Changing Urban Phosphorus Metabolism: Evidence from Longyan City, China
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Science of the Total Environment 536 (2015) 924–932 Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv Changing urban phosphorus metabolism: Evidence from Longyan City, China Shenghui Cui a,b,⁎,SuXua,b, Wei Huang a,b, Xuemei Bai c, Yunfeng Huang d,GuilinLia,b a Key Lab of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China b Xiamen Key Lab of Urban Metabolism, Xiamen 361021, China c Fenner School of Environment and Society, College of Medicine, Biology and Environment, Australian National University, Canberra 0200, Australia d School of Biotechnology Engineering, Jimei University, Xiamen 361021, China HIGHLIGHTS GRAPHICAL ABSTRACT • Both input P and output P increased sig- nificantly from 1985 to 2010. • The agricultural subsystem contributed 85% of total P input. • The share of P input lost to the environ- ment increased from 66% to 72%. • Food production efficiency decreased from 48% to 29%. • Per capita P input shows different curves with HDI, urbanization rate, and income. Phosphorus flow of Longyan in 1985(a) and 2010(b) (Unit: t P). Arrows are sized relative to the magnitude of the flow; red arrows are P input flows; blue arrows are P output flows; orange arrows are P flows internal to the sys- tem; green arrows are P recycling flows internal to the system. The percentages are used to express the ratio of the input, output or stock categories to the total P input. article info abstract Article history: Rapid worldwide urbanization calls for a better understanding of phosphorus (P) metabolism and the interaction Received 8 March 2015 of the physical, ecological and social drivers of P cycling in urban systems. We quantified the P metabolism in Received in revised form 16 May 2015 Longyan, a city with a major agricultural economy, and analyzed its long-term trends over the rapid urbanization Accepted 19 June 2015 period of 1985–2010. Both input P (from 4811 t P to 14,296 t P) and output P (from 4565 t P to 13,509 t P) Available online 2 July 2015 increased significantly. The agricultural subsystem contributed most to the P metabolism, accounting for 85% Editor: D. Barcelo of total P input. The share of P input lost to the environment, i.e. discharge to water, accumulation in the soil and landfill, increased from 66% to 72%, while food production efficiency decreased from 48% to 29%. Per capita Keywords: P input showed linear relationships with the Human Development Index (HDI), S-curve relationship with the Phosphorus urbanization rate, and logistic curve relationship with per capita disposable income. A more meat-based diet Substance flow analysis shift both in Longyan and surrounding cities greatly affected Longyan's food production structure. Our results Urban metabolism demonstrate that P metabolic quantity, configuration, and efficiency in production systems can change drastically Urbanization in response to changes in consumer and producer behavior as well as in socioeconomic structure. A larger China regional scale should be considered in urban P management, when trying to mitigate the increase in P use. ⁎ Corresponding author at: Institute of Urban Environment, Xiamen, China. E-mail address: [email protected] (S. Cui). http://dx.doi.org/10.1016/j.scitotenv.2015.06.073 0048-9697/© 2015 Elsevier B.V. All rights reserved. S. Cui et al. / Science of the Total Environment 536 (2015) 924–932 925 The results also imply that sustainable urban P management will require a system-wide, cross-sector and cross-boundary approach. © 2015 Elsevier B.V. All rights reserved. 1. Introduction static P metabolism analysis; very few have presented any long term trends of the city phosphorus budget. Consequently, the underlying Phosphorus (P) is an essential nutritional element for all living drivers of such trends are poorly understood. In this study, we aim to beings (Smil, 2000) and a critical resource for agricultural production. address these challenges by taking Longyan City, China as a case Because most soils contain only low concentrations of this nutrient study. We established a phosphorus metabolism model in Longyan (Cordell et al., 2011; Matsubae et al., 2011), phosphate fertilizer, made City to identify and quantify the P flow, aim to answer the following from phosphate rock, is a key component of high-yield agriculture questions: (1) How has the P flow changed between 1985 and 2010, (Tilman et al., 2001, 2002). It is estimated that 20 million tonnes of and do these changes differ in various subsystems in the city? phosphorus is mined annually around the world (Bennett et al., 2001; (2) How important are changing P metabolism, especially shifts in Mackenzie et al., 2002). However, at the current rate of mining, world food production efficiency, in explaining changes in environmental P phosphorus reserves will be depleted in the next 50 to 100 years loss? (3) What are the key socioeconomic drivers of changing urban P (Gilbert, 2009). Furthermore, the quantity of P flowing into the oceans metabolism? The study adds a rather unique empirical evidence of has crossed to the planetary boundary and at high risk (Rockstrom city P metabolism, where urban system shows a high throughput in- et al., 2009; Steffen et al., 2015). In China, a major phosphorus producer cluding high ratio of P export in agricultural product. as well as a consumer of phosphate fertilizers (Chen et al., 2008; Cooper et al., 2011; Van Kauwenbergh, 2010), it is predicted that phosphate ore 2. Materials and methods can only be exploited for about 70 more years, and that no more than 20% of the phosphate ores in China have a sufficiently high content of 2.1. Description of study area phosphorus (N30% P2O5)(NBSC, National Bureau of Statistics of China, 2011). To counteract such environment problems and issues of scarcity The study area is within the administrative boundaries of Longyan of P, serious attention should be paid by all sections of the community. City (24°23′N – 26°02′N, 115°51′–117°45′E), which is located in Many studies have estimated how phosphorus use proceeds at the west of Fujian Province, China (Figure S1) and covers an area of different geographical scales. Metson et al. have found, through 1.9 × 104 km2, including the built up area of 45 km2. Between the global-scale research, that dietary choices have a large influence on years 1985 and 2010, the GDP of Longyan experienced a significant the demand for P, and that the global per capita P footprint increased growth, from approximately 1 billion Yuan (Yuan = Chinese Yuan 38% between 1961 and 2007 (Metson et al., 2012a). Urban systems [RMB], 1 Chinese Yuan ≈ 0.164 USD in 2014) to 99 billion Yuan and have been playing a major role in changing biogeochemical cycles at the urbanization rate increased from 27% to 45% (LSB, Longyan different scales (Cui et al., 2013; Grimm et al., 2008; Kaye et al., 2006), Statistics Burean and NBSC, National Bureau of Statistics of China, including the increased movement of P from mineral deposits to rivers 1986–2011), indicating that more than 50% of the population were and oceans, leading to eutrophication of aquatic ecosystems (Cordell still engaged in agricultural activities. But the agricultural industry et al., 2009; Wang et al., 2015). Such increases are principally due to only contributes 12% of the GDP of Longyan City in 2010. The local live- three changes in the systems: increases in population, which require stock industry contributed 40% of local total agricultural output value an overall increase in food production (Cordell et al., 2009); changes (Wu, 2009), and produced 26% of the pigs slaughtered in the entire in diet to more P intensive products (Schmid Neset et al., 2008); and province (Ruan et al., 2011). The discharge of pig excreta can greatly structural composition of P intensive industries (Liu et al., 2007). For ex- affect downstream areas, especially since Longyan is located at the ample, in cities where agriculture is the main economic component, river source area of the Minjiang, Jiulong and Ting rivers, which are changes in P use efficiency, including intensification of fertilizer inputs the three principal rivers of Fujian Province. The concentrations of nitro- to increase yields, and in P recovery efficiency (Cordell et al., 2013; gen and phosphorus in the river were blamed for the recent algal bloom Schroder et al., 2011; Godfray et al., 2010) alter overall P metabolic char- incidents in one of the rivers (Li et al., 2011). acteristics. Urban P metabolism analysis— an approach to identifying the P flow pathways and quantifying them at the city scale, has been 2.2. The P metabolism model and calculation processing conducted in many cities (Dokulil et al., 2000; Han et al., 2011; Li et al., 2010; Metson et al., 2012b; Nyenje et al., 2010; Qiao et al., 2011; In this study, considering the actual situation, data availability and Yuan et al., 2011b). P flows have changed dramatically during the past theoretical assumptions, we firstly present a model used in this study few decades, with more variation in key phosphorus flows, largely to map the P metabolism of the socioeconomic system of Longyan City because they represent specific characteristics of the urban system, in- (Fig. 1). And then, we divided the socio-economic system related to P cluding size, industry type, infrastructure and stage of development metabolism into four subsystems: the crop production subsystem, the (Cordell et al., 2012). Many of these studies show that the “upstream” livestock subsystem, the human consumption subsystem and the indus- urban P nutrient demand, the “downstream” urban P waste increase, trial subsystem. After that, we collected data to calculate every subsys- and the cycle of P within the city itself often show unidirectional flow.