Heavy Metal Pollution in Different Types of Land Use in Baiyangdian Lake

Feng-ju Li , Bao-shan Cui∗, Yan Lan, Wen-ting Lin, Yongyan Liu, Ya-li Tong

School of Environment, Beijing Normal University, Beijing100875,China

——— ∗ Corresponding author. Tel.: +86-010-58802079; fax: +86-010-58802079; e-mail: cuibs@163.com

Abstract—Based on the study of soil samples collected from reed field, poplar plantation, corn field and foul land in Baiyangdian Lake, we investigated the distribution of heavy metal pollutions including Cd ,Cr, Cu, Ni ,Pb and Zn which seriously threaten soil environment and human health. These following conclusions have been reached: Cr ,Cu, Ni , Pb and Zn in different types of land use was concentrated in the soil layer of 0-40 cm, the content of Cr, Cu, Ni, Pb and Zn decreased with land depth. The highest concentration of heavy metals presented at 0-20 cm in the reed field, whereas the others at 20-40 cm. The reason may be that the local residents turned deep soil to the surface land for enhancing soil fertility in these land uses in former years. The average concentration of Cr, Cu, Ni, Pb, and Zn is similar in reed field, poplar plantation and corn field, and it is higher than foul land obviously. The concentration of Cd is similar in four types of land use, and the content tends to increase with land depth. Cd tends to concentrate in deep soil. These conclusions can provide some basis to control heavy metal pollution in Baiyangdian Lake in future. Because only the content of Cd element exceeds the Standard of Soil Environmental Quality (GB 15618-1995), the pollution control of Cd should be the key point. Keywords: Baiyangdian Lake;Land use type;Heavy metal

. INTRODUCTION Heavy metal pollution is one of global environmental

pollution problems. It is also serious in China. The statistical results of Ministry of Agriculture showed that the land area polluted by the heavy metals reached approximately 20,000,000 square kilometer and most have not be controlled. The statistical data also showed that more than 30,000 hectare were polluted by mercury. Cadmium pollution could reach 10,000 hectare. The accumulation, migration and transformation of heavy metal pollutants in environment lead to the ecological and environmental deterioration which threatens human's health[1,2].

Up to now, some countries such as China, America and European countries have developed territorial investigation on soil background concentrations of heavy metals [3]. Though the study on heavy metal accumulation in soil form the view of land-use type has been carried out, most surveys concentrate on the region surrounding cities and it is rare to investigate the natural ecological environment especially different land-use types in the same watershed. By taking different land use in Baiyangdian Lake as the research object, this present study explored regularity of vertical distribution of heavy metal elements in soil and the difference of the content of different heavy metal in various land use by samples analysis in site. This will provide theoretical and data support for heavy metal pollution treatment more pertinently and basis for the evaluation of land

applicability [4]. It is helpful to protect wetland ecological environment of Baiyangdian Lake.

. MATERIALS AND METHODS 2.1. Study Site

Baiyangdian Lake was located in the lowland area in the north China rift zone of the neo-cathaysian structural system. In topography, west part of this region is slightly higher than the south part and the natural slope of it is between 1/2000 to 1/200. With distinct seasons as well as rainfall and heat resources in the same season, Baiyangdian Lake belongs to the zone of the continental monsoon climate. Located in the central part of North China Plain, Baiyangdian Lake is in the center of Beijing, Tianjin and Shijiazhuang. It’s 39.5 km long from east to west and 28.5 km wide from south to north, with an area of 366 km2. Surrounding by dams, it’s the biggest grass type lake in the North China Plain.

2.2. Study Method

2.2.1 Collection and Analysis of Samples

There are several land utilization types in Baiyangdian Lake. In the study, we chose four typical land of different uses (reed land, poplar plantation, corn field and foul land) as the research object and then collected soil samples from each kind of the land in proper sites in July, 2011. In each sampling place, we collected five soil samples at 20 meters apart in the soil profile from the surface to 1 meter below the surface, and then each of them have 3 replications.

After the soil samples natural air drying and grinding indoor and then through the 100 meshes nylon screen, we determined the contents of Cd, Cr ,Cu, Ni, Pb, Zn by ICP.

2.2.2 Statistic Analysis

We processed the data by variance analysis, regression analysis and SPSS, and then we use Origin to analyze them.

. RESULTS AND DISCUSSION Based on the study monitored six kinds of heavy metal

in reed land, poplar plantation, corn field and foul land (0-100cm), we investigated the distribution and content of them. According to the result, we can see that the contents of these six heavy metal elements do not only have a simple negative linear correlation with the vertical dimension. But the vertical distribution laws of five metal elements(Cr, Cu, Ni, Pb, Zn (Cd excepted)) in the same kind of land are similar with each other, and for one metal element, the contents and distribution laws are different in each kind of land. For Cd, it has its own unique content

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DOI 10.1109/ISDEA.2012.193

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and distribution laws. So we make a more detailed analysis combining with the soil’s basic physical and chemical properties in different types of land use.

According to the physicochemical properties of soil from different land use types (Fig1), these following conclusions have been reached: 3.1. The vertical distribution laws of heavy metal

elements in the same soil profile

3.1.1 Reed Land

For the soil profile of the reed land, the concentrations of Cr, Cu, Ni, Pb and Zn in vertical direction intend to decrease with depth, and the enrichment degree appears higher in the upper soil layer. elaborate equations or references to other parts of the paper or to the reference listing at the end(Table1).

Table 1. The content of heavy metal elements in the soil profile of reed field Soil depth/cm

Element 0-20 20-40 40-60 60-80 80-100

Cd/mg.kg-1 0.69 0.84 1.065 1.065 1.005

Cr/mg.kg-1 64.45 64.40 65.25 62.50 61.85

Cu/mg.kg-1 37.15 36.1 34.0 34.2 33.8

Ni/mg.kg-1 35.0 35.0 33.7 33.6 32.7

Pb/mg.kg-1 22.4 20.85 19.5 19.3 18.25

Zn/mg.kg-1 70.3 64.85 65.2 62.2 61.7

3.1.2 Foul Land

For the soil profile of the foul land, the concentrations of these five elements in vertical direction tend to increase from the depth of 0 to 20 cm to the depth of 20 to 40 cm, and tend to decrease with the land depth from

the depth of 20 to 40 cm. Nevertheless, having little difference between the enrichment degrees in the soil of different depth, the changing range of the contents is less and the vertical distribution laws are not obvious (Table 2).

Table 2. The content of heavy metal elements in the soil profile of foul land Soil depth/cm

Element 0-20 20-40 40-60 60-80 80-100

Cd/mg.kg-1 0.945 0.995 0.995 1.050 0.935

Cr/mg.kg-1 49.0 52.95 51.95 52.30 51.00

Cu/mg.kg-1 27.60 28.10 27.00 27.20 25.65

Ni/mg.kg-1 23.50 25.60 25.45 25.35 24.95

Pb/mg.kg-1 16.2 17.00 15.85 16.00 15.15

Zn/mg.kg-1 57.6 58.50 55.25 55.50 49.75

3.1.3 Poplar Plantation

For the soil profile of the poplar plantation, the concentrations of these five elements in vertical direction tend to increase from the depth of 0 to 20 cm to the depth of 20 to 40 cm, and tend to decrease with the depth from the depth of 20 to 40 cm. the concentrations have wide ranges and the vertical distribution laws are evident. In this kind of land, the heavy metals were mainly enriched in the soil layer in the depth of 0 to 40 cm, in which the contents of these five metals are obviously higher than the deep soil layer (Table 3).

3.1.4 Corn Land

For the soil profile of the corn land, the concentrations of these five elements in vertical direction tend to increase from the depth of 0 to 20 cm to the depth of 20 to 40 cm, and tend to decrease with depth from the depth of 20 to 40 cm. The content is highly variable and the vertical distribution laws are evident. The contents of the heavy metal elements in the soil of 0-20 cm depth is obviously lower than that the soil of 20-100 cm depth, while the enrichment degree reaches maximum in the soil of 20-40 cm depth.

Table 3. The content of heavy metal elements in the soil profile of poplar plantation Soil depth/cm

Element 0-20 20-40 40-60 60-80 80-100

Cd/mg.kg-1 0.95 0.99 1.08 1.26 1.19

Cr/mg.kg-1 62.3 62.35 59.3 58.1 57.0

Cu/mg.kg-1 34.5 35.4 31.5 30.0 28.4

Ni/mg.kg-1 32.8 33.0 29.4 28.8 28.2

Pb/mg.kg-1 19.3 20.1 19.5 18.7 17.8

Zn/mg.kg-1 67.5 68.1 65.5 63.4 63.0

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Table 4. The content of heavy metal elements in the soil profile of corn land Soil depth/cm

Element 0-20 20-40 40-60 60-80 80-100

Cd/mg.kg-1 0.76 0.80 1.035 1.40 1.385

Cr/mg.kg-1 55.05 70.3 67.2 64.8 65.95

Cu/mg.kg-1 26.3 37.9 38.15 35.7 35.0

Ni/mg.kg-1 27.85 39.4 39.5 36.05 36.6

Pb/mg.kg-1 17.15 21.1 21.75 21.3 20.35

Zn/mg.kg-1 57.8 73.3 73.45 70.25 70.3

On the whole, after the material of higher heavy metal element content into the soil, the elements in them precipitate into the soil surface under the action of mechanical interception, colloid adsorption and bioaccumulation, which results that the concentrations of heavy metals are high in the soil surface and the elements are mainly enriched in the soil of 0-40 cm depth. And under the action of retention of soil, the contents are gradually reduced as the depth increases.

According to the soil s basic physical and chemical properties, the concentrations of the metal elements in soil are related to the concentrations of N, P and organic matter, which tend to decrease with depth. For reed land, the soil moisture is high, while the concentrations of N, P and organic matter in soil of 0-20 cm depth is obviously higher than that in other kind of land and that in the soil of 20-40 cm depth in foul land, which may strengthen the retention effect to the metals [5,6]. For other three kinds of land, the soil moisture is much lower than foul land,

while the concentrations of N, P and organic matter in soil of 0-20 cm depth is low and is close to that in the soil of 20-40 cm depth, which may weaken the retention effect of soil. That may be the result that the concentration in soil of 0-20 cm depth is high while the concentrations in other three kinds of land is high in the soil of 20-40 cm depth and low in the soil of 0-20 cm depth[7,8]. For corn land, as there are always crop, the metals in the upper soil layer may decrease greatly with the loss of N, P and organic matter, which may be the result of its distribution laws[9].

3.2 The differences of one element in different land utilization types

Compared with the results of the statistic analysis(Fig 2), the average concentration of heavy metals in foul land is the lowest one in all of these four kinds of land, while the average concentration of the same element is similar with each in the other three kinds of land, which are all higher than foul land.

Fig 1. Physicochemical Properties of soil

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Fig 2. The Content of Cr, Cu, Ni, Pb, Zn in four land use types

There are large green plant in the reed land, poplar forest land and corn land. And the common characteristic of these three kinds of land is that the soil’s basic physical and chemical properties and the concentrations of the heavy metal elements are interfered highly by the anthropogenic disturbance. What’s more, in the process of the plant growth, there may be the application of fertilizer and pesticides. And in the foul land, the ecological environment is interfered less by the anthropogenic disturbance, which may be an important reason for its lower concentrations of the heavy metals elements [10].

3.3 The content and distribution regularity of Cd in different land utilization types

The concentrations of Cd in the four kinds of land are nearly same, and the vertical distribution law is similar with each other (Fig 3). In the soil of 0-80 cm depth, the concentration tends to increase with depth, and reaches the maximum in the soil of 60-80 cm depth, while the element is mainly enriched in the soil of 60-100 depth.

Maybe this phenomenon is related to the migration regularity of Cd in the soil[11].

Fig 3. The Content of Cd in four land use types

. CONCLUSIONS

According to the investigation of the content and distribution regularity of several heavy metal elements in different types of land use, the following conclusions can be reached:

(1) Cr, Cu, Ni, Pb and Zn in different types of land use are enriched in the upper soil layer of 0-40 cm depth, and the concentrations tend to decrease with depth. The enrichment degree reaches maximum in the soil of 0-20 cm depth in the reed land, while it reaches maximum in the soil of 20-40 cm depth in the other three types of land use. The reason may be that the local residents turned deep soil to the surface land for enhancing soil fertility in these land uses in former years, which lead to the migration of the heavy metals.

(2) The Average concentration of Cr, Cu, Ni, Pb, and Zn is similar in reed land, poplar forest land and corn land, and it is higher than foul land obviously. We can see from it that in the area that are interfered highly by the anthropogenic disturbance, the heavy metal pollution is serious than others.

(3) Cd is different from other five elements. The concentration of Cd is similar in four types of land use, and the concentration tends to increase with depth, with the enrichment degree reaches maximum in the deep soil.

(4) According to the results of the monitor and the Standard of Soil Environmental Quality (GB 15618-1995),the concentrations of Cr, Cu, Ni , Pb and Zn don t exceed the standard and the natural background value. However, the over standard of Cd is serious, while some of them exceed the standard of grade . So in pollution treatment of Baiyangdian Lake, we should strengthen the administering force of Cd, and make the proper management measures according to the content and distribution regularity of Cd as well as the actual factors pertinently.

ACKNOWLEDGMENTS Our sincere gratitude goes to National Water Pollution

Control and Treatment in China (2009ZX07209-008) which supported this research financially.

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