Analysis of the Spatial Distribution Characteristics of Livestock and Poultry Farming Pollution and Assessment of the Environmental Pollution Load in Anhui Province

Abstract

Anhui Province is located in the eastern China, in the middle and lower reaches of the Yangtze River and Huaihe River, and contains three major basins, i.e., the Yangtze River, Huaihe River, and Xin’an River basins. Based on the statistical data of livestock and poultry quantity and farmland area in Anhui Province in 2019, ArcGIS was used to analyze the spatial distribution characteristics of the livestock and poultry excreta (LPE) pollutants in Anhui Province in order to explore the potential pollution risk posed by livestock and poultry farming to the farmland and the water environment in Anhui Province. The equivalent pollution load method was adopted to compare and assess the release of LPE pollutants in various cities and to analyze the causes. Through the calculation of the farmland carrying capacity load and early warning value of LPE and the water load of livestock and poultry pollutant release based on the equivalent pollution index method, a comprehensive assessment of the potential pollution risk posed by livestock and poultry farming on farmland and the water environment in Anhui Province was carried out. In this study, the spatial distribution of the livestock and poultry pollution in Anhui Province was analyzed, the effect of the pollution load of the livestock and poultry on the cultivated land and water environment was evaluated, and suggestions for environmental protection measures are provided. The results of this study revealed that the total pig equivalent of the livestock and poultry farming in Anhui Province was 55,068,400 and the LPE output was 47,778,600 t in 2019. The LPE pollutant output was 1,707,700 t, and the total release was 510,400 t. The release of pollutant chemical oxygen demand (COD) accounted for 71.67% of the total release. The average farmland load of the pig manure equivalent was 8.09 t/hm² in the province. The average pollutant diffusion concentration of in the water was 31.63 mg/L. The average equivalent pollution index of LPE was 5.23, indicating a mild pollution impact on the water environment. Overall, the spatial distribution of the LPE pollutant output and pig manure equivalent farmland load in Anhui Province increased from south to north. Fuyang and Suzhou cities had a high risk of water environment pollution and should be the key regions for livestock and poultry pollution prevention and control measures. The optimization of the layout of livestock and poultry farming areas, smoothing the cycles of crop and livestock farming, and the vigorous promotion of the resource utilization of the LPE are proposed.

1. Introduction

China is one of the largest intensive agricultural developing countries in the world [1]. The discharge of the chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) from agricultural production accounts for 49.77%, 51.97%, and 67.22%, respectively, of the total pollutant discharge [2]. In livestock and poultry farming, the effective treatment rate of animal manure is less than 50% [3]. The large quantity of livestock and poultry excreta (LPE) has become a direct or indirect factor of ecological environment pollution in most regions [4]. Located in the middle and lower reaches of the Yangtze River and Huaihe River in eastern China, Anhui Province crosses contains three major basins, i.e., Yangtze River, Huaihe River, and Xin’an River basins, forming three natural regions, the Huaibei plain, Jianghuai hills, and southern Anhui mountain area. With a total area of 140,100 km², Anhui Province is not only an important part of the Yangtze River Delta, but it is also a major production base for agricultural and animal husbandry products in China. The release of pollutants rich in the manure is a critical factor in agricultural non-point source pollution in the basins, which has an adverse impact on the safety of drinking water resources and the environment [5,6].

A large number of studies have been carried out on LPE utilization and environmental problems. In the process of livestock and poultry farming, farmland is often used as an area to absorb LPE [7]. Certain scholars believe that LPE is the main source of nitrogen and phosphorus pollution in the ecosystem [8]. Therefore, nutrient management of LPE has gradually become the focus of agricultural and animal husbandry production and environmental pollution prevention and control [9,10]. Mallin et al. [8] found that on the coastal plains of North Carolina, livestock produced an estimated 124,000 t of nitrogen and 29,000 t of phosphorus per year. Many farms are located in nutrient-sensitive watersheds, where the discharge of untreated waste can lead to the eutrophication of streams, rivers, and estuaries. It is suggested that the federal government should protect the environment and human health from livestock and poultry pollution. Centner et al. [9] reported that LPE makes an important contribution to the soil nutrient input. In many developing countries, LPE is an important input. In some developed countries with large animal husbandry industries, such as the Netherlands and Japan, the proportion of fertilizer is expected to increase and the demand for fertilizer will decline. Mishima et al. [11] estimated the application amount of manure and proposed a reasonable fertilization level by tracing the use destination of LPE. Based on data on the climate, soil, and crop types, Bassanino et al. [12] analyzed the environmental effects of LPE application from the perspective of its environmental effects through a spatial description of the different agricultural environments. Arthur et al. [13] carried out research on the resource utilization of LPE and proposed effective LPE utilization approaches. Based on research, several scholars have suggested that the government should formulate effective measures to control excessive nitrogen produced by LPE [14] in order to prevent environmental pollution. Furthermore, certain scholars have conducted a great deal of basic research on the relationships between environmental effects and factors such as the farm size and the distance between farm and residential areas or water resources [9].

In recent years, the total amount of LPE returned to the field and the pollution risk it poses in China have been studied [15–20]. Livestock rearing in China was found to be within the environmental carrying capacity, but some regions faced potential livestock pollution. In the middle and lower reaches of the Yangtze River, LPE can be accommodated in the farmland environment if the livestock breeding quantity does not increase [15]. However, it has also been reported that N and P transfer from agriculture is the main cause of poor water quality. A comprehensive evaluation of the risks posed by N and P runoff into surface water bodies and risk analysis of nutrient losses to water from manure management are needed. The regions where N and P concentrations are too high should be defined as vulnerable zones, in which immediate policies and actions should be implemented [16]. Tao et al. [17] proposed the concept of potential pollution between pollutant output and discharge, which means that the unused or untreated pollutants can reflect the preliminary pollutant treatment efficiency of when indicators such as the comprehensive utilization rate of LPE are fully considered. Anhui Province is a large agricultural province and contains nearly 10,000 large-scale farms. Song et al. [18] conducted a risk assessment of the status of the environmental pollution caused by livestock and poultry farming in Anhui Province in 2012 based on the quantitative estimation of the LPE. Zhang et al. [19] estimated the LPE discharges and the changes in the pollutant content changes in Anhui Province by using the livestock and poultry pollutant discharge coefficient method, and then they analyzed the temporal and spatial distributions of the nutrients in the excreta of different types of livestock and poultry in the province. Moreover, Geng et al. [20] calculated the environmental carrying capacity of animal husbandry and the potential of manure to replace chemical fertilizer in Anhui Province from the perspective of the soil nutrient demand, and then they estimated the environmental carrying capacity of animal husbandry in the province.

In view of the lack of systematic research on the scope of the calculation standards and LPE pollution assessment methods, the environmental carrying capacity and the potential of manure replacing chemical fertilizer have been mostly calculated based on the output of LPE. Furthermore, the estimated livestock and poultry farming scale under different standards have been determined. However, there are few reports on the comprehensive pollution assessment of LPE for regional farmland and the water environment. Calculations and assessments based on pollutant discharges also fail to reflect the impact of factors such as the farmland area and the total water resources on the degree of pollution. The changes in the regional environmental protection policies have had a large impact on the changes in the regional environmental pollution load [21]. From 2018 to 2020, Anhui Province implemented the three-year action plan for the resource utilization of LPE, further defined the development idea of government support for animal husbandry from a legal perspective, and strengthened the resource treatment of livestock and poultry based on these measures. The existing reports lack the latest research results on the pollution status on the municipal scale in Anhui Province. It is of great significance to systematically analyze the spatial distribution pattern of livestock and poultry farming pollution in Anhui Province and to clarify the farmland load of LPE and its environmental effects to ensure the sustainable development of the livestock and poultry farming industry and agriculture.

In this study, ArcGIS was used to analyze the characteristics of LPE and the urine output, pollutant output, and spatial distribution of the LPE pollution in Anhui Province in 2019. The equivalent pollution load assessment method was adopted to compare and evaluate the LPE pollutant release in cities and to analyze the causes. Through the calculation of the farmland carrying capacity load and early warning value of the LPE and calculation of the water load of the LPE released based on the equivalent pollution index method, the potential pollution risk posed by livestock and poultry farming to farmland and the water environment in Anhui Province was comprehensively assessed in order to provide a theoretical basis for the scientific development of the livestock and poultry farming industry and the protection of the ecological environment.

2. Materials and methods

2.1. Data Sources

The data were obtained from the Anhui Statistical Yearbook (2020). The major pollutant indicators used in this paper are as follows: total nitrogen (TN), total phosphorus (TP), chemical oxygen demand (COD), and ammonia nitrogen (NH₃-N).

2.2. Research Methods

2.2.1. Calculation of LPE Output, Pollutant Output, and Pollutant Release

According to the quantities, feeding cycles, and discharge coefficients of the different types of livestock and poultry, the LPE output, pollutant output, and pollutant release in Anhui Province were calculated using the output coefficient model using Equations (1)–(3), respectively.

$$W=\frac{L_q\times T\times C}{1000}$$

(1)

$$L_p=\frac{W\times L_c}{1000}$$

(2)

$$V_q=L_p\times V_r$$

(3)

In Equations (1)–(3), W is the annual LPE output (t), L_q is the number of livestock and poultry (item), T is the feeding cycle (d), C is the daily discharge coefficient (kg/d), L_p is the LPE pollutant output (t), L_c is the pollutant content (kg/t), V_q is the pollutant release (t), and V_r is the rate of release into the water (%). The quantity of the relevant livestock and poultry was calculated according to the number of pigs and poultry slaughtered and the cattle and sheep stock. Based on the concept the one pig is defined as the one pig equivalent, 100 pigs are equivalent to 20 cattle, 250 sheep, or 2500 poultry [22]. The feeding cycle of cattle and sheep is 365 d, while those of pigs and poultry are 199 d and 210 d, respectively [23]. The parameters of the discharge coefficient and average LPE pollutant content [23,24,25] were mainly obtained from relevant recent research results. The details are provided in

Table 1. Discharge coefficient and pollutant content of LPE.

Parameter		Cattle		Pigs		Sheep	Poultry
		Manure	Urine	Manure	Urine	Manure	Manure
Discharge coefficient (kg·d−1)		20.00	10.00	2.00	3.30	2.60	0.12
Pollutant content (kg·t−1)	TN	4.37	8.00	5.88	3.30	7.50	10.40
	TP	1.18	0.40	3.14	0.52	2.60	5.80
	NH3-N	1.71	3.47	3.08	1.43	2.10	2.80
	COD	31.00	6.00	52.00	9.00	4.63	45.70

Notes: TN: total nitrogen; TP: total phosphorus; COD: chemical oxygen demand; NH₃-N: ammonia nitrogen.

. Furthermore, the percentage of LPE pollutants released into the water was defined as 30% [23].

2.2.2. Calculation of the Farmland Carrying Capacity Load and Early Warning Value of LPE

The farmland carrying capacity of the LPE refers to the capacity of an area of farmland of a certain size to absorb the LPE in a certain amount of time. According to the amount of LPE in the various regions of Anhui Province, the pig manure equivalent conversion coefficients for the LPE were calculated [23]. The conversion coefficients of pig manure and pig urine were 1.00 and 0.51, those of cattle manure and cattle urine were 0.69 and 1.23, and those of sheep manure and poultry manure were 1.23 and 2.10, respectively. The pig manure equivalents of the LPE were calculated. The farmland environmental carrying capacity is expressed as the pig manure equivalent load per unit of farmland area. The pig manure equivalent load was calculated using Equation (4), and that of the farmland early warning by using Equation (5).

$$q=\frac{Q}{S}={\displaystyle \sum \frac{X\times K}{S}}$$

(4)

$$R=\frac{q}{P}$$

(5)

In Equations (4) and (5), q is the pig manure equivalent load of livestock and poultry per area of farmland (t/hm²), Q is the pig manure equivalent of LPE (t), S is the effective farmland area (hm²), X is the discharge of a given type of LPE (t), K is the conversion of pig manure equivalents for a given type of LPE, R is the farmland early warning value, and P is the theoretical applicable quantity (t/hm²). The classification of the farmland early warning value [23] is shown in

Table 2. Classification of the farmland load early warning value of the livestock and poultry excreta pig manure equivalent.

Farmland Early Warning Value	Load Class	Environmental Threat
R ≤ 0.4	I	No threat
0.4 < R ≤ 0.7	II	Minor threat
0.7 < R ≤ 1.0	III	Threat
1.0 < R ≤ 1.5	IV	Severe threat
1.5 < R	V	Very severe threat

Notes: R is the farmland early warning value.

below.

2.2.3. Calculation of the Water Load of LPE Release

The equal standard pollution index method is an evaluation index that is often used in pollution evaluation. It mainly reflects the potential pollution level of the pollution source itself. The emission of pollutants is divided using the limit standard of pollutants in the environment, and the emission of pollutants is transformed into the volume of water required to dilute all of the pollutants to the evaluation standard. The calculation results not only reflect the impact of the pollutants on the environment from the quantity of pollutants, but they also reflect the impact of the pollutants on the environment in the degree of pollution. After the unified transformation, it is possible to compare the potential impacts of the pollutants discharged by different pollution sources on the environment. The equal standard pollution index method [18] was adopted to assess the pollution loads of the various pollution sources. TN, TP, NH₃-N, and COD were selected as the assessment factors. The pollutant diffusion concentration in each region was calculated according to the ratio of the pollutant release and the total amount of water resources in the region (Equation (6)). The equivalent pollution discharge of pollution sources in each region was calculated, as shown in Equation (7). The equivalent pollution index, ε, was calculated using the ratio of the equivalent discharge of pollution sources in each region to the total amount of water resources in the region, shown as Equation (8):

$$W=\frac{V\mathrm{q}}{T_{\mathrm{i}}}\times {10}^6$$

(6)

$$P_i=\frac{C_{\mathrm{i}}}{C_{\mathrm{o}}}\times {10}^6$$

(7)

$$\epsilon =\frac{P\mathrm{i}}{T_{\mathrm{i}}}$$

(8)

In Equations (6)–(8), W is the pollutant diffusion concentration in each region (mg/L), V_q is the amount of pollutant released (t), T_i is the total amount of water resources in each region (m³), P_i is the equivalent pollution discharge of pollutant i (m³), C_i is the release of pollutant i (t/a), C_o is the pollutant valve concentration according to the GB 3838-2002 Class III standard series (COD is 20 mg/L, NH₃-N is 1 mg/L, TN is 1 mg/L, and TP is 0.2 mg/L), and ε is the equivalent pollution index value. The water load equivalent pollution index classification and pollution level of the livestock and poultry pollutants are presented in

Table 3. Classification of the water load equivalent pollution index of livestock and poultry pollutants.

Pollution Index	Load Class	Environmental Pollution Impact	Environmental Pollution Level	Class Color
ε ≤ 5	I	No pollution	No impact
5 < ε ≤ 10	II	Mild pollution	Low impact
10 < ε ≤ 15	III	Moderate pollution	Moderate impact
15 < ε ≤ 20	IV	Heavy pollution	Heavy impact
20 < ε	V	Severe pollution	Severe impact

Notes: ε is the equivalent pollution index value; green represents load class I, light green represents load class II, yellow represents load class III; orange represents load class IV and red represents load class V.

.

2.3. Data Processing and Image Rendering

The SPSS 22.0 (Version 22.0, SPSS Inc., Chicago, Illinois, USA) data statistical analysis module was used for the statistical processing of the original data. The data import module in the Origin 8.0 software (Origin Lab, Northampton, MA, USA) toolbox was used to import the production amount and diffusion concentration of the LPE pollutants, and bar charts were drawn using the drawing module. The data import module in the ArcGIS10.2 (Environmental Systems Research Institute, Inc., RedLands, CA, USA) toolbox was used to import the map of Anhui Province and the production of LPE and other data, and the spatial analysis tool was used to process and analyze the data. The spatial distribution map of the production and loss of LPE was drawn in the map layer for Anhui Province, and the spatial information visualization of the data was realized through the layout.

3. Results and Analysis

3.1. Livestock and Poultry Farming Status and Spatial Distribution Characteristics of Total LPE Output

3.1.1. Characteristics of Livestock and Poultry Farming Status

In 2019, the total number of pigs slaughtered in Anhui Province was 24,902,700 and that of poultry was 283,077,300. The quantities of cattle and sheep were 830,800 and 5,567,000, respectively, and the total pig equivalent was 55,068,400 (

Table 4. Total numbers of livestock and poultry slaughtered in the cities in Anhui Province in 2019.

Region	Cattle (104)	Pigs (104)	Sheep (104)	Poultry (104)	Total Pig Equivalent (104)	Proportion (%)
Hefei	4.42	203.63	11.16	3390.99	432.17	7.85
Huaibei	1.99	48.85	20.61	743.93	126.66	2.30
Bozhou	6.92	249.75	81.79	1151.00	466.91	8.48
Suzhou	10.94	331.43	160.72	2548.80	716.38	13.00
Bengbu	13.20	166.02	59.23	2586.61	557.12	10.12
Fuyang	20.84	380.01	129.53	2916.53	965.31	17.53
Huainan	4.05	101.83	25.61	1009.10	233.36	4.24
Chuzhou	4.22	261.05	27.22	2054.00	438.54	7.96
Lu’an	4.00	257.22	18.70	1839.36	418.34	7.60
Ma’anshan	0.90	39.21	4.69	608.65	83.53	1.52
Wuhu	0.94	46.52	2.49	1501.80	126.42	2.30
Xuancheng	2.20	80.36	5.70	3348.29	260.52	4.73
Tongling	0.20	22.70	0.51	700.65	55.02	1.00
Chizhou	0.46	60.83	0.69	763.00	100.84	1.83
Anqing	6.19	191.74	6.31	2680.34	425.30	7.72
Huangshan	1.60	49.12	1.74	464.68	100.42	1.82
Anhui Province	83.08	2490.27	556.70	28,307.73	5506.84	100

). The farming scale of the livestock and poultry in Fuyang accounted for a large proportion of the total amount in the province, among which the slaughter number of live pigs was the highest in the province, reaching 3,800,100. The total pig equivalent was 9,653,100, accounting for 17.53% of the total pig equivalent in the province. The total pig equivalent of in Suzhou accounted for 13.00% of the pig equivalent in the province, of which the quantity of sheep was the highest in the province, reaching 1,607,200. Due to the small areas of Tongling and Ma’anshan, each city only accounted for about 1.00% of the total pig equivalent in the province. Moreover, the total quantity of livestock and poultry was low. Overall, the regional distribution of the livestock and poultry farming scale in Anhui Province was ranked as follows: Huaibei Plain > Jianghuai hilly area > southern Anhui. The total quantity of livestock and poultry gradually increased from south to north.

By analyzing the spatial distribution and density of the main livestock and poultry farms in Anhui Province in 2019 (Figure 1), it was found that the number of farms in the northern cities in Anhui Province, such as Fuyang City, Huainan City, Bengbu City, and Huaibei City, was relatively large, the farms were concentrated, and the breeding scale of each farm was large. The distribution of the livestock and poultry farms in the southern cities in Anhui Province, such as Anqing City, Chizhou City, and Xuancheng City, was relatively scattered, and the number and size of the farms were small. Overall, the spatial distribution of the livestock and poultry farms in Anhui Province was concentrated in the north and scattered in the south.

3.1.2. Spatial Distribution Characteristics of LPE Output

The total LPE output in the cities in Anhui Province is shown in Figure 2. The LPE output in the cities in of Anhui Province was 47,778,600 t in 2019. The total LPE outputs were high in Fuyang and Suzhou, reaching 8,254,300 t and 6,860,600 t, respectively. The total LPE outputs in Bozhou and Bengbu were also relatively high. The main reasons for this are that these four cities are major cities in northern Anhui, they are the main pig producing areas in the province, and the quantities of cattle and sheep are relatively high. The LPE outputs were less than 1 million t in Ma’anshan, Wuhu, Tongling, Chizhou, and Huangshan. The above cities are located in the region along the river in southern Anhui. Farming is prohibited in certain parts of this region. The main farming type was poultry, and the total output of poultry excreta was not high. Overall, the main source of LPE in northern and central Anhui was the farming of pigs and cattle, while that in southern Anhui was the farming of pigs and poultry. Within the province, the total LPE output gradually increased from southwest to north.

The total amounts of manure and urine produced by the various types of livestock and poultry in the various watersheds of Anhui Province are shown in Figure 3. Anhui Province is divided into the Yangtze River, Huaihe River, and Xin’an River basins. The total amount of LPE produced in the Huaihe River Basin was 29,598,400 t, which is mainly due to the large area of the Huaihe River Basin and the large amount of livestock and poultry breeding in Suzhou, Bozhou, and Fuyang. The total amount of LPE produced in the Yangtze River Basin was 17,477,400 t. As an important water conservation area in Anhui Province, the Yangtze River Basin has many breeding-prohibited areas, so the total amount of LPE was not high. The total amount of LPE produced in Xin’an River Basin was only 703,000 t. The main reasons for this are that the area of the Xin’an River Basin is small, and due to the requirements of the government’s environmental protection policies, the basin is mainly dominated by poultry breeding and the breeding quantity is not high. At the watershed scale, the total amount of LPE produced in the Huaihe River Basin was much greater than those produced in the Yangtze River Basin and Xin’anjiang River Basin.

3.2. Spatial Distribution Characteristics of LPE Pollutant Output and Release

3.2.1. Spatial Distribution Characteristics of LPE Pollutant Output

The LPE pollutant output in Anhui Province was 1,707,700 t in 2019, of which the output of the COD was the highest, reaching 1,219,200 t and accounting for 71.40% of the total pollutant output. The main reason for this is the high content of COD in livestock excreta. The output of TN was 276,800 t, accounting for 16.21% of the total output. As for TP and NH₃-N, their outputs accounted for about 6% of the total pollutant output. The spatial distribution of the TN, TP, NH₃-N, and COD outputs produced by LPE in the cities in Anhui Province is shown in Figure 4. The analysis indicates that the LPE pollutant output in Fuyang, Bozhou, Suzhou, and Bengbu in northern Anhui was 792,000 t, accounting for 46.38% of the total pollutant discharge in Anhui Province. The total LPE pollutant output was high. The main reason for this is that the livestock and poultry farming in northern Anhui mainly includes large quantities of pigs and cattle. Due to the small areas of Huaibei and Huainan, the total LPE output and pollutant output were not high. The total output of pollutants in Tongling, Ma’anshan, and Huangshan was low. The LPE pollutant output was about 30,000 t. Overall, the spatial distribution of LPE pollutants was largely consistent with that of the LPE in the cities in Anhui Province; i.e., it gradually increased from south to north.

3.2.2. Analysis of LPE Pollutant Release Characteristics

The livestock and poultry pollutant release in the cities in Anhui Province in 2019 is presented in

Table 5. Pollutant release form livestock and poultry farming in the cities in Anhui Province in 2019.

Region	Pollutant Release from Livestock and Poultry Farming (104 t)					Equivalent Pollution Load Ratio (%)
	TN	TP	NH3-N	COD	Total	TN	TP	NH3-N	COD	Total
Hefei	0.65	0.26	0.24	3.14	4.30	15.12	6.05	5.58	73.02	8.42
Huaibei	0.21	0.07	0.07	0.82	1.18	17.80	5.93	5.93	69.49	2.30
Bozhou	0.73	0.24	0.29	3.01	4.27	17.10	5.62	6.79	70.49	8.38
Suzhou	1.19	0.41	0.45	4.55	6.60	18.03	6.21	6.82	68.94	12.93
Bengbu	0.80	0.25	0.30	3.28	4.62	17.32	5.41	6.49	71.00	9.06
Fuyang	1.40	0.43	0.54	5.76	8.14	17.20	5.28	6.63	70.76	15.95
Huainan	0.35	0.12	0.13	1.50	2.09	16.75	5.74	6.22	71.77	4.10
Chuzhou	0.65	0.25	0.26	3.14	4.30	15.12	5.81	6.05	73.02	8.43
Lu’an	0.61	0.23	0.25	3.01	4.09	14.91	5.62	6.11	73.59	8.02
Ma’anshan	0.13	0.05	0.05	0.60	0.82	15.85	6.10	6.10	73.17	1.61
Wuhu	0.20	0.09	0.07	0.96	1.33	15.04	6.77	5.26	72.18	2.61
Xuancheng	0.42	0.19	0.14	1.97	2.73	15.38	6.96	5.13	72.16	5.35
Tongling	0.09	0.04	0.03	0.44	0.60	15.00	6.67	5.00	73.33	1.18
Chizhou	0.15	0.07	0.06	0.78	1.06	14.15	6.60	5.66	73.58	2.08
Anqing	0.60	0.22	0.23	2.93	3.98	15.08	5.53	5.78	73.62	7.80
Huangshan	0.14	0.05	0.05	0.67	0.91	15.38	5.49	5.49	73.63	1.79
Anhui Province	8.30	2.98	3.18	36.58	51.04	16.26	5.84	6.23	71.67	100.00
Proportion (%)	16.27	5.84	6.22	71.67	100.00	-	-	-	-	-

Notes: TN: total nitrogen; TP: total phosphorus; COD: chemical oxygen demand; NH₃-N: ammonia nitrogen.

. The total pollutant release from livestock and poultry farming industry in Anhui Province was 510,400 t in 2019, of which the amounts of TN, TP, NH₃-N, and COD released were 83,000 t, 29,800 t, 31,800 t, and 365,800 t, respectively. Based on the analysis conducted using the equivalent pollution load method, the pollutant type was mainly COD release, accounting for 71.67% of the total pollutant release. From the perspective of the spatial distribution of the pollutant release, the equivalent pollution load ratio of the LPE pollutant release was high in Fuyang and Suzhou, accounting for 15.95% and 12.93%, respectively, of the total pollutant release in Anhui Province. Compared with the relevant data from in the Bulletin of the Second National Pollution Sources Census in Anhui Province, the total pollutant release from the livestock and poultry farming industry in Anhui Province in 2019 dropped to 13,200 t compared with 2017. The reduction rate was 2.52%. The implementation of the three-year action plan for the resource utilization of LPE in Anhui Province contributed to the reduction in the discharge of livestock and poultry farming pollutants.

3.3. Potential Pollution Risk Assessment of Livestock and Poultry Farming Pollutants on Farmland

According to the agricultural land distribution map of Anhui Province (Figure 5), the urban cultivated land area in the northern part of Anhui Province is large, the cultivated land resources increase from south to north, and the forest land resources gradually decrease from south to north. The northern part of Anhui is mostly plains, which are suitable for the reclamation of cultivated land. The central region is dominated by hills, and the southern region is dominated by low mountains and hills.

The annual nitrogen application rate for LPE is related to the natural conditions such as the soil fertility, crop type, and climate. The European Union’s agricultural policy stipulates a standard limit of 170 kg·hm⁻² for the annual application rate of manure nitrogen (N) to soil [13]. The annual manure phosphorus application rate in soil shall not exceed 35 kg·hm⁻² [26]. The application of excessive phosphorus will cause soil phosphorus leaching and environmental pollution. Considering the practical situation of agricultural production, the appropriate application of the pig manure equivalent is 15–30 t/hm² based on 225 kg·hm² of pure nitrogen applied at the customary rate of chemical fertilizer in farmland every year [19]. The farmland early warning value R₁ was calculated according to the annual pig manure equivalent application of 15 t/hm², while the farmland early warning value R₂ was calculated according to an application rate of 30 t/hm². The results presented in

Table 6. Livestock and poultry pig manure equivalent load and farmland early warning value classes in the cities in Anhui Province in 2019.

Region	Farmland Area (104 Hm2)	Pig Equivalent (/104 t)	Load (t·Hm−2)	Early Warning Value	Class	Early Warning Value	Class
				R1		R2
Hefei	55.88	383.84	6.87	0.46	II	0.23	I
Huaibei	16.75	118.19	7.06	0.47	II	0.24	I
Bozhou	59.95	405.35	6.76	0.45	II	0.23	I
Suzhou	57.63	669.57	11.62	0.77	III	0.39	I
Bengbu	37.88	453.42	11.97	0.80	III	0.40	II
Fuyang	64.81	782.60	12.08	0.81	III	0.40	II
Huainan	34.08	196.48	5.77	0.38	I	0.19	I
Chuzhou	71.64	372.02	5.19	0.35	I	0.17	I
Lu’an	52.72	345.82	6.56	0.44	II	0.22	I
Ma’anshan	17.45	75.04	4.30	0.29	I	0.14	I
Wuhu	26.79	125.45	4.68	0.31	I	0.16	I
Xuancheng	24.86	263.68	10.61	0.71	III	0.35	I
Tongling	9.41	56.26	5.98	0.40	II	0.20	I
Chizhou	13.84	90.15	6.52	0.43	II	0.22	I
Anqing	38.08	348.72	9.16	0.61	II	0.31	I
Huangshan	6.84	77.87	11.39	0.76	III	0.38	I
Anhui Province	588.60	4764.48	8.09	0.54	II	0.27	I

show that the average pig manure equivalent load was 8.09 t/hm² in Anhui Province. When the annual pig manure equivalent application to farmland was 15 t/hm², the R₁ value of the pig manure equivalent load of the LPE in the cities in Anhui Province was 0.54, which is in the Class II load level; that is, it exceeds the farmland consumption capacity with potential environmental pollution risk. Suzhou, Bengbu, Fuyang, Xuancheng, and Huangshan had Class III load level, which is high. The main reason for this is that Suzhou, Bengbu, and Fuyang have large pig manure equivalents due to the large amount of pig farming. Although the pig farming quantity in Xuancheng and Huangshan was not high, the farmland area in the region is small. Therefore, the regional pig manure equivalent pollution load was relatively high. When the annual pig manure equivalent application to farmland was 30 t/hm², the R₂ value of the pig manure equivalent load of the LPE in cities of Anhui Province was 0.27, which is in the Class I load level. Only Fuyang and Bengbu had a pollution load early warning values that exceeded 0.4, i.e., Class II load levels. Furthermore, the pig manure equivalent of the livestock and poultry exceeded the annual farmland consumption.

3.4. Potential Pollution Risk Assessment of Livestock and Poultry Farming Pollutants in Water

The LPE pollutant output in Anhui Province was 1,707,700 t (Figure 6). The average pollutant diffusion concentration was 31.63 mg/L. There were considerable differences in the pollution diffusion concentrations among the different cities in the province. Fuyang, Bengbu, and Suzhou had the highest diffusion concentrations, reaching 159.63 mg/L, 145.84 mg/L, and 123.85 mg/L, respectively, and had a high risk of water pollution. The main reasons for this are that the total amount of livestock and poultry farming in the above three cities was high, and they are located in northern Anhui where the amount of precipitation is relatively low. The diffusion concentration in Huangshan was the lowest (2.85 mg/L). The main reason is that Huangshan is located in southern Anhui Province, which has abundant rainfall, developed river systems, and numerous total water resources. The diffusion concentrations in Chizhou and Xuancheng were 6.63 mg/L and 9.41 mg/L, respectively. The risk of water pollution was also relatively low.

According to the water distribution map of Anhui Province (Figure 7), as well as the locations of the Huaihe River, Yangtze River, and Xin’an River, the distribution of the water resources decreases from south to north. Because the number of water resources is affected by precipitation, the causes were analyzed according to the factors affecting precipitation. The precipitation in Anhui Province is affected by the east monsoon. The southeast monsoon weakens from south to north, and the precipitation decreases from south to north.

The water load equivalent pollution index of the LPE pollutants increased from south to north in Anhui Province (Figure 8). The average value of the water load equivalent pollution index of the LPE pollutants was 5.23 in the province. The release of LPE pollutants slightly polluted the water environment, i.e., a low impact level. The equivalent pollution index was less than 5.00 in Huangshan, Anqing, Lu’an, Ma’anshan, Wuhu, Xuancheng, Tongling, and Chizhou. The above eight cities are located in southern Anhui and the region along the river. The total farming quantity was not high in the region, and the total amount of water resources was abundant. The equivalent pollution index level was Class III in Hefei, Chuzhou, Huaibei, and Huainan, indicating a risk of environmental pollution. The equivalent pollution index was greater than 20.00 in Fuyang, Bengbu, and Suzhou, indicating a serious risk of water environmental pollution. The equivalent pollution index was Class IV in the above three cities, reaching a high environmental pollution impact level.

4. Discussion

4.1. Selection of Pollution Risk Assessment Parameters

The spatial distribution of the LPE pollutants in the cities in Anhui Province was basically the same as that of the LPE output. Overall, the spatial distribution gradually increased from south to north, which is consistent with the research results of Song et al. [18] and Zhang et al. [19]. According to the analysis of the assessment of the potential pollution risk posed by LPE to farmland, the difference between the reference values of 15 t/hm² and 30 t/hm² for the theoretical applicable amount of pig manure equivalent had a strong impact on the assessment results of the farmland early warning value level. The equivalent pollution index for LPE pollutants in the water bodies in Anhui Province in 2008 was 7.03 [18]; in this study, it was found that the equivalent pollution index for the LPE pollutants in the water bodies in Anhui Province in 2019 was 5.23. This comparison shows that the risk posed by livestock and poultry breeding related pollution to the water environmental is decreasing. The emission of LPE in Anhui Province in 2018 was 45,110,000 t [19]. The emission of LPE in Anhui Province in 2019 calculated in this study was 47,778,600 t. The increase in the breeding quantity was the main reason for the change in the LPE emissions. Geng et al. [20] showed that the risk posed by animal husbandry waste related pollution to agricultural land in Anhui Province was not high. The main reason for this is that their study took cultivated land, grassland, and forest land in agricultural land as the consumption place; in this study, only farmland was taken as the consumption place of livestock and poultry breeding pollutants.

This reflects the effects of the different selection of parameters and the sensitivity to the change in the environmental pollution risk of the assessment of the potential pollution risk posed by livestock and poultry farming pollutants to farmland. The theoretical applicable amount of pig manure equivalent in different regions should be reasonably determined based on the livestock and poultry types and the planting industry status in the region, as well as the quality of the farmland. At present, the calculation of the land carrying capacity for LPE is mostly based on the calculation of the nitrogen and phosphorus nutrient discharges. Other pollutants contained in LPE are not fully considered. When considering the discharge of nitrogen and phosphorus, the main index elements such as heavy metals and antibiotics should be included and should be comprehensively determined based on the weighted average of multiple pollutants.

4.2. Regional Environmental Protection

The implementation of regional environmental protection policies and schemes is a key reason for the change in the environmental pollution load [21]. Through the implementation of the three-year action plan for the resource utilization of LPE, Anhui Province has established standardized demonstration farms for livestock and poultry farming. The proportion of large-scale livestock and poultry farming has been further improved. However, the comprehensive utilization rate of LPE and the matching rate of manure treatment facilities and equipment need to be further enhanced for large-scale farms. The LPE treatment and comprehensive utilization techniques should be popularized. The basic conditions of large-scale livestock and poultry farms should be improved to carry out solid–liquid separation, anaerobic digestion, and aerobic biological treatments [27]. Furthermore, the local and nearby return of livestock and poultry manure to farmland should be promoted for resource utilization, which is conducive to reducing livestock and poultry farming pollution and improving farmland fertility and crop quality.

4.3. Agricultural Green Development

Pollution prevention and control should be carried out from the source according to the livestock and poultry farming status. Yuan et al. [28] reported that adjusting the diet structure of livestock and poultry can control the total amount of LPE pollution. They suggested that the feeding method should be adjusted in livestock and poultry farming, the feed ratio should be improved, and cleaner production measures should be taken to reduce the total output of LPE pollution. The production layout should be further optimized and the coordinated development among regions should be strengthened according to the regional characteristics of the northern and southern parts of Anhui Province [29]. Garrett et al. [30] suggested that crop livestock systems should be integrated to improve the sustainability of agriculture. Based on the characteristics of animal husbandry and planting in the province, a new combination model of large-scale farming and farmland utilization should be actively explored. The supervision system of manure returned to farmland should be improved. Economic, efficient, flexible, and diversified modes of combining crop and animal farming should be popularized. Point blocking crop and animal farming cycles should be implemented. The scientific and rational application of organic fertilizer should be promoted. Chemical fertilizer reduction and efficiency should be enhanced. Furthermore, the improvement of farmland quality and the green development of agriculture should be promoted.

4.4. Watershed Environmental Measures

Standardized production in large-scale livestock and poultry farms and the resource utilization mode of LPE should be promoted in the Huaihe River Basin. Further improvement of the livestock and poultry breeding technology should be encouraged, to achieve the transformation to technology-intensive modern animal husbandry. The optimization of the farm layout should be promoted, and the construction of digital and information-based intelligent pasture should be supported. The layout of pig breeding should be optimized and the total amount of pig breeding should be reduced in the Yangtze River Basin. We should give full play to the advantages of centralized poultry breeding in southern Anhui to guide the appropriate development of waterfowl in the basin. We should actively develop herbage farming and support the standardization and upgrading of large-scale livestock and poultry farms and enclosures and the upgrading of equipment. The Xin’an River Basin should adhere to moderate scale operations as the main task and standardize production as the direction. The inexpensive return of LPE to fields should be promoted, and the pollution control of breeding should be actively and steadily promoted.

5. Conclusions

In 2019, the total pig equivalent of livestock and poultry farming in Anhui Province was 55,068,400 and the total pollutant release was 510,400 t. COD emissions accounted for 71.67% of the total pollutant emissions. The farmland load of the pig manure equivalent was 8.09 t/hm². The water load equivalent pollution index of the LPE pollutants was 5.23, i.e., a mild pollution risk to the water environment. The spatial distributions of the LPE, pollutant output, farmland load of pig manure equivalent, and pig manure equivalent pollution index of the LPE in the province increased from south to north. The cities of Fuyang, Bengbu, and Suzhou have a high water environmental pollution risk and should be the regarded as key regions for livestock and poultry pollution prevention and control.