Regional estimation of net anthropogenic nitrogen inputs (NANI) and the relationship with socio-economic factors

Abstract Background: The accurate evaluation of net anthropogenic nitrogen inputs (NANI) is very important for making countermeasures to control N pollution. The N inputs of Hubei has a crucial impact on the eco-environment of the downstream Yangtze Basin. Our objective was to estimate the NANI of Hubei province and access the relationships between the components of NANI and socio-economic indices for controlling N pollution in the Yangtze River basin. Methods: The spatiotemporal distribution and the main components of NANI at city scale in Hubei province from 2008-2018 were discussed by the NANI model with ArcGIS 10.6. The relationships between the components of NANI and 6 economic factors, including gross industrial output value per unit area (GIOV), gross agricultural output value per unit area (GAOV), grain yield per unit area (GY), fertilizer consumption density (FCD), population density(PD) and, cultivated land area per unit area(CLA), was estimated using a Pearson analysis. Results: NANI in Hubei tended to increase from 14782.62 kg/(km2∙a) in 2008 to 16700.32 kg/(km2∙a) in 2012, and then fell to 13630.40 kg/(km2∙a) in 2018. NANI was higher in center and east than in west and southeast of Hubei province. N fertilizer use (Nfer), which accounted for 61.27% of NANI, was the largest N input source, followed by net N import in food＆feed (Nim), atmospheric N deposition (Ndep), N fixation (Nfix), and seeding N (Nsee). Pearson correlation analysis showed that FCD was the primary factor responsible for NANI in Hubei province (r=0.956), followed by GAOV (r=0.606) and CLA (r=0.527). The most direct driving factors of Ndep, Nfer, Nsee and Nim were GIOV (r=0.466), FCD (r=0.979), CLA (r=0.813) and GAOV (r=0.745), respectively. All factors had a significant negative impact on Nfix. Conclusions: The NANI decline strategy is to control the fertilizer application amount, as well as improving agricultural construction. Also, it’s necessary to eliminate some backward technology as well as high pollution industries, and support the development of ecological industries, which is beneficial to reduce the risk of N pollution.Highlight:(1) The calculation method of N import in food was improved by distinguishing the diet structure of urban population and rural population.(2) NANI was higher in plain areas and smaller in the mountain areas. (3) NANI increased first and then decreased from 2008 to 2018 in Hubei.(4) N fertilizer use was the largest N input source and fertilizer consumption was the primary factor to NANI.