The Temporal and Spatial Distribution of Heavy
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中国科技论文在线 http://www.paper.edu.cn The Temporal and Spatial Distribution of Heavy Metals in Helice tridens in the Tidal Flat of Yancheng YU Na, SUN Xinjin, LI Xiaobo, WANG Qun School of Life Science, East China Normal University, Shanghai (200062) E-mail: [email protected] Abstract Between November 2006 and July 2007, we determined the heavy metal content in Helice tridens crabs inhabiting the tidal flat of Yancheng. The results showed that the accumulation of the essential elements Fe, Zn, Cu, Mn, and Ni was higher than that of the toxic element Pb; the specific relationship between elemental concentrations was Fe > Zn > Cu > Mn > Ni > Pb. We analyzed the seasonal distribution of the heavy metal content in the crabs, and found that there were seasonal differences in the contents of the six heavy metals. The seasonal distributions of the elements were in the following order: Fe content in spring > summer > autumn; Cu and Mn content in autumn > summer > spring; Zn, Ni, and Pb content in summer > spring > autumn. Thus, it was considered that temperature is not the principal factor influencing the accumulative rate of the heavy metals in H. tridens individuals. For example, there were certain differences in the heavy metal content in the crabs collected from different sampling points in autumn. In the cluster analysis, ten sampling points were approximately classified into three groups, which represented the coastal salt-industry culture area, the nature-reserve central area, and the estuarine industrial water area. The results of the cluster analysis suggested that the pollutants in the crabs’ habitats influenced the accumulation of heavy metals in their bodies. Moreover, we compared related data and found that Cu accumulation in the bodies of the crabs inhabiting the tidal flat of Yancheng was relatively low while the accumulation of Zn, Mn, Ni, and Pb was relatively high. Keywords: Tidal flat of Yancheng, Helice tridens, heavy metal distribution Yancheng, which is located in eastern China, has a 582-km-long eastern coastline bordered by the Yellow sea. The tidal flat of Yancheng, with its northern end in the Guanhe estuary in junction with Lianyungang and its southern end in the new port gate bordering Nantong, has an area of 457,000 hm2, which accounts for 3/4th of the area of Jiangsu province and 1/7th of the area of the entire country. It is the most extensive tidal flat in China, and it is one of the 17 key biodiversity areas that have been chosen as priority conservation areas in China (State Environmental Protection Administration, 2003). The tidal flat has an exceptionally large resource potential for Jiangsu province and for the whole country. However, in recent years, continuous discharge of large amounts of wastewater from the towns and industries, particularly the discharge of water containing heavy metal pollutants that can accumulate continuously in tidal flat sediments and animal bodies, has resulted in direct and potential damage to the tidal-flat ecosystem(Chen et al., 2000). The zoobenthos, which inhabit the tidal flats for their entire lifetime, are one of the members of the food chain of the tidal-flat ecosystem, and the pattern of heavy metal accumulation in their bodies can partly reflect the status of the habitat (Li et al., 2007). In this study, we aimed to provide basic information for facilitating ecological protection of the Yancheng tidal flat. Therefore, between November 2006 and July 2007, we collected H. tridens crabs inhabiting the Yancheng tidal flat and analyzed the temporal and spatial distribution of heavy metals in the bodies of the crabs. 1 Sampling and analysis 1.1 Sampling-point arrangement and sample collection We selected 10 representative sampling points between the northern and southern ends of the tidal flat. The sediment samples and biotic samples were collected in three quarters, i.e., early November (autumn) in 2006, early April (spring) in 2007, and early July (summer) in 2007. - 1 - 中国科技论文在线 http://www.paper.edu.cn Sampling was carried out once in a quarter. The sampling points were Zhongshan estuary, Binhai port, Guhuang estuary, Biandan port, the north of the Sheyang estuary, the core protected district, Simaoyou port, Zhugang gate, Chuanshui port, and the Dongtai Chinese sturgeon reserve, as shown in Figure 1. No. Sampling points Latitude Longitude 1 Zhongshan estuary 34°21′20.4″ 120°09′00.7″ 2 Binhai port 34°16′56.9″ 120°16′43.7″ 3 Guhuang estuary 34°15′29.1″ 120°16′66.3″ 4 Biandan port 34°06′45.6″ 120°19′13.9″ 5 North of the Sheyang estuary 33°49′13.3″ 120°28′33.3″ 6 Core protected district 33°34′30.3″ 120°32′49.0″ 7 Simaoyou port 33°20′13.2″ 120°41′05.4″ 8 Zhugang gate 33°03′03.8″ 120°48′57.3″ 9 Chuanshui port 32°57′13.0″ 120°57′34.1″ 10 Dongtai Chinese sturgeon 32°44′35.4″ 120°51′51.6″ Figure 1 Sampling points on the tidal flat of Yancheng 1.2 Sample preparation and analysis The crabs were cleaned with water from the sample points, sealed in plastic bags, and preserved in a portable freezer, which was taken back to the laboratory within two days. Then, the body of the animal was wiped dry and weighed. We randomly selected 10 adults with similar body sizes. The entire soft bodies, except for the legs, were properly dried, fully ground in an agate mortar, and passed through a 100-mesh sieve. Each sample was accurately weighed using an electronic balance, placed in a 25-ml porcelain crucible, and cinerated in a muffle furnace at 500℃ for 24 hours to remove the organic matter. All the measurements of weight performed during the cineration process were exact to 0.01 mg. The acid-dissolution method (HNO3-HF-HClO4) was used to digest and dilute the samples. We used an M6-type atomic absorption-spectrometry apparatus (ThermoElemental Ltd., UK) to determine the Fe, Zn, Cu, Pb, Mn, and Ni contents and analyze the blank solutions. 1.3 Analysis Method The heavy metal accumulation in the organism was calculated on the basis of dry weight (DW). Statistica 6.0 was used for cluster analysis of the accumulation of the six heavy metals in the bodies of the animals. 2 Results 2.1 Seasonal distribution of heavy metals in H. tridens H. tridens is a common species of crab found in the Yancheng tidal flat. In this study, we analyzed the accumulation of six heavy metals in the bodies of these crabs in autumn, spring, and summer. The results show that there are differences between the average accumulation of different - 2 - 中国科技论文在线 http://www.paper.edu.cn heavy metals in the bodies of the crabs; the relative distribution of the six heavy metals in the three seasons was Fe > Zn > Cu > Mn > Ni > Pb (see Figure 2). 200 DW 150 (mg/K 100 g ) 50 0 Autumn Fe Zn Spring Cu Summer Mn Ni Pb Figure 2 The temporal distribution of the six heavy metals in Helice tridens individuals There were differences in the accumulation of the six heavy metals, but the differences were insignificant. The seasonal differences in the accumulation of heavy metals in the bodies of the crabs can be observed in Figure 2. The seasonal variation in Fe accumulation was in the following order: spring (153.09 mg/kg) > summer (148.43 mg/kg) > autumn (143.87 mg/kg), and the Fe accumulation in spring was higher than the average value (148.46 mg/kg) of the three seasons. The seasonal changes in the accumulation of Cu and Mn were in the order autumn > summer > spring; the Cu concentrations were 52.37 mg/kg, 47.87 mg/kg, and 46.80 mg/kg, with an average value of 49.01 mg/kg. The Mn concentrations were 14.39 mg/kg, 13.47 mg/kg, and 11.51 mg/kg, with an average value of 13.12 mg/kg. The seasonal changes in the accumulation of Zn, Ni, and Pb were in the order summer > spring > autumn. The accumulation of Zn in summer, spring, and autumn was 144.00 mg/kg, 143.91 mg/kg, and 143.39 mg/kg, respectively; the Zn content in summer was higher than the average value (143.77 mg/kg) of the three seasons. The Ni concentrations in the three seasons were 8.00 mg/kg, 7.34 mg/kg, and 6.68 mg/kg; the Ni content in summer and spring was higher than the average value (7.34 mg/kg) of the three seasons. The Pb concentrations in the three seasons were 5.11 mg/kg, 4.54 mg/kg, and 3.97 mg/kg; the Pb content in autumn was lower than the average value (4.54 mg/kg) of the three seasons. 2.2 Horizontal distribution of heavy metal in H. tridens The horizontal distribution of the heavy metal accumulation in the bodies of H. tridens individuals is slightly different in the three seasons (no details in this paper). In this study, the sediment structure and the biological community structure of the sample plot were influenced by the Sea Embankment Target Project, which was started in early 2007 in the northern region of the Yancheng tidal flat, and the First Phase Regulation Project of the Channel under the Sheyang River Gate. Therefore, we analyzed only the accumulation of heavy metals in the crabs collected from the 10 sampling points during the autumn of 2006. The results show that there are certain differences in the accumulation of heavy metals in the crabs collected from different sampling points, as seen in Figure 3.