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Article

Speciation Distribution Characteristic and Ecological Risk of Heavy Metals in Surface Sediments of Cascading Hydropower Dams in Lancang River

1
China Waterborne Transport Research Institute, Beijing 100088, China
2
Instrumental Analysis Center, Hebei Normal University, Shijiazhuang 050024, China
3
The Appraisal Center for Environmental and Engineering, The Ministry of Ecology and Environment, Beijing 100012, China
*
Author to whom correspondence should be addressed.
Water 2022, 14(20), 3248; https://doi.org/10.3390/w14203248
Submission received: 7 September 2022 / Revised: 1 October 2022 / Accepted: 11 October 2022 / Published: 14 October 2022
(This article belongs to the Special Issue Water and Sediment Quality Assessment)

Abstract

:
In order to study the speciation, contamination statues, and distribution characteristic of heavy metals in the surface sediments of cascading dams, the reservoir regions of Manwan and Dachaoshan cascading dams were sampled and investigated. The speciation and its contents of heavy metals (As, Cd, Cr, Cu, Pb, and Zn) were analyzed by the modified European Community Bureau of Reference (BCR) sequential method. The ecological risk assessment of heavy metals was performed by the ratio of secondary phase and primary phase (RSP) method. The source identification of heavy metals was performed by correlation analysis (CA) and principal component analysis (PCA). The results indicated that the values of RSPcd were from heavy pollution (IV level), and those of RSPZn were from light pollution (II level) to moderate pollution (III level) in the lacustrine zone of the upper-stream Manwan dam. The values of the RSP were no pollution (I level) in the downstream of the Dachaoshan dam. The ecological risk assessment of heavy metals (Cd, Zn, and As) at the upper stream of the Manwan dam was generally higher than that at the downstream Dachaoshan dam. Cascading dams operation showed significant accumulation effects on heavy metals in surface sediments. The source identification of heavy metals showed that Cd and Zn were mainly from anthropogenic activities; As, Cu, and Pb were affected by both natural processes and anthropogenic activities; and Cr was mainly from natural processes.

1. Introduction

The cascading hydropower dams exploitation on larger rivers is thought to profoundly impact on the natural environment and ecosystem, such as the hydrological regime, water quality, sediment transport, and terrestrial and aquatic organisms [1,2,3,4]. Globally, by 2025, more than 70% of rivers will be separated and controlled by the large dams; otherwise, it was only more than half in 2005 [5,6]. As the main component of the aquatic ecosystem, the sediments and its transport rate are obviously affected by the interception effect in a dammed river [7]. Because of sediments interception and accumulation effect, approximately 0.5–1.0% of reservoir storage is globally lost each year [8].
As a persistent contamination in sediments, heavy metals are a great threat to water quality, public health, environment, and ecosystems health through suspended particles, bioaccumulations, and trophic chains [9]. Especially, the heavy metals Cd and Pb (which are highly toxic) and an excessive intake of Cu can cause various diseases and disorders in humans [10,11]. In recent years, the characteristic of heavy-metal pollution in the reservoir region has been widespread and concerned globally larger damming rivers such as the Three Gorge Dam in the Yangtze River [12,13], Xiaolangdi Reservoir in the Yellow River [14,15], Lancang-Mekong River [16,17,18], and Indus River [19]. Otherwise, relatively few studies focus on heavy-metal pollution variation after long-term monitoring associated with cascading dams operation.
Sediments play an important role in heavy-metals transport and transformation in an aquatic ecosystem [9]. The heavy metals, nutrients, and organic pollutants were mostly enriched and deposited in the reservoir sediment by precipitation, adsorption, and biological absorption process [20,21]. Because heavy-metals concentration in sediments is relatively higher in a water column, the source and trace identification has become important to distinguish the natural process and anthropogenic activities [22,23]. Multivariate statistical analysis methods, especially correlation analysis (CA) and principal component analysis (PCA), were widely conducted to assess the sediment quality and identify the source of heavy-metal pollutions [24,25].
As the first two cascading dams in the mainstream of the Lancang River, the Manwan and Dachaoshan cascading dams have operated since 1995 and 2003, respectively. After the upstream of Xiaowan (2010) and Gongguoqiao (2013) cascading dams’ operation and regulation, the hydrological regime and hydrodynamic and sedimentary environment have remained relatively stable in their reservoir regions [26]. Although the heavy-metal pollution in the Manwan dam was evaluated from 2011 to 2012 [17,18], the heavy-metal pollution in the surface sediment has greatly changed and varied after the upper-stream cascading dam’s operation. Based on the above analysis, the surface sediment of cascading hydropower dams including the Manwan and Dachaoshan dams was investigated in 2016. The objectives of this study were listed as follows: (1) to explore the distribution pattern of surface sediment grain size associated with cascading dams; (2) to understand the speciation distribution characteristic of heavy metals in cascading dams; (3) to evaluate the ecological risk and pollution levels of the heavy metals, combined with the historical survey in 2013; and (4) to identify the heavy-metal sources in cascading dams.

2. Methods

2.1. Study Area and Survey Methods

In China, the middle and lower reaches of the Lancang River were identified as a key region for hydropower exploitation [27]. At the end of 2021, 6 cascading hydropower dams have operated in this region. The Manwan (M) and Dachaoshan (D) cascading dams, operating since 1995 and 2003, respectively, were selected as the study area in 2016. Following the classification criteria of the longitudinal zonation in the study area [28], 12 surface sediment sampling sites were selected in the Manwan (M1–M6) and Dachaoshan (D1–D6) cascading dams. The longitudinal zonation of the study area can be divided into three habitats: the lacustrine zone (M1, M2, D1, D2, and D3); transitional zone (M3, M4, D4, and D5); and riverine zone (M5, M6, and D6). Figure 1 demonstrates the location of the surface sediment sampling sites in these cascading dams.
By using the Peterson grab (1/50 m2), the surface sediments were investigated in both dry (April) and rainy (October) seasons. At each sampling site, the surface sediments were collected with three parallel samples and subsequently mixed in equal parts for further determination. The grain size of the sediments was determined using a laser particle size analyzer (Mastersize 2000, UK). According to the Udden–Wentworth classification standard [29], the grain size type can be classified as clay (<4 μm), silt (4–64 μm), and sand (>64 μm).

2.2. Speciation Analysis of Heavy Metals

According to the modified European Community Bureau of Reference (BCR) sequential method [30,31,32,33], the speciation of heavy metals (As, Cd, Cr, Cu, Pb, and Zn) in surface sediments can be classified into five forms:
(1) Fraction 1 (F1): exchangeable and carbonate bound. One gram of sediment sample was put into 40 mL HAc at 0.11 mol/L. The solution was agitated for 16 h at room temperature. Then, the solution was centrifugally separated at 4000 round/min for 20 min, and the supernatant solution was separated. The solid residue was rinsed with 8 mL HAc at 0.11 mol/L, agitated for 16 h, and centrifugally separated at 3000 round/min for 20 min, and the supernatant solution was separated. Subsequently, the supernatant solution was merged and diluted at 50 mL for analysis. The solid residue was retained for the next-step extraction of fraction 2.
(2) Fraction 2 (F2): Fe/Mn oxide bound. The solid residue from fraction 1 was put into 40 mL NH2OH· HCl (HNO3 adjust pH to 3.0) at 0.1 mol/L, agitated, and centrifugally separated, and the supernatant solution was separated. The solid residue was rinsed with 8 mL NH2OH· HCl at 0.11 mol/L, agitated, and centrifugally separated, and the supernatant solution was separated. Subsequently, the supernatant solution was merged and diluted at 50 mL for analysis. The solid residue was retained for the next-step extraction of fraction 3.
(3) Fraction 3 (F3): Organic substance bound. The solid residue from fraction 2 was put into 40 mL NaOH at 0.01 mol/L, agitated, and centrifugally separated, and the supernatant solution was separated. The solid residue was rinsed with 8 mL NaOH at 0.01 mol/L, agitated, and centrifugally separated, and the supernatant solution was separated. Subsequently, the supernatant solution was merged and diluted at 50 mL for analysis. The solid residue was put into 40 mL NH2OH· HCl (0.02 mol/L HCl) at 0.1 mol/L. The solution was agitated for 16 h at room temperature. Then, the solution was centrifugally separated, and the supernatant solution was separated. The solid residue was rinsed with 8 mL NH2OH· HCl (0.02 mol/L HCl) at 0.1 mol/L and centrifugally separated, and the supernatant solution was separated, merged, and diluted at 50 mL for analysis. The solid residue was retained for the next-step extraction of fraction 4.
(4) Fraction 4 (F4): Sulfide bound. The solid residue from fraction 3 was put into 10 mL H2O2 at 30% (v/v), mixed, and heated in water bath for 1 h with intermittent shaking. Then, the residue was heated in water bath at 85 ± 2 °C with the remaining approximately 2 mL and 10 mL H2O2 was added at 30%. The above-mentioned operation was repeated to the remaining approximately 2 mL, which was allowed to cool down. It was put into 3 mL HAc (HNO3 adjust pH to 2.0) at 1.0 mol/L. The solution was agitated for 0.5 h and centrifugally separated, and the supernatant solution was separated. The solid residue was rinsed with 4 mL HAc (HNO3 adjust pH to 2.0) at 1 mol/L, agitated for 0.5 h, and centrifugally separated, and the supernatant solution was separated. Subsequently, the supernatant solution was merged and diluted at 10 mL for analysis. The solid residue was retained for the next-step extraction of fraction 5.
(5) Fraction 5 (F5): Residual. The residue from fraction 4 was digested in 50 mL Teflon beakers with 10 mL HF and 2 mL HClO4 for analysis.
Heavy-metal concentrations (As, Cd, Cr, Cu, Pb, and Zn) in these extracted solutions were determined using inductively coupled plasma mass spectrometry (ICP-MS, Thermo Fisher Scientific, Waltham, MA, USA). Each sample was tested 3 times to take its average value. The quality control was carried out by using standard reference materials of stream sediment (GBW07309), blank samples, and replicable samples. The recovery rates of heavy metals were between 85% and 115%. The total concentration of each heavy metal in surface sediments was calculated by the sum of F1, F2, F3, F4, and F5 contents.

2.3. Data Analysis

2.3.1. Ratio of Secondary Phase and Primary Phase (RSP)

Based on the speciation of heavy metals, the ratio of secondary phase and primary phase (RSP) method was employed to evaluate the potential ecological risk of heavy metals [34]. It was calculated as follows:
RSP = M s e c / M p r i m
where Msec is the secondary phase (F1 + F2 + F3 + F4) of heavy-metal concentration in sediments, Mprim is the primary phase (F5); 0 < RSP ≤ 1 means there is no pollution (I level); 1 < RSP ≤ 2, lightly pollution (II level); 2 < RSP ≤ 3, moderate pollution (III level); and RSP > 3, heavy pollution (IV level).

2.3.2. Statistical Analysis

Using the statistical package, the Pearson correlation analysis and principal component analysis (PCA) were employed to identify the heavy-metal sources.

3. Results and Analysis

3.1. Grain Size and Distribution Pattern of Surface Sediments

Figure 2 shows that the type of grain size was mainly clayey silt in the surface sediments. Along the longitudinal gradient of the river, the lacustrine zone of the Manwan dam was mainly clayey silt, the transition zone was mainly silty clay and sand–silt–clay, and the riverine zone was mainly sand–silt–clay. Downstream of the Dachaoshan dam, the type of grain size had large variation along the longitudinal gradient. The lacustrine zone was sand–silt–clay in the dry season and silty clay in the rainy season. The transition zone was clayey silt in both the dry and rainy seasons. In addition, in the riverine zone of sampling sites D6 and M6, the water with rapid flow, no surface sediments were acquired.

3.2. Speciation of Heavy Metals in Surface Sediments

Figure 3 shows that heavy metals (Cd and Zn) in the upstream of the Manwan dam, especially in the lacustrine zone, had relatively higher contamination than in the downstream of the Dachaoshan dam in 2016. In the Manwan dam, the speciation of Cd was mainly from F1, whereas that of Zn was mainly from F5, F3, and F1. In the Dachaoshan dam, the speciation of Cd and Zn was mainly from F5. Otherwise, the heavy metal As in the upstream of the Manwan dam, especially in the lacustrine zone, had relatively lower contamination than in the downstream of the Dachaoshan dam. In the Manwan dam, As was mainly from F5, F4, and F3. In the Dachaoshan dam, As was mainly from F5. The other heavy metals’ (Cr, Cu, and Pb) contamination had relatively small difference from the upstream to downstream in cascading dams. The speciation of heavy metals (Cr, Cu, and Pb) was mainly from F5.

3.3. Ratio of Secondary Phase and Primary Phase (RSP) Analysis

Figure 4 shows that the values of RSP (As, Cd, and Zn) in the upstream of the Manwan dam were relatively higher than those in the downstream of the Dachaoshan dam. In the Manwan dam, the values of RSPCd were heavy pollution (IV level) in the lacustrine zone, those of RSPAs were from no pollution (I level) to light pollution (II level) in the lacustrine zone, and those of RSPZn were from light pollution (II level) to moderate pollution (III level) in the lacustrine and transition zones. The values of RSP in the downstream Dachaoshan dam were no pollution (I level) in 2016.

3.4. Correlation Analysis

The Pearson correlation analysis was employed to analyze the source of heavy metals. Table 1 shows the Pearson correlation coefficient between the heavy metals in the Manwan and Dachaoshan cascading dams. Cd was significantly correlated with Zn (r = 0.872, p < 0.01), Cu (r = 0.722, p < 0.01), and Pb (r = 0.673, p < 0.01). As was significantly correlated with Pb (r = 0.741, p < 0.01) and Cu (r = 0.645, p < 0.01). Cr was significantly correlated with Fe (r = 0.601, p < 0.01).

3.5. Principal Component Analysis (PCA)

The principal component analysis (PCA) was also employed to analyze the source of the heavy metals. The result shows that the Kaiser–Meyer–Olkin (KMO) measure of the sampling adequacy value was 0.755, and Bartlett’s test value was 0.000 (p < 0.05). Table 2 shows that the cumulative percentage of variance of components 1 and 2 was 81.316%. Component 1 represented the source of anthropogenic activities, whereas component 2 represented the source of natural processes. Component 1 had a relatively high percentage of variance of 58.314%; Cd and Zn had relatively high factor loadings of 0.962 and 0.921, respectively. Component 2 had a percentage of variance of 23.001%; Cr and Fe had relatively high factor loadings of 0.876 and 0.871, respectively. Component 1 of As, Cu, and Pb had relatively higher loading than component 2. Figure 5 also shows that the heavy metals Cd, Zn, Cr, Fe, As, Cu, and Pb have a similar source.

4. Discussion

4.1. Deposit Environmental and Habitat Change before and after Cascading Dams

Before cascading dams’ impoundment and operation, the natural Lancang River was running through a deep valley, the riverbed was mainly bedrock, and the suspended matter was not easy to deposit [35]. The dam construction and operation, especially the cascading dams, are believed to be the predominant factors that influenced the sediment deposition and flow discharge [36]. After the Manwan and Dachaoshan cascading dams operation, the diverse lotic habitat had changed into a cascading reservoir habitat including the lacustrine, transitional, and riverine zones [37]. With the water level and retention time increasing, the water velocity decreased to 0.1 m·s−1, and most of the suspended sediment was deposited in the reservoir region especially the lacustrine zone [12]. In a 2016 survey, the water depth was only 40–45 m and 50–60 m in the front of the Manwan and Dachaoshan cascading dams, respectively. In the upper stream of the Manwan dam, the sediment accumulation rate was relatively higher than that in the downstream of the Dachaoshan dam [26]. Along the longitudinal gradient of cascading dams, the type of the surface sediment grain size increased from clayey silt to sand–silt–clay. The sedimentary environment has remained relatively stable after cascading hydropower dams’ operation.

4.2. Contamination Characteristic Change of Heavy Metals in Cascading Dams

The operation of cascading dams has remarkable accumulation effects on heavy-metal contamination that has been absorbed by surface sediments [37,38]. Along the longitudinal gradient of cascading dams, the lacustrine zone had relatively higher contamination of heavy metals than the transitional and riverine zones. Moreover, in the upper stream of the Manwan dam, the concentration of heavy metals (As, Cd, and Zn) and its values of RSP are relatively higher than those in the downstream of the Dachaoshan dam.
Concerning the speciation of the heavy-metal variance, the speciation of Cd was mainly from exchangeable and carbonate bound in the Manwan dam. The values of RSPCd were heavy pollution (IV level) in its lacustrine zone. Downstream of the Dachaoshan dam, the speciation of heavy metals (As, Cd, and Zn) was mainly from residual. The values of the RSP were no pollution (I level) in 2016. Therefore, the heavy metal Cd had the biggest ecological risk, followed by As and Zn. It was similar with the Manwan dam in a 2013 survey and the heavy-metal pollution characteristic in China reservoirs and lakes [18,38,39,40]. This research also indicated that the sediment has obviously absorptive effect on the heavy metals of Cd and As [21].

4.3. Source Identification of Heavy Metals in Surface Sediment of Cascading Dams

Combined with the historical survey in 2013 (Table 3) [32], the values of RSPCd, RSPCu, RSPPb, and RSPZn obviously decreased in cascading dams. Otherwise, the values of RSPAs increased in the upstream of the Manwan dam, especially in the lacustrine zone, and decreased in the downstream of the Dachaoshan dam.
The correlation analysis (CA), principal component analysis (PCA), and contamination characteristic change of heavy metals (Table 3) demonstrated the source difference among the heavy metals [22,23,24,25]. The heavy metals Cd and Zn were mainly from anthropogenic activities and accumulated in the Manwan dam lacustrine zone that was mainly from the upper reach of the Lancang River lead–zinc mining activity [16,38]. The heavy metals (As, Cu, and Pb) were affected by natural processes and anthropogenic activities. Cu and Pb were mainly from the upper reach. Along with the upper stream of Xiaowan (designed as a storage dam) and Gongguoqiao (designed as a runoff dam), impounded after 2010 and 2013, respectively, the suspended sediment obviously reduced, and the heavy-metal pollution (Cd, Cu, Pb, and Zn) may be accumulated in the upper cascading dams. Because RSPAs obviously increased in the lacustrine zone of the Manwan dam in 2016, it demonstrated that the source of As pollution mainly originated from the subbasin of the Manwan reservoir. Cr was mainly from natural processes, and the values of RSPCr did not obviously change.
Due to the barrier effect by cascading dams, the heavy-metal pollution and ecological risk demonstrated the fragmentation trends from the upper stream to downstream in the Lancang River [37]. Otherwise, some research reported that sediment properties such as pH and organic materials can also affect the speciation, distribution pattern, and transportation of heavy-metal contamination [23].

5. Conclusions

In this study, the speciation distribution characteristic and ecological risk of heavy metals were investigated in the Manwan and Dachaoshan cascading dams. After the cascading dams operation in 2016, the sedimentary environment had remained relatively stable, and the grain sizes were clayey silt to sand–silt–clay in the lacustrine zone. The operation of cascading dams has obvious accumulation effects on heavy-metal contamination in surface sediments. Along the longitudinal gradient, the lacustrine zone had relatively higher contamination of heavy metals than the transitional and riverine zones. The correlation analysis (CA) and principal component analysis (PCA) demonstrated that the heavy metals had a different source and spatial distribution in cascading dams. Therefore, long-term and fixed-point monitoring should be carried out to explore the heavy-metal-contamination variations in cascading dams.

Author Contributions

Conceptualization, J.L.; methodology, J.L. and A.Z.; software, J.L.; validation, J.L.; formal analysis, A.Z. and J.L.; investigation, J.L., H.X., and X.Y.; resources, J.L. and H.X.; data curation, J.L.; writing—original draft preparation, J.L.; writing—review and editing, J.L.; visualization, J.L.; supervision, J.L.; project administration, J.L.; funding acquisition, J.L. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Natural Science Foundation of China, grant number 51509116, and Central Public-Interest Scientific Institution Basal Research Fund of China, grant number WTI-62203.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Location of surface sediment sampling sites in Manwan (M) and Dachaoshan (D) cascading dams.
Figure 1. Location of surface sediment sampling sites in Manwan (M) and Dachaoshan (D) cascading dams.
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Figure 2. Shepard triangle classification diagram of surface sediment sampling sites in Manwan (M) and Dachaoshan (D) cascading dams.
Figure 2. Shepard triangle classification diagram of surface sediment sampling sites in Manwan (M) and Dachaoshan (D) cascading dams.
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Figure 3. Speciation of heavy metal in surface sediments of Manwan (M) and Dachaoshan (D) cascading dams. A = Dry season, April 2016. O = rainy season, October 2016; F1 = exchangeable and carbonate bound; F2 = Fe/Mn oxide bound; F3 = organic substance bound; F4 = sulfide bound; F5 = residual; total = total concentration of heavy metals.
Figure 3. Speciation of heavy metal in surface sediments of Manwan (M) and Dachaoshan (D) cascading dams. A = Dry season, April 2016. O = rainy season, October 2016; F1 = exchangeable and carbonate bound; F2 = Fe/Mn oxide bound; F3 = organic substance bound; F4 = sulfide bound; F5 = residual; total = total concentration of heavy metals.
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Figure 4. Ratio of secondary phase and primary phase (RSP) of heavy metals in Manwan (M) and Dachaoshan (D) cascading dams. A = dry season, April 2016. O = rainy season, October 2016.
Figure 4. Ratio of secondary phase and primary phase (RSP) of heavy metals in Manwan (M) and Dachaoshan (D) cascading dams. A = dry season, April 2016. O = rainy season, October 2016.
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Figure 5. Principal components 1 and 2 of heavy metals in Manwan (M) and Dachaoshan (D) cascading dams.
Figure 5. Principal components 1 and 2 of heavy metals in Manwan (M) and Dachaoshan (D) cascading dams.
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Table 1. Pearson correlation coefficient between heavy metals in Manwan (M) and Dachaoshan (D) cascading dams. ** means significant correlation at 0.01 level (bilateral); * means significant correlation at 0.05 level (bilateral).
Table 1. Pearson correlation coefficient between heavy metals in Manwan (M) and Dachaoshan (D) cascading dams. ** means significant correlation at 0.01 level (bilateral); * means significant correlation at 0.05 level (bilateral).
AsCdCrCuPbZnFe
As1.000
Cd0.584 *1.000
Cr0.4030.1421.000
Cu0.645 **0.722 **0.580 *1.000
Pb0.741 **0.673 **0.592 **0.821 **1.000
Zn0.3840.872 **0.0650.660 **0.601 **1.000
Fe0.2720.0190.601 **0.521 *0.383−0.0221.000
Table 2. Principal component analysis (PCA) of heavy metals in Manwan (M) and Dachaoshan (D) cascading dams.
Table 2. Principal component analysis (PCA) of heavy metals in Manwan (M) and Dachaoshan (D) cascading dams.
Heavy MetalsRotated Component Matrix
Component 1Component 2
As0.6490.433
Cd0.962−0.008
Cr0.1470.876
Cu0.7560.567
Pb0.7540.539
Zn0.921−0.106
Fe−0.1050.871
Eigenvalues4.0821.610
% of variance58.31423.001
Cumulative %58.31481.316
Table 3. Ratio of secondary phase and primary phase (RSP) variations of heavy metals in Manwan (M) and Dachaoshan (D) cascading dams.
Table 3. Ratio of secondary phase and primary phase (RSP) variations of heavy metals in Manwan (M) and Dachaoshan (D) cascading dams.
DamHabitatAs (Mean)Cd (Mean)Cr (Mean)Cu (Mean)Pb (Mean)Zn (Mean)
201320162013201620132016201320162013201620132016
Manwan (M)Lacustrine zone0.661.349.495.640.160.232.120.714.580.521.481.57
Transitional zone0.551.1010.672.390.130.162.380.484.150.432.671.40
Riverine zone0.590.194.001.030.100.351.210.291.430.251.270.64
Dachaoshan (D)Lacustrine zone0.870.315.060.570.190.301.090.352.000.330.560.49
Transitional zone0.840.503.910.550.200.471.230.382.160.270.500.45
Riverine zone0.480.503.720.340.200.211.330.281.320.270.870.32
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Li, J.; Zhao, A.; Xuan, H.; You, X. Speciation Distribution Characteristic and Ecological Risk of Heavy Metals in Surface Sediments of Cascading Hydropower Dams in Lancang River. Water 2022, 14, 3248. https://doi.org/10.3390/w14203248

AMA Style

Li J, Zhao A, Xuan H, You X. Speciation Distribution Characteristic and Ecological Risk of Heavy Metals in Surface Sediments of Cascading Hydropower Dams in Lancang River. Water. 2022; 14(20):3248. https://doi.org/10.3390/w14203248

Chicago/Turabian Style

Li, Jinpeng, Aidong Zhao, Hao Xuan, and Xiaoguang You. 2022. "Speciation Distribution Characteristic and Ecological Risk of Heavy Metals in Surface Sediments of Cascading Hydropower Dams in Lancang River" Water 14, no. 20: 3248. https://doi.org/10.3390/w14203248

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