Temporal and Spatial Changes of Non-Point Source N and P and Its Decoupling from Agricultural Development in Water Source Area of Middle Route of the South-to-North Water Diversion Project

Liguo Zhang,Yongpeng Fu,Chao Wei,Ji Chai,Zhanqi Wang,Ying Wang

doi:10.3390/su11030895

Liguo Zhang, Yongpeng Fu + Show 4 more

Open Access

https://doi.org/10.3390/su11030895

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Abstract

The quantitative estimation of non-point source (NPS) pollution provides the scientific basis for sustainability in ecologically sensitive regions. This study combined the export coefficient model and Revised Universal Soil Loss Equation to estimate the NPS nitrogen (NPS-N) and NPS phosphorus (NPS-P) loads and then evaluated their relationship with Primary Industrial Output Value (PIOV) in the water source area of the middle route of South-to-North Water Diversion Project (SNWDP) for 2000–2015. The estimated results show that: (1) dissolved nitrogen (DN) load increased 0.55%, and dissolved phosphorus (DP) load decreased 4.60% during the 15 years. Annual loads of adsorbed nitrogen (AN) and adsorbed phosphorus (AP) increased significantly before 2005 and then decreased after 2005. Compared with 2000, AN and AP loads in 2015 significantly decreased by 32.72% and 30.81%, respectively. Hanzhong Basin and Ankang Basin are key areas for controlling dissolved pollution, and southern and northern regions are key areas for adsorbed pollution. (2) From 2000 to 2005, NPS pollutants and PIOV showed weak decoupling status. By 2015, NPS pollutants had strong decoupling from PIOV in most counties. (3) Land use has been the main source of NPS-N and NPS-P pollution, accounting for about 75% of NPS-N and 50% of NPS-P based on the average value over the study period. In the future, various measures—such as returning cropland to forest and reducing the number of livestock—could be adopted to reduce the risk of NPS pollution. NPS pollution caused by livestock was grown over the past 15 years and had not yet been effectively controlled, which still needs to be urgently addressed. Collecting ground monitoring data and revising parameters are effective means to improve the accuracy of simulation, which deserve further study. The results will also provide scientific support for sustainable development in similar regions.

Highlights

With living standards improving, people have higher demands for their living environments, in particular water quality
Due to the attention received by the community, point source pollution has, for the most part, been effectively curbed, and non-point source (NPS) pollution has gradually become the dominant contributor to water pollution
The coefficients that we adopted were the previous results in adjacent regions with similar natural and social conditions, and our focus was more on the temporal changes and spatial comparisons of NPS pollution in the are important, which will surely improve the simulation accuracy for environmental assessment—this deserves further research

Summary

Introduction

People have higher demands for their living environments, in particular water quality. Water pollution caused by human activities is becoming increasingly prominent—it has aroused widespread concern worldwide [1,2]. Due to the attention received by the community, point source pollution has, for the most part, been effectively curbed, and NPS pollution has gradually become the dominant contributor to water pollution. Non-point source pollution has always been an important factor affecting water quality in the United States [4]. In Miksa City, Japan, 61.5% of the nitrogen load comes from non-point source pollution caused by high-intensity agricultural activities [6]. Non-point source nitrogen and phosphorus lead to eutrophication and the decrease in dissolved oxygen in surface water, which damages the aquatic environment and the balance of the ecosystem, and seriously affects the quality of human life, health, and regional sustainability [9]

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