Spatial and temporal variation of atmospheric nitrogen deposition in the North China Plain

Spatial and temporal variation of atmospheric nitrogen deposition in the North China Plain

ACTA ECOLOGICA SINICA Volume 26, Issue 6, June 2006 Online English edition of the Chinese language journal Cite this article as: Acta Ecologica Sinica...

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ACTA ECOLOGICA SINICA Volume 26, Issue 6, June 2006 Online English edition of the Chinese language journal Cite this article as: Acta Ecologica Sinica, 2006, 26(6), 1633−1639.

RESEARCH PAPER

Spatial and temporal variation of atmospheric nitrogen deposition in the North China Plain Zhang Ying1, 2, Liu Xuejun2, *, Zhang Fusuo2, Ju Xiaotang2, Zou Guoyuan3, Hu Kelin2 1 State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, CAS, Nanjing 210008, China 2 College of Resources and Environmental Sciences, China Agricultural University, Beijing 100094, China 3 Institute of Plant Nutrition and Resources, Beijing Academy of Agro-Forestry Sciences, Beijing 100089, China

Abstract: A monitoring network of nine sites was established to determine the spatial and temporal variation of atmospheric nitrogen (N) deposition in the North China Plain (NCP) over a two-year period. The annual bulk deposition of inorganic N in the North China Plain ranged from 18.4 to 38.5 kg/hm2 and averaged 28.0 kg/hm2. The concentration of NH4+-N and NO3¯-N in rainwater averaged 3.76 and 1.85 mg/L, respectively, which were significantly higher than the values at background sites in China (normally less than 0.5 mg/L). Annual bulk deposition of inorganic N in the Beijing area (32.5 kg/hm2) was higher than that in Shandong and Hebei provinces (21.2 kg/hm2 on an average). Also bulk N deposition was much greater in Dongbeiwang and Fangshan than in Yanqing and Shunyi counties. Significant spatial variation of bulk deposition was observed in the Beijing area because of variation of precipitation, and 60% of bulk deposition occurred from June to September. Bulk deposition of NH4+-N was 2.0 times that of NO3¯-N deposition at the rural monitoring sites. However, the situation was reversed at the Beijing Academy of Agricultural-Forestry Sciences (BAAFS), the unique urban monitoring site. The results suggest that reduced N in precipitation is dominant in rural regions, but oxidized N is the major form in urban regions. The positive relationship between inorganic N deposition and precipitation can be fitted by a power equation (r2 = 0.67), showing an increase of NH4+-N and NO3¯-N inputs with increased precipitation. Wet deposition of N accounted for 73% of the bulk deposition, implying that dry deposition of N, particularly NH4+-N from dust, is important in the North China Plain. Key Words: atmospheric deposition; nitrogen; precipitation; North China Plain; agro-ecosystem

Atmospheric reactive N components have increased sharply because of human activities, such as fertilizer use, fossil - combustion, and intensive husbandry[1 3], which have resulted in the globalization of atmospheric N deposition[4]. The average values of atmospheric N deposition were 5 kg/(hm2·a) all over the world[2], 10 kg/(hm2·a) for Europe[5], and 7 kg/(hm2·a) for Asia[6] and Central North America. Western Europe, China, and India are the three regions with the highest N deposition in the world[7]. Concern about atmospheric N deposition, as a nutrient resource and as a part of acid deposition, is increasing with the acceleration of global N cycling[8] all over the world, - including China[9 11]. However, information on atmospheric N deposition, especially the spatial and temporal variation of N deposition in the intensive agro-ecosystems within the North China Plain, is still scarce.

The North China Plain (NPC), called “China’s granary”, is one of the most intensive agricultural regions in China. Excessive use of fertilizer N is very common, particularly in regions with high population densities. In the Beijing area, for example, the average N application rate was up to 565 kg/hm2 in the wheat–maize double-cropping rotation system[12]. Overuse of fertilizer has resulted in the accumulation of nitrates in the soil[13], nitrate leaching[14], intensive ammonia emission[15], and N2O emission[16], which have seriously influenced the development of the agro-economy and the environment. Moreover, unnecessary loss of N fertilizer, especially NH3 volatilization, increases the concentration of atmospheric reactive N and enhances the overloaded N budget. In this study, we aimed at determining the budgets, and spatial and temporal variation of atmospheric N deposition in the NCP to assist in the develop-

Received date: 2005-02-23; Accepted date 2005-07-20. *Corresponding author. E-mail: [email protected] Copyright © 2006, Ecological Society of China. Published by Elsevier BV. All rights reserved.

ZHANG Ying et al. / Acta Ecologica Sinica, 2006, 26(6): 1633–1639

ment of integrated N management and the assessment of the effect of N deposition on the surrounding ecosystems.

1

Materials and methods

1.1 Monitoring sites A monitoring network has been gradually established at nine monitoring sites in the NCP since 2003 (Table 1). All the sites are located in vegetated, flat areas without obstacles. The temperate, semimoist, and continental climate is influenced by the monsoon, with 400–800 mm annual precipitation, mainly between June and September. The mean temperature is 8–14℃, and the annual accumulated temperature (>0℃) is 3200–4500℃. 1.2 Sampling and analysis The study had been carried out since January 2003, with rain gauges (SDM6, Tianjin Weather Equipment Inc., China) installed at all sites (Table 1). A wet-only sampler (APS-III, Wuhan Tianhong Inc., China) was installed at the same time as the bulk gauge at DBW in Beijing. The wet-only samples have been collected since June 2003. Bulk deposition (wet deposition with part of dry deposition such as N from dust) was collected, thoroughly mixed, and stored in plastic bottles, immediately after each rain event. It was then frozen unfiltered at − 17℃ in a refrigerator until analysis for NH4-N and NO3-N by a Continuous Flow Analyzer (TRACC2000, Germany) within three months. Rain gauges were cleaned with deionized water after each collection. The procedures for collection and analysis of wet-only deposition were the same as those for bulk deposition. Bulk or wet-only deposition of NH4-N and NO3-N was then calculated using the following equations, as introduced by Liu et al[17]: N deposition per event (g/m2) = 0.001×precipitation (mm) ×NH4-N or NO3-N concentration in rainwater (mg/L) 2 N deposition per month or year (kg/hm ) = 10×ΣN deposi2 tion (g/m ) per event in a month or a year

2

Results and discussion

2.1 Spatial variation of bulk N deposition As shown in Table 2, annual bulk N deposition ranged from 19.2 to 38.5 kg/hm2 and averaged 28.0 kg/hm2 in the NCP in

2003 and 2004; variation in deposition was mainly because of the considerable variation in rainfall (384–639 mm) over the same period. Such a high N input meant that atmospheric N deposition was an important N source to the agro-ecosystems in the NCP. The concentrations of ammonium and nitrate N in rainwater were 3.76 and 1.85 mg/L on an average, respectively, which were 3–5 times of the mean inorganic N concentrations of precipitation in China[18]. Our results show that ammonium and nitrate N concentrations in rainwater in NCP were 5–8 and 3–4 times of those observed in the precipitations in Europe[19], North America[20], and Japan[21]. Ammonium N deposition and nitrate N deposition correspondingly accounted for 67% and 33% of the total inorganic N deposition in the NCP, and the ratio of ammonium N deposition to nitrate N deposition (about 2.0) was similar to the ratio of bulk N deposition in China, as well as nonurban areas in North America and Western Europe[22,23]. Bulk N deposition was up to 32.5 kg/(hm2·a) in the Beijing area (CEF and DBW), while less N was deposited (21.2 kg/(hm2·a) on an average) in Shandong (Huimin) and Hebei (Quzhou) provinces, China (Table 2). Sun et al[24] reported a similar annual bulk N deposition (averaged 30.9 kg/hm2) at a suburb near the Chinese Academy of Agricultural Sciences, Beijing, China, in a seven-year study (1986 to 1992). However, the annual rainfall decreased from about 600 mm in the 1980s to less than 500 mm in our study period, resulting in an increasing N concentration in precipitation. Furthermore, the concentrations of N components in Beijing were greater than those in Shandong and Hebei provinces (Table 2), illustrating heavy pollution in the Beijing area. There was also a spatial variation of bulk N deposition in the Beijing area (Table 2). For example, DBW and Fangshan received much higher bulk N deposition than Shunyi and Yanqing. Reduced N deposition was dominant in rural regions, while oxidized N deposition was dominant at the urban sites (BAAFS) because of traffic sources. Bulk deposition of ammonium was 1.8 times that of nitrate deposition in nonurban monitoring sites, but the situation was reversed in the urban region (Table 2). Bulk N deposition ranged from 6.6 to 23.1 kg/(hm2·a) in South China[9,10,25,26] and 5.1 to 25.4 kg/(hm2·a) in North - China[11,27 29], which was much lower than the values obtained

Table 1 Introduction of the atmospheric nitrogen deposition monitoring sites in the North China Plain Province

Monitoring site

Beijing

Dongbeiwang CEF Fangshan BAAFS Shunyi Daxing Yanqing Huimin Quzhou

Shandong Hebei

Location 40º03′ N, 116º17′ E 39º50′ N, 116º25′ E 39º41′ N, 116º08′ E 39º56′ N, 116º17′ E 40º03′ N, 116º41′ E 39º35′ N, 116º20′ E 40º26′ N, 115º55′ E 37º29′ N, 117º32′ E 36º52′ N, 115º01′ E

CEF (Campus Experimental Farm); BAAFS (Beijing Academy of Agro-Forestry Sciences)

Period of monitoring 2003.01-2004.12 2003.01-2004.12 2004.04-2004.09 2004.04-2004.08 2004.04-2004.09 2004.04-2004.09 2004.04-2004.09 2003.01-2004.12 2003.01-2004.12

Monitoring type Suburb site Suburb site Rural site Urban site Rural site Rural site Rural site Rural site Rural site

ZHANG Ying et al. / Acta Ecologica Sinica, 2006, 26(6): 1633–1639

Table 2 Spatial and temporal variation of atmospheric nitrogen deposition in the North China Plain Monitoring site

Year

(mm)

Input (kg/hm2)

Concentration (mg/L)

Precipitation +

NH4 -N

NO3¯-N





NH4 -N

NO3¯-N

NH4+-N/ ∑

NO3¯-N

North China Plain CEF

2003.01–12

483.0

5.19

2.44

7.63

25.07

11.79

36.86

2.13

2004.01–12

446.2

3.25

2.18

5.43

14.50

9.73

24.23

1.49

2003.01–12

484.9

5.60

2.33

7.93

27.17

11.29

38.46

2.41

2004.01–12

472.8

4.45

1.95

6.40

21.03

9.23

30.26

2.28

2003.01–12

620.5

2.30

0.80

3.10

14.26

4.96

19.22

2.88

2004.01–12

639.4

1.81

1.08

2.89

11.55

6.89

18.44

1.68

2003.01–12

624.2

2.82

1.13

3.95

17.59

7.04

24.63

2.50

2004.01–12

384.1

3.71

2.13

5.84

14.25

8.2

22.45

1.74

CEF

2004.04–09

419.8

2.88

2.10

4.98

12.09

8.83

20.92

1.37

Dongbeiwang

2004.04–09

443.1

3.83

1.64

5.47

16.99

7.26

24.25

2.34

Dongbeiwang

Huiming

Quzhou

Beijing area

Daxing

2004.04–09

435.0

2.85

1.35

4.20

12.41

5.86

18.27

2.12

Shunyi

2004.04–09

435.0

2.09

1.61

3.70

9.08

6.99

16.07

1.30

Fangshan

2004.04–09

499.3

3.27

1.75

5.02

16.32

8.74

25.06

1.87

Yanqing

2004.04–09

398.0

2.15

1.37

3.53

8.56

5.47

14.06

1.57

BAAFS

2004.04–08

361.5

2.10

2.65

4.75

7.58

9.60

17.18

0.79

Fig. 1 Relationship between rainfall and nitrogen deposition

in our study. Even in the same area, N inputs from atmospheric deposition to agro-ecosystems were often higher than those to forest ecosystems[30,31]. Compared with N deposition from precipitation (1.8–3.2 kg/(hm2·a)) in remote areas of the - world[32 34], the heavy N deposition in NCP (28 kg/(hm2·a) on

an average) could be only explained by the large emission of gaseous N species from intensive agricultural and industrial activities. 2.2 Temporal variation of bulk N deposition Bulk deposition of inorganic N showed a large monthly

ZHANG Ying et al. / Acta Ecologica Sinica, 2006, 26(6): 1633–1639

Table 3 Comparison of bulk N deposition and wet N deposition at Dongbeiwang site Type of deposition

No. events sampled

2

Deposition (kg/hm )

Concentration (mg/L) +



NH4 -N

NO3 -N



+

NH4 -N



NO3 -N



2003.06–11(rainfall: 370mm) Bulk deposition

33

5.19

1.92

7.11

19.21

7.09

26.30

Wet deposition

33

3.51

1.34

4.85

13.00

4.96

17.96

1.68

0.58

2.26

6.21

2.13

8.34

Difference

0.68

Dw/Db 2004.04–11(rainfall: 458mm) Bulk deposition

39

3.95

1.78

5.73

18.11

8.17

26.28

Wet deposition

39

3.07

1.43

4.50

14.05

6.53

20.58

0.88

0.35

1.23

4.06

1.64

5.70

Difference

0.78

Dw/Db Dw: Wet deposition; Db: Bulk deposition

variation, because of the monthly variation in precipitation; 60% of bulk N deposition occurred between June and September (data not shown). Results for DBW, CEF, HM, and QZ between 2003 and 2004 showed that there was a positive relationship between N deposition and rainfall (r2 = 0.67, Fig. 1), supporting the hypothesis that the temporal variation of bulk N deposition in the NCP was mainly driven by the rainfall. 2.3 Wet deposition of N Bulk deposition, including wet deposition and some dry deposition (mostly dust), was always higher than wet deposition. Wet N deposition was 18.0 and 20.6 kg/hm2 in 2003 (June to November) and 2004 (April to November) in comparison with bulk N deposition of 26.3 kg/hm2 at each period (Table 3). Wet N deposition only accounted for 73% of bulk N deposition on an average. The percentage of wet N deposition to bulk N deposition tended to increase with rainfall. The difference between wet and bulk deposition was smaller in July and August, the rainy season, compared with that in other drier months, especially in the spring season (Fig. 2). But bulk N deposition included only a part of the dry deposition, such as particulates (accounting for 27% of the bulk N deposition). Taking the N inputs from aerosols and gases into account, the

ratio of dry N deposition to wet N deposition in the NCP would be much higher than that in Europe and North Amer- ica[35 37], and the total N deposition would be no less than the level in the high N-deposition region of Europe[38,39].

3

Conclusions

Annual N inputs from precipitation in the NCP can be as high as 28 kg/hm2, making this a polluted area. N deposition and rainfall can be modeled by a power equation, with 60% N deposition occurring from June to September. Except for the monitoring site in the urban area, ammonium N was the dominant component of inorganic N, and was about twice that of nitrate N on an average. Wet N deposition only accounted for 73% of the bulk N deposition, implying that dry N deposition was a significant form in this area. The total N deposition in the NCP is probably much higher than that measured as bulk deposition because inputs from aerosols and gases, as well as organic N, were not measured.

Acknowledgements We thank Prof. Dr. Keith Goulding in Rothamsted Research, UK for his kind help in the revision of the English in this article. The study was supported by the National Natural Science Foundation of China (Grant No. 30370287, 20577068 and 30390080), the 948 Key Import Project of Chinese Ministry of Agriculture (202003-Z53), the Ph.D Foundation of Chinese Ministry of Education (20030019038), and the Sino-German Cooperative Project (DFG International Research Training Groups, JK1070).

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