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This study found that the variations of pH in surface water at pre-flood season changed greatly along the tail reaches, while those at post-flood season showed little fluctuations (Fig. 2a). Previous studies have indicated that the variation of pH was mainly dependent on the buffering capacity of water, which was correlated with the balance systems of carbon dioxide (CO2) in water (e.g., gas dissolution and escape, precipitation formation and dissolution, and the reactions of acid and alkali substances) (Dai, 2006; Zhang and Zhang, 2007). At pre-flood season, the great fluctuations of pH in surface water might be related to the weak hydrodynamic condition of tail reaches. As shown in Fig. 7, the runoff and sediment loading of the tail reaches at pre-flood season (April) were very low, implying that the transportation of nutrients and pollutants might be unsmooth, which might cause the water quality in some sampling stations (e.g. S2, S5−S9 and S17) to be deteriorated. The increased nutrients in water might provide abundant material basis for the thriving of hydrophyte (particularly phytoplankton), which induced the CO2 dissolved in water to be greatly consumed (Zhang and Zhang, 2007), resulting in the elevation of pH. The lower pH in S15 and S16 stations at pre-flood season might be related to the longer retention time of organic matter and its sufficient degradation process since the gradient ratios of the two stations declined slightly (Li et al., 1991). Due to the sufficient degradation of organic matter, mass CO2 were generated and dissolved in water (Guo et al., 2015), resulting in the decline of pH. At flood season, large amounts of freshwater and sediment were discharged into estuary (Fig. 7) due to the heavy rainfall in the Yellow River basin and the implementation of FSRP. Simultaneously, the original status of hydrodynamic condition along tail reaches was broken (Sun et al., 2016) and the transportation of nutrients and pollutants was smooth, which might induce the slight fluctuations of pH along the tail reaches at post-flood season (Fig. 2a). Moreover, compared to flood season, the hydrodynamic condition at post-flood season weakened (Fig. 7) and the possibility of sediment re-suspension declined (Tang, 2011), which induced the SPM in surface water along the tail reaches to be decreased greatly (Fig. 2c).
Figure 7. Temporal variations of runoff and sediment loading in tail-reaches of the Yellow River in 2016. Data source: Yellow River Conservancy Commission of the Ministry of Water Resources (2017)
This study also found that the fluctuations of As and most metals in surface water at pre-flood season were more obvious than those at post-flood season (Fig. 3, Appendix Table 1). One possible reason might be related to the difference in hydrodynamic conditions of tail reaches between pre-flood and post-flood seasons. As mentioned above, the runoff and sediment loading of the tail reaches at pre-flood season were very low (Fig. 7) and the transportation of pollutants in some local reaches was unsmooth. Under such hydrological conditions, the fluctuations of pH, EC and SPM along the tail reaches were more evident at pre-flood season compared to post-flood season. Particularly, significant differences in EC and SPM occurred between pre-flood and post-flood seasons (P < 0.01) (Fig. 2). All these might induce the great fluctuations of As and most metals along the tail reaches. Although the runoff and sediment loading of the tail reaches at post-flood season (October) was slightly lower than those at pre-flood season (April) (Fig. 7), the transportation of pollutants in tail reaches might be more smooth after flood season (Liu et al., 2008), which might induce the slight fluctuations of As and most metals along the tail reaches.
This study indicated that the levels of As, Cr, Cu, Ni, Pb and Zn in freshwater reach at pre-flood season were lower than those in low-salinity reach, but only the value of Ni in freshwater reach at post-flood season was lower than that in low-salinity reach (Appendix Table 1). The probable reason was related to the increasing of salinity (represented by EC) in a seaward direction (Fig. 2b), and this could be partly explained by Pearson correlation analyses which showed that, in freshwater reach, significantly positive correlations were observed between As (Cr or Ni) and EC (P < 0.01 or P < 0.05) at pre-flood season and between Ni and EC at post-flood season (P < 0.01) (Table 1). Previous studies have reported that the salinity in water could promote the mobility of heavy metals through complexation with salt anions and ion exchange between the cations and the metal ions (Du Laing et al., 2008; Li et al., 2011). Thus, compared to low-salinity reach, the quite lower salinity in freshwater reach might induce the lower metal concentrations. It was also reported that, in the process of river water and seawater mixing, negative correlation generally occurred between the dissolved-particulate partitioning coefficient of metals (e.g., Zn) and the salinity, which implied that the partitioning coefficient decreased with increasing salinity and the metals were apt to transfer from particulate to dissolved state (Turner, 1996). In this study, the maximums of As, Ni, Zn, Cu, Pb and Cr occurred in S22 station at pre-flood season and the higher values of Ni and Zn occurred in S20 station at post-flood season (Fig. 3), to a great extent, might be dependent on the above mechanisms. Pearson correlation analyses also indicated that, in surface water of low-salinity reach, significantly positive correlations occurred between Cd and pH at pre-flood season (P < 0.05) (Table 1). At neutral and alkaline conditions, the soluble Cd2+ (CdSO4) were more easily precipitated (Wang et al., 1981; He et al., 2011). In this study, the pH in surface water at pre-flood season generally showed a decreasing trend in low-salinity reach and the values varied from 7.10 to 7.68 (Fig. 2a), which might induce the Cd levels in surface water of low-salinity reach to be lower than those of freshwater reach (Appendix Table 1).
Periods Items Indices Reach As Cd Cr Cu Ni Pb Zn Pre-floodseason Surface water pH F 0.06 −0.11 0.02 0.04 0.12 −0.07 −0.20 L 0.37 0.90* 0.27 0.36 0.22 0.76 0.83 EC F 0.49* 0.37 0.57** 0.13 0.46* 0.43 0.41 L 0.24 −0.10 0.16 0.17 0.18 −0.18 −0.02 SPM F 0.25 −0.05 0.19 −0.02 0.12 0.03 −0.06 L −0.45 −0.55 −0.89 −0.46 −0.53 −0.39 −0.55 SPM pH F 0.02 0.06 −0.04 0.05 −0.05 −0.08 −0.03 L −0.01 0.23 −0.08 −0.14 −0.01 −0.13 −0.12 EC F −0.21 −0.16 −0.02 −0.13 −0.18 −0.25 −0.16 L −0.15 −0.01 −0.23 0.02 −0.28 −0.36 −0.14 SPM F −0.13 −0.19 0.35 −0.17 0.12 −0.03 −0.04 L 0.13 −0.16 0.23 0.06 0.26 0.33 0.15 Post-flood season Surface water pH F −0.28 −0.37 −0.22 −0.38 0.25 −0.51* −0.08 L 0.40 0.74 0.17 0.36 0.27 0.77 0.68 EC F −0.15 0.11 −0.12 −0.23 0.57** −0.21 0.12 L 0.36 0.11 0.53 0.40 −0.34 −0.05 −0.27 SPM F 0.35 0.09 0.29 0.38 −0.18 0.34 0.11 L 0.09 0.34 −0.17 0.04 0.29 0.70 0.42 SPM pH F −0.15 0.05 0.24 0.18 0.05 0.20 0.21 L 0.74 0.64 0.59 0.72 0.74 0.67 0.59 EC F −0.035 −0.18 0.12 0.02 −0.10 −0.10 0.16 L −0.76 −0.87 −0.97** −0.76 −0.84 −0.84 −0.08 SPM F −0.31 −0.43 −0.15 −0.45* −0.31 −0.41 −0.30 L 0.74 0.85 0.87 0.70 0.81 0.70 0.66 Notes: F, Freshwater reach (n = 20); and L, Low-salinity reach (n = 5). **P < 0.01; and *P < 0.05 Table 1. Correlation coefficients between As or metals and pH, EC and suspended particulate matter (SPM) in tail-reaches of the Yellow River
This study also indicated that the concentrations of As, Cd, Cu, Ni, Pb and Zn in SPM of freshwater reach at pre-flood season were lower than those of low-salinity reach (Appendix Table 2). Previous studies have shown that SPM was the main carrier of metals in water and it played an important role in metal migration and transformation (Moran et al., 1996; Zhou, 2016). The metal levels in SPM were directly affected by its substance composition, concentration and particle-size and indirectly influenced by physico-chemical conditions such as hydrodynamic force, salinity, pH and redox potential (Calmano and Hong, 1993; Bai et al., 2012). Du (2011) found that, at pre-flood season, the contents of sand, coarse silt, medium silt, fine silt and fine silty clay in SPM of Lijin hydrological station were 3.0%, 6.1%, 13.5%, 25.8% and 51.6%, respectively. Zhou (2016) reported that the contents of clay, silt and sand in SPM of the Yellow River estuary (low-salinity reach) at drought season varied from 20.2% to 29.7%, between 55.5% and 72.5%, and from 0.6% to 22.1%, respectively. Obviously, both fine silt and clay were the main composition of SPM in freshwater reach or low-salinity reach at pre-flood season. In low-salinity reach, the low flows of the Yellow River at pre-flood season caused a significant decrease in coarse particles and the increased fine particles promoted the sorption of As and metals. Moreover, as affected by the interaction of hydrodynamic forces between the Yellow River and the Bohai Sea, the increased salinity in a seaward direction (Fig. 2b) might result in the higher concentrations of As and metals in SPM through complexation with salt anions and ion exchange between the cations and the metal ions (Du Laing et al., 2008; Li et al., 2011). This study also implied that the levels of As and six metals in SPM of freshwater reach at post-flood season were higher than those of low-salinity reach (Appendix Table 2 ). Compared to pre-flood season, large volume of runoff discharge (4.07 billion m3, accounting for 40.28% of annul runoff) and higher sediment loading (0.08 × 108 t, accounting for 52.12% of annul loading) at flood season (Fig. 7) produced a significant dilution on the levels of As and metals in SPM of low-salinity reach. The above reason could also be used to explain the higher levels of As and metals in SPM at pre-flood season compared to post-flood season (Appendex Table 2). The lower levels of some metals in SPM of low-salinity reach at post-flood season might also rest with the variations of EC and SPM. Pearson correlation analyses showed that significantly negative correlation occurred between Cr and EC in low-salinity reach (P < 0.01) (Table 1). The higher EC in low-salinity reach could better explain the lower Cr levels in a seaward direction (Fig. 2b, Fig. 4b). Moreover, the lower levels of As and metals in S23 station at post-flood season (Fig. 4b) might be partly illustrated by the lower content of SPM (Fig. 2c) since positive correlations occurred between As and metals and SPM in low-salinity reach (Table 1).
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The status of As and metal pollution in surface water of freshwater reach and low-salinity reach were assessed by comparing As and metal concentrations with the Environmental Quality of Surface Water in China (GB 3838–2002) (State Environmental Protection Administration and General Administration of Quality Supervision, Inspection and Quarantine of the People’s Republic of China, 2002) and the Seawater Quality in China (GB 3097–1997) (State Environmental Protection Administration, 2004), respectively. At pre-flood season, only the Zn level in S14 station at freshwater reach exceeded the criteria of Class I recommended by GB 3838–2002, while the Cu level in S22 station, the Zn levels in S20–S22 stations and the Pb levels in S20–S22 and S24 stations at low-salinity reach exceeded the criteria of Class I recommended by GB 3097–1997. At post-flood season, the Cr levels in S1, S5, S8–S11, S15 and S18–19 stations, the Cu level in S3 station and the Ni level in S18 station at freshwater reach exceeded the Class I criteria of GB 3838–2002, whereas the Ni levels in S21, S23 and S24 stations and the Pb levels in S21 and S24 stations at low-salinity reach exceeded the Class I criteria of GB 3097–1997. The pollution level of As and metals in SPM of freshwater reach and low-salinity reach were evaluated by comparing As and metal concentrations with the Sediment Quality Guidelines (SQGs) for coastal ecosystem in China (GB 18668−2002) (General Administration of Quality Supervision, Inspection and Quarantine of the People’s Republic of China, 2002), the mean levels of chemical elements in sediments of rivers in China (Yan et al., 1995) and the TEL (Threshold effect level) /PEL SQGs (MacDonald et al., 1996, 2000) (Table 2). According to the background values of As and metals in loess materials of the Yellow River (CNEMC, 1990), the mean levels of As and metals in SPM of freshwater reach and low-salinity reach at pre-flood or post-flood season exceeded their background values. In freshwater reach, only the average level of Pb in SPM at post-flood season was slightly lower than that in sediments of rivers in China, but, in low-salinity reach, only the mean levels of Cd, Cr, Cu and Ni at pre-flood season exceeded the Class I criteria of SQGs for coastal ecosystem in China. According to the TEL/PEL SQGs, 35% stations contained Cr, 30% stations contained Ni, 45% stations contained Cu, 10% stations contained Zn, 50% stations contained As, 20% stations contained Pb and 15% stations contained Cd in SPM of freshwater reach at pre-flood season exceeded the corresponding TEL values and approximately 65%, 14% and 50% of stations contained concentrations exceeded the PEL values for Cr, Ni and As, respectively. For low-salinity reach, 20% stations contained Ni, 80% stations contained Pb and 100% stations contained Cr, Cu and As exceeded the corresponding TEL values and about 80% stations contained levels exceeded the PEL value for Ni. At post-flood season, 85% stations contained Cr and Ni and 100% stations contained As in SPM of freshwater reach exceeded the corresponding TEL values and only 15% stations contained concentrations exceeded the PEL values for Cr and Ni. In low-salinity reach, 85% stations contained Cu and 100% stations contained Cr, Ni and As exceeded the corresponding TEL values. Overall, As and Cr were identified as contaminants of primary concern in freshwater reach and low-salinity reach at pre-flood or post-flood season. Moreover, Cu, Cd and Ni in low-salinity reach at pre-flood season, Ni in freshwater reach and Cu and Ni in low-salinity reach at post-flood season were of primary concerns.
Items As Cd Cr Cu Ni Pb Zn References Mean levels of As and metals in SPM of tail reaches of the Yellow River / (mg/kg) Freshwater reach Pre-flood season 17.42 ± 3.59 0.49 ± 0.11 108.62 ± 34.13 34.62 ± 8.13 45.26 ± 14.22 29.24 ± 5.95 92.79 ± 22.43 This study Post-flood season 12.79 ± 1.39 0.36 ± 0.05 82.21 ± 11.95 23.87 ± 4.01 31.79 ± 4.70 21.79 ± 2.69 74.28 ± 20.79 Low-salinity reach Pre-flood season 18.57 ± 3.22 0.54 ± 0.10 107.35 ± 19.09 39.20 ± 7.60 49.93 ± 11.53 31.12 ± 5.23 103.72 ± 19.15 Post-flood season 11.44 ± 2.38 0.30 ± 0.10 79.71 ± 14.87 22.16 ± 7.19 30.66 ± 6.41 21.07 ± 3.86 70.69 ± 20.40 Background values / (mg/kg) Loess materials 10.7 0.095 59 21.1 27.8 21.6 64.5 CNEMC (1990) Sediment quality guidelines / (mg/kg) SQGs for freshwater ecosystem TEL 5.9 0.596 37.3 35.7 18 35 123 MacDonald et al. (2000) PEL 17 3.53 90 197 36 91.3 315 SQGs for coastal ecosystem TEL 7.24 0.68 52.3 18.7 15.9 30.2 124 MacDonald et al. (1996) PEL 41.6 4.21 160 108 42.8 112 271 SQGs for coastal ecosystem in China Class I 20 0.5 80 35 34a 60 150 General Administration of Quality Supervision, Inspection and Quarantine of the People’s Republic of China (2004) Class II 65 1.5 150 100 40a 130 350 Mean concentrations of As and metals in fluvial deposit of China Means 9.1 0.14 38 21 24 25 68 Yan et al. (1995) Notes: a Sediment quality benchmark in Hong Kong SAR (Environmental Protection Department of Hong Kong, 2005); TEL, Threshold effect level, it was applied to present chemical concentrations below which adverse biological effects rarely occur; and PEL, probable effect level, it was used to present chemical concentrations above which adverse biological effects frequently occur Table 2. Comparison for the concentrations of As and metals in suspended particulate matter (SPM) of tail reaches, loess materials and sediment quality guidelines (SQGs)
Based on the analyses for Igeo values, it was found that the SPM in freshwater reach at pre-flood season were polluted by Cd, As, Cr, Cu and Ni, while those in low-salinity reach were polluted by Cd and Cr. At post-flood season, the SPM in freshwater reach were polluted by Cd and Pb, whereas those in low-salinity reach were polluted by Cd and Cr. Although the conclusion was generally in agreement with the results of pollution assessment, Cu, Ni and As pollution status at low-salinity reach might be underestimated since both the SQGs for coastal ecosystem in China and the TEL/PEL showed that the sampled stations were polluted by these elements. Moreover, Cd pollution was serious in both freshwater reach and low-salinity reach at pre-flood or post-flood season. This study also found that, in freshwater reach, 50% of stations for ΣTUs at pre-flood season and the value at S18 station at post-flood season exceed 4 (Fig. 6), implying that these stations showed high potential toxicity (Pedersen et al., 1998). The ΣTUs of all stations in low-salinity reach at pre-flood or post-flood season were less than 4 (Fig. 6), which showed no potential toxicity (Pedersen et al., 1998). The above analyses further showed that the potential toxic risk of As and metals in SPM of tail reaches at pre-flood season were much higher than that at post-flood season, indicating that the implementation of FSRP during flooding season, to a great extent, reduced the potential toxic risk caused by the combined effects of these elements in SPM. Over all sampling stations, Cr, Ni and As in SPM of tail reaches at pre-flood and post-flood seasons showed great contributions to ΣTUs (Fig. 6). It was worth noting that, along the tail reaches, Cd showed a lower toxicity contribution at pre-flood or post-flood season (Fig. 6) despite its higher pollution level on the basis of Igeo assessment (Fig. 5), indicating that the evaluation of TUs approach might underestimate its toxicity because of the higher PEL value for Cd.
To investigate the pollution status of As and metals in surface water or SPM in tail reaches as affected by the long-term implementation of FSRP, the results of this paper and present studies were compared (Fig. 8). The existed data set for As and metal levels in surface water indicated that the levels of Cr, Cu and Pb in freshwater reach at pre-flood or post-flood season generally increased during 2009–2016. For the low-salinity reach, the Zn levels at pre-flood season significantly decreased during 2005–2010, after which the values increased slightly. The levels of Cu, Pb and As at pre-flood season decreased significantly during 2005–2009 and then increased greatly before 2010, after which the values decreased greatly again. The levels of Zn, Cu, Cr and Pb at post-flood season significantly increased during 2004–2005, after which the values decreased significantly. The Cd levels at pre-flood and post-flood seasons generally decreased during 2004–2016 (Fig. 8a). Comparison of existed data set for SPM implied that the levels of Cr, As, Pb and Cu in freshwater reach at pre-flood season generally increased during 2009–2016. By contrast, the concentrations of Zn, Ni, Cu and Pb at post-flood season decreased before the implementation of FSRP (2000–2001), after which the values of Ni, As and Zn generally increased. Only the levels of Cu, Pb and Cd at post-flood season during 2009–2016 decreased greatly. For the low-salinity reach, the levels of As and six metals at pre-flood season generally increased during 2010–2016. By comparison, the concentrations of Zn, Pb and Cu at post-flood season increased significantly during 2010–2013, after which the values decreased greatly before 2016.,The levels of Cr at post-flood season increased during 2013–2016, while those of Ni decreased at the same period. Moreover, the levels of As and Cd generally showed an increasing trend during 2010–2016 (Fig. 8b). In summary, the levels of Cr, Cu and Pb in surface water of freshwater reach at pre-flood and post-flood seasons generally showed an increasing trend, while those of As and most metals in low-salinity reach showed a decreasing trend. For the SPM in freshwater reach or low-salinity reach, the levels of As and most metals at pre-flood or post-flood seasons showed an increasing trend in recent years. Although the pollutants imported into the Yellow River estuary decreased greatly in recent years, the loading of As and metals still maintained a high level (Sun et al., 2015; Tian et al., 2018). With the long-term implementation of FSRP in future, the pollution levels of As and metals (particularly for Cd) in SPM in tail reaches might be elevated and the potential toxic risk primarily produced by Cr, Ni and As might be increased if measures were not taken to control the loading of pollutants. In addition, further studies should be strengthened to identify the potential sources of Cr, Ni and As, and this would provide scientific basis for minimizing their toxic risks on aquatic organisms.
Figure 8. Existed data set for As and metal levels in surface water (a) or suspended particulate matter (SPM) (b) in tail reaches of the Yellow River reported in this paper and present studies. Data sources: Huang et al. (1992), Qiao et al. (2007), Wu (2007), Liu et al. (2008), Tang et al. (2010), Tang (2011), Zhang et al. (2013) and Zhou (2016). Data in 2016 were provided by this study
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Periods Elements Freshwater reach Low-salinity reach Tail reaches Range Mean ± S.D. CV (%) Range Mean ± S.D. CV (%) Range Mean ± S.D. CV (%) Pre-flood season As 0.80–2.79 1.20 ± 0.46 39.17 0.63–3.39 1.53 ± 1.20 78.45 0.63–3.39 1.27 ± 0.66 51.87 Cr 0.51–2.02 1.03 ± 0.41 39.28 0.55–10.33 3.02 ± 4.11 136.16 0.51–10.33 1.43 ± 1.94 136.87 Ni 1.22–3.75 2.17 ± 0.70 32.31 1.48–13.02 4.39 ± 4.87 110.94 1.22–13.02 2.60 ± 2.32 89.23 Cu 1.56–8.58 3.28 ± 1.60 48.83 1.54–10.22 4.04 ± 3.68 91.19 1.54–10.22 3.38 ± 2.12 62.78 Zn 6.96–62.18 22.85 ± 14.58 63.81 16.85–40.30 29.61 ± 11.50 38.84 6.96–62.18 23.62 ± 14.06 59.53 Cd 0.03–0.93 0.10 ± 0.20 188.73 0.02–0.12 0.08 ± 0.05 61.74 0.02–0.93 0.10 ± 0.18 182.11 Pb 0.96–9.13 2.27 ± 1.70 74.99 0.90–4.46 2.35 ± 1.46 62.27 0.90–9.13 2.28 ± 1.66 72.69 Post-flood season As 0.71–2.36 1.63 ± 0.53 32.51 0.75–2.05 1.43 ± 0.55 38.42 0.71–2.36 1.62 ± 0.51 31.34 Cr 4.15–11.98 8.66 ± 2.73 31.56 4.15–9.65 7.69 ± 2.43 31.66 4.15–11.98 8.64 ± 2.55 29.53 Ni 3.19–31.88 8.15 ± 7.10 87.16 4.18–31.88 11.15 ± 11.65 104.49 3.19–31.88 7.78 ± 6.52 83.83 Cu 1.51–19.79 4.05 ± 3.85 95.00 1.58–4.25 3.01 ± 1.13 37.51 1.51–19.79 3.94 ± 3.53 89.50 Zn 6.56–23.21 13.58 ± 4.83 35.58 7.91–16.00 11.46 ± 3.30 28.79 6.56–23.21 13.04 ± 4.65 35.63 Cd 0.02–0.10 0.05 ± 0.02 35.00 0.03–0.06 0.04 ± 0.01 25.59 0.02–0.10 0.05 ± 0.02 33.23 Pb 0.55–2.03 1.11 ± 0.40 35.79 0.42–1.54 0.90 ± 0.41 46.20 0.42–2.03 1.08 ± 0.40 37.33 Note: CV, coefficient of variation; S. D., standard deviation Table 1. Concentrations of As and metals in surface water in tail reaches of the Yellow River / (μg/L)
Periods Elements Freshwater reach Low-salinity reach Tail reaches Range Mean ± S.D. CV (%) Range Mean ± S.D. CV (%) Range Mean ± S.D. CV (%) Pre-flood season As 8.02–22.94 17.42 ± 3.59 20.61 13.05–20.87 18.57 ± 3.22 17.32 8.02–22.94 17.84 ± 3.35 18.78 Cr 56.60–216.13 108.62 ± 34.13 31.42 73.67–120.62 107.35 ± 19.09 17.78 56.60–216.13 109.81 ± 30.51 27.78 Ni 18.59–73.41 45.26 ± 14.22 31.41 29.57–57.27 49.93 ± 11.53 23.09 18.59–73.41 46.89 ± 13.18 28.12 Cu 12.49–46.04 34.62 ± 8.13 23.48 26.73–46.98 39.20 ± 7.60 19.38 12.49–46.98 35.90 ± 7.88 21.94 Zn 37.03–142.41 92.79 ± 22.43 24.18 71.10–121.40 103.72 ± 19.15 18.47 37.03–142.41 95.97 ± 21.32 22.22 Cd 0.17–0.65 0.49 ± 0.11 22.97 0.39–0.62 0.54 ± 0.10 17.88 0.17–0.65 0.50 ± 0.11 21.28 Pb 16.27–37.97 29.24 ± 5.95 20.34 21.89–34.26 31.12 ± 5.23 16.82 16.27–37.97 29.94 ± 5.53 18.47 Post-flood season As 10.51–15.11 12.79 ± 1.39 10.85 7.37–13.13 11.44 ± 2.38 20.77 7.37–15.11 12.56 ± 1.65 13.11 Cr 61.18–118.33 82.21 ± 11.95 14.53 54.55–91.00 79.71 ± 14.87 18.66 54.55–118.33 81.32 ± 12.13 14.92 Ni 23.95–42.09 31.79 ± 4.70 14.77 19.49–35.62 30.66 ± 6.41 20.92 19.49–42.09 31.57 ± 4.95 15.69 Cu 17.82–35.13 23.87 ± 4.01 16.80 9.71–27.43 22.16 ± 7.19 32.46 9.71–35.13 23.56 ± 4.67 19.81 Zn 51.46–142.89 74.28 ± 20.79 27.98 34.65–82.11 70.69 ± 20.40 28.85 34.65–142.89 73.27 ± 20.28 27.68 Cd 0.25–0.43 0.36 ± 0.05 15.22 0.13–0.37 0.30 ± 0.10 32.50 0.13–0.43 0.35 ± 0.07 19.11 Pb 16.97–26.63 21.79 ± 2.69 12.33 14.22–23.30 21.07 ± 3.86 18.30 14.22–26.63 21.57 ± 2.86 13.24 Note: CV, coefficient of variation; S. D., standard deviation Table 2. Concentrations of As and metals in suspended particulate matter (SPM) in tail reaches of the Yellow River (mg/kg)
Spatial Variation and Risk Assessment of Arsenic and Heavy Metals in Surface Water and Suspended Particulate Matter in Tail Reaches of the Yellow River, China
doi: 10.1007/s11769-021-1182-z
- Received Date: 2020-02-21
- Available Online: 2021-12-31
- Publish Date: 2021-01-05
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Key words:
- arsenic and heavy metals /
- surface water /
- suspended particulate matter /
- tail reaches /
- Yellow River
Abstract: To determine the pollution levels and potential toxic risks of arsenic (As) and heavy metals (Cr, Ni, Cu, Zn, Pb and Cd) in water and suspended particulate matter (SPM) in tail reaches (including freshwater reach and low-salinity reach) of the Yellow River as the Flow-Sediment Regulation Project (FSRP) has been carried out for approximately 15 yr, the surface water and SPM were sampled at pre-flood (April) and post-flood seasons (October). Results showed that similar changes of As and metal levels in water and SPM were observed along the tail reaches at pre-flood or post-flood season. Compared to pre-flood season, the levels of As, Cu, Cr and Ni in freshwater reach and the concentrations of Cr and Ni in low-salinity reach rose greatly at post-flood season. The levels of As and metals in SPM of freshwater reach or low-salinity reach at pre-flood season were significantly higher than those at post-flood season (P < 0.01). The pollutions of As and metals in surface water of tail reaches at pre-flood or post-flood season were not serious. The SPM in freshwater reach at pre-flood season were polluted by Cd, As, Cr, Cu and Ni while those in low-salinity reach were polluted by Cd and Cr. The SPM in freshwater reach at post-flood season were polluted by Cd and Pb while those in low-salinity reach were polluted by Cd and Cr. Cd was identified as heavy metal of primary concern at both pre-flood and post-flood seasons. Combined with the existed data reported in present research, this study found that the toxic risk of As and metals in SPM of tail reaches at pre-flood season was higher than that at post-flood season, implying that the implementation of FSRP during flooding season, to a great extent, reduced the toxic risk of these elements. With the long-term implementation of FSRP, the pollution levels of As and metals (particularly for Cd) in SPM of tail reaches might be elevated and the potential toxic risk primarily produced by Cr, Ni and As might be increased if effective measures were not taken in future.
Citation: | SUN Zhigao, LI Jing, TIAN Liping, CEHN Bingbing, HU Xingyun, 2021. Spatial Variation and Risk Assessment of Arsenic and Heavy Metals in Surface Water and Suspended Particulate Matter in Tail Reaches of the Yellow River, China. Chinese Geographical Science, 31(1): 181−196 doi: 10.1007/s11769-021-1182-z |