The content, form and regional geochemical
characteristics of heavy metals in the Changjiang (Yangtze) River system
Zhang
Licheng and Wei Chaoyang
(Institute of Geography, Chinese Academy of Sciences,
Beijing 100101, China)
ABSTRACT
Based on the analysis of more than 10 heavy metal
elements in dissolved and suspended parts in water and different forms in
sediments using filter paper and continuous separation technique respectively
in more than 400 sampling sites of Changjiang river system, the element content,
form and their geochemical characteristics as well as the impact of the climate
and geological condition are discussed in this paper.
Key words:
Element, Content, Form, the Changjiang river, Geochemical characteristics
INTRODUCTION
The Changjiang river ranks the first in China and
the third in the world, with 6300 km length and approximately 1,800,000 km2
watershed area and 1000 billion
cubic meters of total runoff. From the source to the mouth, the sea level falls
more than 5km with great changes in natural conditions. Under the influence of south-east
monsoon, the >10℃
accumulate temperature is <200℃and
>6000℃,
and the rainfall is <300mm and >1800mm in source.and mouth
, respectively. Frost action dominates over chemical and bio-chemical weathering
in the source area due to the dry and cold climate. In the lower reaches the
weather is damp and hot, strong chemical weathering action dominates.
Geological conditions change greatly in the vast valley of Changjiang. It is
sedimentary clastic rock in the source area and metamorphic rock in the south
bank of Jinshajiang system (a branch in the upper Changjiang river). Limestone dominates
in the upper and granite in the middle-lower of Xiangjiang that is emptied into
Changjiang in the middle. The Han river flowing into the Changjiang in the
middle from north bank are sedimentary rock region. The valley of lake Poyang
are granite and basic eruptive rock area. The water, climate, rock type and
topography are major factors that influence the natural contents and species of
heavy metal elements.
METHODOLOGY
The positions of the sampling sites are shown on
Fig1, the water sites are relative clear with no immediate pollution. The
sediment sites of Xiangjiang river and Xiangjiang river (lake Poyang system)
were contaminated by pb-zn mining and cu mining respectively
The water phase were separated into suspended and
dissolved species through 0.45μm filter paper (filtered
water), and the sediments separated by a 63μm sieve into
<63μm.
part and <2mm raw mud-silt through 2mm sieve. The separation and analysis of
geochemical form of heavy metals in sediments are mainly adapted from Tessier
but with some revision as using teflon centrifugal tube for continuous
separation and analysis without removing the remains during every step of the
process.
Table 1
Elements content in sediment of the Changjiang river[ 
mgkg-1, (Fe %)]
|
|
Cu
|
Pb
|
Zn
|
Cd
|
Co
|
Ni
|
As
|
Hg
|
Cr
|
V
|
Mn
|
Fe
|
|
sample
|
261
|
261
|
260
|
261
|
260
|
260
|
260
|
258
|
259
|
52
|
261
|
262
|
|
244
|
243
|
245
|
243
|
243
|
243
|
243
|
238
|
197
|
39
|
245
|
244
|
|
Range number
|
2.53-166.2
|
2.2-566.9
|
13.4-742
|
0.06-2.56
|
1.0-52.70
|
1.07-88
|
1.23-405.6
|
0.009-1.40
|
3.11-29.30
|
50.5-489
|
4.2-3830
|
0.27-17.30
|
|
9.80-197.4
|
7.5-570.4
|
5.98-770.4
|
0.007-9.0
|
0.9-56.98
|
2.84-98
|
0.40-60.10
|
0.004-1.73
|
7.65-25.40
|
50.5-377
|
2.0-3879
|
1.34-12.67
|
|
Distribution type
|
DD
|
DD
|
DD
|
GI
|
DD
|
DD
|
DD
|
DD
|
GI
|
GI
|
DD
|
DD
|
|
DD
|
DD
|
DD
|
GI
|
DD
|
AN
|
AN
|
AN
|
AN
|
AN
|
DD
|
DD
|
|
Background value
|
22.00
|
21.99
|
73.64
|
0.159
|
12.29
|
26.56
|
7.83
|
0.035
|
52.02
|
114.35
|
580.0
|
2.48
|
|
26.91
|
25.47
|
88.00
|
0.225
|
13.80
|
29.66
|
8.93
|
0.042
|
60.00
|
107.91
|
670.0
|
3.37
|
Note: AN, normal distribution; GI, logarithmic normal distribution; DD,
deviated distribution.
RESULT AND
DISCUSSION
1.
content
and species of elements in water
Table 1 shows an example of the element content
in the river water and filtered water. Regardless of the content in the river
water and filtered water, all were relative lower than the river of the world
and east of China, The data distribution appears as deviate shape with large
dispersion as the same element differs of more than 3-4 magnitude, which
reflects the difference in the geological, water, climate and topographical
factors. Generally, from the source to lower, in the water system the element
content become gradualy lower. For example, the content of Fe in the source and
upper of the south into Jinshajiang river is 1996.2μgL-1
and 241.5μgL-1
in the lake Poyang system and Qingeyjiang river of the lower Changjiang.
The proportion of dissolved to total content of
the elements in the Changjiang river is relatively higher than world and other
Chinese river. For example, dissolved accounted for 50-92% for F, Se, Ni, Hg, Cd, Zn and Cr, whereas that of Fe、Mn、Cr
and As are relatively low with the highest proportion of only 8% and 9% for Fe
and As respectively among them. In the river water, the dissolved element
content increase not evident than the ratio of dissolved to total from source
to lower. For example, the dissolved Fe in source and north bank of upper
Jinshajiang river increase from 12.53μgL-1 and 9.12μgL-1
to 45.92μgL-1
and 24.45μgL-1
in the lower Changjiang of Lake Dongting and Poyang system, whereas the
proportion of dissolved to total raises from 0.6% and 0.5% to 19% and 20.1% respectively. The proportion of Mn increase from 3.7% and 4.6% to
27.6% and 45.8% between the same two area, anb the dissolved Ni content increase
from 11.03μgL-1 to 59.7μgL-1 while the
proportion raises from 32.6% to 64.5%. The same trend are also clear among the
elements of Zn, Cd, Hg, Cr and V. The dissolved Cu, Zn, Ni and Hg become the
main species in water phase in some branches in the middle of Changjiang river
as the proportion of dissolved to total exceed 50%. The dissolved part are
dominant species among Mo, Hg, As and F in the water phase from source to
middle-lower reaches of the Changjiang river.
2. Content of heavy metals in
the sediments
1)
The metal content
in the sediments
From table 2 it can be found that the heavy metal
content is relatively lower than some river in the world and China both in raw
sediments and <63 sediments, but data are quite dispersed with the same
element differ 2-3 magnitude. The accumulation coefficient of <63 μm
sediments to the raw sediments is 10% or so, except Cd>42% and Cu>22% .
it is confirmed that heavy metals mainly exist in primary mineral.
2) Heavy
metal forms in the sediments of the Changjiang river water system
⑴ Heavy metal forms in
the sediments in the source area
Owing to the extensive distribution of
sedimentary rock in the source area, and the physical weathering play a
dominant role in the weathering process, the supply of free metal ions released
into river are rare. For this reason, the process of exchange, co-precipitation
between carbonate and Fe-Mn oxides as well as the chelation of organic-sulfide
are all not dominant characteristics, whereas the element’s property play an
important role. Zn and Cd mainly tend to integrate with carbonate, Cur with
organic-sulfide and Pb with Fe/Mn oxide. Generally the carbonate
co-precipitation is the dominant factor affecting the transport of heavy metals
into sediments from water (Fig2).
Table2
Elements background in Changjiang river (
, mgkg-1)
|
|
Cu
|
Pb
|
Zn
|
Cd
|
Hg
|
As
|
Co
|
Ni
|
Cr
|
Se
|
Mn
|
Mo
|
V
|
Fe
|
F
|
|
Source
System
|
3.01
|
3.18
|
6.46
|
0.046
|
0.009
|
3.32
|
0.94
|
1.17
|
12.60
|
|
30.19
|
0.99
|
3.58
|
1996.20
|
0.19
|
|
0.63
|
0.76
|
0.68
|
0.015
|
0.002
|
0.86
|
0.24
|
0.18
|
0.26
|
0.127
|
2.53
|
0.72
|
0.23
|
12.53
|
0.19
|
|
Jingsha
(north bank)
|
3.53
|
1.49
|
7.78
|
0.074
|
0.007
|
1.92
|
1.34
|
4.04
|
4.49
|
0.21
|
46.31
|
0.81
|
6.24
|
1806.01
|
0.13
|
|
0.74
|
0.14
|
0.86
|
0.021
|
0.003
|
1.08
|
0.26
|
0.24
|
0.62
|
0.19
|
2.21
|
0.41
|
0.96
|
9.21
|
0.12
|
|
Jingsha
(south bank)
|
1.50
|
1.80
|
1.45
|
0.097
|
0.024
|
0.59
|
0.55
|
0.49
|
1.15
|
0.18
|
23.68
|
0.39
|
1.70
|
354.5
|
0.12
|
|
0.95
|
0.65
|
0.97
|
0.043
|
0.014
|
0.46
|
0.36
|
0.31
|
0.58
|
0.014
|
3.52
|
0.30
|
0.50
|
21.03
|
0.11
|
|
Wu river
|
1.27
|
0.29
|
3.62
|
0.015
|
0.023
|
0.71
|
0.16
|
0.21
|
1.54
|
0.11
|
16.97
|
0.68
|
1.49
|
165.80
|
0.07
|
|
0.46
|
0.16
|
2.30
|
0.008
|
0.014
|
0.28
|
0.05
|
0.14
|
0.55
|
0.065
|
3.01
|
0.52
|
0.40
|
4.75
|
0.07
|
|
Min river
|
0.88
|
0.46
|
2.57
|
0.012
|
0.030
|
1.22
|
0.18
|
1.30
|
0.64
|
0.21
|
11.28
|
0.90
|
2.25
|
109.00
|
0.17
|
|
0.39
|
0.20
|
1.92
|
0.006
|
0.023
|
0.55
|
0.05
|
0.09
|
0.32
|
0.17
|
3.29
|
0.72
|
1.80
|
13.00
|
0.16
|
|
Han river
|
3.25
|
0.87
|
3.39
|
0.018
|
0.030
|
1.00
|
0.11
|
0.41
|
0.88
|
0.054
|
7.60
|
0.70
|
1.05
|
338.9
|
0.20
|
|
2.53
|
0.51
|
3.08
|
0.014
|
0.027
|
0.73
|
0.07
|
0.24
|
0.50
|
0.025
|
2.80
|
0.53
|
0.79
|
8.72
|
0.18
|
|
Qingye
River
|
0.74
|
0.44
|
6.55
|
0.065
|
0.006
|
0.80
|
0.20
|
0.59
|
0.79
|
0.138
|
20.99
|
0.59
|
1.29
|
241.53
|
0.16
|
|
0.60
|
0.08
|
2.89
|
0.034
|
0.004
|
0.44
|
0.03
|
0.40
|
0.15
|
0.102
|
7.71
|
0.38
|
0.68
|
13.29
|
0.15
|
|
Poyang
Lake system
|
0.78
|
0.85
|
6.21
|
0.012
|
0.006
|
0.85
|
0.17
|
0.35
|
0.82
|
0.142
|
16.34
|
0.16
|
0.42
|
121.58
|
0.15
|
|
0.47
|
0.32
|
4.81
|
0.006
|
0.003
|
0.60
|
0.08
|
0.24
|
0.71
|
0.105
|
7.53
|
0.13
|
0.29
|
24.45
|
0.13
|
⑵
Heavy metals forms in the sediments in middle-lower Changjiang
The Kangjiaxi river is a
tributary of Xiangjiang river in middle Changjiang affected by Pb-Zn mining
pollution. In upper Xiangjiang river there distributed extensive limestone and
carbonate dissolve and release are affected strongly for this reason, the
proportion of carbonate form is relatively higher (Table 2). The Kangjiaxi
river flow into the Xiangjiang in the middle, with sandstone vastly distributed
in the valley, the Fe/Mn Oxide form is dominant in the sediments. This fully
reflected regional geochemical feature of damp-hot climate condition. Because
of the mining pollution, the proportion of organic-sulfide is quite high. As
the climate is damp and hot and igneous rock extensively distributed in the valley
of Xiangjiang river, the organic-sulfide and Fe/Mn oxide form are obviously
dominant (Fig 3).