From Production to Consumption: A Coupled Human–Environmental

Jan 30, 2018 - Finally, we provide suggestions to improve the N management practices and reduce the N losses from the environment in China. These meth...
0 downloads 9 Views 1MB Size
Subscriber access provided by University of Florida | Smathers Libraries

Article

From production to consumption: A coupled humanenvironmental nitrogen flow analysis in China Zhibo Luo, Shanying Hu, Dingjiang Chen, and Bing Zhu Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.7b03471 • Publication Date (Web): 30 Jan 2018 Downloaded from http://pubs.acs.org on January 30, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Environmental Science & Technology is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 27

Environmental Science & Technology

1

From production to consumption: A coupled human-

2

environmental nitrogen flow analysis in China

3

Zhibo Luo§, Shanying Hu∗,§, Dingjiang Chen§, Bing Zhu§

4

§ Center for Industrial Ecology, Department of Chemical Engineering, Tsinghua University, Beijing 100084,

5

China

6

*Corresponding email: [email protected]

7 8

ABSTRACT

9

Anthropogenic inputs of reactive nitrogen (Nr) provide sufficient food, energy and industrial products to meet human

10

demands; however, only a fraction of Nr is consumed as food and nonfood goods, and the rest is lost to the

11

environment and negatively affects ecosystems. High-resolution studies of nitrogen flows are invaluable to increase

12

nitrogen use efficiencies and reduce environmental emissions. In this study, a comprehensive substance flow analysis

13

of nitrogen for China in 2014 is presented. Based on the conceptual framework, which highlights the key roles of

14

human drivers, the analysis of the synthetic ammonia supply and demand balance shows that 75% of ammonia is used

15

for agricultural purposes. Moreover, the life cycle analysis of food nitrogen shows that human food consumption

16

accounts for approximately 7% of the total Nr inputs. A quantitative analysis of pollutant emissions shows that

17

industrial and crop production are the main sources of atmospheric emissions, while livestock farming and crop

18

production are the main sources of water emissions. Finally, we investigate four scenarios (efficiency improvement,

19

high recycling rate, nitrogen oxide emission reduction and a combined scenario) and provide relevant policy

20

recommendations (large farm size, standardized agricultural production model, flue gas denitration, etc.) for improving

21

nitrogen management practices.

ACS Paragon Plus Environment

Environmental Science & Technology

Page 2 of 27

22 TOC Art

23 24 25

INTRODUCTION

26

Nitrogen (N) is one of the most important elements in natural ecosystems and is the main factor that influences the

27

species composition, diversity, functions and dynamic change of ecoystems1, 2. Because N is related to different kinds

28

of biochemical reactions and compound forms, it is difficult to accurately measure and quantify, thereby affecting the

29

large-scale estimations and simulations3, 4. Before the 20th century, N was naturally cycled and regulated during the

30

operation of natural ecosystems by biological N fixation (BNF), lightning N fixation (LNF), N deposition and

31

denitrification4, 5. Since the invention of Haber-Bosch nitrogen fixation (HBNF), a large amount of reactive N (all N

32

species other than N2, Nr) has been added to terrestrial ecosystems (an increase of 14 times from 1890 to 20106) to

33

ensure global food security and meet the food demands of approximately 48% of the world population7, 8. Such

34

processes have greatly altered the N cycles in terrestrial ecosystems and marine ecosystems5, 9, 10.

35

The Nr cascade effect also creates various environmental problems11-13, such as nitrate enrichment in groundwater14,

36

freshwater eutrophication15, air pollution16 (photochemical smog and particulate matter), stratospheric ozone

37

depletion17, loss of biodiversity18, climate change19 and the deterioration of coastal ecosystems20, which have seriously

38

threatened human health and safety21. Some scholars believe that N pollution is the third largest environmental problem

39

in the world following biodiversity reduction and global warming21-24.

40

With population growth and urbanization, China has become the largest Nr producer and consumer in the world25-27.

41

The problems of accelerated Nr creation and emission (e.g., lake water eutrophication14, 15, haze and nitrogen oxide

42

emissions16, etc) in China have posed important and growing impacts to human and ecosystem health28. Thus, efficient

ACS Paragon Plus Environment

Page 3 of 27

Environmental Science & Technology

43

resource management, including the reduction of Nr losses and improvement of the Nr use efficiencies across different

44

sectors of the Nr nexus, is key to securing food production and reducing environmental pressure in China29, 30.

45

To map the potential of the recovery and reuse of Nr, high-resolution information regarding Nr streams is critical.

46

Substance flow analysis31 (SFA) allows for the quantification of Nr flows throughout processes driven by human

47

consumption, and the approach can identify Nr hot spots and losses to the environment; thus, SFA provides an

48

important tool for the transition toward sustainable Nr management. Moreover, the input of anthropogenic Nr is mainly

49

required to meet human demands for food, energy and nonfood goods26; therefore, highlighting the key roles of human

50

consumption is particularly important32, 33. These human drivers are critical regulators of Nr flows and the associated

51

spatial interactions, as the environmental system is most directly affected by anthropogenic perturbations4, 21, 34. The

52

conceptual framework of an “N footprint” was developed to provide a tool to determine the contribution of an entity to

53

Nr losses to the environment from personal resource uses26, 35. The N footprint has become a well-established method

54

for describing how human activities impose various types of burdens and impacts on the life support systems of Earth

55

and showing how changing behavior patterns have altered Nr losses in recent years26, 36-39. The underlying calculation

56

methods and corresponding indicators for the N footprint method have gained increasing public attention and been

57

applied at several scales37, 40-44.

58

The previous large-scale studies of N flows have mainly focused on specific aspects of the nutrient chain41, 42, 45, 46,

59

industrial systems47, 48 or environmental impacts49, 50, and in-depth studies of the historical trends of several major N

60

flows (e.g., HBNF, BNF, LNF and fossil fuel combustion) have been performed at global5, national27 and regional51

61

scales; however, a holistic and detailed approach is still lacking. Notably, the current N footprint model is a bottom-up

62

calculation approach that is mainly based on personal estimates of food and energy consumption, and industrial

63

products and non-food agricultural products are not considered in the model35. The research on N metabolism from a

64

limited perspective will ignore some of the sudden hot spots and new pollution sources, such as the rapid growth of

65

industrial N emissions in China in recent years19, which will result in a missed opportunity to guard against these

66

becoming sources of pollution in the future. Therefore, it is particularly important to provide high-quality data

67

acquisition and detailed analysis that can form an interesting tool for the transition towards sustainable N management.

68

The primary purposes of this study are to develop a new coupled human-environmental N cycle model at the national

ACS Paragon Plus Environment

Environmental Science & Technology

Page 4 of 27

69

scale and then use this model to assess and quantify the contributions of different N sources to the overall N pollution

70

in China. The model core is based on the human drivers of N metabolism and the associated effects on various

71

subsystems. This study is beneficial for understanding N trends and proposing effective policy measures (Fig. 1).

72

We conducted an N balance analysis from the perspective of consumption, including a supply and demand balance

73

analysis of synthetic ammonia and a life cycle analysis of food-based N. Then, the impact of the N flow process on the

74

environment was quantitatively estimated. In addition, we investigated future agricultural, industrial and waste

75

management scenarios that could minimize total N emissions while meeting N production demands. Finally, we

76

provide suggestions to improve the N management practices and reduce the N losses from the environment in China.

77

These methods and results can function as decision support tools in other nutrient intensive regions.

78 79

METHODS

80

Model Description

81

In this study, the national N cycle based on human-environmental coupling (Fig. 1) is divided into six subsystems:

82

industry, agriculture, human consumption, waste management, the atmosphere and the hydrosphere (excluding the

83

ocean). The agricultural subsystem is subdivided into five modules: cropland, grassland, livestock, forest and

84

aquaculture. The industrial subsystem includes energy production, food industry, feed industry, chemical industry,

85

process transportation and other industries. The human consumption subsystem is defined as the consumption of food,

86

energy, and nonfood goods, which is a node that helps to understand the relationship between biological communities

87

and the physical environment. The main features of the waste management subsystem are industrial digester,

88

incineration, landfill, wastewater treatment, manure processing and secondary composting. The atmospheric and

89

hydrological subsystems are mainly used to quantify the N stock and its cascade effect. Each subsystem can be viewed

90

as a dynamic system and an N reservoir. The N balance framework involves processes, flows, assumptions and

91

calculations for each subsystem, as described in the supporting information. Based on the law of the conservation of

92

mass, the N balance is given in Eq. 1. The N input and output elements include both new (e.g., HBNF and BNF

93

induced by cultivation) and recycled Nr (e.g., manure N and straw N). The results are aggregated to the national level

94

to analyze the Nr fate and flux across subsystems throughout the country.

ACS Paragon Plus Environment

Page 5 of 27

95 96 97

Environmental Science & Technology

  ∑    ∑   ∑



[Eq. 1]

where  and  represent the different N flow inputs and outputs, respectively.

 represents the different N accumulations. The detailed calculations for each subsystem are shown in the supporting information.

98 99

Figure 1. Coupled human-environmental N cycle model in China at the national scale, with 2014 as an example. The units

100

are Tg N yr-1 (1 Tg = 106 t).

ACS Paragon Plus Environment

Environmental Science & Technology

101

Page 6 of 27

Data Resources

102

The main data sources used in the model of the national N cycle are as follows: (1) a number of national statistical

103

databases for 2014; (2) national resource survey statistics for 2014, such as rural and urban populations and forest,

104

grassland and lake resource information; and (3) the statistics, parameters and methodologies available in the existing

105

literature. A detailed description of the data resources and an uncertainty analysis are given in the supporting

106

information.

107

Scenarios for the Potential Reduction of Waste N

108

We treated the total N emissions estimated in this study, including gas emissions and water emissions, as a baseline

109

scenario. In addition to the baseline scenario, we established four scenarios to study the potential for the reduction of

110

total waste N emissions (a detailed description is provided in the supporting information).

111

Scenario S1: Efficiency improvement. In this scenario, we suggest improved N use efficiency in the agricultural

112

subsystem. These improvements focus on large farms (N fertilization can be reduced by approximately 40% for an

113

average farm size of 36.6 ha52), fertilization methods (issuing conventional fertilization recommendations for specific

114

farming systems; the average fertilization intensity of N fertilizer was reduced to 130 kg/ha53) and a new form of N

115

fertilizer (which increases N fertilizer utilization by 8%54).

116

Scenario S2: High recycling rate. This scenario reflects a change in the N recycling rate. We assumed that the

117

manure (including human and livestock excretions) and straw waste recycling rates reached the current optimal levels

118

worldwide52, 55, 56, and the specific values were as follows: livestock excretion recycling ratio of 80%, human excretion

119

recycling ratio of 50% and straw recycling ratio of 100%.

120

Scenario S3: Nitrogen oxide emission reduction. Industrial flue gas denitration technology (assuming that 90% of

121

industrial flue gas is removed by selective catalytic reduction (SCR)57-59 and selective non-catalytic reduction (SNCR)

122

denitration technologies60), motor vehicle denitration plants (assuming that 90% of the motor vehicle exhaust is treated

123

with denitration techniques61) and clean energy alternatives to fossil fuels (assuming that 30% of fossil fuels are

124

replaced by new energy sources62, 63) are proposed in this scenario.

125

Scenario S4: Combined scenario. This scenario combines all the measures implemented in scenarios S1, S2, and S3.

126

By subtracting the overlapping portions of the measures in each scenario, the total emissions of waste N in the

127

combined scenario can be obtained.

ACS Paragon Plus Environment

Page 7 of 27

Environmental Science & Technology

128 129

RESULTS

130

Analysis of the N Balance in an Integrated Human Consumption-Driven System

131

We combined the industry, agriculture, human consumption, and waste management subsystems into an integrated

132

system driven by human consumption, which is conducive to understanding the creation, consumption and emissions of

133

Nr. In addition, the atmospheric and hydrological subsystems are environmental systems that are used to assess the

134

environmental impact of N cycling in the context of human disturbances. Figure 2a shows the Nr inputs and outputs of

135

the integrated system, and the larger lines represent the larger Nr fluxes and vice versa. In the integrated system, the

136

total Nr input is 103.1 Tg N yr-1, where the anthropogenic Nr (excluding BNF and atmospheric deposition) totaled 70.7

137

Tg N yr-1, which is more than 2 times the natural Nr level (Fig. 2b). The top three Nr inputs were HBNF, atmospheric

138

deposition and N fixation due to fossil fuel combustion. HBNF, which accounted for 46% of the Nr, is utilized to meet

139

the N fertilizer and industrial N application requirements, and it greatly affects the N cycle in China. Notably, in the

140

near future, HBNF will likely exceed half of the total anthropogenic Nr input6. The total Nr output of the integrated

141

system is 76.5 Tg N yr-1, of which air emissions account for approximately 79% and water emissions account for

142

approximately 20% (Fig. 2c). As a result of the Nr inputs and outputs in the integrated system, approximately 75% of

143

the Nr was ultimately discharged into the environment. This large flux of Nr emissions could lead to serious

144

environmental problems.

ACS Paragon Plus Environment

Environmental Science & Technology

Page 8 of 27

145 146

Figure 2. N balance analysis in a human consumption-driven system. (a) The Nr input and output diagram of the integrated

147

system (units of Tg N yr-1). (b) The proportions of Nr inputs. (c) The proportions of Nr outputs.

148 149

Analysis of N Accumulation in the Agricultural Subsystem

150

The agricultural subsystem has complex interactions with other subsystems through N input-biotransformation-waste

151

N emission processes. The new Nr (through HBNF and BNF process induced by cultivation)35 in the agricultural

152

subsystem accounted for 69% of the integrated system (Fig. 2a and Fig. S1). Moreover, the agricultural subsystem is

153

the largest subsystem in terms of the emissions of waste N (Fig. 2a). To understand the origin and fate of Nr in

154

agroecosystems and determine the reasons for the high consumption of Nr for agriculture in China, which results in

155

considerable pollution33, 34, 55, we split the agricultural subsystem into five modules: cropland, grassland, livestock,

156

forest and aquaculture. The N balance analysis is shown in Figure S1. The numbers in the red boxes in Figure S1

157

indicate the amount of Nr that accumulates in each module. Approximately 11% of the Nr accumulates in the cropland

158

module, which suggests that the retention capacity of Nr is small in cropland areas. The accumulation of Nr in

159

grassland areas is very small, while the rate of Nr accumulation associated with livestock is 12%. For the forest

160

module, the input of Nr is dominated by natural processes, and few anthropogenic processes are involved, but the

ACS Paragon Plus Environment

Page 9 of 27

Environmental Science & Technology

161

accumulation rate is the highest among the five modules, reaching 79%; therefore, forest areas are important N storage

162

pools. Moreover, aquaculture is the only module that exhibited negative Nr accumulation, which may be due to

163

overfishing in the current year. Thus, China must introduce appropriate policy measures to guide the healthy

164

development of aquaculture.

165

Analysis of the Ammonia Supply and Demand Balance

166

The success of the synthetic ammonia industry has changed the history of world food production and solved the food

167

requirements for the growing population8. HBNF is one of the most important inventions and innovations of the 20th

168

century64. Because the Nr created by HBNF profoundly affects the Nr trends in China, we established a model of

169

ammonia supply and demand balance using e!Sankey 4 software (Digital River Ireland Ltd., 2016). The model is

170

shown in Figure 3. Exploring the balance of supply and demand of synthetic ammonia will help reveal the pattern of

171

the N industry in China. This method also helps to understand the entire process (from creation to consumption) of

172

anthropogenic Nr.

173

The total ammonia production in China in 2014 was 46.9 Tg N yr-1 65, accounting for approximately 30% of the

174

global production66. Figure 3 shows that synthetic ammonia in China is mainly used in agriculture, including N

175

fertilizer and ammoniated feed production. These uses account for 75% of the total ammonia production. To meet the

176

human consumption demands, synthetic ammonia has been increasingly used to synthesize artificial N products,

177

including synthetic fibers, artificial pharmaceuticals, synthetic rubber, synthetic detergents, plastics, nitric acid,

178

explosives and other products (details are provided in the industrial subsystem section of the supporting information).

179

In addition, approximately 9% of synthetic ammonia is used for flue gas denitration, where the main flue gas refers to

180

NOx emissions from thermal power, cement, and ceramic production processes. Currently, the main NOx control

181

technologies are SCR and SNCR57, 59, 60, and these two technologies use synthetic ammonia as a reducing agent. As

182

industrial flue gas denitration in China gradually progresses, more denitration agents will be consumed, which will lead

183

to flue gas denitration and agricultural competition. In addition, the supply and demand balance model of synthetic

184

ammonia shows that the proportion of waste N emissions is extremely small, which suggests that the use of synthetic

185

ammonia as a raw material in industrial production processes is extremely efficient. It is conceivable that in the future,

186

the production of Nr by HBNF must be controlled to reduce anthropogenic Nr. Furthermore, HBNF is the basis for

187

ensuring food safety and meeting the industrial N and flue gas denitration demands; therefore, the rational use of

ACS Paragon Plus Environment

Environmental Science & Technology

188

Page 10 of 27

ammonia is the key to achieving these goals.

189 190

Figure 3. Synthetic ammonia supply and demand balance model. The net imports of synthetic ammonia are equal to the

191

total imports minus the export volume. The original raw materials for synthetic industrial N products are derived from

192

synthetic ammonia. In addition, China still imported a small amount of raw industrial N materials in 2014. It would be more

193

accurate to deduct the synthetic industrial N products from the imports of raw industrial N materials in the calculations of

194

the ammonia supply and demand model.

195 196

Life Cycle Analysis of the Food N Flow

197

Increased anthropogenic inputs of Nr provide sufficient food for most of the human demands; however, only a

198

fraction of Nr is actually consumed as food, and the rest is lost to the environment and negatively affects ecosystems33.

199

Increasing the productivity of agricultural ecosystems and reducing the N losses during food production processes are

200

currently imminent. Taking this concern, life cycle analyses of food N are beneficial to understanding the context of

201

food N and Nr utilization efficiency. Figure 4, which was created using e!Sankey 4 software, intuitively shows the

202

analysis process from food (including crops, livestock and aquatic products) production to consumption. Nr is created

203

to sustain food production, but only a small fraction of this N (32%) is consumed as raw food material (17.4 Tg N yr-1)

204

and raw industrial materials (10.8 Tg N yr-1). In addition, 7.6 Tg N yr-1 is lost during food processing, and human food

205

consumption is 6.1 Tg N yr-1, which is only 7% of the total Nr inputs (including net food imports). From a life cycle

ACS Paragon Plus Environment

Page 11 of 27

Environmental Science & Technology

206

perspective, the loss or accumulation of Nr before it is consumed by humans as food (47.2 + 7.6 = 54.8 Tg N yr-1, the

207

detailed data on N loss and N accumulation are shown in Fig. 1 and Fig. S1) in the food flow processes account for 59%

208

of the total Nr inputs (including net food imports); thus, this negatively affects soils, ecosystems and the local climate.

209

With the development of chemical technology, N fertilizers and pesticides have made significant contributions to

210

improving crop yields and livestock populations. In the food production process, only N fertilizer inputs have exceeded

211

natural Nr inputs (BNF and atmospheric deposition), accounting for 35% of the total Nr inputs. China has historically

212

used environmentally friendly organic fertilizers, but the application of processed manure has recently increased. In

213

addition, only 52% of livestock manure, 30% of crop straw and 33% of human excreta are returned to the field as

214

organic fertilizer (details are shown in Tables S2, S5, S11, S16 and S25). The remaining livestock manure (48%), straw

215

(12%) and human excreta (33%) that are not consumed for industrial use or harmless treatments, are lost to the

216

environment and can cause serious environmental pollution.

217 218

Figure 4. Life cycle analysis of the flow of food N.

219 220 221

Analysis of the Input-output Ratio of N in the Agricultural and Industrial Subsystems Efficient use of N is one of the major assets of eco-efficient and sustainable production67. Intensive N use has

ACS Paragon Plus Environment

Environmental Science & Technology

Page 12 of 27

222

triggered problems that threaten public health and the environment. A low input of N compared to the output of

223

products and services is a sustainable practice68. Here, we used the N input-output ratio, which is calculated as the total

224

N product outputs (in the forms of products and raw materials) divided by the N inputs, to evaluate the N utilization

225

efficiency of these six production sectors (Figure S2).

226

There are three main levels of input-output ratios in these sectors. The first level includes the industrial subsystem

227

and the aquaculture module, with an input-output ratio ranging from 60-70%. The high input-output ratio of N in the

228

industrial subsystem is due to advanced industrial processing technology, and there is room for improvement. In

229

addition, the high N input-output ratio of the aquaculture module is mainly due to overfishing, rather than precision

230

farming techniques. This finding is reflected by the negative accumulation of the aquaculture module (Figure S1).

231

Overfishing leads to high aquatic product yields, which further improve the input-output ratio, but this is a false

232

impression.

233

The second level includes croplands and grasslands, which have input-out ratios ranging from 30-40%. The main

234

reason for the low input-output ratio of N associated with croplands is that the application amounts and methods are

235

often not optimal. To ensure food security, high-yield areas in China will pursue high yields and excessively use N

236

fertilizer. In addition, overexposure to N fertilizer in the early stages of crop growth is often emphasized as an

237

application method69. However, the crop root absorption capacity is weak during the early growth stages, especially for

238

surface fertilization; therefore, the utilization rate is low, and the N losses are large70.

239

The third level includes livestock and forestry and is characterized by an input-output ratio of less than 20%. In

240

contrast to vegetable crop production, the N input-output ratio of animal food production is approximately half that of

241

crop production. Table S5 shows that the total amount of excreta produced during livestock farming is 13.4 Tg N yr-1,

242

accounting for 72% of the total N input of this module; therefore, the input-output ratio may be limited by the growth

243

and development of animals. Among these six sectors, the largest proportion of waste management is associated with

244

livestock. In addition, livestock manure can be used to achieve optimal resource use. Increasing the proportion of waste

245

management is an effective way to reduce N emissions and improve N use efficiencies. The extremely low N input-

246

output ratio of the forest module is due to the large amount of Nr stored (79%) in forest ecosystems. In addition, the

247

forest ecosystem plays an important regulatory role in the N biogeochemical cycle71. Hence, the forest ecosystem is a

248

repository of environmental N and plays a significant role in climate regulation and pollution control.

ACS Paragon Plus Environment

Page 13 of 27

249

Environmental Science & Technology

Environmental Fate and Flow Analysis of N

250

The atmosphere and hydrosphere are considered an environmental subsystem. The air emissions and water emissions

251

of each module to the environmental subsystem during the N cycle are shown in Figure 5. The N air emission types can

252

be divided into N2, NH3, NOx (not including N2O), and N2O, and the types of water emissions include nitrate N

253

( − ), nitrite N ( − ), ammonia N ( − ) and organic N (ORG-N). As presented in Figure 2c, the total

254

amount of air emissions is close to four times the total amount of water emissions, which suggests that most N loss

255

occurs in the form of gas.

256

A significant portion of air emissions is N2, especially in the agricultural subsystem (Fig. 5a). During the natural

257

biogeochemical cycling of N, Nr mainly returns to the atmosphere as harmless N2 (N2 is generally considered to be

258

inert and, therefore, does not react with the other elements, which in turn affects the environment and human health1)

259

through denitrification72. Due to human disturbances, harmful nitrogenous gases (such as NH3, NOx, and N2O) are

260

released into the atmosphere, followed by atmospheric flows and secondary reactions, which can cause gaseous

261

pollution, such as haze, over large areas73. The main sources of NOx are the industrial, human consumption and waste

262

management subsystems, which account for 76%, 17% and 7% of the NOx emissions, respectively (Fig. 5c). Most of

263

the NOx emissions, which are driven by human activities, are from fossil fuel combustion, such as by automobiles,

264

aircrafts, internal combustion engines and industrial furnaces. In addition, NOx is emitted during the production and use

265

of nitric acid, such as N from fertilizer plants, organic intermediates, and nonferrous and ferrous metal smelters. NH3

266

emissions are mainly associated with agricultural production processes, especially planting and the irrational use of N

267

fertilizer. In this study, we consider N2O alone because its warming potential is 298 times that of CO2 (IPCC, 2007),

268

and the warming effect on the global climate has increased over time74. In natural biogeochemical cycles, N2O is a

269

byproduct of nitrification and denitrification processes75. Currently, the intensity of N cycling in farmland ecosystems

270

is high, resulting in an increase in N2O emissions. In addition, nitrification and denitrification associated with industrial

271

and waste treatment processes can produce N2O emissions. In 2014, the total N2O emissions in China were estimated to

272

be 2.1 Tg N yr-1, and if the N2O warming potential is converted to CO2, the equivalent CO2 emissions would total

273

approximately 996.7 million tons, which is equivalent to 10% of the total estimated CO2 emissions from China

274

(10291.9 million tons) in 201476. Thus, N exhaust gas emissions in China must receive increased attention, and

275

measures must be implemented to reduce these emissions.

ACS Paragon Plus Environment

Environmental Science & Technology

Page 14 of 27

276

Excessive Nr in water can cause eutrophication and water quality deterioration, as well as affect the growth and

277

reproduction of aquatic organisms14, 15. Figure 5b shows that Nr in the water mainly comes from processes associated

278

with livestock production, the loss of N fertilizer, and the discharge of industrial wastewater and domestic sewage, with

279

the main forms being  −  and ORG-N. Due to the characteristics of the small-scale peasant economy in China,

280

the distribution of agriculture is relatively scattered and not conducive to the unified treatment of agricultural

281

wastewater. In addition, due to the production level, Nr that is used in agriculture often results in surface and

282

groundwater pollution through surface runoff and leakage from farmlands25. In particular, the livestock breeding

283

industry, which has rapidly grown in China, is the largest source of N water emissions due to the emission of livestock

284

manure that has not been treated and poor resource utilization. Because industrial wastewater can be discharged after

285

treatment, the total associated emissions are slightly less than those from agriculture. Moreover, the discharge of

286

domestic wastewater cannot be ignored. In addition, with the advancement of urbanization and the improvement of

287

living standards, the discharge of domestic sewage will continue to increase.

ACS Paragon Plus Environment

Page 15 of 27

Environmental Science & Technology

288 289 290

Figure 5. N loss in each module during N cycle analysis. (a) N air emission forms and fluxes. (b) N water emission forms and fluxes. (c) The proportion of waste N emissions in each module.

291 292

Future Scenario Analysis of N Environmental Emissions and Policy Implications

293

Clearly, the increasing rate of Nr creation and the declining N retention capacity of the environmental ecosystem

294

conflict. There is great interest in reducing the environmental emissions of N (including gas emissions and water

295

emissions) while ensuring that the growing human consumption demands are met. In this section, we analyze future

296

scenarios. Specifically, the scenarios are compared with the baseline scenario to assess the effects of policy measures

297

on reducing N emissions to the environment (Table 1). Compared to the baseline scenario, the trends in waste N

298

emissions suggest that emissions could be significantly mitigated in all scenarios, especially by controlling larger farms

299

(by 25%), issuing conventional fertilization recommendations for specific farming systems (by 25%) and implementing

ACS Paragon Plus Environment

Environmental Science & Technology

Page 16 of 27

300

flue gas denitration measures (by 25%). Furthermore, the results of the scenario analysis reveal that the use of

301

agricultural N fertilizer in China is excessive. The inefficient use of N fertilizer is the cause of the substantial waste N

302

emissions from farming. The large amount of untreated NOx is another significant problem that could be addressed for

303

waste N abatement. The combination of all measures represents the most effective strategy for mitigating waste N

304

emissions.

305

Table 1. Analyses of future scenarios for reducing N emissions to the environment

Scenario

Baseline scenario

Total waste N emissions

Relative reduction

excluding N2 (Tg N yr-1)

percentage (%)

-

47.3

-

Large farm size

35.6

25%

35.7

25%

45.1

5%

42.6

10%

Higher straw recycling ratio

46.2

2%

Flue gas denitration

35.4

25%

Vehicle exhaust denitration

44.9

5%

New energy applications

42.2

11%

All

7.5

84%

Measure(s)

Issuing conventional fertilization Efficiency improvement recommendations for specific farming systems New forms of N fertilizer Higher manure recycling High recycling rate

ratio

Nitrogen oxide emission reduction

Combined scenario

306 307

The emission reduction potential of each policy measure can be seen from the results of the scenario analysis.

308

Relevant agricultural regulations and measures must be adopted and enforced to eliminate the overuse of N fertilizer in

309

agricultural activities. Such measures include encouraging large-scale agriculture, promoting a standardized

310

agricultural production model77, prescribing recommended N application rates78, and issuing conventional fertilization

ACS Paragon Plus Environment

Page 17 of 27

Environmental Science & Technology

311

recommendations for specific farming systems53. In addition, other approaches include improving the livestock manure,

312

human feces and straw recycling rates; systematic crop rotation; optimum fertilizer timing, placement, and formulation;

313

the effective use of nitrification inhibitors; and watershed management to mitigate or redirect N losses from fields27, 79.

314

In addition to the effects of agriculture activities, the treatment measures that correspond to fossil fuel combustion and

315

N production in industrial processes can also result in changes in Nr losses. Gradually promoting industrial flue gas

316

denitration80 and vehicle exhaust denitration61 and expanding the use of new energies to transition away from the

317

current coal-based consumption structure are ideal strategies in China. These proactive measures require the

318

cooperation of relevant sectors and industries (e.g., the agriculture and fertilizer industries, environmental sector,

319

industrial sector, energy sector, and political sector) and the implementation of coordinated measures (e.g., denitration

320

processes, environmental regulations, energy policies, and new material development).

321 322

DISCUSSION

323

A high-resolution SFA approach was applied in this study to quantify the N balance in China. This analysis resulted

324

in comprehensive descriptions of the different economic and ecologic processes based on 6 subsystems and 45

325

individual N flows in the model. Therefore, the model offers a higher resolution and more comprehensive perspective

326

than previous national and regional N flow models, such as the national model of Nr cycling in China constructed by

327

Cui et al.27 (3 subsystems, 18 flows), the European N balance by Leip et al.41 (4 subsystems, 20 flows), the N flows

328

analysis for food production in China by Ma et al.81 (4 subsystems, 17 flows), the N budget model of mainland China

329

by Ti et al.82 (3 subsystems, 18 flows) and the net anthropogenic N accumulation analysis in Beijing reported by Han et

330

al51. (3 subsystems, 12 flows). In addition, portions of our findings are in line and consistent with the existing literature.

331

For example, the N deposition and recycling rate of animal manure in our study were 17.6 Tg N yr-1 and 53% in 2014,

332

respectively, while they were estimated by Cui et al.27 to be 16.0 Tg N yr-1 and approximately 55% in 2010,

333

respectively. Nevertheless, some of the results estimated in this study are different from previous reports. For example,

334

we found that the rate of water emissions from waste management in 2014 was 0.4 Tg N yr-1, and the calculation by

335

Cui et al.27 was 1.3 Tg N yr-1 in 2010. Although there is a time lag between the reported values of the two studies, the

336

difference in wastewater treatment rates have more significant effects. China has made significant improvements in the

337

environmental protection requirements in recent years, so we have adopted a higher wastewater treatment rate. As a

ACS Paragon Plus Environment

Environmental Science & Technology

Page 18 of 27

338

result, we estimated lower water emissions from waste management than were estimated by Cui et al.27. Another

339

example is the average N use efficiencies of food throughout the food chain, which was estimated to be 9% in 2005 by

340

Ma et al.81, while it was 7% in 2014 in our study. The main reason for the difference is the dramatic increase in the total

341

amount of N fertilizer and atmospheric deposition between 2005 and 2014. In 2005, the total amount of N fertilizer

342

used in China and atmospheric deposition were 27.0 and 2.0 Tg N yr-1, respectively, while in 2014 these values were

343

31.3 and 17.6 Tg N yr-1, respectively.

344

Similar to the N footprint model reported by Gu et al.26, we first constructed a coupled human-environmental N cycle

345

model on the national scale at high resolution. After that, we evaluated the specific aspects of the models with a

346

different perspective than in the existing literature. The balance analysis of synthetic ammonia supply and demand in

347

this study provides the framework for connecting the industrial and agricultural subsystems, whereas the associations

348

between industry and agriculture were weak in previous studies. For example, Gu et al. attempted to assess the

349

production perspective and not the consumption structure of goods and services26. This study also focuses on a life

350

cycle analysis of food N, which reflects the driver of human consumption in the N cycle. Moreover, it is intuitive and

351

novel to apply input-output ratios for industrial and agricultural subsystems, such as a production system in the

352

economic field, to measure N use efficiency. The application of an input-output ratio as an indicator is helpful for

353

analyzing the differences in the development status within the human-consumption integrated system under the same

354

dimension, which can also function as a decision support tool for other elements of metabolism.

355

Population growth, economic development and urbanization strongly affect the N cycle process of Chinese

356

ecosystems. For example, the Nr input of crop production in 2000 was approximately 21.0 kg N yr-1 per capita, as

357

estimated by Liu et al.33, which is slightly lower than the global per-capita average (22.3 kg N yr-1 per capita). In our

358

study, China reached approximately 64.0 kg N yr-1 per capita in 2014. The growth of human consumption (food,

359

products, energy and services) further drives Nr emissions and environmental accumulation. The estimates of Chinese

360

NH3, NOx, N2O emission in 2005 by Gu et al.16 are 10.9 Tg N yr-1, 5.3 Tg N yr-1 and 1.0 Tg N yr-1, respectively. We

361

estimate that the emissions in 2014 are 12.1 Tg N yr-1, 17.4 Tg N yr-1 and 2.1 Tg N yr-1, respectively. For water

362

emissions, there is a certain degree of growth. The total Nr leakage to the hydrosphere in 2008 was reported to be

363

approximately 5.0 Tg N yr-1 14, while in 2014, this value was approximately 15.6 Tg N yr-1. In addition, our study notes

364

and highlights the key role of policy in reducing waste N impacts through the simulation and assessment of scenarios,

ACS Paragon Plus Environment

Page 19 of 27

Environmental Science & Technology

365

rather than simply discussing the development of N industry technologies and N pollution control measures. Because

366

the development of the N industry process differs in different countries and regions, a general policy cannot easily

367

solve such problems; thus, a case-by-case analysis is necessary, and a quantitative scenario analysis should be

368

performed.

369

Several potential improvements could be made to our methodology. First, the primary data source in our model is the

370

Statistical Yearbook, which is less evidence-based than other methods. Moreover, the statistical yearbook data mainly

371

record the statistics of domestic enterprises above the state-designated scale. As China is a developing country, there

372

are still some small microenterprises and self-employed individuals, especially in the agricultural sector. The possible

373

missing relevant data results in data deviation (the data will be relatively smaller than the actual situation). Thus,

374

additional data validation will be required in the future, especially for N cycle processes that are driven by human

375

activities. Second, the parameters in the model are mainly reported in the literature and are considered to be the overall

376

mean values for a country. Due to the differences in natural conditions, social development and cultures in the different

377

regions of China, the parameters will vary regionally. The averaging of the parameters used in the analysis process also

378

makes the result somewhat uncertain. The next steps in the development of the human-environmental coupled N cycle

379

model will be to link the Nr losses to effects35. For example, the establishment of high-precision atmospheric remote

380

sensing, ground-based remote sensing, geographic information systems and other technologies can improve the

381

accuracy of the systematic spatial analysis. Finally, as living standards improve, the demand for urban greening will

382

increase. In addition, pets are popular in many areas. The urban-greening and pet-breeding modules will also involve N

383

recycling, which has not been previously considered due to the small proportions of these N amounts and the lack of

384

statistical data. In the future, studies of these two modules could be integrated into the coupled human consumption-

385

environmental system.

386 387 388

ASSOCIATED CONTENT Supporting Information

389

This section includes the details of the system definition, data sources, Nr flow description and uncertainty analysis;

390

a figure associated with the N accumulation analysis in the agricultural subsystem; and a figure associated with the

391

analysis of the input-output ratio of N in the industrial and agricultural subsystems. Overall, the supporting information

ACS Paragon Plus Environment

Environmental Science & Technology

Page 20 of 27

392

contains 67 pages, 2 figures and 26 tables. This information is available free of charge via the Internet at

393

http://pubs.acs.org.

394 395 396

AUTHOR INFORMATION Corresponding author *Phone & Fax: +86 10 62794513; e-mails: [email protected] (S.H.).

397 398

ORCID Shanying Hu: 0000-0002-3447-6395

399 400

Notes The authors declare no competing financial interests.

401 402 403

ACKNOWLEDGMENTS This study was supported through National Natural Science Foundation of China (Project Code: L1522024) and

404 405

Chinese Academy of Engineering (Project Code: 2015-ZCQ-05).

406 407

REFERENCES

408

1.

409

Seitzinger, S. P.; Sutton, M. A., Transformation of the nitrogen cycle: recent trends, questions, and potential solutions.

410

Science 2008, 320, (5878), 889-892.

411

2.

412

Biogeochemistry 1991, 13, (2), 87-115.

413

3.

Robertson, G.; Groffman, P., Nitrogen transformations. Soil Microbiology Ec. 2007, 3, 341-364.

414

4.

Galloway, J. N.; Leach, A. M.; Bleeker, A.; Erisman, J. W., A chronology of human understanding of the

415

nitrogen cycle. Philos. T. R. Soc. B. 2013, 368, (1621), 20130120.

416

5.

417

(7176), 293-296.

Galloway, J. N.; Townsend, A. R.; Erisman, J. W.; Bekunda, M.; Cai, Z.; Freney, J. R.; Martinelli, L. A.;

Vitousek, P. M.; Howarth, R. W., Nitrogen limitation on land and in the sea: how can it occur?

Gruber, N.; Galloway, J. N., An Earth-system perspective of the global nitrogen cycle. Nature 2008, 451,

ACS Paragon Plus Environment

Page 21 of 27

Environmental Science & Technology

418

6.

Fowler, D.; Coyle, M.; Skiba, U.; Sutton, M. A.; Cape, J. N.; Reis, S.; Sheppard, L. J.; Jenkins, A.; Grizzetti,

419

B.; Galloway, J. N., The global nitrogen cycle in the twenty-first century. Phil. Trans. R. Soc. B 2013, 368, (1621),

420

20130164.

421

7.

422

H.; Tilman, D. G., Human alteration of the global nitrogen cycle: sources and consequences. Ecol. Appl. 1997, 7, (3),

423

737-750.

424

8.

425

synthesis changed the world. Nat. Geosci. 2008, 1, (10), 636-639.

426

9.

427

2002, 31, (2), 64-71.

428

10.

429

driver in the global nitrogen cycle: 50-year trends. Biogeochemistry 2014, 118, (1-3), 225-241.

430

11.

431

208.

432

12.

433

The nitrogen cascade. Bioscience 2003, 53, (4), 341-356.

434

13.

435

nitrogen transfers at regional watershed and global scales. Phil. Trans. R. Soc. B 2013, 368, (1621), 20130123.

436

14.

437

Global Environ. Chang. 2013, 23, (5), 1112-1121.

438

15.

439

high nitrogen loading region. Environ. Sci. Technol. 2015, 49, (3), 1427-1435.

440

16.

441

China: Sources, recent trends, and damage costs. Environ. Sci. Technol. 2012, 46, (17), 9420-9427.

442

17.

443

Folke, C.; Schellnhuber, H. J., A safe operating space for humanity. Nature 2009, 461, (7263), 472-475.

444

18.

Vitousek, P. M.; Aber, J. D.; Howarth, R. W.; Likens, G. E.; Matson, P. A.; Schindler, D. W.; Schlesinger, W.

Erisman, J. W.; Sutton, M. A.; Galloway, J.; Klimont, Z.; Winiwarter, W., How a century of ammonia

Galloway, J. N.; Cowling, E. B., Reactive nitrogen and the world: 200 years of change. AMBIO J. Human Env.

Lassaletta, L.; Billen, G.; Grizzetti, B.; Garnier, J.; Leach, A. M.; Galloway, J. N., Food and feed trade as a

Schlesinger, W. H., On the fate of anthropogenic nitrogen. Proc. Natl. Acad. Sci. U. S. A. 2009, 106, (1), 203-

Galloway, J. N.; Aber, J. D.; Erisman, J. W.; Seitzinger, S. P.; Howarth, R. W.; Cowling, E. B.; Cosby, B. J.,

Billen, G.; Garnier, J.; Lassaletta, L., The nitrogen cascade from agricultural soils to the sea: modelling

Gu, B.; Ge, Y.; Chang, S. X.; Luo, W.; Chang, J., Nitrate in groundwater of China: Sources and driving forces.

Zhao, Y.; Xia, Y.; Ti, C.; Shan, J.; Li, B.; Xia, L.; Yan, X., Nitrogen removal capacity of the river network in a

Gu, B.; Ge, Y.; Ren, Y.; Xu, B.; Luo, W.; Jiang, H.; Gu, B.; Chang, J., Atmospheric reactive nitrogen in

Rockström, J.; Steffen, W.; Noone, K.; Persson, Å.; Chapin, F. S.; Lambin, E. F.; Lenton, T. M.; Scheffer, M.;

Dodds, W. K., Nutrients and the “dead zone”: the link between nutrient ratios and dissolved oxygen in the

ACS Paragon Plus Environment

Environmental Science & Technology

Page 22 of 27

445

northern Gulf of Mexico. Front. Ecol. Environ. 2006, 4, (4), 211-217.

446

19.

447

2015, 5, 8118.

448

20.

449

Ganeshram, R., Impacts of atmospheric anthropogenic nitrogen on the open ocean. Science 2008, 320, (5878), 893-897.

450

21.

451

Vries, W., Consequences of human modification of the global nitrogen cycle. Phil. Trans. R. Soc. B 2013, 368, (1621),

452

20130116.

453

22.

454

287.

455

23.

Boyle, E., Nitrogen pollution knows no bounds. Science 2017, 356, (6339), 700-701.

456

24.

Gorman, D.; Turra, A.; Connolly, R. M.; Olds, A. D.; Schlacher, T. A., Monitoring nitrogen pollution in

457

seasonally-pulsed coastal waters requires judicious choice of indicator species. Mar. Pollut. Bull. 2017, 122, (1-2), 149-

458

155.

459

25.

460

environment and best management strategies. Nutr. Cycl. Agroecosys. 2002, 63, (2), 117-127.

461

26.

462

food, energy, and nonfood goods. Environ. Sci. Technol. 2013, 47, (16), 9217-9224.

463

27.

464

fate of reactive nitrogen in China (1910–2010). Proc. Natl. Acad. Sci. U. S. A. 2013, 110, (6), 2052-2057.

465

28.

466

P.; Epstein, P. R.; Holland, E. A.; Keeney, D. R., Human health effects of a changing global nitrogen cycle. Front.

467

Ecol. Environ. 2003, 1, (5), 240-246.

468

29.

469

challenges. J. Environ. Manage. 2010, 91, (8), 1623-1633.

470

30.

471

China. Proc. Natl. Acad. Sci. U. S. A. 2015, 112, (28), 8792-8797.

Shi, Y.; Cui, S.; Ju, X.; Cai, Z.; Zhu, Y., Impacts of reactive nitrogen on climate change in China. Sci. Rep.

Duce, R.; LaRoche, J.; Altieri, K.; Arrigo, K.; Baker, A.; Capone, D.; Cornell, S.; Dentener, F.; Galloway, J.;

Erisman, J. W.; Galloway, J. N.; Seitzinger, S.; Bleeker, A.; Dise, N. B.; Petrescu, A. R.; Leach, A. M.; de

Erisman, J. W., The Nanjing declaration on management of reactive nitrogen. Bioscience 2004, 54, (4), 286-

Zhu, Z.; Chen, D., Nitrogen fertilizer use in China–Contributions to food production, impacts on the

Gu, B.; Leach, A. M.; Ma, L.; Galloway, J. N.; Chang, S. X.; Ge, Y.; Chang, J., Nitrogen footprint in China:

Cui, S.; Shi, Y.; Groffman, P. M.; Schlesinger, W. H.; Zhu, Y., Centennial-scale analysis of the creation and

Townsend, A. R.; Howarth, R. W.; Bazzaz, F. A.; Booth, M. S.; Cleveland, C. C.; Collinge, S. K.; Dobson, A.

Zhang, D. Q.; Tan, S. K.; Gersberg, R. M., Municipal solid waste management in China: status, problems and

Gu, B.; Ju, X.; Chang, J.; Ge, Y.; Vitousek, P. M., Integrated reactive nitrogen budgets and future trends in

ACS Paragon Plus Environment

Page 23 of 27

Environmental Science & Technology

472

31.

Coppens, J.; Meers, E.; Boon, N.; Buysse, J.; Vlaeminck, S. E., Follow the N and P road: High-resolution

473

nutrient flow analysis of the Flanders region as precursor for sustainable resource management. Resour. Conserv. Recy.

474

2016, 115, 9-21.

475

32.

476

Kremen, C., Systems integration for global sustainability. Science 2015, 347, (6225), 1258832.

477

33.

478

30104.

479

34.

480

Bonsch, M.; Humpenöder, F., Reactive nitrogen requirements to feed the world in 2050 and potential to mitigate

481

nitrogen pollution. Nat. Commun. 2014, 5, 3858.

482

35.

483

help consumers understand their role in nitrogen losses to the environment. Environ. Dev. 2012, 1, (1), 40-66.

484

36.

485

past, present and future. Environ. Res. Lett. 2014, 9, (11), 115003.

486

37.

487

Footprint Model for a University. Sustainability J. Rec. 2013, 6, (4), 211-219.

488

38.

489

Australia’s high nitrogen footprint. Sci. Rep. 2016, 6, 39644.

490

39.

491

Kimiecik, J.; Lantz-Trissel, J.; Reguera, E. d. l., The Nitrogen Footprint Tool Network: A multi-institution program to

492

reduce nitrogen pollution. Sustainability J. Rec. 2017, 10, (2), 79-88.

493

40.

494

footprint during urbanisation from 1990 to 2009. Environ. Int. 2016, 97, 137-145.

495

41.

496

Union. J. Agr. Sci. 2014, 152, (S1), 20-33.

497

42.

498

model to predict the loss of nitrogen to the environment. Environ. Res. Lett. 2014, 9, (11), 115013.

Liu, J.; Mooney, H.; Hull, V.; Davis, S. J.; Gaskell, J.; Hertel, T.; Lubchenco, J.; Seto, K. C.; Gleick, P.;

Liu, J.; Ma, K.; Ciais, P.; Polasky, S., Reducing human nitrogen use for food production. Sci. Rep. 2016, 6,

Bodirsky, B. L.; Popp, A.; Lotze-Campen, H.; Dietrich, J. P.; Rolinski, S.; Weindl, I.; Schmitz, C.; Müller, C.;

Leach, A. M.; Galloway, J. N.; Bleeker, A.; Erisman, J. W.; Kohn, R.; Kitzes, J., A nitrogen footprint model to

Galloway, J. N.; Winiwarter, W.; Leip, A.; Leach, A. M.; Bleeker, A.; Erisman, J. W., Nitrogen footprints:

Leach, A. M.; Majidi, A. N.; Galloway, J. N.; Greene, A. J., Toward Institutional Sustainability: A Nitrogen

Liang, X.; Leach, A. M.; Galloway, J. N.; Gu, B.; Lam, S. K.; Chen, D., Beef and coal are key drivers of

Castner, E. A.; Leach, A. M.; Leary, N.; Baron, J.; Compton, J. E.; Galloway, J. N.; Hastings, M. G.;

Cui, S.; Shi, Y.; Malik, A.; Lenzen, M.; Gao, B.; Huang, W., A hybrid method for quantifying China's nitrogen

Leip, A.; Weiss, F.; Lesschen, J.; Westhoek, H., The nitrogen footprint of food products in the European

Shibata, H.; Cattaneo, L. R.; Leach, A. M.; Galloway, J. N., First approach to the Japanese nitrogen footprint

ACS Paragon Plus Environment

Environmental Science & Technology

Page 24 of 27

499

43.

Hutton, M. O.; Leach, A. M.; Leip, A.; Galloway, J. N.; Bekunda, M.; Sullivan, C.; Lesschen, J. P., Toward a

500

nitrogen footprint calculator for Tanzania. Environ. Res. Lett. 2017, 12, (3), 034016.

501

44.

502

University’s sustainability plan. Sustainability J. Rec. 2017, 10, (2), 89-95.

503

45.

504

assessment on global nitrogen flows in cropland. Proc. Natl. Acad. Sci. U. S. A. 2010, 107, (17), 8035-8040.

505

46.

506

consumption patterns in Austria. Food Policy 2014, 49, 128-136.

507

47.

Domene, L.; Ayres, R. U., Nitrogen's role in industrial systems. J. Ind. Ecol. 2001, 5, (1), 77-103.

508

48.

Gu, B.; Chang, J.; Min, Y.; Ge, Y.; Zhu, Q.; Galloway, J. N.; Peng, C., The role of industrial nitrogen in the

509

global nitrogen biogeochemical cycle. Sci. Rep. 2013, 3, 2579.

510

49.

511

life-cycles of staple food production in China and their mitigation potential. Sci. Total Environ. 2016, 556, 116-125.

512

50.

513

anthropogenic nitrogen loads to fresh water. Environ. Sci. Technol. 2015, 49, (21), 12860-12868.

514

51.

515

Sci. Pollut. R. 2011, 18, (3), 485-496.

516

52.

517

Environ. Chang. 2016, 41, 26-32.

518

53.

519

recommendation for maize in China based on yield response and agronomic efficiency. Field Crop. Res. 2014, 157, 27-

520

34.

521

54.

522

coated urea and sulfur fertilization on yield, nitrogen use efficiency and leaf senescence of cotton. Field Crop. Res.

523

2016, 187, 87-95.

524

55.

525

environmental risk by improving N management in intensive Chinese agricultural systems. Proc. Natl. Acad. Sci. U. S.

Kimiecik, J.; Baron, J. S.; Weinmann, T.; Taylor, E., Adding a nitrogen footprint to Colorado State

Liu, J.; You, L.; Amini, M.; Obersteiner, M.; Herrero, M.; Zehnder, A. J.; Yang, H., A high-resolution

Pierer, M.; Winiwarter, W.; Leach, A. M.; Galloway, J. N., The nitrogen footprint of food products and general

Xia, L.; Ti, C.; Li, B.; Xia, Y.; Yan, X., Greenhouse gas emissions and reactive nitrogen releases during the

Mekonnen, M. M.; Hoekstra, A. Y., Global gray water footprint and water pollution levels related to

Han, Y.; Li, X.; Nan, Z., Net anthropogenic nitrogen accumulation in the Beijing metropolitan region. Environ.

Ju, X.; Gu, B.; Wu, Y.; Galloway, J. N., Reducing China’s fertilizer use by increasing farm size. Global

Xu, X.; He, P.; Pampolino, M. F.; Johnston, A. M.; Qiu, S.; Zhao, S.; Chuan, L.; Zhou, W., Fertilizer

Geng, J.; Ma, Q.; Chen, J.; Zhang, M.; Li, C.; Yang, Y.; Yang, X.; Zhang, W.; Liu, Z., Effects of polymer

Ju, X.; Xing, G.; Chen, X.; Zhang, S.; Zhang, L.; Liu, X.; Cui, Z.; Yin, B.; Christie, P.; Zhu, Z., Reducing

ACS Paragon Plus Environment

Page 25 of 27

Environmental Science & Technology

526

A. 2009, 106, (9), 3041-3046.

527

56.

528

assessment of management options for nutrient flows in the food chain in China. Environ. Sci. Technol. 2013, 47, (13),

529

7260-7268.

530

57.

531

Denitration Project. Adv. Mat. Res. 2014, 977, 285-289.

532

58.

533

Pseudomonas aeruginosa PCN-2 in nitrogen oxides (NOx) removal from flue gas. J. Hazard. Mater. 2016, 318, 571-

534

578.

535

59.

536

by ammonia SCR. Ind. Eng. Chem. Res. 2002, 41, (15), 3512-3517.

537

60.

538

gas by catalytic oxidation-removal process with H2O2. Chem. Eng. J. 2014, 243, 176-182.

539

61.

540

soil and livestock source signatures. Atmos. Environ. 2014, 92, 359-366.

541

62.

542

5, (4), 329-332.

543

63.

544

2013, 52, 797-809.

545

64.

546

(18), 2004-2008.

547

65.

Sheng, L., China Statistical Yearbook (in Chinese). China Statistics Press: Beijing, P. R. China, 2015.

548

66.

FAOSTAT: FAO Statistical Databases; Food and Agriculture Organization of the United Nations: Rome, Italy,

549

2015; http://faostat.fao.org/default.aspx (accessed April 20, 2017).

550

67.

551

2009, 86, (7), 1354-1358.

552

68.

Ma, L.; Wang, F.; Zhang, W.; Ma, W.; Velthof, G.; Qin, W.; Oenema, O.; Zhang, F., Environmental

Cheng, Y. K.; Wang, L. X.; Huo, P., Environmental Study of the Design and Operation of the SCR Flue Gas

Zheng, M.; Li, C.; Liu, S.; Gui, M.; Ni, J., Potential application of aerobic denitrifying bacterium

Madia, G.; Koebel, M.; Elsener, M.; Wokaun, A., The effect of an oxidation precatalyst on the NOx reduction

Ding, J.; Zhong, Q.; Zhang, S.; Song, F.; Bu, Y., Simultaneous removal of NOx and SO2 from coal-fired flue

Felix, J. D.; Elliott, E. M., Isotopic composition of passively collected nitrogen dioxide emissions: Vehicle,

Nykvist, B.; Nilsson, M., Rapidly falling costs of battery packs for electric vehicles. Nat. Clim. Change 2015,

Höök, M.; Tang, X., Depletion of fossil fuels and anthropogenic climate change—A review. Energ. Policy

Schlögl, R., Catalytic Synthesis of Ammonia—A “Never Ending Story”? Angew. Chem. Int. Edit. 2003, 42,

Kizilaslan, H., Input–output energy analysis of cherries production in Tokat Province of Turkey. Appl. Energ.

Ozkan, B.; Akcaoz, H.; Fert, C., Energy input–output analysis in Turkish agriculture. Renew. Energ. 2004, 29,

ACS Paragon Plus Environment

Environmental Science & Technology

Page 26 of 27

553

(1), 39-51.

554

69.

555

Römheld, V., Integrated soil–crop system management for food security. Proc. Natl. Acad. Sci. U. S. A. 2011, 108,

556

(16), 6399-6404.

557

70.

558

achieve food and environmental security. Environ. Sci. Technol. 2014, 48, (10), 5780-5787.

559

71.

560

to climate change. Proc. Natl. Acad. Sci. U. S. A. 2012, 109, (9), 3406-3411.

561

72.

562

are significant sources of N2O and NO under low oxygen availability. Proc. Natl. Acad. Sci. U. S. A. 2013, 110, (16),

563

6328-6333.

564

73.

565

7, 403-423.

566

74.

567

Nat. Geosci. 2009, 2, (9), 659-662.

568

75.

569

emissions from soils: how well do we understand the processes and their controls? Phil. Trans. R. Soc. B 2013, 368,

570

(1621), 20130122.

571

76.

572

https://data.worldbank.org/indicator/EN.ATM.CO2E.KT?order=wbapi_data_value_2007%20wbapi_data_value%20wb

573

api_data_value-last&sort=desc (accessed October 15, 2017).

574

77.

575

loss from agriculture: A review of methods. Sci. Total Environ. 2008, 406, (1), 1-23.

576

78.

577

Rev. Env. Resour. 2009, 34, 97-125.

578

79.

579

44, (16), 6450-6456.

Chen, X.; Cui, Z.; Vitousek, P. M.; Cassman, K. G.; Matson, P. A.; Bai, J.-S.; Meng, Q.; Hou, P.; Yue, S.;

Cui, Z.; Wang, G.; Yue, S.; Wu, L.; Zhang, W.; Zhang, F.; Chen, X., Closing the N-use efficiency gap to

Bernal, S.; Hedin, L. O.; Likens, G. E.; Gerber, S.; Buso, D. C., Complex response of the forest nitrogen cycle

Zhu, X.; Burger, M.; Doane, T. A.; Horwath, W. R., Ammonia oxidation pathways and nitrifier denitrification

Devol, A. H., Denitrification, anammox, and N2 production in marine sediments. Annu. Rev. Mar. Sci. 2015,

Davidson, E. A., The contribution of manure and fertilizer nitrogen to atmospheric nitrous oxide since 1860.

Butterbach-Bahl, K.; Baggs, E. M.; Dannenmann, M.; Kiese, R.; Zechmeister-Boltenstern, S., Nitrous oxide

The

World

Bank

Data:

CO2

Emissions;

Cherry, K.; Shepherd, M.; Withers, P.; Mooney, S., Assessing the effectiveness of actions to mitigate nutrient

Robertson, G. P.; Vitousek, P. M., Nitrogen in agriculture: balancing the cost of an essential resource. Annu.

Xue, X.; Landis, A. E., Eutrophication potential of food consumption patterns. Environ. Sci. Technol. 2010,

ACS Paragon Plus Environment

Page 27 of 27

Environmental Science & Technology

580

80.

Li, W.; Zhang, L.; Liu, N.; Shi, Y.; Xia, Y.; Zhao, J.; Li, M., Evaluation of NO removal from flue gas by a

581

chemical absorption–biological reduction integrated system: complexed NO conversion pathways and nitrogen

582

equilibrium Analysis. Energ. Fuel. 2014, 28, (7), 4725-4730.

583

81.

584

chain of China. J. Environ. Qual. 2010, 39, (4), 1279-1289.

585

82.

586

Biogeochemistry 2012, 108, (1-3), 381-394.

Ma, L.; Ma, W.; Velthof, G.; Wang, F.; Qin, W.; Zhang, F.; Oenema, O., Modeling nutrient flows in the food

Ti, C.; Pan, J.; Xia, Y.; Yan, X., A nitrogen budget of mainland China with spatial and temporal variation.

587

ACS Paragon Plus Environment