Nitrate Groundwater in Zhangye

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O R I G I N AL A R T I C L E

Nitrate contamination of groundwater in an agroecosystemin Zhangye Oasis, Northwest China

Rong Yang • Wenjie Liu

Received: 1 January 2009 / Accepted: 13 October 2009 / Published online: 4 November 2009

Springer-Verlag 2009

Abstract In order to assess the extent of groundwater

contamination by nitrate (NO3-–N) and to provide infor-mation about the deterioration of the groundwater quality

in Zhangye Oasis, Northwest China, a study was conducted

in this area. The mean value of NO3

-–N concentrations in

groundwater samples was 10.66 ± 0.19 mg l-1. NO3

-–N

concentrations exceeding 10 mg l-1 (the threshold for

drinking water set by the World Health Organization) were

found in 32.4% of 71 wells, and were 13, 33.3, 52.4 and

50.0% in the groundwater samples from drinking wells,

irrigation wells, hand-pumping wells and groundwater

table observation wells, respectively. The result showed

that the groundwater samples that had NO3

-–N concen-

trations exceeding the threshold for drinking water were

mostly collected from a depth of less than 20 m. Ground-

water NO3

-–N concentrations in areas used for the culti-

vation of vegetables, seed maize and intercropped maize

were significantly higher than those in urban or paddy

areas. NO3

-–N contamination of groundwater in areas with

sandy soil was more severe than in those with loam soil.

Keywords NO3

-–N Soil Land use systems

Irrigation

Introduction

In the next several decades, the increasing demand for food

for the growing world population will exert greater stress

on the global environment. More intensive agricultural

production will be required to feed the growing population,

and more widespread use of N fertilizers may, if not

managed properly, exacerbate the problem of groundwater

contmination by NO3

-–N (Di and Cameron 2002). High

NO3

-–N concentrations in drinking water are deemed

harmful to human health. This can interfere with the

transport of oxygen in the blood, causing methemoglobi-

nemia in infants less than 1 year of age (Addiscott 1996),

and is possibly linked with stomach cancer in adults and

with childhood diabetes (Mckinney et al. 1999). High

NO3

-–N concentrations in drinking water are also toxic to

livestock and can cause abortions in cattle. NO3

-–N

draining into bodies of surface water, e.g., rivers, lakes or

estuaries, can cause deterioration of the quality of surface

water, resulting in eutrophication, algal bloom and fish

poisoning (Howarth 1988).

Groundwater NO3

-–N pollution has become a major

concern worldwide. NO3

-–N concentrations exceeding the

drinking water standard were observed in 1,290 groundwater

samples (27%) of 4,967 water samples in a study carried out

in 17 Indian states by NEERI (Nagireddi 2006). A maximum

NO3

-–N concentration of about 450 mg NO3

- l-1 was

observed in the lower portions of the Vamasadhara and

Godavari River basins (Rao 1996). An investigation con-

ducted by Goss et al. (1998) in Ontario, Canada, demon-

strated that 14% of groundwater samples contained NO3

-–N

concentrations exceeding the 10 mg l-1 limit. Excessive

mineral N fertilization has become common in most major

grain and cash crop-producing regions in China (Fang et al.

2006), which has caused large amounts of NO3

-–N

R. Yang (&) W. Liu

Linze Inland River Basin Research Station,

Cold and Arid Regions Environmental and Engineering

Research Institute, Chinese Academy of Sciences, 320

Donggang West Road, CAREERI Building 2, L310,

730000 Lanzhou, China

e-mail: [email protected]

1 3

Environ Earth Sci (2010) 61:123–129

DOI 10.1007/s12665-009-0327-7



accumulation in the soil and increased the risk of ground-

water contamination. A survey conducted by the CAAS in

the provinces of Beijing, Tianjin, Hebei, Shangdong and

Shanxi showed that the proportion of groundwater samples

exceeding the WHO (World Health Organization) and

European limits for NO3

-–N concentration in drinking water

was about 46%of 600groundwater samples, with the highest

NO3-–N concentration reaching 500 mg l-1 (Zhang et al.1996). An investigation conducted in Shouguang County of

Shangdong Province showed that 29% of 80 samples

exceeded the limit in 1998, while the proportion reached

49% in 2001(Ju et al. 2004). However, information was not

available for the Zhangye Oasis where agricultural produc-

tion mainly relies on widespread use of N fertilizers. The

objective of this study, therefore, was to investigate and

assess NO3

-–N contamination of groundwater in the agro-

ecosystem in this area and to discuss management strategies

and practices that can be used to mitigate the problem.

Materials and methods

The study area

The study area is located in the Zhangye Oasis of the Hexi

Corridor region, Gansu Province, Northwest China. This

area is an important base for seed corn and vegetable

cultivation in China, with a land area of 3,943,633.33 ha

(69.32% is used as agricultural land) and a population of

1,278,100 inhabitants. The mean annual temperature and

precipitation are 7.6C and 117 mm, respectively, with

most precipitation distributed from July through Septem-

ber. Mean annual evaporation is 2,390 mm. The zonal soils

are mainly Ari-Sandic Primosols, Ustic Cambosols, Siltigi-

Otrthic Anthrsols and Calci-Orthic Aridosols. Grain crops,

particularly seed maize, are densely cultivated in the

agricultural area of the Oasis, sustained by the continuous

application of chemical nitrogen fertilizers (mainly urea

and salvolatile). In 2005, the total amount of nitrogen

fertilizers applied on the maize fields was more than

300 kg ha-1 year-1 and, more recently, was more than

450 kg ha-1 year-1 (Su et al. 2007).

Collection of groundwater samples

In May 2007, 71 groundwater samples were taken from

irrigation, groundwater table observation, drinking and

hand-pumping wells in courtyards distributed in Ganzhou,

Linze and Gaotai counties. These samples were pumped

more than 5 min before being collected into polythene

bottles that were washed five times with groundwater

samples. These bottles had been thoroughly washed with

acid and then with distilled water five times in the

laboratory before being filled with the groundwater sam-

ples. The distribution of the sampling points is shown in

Fig. 1. Meanwhile, detailed information, including the

collection depth of samples, land use type and soil texture

around the wells, was gathered. Four types of groundwater

were defined based on the depth and utilization of the well:

irrigation wells of about 70–120 m, drinking wells of about

70–150 m, hand-pumped wells of about 6–20 m andgroundwater table observation wells of about 2–10 m

depth.

Measure of groundwater NO3

-–N and estimate

standards

NO3

-–N concentrations were determined by ion exchange

chromatography (Greengerg et al. 1992).

The World Health Organization (WHO) established

drinking water standards in 1984, limiting NO3

-–N con-

centrations to a maximum of 10–11.3 mg NO3

-–N l-1,

equal to 45–50 mg NO3- l-1(Di and Cameron 2002). Inthis paper, a NO3

-–N concentration standard issued by

China in 1986 was used to assess groundwater quality.

According to NO3

-–N concentrations, groundwater sam-

ples were classified as: fine quality groundwater (NO3

-–N

concentrations fall between 0 and 2 mg l-1), fair quality

groundwater (NO3

-–N concentrations fall between 2 and

5 mg l-1), qualifying groundwater (NO3

-–N concentra-

tions fall between 5 and 10 mg l-1), groundwater

exceeding the stipulated standards (NO3

-–N concentra-

tions fall between 5 and 10 mg l-1) and groundwater far

exceeding the stipulated standards (NO3

-–N concentra-

tions above 20 mg l-1).

Results and discussion

Status of groundwater NO3

-–N pollution

The statistical summary for the NO3

-–N concentrations

from 71 water samples is presented in Table 1. The average

NO3

-–N concentration of 10.66 mg l-1 (range 0.35–

73.82 mg l-1) was marginally higher than the drinking

water standards of the World Health Organization (WHO).

However, the maximum was 73.82 NO3-–N mg l-1, and

NO3

-–N concentrations exceeding 10 and 20 mg l-1 were

found in 32 and 16.9% of all samples, respectively.

Groundwater samples collected from Linze showed

higher NO3

-–N concentrations (0.48–54.9 mg l-1) than

those from Ganzhou (0.83–30.99 mg l-1) and Gaotai

(0.35–73.82 mg l-1). Table 2 shows that NO3

-–N con-

centrations in 43% of the sites were above 10 mg l-1 in

Linze; however, they were 25 and 26% in Ganzhou and

Gaotai, respectively, suggesting that groundwater NO3

-–N

124 Environ Earth Sci (2010) 61:123–129

1 3



Fig. 1 Location of sample

wells in the survey

Table 1 Groundwater NO3

-–N concentrations and frequency distribution

Region NO3-–N concentration

(mg l-1)

C.V. (%) Scope (mg l-1) Frequency of NO3-–N concentration (%)

NO3

-–N concentrations classifications (mg l-1)

0–2 2–5 5–10 10–20 [20

Ganzhou (n = 23) 8.17 ± 0.32 89.6 0.83–30.99 13.0 26.1 34.8 17.4 8.7

Linze (n = 28) 12.03 ± 0.48 111.5 0.48–54.9 25.0 17.9 14.3 17.9 25.0

Gaotai (n = 20) 11.59 ± 0.95 163.2 0.35–73.82 35.0 25.0 15.0 10.0 15.0

Total (n = 71) 10.66 ± 0.19 128.1 0.35–73.82 23.9 22.5 21.1 15.5 16.9

Table 2 Groundwater NO3

-–N concentrations and frequency distribution of different types of wells

Type of well NO3

-–N concentration

(mg l-1)

C.V. (%) Scope

(mg l-1)

Frequency of NO3

-–N concentration (%)

NO3

-–N concentrations classifications

(mg l-1)

0–2 2–5 5–10 10–20 [20

Drinking well (n = 32) 5.75 ± 0.20 110.82 0.48–31.14 21.9 40.6 25.0 6.3 6.3

Irrigation well (n = 6) 11.44 ± 1.70 89.24 1.12–30.99 16.7 0.0 50.0 16.7 16.7

Hand-pumped well (n = 21) 17.41 ± 0.96 116.2 0.35–73.82 33.3 4.8 9.5 23.8 28.6

Observation well of groundwater table (n = 12) 11.53 ± 0.92 95.46 0.7–35.54 16.7 16.7 16.7 25.0 25.0

Environ Earth Sci (2010) 61:123–129 125

1 3



pollution in Linze was more serious than in Ganzhou and

Gaotai.

NO3

-–N contamination in different well types

The average NO3

-–N concentration was 5.75 mg l-1 (0.7–

21.7 mg l-1) in the drinking wells. Among them, there

were only four wells with NO3-–N concentrations greaterthan 10 mg l-1, 12.5% of the total drinking wells; the

water in 87.5% of the drinking wells was safe to drink.

The average NO3

-–N concentration of 11.44 mg l-1 (1.12–

30.99 mg l-1) in the irrigation wells was 49.7% higher than in

drinking wells. Among these, 33.3% of all the irrigation wells

had NO3

-–N concentrations greater than 10 mg l-1.

NO3

-–N contamination was of concern of in both hand-

pumped and groundwater table observation wells. The

average NO3

-–N concentration was 17.41 mg l-1 (0.35–

73.81 mg l-1) and 11.53 mg l-1 (0.70–35.54 mg l-1) in

hand-pumped wells and groundwater table observation

wells, respectively; 52.4% of hand-pumped wells and50.0% of groundwater table observation wells had NO3

-–

N concentrations greater than 10 mg l-1 (Table 2).

NO3

-–N concentrations of groundwater samples

from different collection depths

From Table 3, we can see that NO3

-–N concentrations were

related to sampling depth. Twenty-three water samples had

NO3

-–N concentrations exceeding the allowed values set by

the WHO. Among them, 19 water samples were collected

from 0- to 20-m water level, three samples were collected

from 20- to 100-m water level, and only one sample was

collected from[100-m water level, indicating the NO3

-–N

contamination mainly occurred at shallow water levels. That

NO3

-–N concentrations decrease with sampling depth may

be logical if the main source of NO3

-–N in groundwater is

the leaching of N through soil. Furthermore, the groundwater

close to the Heihe River where the water level is relatively

lower has a high risk of being polluted by NO3

-–N, which

accordingly threatens the water quality of this river.

Figure 2 shows the relationship between groundwater

NO3

-–N concentration and sampling depth. In general,

high concentrations were found at shallow levels, but there

was not a significant correlation between NO3

-–N con-

centration and sampling depth, because other factors may

be influential.

Influence of land use and soil texture on NO3

-–N

contamination of groundwater

The results of the investigation of NO3

-–N contamination of

groundwater in relation to different types of agricultural land

use showed that the average NO3


(29.50 mg l-1) in the greenhouse areas were characteristi-

cally high, followed by those in the seed maize

(19.43 mg l-1) and vegetable cultivation areas

(12.67 mg l-1). The main factor contributing to the differ-

ence in concentrations of NO3-–N in groundwater amongland use types could be the different kinds of fertilizer

management.

About 40 and 60% of intercropped maize with wheat

and seed maize areas were associated with unacceptable

concentrations of groundwater NO3

-–N (NO3

-–N con-

centrations beyond the allowed values set by the WHO),

respectively. Exceptionally unacceptable concentrations

were found in all groundwater samples collected from the

greenhouse and vegetable cultivation areas. This could be

attributed either to high N fertilizer input or high irrigation

rates in these area. There were no unacceptable concen-

trations found in groundwater sampling from paddy and

urban areas.

Groundwater sampling from the seed maize area and

sampling depth below 20 m were obtained to estimate the

effect of soil texture on NO3

-–N concentration. Data from

Table 3 Range of NO3

-–N concentrations in groundwater at dif-

ferent sampling depths

NO3

-–N

concentration (mg l-1

)

Number of samples

Sampling depth (m)

\20 20–100 [100

0–2 9 6 2

2–5 5 4 7

5–10 5 6 4

10–20 9 1 1

[20 10 2 0

y = -3.25ln( x ) + 21.00 R² = 0.088

0

10

20

30

40

50

60

70

80

0 50 100 150 200

N O 3

- - N c o n c e n t r a t i o n ( m g L - 1 )

Dept h of colledted sample (m)

Fig. 2 Correlation analyses of groundwater NO3


and collection depth


1 3



20 samples are given in Table 4; the result showed that soil

texture had an apparently direct effect on NO3

-–N con-

centrations in groundwater, which could be due to NO3

-–N

leaching in sandy soils being easier than in loamy soils.

Discussion

Status of NO3

-–N contamination of groundwater

at the study area

Over the past several years, there has been growing con-

cern about nitrate pollution of groundwater. In China, this

problem is becoming serious due to surplus application of

N fertilizers with continuously decreasing recovery rates in

the crop fields. Many investigations of nitrate concentra-

tions in groundwater in China have showed that the sam-

ples exceeded the WHO and European limits for NO3

-–N

concentrations in drinking water of 10–11.3 mg NO3

-–

N l-1 (Yu et al. 2006; Ju et al. 2004). Although these

investigation data cannot reflect the whole situation of

groundwater NO3-–N concentrations in China, they doshow that groundwater in some regions is facing the threat

of NO3

-–N contamination. In the Zhangye Oasis located in

the middle reaches of the Heihe River, Northwest China,

where groundwater is a major source of drinking water and

agriculture relies on large applications of N fertilizer, the

problem of nitrate contamination of groundwater has been

given little attention in the last decades. However, 32.4%

of groundwater samples had NO3


exceeding 10 mg l-1.

Factors that have an effect on the NO3

-–N

contamination of groundwater

Different land use systems had a significant impact on the

amount of NO3

-–N leaching losses, thus having a signifi-

cant impact on the NO3


(Kulabako et al. 2007; Bohm et al. 2008). An investigation

conducted in the Kakamigahara Heights, Gifu Prefecture,

central Japan, showed that the NO3

-–N concentration of

groundwater under vegetable fields was significantly higher

than that under urban land or paddy fields, and most of the

unacceptable NO3

-–N levels were encountered in bore-

holes in the vegetable fields, but a few were also found in

boreholes in the urban area (Insaf et al. 2004). A similar

result was reached in this investigation. The concentration

of NO3

-–N in groundwater under areas growing vegeta-

bles, seed maize and intercropped maize areas, and espe-

cially under greenhouse areas was significantly higher than

that under urban land or paddy areas.

In general, the actual amount of N leached from a par-

ticular land use system depends on the soil (Kohler et al.2006) and on management practices. The NO3

-–N leach-

ing losses are usually less from fine-textured soil than from

coarse-textured soils because of slower drainage and

greater potential for denitrification. This was indeed the

case in this study, as concentrations of NO3

-–N in

groundwater were significantly (2.74 times) higher in

sandy than in loamy soil.

Moreover, the depth of soil above the groundwater level

or above gravel is also an important factor affecting NO3

-–

N concentrations in groundwater, with NO3

-–N reaching

the groundwater quicker in shallow soils than in deep soils

(Kolpin et al. 1994). A study indicated that low ground-water tables caused the contamination (Ruijter et al. 2007).

In this investigation, most of the groundwater samples in

which the NO3

-–N concentration was greater than the

allowed values set by the WHO were sampled from less

than 20-m depth.

Strategies to mitigate NO3

-–N contamination

of groundwater

As can be seen from this study, groundwater in this area is

facing the threat of NO3

-–N pollution and is affected by

the type of well, soil texture and land use and by collection

depth. The reduction of NO3

-–N contamination of

groundwater requires an integrated approach to minimize

NO3

-N accumulation and leaching from soil. Some of the

advice that has been given is as follows.

Optimizing N fertilizer application

Reducing total N input is one of the effective options for

reducing NO3

-–N leaching. Obviously, the optimum

Table 4 Influence of soil texture on NO3


Soil texture NO3

-–N concentration

(mg l-1)

Scope

(mg l-1)

Frequency of NO3

-–N concentration (%)

NO3

-–N concentrations classifications (mg l-1)

0–2 2–5 5–10 10–20 [20

Sandy soil (n = 11) 27.20 ± 1.96 0.70–73.82 18.2 9.1 0.0 9.1 63.6

Loamy soil (n = 9) 9.93 ±

0.87 0.48–26.18 11.1 11.1 33.3 33.3 11.1Total (n = 20) 19.43 ± 0.95 0.48–73.82 15.0 10.0 15.0 10.0 50.0


1 3



amount of N required varies depending on the particular

production system. Synchronizing the N supply with plant

N demand together with a proper application rate is the best

way to avoid the accumulation of mineral N in the soil.

This approach requires a good understanding of a plant’s N

requirements at different growing periods and the capacity

to apply it to the soil to meet that demand. Plant tissue

analysis will help in deciding the N requirements, and thebiggest challenge is to determine the amount of soil N that

can be released for plant uptake (Di and Cameron 2002).

Improved irrigation management

Drainage volume is a main factor to determine the amount

of NO3

-–N leached from the plant root zone to ground-

water. Reducing the amount of irrigation and improved

irrigation strategies may also reduce the leaching potential

of NO3

-–N.

Improved efficiency of N use

Balancing the input of other nutrients, precision cultiva-

tion, crop rotation, etc., can improve the efficiency of N use

to reduce the amount of N remaining in the soil, thereby

reducing the threat of contaminating the groundwater with

NO3

-–N.

Agricultural environmental policies and legislation

Application of agricultural environmental policies and

legislation depends on factors such as type of soil, climate

conditions, rotation systems and yield levels (Kirchmann

et al. 2002). So far, no fertilization norms and ordinances

exist in China, although the ‘‘Agricultural Law’’ has some

articles referring to fertilization, but no detailed instruc-

tions. Some scholars and agriculture policy makers are

currently discussing possible future fertilization norm

ordinances in order to control the contamination of

groundwater by NO3

-–N.

Conclusion

The results showed that 32.4% of the groundwater well

samples in Zhangye Oasis, Northwest China, had NO3

-–N

concentrations greater than the allowed values set by the

WHO. The average concentration of NO3

-–N in tested

wells was 10.66 ± 0.19 mg l-1. The results suggest that

the environmental factors that control NO3

-–N concen-

trations in groundwater are: the type of well, soil texture,

type of land use and sampling depth of the groundwater. It

is suggested that concrete policies for pollution control

and/or prevention measures could be adopted to better

control NO3

-–N contamination of groundwater in this

region.

Acknowledgments The authors are grateful to the editor and the

two anonymous reviewers for their comments and revision of the

manuscript. This work was supported by The National Basic Research

Program of China (no. 2009CB421302) and Natural Science Foun-

dation of Gansu Province (no. 0710RJZA123).

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Nitrate Groundwater in Zhangye

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