Surface water quality of factory-based and vegetable-based peri-urban areas in the Yangtze River Delta region, China

Catena 69 (2007) 57 – 64 www.elsevier.com/locate/catena

Surface water quality of factory-based and vegetable-based peri-urban areas in the Yangtze River Delta region, China ¨ born c, K. Blomba¨ck c, QingLi Zhang a,b, XueZheng Shi a,*, Biao Huang a, DongSheng Yu a, I. O a d d HongJie Wang , T.F. Pagella , F.L. Sinclair a

State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, the Chinese Academy of Sciences, 71 East Beijing Road, Nanjing, 210008, China b Department of Territory Resources and Surveying Engineering, Xuzhou Normal University, Xuzhou, 221116, China c Department of Soil Science, the Swedish University of Agricultural Sciences, SE-75007, Uppsala, Sweden d School of Agricultural and Forest Sciences, University of Wales, Bangor, LL57 2UW, UK

Abstract Detailed surveys of surface water in two contrasting peri-urban areas in the Yangtze River Delta region of China were conducted to determine the distribution of heavy metals, nitrogen (N) and phosphorus (P) as well as the speciation of N and P. A factory-based (FB) area was compared with a vegetable-based (VB) area during the dry season. The concentrations of heavy metals in the surface water in the FB area were higher than those in the VB area, suggesting modest contamination of surface water with Zn, Cu, Cr and Pb but not Cd, from discharge of factory effluent in the FB area but not the VB area. Although total N (TN) and total P (TP) levels in the surface water were high in both areas, the surface water in the VB area had significantly higher levels of nitrate N (NO3 – N), organic N (ON) and TN than those in the FB area. In both areas, the levels of water-soluble P (WP), organic P (OP) and TP were high in the river water that received municipal wastewater. The distribution of N and P species throughout the surface water system indicated that the NO3 – N and ON mainly came from vegetable fields, while ammonium N (NH4 – N), WP and OP were mainly from municipal wastewater. Treatment of municipal wastewater prior to discharge to reduce N and P by purification is recommended together with research and extension to develop more efficient use of N and P fertilizer by vegetable farmers. D 2006 Elsevier B.V. All rights reserved. Keywords: Peri-urban; Surface waters; Heavy metals; Nitrogen; Phosphorus; Yangtze River Delta region

1. Introduction With increasing concern about the degradation of the water environment, much research on surface water quality has been done in the past decade (Irmer et al., 1995; Arambarri et al., 1996; Fisher et al., 2000; Tong and Chen, 2002; Cheung et al., 2003). Barros et al. (1995) evaluated the surface water quality in some reservoirs in Portugal using a Water Quality Index (WQI) and found a tendency towards further deterioration of water quality in those reservoirs in which the water quality was already low. In

* Corresponding author. Tel.: +86 25 86881273; fax: +86 25 86881000. E-mail address: [email protected] (X. Shi). 0341-8162/$ - see front matter D 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.catena.2006.04.012

Switzerland, Cu and Zn concentrations of the water in the River Kleine Aa exceeded regulatory values of Swiss Water Quality Criteria (2 Ag l 1 Cu and 5 Ag l 1 Zn) on several occasions (Xue et al., 2003). To assess the surface water quality in the North of Greece, Simeonova et al. (2003) conducted a 3-year survey of major river systems using multivariate statistical approaches to apportion pollutant sources. Since the end of 1970s, China opened its economy and embarked on economic reform that has been associated with rapid urbanization (Qin and Chen, 2001). With urbanization, there have been considerable changes in land use, particularly in fast-growing peri-urban areas. A large proportion of the peri-urban landscape has changed from agriculture or residential uses to become predominantly industrial, whilst

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other areas have shifted from predominantly paddy rice to intensive vegetable production. Growing concern has arisen about potential surface water contamination in the rapidly urbanizing areas of China, specifically with respect to pollution from heavy metals, N, and P. Study of surface water from 16 sites in the Pearl River Delta, South China, showed a clear enrichment of P and NH4 – N and contamination with Ni and Zn in some local surface waters (Cheung et al., 2003). Qian et al. (2002) found that most rivers in the Yangtze River Delta were heavily polluted with N and P, especially in peri-urban areas. The highest concentrations of NH4 – N and TP were found in river water in peri-urban areas around Shanghai, East China. Those concentrations had reached 9.2 mg l 1 for NH4 – N and 1.4 mg l 1 for TP, much higher than the threshold level for agricultural water which is 1.5 mg l 1 for NH4 –N and 0.2 mg l 1 for TP set out in the Environmental Quality Standards for Surface Water by the National Environment Protection Agency of China (GHZB 1-1999). Peri-urban areas are not only generators but also receivers of various pollutants. The water in peri-urban areas is the source of irrigation water for farmers. There are few studies focused on surface water pollution in peri-urban areas or on the environmental impact of changes of land usage within these areas. The comparative study of surface water quality in two peri-urban areas with different patterns of land use in the Yangtze River Delta region presented here is important to identify sources of pollutants and develop strategies to improve water quality. In general, the concentrations of pollutants in surface waters are significantly higher during the dry season than the wet season because of the dilution by large quantities of rainfall in the wet season. Surface water is an important source for irrigation, especially during the dry season. Irrigation can be a significant pathway for entry of water pollutants to the soil – plant system (Grimshaw et al., 1976; Dassenakis et al., 1998; Markich and Brown, 1998). It is, therefore, particularly important to assess the quality of

surface water in rivers in peri-urban areas during the dry season and to identify potential sources of pollutants. The objectives of this study were (i) to determine the distribution of heavy metals, N and P and their speciation in the surface waters of two peri-urban areas with contrasting land usage; (ii) to evaluate the quality of the surface water as irrigation sources in the dry season; and (iii) to explore the possible sources of pollution and propose strategies to protect surface water quality.

2. Materials and methods 2.1. Regional background The Yangtze River Delta region, located in east China (Fig. 1), is one of the most important economic areas in China. It covers only 1% of the total area of China but houses 6% of the nation’s population and produces 16% of the GDP (Chen et al., 2001). In this region, the annual precipitation is 1000 – 1800 mm, which mainly falls from May to September. The mean annual temperature is about 15– 17 -C. Paddy soils dominate on the flat plain that comprises the major landform in this region. The total accessible freshwater resource is about 123 billion m3 representing about 1700 m3 per capita (Yuan and Yang, 1996). In this study, two typical peri-urban areas in Jiangsu province were selected (Fig. 1). In the first site in Wuxi, the dominant land use was industrial, and it is referred to as factory-based (FB), while vegetable farming was a more significant land use at the second site in Nanjing, that we refer to as a vegetable-based (VB) peri-urban area. 2.2. Description of the study areas A town in Wuxi was selected as an example of a factory-based peri-urban area. The town had an official population of 34,370 in 2002. This did not include

Fig. 1. Map showing the location of Nanjing city and Wuxi city in China.

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temporary migrants living in the area but still registered in their places of origin. There are about 400 small-scale factories dispersed within the 25-km2 area of the town. These factories produce a variety of materials including chemicals, fertilizers, pesticides and steel. Most of the arable land is used to grow rice or a rotation of rice and either wheat or rape each year with only a small area devoted to vegetables. Farmers’ incomes in this area mainly come from employment in local factories. A main river with a dense network of tributaries flows through the area, and a number of ponds used for aquaculture and irrigation are scattered throughout (Fig. 2). The river is both a receiver of various wastewaters and the main source of water for agricultural irrigation. The second town with a population of 23,580 in Nanjing city was selected as a typical vegetable-based peri-urban area. Nanjing is the capital of Jiangsu province. Vegetable production has been conducted in this area for more than 30 years. Currently, vegetable production covers 400 ha representing 23% of the total land area of the town. It produces around 30,000 t yr 1 of fresh vegetables according to local government records, making it one of the most important vegetable resources for Nanjing city. Farmers in the area mainly get their incomes from vegetable production. A canal connected to the Yangtze River flows through the whole town, and a large number of rain-fed irrigation ponds are scattered throughout the vegetable land (Fig. 3). Local farmers use both river and pond water for irrigation, but rain-fed pond water is much more prevalent than in the FB area. 2.3. Water sampling River and pond water samples were collected within the studied areas in October 2002. There were 30 sampling sites including four ponds, 10 main river channel sites and 16

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Fig. 3. Map of sample sites of surface water in Nanjing peri-urban area (NPA). The same symbols of sample sites present the same group of samples based on the result of cluster analysis.

tributary river channel sampling sites in the FB area (Fig. 2) and 14 sampling sites including 8 pond and 6 river water sampling sites in the VB area (Fig. 3). Duplicate water samples were collected with a stainless steel container at each selected sampling site. The water samples were placed in 1000-ml plastic bottles that had been soaked in dilute hydrochloric acid (HCl), then in dilute nitric acid each for 24 h, and rinsed thoroughly with de-ionized water. After water samples were brought to the laboratory, their pH was measured, and then a few drops of concentrated HCl were added. These samples were then stored in a refrigerator at 4 -C for further analysis.

Fig. 2. Map of sample sites of surface water in Wuxi peri-urban area (WPA). The same symbols of sample sites present the same group of samples based on the result of cluster analysis.

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2.4. Chemical analyses The concentrations of Pb, Zn, Cu, Cd, and Cr in the water samples were analyzed using a graphite furnace atomic absorption spectrophotometer (Varian Spectr AA 110/220) after water samples were filtered through ash-less quantitative filter paper (Whatman, No. 42). NH4 –N was determined by titration with HCl after distillation with NaOH. Briefly, 50 ml of water was pipetted into a Kjieldhal flask, and then sufficient 10 M NaOH was added to form 1 – 2 M of NaOH in the solution. The solution was heated and the ammonia distillate was absorbed in 10 ml of 2% boric acid. The boric acid was then titrated with 0.01 M HCl. NO3 –N in the water was directly determined using an ultraviolet spectrophotometer (Lu, 2000, p. 133). Water samples were digested by concentrated sulfuric acid and hydrogen peroxide, and then Kjieldhal N (not including NO3 – N) was measured by the distillation method as described above for NH4 –N. Total N was calculated by summing Kjieldhal N and NO3 – N. Water-soluble P (WP) was directly measured by the Murphy and Riley method (Lu, 2000), and total P (TP) was determined by the above method after digestion with concentrated sulfuric acid and a few drops of hydrogen peroxide (Lu, 2000, p. 134– 135). Organic N (ON) was calculated by the difference between Kjieldhal N and NH4 –N. Organic P (OP) was calculated by the difference between TP and WP. Twenty percent of all samples were replicated to ensure quality control. The maximum relative errors were controlled to below 5% for N and P and below 20% for the heavy metals. 2.5. Data analyses Hierarchical cluster analysis (Yu and He, 2003) was used to classify the water samples into different groups based on the relationships among their components. Since the concentration of water components varied greatly, the raw data were standardized by transformation to a maximum magnitude of one before the execution of cluster analysis. Measures for intervals between samples were expressed by Euclidean distance. The concentrations of each component were averaged within each group for further comparisons among the groups by independent-samples t-test (Yu and He, 2003). Independent-samples t-tests were conducted to determine the significant differences among water components between FB and VB for both river and pond water, as well as between river and pond water within each area.

3. Results and discussion 3.1. Grouping of water samples Results of cluster analysis for the 44 water samples using their chemical components (Pb, Zn, Cu, Cd, Cr, TN, NH4 –

N, NO3 – N, ON, TP, WP and OP) were illustrated with a tree dendrogram (Fig. 4). Using a criterion value of the rescaled distance between 4 and 5, the samples were classified into five groups. The average concentrations of the studied components and their speciation in each group are presented in Table 1. These groups can be characterized as follows. Group I: included all 8 pond water samples from the VB area (Fig. 3). The water contained relatively high concentrations of almost all forms of N except NH4 –N, but was low in the five heavy metals and the three forms of P (Table 1). Group II: included all 6 river water samples from the VB area (Fig. 3). The water was relatively high in TP, WP and almost all forms of N, but low in the OP and the five metals. Group III: was composed of the water samples from the main river channel in the FB area (Fig. 2). The water was high in heavy metals, but low in all forms of N and P. Group IV: included all four pond water samples in the FB area and 10 river water samples from tributaries outside the major industrial area of the town in the FB area (Fig. 2). The water was low in all forms of N and P while Pb, Zn and Cu were generally higher than in the VB area, but lower than in the main channel river water. Cr concentration was not significantly different from water in the VB area and lower than the main river channel of the FB area. Cd was high, as in all of the FB water types. Group V: included all the water samples from tributaries within the industrial area of the town in the FB area and one tributary outside the industrial area located near to a large residential area from which it received large quantities of wastewater (Fig. 2). The water contained high concentrations of all forms of P. The concentrations of TN and ON were between group II and III. The concentration of NH4 –N was higher than any other groups. The level of NO3 – N was lower than that of group I and II. The levels of Pb and Cd were relatively high and the level of Cr was relatively low. The level of Zn in this group was between group III and IV and the level of Cu was between Group II and III. The characteristics of the samples in each group indicated that the concentrations of metals and nutrients depended to some extent on the type of water (river, tributary or pond) and its location. There were much higher heavy metal concentrations in the FB area than the VB area, except for Zn and Cr. While Zn and Cr concentrations were much higher in the main river channel of the FB area than in the VB area, they were not significantly higher in the

Q. Zhang et al. / Catena 69 (2007) 57 – 64

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Fig. 4. Dendrogram from cluster analysis of 44 water samples based on their chemical components. Vertical axis: the letters N and W denote NPA and WPA, respectively; the numbers denote the sample number of water.

tributary and ponds in the FB than in the VB area because of the high variability among samples within groups. Within the FB area, concentrations of Zn, Cu and Cr were higher in the main river channel water than all tributaries and pond

water. Distribution of Pb followed a similar pattern in the water systems outside the industrial zone while Cd varied little throughout the FB site. 3.2. Assessment of the surface water quality

Table 1 Comparison of means of metals and nutrients in the surface waters among groups Component Pb (Ag l 1) Zn (Ag l 1) Cu (Ag l 1) Cd (Ag l 1) Cr (Ag l 1) TN (mg l 1) ON (mg l 1) NH4 – N (mg l NO3 – N (mg l TP (mg l 1) OP (mg l 1) WP (mg l 1)

Group I 0.11 c 4.40 d 1.69 c 0.010 b 1.08 c 31.57 ab 15.57 a 1 ) 1.16 d 1 ) 14.85 a 0.16 b 0.07 c 0.08 b

Group II Group III Group IV Group V 0.11 c 7.77 a 5.60 b 16.50 cd 115.81 a 32.10 c 2.15 c 26.42 a 7.95 b 0.008 b 0.038 a 0.045 a 1.07 c 24.38 a 4.28 c 39.56 a 9.96 c 8.08 c 15.65 a 3.29 c 3.36 c 7.73 b 4.79 bc 3.08 cd 16.19 a 1.87 b 1.64 b 1.31 a 0.31 b 0.32 b 0.24 b 0.16 bc 0.19 b 1.07 a 0.15 b 0.13 b

5.70 ab 78.90 b 7.88 b 0.045 a 6.50 bc 30.07 b 8.61 b 20.09 a 1.37 b 1.51 a 0.52 a 0.99 a

Values with different letters in the same row indicate that the means are significantly different at p = 0.05 probability level.

3.2.1. Metals in the surface water The overall mean concentrations of all the heavy metals measured in the VB area were lower than other sites in China, except for Cr that was higher than measurements from Badongbei in central China, and in all cases well below national quality thresholds defined by the Environment Protection Agency of China (Table 2). In contrast, overall mean concentrations of Cu and Cr in the FB periurban area were much higher than in other sites in China and exceeded the first quality threshold which is for river water in national parks (Table 2). The Zn concentration of FB surface water also exceeded the first quality threshold and while comparable with Badongbei in central China was considerably lower than Ha’erbin in Northeast China (Table 2). While the Pb concentration was higher than all

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Table 2 Comparison of river water quality among different sites in China Sites

Location

Pb (Ag l

VB peri-urban area FB peri-urban area Badongbei (Li et al., 2002) Guiyang (Wang et al., 1999) Shanghai (Chen et al., 2001) Ha’erbin (Liu, 1995) Jiangmen (Kang et al., 2000)

Nanjing, E. China Wuxi, E. China Central China Southwest China East China Northeast China South China

Zn 1

0.11 6.55 3.08 12.5 – 7.4 2.85

Environmental quality standard for surface water(GHZB1-1999) I 10 II 50 III 50 IV 50 V 100

Cu

Cd

Cr

)

TP

NH4 – N

NO3 – N

1.31 0.64 – – 0.44 – 0.38

7.73 8.38 – – 4.73 2.01 2.31

16.2 1.65 – 0.84 – – –

0.02 0.1 0.1 0.2 0.2

0.5 0.5 0.5 1.0 1.5

10 10 10 20 25

(mg l 16.5 75.5 79.3 – – 181 –

50 1000 1000 2000 2000

2.15 14.6 3.92 – – 8.15 –

10 1000 1000 1000 1000

0.008 0.043 0.063 10 – 1.1 0.717

1 5 5 5 10

1.07 12.2 0.76 2.5 – 2.33 0.63

10 50 50 50 100

1

)

– : No data available.

other sites except Ha’erbin and approached the first quality threshold, the concentration of Cd was much lower than other sites in China and well below the first quality threshold (Table 2). Within the FB site, while water in the main river channel exceeded the first quality threshold for Zn, Cu and Cr, the pond and tributary water in the rural zone were below the threshold for all five metals and the water in tributaries in the industrial zone exceeded the first quality threshold for Zn but not any of the other metals (Tables 1 and 2). 3.2.2. N and P in the surface water In terms of nutrients, both NH4 –N and TP concentrations in all types of surface water at both sites were higher than other sites in China and above even the fifth quality standard (for agriculture and generic landscapes), except for FB pond water which exceeded the third standard (for drinking water sources, generic fisheries and swimming) for TP and the fourth (for generic industry and entertainment) for NH4 – N (Tables 1 and 2). In contrast, NO3 – N at the FB site was below the first threshold for all types of surface water but higher than Guiyang in Southwest China, the only comparative site for which data are presented, while both pond and river water in the VB area were above the third quality threshold. 3.3. Sources of pollutants in the surface water 3.3.1. Sources of heavy metals There were no factories in the VB area so the main sources of heavy metals in surface water are likely to have been traffic emissions, city wastewater and biosolids used as fertilizer. Given the low concentrations of heavy metals in the pond and river water in this area there is no evidence to suggest that these sources pose a significant risk of heavy metal pollution. The heavy metals in the surface waters of the FB area were significantly higher than in the VB area

(Table 3), and except for Cd, significantly higher in the main river than in farmland tributaries and ponds (Table 1). Many small- to medium-scale factories, such as steel and iron smelting plants, steel pipe plants, and galvanizing plants were distributed along the main river and discharged effluent into it from time to time. Even though the effluent was treated before discharging, the modest contamination with heavy metals found in the main river water may have originated from the factory discharge, while the lower concentrations in water from ponds and tributaries is consistent with aerial deposition of factory emissions (Wong et al., 2003). 3.3.2. Sources of N and P The contributions of NO3 and PO43 to fresh surface water from the chemical weathering of rocks is generally negligible and the contribution of N and P in rainfall is generally low (Markich and Brown, 1998). Nutrient monitoring of 270 Danish streams indicated that 94% of Table 3 Comparison of water quality between the VB and the FB peri-urban area River water Pb (Ag l 1) Zn (Ag l 1) Cu (Ag l 1) Cd (Ag l 1) Cr (Ag l 1) TN (mg l 1) NH4 – N (mg l NO3 – N (mg l ON (mg l 1) TP (mg l 1) WP (mg l 1) OP (mg l 1)

1 1

) )

Pond water

VB area

FB area

VB area

FB area

0.11 b 16.5 b 2.15 b 0.008 b 1.07 a 39.6 a 7.73 a 16.2 a 15.6 a 1.31 a 1.07 a 0.24 a

6.55 a 75.5 a 14.6 a 0.043 a 12.2 a 14.6 b 8.38 a 1.65 b 4.62 b 0.64 b 0.38 b 0.26 a

0.11 b 4.40 b 1.69 b 0.010 b 1.08 b 31.6 a 1.16 a 14.8 a 15.6 a 0.16 a 0.08 a 0.07 a

4.54 a 20.4 a 6.31 a 0.046 a 2.08 a 8.11 b 2.24 a 1.63 b 4.23 b 0.30 a 0.06 a 0.24 a

Values with different letters indicate the means are significantly different at p = 0.05 probability level between the two sites.

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N loading and 52% of P loading arose from non-point source pollution, primarily from agricultural activities (Kronvange et al., 1996). In the present study, most of the N and P in the surface water was probably derived from anthropogenic inputs. The nutrients in pond water could mainly come from field runoff, while the nutrients in river water might have two potential sources, field runoff and inputs of municipal waste. In the FB area, the concentrations of NH4 – N, WP and OP were highest in water in tributaries running though industrial and residential areas (Table 1), implying that municipal wastewater might be the main source of these nutrients. In the VB area, the higher concentrations of NH4 –N, WP and OP in river water than in pond water (Table 1) similarly suggest municipal wastewater as a major source. The concentrations of N (except NH4 – N) in both pond and river water were significantly higher in the VB area than in the FB area (Table 3). The concentration of P (except OP) in the river water of the VB area was significantly higher than that of the FB area (Table 3). Intensive vegetable production uses high inputs of fertilizer, often exceeding crop uptake, which may be transported to watercourses through surface runoff and leaching (Ma and Fang, 2000). Associated research on the vegetable production systems in the VB area revealed that biosolids were the main fertilizers used, with farmers having applied more than 75 t ha 1 year 1 of cattle manure for more than 20 years (Huang et al., 2006). Smith et al. (2001a,b) found that the application of cattle farmyard manure to soil greatly increased the amount of N (2001a) and P (2001b) in surface water flow. Heavy application of cattle manure in the VB area could be an important source of N and P to the surface water in this area.

4. Conclusions These results indicate modest contamination of surface water with Zn, Cr, Cu and possibly Pb, in the factory-based area but not the vegetable-based area, probably arising from discharge of factory effluent. The measurements were well distributed spatially across the two areas and made under relatively low dry season flow rates (0.1 – 0.3 m s 1) but at one point in time, that may not sample all episodic discharges. Severe contamination of river sediments in the factory-based area with Cu, Zn and Cr and some contamination with Pb (Zhao et al., in review) suggest that, despite the relatively low instantaneous concentrations measured in surface water, accumulation of heavy metals through time in the river bed may be a problem. N and P in the surface water of both the peri-urban areas presently studied in the Yangtze River Delta region where higher than in surface water reported from other districts of China and above quality standards set by the Environment Protection Agency in China, except for NO3 in the factory-

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based site. The distribution of N and P in the surface water system indicated that municipal wastewater was probably a major source of N and P in both the factory-based and vegetable-based peri-urban areas, while biosolids, principally cattle manure, used as fertilizer for vegetable production, was likely to have been an additional source of N and P in the vegetable-based area. This study suggests an urgent need to protect surface water from N and P pollution in peri-urban areas of Yangtze River Delta region. Treatment of municipal wastewater before discharge is an immediate priority. Further evaluation of the use of fertilizers by vegetable farmers, with a view to reducing surplus N and P application is also required. Enhancing local peoples’ awareness of the causes and consequences of environmental pollution is likely to be important in pursuing these environmental protection goals.

Acknowledgements We gratefully acknowledge the support for this research from EU project RURBIFARM (Contract No: ICA4-CT2002-10021), Knowledge Innovation Project of Chinese Academy of Sciences (No: KZCX3-SW-427), the Natural Science Foundation of Jiangsu Province (No: BK2002504) and National Key Basic Research Support Foundation (G1999011810).

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