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Multi-element geochemistry of sediments from the Pearl River system, China
Applied Geochemistry 16 (2001) 1251±1259
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Multi-element geochemistry of sediments from the Pearl River system, China Chaosheng Zhang *, Lijun Wang Institute of Geography, Chinese Academy of Sciences, Beijing 100101, China Received 24 May 2000; accepted 15 December 2000 Editorial handling by C. Reimann
Abstract Sediment samples were taken along the West, North, and East rivers of the Pearl River system at 28 locations in 1998, and a total of 49 elements were determined by ICP±AES, ICP±MS and INAA. The probability features of the datasets were studied, and the average concentrations of these elements in sediments of the three rivers were calculated. Signi®cant dierences in element concentrations among the three rivers were observed and the results were con®rmed by statistical tests including analysis of variance (ANOVA), Kruskal±Wallis test, and t-test. Spatial distribution maps of element concentrations were produced using a geographical information system (GIS). The immobile trace elements (such as Sc, Ti, V, Cr, Mn, Fe, Co, and Ni) are enriched in the West River where limestone dominates the rock types in the watershed. Because of the strong weathering, immobile trace elements are enriched and reside in secondary minerals of the weathering products. All three rivers have high concentrations of rare earth elements (REEs) because of strong weathering, but relatively higher concentrations of REEs are observed in sediments of the East River where granite dominates the rock type. Granite contains high concentrations of REEs and the sediments have inherited this feature from their bedrock. Alkaline element (Li, Na, K, Rb, and Cs) concentrations are elevated in sediments of the East River, these may reside in granitic primary minerals. Relatively high concentrations of alkaline earth elements (Mg, Ca, Sr, and Ba) are observed in the West River, inherited from the limestone bedrock. High Pb and Bi concentrations are found in the North River and are caused by Pb mineralization and the discharge of a smelter in the upper reaches of the river. However, statistical tests did not indicate a signi®cant dierence between Pb concentrations in the North River and the other two rivers, which suggests that statistical results should be carefully used and explained. # 2001 Published by Elsevier Science Ltd.
1. Introduction The chemistry of river sediments has been receiving much attention for a number of years as it re¯ects the natural processes and human activities in the watershed, and studies of the element concentrations can contribute to a better understanding of these processes. The bioavailability of elements in sediments has been widely studied (e.g. Campbell et al., 1988; Burton Jr., 1991), and
* Corresponding author at current address: Department of Geography, National University of Ireland, Galway, Ireland. Fax: +353-91-525700. E-mail address: [email protected] (C. Zhang).
much attention has been paid to heavy metals (e.g. Fergusson, 1990; Chen and Zhou, 1992) because heavy metal pollution in the aquatic environment is a problem world-wide. The Zhujiang (Pearl) River is one of the major rivers in China, with a length of 2214 km and a drainage area of 453,690 km2. It ¯ows to the South China Sea, and consists of three main rivers: the Xijiang (West) River, the Beijiang (North) River, and the Dongjiang (East) River. The lower reaches of the three rivers form the Pearl River Delta (Figs. 1 and 2). The West River basin is dominated by limestone, whilst in the East River basin, granite and shales are the main rock types. The upper reaches of the West River drain the world famous karstic limestone areas in south China, whereas the East
0883-2927/01/$ - see front matter # 2001 Published by Elsevier Science Ltd. PII: S0883-2927(01)00007-5
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C. Zhang, L. Wang / Applied Geochemistry 16 (2001) 1251±1259
Fig. 1. Simpli®ed rock type distribution in the Pearl River basin.
Fig. 2. Sampling locations of sediments from the Pearl River system.
C. Zhang, L. Wang / Applied Geochemistry 16 (2001) 1251±1259
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River drains the south China granite area. The North River basin is composed of dierent rock types, including limestone, shales, clastic rocks and granite (Fig. 1). The climate of the Pearl River system is humid, with an annual average temperature of about 22 C. In summer, it is around 28 C, and in winter, about 14 C. The annual precipitation is more than 1500 mm (Liu, 1998). In this study, concentrations of 49 chemical elements in sediments from the three rivers of the Pearl River system are reported, and the dierences in concentrations among the three rivers are examined using statistical methods and GIS mapping.
9000 from Thermo-Jarrell-Ash Company, USA, and the ICP±MS instrument was the PQII Turbo, VG, UK. For INAA, samples were irradiated at a ¯ux of 61013 neutrons/cm2/s for 24 h in a nuclear reactor, and analyzed by a Ge detector Ð multichannel analyzer (PCA-II) Ð microcomputer system. The elements determined in this study are shown in Table 1. The Chinese national standard sediment samples GSD-1, GSD-4 and soil sample of GSS-3 were used to monitor the analyses. The results from the analyses were consistent with the reference values, with the differences for most elements less than 10% (many of which were less than 5%) (Fig. 3).
2. Methods
2.3. Data treatment
2.1. Sampling
The raw data were visually checked, and the concentration of Zn in sample No. 1 was found to be abnormally high. The result from ICP±AES and ICP± MS was 1090 and 991 mg/kg, respectively, while the median value for the Pearl River was 186 mg/kg (see Table 3). Therefore, this value was regarded as an outlier, and was replaced by the average values of the Zn concentrations of sample Nos. 2 and 3. Further analysis may be carried out to establish the reason for the high Zn value of this sample. All the other data were accepted for the following statistical analyses. For elements determined by both ICP±AES and ICP±MS, the average values from the two methods were used, as the results from the two methods are consistent (Fig. 4). Data probability distribution patterns were analyzed by the Kolmogorov±Smirnov test. The dierences in element concentrations between the three rivers were statistically tested by analysis of variance (ANOVA), the Kruskal± Wallis test and the t-test.
In June 1998, a total of 28 sediment samples were collected along the West, North, and East rivers, and the Pearl River delta from the locations shown in Fig. 2. The samples in the delta were grouped according to the location of main channels of the three rivers. Samples Nos. 1 to 10 were located on the West River (n=10); the North River had samples Nos. 11 to 21 (n=11), and samples Nos. 22 to 28 were taken from the East River (n=7). The locations were relatively evenly distributed along the river channels, and were chosen based on trac conditions. Most of the samples were ®ne-grained mud. About 1 kg of each sample was taken near the bank under a water depth of 20 to 100 cm. The samples were stored in plastic bags and sent to a laboratory. They were air-dried, and then passed through a 20 mesh nylon sieve (about 1 mm aperture size) prior to analysis. 2.2. Analytical methods About 0.1 g of each sediment sample was taken and precisely weighed, and then digested by multi-acid in a Pt crucible with electric heating. The digested samples were analyzed by inductively coupled plasma±atomic emission spectrometry (ICP±AES) and inductively coupled plasma±mass spectrometry (ICP±MS). Of the 28 samples, 6 sediment samples (2 from each river) were chosen for instrumental neutron activation analysis (INAA). The ICP±AES equipment used was the ICAP-
3. Results and discussion 3.1. Probability distribution of the datasets For calculation of the mean value and application of statistical methods, the probability distribution features of a dataset should be studied. The distribution parameters of skewness and kurtosis of the datasets were calculated, and are illustrated in Table 2. The sig-
Table 1 Elements determined by ICP±AES, ICP±MS, and INAA Detection method Elements detected ICP±AES ICP±MS INAA
Al, Ba, Ca, Ce, Co, Cr, Cu, Fe, Ga, K, La, Li, Mg, Mn, Mo, Na, Nb, Ni, P, Pb, Sc, Sn, Sr, Ta, Ti, V, Y, Yb, Zn Ba, Bi, Ce, Co, Cr, Cs, Cu, Dy, Er, Eu, Gd, Ho, La, Lu, Nb, Nd, Ni, Pb, Pr, Rb, Sm, Sn, Sr, Ta, Tb, Th, Ti, Tm, U, Y, Yb, Zn As, Hf, Sb, Zr
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centrations of the 4 elements As, Hf, Sb, and Zr, which were analyzed by INAA, are shown in Table 4. The dierences between the three rivers are obvious. Concentrations of most of the immobile trace elements, especially the transition elements in the fourth period of the periodic table including Sc, Ti, V, Cr, Mn, Fe, Co, and Ni are highest in sediments of the West River. Compared with average shales (Haskin et al., 1968; Taylor and McLennan, 1985), high concentrations of rare earth elements (REEs: La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y) are observed in the Pearl River system, but they are relatively more enriched in sediments of the East River than those of the other two rivers. Very high Pb and Bi concentrations are found in the North River. Relatively high concentrations of alkali metals (Li, Na, K, Rb, and Cs) and the immobile elements Zr and Hf are observed in the East River, and concentrations of alkaline earth metals (Mg, Ca, Sr, Ba) are comparatively high in the West River. The enrichment of the immobile trace elements, such as heavy metals, in sediments of a limestone area has been observed in the Yangtze River basin in the authors' previous studies (Zhang et al., 1995, 1998), and the results in the West River can be explained in the same way. Limestone is easily weathered under humid and warm climate conditions. The immobile elements are released from limestone and reside in the weathering products, such as clay minerals. In the whole area of the Pearl River system, strong weathering has also caused high concentrations of REEs in the sediments. The sediments in the East River have inherited the feature of high concentrations of REEs from the granitic parent rock and the REEs are held in primary heavy minerals. The very high concentrations of Pb and Bi in the North River are probably the result of mineralization and industrial activities. Lead mineralization in the upper
Fig. 3. Comparison between measured values by ICP±MS and reference values of GSD1.
ni®cance levels of Kolmogorov±Smirnov test for the normality of the datasets are also shown in Table 2. Most of the absolute values for skewnesses and kurtoses are small, and are close to the reference value of 0 for a normal distribution. However, some of the elements, such as Ba, Bi, Cu, Pb, have rather high skewnesses and kurtoses. The results from the Kolmogorov± Smirnov test show that Ba, Bi, and Pb do not follow a normal distribution at a signi®cance level of less than 0.05, while all the other 42 elements passed the normality test. The high skewness and non-normality of Ba, Bi, and Pb imply that there are some very high values in the datasets, which may relate to environmental factors, such as pollution or mineralization. 3.2. Mean concentrations of multi-elements in sediments As the samples were taken from three dierent river channels, the element concentrations in the three rivers may be considered separately. The arithmetic mean values for the three rivers and the average and median values for all samples were calculated (Table 3). Con-
Table 2 Distribution parameters of the datasets: skewness, kurtosis and signi®cance probability of Kolmogorov±Smirnov (K±S) test Al Skewness Kurtosis K±S test sig.
0.12 0.44 0.92 Ho
Skewness Kurtosis K±S test sig.
0.59 0.12 0.93 Rb
Skewness Kurtosis K±S test sig.
0.03 1.44 0.56
Ba 1.42 1.13 0.01 K 0.02 0.89 0.99 Sc 0.34 2.14 0.95
Bi 2.09 3.65 0.02 La 0.70 0.49 0.48 Sm 0.44 0.53 0.92
Ca 0.81 0.58 0.24 Li 1.39 2.54 0.48 Sn 0.28 2.95 0.79
Ce 0.32 0.60 0.87 Lu 0.39 0.10 0.98 Sr 0.32 1.04 0.68
Co 0.16 0.57 0.96 Mg 0.20 0.39 0.99 Ta 0.58 2.91 0.71
Cr 0.02 0.09 0.97 Mn 0.45 0.48 0.72 Tb 0.62 0.17 0.90
Cs 0.85 0.89 0.66 Mo 0.25 0.23 1.00 Th 0.22 1.22 0.82
Cu 1.78 3.74 0.26 Na 0.90 2.30 0.68 Ti 0.19 0.06 0.88
Dy 0.28 0.40 0.76 Nb 0.73 0.73 0.64 Tm 0.86 0.22 0.32
Er
Eu
0.40 0.02 0.52 Nd
1.12 1.32 0.61 Ni
0.37 0.60 0.96 U 0.43 1.14 0.85
Fe
0.31 0.78 1.00 V
0.63 1.90 0.85 P
0.36 1.43 0.98 Pb
0.20 0.31 1.00 Y
0.03 0.67 0.91
Ga
0.45 0.00 0.54
2.09 4.79 0.07 Yb 0.37 0.13 0.95
Gd 0.35 0.42 0.90 Pr 0.61 0.45 0.80 Zn 0.91 0.34 0.57
C. Zhang, L. Wang / Applied Geochemistry 16 (2001) 1251±1259
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Table 3 Average concentrations of the elements in sediments of the West, North, and East rivers in the Pearl River system (units: mg/kg, except Al, Ca, Fe, K, Mg, Na:%)
All (average, n=28) All (median, n=28) West River (average, n=10) North River (average, n=11) East River (average, n=7)
All (average, n=28) All (median, n=28) West River (average, n=10) North River (average, n=11) East River (average, n=7)
All (average, n=28) All (median, n=28) West River (average, n=10) North River (average, n=11) East River (average, n=7)
Al
Ba
Bi
Ca
Ce
Co
Cr
Cs
Cu
Dy
Er
Eu
Fe
Ga
Gd
8.50 8.42 8.24 7.84 9.93
444 422 502 410 415
5.02 2.92 1.96 9.08 3.02
0.81 0.66 1.12 0.76 0.43
114 114 106 105 140
16.2 15.8 19.1 15.0 14.0
71.4 69.6 87.4 65.3 58.1
12.4 12.6 10.3 13.4 13.7
54.5 49.4 54.1 62.1 43.3
5.99 5.89 5.82 5.34 7.26
3.25 3.23 3.18 2.90 3.90
1.70 1.76 1.81 1.49 1.88
4.42 4.47 4.96 4.21 3.96
13.1 13.0 14.9 12.4 11.7
8.95 8.62 8.61 7.89 11.12
Ho
K
La
Li
Lu
Mg
Mn
Mo
Na
Nb
Nd
Ni
P
Pb
Pr
1.19 1.14 1.17 1.06 1.40
1.97 2.01 1.84 1.95 2.18
58.9 56.1 54.2 53.1 74.6
40.1 38.3 36.0 41.9 43.1
0.469 0.460 0.461 0.422 0.552
0.715 0.720 0.827 0.734 0.525
908 936 1034 960 646
2.47 2.46 2.42 2.30 2.80
1.00 1.03 1.02 0.93 1.07
24.6 24.8 25.0 22.4 27.4
50.1 49.9 47.8 46.0 60.0
37.7 37.7 43.4 34.7 34.0
715 704 812 657 667
97.1 85.8 79.6 118.1 89.4
13.2 12.7 12.2 12.0 16.5
Rb
Sc
Sm
Sn
Sr
Ta
Tb
Th
Ti
Tm
U
V
Y
Yb
Zn
151 147 123 149 194
8.98 8.97 9.78 8.49 8.60
9.38 9.17 8.84 8.54 11.48
1.46 1.46 1.48 1.40 1.54
68.4 67.1 86.3 62.9 51.7
1.83 1.82 2.02 1.76 1.67
1.19 1.15 1.15 1.06 1.45
25.7 24.7 20.6 25.0 33.8
5812 5723 6796 5237 5308
0.503 0.468 0.484 0.455 0.605
6.33 5.95 4.78 6.17 8.81
113 110 140 103 89
35.0 33.9 34.0 30.9 43.0
2.66 2.58 2.61 2.41 3.11
202 186 206 203 196
Table 4 Concentrations of As, Hf, Sb, and Zr in the sediments (in mg/ kg) Sample no.
River
As
Hf
Sb
Zr
4 8 15 21 22 25
West West North North East East
46.6 43.5 96.8 39.5 15.7 27.4
9.12 7.71 6.24 8.90 12.70 8.20
5.02 10.32 6.17 6.44 0.90 1.68
282 293 259 298 473 266
44.9
8.81
5.09
312
Average Fig. 4. Comparison of the Ba concentrations detected by ICP± AES and ICP±MS.
reaches of the North River is signi®cant, and there are two major Pb mines at Lechang and Fankou, located north of Shaoguan City (Fig. 2). The Shaoguan Pb smelter discharges large quantities of Pb into the North River, e.g. in 1993, the discharge of Pb from the smelter was 17.98 tons (Chen and Lu, 1994). The discharges of Pb from the Lechang and Fankou mines were 2.315 and 2.728 tons in 1993, respectively (Chen and Lu, 1994). The element Bi, which is known to be usually associated with lead deposits (Garavelli et al., 1997) is also enriched in the North River. The relatively high concentrations of the alkali metals (Li, Na, K, Rb, and Cs) in the East River have the same origin as REEs, because granites have high concentrations of alkali metals. The alkali metals are quite mobile in the aquatic environ-
ment, but they may reside in the primary light minerals, such as feldspar. The immobile elements Zr and Hf may reside in the primary heavy minerals of granites, such as Zircon, in the East River. Relatively high concentrations of alkaline earth elements (Mg, Ca, Sr, and Ba) in the sediments of the West River are related to the limestone bedrock which contains high concentrations of these elements, even though the strong weathering may remove a large part of them. 3.3. Spatial distribution of the elements Fig. 5 illustrates the spatial distribution of Pb and Bi concentrations in sediments of the West, North, and East rivers. Signi®cantly high concentrations of both Pb and Bi are observed in the upper and middle reaches of
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C. Zhang, L. Wang / Applied Geochemistry 16 (2001) 1251±1259
Fig. 5. Spatial distribution of Pb and Bi concentrations in sediments of the West, North, and East rivers.
the North River, while concentrations in all the other samples are not high. The mines of Lechang and Fankou and the Shaoguan Smelter are geographically located in the upper reaches of the North River. The map, produced by GIS, supports the conclusion that mineralization and industrial activities are the main sources of the high Pb and Bi concentrations in the North River. Fig. 6. shows the spatial distribution of REEs in sediments of the study area. As all the individual REEs have similar spatial distribution maps, the distribution map of REE [the total concentrations of REEs from La (57) to Lu (71)] is shown. Strong weathering has caused the high concentrations of REEs in the Pearl River system, but dierences among the three rivers exist. All the sampling sites in the East River have very high concentrations of REE, and the samples from the West and North rivers have relatively lower REE, with minor exceptions. The dierences of REE among the three rivers are clearly visualized from the map. 3.4. Statistical tests for the dierences among the element concentrations in sediments of the three rivers To further study the dierences of the element concentrations among the three rivers, statistical tests were applied. The 28 samples were divided into 3 groups
according to the river where they were taken from (see Section 2.1). Analysis of variance (ANOVA) is used to test if there are signi®cant dierences among the three rivers. Most of the variables satis®ed the homogeneity of variance test, with the Levene statistic signi®cance level being higher than 0.05 (Table 5), and thus ANOVA was applied. However, Ba, Bi, Cs, Cu, Eu, Nb, Pb, Ti, and V failed, and the non-parametric Kruskal± Wallis test was applied for these variables instead. Both the results of ANOVA and Kruskal±Wallis tests are shown in Table 5. Most of the elements have statistically signi®cant differences among the three rivers with signi®cance levels of lower than 0.05. The elements Ba, Cu, Li, Na, Pb, Sn, and Zn do not have signi®cantly dierent concentrations among the three rivers, shown by both the ANOVA and Kruskal-Wallis methods at the signi®cance levels of greater than 0.05. To compare the dierences among the three rivers in detail, the Duncan method for multiple comparison of ANOVA was applied.For those variables that cannot pass the homogeneity of variance test, the t-test for equality of means with equal variances not being assumed was carried out, and the results are listed in Table 6. Based on the two methods, the elements that have signi®cantly dierent concentrations among the three rivers are shown in Table 7.
C. Zhang, L. Wang / Applied Geochemistry 16 (2001) 1251±1259
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Fig. 6. Spatial distribution of REE in sediments of the West, North, and East rivers.
Table 5 Signi®cance probabilities of the Levene statistic, one-way ANOVA and Kruskal±Wallis test
Levene statistic sig. One-way ANOVA sig. Kruskal±Wallis test sig.
Levene statistic sig. One-way ANOVA sig. Kruskal±Wallis test sig.
Levene statistic sig. One-way ANOVA sig. Kruskal±Wallis test sig.
Al
Ba
Bi
Ca
Ce
Co
Cr
Cs
Cu
Dy
Er
Eu
Fe
Ga
Gd
0.92 0.01 0.01
0.00 0.06 0.12
0.00 0.00 0.00
0.06 0.00 0.00
0.64 0.00 0.00
0.21 0.01 0.00
0.15 0.00 0.00
0.03 0.09 0.04
0.00 0.16 0.10
0.29 0.00 0.00
0.54 0.00 0.00
0.02 0.01 0.02
0.43 0.00 0.00
0.46 0.00 0.00
0.78 0.00 0.00
Ho
K
La
Li
Lu
Mg
Mn
Mo
Na
Nb
Nd
Ni
P
Pb
Pr
0.31 0.00 0.01
0.12 0.03 0.03
0.65 0.00 0.00
0.22 0.14 0.06
0.89 0.00 0.00
0.29 0.00 0.00
0.32 0.01 0.02
0.74 0.01 0.02
0.72 0.48 0.47
0.01 0.05 0.03
0.62 0.00 0.00
0.49 0.01 0.01
0.13 0.05 0.02
0.01 0.09 0.11
0.99 0.00 0.00
Rb
Sc
Sm
Sn
Sr
Ta
Tb
Th
Ti
Tm
U
V
Y
Yb
Zn
0.10 0.00 0.00
0.25 0.03 0.00
0.71 0.00 0.00
0.30 0.25 0.31
0.05 0.00 0.00
0.58 0.02 0.00
0.53 0.00 0.00
0.14 0.00 0.00
0.01 0.02 0.02
0.37 0.00 0.00
0.19 0.00 0.00
0.04 0.00 0.00
0.26 0.00 0.00
0.27 0.00 0.00
0.91 0.96 0.78
Out of the 45 elements, a total of 35 elements have shown signi®cantly dierent concentrations between the West River and the East River, which demonstrates that the dierences between these two rivers are greatest. The dierences of the rock types within these two rivers may be the major factor for this phenomenon. The dier-
ences between the West and North rivers are relatively slight. Most of REEs, which are enriched in the East River, show signi®cant dierences between the East River and the North River. For most of the elements, the results from the mathematical calculation, GIS visualization, and the statistical
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C. Zhang, L. Wang / Applied Geochemistry 16 (2001) 1251±1259
Table 6 Signi®cance levels of t-test for equality of means (equal variances not assumed)
West River vs. North River West River vs. East River North River vs. East River
Ba
Bi
Cs
Cu
Eu
Nb
Pb
Ti
V
0.06 0.06 0.84
0.01 0.06 0.02
0.09 0.01 0.88
0.39 0.08 0.08
0.02 0.43 0.01
0.20 0.04 0.02
0.06 0.33 0.13
0.02 0.00 0.89
0.00 0.00 0.18
Table 7 Results of multiple comparison of ANOVA (Duncan method) and t-test, showing the elements which have signi®cantly dierent concentrations among the West, North, and East rivers West River
North River
North River
Bi Ca Co Cr Eu Fe Ga Ni P Sc Sr Ta Ti V
East River
Al Ca Ce Co Cr Cs Dy Er Fe Ga Gd Ho K La Lu Mg Mn Mo Nb Nd Ni P Rb Sc Sm Sr Ta Tb Th Ti Tm U V Y Yb
tests are consistent. However, inconsistent results are observed for Pb. The North River has very high concentrations of Pb (Table 3 and Fig. 5), but the statistical tests of both ANOVA and t-test conclude that that the dierences of Pb concentrations among the three rivers are insigni®cant (with the signi®cance level >0.05) (Tables 5 and 6). When the spatial distribution map is looked at (Fig. 5), the high Pb concentrations are observed only in the upper and middle reaches of the North River (sample Nos. 11 to 15). In the lower reaches of the North River, the Pb concentrations are not high. As all the samples in the North River were in one group for the above statistical tests, this mixed information has handicapped the statistical methods. Therefore, the statistical tests did not highlight this feature, which suggests that statistical methods should be used with caution. 4. Conclusions Concentrations of 49 elements in sediments from the West, North, and East rivers of the Pearl River system were detected by ICP±AES, ICP±MS, and INAA, and reported in this study. Signi®cant dierences in the concentrations for most elements among the three rivers are observed by statistical analyses. GIS mapping technology is helpful in explaining the spatial relationships between human and environmental sources of elements and the element concentrations in river sediments. Most of the immobile trace elements are elevated in the West River, and a combination of strong weathering and the easily weathered limestone rock type is the reason for the enrichment of the immobile elements in sediments of the area. High concentrations of REEs are
Al Bi Ce Dy Er Eu Gd Ho La Lu Mg Mn Mo Nb Nd Rb Sm Tb Th Tm U Y Yb
observed in the Pearl River system in general, but relatively higher REE concentrations are found in the East River where granite is the main rock type. Granite contains high concentrations of REEs and the sediments have inherited this feature from their bedrock. Alkali metals are elevated in the East River, again deriving from the granites. Relatively high concentrations of alkaline earth elements are observed in the West River, re¯ecting the limestone bedrock. High Pb and Bi concentrations are found in the North River associated with Pb mineralization and the discharge from the Shaoguan Smelter. Statistical tests did not highlight the high concentrations of Pb in the North River compared with the other two rivers, which suggests that statistical tests should be used with caution when examining spatial geochemical data. Acknowledgements This study was supported by the National Natural Science Foundation of China (No. 49601016) and the ``Hundreds of Talents Program'' of the Chinese Academy of Sciences. Discussion with Professor Gerald Lalor, and helpful comments from the two reviewers, are acknowledged.
References Burton Jr., G.A., 1991. Annual review: assessing the toxicity of freshwater sediments. Environmental Toxicology and Chemistry 10, 1585±1627. Campbell, P.G.C., Lewis, A.G., Chapman, P.M., Crowder, A.A., Fletcher, W.K., Imber, B., Luoma, S.N., Stokes, P.M.,
C. Zhang, L. Wang / Applied Geochemistry 16 (2001) 1251±1259 Winfrey, M., 1988. Biologically available metals in sediments. NRCC/CNRC, Ottawa, Canada. Chen, C.Y. and Lu, Z.B. (editors-in-chief), 1994. Year Book of Environmental Monitoring, Guangdong Province, 1994. Guangdong Environmental Monitoring Center, China. p. 459 (in Chinese). Chen, J.S., Zhou, J.Y. (Eds.), 1992. Studies on Heavy Metals in the Aquatic Environment in China. China Environmental Sciences Press, Beijing (in Chinese). Fergusson, J.E., 1990. The Heavy Elements: Chemistry, Environmental Impact and Health Eects. Pergamon Press, Oxford (276±282). Garavelli, A., Laviano, R., Vurro, F., 1997. Sublimate deposition from hydrothermal ¯uids at the Fossa crater Ð Vulcano, Italy. European Journal of Mineralogy 9, 423±432. Haskin, L.A., Haskin, M.A., Frey, F.A., Wildeman, T.R.,
1259
1968. Relative and absolute terrestrial abundances of the rare earths. In: Ahrens, L.H. (Ed.), Origin and Distribution of the Elements. Pergamon Press, Oxford, pp. 889±912. Liu, M.G. (editor-in-chief), 1998. Atlas of physical geography, China. Version 2. Beijing: China Map Press, p. 252 (in Chinese). Taylor, S.R., McLennan, S.M., 1985. The Continental Crust: Its Composition and Evolution. Blackwell, Oxford. Zhang, C.S., Zhang, S., Wang, L.J., Wang, L.Z., 1998. Comparison of geochemistry of metals in sediments from some typical rock areas. Acta Scientiae Circumstantiae 18, 172± 176. Zhang, C.S., Zhang, S., Zhang, L.C., Wang, L.J., 1995. Background contents of heavy metals in sediments of the Changjiang River system and their calculation methods. J. Environ. Sci. 7, 422±429.
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Multi-element geochemistry of sediments from the Pearl River system, China Chaosheng Zhang *, Lijun Wang Institute of Geography, Chinese Academy of Sciences, Beijing 100101, China Received 24 May 2000; accepted 15 December 2000 Editorial handling by C. Reimann
Abstract Sediment samples were taken along the West, North, and East rivers of the Pearl River system at 28 locations in 1998, and a total of 49 elements were determined by ICP±AES, ICP±MS and INAA. The probability features of the datasets were studied, and the average concentrations of these elements in sediments of the three rivers were calculated. Signi®cant dierences in element concentrations among the three rivers were observed and the results were con®rmed by statistical tests including analysis of variance (ANOVA), Kruskal±Wallis test, and t-test. Spatial distribution maps of element concentrations were produced using a geographical information system (GIS). The immobile trace elements (such as Sc, Ti, V, Cr, Mn, Fe, Co, and Ni) are enriched in the West River where limestone dominates the rock types in the watershed. Because of the strong weathering, immobile trace elements are enriched and reside in secondary minerals of the weathering products. All three rivers have high concentrations of rare earth elements (REEs) because of strong weathering, but relatively higher concentrations of REEs are observed in sediments of the East River where granite dominates the rock type. Granite contains high concentrations of REEs and the sediments have inherited this feature from their bedrock. Alkaline element (Li, Na, K, Rb, and Cs) concentrations are elevated in sediments of the East River, these may reside in granitic primary minerals. Relatively high concentrations of alkaline earth elements (Mg, Ca, Sr, and Ba) are observed in the West River, inherited from the limestone bedrock. High Pb and Bi concentrations are found in the North River and are caused by Pb mineralization and the discharge of a smelter in the upper reaches of the river. However, statistical tests did not indicate a signi®cant dierence between Pb concentrations in the North River and the other two rivers, which suggests that statistical results should be carefully used and explained. # 2001 Published by Elsevier Science Ltd.
1. Introduction The chemistry of river sediments has been receiving much attention for a number of years as it re¯ects the natural processes and human activities in the watershed, and studies of the element concentrations can contribute to a better understanding of these processes. The bioavailability of elements in sediments has been widely studied (e.g. Campbell et al., 1988; Burton Jr., 1991), and
* Corresponding author at current address: Department of Geography, National University of Ireland, Galway, Ireland. Fax: +353-91-525700. E-mail address: [email protected] (C. Zhang).
much attention has been paid to heavy metals (e.g. Fergusson, 1990; Chen and Zhou, 1992) because heavy metal pollution in the aquatic environment is a problem world-wide. The Zhujiang (Pearl) River is one of the major rivers in China, with a length of 2214 km and a drainage area of 453,690 km2. It ¯ows to the South China Sea, and consists of three main rivers: the Xijiang (West) River, the Beijiang (North) River, and the Dongjiang (East) River. The lower reaches of the three rivers form the Pearl River Delta (Figs. 1 and 2). The West River basin is dominated by limestone, whilst in the East River basin, granite and shales are the main rock types. The upper reaches of the West River drain the world famous karstic limestone areas in south China, whereas the East
0883-2927/01/$ - see front matter # 2001 Published by Elsevier Science Ltd. PII: S0883-2927(01)00007-5
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Fig. 1. Simpli®ed rock type distribution in the Pearl River basin.
Fig. 2. Sampling locations of sediments from the Pearl River system.
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River drains the south China granite area. The North River basin is composed of dierent rock types, including limestone, shales, clastic rocks and granite (Fig. 1). The climate of the Pearl River system is humid, with an annual average temperature of about 22 C. In summer, it is around 28 C, and in winter, about 14 C. The annual precipitation is more than 1500 mm (Liu, 1998). In this study, concentrations of 49 chemical elements in sediments from the three rivers of the Pearl River system are reported, and the dierences in concentrations among the three rivers are examined using statistical methods and GIS mapping.
9000 from Thermo-Jarrell-Ash Company, USA, and the ICP±MS instrument was the PQII Turbo, VG, UK. For INAA, samples were irradiated at a ¯ux of 61013 neutrons/cm2/s for 24 h in a nuclear reactor, and analyzed by a Ge detector Ð multichannel analyzer (PCA-II) Ð microcomputer system. The elements determined in this study are shown in Table 1. The Chinese national standard sediment samples GSD-1, GSD-4 and soil sample of GSS-3 were used to monitor the analyses. The results from the analyses were consistent with the reference values, with the differences for most elements less than 10% (many of which were less than 5%) (Fig. 3).
2. Methods
2.3. Data treatment
2.1. Sampling
The raw data were visually checked, and the concentration of Zn in sample No. 1 was found to be abnormally high. The result from ICP±AES and ICP± MS was 1090 and 991 mg/kg, respectively, while the median value for the Pearl River was 186 mg/kg (see Table 3). Therefore, this value was regarded as an outlier, and was replaced by the average values of the Zn concentrations of sample Nos. 2 and 3. Further analysis may be carried out to establish the reason for the high Zn value of this sample. All the other data were accepted for the following statistical analyses. For elements determined by both ICP±AES and ICP±MS, the average values from the two methods were used, as the results from the two methods are consistent (Fig. 4). Data probability distribution patterns were analyzed by the Kolmogorov±Smirnov test. The dierences in element concentrations between the three rivers were statistically tested by analysis of variance (ANOVA), the Kruskal± Wallis test and the t-test.
In June 1998, a total of 28 sediment samples were collected along the West, North, and East rivers, and the Pearl River delta from the locations shown in Fig. 2. The samples in the delta were grouped according to the location of main channels of the three rivers. Samples Nos. 1 to 10 were located on the West River (n=10); the North River had samples Nos. 11 to 21 (n=11), and samples Nos. 22 to 28 were taken from the East River (n=7). The locations were relatively evenly distributed along the river channels, and were chosen based on trac conditions. Most of the samples were ®ne-grained mud. About 1 kg of each sample was taken near the bank under a water depth of 20 to 100 cm. The samples were stored in plastic bags and sent to a laboratory. They were air-dried, and then passed through a 20 mesh nylon sieve (about 1 mm aperture size) prior to analysis. 2.2. Analytical methods About 0.1 g of each sediment sample was taken and precisely weighed, and then digested by multi-acid in a Pt crucible with electric heating. The digested samples were analyzed by inductively coupled plasma±atomic emission spectrometry (ICP±AES) and inductively coupled plasma±mass spectrometry (ICP±MS). Of the 28 samples, 6 sediment samples (2 from each river) were chosen for instrumental neutron activation analysis (INAA). The ICP±AES equipment used was the ICAP-
3. Results and discussion 3.1. Probability distribution of the datasets For calculation of the mean value and application of statistical methods, the probability distribution features of a dataset should be studied. The distribution parameters of skewness and kurtosis of the datasets were calculated, and are illustrated in Table 2. The sig-
Table 1 Elements determined by ICP±AES, ICP±MS, and INAA Detection method Elements detected ICP±AES ICP±MS INAA
Al, Ba, Ca, Ce, Co, Cr, Cu, Fe, Ga, K, La, Li, Mg, Mn, Mo, Na, Nb, Ni, P, Pb, Sc, Sn, Sr, Ta, Ti, V, Y, Yb, Zn Ba, Bi, Ce, Co, Cr, Cs, Cu, Dy, Er, Eu, Gd, Ho, La, Lu, Nb, Nd, Ni, Pb, Pr, Rb, Sm, Sn, Sr, Ta, Tb, Th, Ti, Tm, U, Y, Yb, Zn As, Hf, Sb, Zr
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centrations of the 4 elements As, Hf, Sb, and Zr, which were analyzed by INAA, are shown in Table 4. The dierences between the three rivers are obvious. Concentrations of most of the immobile trace elements, especially the transition elements in the fourth period of the periodic table including Sc, Ti, V, Cr, Mn, Fe, Co, and Ni are highest in sediments of the West River. Compared with average shales (Haskin et al., 1968; Taylor and McLennan, 1985), high concentrations of rare earth elements (REEs: La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y) are observed in the Pearl River system, but they are relatively more enriched in sediments of the East River than those of the other two rivers. Very high Pb and Bi concentrations are found in the North River. Relatively high concentrations of alkali metals (Li, Na, K, Rb, and Cs) and the immobile elements Zr and Hf are observed in the East River, and concentrations of alkaline earth metals (Mg, Ca, Sr, Ba) are comparatively high in the West River. The enrichment of the immobile trace elements, such as heavy metals, in sediments of a limestone area has been observed in the Yangtze River basin in the authors' previous studies (Zhang et al., 1995, 1998), and the results in the West River can be explained in the same way. Limestone is easily weathered under humid and warm climate conditions. The immobile elements are released from limestone and reside in the weathering products, such as clay minerals. In the whole area of the Pearl River system, strong weathering has also caused high concentrations of REEs in the sediments. The sediments in the East River have inherited the feature of high concentrations of REEs from the granitic parent rock and the REEs are held in primary heavy minerals. The very high concentrations of Pb and Bi in the North River are probably the result of mineralization and industrial activities. Lead mineralization in the upper
Fig. 3. Comparison between measured values by ICP±MS and reference values of GSD1.
ni®cance levels of Kolmogorov±Smirnov test for the normality of the datasets are also shown in Table 2. Most of the absolute values for skewnesses and kurtoses are small, and are close to the reference value of 0 for a normal distribution. However, some of the elements, such as Ba, Bi, Cu, Pb, have rather high skewnesses and kurtoses. The results from the Kolmogorov± Smirnov test show that Ba, Bi, and Pb do not follow a normal distribution at a signi®cance level of less than 0.05, while all the other 42 elements passed the normality test. The high skewness and non-normality of Ba, Bi, and Pb imply that there are some very high values in the datasets, which may relate to environmental factors, such as pollution or mineralization. 3.2. Mean concentrations of multi-elements in sediments As the samples were taken from three dierent river channels, the element concentrations in the three rivers may be considered separately. The arithmetic mean values for the three rivers and the average and median values for all samples were calculated (Table 3). Con-
Table 2 Distribution parameters of the datasets: skewness, kurtosis and signi®cance probability of Kolmogorov±Smirnov (K±S) test Al Skewness Kurtosis K±S test sig.
0.12 0.44 0.92 Ho
Skewness Kurtosis K±S test sig.
0.59 0.12 0.93 Rb
Skewness Kurtosis K±S test sig.
0.03 1.44 0.56
Ba 1.42 1.13 0.01 K 0.02 0.89 0.99 Sc 0.34 2.14 0.95
Bi 2.09 3.65 0.02 La 0.70 0.49 0.48 Sm 0.44 0.53 0.92
Ca 0.81 0.58 0.24 Li 1.39 2.54 0.48 Sn 0.28 2.95 0.79
Ce 0.32 0.60 0.87 Lu 0.39 0.10 0.98 Sr 0.32 1.04 0.68
Co 0.16 0.57 0.96 Mg 0.20 0.39 0.99 Ta 0.58 2.91 0.71
Cr 0.02 0.09 0.97 Mn 0.45 0.48 0.72 Tb 0.62 0.17 0.90
Cs 0.85 0.89 0.66 Mo 0.25 0.23 1.00 Th 0.22 1.22 0.82
Cu 1.78 3.74 0.26 Na 0.90 2.30 0.68 Ti 0.19 0.06 0.88
Dy 0.28 0.40 0.76 Nb 0.73 0.73 0.64 Tm 0.86 0.22 0.32
Er
Eu
0.40 0.02 0.52 Nd
1.12 1.32 0.61 Ni
0.37 0.60 0.96 U 0.43 1.14 0.85
Fe
0.31 0.78 1.00 V
0.63 1.90 0.85 P
0.36 1.43 0.98 Pb
0.20 0.31 1.00 Y
0.03 0.67 0.91
Ga
0.45 0.00 0.54
2.09 4.79 0.07 Yb 0.37 0.13 0.95
Gd 0.35 0.42 0.90 Pr 0.61 0.45 0.80 Zn 0.91 0.34 0.57
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Table 3 Average concentrations of the elements in sediments of the West, North, and East rivers in the Pearl River system (units: mg/kg, except Al, Ca, Fe, K, Mg, Na:%)
All (average, n=28) All (median, n=28) West River (average, n=10) North River (average, n=11) East River (average, n=7)
All (average, n=28) All (median, n=28) West River (average, n=10) North River (average, n=11) East River (average, n=7)
All (average, n=28) All (median, n=28) West River (average, n=10) North River (average, n=11) East River (average, n=7)
Al
Ba
Bi
Ca
Ce
Co
Cr
Cs
Cu
Dy
Er
Eu
Fe
Ga
Gd
8.50 8.42 8.24 7.84 9.93
444 422 502 410 415
5.02 2.92 1.96 9.08 3.02
0.81 0.66 1.12 0.76 0.43
114 114 106 105 140
16.2 15.8 19.1 15.0 14.0
71.4 69.6 87.4 65.3 58.1
12.4 12.6 10.3 13.4 13.7
54.5 49.4 54.1 62.1 43.3
5.99 5.89 5.82 5.34 7.26
3.25 3.23 3.18 2.90 3.90
1.70 1.76 1.81 1.49 1.88
4.42 4.47 4.96 4.21 3.96
13.1 13.0 14.9 12.4 11.7
8.95 8.62 8.61 7.89 11.12
Ho
K
La
Li
Lu
Mg
Mn
Mo
Na
Nb
Nd
Ni
P
Pb
Pr
1.19 1.14 1.17 1.06 1.40
1.97 2.01 1.84 1.95 2.18
58.9 56.1 54.2 53.1 74.6
40.1 38.3 36.0 41.9 43.1
0.469 0.460 0.461 0.422 0.552
0.715 0.720 0.827 0.734 0.525
908 936 1034 960 646
2.47 2.46 2.42 2.30 2.80
1.00 1.03 1.02 0.93 1.07
24.6 24.8 25.0 22.4 27.4
50.1 49.9 47.8 46.0 60.0
37.7 37.7 43.4 34.7 34.0
715 704 812 657 667
97.1 85.8 79.6 118.1 89.4
13.2 12.7 12.2 12.0 16.5
Rb
Sc
Sm
Sn
Sr
Ta
Tb
Th
Ti
Tm
U
V
Y
Yb
Zn
151 147 123 149 194
8.98 8.97 9.78 8.49 8.60
9.38 9.17 8.84 8.54 11.48
1.46 1.46 1.48 1.40 1.54
68.4 67.1 86.3 62.9 51.7
1.83 1.82 2.02 1.76 1.67
1.19 1.15 1.15 1.06 1.45
25.7 24.7 20.6 25.0 33.8
5812 5723 6796 5237 5308
0.503 0.468 0.484 0.455 0.605
6.33 5.95 4.78 6.17 8.81
113 110 140 103 89
35.0 33.9 34.0 30.9 43.0
2.66 2.58 2.61 2.41 3.11
202 186 206 203 196
Table 4 Concentrations of As, Hf, Sb, and Zr in the sediments (in mg/ kg) Sample no.
River
As
Hf
Sb
Zr
4 8 15 21 22 25
West West North North East East
46.6 43.5 96.8 39.5 15.7 27.4
9.12 7.71 6.24 8.90 12.70 8.20
5.02 10.32 6.17 6.44 0.90 1.68
282 293 259 298 473 266
44.9
8.81
5.09
312
Average Fig. 4. Comparison of the Ba concentrations detected by ICP± AES and ICP±MS.
reaches of the North River is signi®cant, and there are two major Pb mines at Lechang and Fankou, located north of Shaoguan City (Fig. 2). The Shaoguan Pb smelter discharges large quantities of Pb into the North River, e.g. in 1993, the discharge of Pb from the smelter was 17.98 tons (Chen and Lu, 1994). The discharges of Pb from the Lechang and Fankou mines were 2.315 and 2.728 tons in 1993, respectively (Chen and Lu, 1994). The element Bi, which is known to be usually associated with lead deposits (Garavelli et al., 1997) is also enriched in the North River. The relatively high concentrations of the alkali metals (Li, Na, K, Rb, and Cs) in the East River have the same origin as REEs, because granites have high concentrations of alkali metals. The alkali metals are quite mobile in the aquatic environ-
ment, but they may reside in the primary light minerals, such as feldspar. The immobile elements Zr and Hf may reside in the primary heavy minerals of granites, such as Zircon, in the East River. Relatively high concentrations of alkaline earth elements (Mg, Ca, Sr, and Ba) in the sediments of the West River are related to the limestone bedrock which contains high concentrations of these elements, even though the strong weathering may remove a large part of them. 3.3. Spatial distribution of the elements Fig. 5 illustrates the spatial distribution of Pb and Bi concentrations in sediments of the West, North, and East rivers. Signi®cantly high concentrations of both Pb and Bi are observed in the upper and middle reaches of
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Fig. 5. Spatial distribution of Pb and Bi concentrations in sediments of the West, North, and East rivers.
the North River, while concentrations in all the other samples are not high. The mines of Lechang and Fankou and the Shaoguan Smelter are geographically located in the upper reaches of the North River. The map, produced by GIS, supports the conclusion that mineralization and industrial activities are the main sources of the high Pb and Bi concentrations in the North River. Fig. 6. shows the spatial distribution of REEs in sediments of the study area. As all the individual REEs have similar spatial distribution maps, the distribution map of REE [the total concentrations of REEs from La (57) to Lu (71)] is shown. Strong weathering has caused the high concentrations of REEs in the Pearl River system, but dierences among the three rivers exist. All the sampling sites in the East River have very high concentrations of REE, and the samples from the West and North rivers have relatively lower REE, with minor exceptions. The dierences of REE among the three rivers are clearly visualized from the map. 3.4. Statistical tests for the dierences among the element concentrations in sediments of the three rivers To further study the dierences of the element concentrations among the three rivers, statistical tests were applied. The 28 samples were divided into 3 groups
according to the river where they were taken from (see Section 2.1). Analysis of variance (ANOVA) is used to test if there are signi®cant dierences among the three rivers. Most of the variables satis®ed the homogeneity of variance test, with the Levene statistic signi®cance level being higher than 0.05 (Table 5), and thus ANOVA was applied. However, Ba, Bi, Cs, Cu, Eu, Nb, Pb, Ti, and V failed, and the non-parametric Kruskal± Wallis test was applied for these variables instead. Both the results of ANOVA and Kruskal±Wallis tests are shown in Table 5. Most of the elements have statistically signi®cant differences among the three rivers with signi®cance levels of lower than 0.05. The elements Ba, Cu, Li, Na, Pb, Sn, and Zn do not have signi®cantly dierent concentrations among the three rivers, shown by both the ANOVA and Kruskal-Wallis methods at the signi®cance levels of greater than 0.05. To compare the dierences among the three rivers in detail, the Duncan method for multiple comparison of ANOVA was applied.For those variables that cannot pass the homogeneity of variance test, the t-test for equality of means with equal variances not being assumed was carried out, and the results are listed in Table 6. Based on the two methods, the elements that have signi®cantly dierent concentrations among the three rivers are shown in Table 7.
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Fig. 6. Spatial distribution of REE in sediments of the West, North, and East rivers.
Table 5 Signi®cance probabilities of the Levene statistic, one-way ANOVA and Kruskal±Wallis test
Levene statistic sig. One-way ANOVA sig. Kruskal±Wallis test sig.
Levene statistic sig. One-way ANOVA sig. Kruskal±Wallis test sig.
Levene statistic sig. One-way ANOVA sig. Kruskal±Wallis test sig.
Al
Ba
Bi
Ca
Ce
Co
Cr
Cs
Cu
Dy
Er
Eu
Fe
Ga
Gd
0.92 0.01 0.01
0.00 0.06 0.12
0.00 0.00 0.00
0.06 0.00 0.00
0.64 0.00 0.00
0.21 0.01 0.00
0.15 0.00 0.00
0.03 0.09 0.04
0.00 0.16 0.10
0.29 0.00 0.00
0.54 0.00 0.00
0.02 0.01 0.02
0.43 0.00 0.00
0.46 0.00 0.00
0.78 0.00 0.00
Ho
K
La
Li
Lu
Mg
Mn
Mo
Na
Nb
Nd
Ni
P
Pb
Pr
0.31 0.00 0.01
0.12 0.03 0.03
0.65 0.00 0.00
0.22 0.14 0.06
0.89 0.00 0.00
0.29 0.00 0.00
0.32 0.01 0.02
0.74 0.01 0.02
0.72 0.48 0.47
0.01 0.05 0.03
0.62 0.00 0.00
0.49 0.01 0.01
0.13 0.05 0.02
0.01 0.09 0.11
0.99 0.00 0.00
Rb
Sc
Sm
Sn
Sr
Ta
Tb
Th
Ti
Tm
U
V
Y
Yb
Zn
0.10 0.00 0.00
0.25 0.03 0.00
0.71 0.00 0.00
0.30 0.25 0.31
0.05 0.00 0.00
0.58 0.02 0.00
0.53 0.00 0.00
0.14 0.00 0.00
0.01 0.02 0.02
0.37 0.00 0.00
0.19 0.00 0.00
0.04 0.00 0.00
0.26 0.00 0.00
0.27 0.00 0.00
0.91 0.96 0.78
Out of the 45 elements, a total of 35 elements have shown signi®cantly dierent concentrations between the West River and the East River, which demonstrates that the dierences between these two rivers are greatest. The dierences of the rock types within these two rivers may be the major factor for this phenomenon. The dier-
ences between the West and North rivers are relatively slight. Most of REEs, which are enriched in the East River, show signi®cant dierences between the East River and the North River. For most of the elements, the results from the mathematical calculation, GIS visualization, and the statistical
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Table 6 Signi®cance levels of t-test for equality of means (equal variances not assumed)
West River vs. North River West River vs. East River North River vs. East River
Ba
Bi
Cs
Cu
Eu
Nb
Pb
Ti
V
0.06 0.06 0.84
0.01 0.06 0.02
0.09 0.01 0.88
0.39 0.08 0.08
0.02 0.43 0.01
0.20 0.04 0.02
0.06 0.33 0.13
0.02 0.00 0.89
0.00 0.00 0.18
Table 7 Results of multiple comparison of ANOVA (Duncan method) and t-test, showing the elements which have signi®cantly dierent concentrations among the West, North, and East rivers West River
North River
North River
Bi Ca Co Cr Eu Fe Ga Ni P Sc Sr Ta Ti V
East River
Al Ca Ce Co Cr Cs Dy Er Fe Ga Gd Ho K La Lu Mg Mn Mo Nb Nd Ni P Rb Sc Sm Sr Ta Tb Th Ti Tm U V Y Yb
tests are consistent. However, inconsistent results are observed for Pb. The North River has very high concentrations of Pb (Table 3 and Fig. 5), but the statistical tests of both ANOVA and t-test conclude that that the dierences of Pb concentrations among the three rivers are insigni®cant (with the signi®cance level >0.05) (Tables 5 and 6). When the spatial distribution map is looked at (Fig. 5), the high Pb concentrations are observed only in the upper and middle reaches of the North River (sample Nos. 11 to 15). In the lower reaches of the North River, the Pb concentrations are not high. As all the samples in the North River were in one group for the above statistical tests, this mixed information has handicapped the statistical methods. Therefore, the statistical tests did not highlight this feature, which suggests that statistical methods should be used with caution. 4. Conclusions Concentrations of 49 elements in sediments from the West, North, and East rivers of the Pearl River system were detected by ICP±AES, ICP±MS, and INAA, and reported in this study. Signi®cant dierences in the concentrations for most elements among the three rivers are observed by statistical analyses. GIS mapping technology is helpful in explaining the spatial relationships between human and environmental sources of elements and the element concentrations in river sediments. Most of the immobile trace elements are elevated in the West River, and a combination of strong weathering and the easily weathered limestone rock type is the reason for the enrichment of the immobile elements in sediments of the area. High concentrations of REEs are
Al Bi Ce Dy Er Eu Gd Ho La Lu Mg Mn Mo Nb Nd Rb Sm Tb Th Tm U Y Yb
observed in the Pearl River system in general, but relatively higher REE concentrations are found in the East River where granite is the main rock type. Granite contains high concentrations of REEs and the sediments have inherited this feature from their bedrock. Alkali metals are elevated in the East River, again deriving from the granites. Relatively high concentrations of alkaline earth elements are observed in the West River, re¯ecting the limestone bedrock. High Pb and Bi concentrations are found in the North River associated with Pb mineralization and the discharge from the Shaoguan Smelter. Statistical tests did not highlight the high concentrations of Pb in the North River compared with the other two rivers, which suggests that statistical tests should be used with caution when examining spatial geochemical data. Acknowledgements This study was supported by the National Natural Science Foundation of China (No. 49601016) and the ``Hundreds of Talents Program'' of the Chinese Academy of Sciences. Discussion with Professor Gerald Lalor, and helpful comments from the two reviewers, are acknowledged.
References Burton Jr., G.A., 1991. Annual review: assessing the toxicity of freshwater sediments. Environmental Toxicology and Chemistry 10, 1585±1627. Campbell, P.G.C., Lewis, A.G., Chapman, P.M., Crowder, A.A., Fletcher, W.K., Imber, B., Luoma, S.N., Stokes, P.M.,
C. Zhang, L. Wang / Applied Geochemistry 16 (2001) 1251±1259 Winfrey, M., 1988. Biologically available metals in sediments. NRCC/CNRC, Ottawa, Canada. Chen, C.Y. and Lu, Z.B. (editors-in-chief), 1994. Year Book of Environmental Monitoring, Guangdong Province, 1994. Guangdong Environmental Monitoring Center, China. p. 459 (in Chinese). Chen, J.S., Zhou, J.Y. (Eds.), 1992. Studies on Heavy Metals in the Aquatic Environment in China. China Environmental Sciences Press, Beijing (in Chinese). Fergusson, J.E., 1990. The Heavy Elements: Chemistry, Environmental Impact and Health Eects. Pergamon Press, Oxford (276±282). Garavelli, A., Laviano, R., Vurro, F., 1997. Sublimate deposition from hydrothermal ¯uids at the Fossa crater Ð Vulcano, Italy. European Journal of Mineralogy 9, 423±432. Haskin, L.A., Haskin, M.A., Frey, F.A., Wildeman, T.R.,
1259
1968. Relative and absolute terrestrial abundances of the rare earths. In: Ahrens, L.H. (Ed.), Origin and Distribution of the Elements. Pergamon Press, Oxford, pp. 889±912. Liu, M.G. (editor-in-chief), 1998. Atlas of physical geography, China. Version 2. Beijing: China Map Press, p. 252 (in Chinese). Taylor, S.R., McLennan, S.M., 1985. The Continental Crust: Its Composition and Evolution. Blackwell, Oxford. Zhang, C.S., Zhang, S., Wang, L.J., Wang, L.Z., 1998. Comparison of geochemistry of metals in sediments from some typical rock areas. Acta Scientiae Circumstantiae 18, 172± 176. Zhang, C.S., Zhang, S., Zhang, L.C., Wang, L.J., 1995. Background contents of heavy metals in sediments of the Changjiang River system and their calculation methods. J. Environ. Sci. 7, 422±429.