| In order to meet the increasing national demand for meat,eggs and milk,the livestock and poultry farming industry has been developed rapidly in recent decades,which has caused serious problems such as surface source pollution and has certain geographical differences and dynamic change characteristics in time sequence.Identifying the spatial and temporal variation characteristics of nitrogen pollution from livestock and poultry farming and analyzing its driving forces are of great theoretical significance and reference value for decision making to clarify the key regulatory factors of nitrogen pollution management,to reasonably coordinate the spatial layout of agricultural planting and livestock and poultry farming industries,and to promote the modernization of pollution management in livestock and poultry farming industry.This paper firstly compiles the year-by-year,province-by-province and species-byspecies total nitrogen emission coefficient system based on the production and emission coefficients disclosed by the two national pollution source censuses,and evaluates the nitrogen pollution load of livestock and poultry farming in China from 2001 to 2020 by taking the provincial area as the research unit;secondly,it analyzes the spatial and temporal changes of nitrogen pollution load of livestock and poultry farming from three aspects:distribution characteristics,aggregation characteristics and center of gravity migration characteristics;then By establishing the EKC hypothesis model of nitrogen pollution load from livestock farming and the distance relationship model of center of gravity of nitrogen pollution load,the driving effects of the level of economic development indexed by regional gross product,the level of social development indexed by regional population density and the level of environmental management indexed by livestock pollution control rate on the spatial and temporal changes of nitrogen pollution load from livestock farming in China were analyzed.The main conclusions of this paper are as follows.(1)There are significant differences in the changes of different livestock emission coefficients over 20 years.The analysis results of the emission coefficient system reflect the variability of emission coefficient changes of different livestock and poultry over 20 years.The inter-provincial variation of total nitrogen emission coefficient of pig farming gradually decreases and tends to be consistent,from 2.48 kg/head～3.94 kg/head to 1.27kg/head～1.53 kg/head.The mean value of total nitrogen emission coefficient of beef cattle breeding in each province decreased,and the inter-provincial differences gradually decreased,from 20.99 kg/head to 40.23 kg/head to 21.20 kg/head to 28.86 kg/head,and the IQR decreased,indicating that the total nitrogen emission coefficient of beef cattle breeding in each province tended to be consistent.The total nitrogen emission coefficient of egg poultry farming was generally low and did not change much,and the mean and median realm of each province were slightly higher,with an overall change from 0.12 kg/feather to 0.13 kg/feather to 0.11 kg/feather to 0.13 kg/feather.The total nitrogen emission factor of dairy cattle farming decreased the most,and the inter-provincial differences gradually decreased from 42.21 kg/head to 54.60 kg/head to 13.91 kg/head to 18.53 kg/head.The total nitrogen emission coefficient of meat and poultry farming decreased significantly,and the inter-provincial differences decreased significantly,from 0.03 kg/feather～0.09 kg/head to 0.01 kg/feather～0.03 kg/head.(2)Livestock and poultry farming produced differential change characteristics in total volume,intensity and structure.In total,livestock and poultry nitrogen pollution load from2001,the trend shows an inverted "U" trend,reaching a maximum in 2006,and decreasing year by year,in 2020 per pig equivalent nitrogen pollution load compared to 2001 reduced by 50%,the variability of each region is also decreasing.Structurally,the proportion of nitrogen pollution load from pigs and meat poultry continues to decrease,while the proportion of beef cattle and egg poultry shows an increasing trend,while the proportion of nitrogen pollution load from cows and sheep basically remains unchanged,and overall the nitrogen pollution load from ruminant livestock and poultry(cattle and sheep)is much larger than that from monogastric livestock and poultry(pigs and poultry).(3)Spatial differences in nitrogen pollution loads from livestock and poultry breeding in various provinces and cities are obvious and show spatial aggregation.In general,the nitrogen pollution load of northern provinces and cities in China is slightly higher than that of southern provinces and cities,and the proportion of nitrogen pollution load from livestock and poultry farming in four provinces,Shandong,Henan,Hebei and Sichuan,has been higher in the total national pollution load during 20 years.2010-2020 global Moran’I of nitrogen pollution load is significant,which indicates the existence of spatial aggregation of nitrogen pollution load,and on the whole In this period,Shandong,Henan,Hebei,and Liaoning show "high-high" clustering characteristics,and the increase of their livestock breeding nitrogen pollution load will lead to the increase of livestock breeding nitrogen pollution load in neighboring provinces and cities;Sichuan Province belongs to the "highlow" clustering type,and its neighboring provinces and cities The nitrogen pollution load of livestock and poultry breeding in Sichuan Province is relatively low;after 2017,Guangdong also began to converge to the pattern of "low-low" clustering.(4)The results of the migration analysis of the center of gravity of pollution show that the nitrogen pollution load of livestock and poultry farming in each province and city shows spatial unevenness,and the migration of the center of gravity of nitrogen pollution load has obvious directional and phased patterns.During the first phase(2001-2007),the center of gravity moved to the northwest under the influence of the increase in the proportion of pollution load in Inner Mongolia Autonomous Region and Liaoning Province,and the proportion of contribution of some northern provinces and cities to the national nitrogen pollution load increased,while the proportion of some southern provinces and cities decreased.During the second stage(2008-2020),the proportion of nitrogen pollution load in provinces and cities such as Sichuan and Guizhou increased,and the proportion of Shandong and Liaoning provinces and cities decreased,resulting in the center of gravity shifted to the southwest,and the contribution of the western and southwestern provinces and cities to the nitrogen pollution load increased more significantly.(5)The reason for the uneven spatial distribution of nitrogen pollution load is influenced by the combined effect of farming activity level and individual discharge capacity of single livestock.the center of gravity of activity level expressed by pig equivalent between 2001 and 2007 mainly shifted in the northwest direction,and the gap between the north and south direction was larger than the east and west direction;after 2007,it continued to move westward in the east-west direction,indicating that the change of livestock farming activity level led to The unevenness of nitrogen pollution load from livestock and poultry farming in each province and city has contributed to the spatial shift of nitrogen pollution load.The individual discharge capacity of individual livestock and poultry characterized by the intensity of farmed nitrogen pollution load changed little before 2007,and its migration direction was similar to the center of gravity of nitrogen pollution load after 2007.(6)The three indicators of regional population density,regional GDP and livestock farming pollution control rate have significant effects on livestock farming nitrogen pollution load.From the results of the time-series change driving force analysis,the regional GDP,regional population density and livestock farming pollution control rate all have significant effects on the time-series change of nitrogen pollution load from livestock farming.There is an inverted U-shaped relationship between economic growth and nitrogen pollution load from livestock and poultry farming,and a total of 11 provinces such as Shandong and Henan jumped over the inflection point of the inverted U-shaped curve in 2020.Regional population density and regional livestock and poultry breeding pollution control level have a significant negative impact on the time-series change of livestock and poultry breeding nitrogen pollution load. |
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