Abstract
The grey water footprint (GWF) is defined as freshwater requirements for diluting pollutants in receiving water bodies. It is widely used to measure the impact of pollutant loads on water resources. GWF can be transferred from one area to another through trade. Although pollution flow has previously been investigated at the national level, there has been no explicit study on the extent to which crop trade affects GWF across regions and the associated changes in grey water stress (GWS). This study analyzes pollution flow associated with interprovincial crop trade based on nitrogen (N) and phosphorus (P) loss intensity of three major crops, namely, maize, rice and wheat, which is simulated by a grid-based crop model for the period 2008–2012, and evaluates the spatial patterns of GWS across China. The results indicate that the integrated national GWF for N and P was 1271 billion m3 yr−1, with maize, rice, and wheat contributing 39%, 37%, and 24%, respectively. Through interprovincial crop trade, southern China outsourced substantial N and P losses to the north, leading to a 30% GWS increase in northern China and 66% GWS mitigation in southern China. Specifically, Jilin, Henan, and Heilongjiang Provinces in the northern China showed increases in GWS by 161%, 114%, and 55%, respectively, while Fujian, Shanghai, and Zhejiang in the south had GWS reductions of 83%, 85%, and 80%, respectively. It was found that the interprovincial crop trade led to reduced national GWF and GWS. Insights into GWF and GWS can form the basis for policy developments on N and P pollution mitigation across regions in China.
Highlights
Nitrogen (N) and phosphorus (P) fertilizer applications are crucial for crop production
Virtual N and P flow estimation via crop trade Virtual N and P flows embodied in interprovincial crop trade were estimated as:
The largest GWFN per unit area is in Shandong Province (2698 m3 ha−1 yr−1), and the largest GWFP is in Liaoning Province (3206 m3 ha−1 yr−1)
Summary
Nitrogen (N) and phosphorus (P) fertilizer applications are crucial for crop production. They boost production to facilitate feeding of the growing world population (West et al 2014). The global N and P use efficiencies decreased from 0.58 to 0.44 and from 0.82 to 0.61, respectively, over the period 1950–2000 (Bouwman et al 2013). This has been associated with continuous increases in N and P losses (Liu et al 2016a, 2018), which reached 120 Tg yr–1 for N and 2–7 Tg yr–1 for P in agricultural soils over the period 2000–2010 (Sutton et al 2013). Substantial N and P losses have resulted in notable environmental issues such as water quality degradation and groundwater contamination, which has caused eutrophication worldwide (Galloway and Cowling 2002, Vitousek et al 2009)
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