supporting information - pnas · document each of the values and the rationale (such as equation,...

Supporting InformationCui et al. 10.1073/pnas.1221638110SI TextThe main purpose of this supporting information is to explain anddocument each of the values and the rationale (such as equation,parameter, and activity data) used to calculate the reactive ni-trogen (Nr) cycling in China. For each of the Nr input or outputitems listed in Tables S3 and S4, we described the assumptionsand possible errors in the calculation. Additional information isprovided for the spatial disparity and future trends of anthro-pogenic Nr creation in mainland China. Finally, the comparisonwith other similar studies in China is discussed.

Spatial Disparity of Anthropogenic Nr Creation in Mainland China.Here, anthropogenic Nr creation only includes chemical fertil-izer application, agricultural biological N fixation, and fossil fuelcombustion. There is considerable variation in the spatial het-erogeneity of Nr creation across China (Fig. S1). For example,total human-induced Nr input to different provinces ranged from2.8 × 10−2 to 4.1 Tg in 2009, which was significantly correlatedwith provincial population (R2 = 0.84) and gross domesticproduct (GDP; R2 = 0.61). Nr input was high in the provinces ineastern and central China (e.g., Henan, Shandong, and Jiangsu)with larger populations and well-developed agro-industrial econ-omies and low in the vast western area with sparse populationand widespread desert. Nr input was relatively low in somenorthern provinces because of low chemical fertilizer applicationand low reserves of fossil fuels (e.g., Guangdong). Dispropor-tional distribution between Nr creation and population size andaffluence [expressed as anthropogenic Nr per capita (pcNr) andanthropogenic Nr per unit GDP (pgNr)] likely led to N over-loading or N scarcity in different regions. Total anthropogenicNr inputs increased steadily in most provinces from 1999 to 2009,except for Beijing and Shanghai municipalities, which had minorreductions, mainly because of lower agricultural activity (1). Thebiggest increase from 1999 to 2009 was in Henan province (from2.8 to 4.1 Tg N) and the Inner Mongolia autonomous region(from 0.84 to 1.7 Tg N). Tibet had the lowest increase, with onlya 6.4 × 10−3-Tg N increase from 1999 to 2009. In contrast, theincrease in eastern and central China was much higher than west-ern China. Anthropogenic Nr creation rate increased from 34 kgN/ha per year in 1999 to 43 kg N/ha per year in 2009, with anannual growth of 2.3%. Creation was highest in East China (150 kgN/ha per year in 1999 and 158 kg N/ha per year in 2009) and lowestin Northwest China (8.4 kg N/ha per year in 1999 and 12 kg N/haper year in 2009) (Fig. S1B).pcNr. Analysis of pcNr is useful for comparing diverse regionswithin and between countries. The average pcNr of China was 27,28, and 31 kg in 1999, 2004, and 2009, respectively. The pcNr ofNorth China and Northeast China was the highest (about 32 and40 kg in 1999 and 2009, respectively), whereas South China wasthe lowest (about 18 and 20 kg in 1999 and 2009, respectively).Outside of North China and East China, the rate of increase inpcNr between 1999 and 2009 was 20–35% (Fig. S1D).Galloway and Cowling (2) estimated pcNr production across

the globe ranging from 7 kg in Africa to 100 kg in NorthAmerica; Asia had 17 kg pcNr. Chinese individuals’ average Nrcreation was less than individuals in North America but morethan individuals in Africa and Asia. By the definition of nitrogenstress levels through pcNr input in cropland by Liu et al. (3),China has shifted from a “no nitrogen stress” level (15–30 kg/capper year) in 1999 to a “nitrogen sufficiency” level (>30 kg/capper year) in 2009 (3); however, the disproportional distributionof population and N input likely resulted in N scarcity or N

surplus in some regions. Additionally, Leach et al. (4) developeda nitrogen footprint calculator in 2010 that defined nitrogenfootprint as the total amount of Nr released to the environmentas a result of an entity’s resource consumption. Preliminarycalculations with this calculator, which have not been tested inChina, suggested that pcNr of China was between the averageindividual N footprint in the United States (41 kg) and TheNetherlands (25 kg).Nr per unit GDP.Rapid economic growth has enhanced the demandfor food and energy in China and accordingly, the consumption ofchemical fertilizer and fossil fuel. pgNr, also termed Nr inputintensity, reflects the ratio between Nr loading and economic orphysical output (Fig. S1E), and it is influenced mainly by tech-nological efficiency. The average pgNr of China has decreaseddrastically from 3.7 × 103 kg N/million in 1999 to 2.2 × 103 kg N/million in 2004 and 1.2 × 103 kg N/million in 2009, indicating thedecline trend in environmental cost for economic development.The pgNr of eastern regions was always higher than westernregions, reflecting differences in the nature and extent of deve-lopment in these regions. Of these regions, the pgNr of North-west China was the highest (6.2 × 103 N/million in 1999 and 2.0 ×103 kg N/million in 2009), whereas South China was lowest (2.1 ×103 N/million in 1999 and 0.60 × 103 kg N/million in 2009).Nr creation by agricultural biological nitrogen fixation. Agriculturalbiological nitrogen fixation (BNF) largely depends on the area ofcropland, and therefore, it is generally higher in East and CentralChina and lower in Northwest and South China. BNF for eachregion was basically stable between 1999 and 2009. The increasemostly occurred in Northeast China because of an increase insoybean cultivation and a reduction of traditional woodland inthis region (5).Nr creation from fertilizer application. Nr input from chemical fertil-izer is higher in East and Central China, where multiple croppingsystems and highly intensive agricultural activities are common,and lower in South China. Between 1999 and 2009, Nr input fromchemical fertilizer dropped slightly in East China but increasedgreatly in other regions. East China was in the transition periodfrom agriculture to industry; although the N fertilizer industrydeveloped quickly, the demand for N fertilizer decreased, leadingto N surplus phenomenon in this region.Nr creation by fossil fuel combustion. Coal combustion is the main Nrinput from the production of energy, and it is concentrated in EastChina, especially in the Bohai and Yangtze River Delta regions,accounting for over one-half of the total coal consumption. NorthChina also contributes a large amount of Nr because of its richstorage of coal and petroleum resources. Between 1999 and 2009,Nr creation from fossil fuel combustion increased substantially,with a growth rate exceeding the rate of chemical fertilizer.

Influencing Factors and Future Trends of Nr Creation in China. TheStochastic Impacts by Regression on Population, Affluence, andTechnology (STIRPAT) model is reformulated from the IPAT(Impact = Population·Affluence·Technology) model developed byDietz and Rosa (6). STIRPAT is a statistical model for assessingthe effects of human activities on the environment (for additionalinformation, please refer to www.stirpat.org), and it has been usedsuccessfully to estimate the impact of anthropogenic factors ongreenhouse gas (GHG) and other contaminating emissions.The standard STIRPAT model is

I = aPbAcTde: [S1]

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After taking logarithms, the model becomes

ln I = a+ b ln P+ c ln A+ d ln T + ln e; [S2]

where b, c, and d are the coefficients of P, A, and T, respectively;a is the constant, and e is the error term.To apply the STIRPAT model, this paper selected sociological

factors (population, GDP per capita, energy intensity, andindustrialization level) and analyzed their effect on the nationalanthropogenic Nr creation and the potential environmental im-pact for the period 1952–2010. Here, we revised Eq. S2 by addingindustrialization level (IL) to the set of factors, resulting in Eq. S3:

ln I = a+ b ln P+ c ln A+ d1 ln T + d2 ln IL+ ln e: [S3]

These factors are discussed in Table S1. The data used in this sec-tion are from the China Compendium of Statistics 1949–2008 andthe China Statistical Yearbook (CSY; 2009–2011).A linear regression estimate of the STIRPAT model was first

used to examine the effect of individual factors. Then, a com-posite equation was developed as follows:

ln I = 2:556 ln P+ 0:286 ln A+ 0:239 ln T − 0:678 ln IL− 21:901:[S4]

As is shown in Table S1, population, GDP per capita, and energyintensity have a positive relation with Nr creation. The creation ofNr increases by 2.6% when population increases by 1.0%. From1952 to 2010, Chinese population grew at 1.5% per annum, ac-companied by a 3.9% annual increase of Nr creation in environmentwith a contribution degree of 93%. Consequently, population hasthe largest potential effect on and also, the largest contributionto Nr creation over the past 60 y. Policies for controlling andrestraining rapid population growth in China should be sustainedto reduce the long-term impact of Nr added to the environment.Likewise, GDP per capita grew faster (average 6.7% per annum)than other factors and had a strong relationship on Nr creation,with a 46% contribution from 1952 to 2010. The economic growthin China was at the expense of environmental quality during theprocess of industrialization. More sustainable economic growthshould consider and balance the environment and the economy.For example, improving the N fertilizer use efficiency and energyefficiency would improve the economic growth pattern. Energyconsumption per unit GDP during this period declined slightly(average 0.7% per annum); as a result, it contributed only −4.2%to Nr creation. Promoting efficiency in energy use is also extremelyimportant to arrest the increase in environmental impacts. Incontrast to these former factors, the level of industrializationhas a negative correlation with Nr creation. Nr use dependsmore on the agricultural activities than the industry. Hence,the rapid growth in industrialization was a major factor re-straining the increase of Nr creation in China. From 1952 to2010, greater industrialization caused an annual decline in Nrcreation of 1.1%, with a negative contribution degree of 26%.Overall, during the past decades, population and GDP per

capita were the key positive factors increasing Nr creation inChina, leading to an Nr increase of 5.8% per annum. Energyintensity, industrialization level, and other factors restrained theincrease of Nr creation, making it decrease by 1.7%. The com-bined effect of these factors resulted in an annual increase of4.1% in anthropogenic Nr creation. Inevitably, China is expectedto continue its fast economic growth, feed its growing popula-tion, and speed up the rate of industrialization through at least2050. If successful, these changes would induce a continuation ofthe 1910–2010 trend in the use of Nr. Given projections of strongsocial–economic development in China (7, 8) (Table S2), an-

thropogenic Nr is predicted to reach 63 Tg by 2050, an increaseof 34% over 2010.

Uncertainties and Limitations Analysis. To account for uncertaintiesassociated with the study, we examined the following areas: (i)uncertainty about model structure, (ii) uncertainty in the esti-mated model parameter values, and (iii) propagation of pre-diction errors. Accordingly, SI Text presents detailed discussionson (i) the definition and description of Nr flow of subsystems.The missing points in the national Nr cycling are the Nr ex-change with external system (such as trade and air transport) andthe marginal Nr fluxes (such as biomass burning and animal di-gestive gas). Also, SI Text discusses (ii) Nr flux with assumptionsand uncertainties. The parameter values (Table S5) used here aremostly the mean values from the studies about China, but someof them are modified from or replaced by the similar factors fromother regions because of the lack of indigenous information.Meanwhile, the influences of temporal variation are not con-sidered in most of the parameters. Finally, SI Text presents (iii)Nr accumulation with an uncertainty range. Because of the un-certainties in model and parameter values, Nr accumulation isdifficult to explained without an uncertainty range (e.g., Nr ac-cumulation in soil and air in our study). Thus, the values of Ninput/output fluxes calculated by the equations are simply as-sumed to have a coefficient of variation (CV) [high (±30%),median (±20%), or low (±10%), respectively] according to theirassumptions, uncertainties, and range of parameters (Tables S3and S4). There has been some evidence to support this assump-tion. (i) The average values of input/output fluxes of N describedin the similar study on cropland (3) were all assumed to havea variation ±10%. (ii) In our paper, the quantitative assignmentsof the CV are further based on their own assumptions, un-certainties, and range of parameters. For example, the N flux ofchemical fertilizer and air deposition has relatively low CV, be-cause the nationwide N deposition rate and N content of fer-tilizer reported in China are broadly consistent; however, the Nflux of denitrification has relatively high CV, because it isinfluenced by many factors, and its dominant end product (N2)has a high background concentration in the environment, whichmakes the process difficult to quantify and highly uncertain. Wetreated all of the Nr inputs/outputs as random variables (i.e.,variables with a probability distribution) and propagated theassumed uncertainties through Eq. 1 using Monte Carlo simula-tion (9) to get Nr accumulation. We built a population of 10,000estimates and ranked ordered the estimates. Ultimately, the re-ported values of Nr accumulation in the text are the median andthe empirical 5th and 95th percentiles.We considered the initial results from this paper to be rea-

sonable in most circumstances. However, there are several im-provements needed in the national N cycling model, including(i) better parameterization of the N interactions with the neigh-boring countries, (ii) better parameterization of the N cycling inocean subsystem, including the natural feedback (BNF, water–sediment exchange, and denitrification), and (iii) better empiri-cal data from direct measurements of atmospheric deposition,nitrate leaching, and total N (TN) content of wastewater andsolid waste.

Definition and Description of Nr Flow of Subsystems. The N cyclingmodel used in this study is based on the model developed byGruber and Galloway (10) and Canfield et al. (11). We did notexplicitly model the processes of environmental and commercialinput and output to/from the system outside of China (such asseawater exchange, air transport, and import and export by trade).Land subsystem. Inputs to the land can be divided into two cate-gories: (i) new Nr produced by BNF, industrial N fixation (INF;chemical fertilizer application and chemical material production),atmospheric deposition, irrigation water, and seed and (ii) re-



cycled N already in the system, such as organic fertilizer, sludge,and solid waste applied to crop fields. The fate of N appliedto crop fields differs from N added to natural ecosystems. Theproteins in the edible parts of crop and grassland plants aretaken into the food chain as human and animal food and con-verted into animal proteins; the protein not absorbed by humansand animals is released into the soil and water as excreta. Ad-ditionally, the processes of food and energy production andconsumption add appreciable N to air and water through sewagedischarge and fossil fuel combustion. N stored in natural vege-tation is transferred to the soil as plant litter. Portions of the Nadded to both crop and natural ecosystems are transferred to airand water through gaseous emissions (denitrification and am-monia volatilization) and leaching. Here, biomass and wasteburning are not included, because the amount is thought to beminor and hard to estimate. The remaining N is stored in soilultimately as humus.Atmosphere subsystem. The atmosphere is not only the largest Npool at the surface of the Earth but also the most importantmedium for N exchange. The major premise for the N bio-geochemical cycle is that N2 in the atmosphere is converted to Nrthat can cycle in the biosphere. Meanwhile, the atmosphere re-ceives NOx from fossil fuel burning and other Nr species fromthe terrestrial and aquatic systems. Most of these Nr are re-turned to the terrestrial and aquatic systems through atmo-spheric dry and wet deposition. Transport of Nr outside of Chinais likely to be the cause of the imbalance of Nr emission anddeposition in the air.Inland and coastal water subsystems. N sources to inland waters in-clude leaching, runoff, erosion, and excreta lost from agriculturalactivities; sewage effluent and direct discharge from industry andhouseholds; and surplus feedstuffs from aquaculture. Thesesources are transported through inland waters to coastal watersand ultimately, the sea. In addition, atmospheric transport of gas-eous phases from the continents to the oceans combines to affectthe coastal regions. We do not consider N cycling processes, suchas denitrification and BNF, in coastal waters, because these pro-cesses are poorly known for China.

Calculation of Nr Flux with Assumption and Uncertainty Analysis.N deposition (N1, N23, N24, and N31). Modeled global N depositionwas in excess of the critical load (12), with wet and dry depositionin mainland China at 7.4, 11, and 16 Tg/y in the 1980s, 1990s, and2000s, respectively (13). One-fourth of this N was deposited intoagro-ecosystems, and the rest was deposited into forest, grass-land, and aquatic ecosystems (14). The distribution of N de-position to inland water was simply calculated by the area ratioof such waters to the mainland. As a result, N deposition in landand inland water was estimated at 4.6 and 16 Tg and 9.0 × 10−2

and 0.30 Tg in 1978 and 2010, respectively. N deposition to thecoastal ecosystem was reported at 21–74 mmol N/m2 per year in1997 (15). The result is consistent with estimated fluxes for theBohai and Yellow Sea (28 × 109 mol/y), which is equivalent to 61mmol N/m2 per year (16), and the East China Sea, equivalent to68 mmol N/m2 per year (17). For many offshore regions (e.g., theEast Sea and the Yellow Sea), atmospheric deposition has sur-passed river input as a source of N for primary production (18).We estimated total N deposition to marine regions of 1.7 Tg in1978 and 5.0 Tg in 2010 using total N deposition fluxes of fourmarine regions given from a spatially explicit global analysis byDuce et al. (19). The combined result was broadly consistentwith results of regional anthropogenic NH3 and NOx emissioninventories IIASA Asia (http://gains.iiasa.ac.at) and EDGAR v4(http://edgar.jrc.ec.europa.eu) for China.INF (N2). The production of synthetic ammonia by the Haber–Bosch process is typically used to product chemical fertilizer andother material. At the regional scale, the rate of Nr created byINF is usually presented with numbers regarding fertilizer con-

sumption rate. Imports and exports have not been involved inthe consumption-based approach. Chemical fertilizer N is usedprimarily in the form of nitrogenous fertilizer (mainly urea andammonium bicarbonate) and compound fertilizer (at least in-cluding two nutrients of nitrogen, phosphorus, and potassium,such as ammonium phosphate). An average N content of 30% ofcompound fertilizer is commonly assumed in China (20). Thedata source of N fertilizer, CSY, provides nitrogenous fertilizerand compound fertilizer consumption from 1978 to 2010, and itsvalue has been converted to pure N equivalent. Therefore, Nrinputs from fertilizer amounted to 7.6 Tg in 1978 and 29 Tg in2010. According to the China Synthetic Ammonia Annual Re-port, we estimated the apparent consumption of synthetic am-monia (convert NH3 to N) from 9.8 to 50 Tg during 1978–2010,and more recently, N fertilizer production accounted for over90% of the total ammonia consumption in China. Deducting theN fertilizer production from CSY, the chemical material pro-duction contributed 2.1 and 5.1 Tg N to the land.Manure (N3-1). Manure management and recycling is increasinglyimportant in China. The calculation of manure Nr input fromanimal excreta is based on livestock and poultry number, animal-specific N excreta rate per capita, feeding period, and the ratioback to field. It is worth pointing out that the number of cattle,sheep, and horses is the year-end number, because their feedingperiod is over 1 y; in contrast, the number of pigs and poultry is theslaughtered number with feeding period of 199 and 55 d, re-spectively. Likewise, the calculation of manure Nr input fromhuman excreta is based on population, N excreta rate per capita,and the ratio back to field. Manure production from humans hasdecreased because of a decline in recycling to fields from 60% to30% in urban regions and from 30% to 10% in rural regions (21),because sewage treatment has become more widespread. Therecycling of human and animal excreta was estimated at 5.4 and7.4 Tg N in 1978 and 2010, respectively. The uncertainties ofthese estimates are mainly from the omission of some kinds oflarge animals (such as asses and mules) and wild animals, whichmight cause a certain underestimation.Crop residue (N3-2). The fraction of crop residues (i.e., the straw) isassumed to be returned to the fields as organic fertilizer; the restof the crop residues is removed from cropland and partly burnt infarm fields or kitchens as cooking fuel. Based on the crop (grain)yield, a Harvest Index [i.e., the ratio of crop harvest economicyield (grain) to biological yield (grain and straw)], the N contentof straw, and the ratio returned to field, we calculated that cropresidues contributed 1.1 and 2.2 TgN to the landscape in 1978 and2010, respectively. Taken together, Nr input from organic fer-tilizers amounted to 6.5 and 9.6 Tg in 1978 and 2010, respectively.Because of the limited statistical data of green manure and feedyield, they were not included in our study.BNF (N4). Terrestrial BNF can result from both natural processesand human cultivation of N fixing plants. The symbiotic N fixationrates of various crops vary widely, with the range of 72–201 kg/haper year (22). The BNF rates of legume, peanut, and greenmanure applied in this paper are within this range (23). Wemultiplied the area planted with leguminous crop species by theN fixation rate specific to each crop type. Similarly, the BNF ofnonleguminous crops, forests, and grasslands was estimated inthe same way. BNF-derived N input was the most stable input tothe land subsystem, ranging around 10–13 Tg from 1978 to 2010.Sludge (N5). The sludge is generated from the treated sewage. Thewastewater can be divided into industrial wastewater and house-hold wastewater. We recorded their disposal rates from the“China Environmental Status Bulletin (CESB),” which showedthat the disposal rate of household wastewater (65% in 2010)was lower than the disposal rate of industry wastewater (95% in2010) in China, although it increased sharply after 2000. Ac-cording to the recent statistical data on production of sludge andsewage, the sludge generation rate (i.e., sludge generated from


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per unit sewage) is between 0.032% and 0.042% (24). Consid-ering the character of the sludge moisture and N content, we cancalculate sludge N production for a given year. Furthermore,sludge is returned to the field, burned, disposed of in the ocean,or stored in waste piles. As a result, the N inputs of sludge ul-timately to the land increased from 0.13 to 0.38 Tg between 1978and 2010.Solid waste compost (N6). Solid wastes mainly include municipalsolid waste (MSW), which refers to waste generated fromhouseholds, and industrial solid waste (ISW). There are threeprimary methods for the treatment and disposal of solid waste:landfills, incineration, and composting (25). At present, about80% of the MSW enters landfills (including dumping) in China,and 20% is used for composting, with moisture percent 50%(5.6–76%) and N percent 1.4% (0.2–3.4%) by weight (mainlyfood, paper, and plastic) (26, 27). Compared with MSW, a largefraction of ISW is reused or stored, and the rest is either dis-posed or discharged to the environment. Because of the com-plexity and instability of ISW, there is not an accepted averagevalue for its N and moisture content. We used values for MSW,modifying its moisture percent to 30% and N content to 1%.Solid waste used for compost increased from 7.0 × 10−2 to 0.97Tg during 1978–2010. Because of the scarce information aboutwastes generated from rural households, only urban waste andISW were considered here.NH3 volatilization (N9). Sources of atmospheric ammonia includeanimal and human wastes, fertilizer application, and some in-dustrial activities. We used the recommended value from theIntergovernmental Panel on Climate Change (IPCC) of 10% forsynthetic fertilizer N application and 20% for manure N as es-timates of average NH3 volatilization (28). NH3 emission factorsused for animals are the mean values of the NH3 emission factorlisted in ref. 29. The livestock number should be modified by thefeeding period for specific animals. Multiplying the NH3 emis-sion factors by the modified livestock and poultry number,population, and NH3-N emissions from animal and human ex-creta gave 2.2 and 1.0 Tg in 1978 and 4.3 and 1.5 Tg in 2010.Collectively, NH3 volatilization contributed 5.1 Tg N in 1978 and10 Tg N in 2010, and it has become the single largest Nr sourceof the atmosphere from land. NH3 emissions from industrialactivities were not included here.Denitrification (N10 and N18). Denitrification is influenced by manyfactors, particularly chemical fertilizer type, use efficiency, andfarming techniques, and the dominant end product of de-nitrification (N2) has a high background concentration in theenvironment, which makes the process difficult to quantify (30).Based on the national mean direct emission factor of N2O-N ofcultivated soils (0.0095 kg N2O-N/kg N with great uncertainty−79% to 135%) (31) and annual N application rates, N2Oemission through denitrification in China reached 0.18 and 0.41Tg in 1978 and 2010, respectively. Globally, N2O comprises 3.9%of the denitrification flux (32). The nationwide N output fromdenitrification (N2 + N2O) can be roughly calculated from 4.7 to11 Tg between 1978 and 2010. The estimate of denitrification isstill highly uncertain because of the large range of emissionfactors and the missing indirect emission from soil. However, thecoincidence that denitrification and BNF are largely balanced inthe modern terrestrial N cycle (11) makes this result reassuring.Leaching and runoff (N11 and N12). N loss through leaching andrunoff from soils in agricultural and nonagricultural ecosystemsdepends on factors such as land use type, form of applied N, soilproperties, and rainfall. There seems to be a frequent significantrelationship betweenN loss and these factors in compiled datasetsof measurements of N leaching and runoff loss (33–36). Most ofthe grasslands are grazed in China, and therefore, they can beconsidered agricultural fields. N applications of fertilizer (in-cluding chemical and organic fertilizers) are an essential com-ponent of cropland farming and livestock grazing (37, 38). It has

been estimated that the total N leaching and runoff loss mightbe equivalent to 2.8% and 5.0% of China’s total N applicationin agricultural fields, respectively (33, 34). Likewise, for vege-tated ecosystem, 22% of dissolved inorganic N (DIN) of thethroughfall input was leached from forest ecosystems in China,which was lower than the 50–59% observed for European forests(35). The runoff and erosion rate averaged at 1.5 kg N/ha peryear for Chinese forests (36). Therefore, the above parametersfrom our compiled dataset were used to estimate leaching andrunoff N of 1.8 Tg in 1978 and 4.3 Tg in 2010, which was possiblyslightly underestimated because of the exclusion of nongrazedgrasslands.Excrement loss (N13). Areas with concentrated livestock operationsoften have elevated nutrients and organic pollutants in surfacewaters (39). The excrement loss is generally by two ways: directdischarge in the process of rearing or indirect loss by leakingfrom stacks because of rainfall or other causes. We simply as-sumed that the remaining N in the excrement N of animals,exclusive of the fraction taken back to field, was loss from land towater bodies. Therefore, the loss from excrement was 1.4 Tg N in1978 and 2.9 Tg N in 2010, which approaches the estimated lossratio (22–30%) in ref. 40. The gas volatilization from excrementhas been included in calculation of NH3 volatilization.Wastewater (N14, N20, N26, N27, and N28).Here, the input and outputpatterns about wastewater were considered together to prescribethe Nr flows in the environment. Generally, wastewater is dis-charged from sewage treatment plants or directly into water bodies.The N of treated wastewater has three sinks: (i) gas dischargethrough the N removal process, (ii) sludge generation, and (iii)residual N content in the effluent from sewage treatment plants.N14. According to the “Integrated discharge standard of waste-water” (GB8978-1996) (41), the standard of wastewater dis-charge about TN and NH3-N is TN = 20 mg/L, NH3-n = 8 mg/L.Because of the lack of TN monitoring data, it can be roughlyestimated that TN is 2.5 times NH3-N. Using the NH3-N dis-charge in wastewater from CSY, we estimated the total waste-water N output from land, which increased from 2.7 Tg in 1978to 3.8 Tg in 2000 before decreasing to 2.6 Tg in 2010.N20. Sewage treatment discharge refers to gaseous N emission fromsewage treatment plants (i.e., the N removal section). Many po-tential new processes for improvingN removal achieve anN removalrate greater than 60% (42). A conservative estimate used in thispaper is 30–40%. As a result, the gaseous N from sewage treatmentplants was 0.48 and 0.86 Tg in 1978 and 2010, respectively.N26 and N27. Household wastewater and industrial wastewaterrefer to wastewater discharged directly from households andfactories to inland waters without treatment. The N dischargesfrom household wastewater increased from 0.56 Tg in 1978 to 1.7Tg in 2001 and then decreased to 0.81 Tg in 2010. N dischargesfrom industrial wastewater decreased slightly from 0.66 Tg in 1978and then dropped quickly during 1995–2001 to recent values of0.030–0.050 Tg. The increases in the treatment rate of waste-water (8–65% for household wastewater and 70–95% for in-dustrial wastewater between 1978 and 2010) were the cause ofthese changes.N28. Sewage works effluent refers to the wastewater dischargedfrom sewage plant after treatment. Deducting the other two sinks(gaseous N emission and sludge N), the rest of N in wastewaterwas discharged from sewage treatment plants, which increasedfrom 1.1 Tg in 1978 to 1.3 Tg in 2010.Crop harvest (N15). A sizable fraction of the N applied to the landsubsystem is absorbed by crop plants, which can be calculated bymultiplying the dry crop yield by the N content of the crops.Exclusive of the straw returned to fields, the harvested grains andstraws accumulated 6.6 and 17 Tg N in 1978 and 2010 in landsubsystem. The recovery rate of N applied [the ratio between cropharvest N and total N input into the land surface; i.e., the



combination of N15 and Ninput (N1 + N2-1 + N3 + N4 + N5 +N6 + N7 + N8) in Table S3] was below 25% during this period.Solid waste storage (N17). As mentioned above, a fraction of solidwastes is used as composting, and they return to the agriculturalsystems. The rest of the solid wastes are stored in the ground(landfill) or on the land surface in piles. Solid waste placed inlandfills represented 0.28–0.92 Tg N before 2000 and surged to3.9 Tg in 2010 because of increasing waste volume and treatmentrate. We used the number of MSW collected and transportedand ISW in stocks directly from CSY and the disposal rate ofMSW to calculate the amount of solid waste stored in landsurface, which contributed 1.8 and 1.9 Tg N between 1978 and2010. Taken together, solid waste N in storage increased from2.1 Tg in 1978 to 5.8 Tg in 2010.Storage in soils and others (N18).The annual Nr accumulation in soilsand other sinks is calculated by the difference between totalaccumulation of Nr in the land subsystem and Nr accumulation asharvested crops, industrial products, and stored solid wastes (N15,N16, and N17). The accumulation of Nr increased from 7.9 to 17Tg during 1978–2010. This accumulation represents not only thenet retention of N applied in the soil but also in natural vege-tation and plant residues. The uncertainties of the equation andthe estimated Nr flux are propagated and ultimately, lead to alarge uncertainly in Nr accumulation in soils and others throughits calculation.Fossil fuel combustion (N21). Nr formation during fossil fuel com-bustion is inadvertent, and the Nr is primarily as NOx, which isemitted directly into the atmosphere. The process is twofold—whereby atmospheric N2 and organic N in the fuel are trans-formed accidentally into NOx—and both result in increased Nr(43). Fossil fuels such as coal, petroleum, and natural gas provideabout 90% of all energy in China. The different fossil fuel spe-cies consumption data are derived from energy balance tables bysources and sectors in CSY. The anthropogenic NOx emissionsare estimated on the basis of economic sector fossil fuel con-sumption, NOx emission factors weighted as NO2 (Table S6)(44), and efficiency of NOx removed by pollution control mea-sures (45) following the equation. Collectively, they contributed1.8 Tg N in 1978 and 8.5 N Tg in 2010. The increase was especiallymarked after 2002, rising from 4.1 to 8.5 Tg because of the en-hancement of energy intensity in China during this period (46).Aquaculture (N25 and N32). With the rapid development of aqua-culture, excess nutrient in feeds enters and affects the waterenvironment (47). The Takeuchi Jun Lang method is usuallyused to estimate the nutrient pollution from aquaculture (48).The principle is similar to the material balance (i.e., the envi-ronmental load is the fraction of feed N over organism N). The

parameters (feed conversion coefficient, N content of the feed,and aquatic product) applied in this paper are the mean valueslisted in refs. 49–53. The feed conversion coefficient is the ratiobetween feed consumption and net product weight gain. A cer-tain underestimation may result, because the number of organ-isms is replaced by the yield of aquatic products. As a result, Ndischarges from freshwater fish farms to water bodies increasedfrom 7.3 × 10−2 to 2.2 Tg for the period 1978–2010, and Ndischarges from marine fish farms increased from 3.7 × 10−2 to0.60 Tg for the period 1978–2010.Riverine flux and sewage outfall (N29 and N30). N moves from land-scape to sea by riverine transport and direct discharge of in-dustrial and sewage outfalls. The main pathway for N transportfrom inland waters to coastal waters is river flow. The transport ofDIN through the threemajor rivers inChina (Changjiang,Huanghe,and Zhujiang) to estuaries increased between 1980 and 1989, withmean annual transportations of 0.78, 0.060, and 0.15 Tg N, re-spectively (54). Data on riverine DIN fluxes from 198 monitoredrivers for the period 2004–2009 from the China EnvironmentalStatus Bulletin show that NH3-N decreased from 1.0 to 0.66 Tg.Taken together, assuming that TN is 2.5 times NH3-N, estimatesof riverine N fluxes to sea were 2.5 Tg in 2004 and 1.6 Tg in 2009.The N fluxes from sewage outfalls were 0.29 Tg in 2004 and 0.48Tg in 2010. Total N fluxes to the East China Sea were thehighest, accounting for 75% of the total N fluxes.A few Nr fluxes can be easily calculated by the corresponding

equation, and therefore, we did not expand here.

Comparison with Other Studies. Xing and Zhu (55) and Ti et al.(20) estimated several of the fluxes that we did for the sameperiod (Table S7). Our results show good agreement with theirreported values for chemical fertilizer, fossil fuel, cultivatedBNF, crop residue, air deposition, riverine transport, crop har-vest, and soil retention. Our estimate for manure N (8.5 Tg) ismuch lower than the estimate by Xing and Zhu (55) (18 Tg) in1995, because we did not consider excrement produced fromwild animals and other large animals, such as donkeys or mules.In addition, we used the year-end or out-of-corral number ofanimals to represent the number of livestock and poultry. Ourestimate of BNF (13 Tg) is higher than the estimate by Ti et al.(20) (10 Tg) in 2007, likely because the N fixation rate that weused for forest is much higher than the values used by Ti et al.(20). Our estimates of NH3 volatilization (9.6 Tg) differed fromthe estimates of Xing and Zhu (55) (6.1 Tg) because of the use ofdifferent NH3 emission factors; however, our estimates are closeto the estimates produced by Klimont (56) (9.6 Tg in 1995).

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Fig. S1. Spatial disparity and variation of anthropogenic Nr creation in mainland China. (A) N input amount (Tg/y). (B) N input density (kg/ha per y). (C)Anthropogenic Nr creation amount and patterns (Tg/y). (D) N input per capita (kg/cap per y). (E) N input per unit GDP (kg/million per y).



Fig. S2. Variations in Nr balance of subsystems for the period 1978–2010. (A) Nr input to the land subsystem. (B) Nr output from the land subsystem. (C) Nrinput to the atmosphere subsystem. (D) Nr input to the inland water subsystem. (E) Nr flux from the terrestrial system to coastal regions.



Fig. S3. Rates of N flux between different environmental subsystems in China (Tg N). Arrow size reflects relative size of the flux. The black real arrowsrepresent N output from the atmosphere; the red real arrows represent N output from the landscape. The black dotted arrows represent N flows between landand inland water. (A) 1978. (B) 2010.

Fig. S4. Conceptual framework of anthropogenic Nr dynamics (including human, social, and economic activities) in China. Human drivers can be divided intotwo categories; one category is similar to the global (universal human drivers), and the other category is more specific to China (specific human drivers; column1). Together, these drivers exert effects on different sectors and stages of social production and consumption (column 2), and ultimately, they lead to Nr inputsto and outputs from different environmental reservoirs (column 3).



Table S1. Descriptions and contributions of influencing factors to the change of Nr creation (1952 prices)

Factors Definition Unit

Averageannual growth

rate (%)Regressioncoefficient

Effect on theannual changeof Nr creation*

Contributiondegree to changeof Nr creation†

AnthropogenicNr creation (I)

Nr creation from human activities Tg 4.1

Population (P) End of year population 104 units 1.5 2.556 3.9 93GDP per capita (A) Gross domestic product per capita Yuan 6.7 0.286 1.9 46Energy intensity (T) Fossil fuel consumption per unit GDP Tg SCE/billion −0.7 0.239 −0.2 −4.2IL Share of industry and construction

business output over the total GDP% 1.6 −0.678 −1.1 −26

Other factors (a) −21.901 −0.4 −9.2

SCE, standard coal equivalent.*Effect on the annual change of Nr creation = average annual growth rate × regression coefficient.†Contribution degree to change of Nr creation = effect on the annual change of Nr creation/average annual growth rate of Nr creation.

Table S2. Projections of Nr creation (1952 prices)

Factor 2020 2030 2050

Population (104) (1) 145,000 146,000 150,000GDP per capita (Yuan) (1) 7,044 9,640 20,304Energy intensity (Tg SCE/billion) (2) 3.3 3.7 2.7IL (%) (1) 50 60 70Amount of anthropogenic Nr (Tg/y)* 56 57 63Amount of anthropogenic Nr per capita (kg/cap per year)† 39 39 42

*Calculated by Eq. S4 based on the predicted population, GDP per capita, energy intensity, and IL.†Derived from the total amount of anthropogenic Nr creation and population.

1. Chinese Academy of Sciences Ecology and Environment Strategic Research Group (2009) The Development Roadmap of Ecological and Environmental Technology in China by 2050(Science Press, Beijing), pp 43–51.

2. The Energy Research Institute of National Development and Reform Commission (2009) China’s Low Carbon Development Pathways by 2050—Scenario Analysis of Energy Demand andCarbon Emissions (Science Press, Beijing), pp 46–85.



Table S3. Nr balance of the land subsystem

Input/output Mathematical equationsAssumedCV (%) Activity data description

Input patterni) N deposition N1 = P1 × P2 ±10ii) INF N2 = N2-1 + N2-2

Chemical fertilizer N2-1 = D1 + D2 × P3 ±10 D1: Consumption of nitrogenous fertilizerD2: Consumption of compound fertilizer

Chemical material N2-2 = D3 × 14/17 − D4 ±10 D3: Consumption of synthetic ammoniaD4: Production of N fertilizer

iii) Organic fertilizer N3 = N3-1 + N3-2Manure N3-1 = D5 × P4 × P7 +

D6 × P5 × P6/365 × P8±20 D5: Population; D6: livestock and poultry number

Crop residue N3-2 = D7 × (1/P9-1) × P10 × P11 ±20 D7: Yield of crop grainsiv) BNF N4 = N4-1 + N4-2 ±20

Agriculture BNF N4-1 = D9 × P12 + (D8 − D9) × P13 D8: Total sown area; D9: sown area of legume cropsForest and grassland BNF N4-2 = D10 × P14 + D11 × P15 D10: Area of forest; D11: area of grassland

v) Sludge back to field N5 = (D12 × D14 + D13 × D15) × P16 ×P17 × (1 − P18) × P19

±30 D12: Number of industrial wastewater dischargeD13: Number of household wastewater dischargeD14: Disposal rate of industrial wastewaterD15: Disposal rate of household wastewater

vi) Solid waste composting N6 = (D16 × D17 + D18) × (1 − P20) ×P21 × (1 − P22)

±30 D16: Number of living wastes collected andtransported

D17: Treated rate of living wastesD18: Number of industrial solid wastes treated

vii) Seed N7 = D19 × P23 × P24 ±20 D19: Sown area of each farm cropvii) Irrigation water N8 = D20 × P25 ±20 D20: Area of cultivated land

Output patterni) NH3 volatilization N9 = N9-1 + N9-2 ±20

From fertilizer N9-1 = N2-1 × P26 + N3-1 × P27 N2-1: Consumption of chemical fertilizerN3-1: Consumption of manure

From excrement N9-2 = (D5 × P28 + D6 × P29 × P6/365) ×14/17

D5: Population; D6: livestock and poultry number

ii) Denitrification (N2 + N2O) N10 = (N2-1 + N3 + N4) × P30/P31 ±30 N3: Consumption of organic fertilizer; N4: BNFiii) Leaching N11 = N11-1 + N11-2 ±30

Agricultural fields N11-1 = (N2-1 + N3) × P32Nonagricultural fields N11-2 = D10 × P33 × P34 D10: Area of forest

iv) Runoff and erosion N12 ±30Agricultural fields N12-1 = (N2-1 + N3) × P35Nonagricultural fields N12-2 = D10 × P36 D10: Area of forest

v) Animal excrement loss N13 = D6 × P5 × P6/365 × (1 − P8) ±10 D6: Livestock and poultry numbervi) Wastewater N14 = (D21 + D22) × P37 ±20 D21: NH3-N number of industrial wastewater

dischargeD22: NH3-N number of household wastewater

dischargeAccumulation patterni) Crop harvest N15 = D7/P9 × P38 − N3-2 ±20 D7: Yield of crop grainsii) Industrial product N16 = N2-2 − D21 × P37 ±20 N2-1: Production of chemical materialiii) Solid waste storage N17 = N16-1 + N16-2 ±30

Landfill N17-1 = (D16 × D17 + D18) ×(1 − P20) × P21 × P22

Pile and store N17-2 = [D16 × (1 − D17) + D23] ×(1 − P20) × P21

D23: Number of industrial solid wastes in stocks

iv) Storage in soils and others N18 = Naccumlation − N15 − N16 − N17



Table S4. Nr balance of the atmosphere, inland water, and coastal water subsystems

Input/output Mathematical equationsAssumedCV (%) Activity data description

AtmosphereInput pattern

i) Denitrification (N2O) N19 = (N2-1 + N3 + N4) × P30 ±30ii) NH3 volatilization Table S3 ±20iii) Sewage treatment discharge N20 = (D21 × D12 + D22 × D13) ×

P37 × P39±20 D21: Number of industrial wastewater NH3-N

dischargeD22: Number of household wastewater NH3-N

dischargeiv) Fossil fuel burning N21 = D24 × P40 × P41 ±30 D24: Consumption of fossil fuelsv) Lightning N22 = P42 × P1/P43 ±30

Output patterni) N deposition N23 = N1 + N24 + N31 ±10

Inland waterInput pattern

i) N deposition N24 = P2 × P44 ±10ii) Freshwater fish farm N25 = (P45 × P46 − P47) × D25 ±30 D25: Yield of freshwater aquatic productsiii) Industrial wastewater N26 = D21 × P37 × (1 − D14) ±20 D21: NH3-N number of industrial wastewater

dischargeD14: Disposal rate of industrial wastewater

iv) Household wastewater N27 = D22 × P37 × (1 − D15) ±20 D22: NH3-N number of household wastewaterdischarge

D15: Disposal rate of household wastewaterv) Sewage works effluent N28 = (D21 × D14 + D22 × D15) ×

P37 × (1 − P39) − N5±20 N5: Sludge back to field

vi) Leaching Table S3 ±30vii) Runoff and erosion Table S3 ±30viii) Animal excrement loss Table S3 ±10

Output patterni) Riverine flux N29 = D26 × P37 ±20 D26: Riverine NH3-N fluxii) Irrigation water Table S3 ±20

Coastal waterTerrestrial to sea transfer

i) Riverine flux N29 = D26 × P37 ±20 D26: Riverine NH3-N fluxii) Sewage outfall from land N30 = D27 × P37 ±20 D27: NH3-N number of sewage outfalls dischargeiii) N deposition N31 = P48 × P49 ±10iv) Marine fish farm N32 = (P45 × P46 − P47) × D28 ±30 D28: Yield of marine aquatic products



Table S5. List of parameters used in Nr cycling model

Parameters Description Unit Value* Refs.

P1 Land area of China ha 9.6 × 108

P2 Deposition rate in mainland kg/ha per year 1980s: 7.55; 1990s: 12.71; 2000s: 16.98 1P3 N content of compound fertilizer % 30 2P4 N excreta rate for human kg/cap per year 5 3P5 N excreta rate for animal kg/cap per year Pig: 8; cattle: 40; sheep: 5; horse: 52; poultry: 0.3 3P6 Feeding period of livestock and poultry d Pig: 199; cattle: 365; sheep: 365; horse: 365;

poultry: 554, 5

P7 Ratio of human excreta back to field % 1980s: urban (30), rural (60); 1990s: urban (15),rural (53); 2000s:,urban (10), rural (30)

6

P8 Ratio of animal excreta back to field % Pig: 60; cattle: 77.7; sheep: 70; horse: 40;poultry: 39

7

P9 Harvest Index of crops — Rice: 0.53; wheat: 0.48; maize: 0.45; soybean:0.50; potato: 0.66; peanut: 0.55; rape: 0.28;sesame: 0.37; sugarcane: 0.67; beet: 0.75;tobacco: 50; cotton: 0.25

8, 9

P10 N content of straws % Rice: 0.91; wheat: 0.65; maize: 0.92; soybean:2.10; potato: 2.51; peanut: 1.82; rape: 0.87;sesame: 1.31; sugarcane: 1.1; beet: 0.25;tobacco: 1.44; cotton: 1.24

8

P11 Ratio of straws back to field % Rice: 41.7; wheat: 40.2; maize: 32.2; soybean:16.8; potato: 50; peanut: 26; rape: 47.6;sesame: —; sugarcane: 10; beet: 90; tobacco:47.6; cotton: 16

8

P12 Symbiotic N fixation rate of arable land kg/ha per year Legume: 105 (70–110); peanut: 112 (72–124);green manure: 130 (130–170)

10

P13 Nonsymbiotic N fixation of arable land kg/ha per year 18.75 11P14 N fixation rate of forest kg/ha per year 43.2 (33.1–47) 12P15 N fixation rate of grassland kg/ha per year 2.7 (2.3–3.1) 13P16 Generation rate of sludge % 0.035 (0.02–0.042) 14, 15P17 N content of sludge % 2.9 (2.0–4.8) 5, 16, 17P18 Moisture content of sludge % 80 (72–98) 15P19 Ratio of sludge back to field % 80 7P20 Moisture content of solid waste % MSW: 50; ISW: 30 18, 19P21 N content of solid waste % MSW: 1.4 (0.02–3.24); ISW: 1 (0.75–1.17) 18–21P22 Ratio of solid wastes landfill % Landfill: 80 (composting: 20) 18–21P23 Sown amount per hectare kg/ha per year Rice: 10; wheat: 225; maize: 30; soybean: 67.5;

potatos:1,312.5; peanut: 180; rape: 1.125;sesame: 202.5; beet: 41.25; cotton: 52.5

22

P24 N content of seed % Rice: 1.4; wheat: 2.1; maize: 1.6; soybean: 5.3;potatoes: 0.32; peanut: 4.4; rape: 4; sesame:3.5; beet: 0.24; cotton: 3

23

P25 N content of irrigation water kg/ha per year 5.2 7P26 Volatilization rate of chemical fertilizer % 10 24P27 Volatilization rate of manure % 20 24P28 NH3 emission factor for human kg/cap per year 1.3 25P29 NH3 emission factor for animal kg/cap per year Pig: 3.8; cattle: 24.1; sheep: 3.1; poultry: 0.24 26P30 N2O emission factor from soil kg N2O-N/kg N 0.0095 27P31 N2O yield ratio of denitrification % 3.9 (2.6–3.9) 28P32 Leaching coefficient of agriculture fields % 2.8 (2.19–4.35) 29P33 Throughfall N input to forest kg N/ha per year 1990s: 21.0; 2000s: 23.1 30P34 Leaching rate of forest % 22 30P35 Runoff coefficient of agriculture fields % 5 31P36 Runoff rate of forest kg N/ha per year 1.54 (0.05–2.79) 12P37 Ratio of TN to NH3-N of sewage 2.5 32P38 Average N content of crop plants % Rice: 1.12; wheat: 1.41; maize: 1.37; soybean:

3.15; potato: 1.04; peanut: 3.25; rape: 1.76;sesame: 2.12; sugarcane: 0.37; beet: 0.24;tobacco: 1.42; cotton: 1.01

P39 Sewage–N removal ratio % 1980s: 30; 1990s: 35; 2000s: 40 7P40 NOx emission factor of fuels % Table S6 33P41 Efficiency of NOx removed % 1978–1990: 0; 1990s: 5–10; 2000s: 10–20 34P42 Global lightning N fixation Tg/y 5 (3–10) 35P43 Area of the earth ha 5.1 × 1010



Table S5. Cont.

Parameters Description Unit Value* Refs.

P44 Inland water area of China ha 1.74 × 107

P45 Feed coefficient — Fish: 2; shrimp: 1.5; crab: 2 36–40P46 N content of feed % Fish: 6.4; shrimp: 4.96; crab: 5.76 36–40P47 N content of acquit products % Fish: 2.86; shrimp: 2.34; crab: 2.97 36–40P48 Coastal area of China ha Bohai Sea: 7.7 × 106; East China Sea: 7.52 × 107;

Yellow Sea: 3.8 × 107; South China Sea:3.52 × 108

P49 Deposition rate in coastal regions mg N/m2 per year Bohai Sea: 1,400–2,100; Yellow Sea: 1,400–2,100;East China Sea: 840–1,400; South China Sea:420–840

41

P50 Denitrification rate of coastal regions μmol/m2 per hour 6 (3.2–7.5) 42

*Values in parentheses indicate estimate range.

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data_reports.htm#1. Accessed July 5, 2010.25. Möller D, Schieferdecker H (1989) Ammonia emission and deposition of NHx in the G.D.R. Atmos Environ 23(6):1187–1193.26. Sun QR, Wang MR (1997) Ammonia emission and concentration in the atmosphere over China. Scientia Atmospherica Sinica 21(5):590–598.27. Zheng XH, Han SH, Huang Y, Wang YS, Wang MX (2004) Re-quantifying the emission factors based on field measurements and estimating the direct N2O emission from Chinese

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Table S6. Emission factors of NOx by sectors and fuel types (kg/t)

Sourcecategory Coal Coke

Crudeoil Gasoline Kerosene Diesel

Residualoil LPG

Naturalgas*

Gasworksgas

Refinerygas

Electric power 9.95 7.24 16.7 21.2 7.4 10.1 3.74 41.0 13.5 0.75Gas works 0.75 0.9 2.19 9.62 5.84 0.26 0.95 0.53Coking/refinery 0.37 0.24Industry 7.5 9 5.09 16.7 7.46 9.62 5.84 2.63 20.9 9.5 0.53Construction 7.5 9 16.7 7.46 9.62 5.84 2.63 20.9 0.53Transportation

Road 21.2 27.4 27.4 27.4 18.1Railway 7.5 9 54.1 54.1Other 7.5 9 5.09 16.7 27.4 36.3 36.3 20.9

Domestic use 1.88 2.25 1.7 16.7 2.49 3.21 1.95 0.88 14.6 7.36 0.18Commerce 3.75 4.5 3.05 16.7 4.48 5.77 3.5 1.58 14.6 7.36 0.32Others 3.75 4.5 3.05 16.7 4.48 5.77 3.5 1.58 14.6 7.36 0.32

*Units: 10−4 kg/m3.

Table S7. Comparison with other studies about Nr budget in mainland China (Tg N/y)

Items

1995 2007

Xing and Zhu (1) This paper Ti et al. (2) This paper

Nr inputsAnthropogenic NrChemical fertilizer 22 22 29 28Fossil fuel burning 4.2 3.9 — 7.5BNF — 11 10 13Cultivated BNF (in agricultural field) 4.3 4.4 — 4.4Food/feed import 0.52 — 1.9 —

Recycled NrManure 18 8.5 — 7.1Crop residue 1.4 1.8 — 2.0Atmospheric N deposition 11 11 13 16

Nr outputsNH3 volatilization 6.1 9.6 10 9.7N transported into water bodies 11 10 9.7 12Denitrification (N2 + N2O) 5–10 9.0 ∼20 10

Nr accumulationCrop harvest (including straws) 14 15 — 18Storage in soils (and others) 12 ∼14 ∼7.9 ∼16

1. Xing GX, Zhu ZL (2002) Regional nitrogen budgets for China and its major watersheds. Biogeochemistry 57(1):405–427.2. Ti CP, Pan JJ, Xia YQ, Yan XY (2012) A nitrogen budget of mainland China with spatial and temporal variation. Biogeochemistry 108(1–3):381–394.



supporting information - pnas · document each of the values and the rationale (such as equation,...

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