Spatiotemporal evolution of agricultural non-point source pollution and its influencing factors in the Yellow River Basin

Abstract: This study aims to investigate the temporal and spatial distribution of the agricultural nonpoint source of pollutant emission in the Yellow River Basin of China. The supplementary calculation was used to analyze the census data of the first and second pollution sources. Influencing factors were explored, including fertilizer usages, quantity of straw resources, pollutant loads from livestock and poultry breeding, and efficiency of pollutant treatment. The targeted prevention and control measures were proposed on the agricultural nonpoint source pollution in the Yellow River Basin. The results showed that: 1) The total amount of pollutant emission in the Yellow River Basin decreased obviously in 2017, compared with 2006. The estimated total amount of chemical oxygen demand, ammonia nitrogen, total nitrogen, and total phosphorus pollutant were 1 705, 53, 185, and 17 thousand tons, respectively, while the amount produced by agricultural production was 962, 12, 79, and 11 thousand tons. There was a significant increase in the proportion of agricultural nonpoint source pollution in the total amount. Inner Mongolia contributed the largest amount of agricultural nonpoint source pollution, but Henan and Shandong provinces presented the largest pollution intensity. Livestock and poultry breeding contributed the largest amount of chemical oxygen demand in 2017, whereas fertilizer was the main pollution source for the ammonia nitrogen, total nitrogen, and phosphorus pollutant. 2) There was a significant linear relationship between different pollutant indices and control factors. The total amount of fertilizer usage increased 83% in Inner Mongolia in 2017, compared with 2016. The reason was that the fertilizer usage increased 41% per unit of the cultivated land, as the cultivated land increased 30%. Additionally, there were too many higher fertilizer usages per unit of the cultivated land in Henan, Shaanxi, and Shandong provinces, because of the large-scale planting of vegetables and fruits with substantial production, especially in Henan Province. 3) Compared with 2006, the straw resources in the Yellow River in 2017 increased 46% with an amount of 0.113 billion tons, where most straw was produced in Inner Mongolia, due mainly to the largest cultivated land in the Basin and the large planting area of sugar and oil crops. In the number of straw resources per unit of the cultivated land, the top three were Henan, Shandong, and Ningxia Hui Autonomous Region. Specifically, the straw resources were attributed the most to the corn and wheat in Henan and Shandong provinces, while the corn was in Ningxia Hui Autonomous Region. 4) The emission amounts from the livestock and poultry breeding decreased by 27% in 2017 than that in 2006, mainly because of the national policy on animal husbandry, such as no breeding areas. 5) More efforts can be made to improve the efficiency of pollutant treatment for all pollution sources in Henan Province, and the fertilizer utilization rate in Shanxi Province. The overall control policy and the targeted strategies can be combined with the measures of agricultural nonpoint source pollution in the Yellow River Basin. The most effective measures can be adopted to control the fertilizer usages of vegetables and fruits in Henan, Shaanxi, and Shandong provinces, together with the comprehensive utilization of straw resources, such as corns in all provinces, and oil crops in Qinghai and Henan provinces and Inner Mongolia Autonomous Region. The treatment can be used to improve the utilization of livestock and poultry breeding, especially for cows and sheep in western provinces and pigs in the middle and lower reaches of the Yellow River. A better ecological cycle can be strengthened to combine planting with livestock and poultry breeding.