basin Jul. 2010 45.0 21.5 87.3 6.7 142.6 81.4 106.9 9.5 508.6 Zhang et al. (2011) Han River basin 2004–2006 38.3 8.2 3.3 1.3 147.6 6.2 32.3 5.8 248.0 Li et al. (2008) Yangtze River Aug. 2006 34.6 7.9 10.5 2.2 112.5 10.6 29.2 3.9 219.7 Chetelat et al. (2008) Yangtze River 1978–1980 40.0 7.4 5.4 1.4 141.9 5.4 20.6 Hu et al. (1982) Yellow River Aug. 2012 50.8 27.9 64.2 2.9 221.4 74.1 98.9 8.0 578.8 Fan et al. (2014) Yellow River Oct. 1978 50.0 21.7 48.8 2.4 225.7 40.3 73.0 Hu et al. (1982) Pearl River 2002 32.6 6.7 7.6 0.1 128.0 2.5 13.1 188.8 Zhang et al. (2007b) Pearl River 1984 38.4 4.5 2.1 0.1 132.0 1.2 7.7 192.0 Chen and He. (1999) Tarim River basin Aug. 2009 53.6 30.5 176.5 15.2 127.9 267.3 317.5 1019.8 Xiao et al. (2012) Amazon 1976–1977 12.0 1.7 3.9 1.2 43.9 3.9 4.0 0.6 80.3 Stallard and Edmond (1983) Orinoco 1982–1985 2.6 0.7 1.5 0.7 10.0 0.9 2.3 0.4 34.2 Lewis and Saunders (1989) St. Lawrence 1981–1983 28.9 6.8 10.4 1.6 84.2 20.9 20 175.1 Tremblay and Rivard (1985) Ganges 1982–1983 25.3 7.0 10.1 2.7 126.9 5.0 7.2 192.6 Sarin et al. (1989) Seine 1994–1997 86.7 2.5 5.6 2.1 230.5 14.4 20.4 22.7 384.6 Roy et al. (1999) Global median / 8.0 2.4 4.7 0.1 30.5 3.9 4.9 1.0 65.0 Meybeck and Helmer (1989) Global median / 15.0 4.1 6.3 2.3 58.4 7.8 11.2 1.0 120.0 Levinson (1974)

Atmospheric inputs inputs exerted less influence on the FÀ concentration in the À river waters (Friv). Thus, it can be proposed that atmo- À The NLB is located in the North China Plain, which is spheric deposition contributed all of Friv. Based on moni- subject to substantial air pollution (Huo et al. 2010). Thus, toring data from rainfall samples in the study region (Huo the chemical compositions of the atmospheric inputs in this et al. 2010), the equivalent ratios of chemicals in rainwater region were proposed to be associated with not only sea are listed in Table S3 (in SM). Then, the contribution of salt and continental dust but also anthropogenic dust, which major ion concentrations from the atmosphere to river was supported by the relatively high concentrations of waters can be obtained by Eq. 1) (in Appendix). 2- - SO4 and NO3 in rainfall (Zhang et al. 2007a). According to this method, the atmospheric contributions Traditionally, chloride has been applied as an index to to river waters were negligible for Na?,Mg2? and Cl- calculate atmospheric inputs to rivers because it was (0.1–0.6, 0.3–1.4, 0.4–2.2 % respectively), can be signifi- assumed to have originated entirely from the atmosphere in cant for K?,Ca2? and Cl- (5–25, 4–13 and 3–32 % - pristine areas where there were no salt rocks or respectively) and can be predominant for NO3 (16–99 %). hydrothermal inputs (Stallard and Edmond 1981; Liu et al. 2013). Unfortunately, such an assumption cannot be Anthropogenic inputs applied in our case because of the mixed evaporite and/or anthropogenic sources of Cl-, as discussed in ‘‘Major The NLB drains several cities, as well as coalfields with ions’’ and ‘‘Comparison with Chinese and world rivers’’. approximately 12.7 billion tons of explored coal. Many Nevertheless, the composition of FÀ can be used to eval- plants and mining factories in the downstream area gen- uate the atmospheric contribution (Chetelat et al. 2008; Fan erated large quantities of wastewater, which was dis- et al. 2014) by a simple method using ratios of ions in rain charged into the rivers. Moreover, the widespread water. The measured concentrations of FÀ in the NLB agricultural activities, including fertilizer application and tributaries varied little, from 9.5 to 36.4 lM/L (Table 1), animal waste, caused additional contamination. In this which was in the range of FÀ concentration in rainwater case, the anthropogenic inputs tentatively contained the (0.9–37.9 lM/L) (Wang et al. 2006). Even at site S19, agricultural and industrial inputs. which had the highest TDS value, the FÀ concentration The industrial influences on major ions in the Yellow (17.3 lM/L) was lower than the mean level of the basin and Yangtze Rivers have been reported by Fan et al. (2014) (19.3 lM/L). This result illustrated that the anthropogenic and Chetelat et al. (2008), respectively. Their studies also

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? 2- exhibited an increase in concentrations of Na ,SO4 and fertilizers and industrial wastewaters, also contributed - - - Cl from 1978 (Hu et al. 1982) to 2012 (Fan et al. 2014) NO3 to river waters (Roy et al. 1999). The natural NO3 and from 1978 (Hu et al. 1982) to 2006 (Chetelat et al. from rock weathering was negligible in the case. By the - 2- ? 2008), respectively (Table 2). The temporal variation trend same calculating method as that for (Cl ? SO4 )/Na , - ? was even more readily discernable in the Pearl River the value for NO3 /Na from industrial inputs was esti- (Zhang et al. 2007b), where concentrations of Na? mated to be 0.05, very close to the results for the Wujiang 2- - increased by 262 %, SO4 by 70 % and Cl by 108 % and Yangtze Rivers (Lang et al. 2006; Chetelat et al. 2008). - from 1984 to 2002 (Table 2). In the NLB, the industrial At the same time, the average equivalent ratio of NO3 / activities, such as the transfer of wastes and the pumping of Na? from anthropogenic inputs was calculated to be 0.15 deep saline waters to the surface in mining projects, were with a maximum at 1.86 (Eqs. 11 and 14). In addition to - considered to be responsible for high concentrations of industrial sources, the excess NO3 mainly originated from ? 2- - Na ,SO4 and Cl in surface waters (Palmer et al. 2010; farming practices (Roy et al. 1999; Chetelat et al. 2008). - - Moquet et al. 2014). This was evidenced by the concen- Agricultural NO3 (NO3 agr) can be calculated according trations being significantly higher in the lower reaches to Eq. 3. Based on the agricultural end-member values (Table 1), as the lithology does not vary substantially from combined by Roy et al. (1999), the concentrations of other the upper section to the lower section. ions from agricultural inputs can also be estimated, and As shown in Fig. 3c, samples fell above as well as close they were found to be one to two orders of magnitude to the 1:1 line, suggesting that industrial activities con- lower than those from industrial inputs. Thus, the anthro- ? - 2- ? 2- - tributed Na in proportion to (Cl ? SO4 )tosome pogenic inputs of Na ,SO4 and Cl are considered to be extent. In the NLB, a large quantity of Na2SO4 was gener- equal to their industrial inputs. As a result, the contribution ated by recovering phenol from coal tar, producing chemical of industrial inputs to TDS was about 13 %, significantly fibers, and dyeing textiles by dozens of factories located in higher than 2 % from agricultural inputs. the downstream area. Consequently, the industrial inputs of ? 2- Na and SO4 to the downstream samples resulted in the Evaporites apparent excess of Na? over Cl- (Fig. 3a) and 2- - 2? 2? (SO4 ? HCO3 )over(Ca ? Mg )(Fig.3d), respec- In the Nansihu Lake area, the crystallized salt layers in the tively. A similar evolution of these ions was also found in Quaternary fluvial sediments drain relatively large areas the Seine due to factory effluents (Roy et al. 1999). (Fig. 1b) and contribute Na?,Ca2?,Mg2?,Cl- and SO42- To assess the industrial end-member, water samples S02 to surface waters. In addition, Tertiary evaporites (covering and S01 in the Guangfu River were chosen. S02 was col- approximately 9 % of the whole basin) are readily weath- lected from the upstream mountain area, and S01 was col- ered to release these ions (Meybeck 1987). Herein, the lected from downstream where the river flows through the contribution of evaporites to surface waters includes the coalfield and industrial district. As shown in Table 1,there weathering of the evaporites and the dissolution of the - were almost no differences in the concentrations of HCO3 , remaining crystallized salt in sediments. K?,Ca2? and Mg2? between S01 and S02, but the con- As shown in Fig. 4, half of the samples plotted near the ? - 2- 2? 2? 2- centrations of Na ,Cl,andSO4 were substantially unity line of (Ca ? Mg )/SO4 , indicating that gyp- higher in S01. In this case, it can be assumed that the sum and kieserite dissolution significantly contributed ? 2- 2? 2? 2- industrial emissions mainly contributed Na ,SO4 and Ca ,Mg and SO4 to riverine solutes. The dominant - - 2- ? Cl . Thus, the equivalent ratio of (Cl ? SO4 )/Na in the contribution of evaporites was also found in the Yellow industrial end-member could be calculated to be 1.1 River (Wu et al. 2005). Such a result was due to the according to Eq. 2 (in Appendix). This value was lower than analogous terrain structures and fluvial sediments in these the range of 1.2–1.5 reported previously (Meybeck 1998; two watersheds (Shao et al. 1989; Liu 1999). In contrast, Roy et al. 1999; Chetelat et al. 2008). In their study, Ca2? some other drainage areas in North China were quite dif- was defined partially from industrial inputs accompanied by ferent due to their carbonate dominance, such as the 2- - SO4 and/or Cl (Chetelat et al. 2008), which was exclu- Beiyuanhe River basin (Jiang et al. 2012) and Hongzehu ded from our case as discussed above. As another possible Lake (Zhang et al. 2011). The proportion of area covered - 2- reason, the contribution of (Cl ? SO4 )fromgypsumand by evaporites in North China is 1 % (Mei and Li 1994), halite might be underestimated in previous studies. which is one-tenth of that in the NLB. - On the other hand, NO3 concentrations in the 20 water Because of the highly variable evaporite compositions samples were at least eight times higher than 1.0 mg/L as from halite to gypsum (kieserite), the evaporite end- the average values for rivers worldwide (Levinson 1974; member value from the literature cannot be applied in this Meybeck and Helmer 1989). In addition to atmospheric case. Moreover, a geochemical survey of evaporite layers inputs, anthropogenic inputs, including agricultural in the NLB is lacking. To achieve the end-member value, 123 453 Page 10 of 16 Environ Earth Sci (2016) 75:453

2- - the equivalent ratio of SO4 /Cl was determined using the not be a suitable proxy in this case because of its anthro- samples with the lowest TDS values (319 mg/L in S14 and pogenic sources, as discussed above. Herein, K? was 360 mg/L in S17), which represented the least anthro- proposed to be supplied entirely from silicate weathering in 2- - 2- pogenic influence on SO4 and Cl . The ratios of SO4 / the NLB. In addition, it was also assumed that the cations Cl- (by subtracting the atmospheric inputs) were 1.59 in were released to waters in the same ratio as their abun- S14 and 1.60 in S17, respectively. The two values were dances in silicates. Based on the above two assumptions, almost the same and were distributed in the range of K? was used as an index (Gupta et al. 2011) for calculating evaporite end-members reported in the Yangtze River the cations in waters from silicate weathering according to (Chetelat et al. 2008). In theory, the ratio of (Ca2? ? - Eqs. 4–7 (in Appendix). In the east of the NLB, the silicate 2? 2- ? - Mg )/SO4 is 1 in gypsum (kieserite) and Na /Cl is 1 rocks mainly consist of Precambrian granite gneiss, in in halite. Therefore, the evaporite end-member value of which the average equivalent ratios of Ca2?/K?,Mg2?/K? 2? 2? ? 2- - ? ? (Ca ? Mg )/Na was equal to that of SO4 /Cl and and Na /K were reported to be 1.75, 1.10 and 2.30, was determined to be 1.60 by using sample S17. On the respectively (Zhang 1991). These ratios were applied as the other hand, the ratio of Mg2?/Ca2? in waters was in the silicate end-member values in the east of the NLB. range of 0.21–2.12, with a mean at 0.75, which is clearly Although K? can also be released into the water by higher than the ratio in the carbonate end-member in the evaporites weathering or vegetation inputs, the uncertainty study region, as discussed below, illustrating the enrich- caused by the assumption that K? was all from silicates ment of magnesium evaporites in the NLB. This result was would be very limited because K? constituted only 2 % of also supported by a stronger correlation between Mg2? and the total cations in waters in the study. In contrast, silicate 2- 2? 2- SO4 (0.58) than that between Ca and SO4 (0.40, rocks seldom crop out in the west of the NLB. The silicate Table S2). sediments of this area are mainly from the Yellow River basin (Li et al. 2011). Furthermore, the rivers draining the Carbonates west of the NLB are connected to the Yellow River (Zhang et al. 2011). Thus, the silicate end-member values com- Carbonate rocks are widely dispersed in the study region piled for the Yellow River were used for the west of the and are mainly covered by Cambrian–Ordovician strata. NLB, where the Ca2?/K?,Mg2?/K? and Na?/K? equiv- Previous study of carbonate-dominated watersheds sug- alent ratios were 1.00, 0.62 and 1.90, respectively (Wu gested that the limestone and dolomite end-members had et al. 2005; Fan et al. 2014). These silicate end-member Mg2?/Ca2? equivalent ratios of 0.1 and 1.1, respectively values are summarized in Table S4 in SM. 2? 2? 2? ? 2? ? ? (Han and Liu 2004). Therefore, the ratio of Mg /Ca in The values of (Ca /K )sil (Mg /K )sil and (Na / ? the carbonate end-member should be determined by the K )sil estimated for granite gneiss were all higher than mixture of limestone and dolomite. Li and Mei (1990) those observed in the Yellow River. This was likely reported that the weight ratios of limestone to dolomite in because the formation of smectite clay during gneiss the study region were 3.10 in Cambrian strata and 3.07 in weathering would limit the mobility of K? rather than Ordovician strata, respectively. According to these ratios, Ca2?,Mg2? or Na? (Gupta et al. 2011). On the other hand, 2? 2? 2? ? the equivalent ratio of Mg /Ca in Cambrian-Ordovician the value of (Ca /Na )gg was lower compared with the strata was calculated to be 0.25, which was applied as the silicate end-member composition of global rivers (Gail- carbonate end-member value in this case. Evidently, this lardet et al. 1999). This was either because of the regional value was close to the ratio of Mg2?/Ca2? at site S02, variability of cations in silicates or because of the signifi- which is covered by carbonate. cantly enhanced release of Ca2? over Na? during gneiss

In areas of carbonate dominance, dissolution of CO2 in weathering (Dalai et al. 2002). Meybeck (1986) reported ? ? water will contribute protons to chemical weathering. (Na /K )sil = 6 by studying rivers draining silicates. This Because of the industrial and coal mining activities in the value was close to that deduced by Millot et al. (2003), but NLB, NCA was likely to be another source of protons. was appreciably higher than that used in this case. For 2? ? Unlike weathering by carbonic acid, no CO2 is consumed Mg /K , the ratio of 1.1 in granite gneiss was compatible in carbonate weathering by NCA. with that deduced for silicate terrain by Galy and France- Lanord (1999) and discussed by Han and Liu (2004). Silicates Chemical budget and estimation of chemical Commonly, the contributions of silicates are estimated on weathering rate the basis of Na? concentrations in waters and the ratios of other ions to Na? in a silicate end-member (Galy and Stoichiometric analysis provides some qualitative infor- France-Lanord 1999; Wu et al. 2013). However, Na? may mation for tracing sources of major ions dissolved in river 123 Environ Earth Sci (2016) 75:453 Page 11 of 16 453 waters. To quantify the relative contributions of atmo- 2007; Chetelat et al. 2008; Rai et al. 2010). Thus, the sphere, anthropogenic inputs and rock weathering to the carbonate contribution and silicate contribution would tributaries of the NLB, the mass balance equation was account for 10–30 and 5–16 % in the Guangfu River, 3–9 applied as Eq. 8. Based on the above discussion, the outline and 6–17 % in the , 9–28 and 2–6 % in the Baima of the calculation process shown in Fig. S1 (in SM) should River, 5–16 and 4–13 % in the , 8–23 and 2–7 % be understandable. The detailed calculations for each ion in the Xinxue River, 7–21 and 3–8 % in the Dongyu River, can be expressed as Eqs. 9–16), and the end-member val- 3–10 and 1–3 % in the Zhuzhaoxin River and 10–29 and ues of individual reservoirs used in these calculations are 2–5 % in the Dayun River, respectively. The contributions also summarized (Tables S3–S4 in SM). of rock weathering were similar to those of some stations in Thus, the contributions of atmospheric deposition, the upper Yellow River in a semi-arid environment (Wu anthropogenic inputs and weathering of three types of et al. 2005). However, this result was different from those rocks (evaporite, carbonate and silicate) to the total catio- dominated by carbonates (Chetelat et al. 2008; Xu and Liu nic TDS in each tributary were individually calculated, and 2010) or by silicates (Pattanaik et al. 2013; Wu et al. 2013). the results are shown in Fig. 5. In all 13 tributaries, the Combining the runoff data (Xu and Liu 2010), the atmospheric contribution was in the range of 1–3 %. The weathering rates (or cationic TDS) of evaporites, carbon- anthropogenic contribution was 0.1–68 %, which was ates and silicates of the eight major tributaries can be much higher than the values for Yangtze and Xijiang estimated on the basis of their weathering contributions, (Chetelat et al. 2008; Xu and Liu 2010), indicating a sig- and the results are shown in Table 3. The detailed calcu- nificant anthropogenic influence on the cationic TDS in the lation is expressed as Eqs. 17–19. Thus, the estimation for NLB. The general trend was an increase from upstream (a the entire area of the NLB was also available. mean of 20 %) to downstream (a mean of 46 %), with a In the case of CWR, it should be linearly correlated with maximum at the Zhuzhaoxin River (S19). Rock weathering runoff under natural conditions, which has been confirmed dominated the dissolved loading, with contributions in the either at the global scale (Gaillardet et al. 1999) or at the range of 31–97 %, included 7–51 % from evaporites, regional scale (Eiriksdottir et al. 2011). Among the tribu- 6–46 % from carbonates and 2–13 % from silicates. taries of the NLB, such a CWR-runoff relationship was Because an uncertainty of ±50 % was assumed in calcu- also observed for the less polluted water samples (with lating silicate contributions (Galy and France-Lanord 1999; anthropogenic contributions of less than 1/3 of the total) Dalai et al. 2002; Moon et al. 2007), an uncertainty for (Fig. 6a), three of which are covered by carbonate. How- carbonate was also prospected to be ±50 % in the case. ever, the samples in the highly polluted environment (with This was because the average uncertainties for the car- anthropogenic contributions of more than 1/3) did not bonate end-member were calculated to be very close to follow the CWR-runoff trend (Fig. 6b), even if half of those for silicate one in China and world-wide (Moon et al. them are covered by carbonate. In the Yangtze River basin,

Table 3 Chemical weathering rates and CO2 consumption for the Nansihu Lake basin and its main rivers River name Discharge Surface area Silicate Carbonate Evaporites Total rocks (108 m3/a) (103 km2) weathering Cationic TDS CO2 Cationic TDS CO2 Cationic TDS Cationic TDS (ton/km2/a) (109mol/a) (ton/km2/a) (109mol/a) (ton/km2/a) (ton/km2/a)

Guangfua 0.90 1.37 1.82 ± 0.91 0.11 ± 0.05 2.79 ± 1.39 0.10 ± 0.05 2.57 7.18 Sib 5.73 2.38 6.83 ± 3.42 0.71 ± 0.36 3.03 ± 1.52 0.19 ± 0.10 19.82 29.68 Baimab 1.48 0.91 2.59 ± 1.29 0.10 ± 0.05 9.92 ± 4.96 0.24 ± 0.12 11.77 24.28 Guob 3.60 0.94 15.51 ± 7.75 0.64 ± 0.32 15.37 ± 7.69 0.39 ± 0.20 78.68 109.56 Xinxuea 4.59 1.44 5.62 ± 2.81 0.35 ± 0.18 15.64 ± 7.82 0.61 ± 0.31 17.15 38.41 Dongyub 4.26 5.92 1.28 ± 0.64 0.31 ± 0.16 3.53 ± 1.77 0.57 ± 0.28 5.70 10.51 Zhuzhaoxinb 2.78 4.20 1.39 ± 0.70 0.24 ± 0.12 3.36 ± 1.68 0.38 ± 0.19 13.36 18.11 Dayuna 1.61 3.36 0.56 ± 0.28 0.08 ± 0.04 3.34 ± 1.67 0.30 ± 0.15 4.16 8.06 Nansihu 29.60 31.71 1.90 ± 0.95 2.61 ± 1.31 5.68 ± 2.84 4.89 ± 2.45 7.32 14.90 Lake basinb The discharge is the average values a The data of discharge and surface area from http://www.infobase.gov.cn/ b The data of discharge and surface area from http://www.sdein.gov.cn/

123 453 Page 12 of 16 Environ Earth Sci (2016) 75:453

Chetelat et al. (2008) also found that the sample dominated Contribution of NCA to chemical weathering by anthropogenic inputs was isolated in the plots of CWR- runoff. In other words, the CWR could be influenced by Weathering of carbonates and silicates by H2CO3 produces - massive anthropogenic activities, especially the intensive HCO3 , and the equivalent charge of cations in solution industrialization in this case. As analyzed in ‘‘Anthro- resulting from carbonate and silicate weathering should be - 2- ? - pogenic inputs’’, the value of (Cl ? SO4 )/Na was 1.1 equal to that of HCO3 . Nevertheless, the equivalent - 2- in the industrial end-member. The excess (Cl ? SO4 ) charges of cations (carb ? sil) were higher than those for ? - 2? 2? over Na can be attributed to NCA (HCl/H2SO4), which HCO3 in this case (Fig. 7). In addition (Ca ? Mg )/ - 2- - would participate to some degree in rock weathering, as HCO3 was positively correlated with SO4 /HCO3 discussed in ‘‘Contribution of NCA to chemical weather- (Fig. 4). Both of them suggested that NCA was involved in ing’’. Although the involvement of NCA could increase the rock weathering. A similar occurrence was observed in weathering rates (Chetelat et al. 2008), the NLB only has South and Southwest China, where NCA was from acid approximately 1/5 of the runoff relative to the large Chi- rain (Han and Liu 2004; Xu and Liu 2007, 2010), but this is nese rivers, resulted in a much lower CWR in the NLB the first time that weathering by NCA has been noted in (5.68 ± 2.84 ton/km2/a) compared with the Yangtze North China. The equivalent charges of protons provided 2 2 þ À (17–56 ton/km /a), Xijiang (29–38 ton/km /a) and by NCA can be calculated by (TZcarbþsil À HCO3 ), and Wujiang (97 ton/km2/a) Rivers (Han and Liu 2004; they ranged from 206 (S02) to 2554 leq/L (S08), with a Chetelat et al. 2008; Xu and Liu 2010). mean of 924 leq/L. In this case, NCA could be released by In contrast with CWR, silicate weathering rate (SWR) natural pyrite oxidation and/or it could be of industrial showed a strong relationship with runoff at the scale of the origin. Differentiating them helped to better understand the NLB (Fig. S2 in SM). The control of runoff on SWR was industrial influence on weathering (Li et al. 2008). Site S12 observed in both small rivers and large rivers world-wide was collected from the upstream of the Guo River, which (Gaillardet et al. 1999; Gurumurthy et al. 2012; Wu et al. flows through the Tengbei Coalfield without factories 2013). The high runoff in Xishui, the Alps and Puerto Rico nearby (the anthropogenic contribution was 11 % in S12). resulted in the high SWRs (Millot et al. 2002; West et al. To separate industrial NCA from natural NCA (H2SO4) 2005; Wu et al. 2013), which were several times higher than produced by pyrite oxidation, one reasonable assumption that in the NLB. In addition to runoff, the influence of tem- was to use the NCA concentration at site S12 as the con- perature was also proposed (Millot et al. 2002). The SWRs in centration of natural NCA in the NLB, although this value Siberia, Canada and Norway were relatively low, which may be overestimated or underestimated in this case. were attributed to the cold climates (Millot et al. 2002; West Accordingly, the equivalent charge of natural NCA was et al. 2005). However, SWR was more variable and was determined to be 201 leq/L, which was close to that influenced by multiple factors in the warm climates (Millot assumed in Southwest China (Li et al. 2008) and lower than et al. 2002; West et al. 2005; Gurumurthy et al. 2012). For that in the Yangtze River (Chetelat et al. 2008). Then, the example, SWR was closely linked to river gradient in the industrial NCA could be calculated by (NCA - NCAS12) NLB (Fig. S3 in SM). The higher rates were observed in the with a mean of 723 leq/L. This result clearly showed that tributaries with higher slope gradients, such as the Guo NCA was mainly of industrial origin in the study region. River, where steeper slopes lead to higher physical erosion in The large scale industry in the study region emerged after the watershed. Together with the distribution of silicates as 1970s, suggesting that the NCA might participate in the mentioned in ‘‘Silicates’’, the rivers in the east of the NLB, rock weathering on short timescales. which drain mountainous landforms, had SWRs varying NCA participating in carbonate and silicate weathering 2 from 1.81 ± 0.90 to 15.51 ± 7.76 ton/km /a, several times might reduce the consumption of CO2 derived acid (H2CO3) to one order of magnitude higher than those in the west of the in weathering. This part of CO2 which should have involved NLB, which drain floodplains (Table 3). in the weathering as H2CO3, was thought as the degassed Subsequently, the CO2 consumptions associated with CO2. Thus, the equivalent charges of NCA in the NLB the weathering of silicates and carbonates by carbonic acid tributaries represented the amount of degassed CO2.Using were calculated on the basis of the cationic charge budget, the runoff data, the fluxes of degassed CO2 by NCA and and the detailed methods are listed as Eqs. 20–21) (in industrial NCA could be calculated individually (Table S5 in 9 Appendix). On the other hand, the participation of NCA in SM). In detail, the degassing of CO2 was 0.70 9 10 mol/a rock weathering caused cation release to waters without for the Xinxue River and 0.29 9 109 mol/a for the Zhuz- consuming CO2. Therefore, the estimated CO2 consump- haoxin River. The flux of degassed CO2 in the Guangfu tion (Table 3) was the upper limit value without the con- River was the lowest, at 0.03 9 109 mol/a. For the Nansihu tribution of NCA (Beaulieu et al. 2011). Lake drainage basin, the fluxes of degassed CO2 associated

123 Environ Earth Sci (2016) 75:453 Page 13 of 16 453

9 with NCA and industrial NCA were 2.74 9 10 and of silicates and carbonates, the consumption of CO2 was 2.15 9 109 mol/a, respectively. The area of the whole basin approximately 7.50 9 109 mol/a for the whole basin. The is approximately 31.71 9 103 km2, and the annual rates of proton contribution of NCA involved in weathering of 2 CO2 degassing were approximately 3.80 and 2.98 ton/km , rocks was identified as being in the range 12–72 % for the respectively. Moreover, of all protons involved in the major tributaries and 34 % on average for the whole basin. weathering of silicate and carbonate rocks, the proportions In the area of the Nansihu Lake drainage basin, the flux of 9 of NCA ranged from 12 % (Dongyu River) to 72 % (Xinxue degassed CO2 was 2.74 9 10 mol/a, and the annual rate 2 River) in the 13 tributaries (Table S5). The average was of CO2 degassing was approximately 3.80 ton/km . 34 % in the area of the NLB. The contribution of NCA to weathering of silicate and carbonate rocks was approxi- Acknowledgments This research was financially supported by the mately three times higher than that in the Xijiang drainage National Nature Science Foundation of China (41372212), the Fun- damental Research Funds for the Central Universities (2652014003), basin (Xu and Liu 2010). The maximum value (72 %) in this the State Key Laboratory of BGEG (GBL2135, GBL201405) and the case was also higher than that of the Wujiang River (55 %, fund for advantage discipline of geochemistry in CUGB. It was also Han and Liu 2004). supported by the Shandong Provincial Department of Land and Nevertheless, the action of NCA participating in rock Resources with the project ‘‘Assessment of ecological and geological environment influenced by Coal mining in the area of Nansihu-Lake weathering is not a direct source of CO2. In term of CO2 (LUKANZI 2012-36)’’. We thank the project members of the Shan- transfers, silicate weathering by NCA is neutral (neither a dong Provincial Institute of Land Surveying and Mapping for their source nor a sink), while carbonate weathering by NCA is help with the field work. neutral over short term timescales and constitutes a net source of CO2 at long timescales (taking into account the - oceanic C cycle). In other words, for 2 mol of HCO3 Appendix: Calculation methods (Eqs. 1–21) released by carbonate weathering, 1 mol of calcite pre- cipitate into the oceans and 1 mol of CO2 is released to the Calculation methods atmosphere over long term timescales (Calmels et al. 2007; Contributions of various reservoirs Beaulieu et al. 2011). By consequence, if carbonate Atmospheric inputs weathering was associated with NCA, NCA would act as a À À Xatm ¼ Fatm  ½ŠX=F rain ð1Þ net source of CO2 only when it contributes to carbonate weathering over long term timescale (3000–10,000 years). Anthropogenic inputs If carbonate weathering was due to protons derived from ÂÃÀÁhÀÁ ClÀ SO2À =Naþ ClÀ SO2À CO , carbonate weathering would be neutral over long þ 4 anth¼ þ 4 S01 2 ÀÁi Âà ð2Þ term timescales. À 2À þ þ À Cl þ SO4 S02 = NaS01ÀNaS02 À À À À NO3 agr ¼ NO3 riv À NO3 atm À NO3 ind ð3Þ Conclusions Silicates The sampling of waters in 13 tributaries in the NLB and the þ þ þ Ksil ¼ KrivÀ Katm ð4Þ analysis of major ions allowed the identification and Âà Ca2þ Kþ Ca2þ=Kþ 5 quantification of the contributions of the reservoirs. The sil ¼ sil  gg ð Þ dominant anions were Cl- and SO42-, but the distribution Âà Mg2þ ¼ Kþ  Mg2þ=Kþ ð6Þ of cations was notably complex due to the dominance of sil sil gg evaporite weathering and the anthropogenic supply of Na? þ þ þ þ Nasil ¼ Ksil  ½ŠNa =K gg ð7Þ in the basin. Through detailed calculation, the contributions of different reservoirs were determined for each tributary, Chemical budget and chemical weathering rate including atmospheric inputs (0.6–2.7 %), anthropogenic estimation inputs (0.1–68 %) and weathering of rocks (31–97 %). The Xriv ¼ Xatm þ Xanth þ Xeva þ Xcarb þ Xsil ð8Þ average contribution from weathering of rocks in the basin FÀ ¼ FÀ ð9Þ was approximately 61 %, including 28 % from evaporites, riv atm þ þ þ 25 % from carbonates and 8 % from silicates. Moreover, Kriv ¼ Katm þ Ksil ð10Þ their weathering rates in the Nansihu Lake drainage area NOÀ ¼ NOÀ þ NOÀ ð11Þ were estimated based on the runoff data. The annual con- 3 riv 3 atm 3 anth À À À À tributions of cationic TDS to waters were 1.90 ± 0.95 ton/ Clriv ¼ Clatm þ Clanth þ Cleva ð12Þ km2 from silicates, 5.68 ± 2.84 ton/km2 from carbonates SO2À ¼ SO2À þ SO2À þ SO2À þ SO2À ð13Þ and 7.32 ton/km2 from evaporites. Based on the weathering 4 riv 4 atm 4 anth 4 eva 4 pyr 123 453 Page 14 of 16 Environ Earth Sci (2016) 75:453

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