Spatial recognition of key regions of atmospheric processes
Based on the WRF-CMAQ two-way coupled system, the average PM2.5 concentrations of typical months (January, April, July, and October as the representative seasonal typical months) in 2025 and 2035 was simulated according to the annual pollutant emissions in 2016 (Fig. 3–4).
As shown in Fig. 3, the SO2 and NOx emissions were mainly concentrated in eastern Anshan city from industrial emission sources, and NH3 emissions were mainly concentrated in the central and northern regions from agricultural sources. Similar to the distribution of SO2 and NOx, the PM2.5 emissions also demonstrated a high concentration in this region of eastern Anshan.
In 2025, the average annual concentration of PM2.5 in Anshan city can be reduced to 38 µg/m3, and the ratio of good days will be increased to 85%. In 2035, the annual average concentration of PM2.5 in Anshan city can be reduced to 35 µg/m3, and the ratio of good days will increase to 87% (Fig. 4).
We formulated the bottom line of atmosphere environmental quality and atmospheric function zoning by considering the following: atmospheric process simulation results combined with pollution-sensitive targets, the built-up area, and natural reserves; land use types when zoning; and industrial emission intensity, urban upwind direction, diffusion channels, and circulation. There were five levels of area division (Fig. 8 (a)).
Recognition of key spatial regions of hydrologic and water pollution processes
The hydrological and water pollution processes were constructed using ArcGIS and SWAT models. The SWAT was well calibrated and validated, and the accuracy can satisfy the needs of our research in the study area. Detailed information can be found in our former works (Zong et al. 2021). The administrative boundaries of the township were combined with the hydrological process simulation, then divided into 69 hydrological control zones via the SWAT model. The model results reflected that the spatial distribution characteristics of total nitrogen and total phosphorus loads were the same (Fig. 5).
By analyzing the characteristics of the terrain elevation catchment, urban pipe network catchment, water system relationship, pollution discharge, and water environment quality distribution characteristics in the urban space, the relationship between the regional catchment and water function areas was identified, and a collection of pollutant discharges was established. Delineated priority protection areas for water source protection; priority protection areas for water ecological protection; key control areas for industrial pollution of water environment; key control areas for water environments subject to urban domestic pollution within the city of Anshan; and key control areas for water environment and agricultural pollution (Fig. 8 (b)).
Identification of key regions of soil pollution
Application of the K-S test confirmed that all heavy metal concentrations were normally distributed. The distribution of As content ranged from 3.6042 to 11.8497 mg/kg. Rock minerals, pesticides, and fertilizers in human production contain As, which may lead to the southeast high distribution, and the high content of As in the northern region may be related to sewage discharge, thereby polluting the soil. The distribution of Cr content ranged from 35.9133 to 110.2030 mg/kg. The high content area may be related to the discharge of soil parent material and Cr compound manufacturing enterprises in this area. The distribution of Hg content ranged from 0.0174 to 0.1174 mg/kg. The main distribution areas are densely populated, and the Hg in production and domestic waste is easily adsorbed and fixed by the soil, resulting in Hg enrichment. The distribution of Ni content ranged from 15.7471 to 33.3874 mg/kg. The distribution of Pb content ranged from 17.3866 to 48.0287 mg/kg. The high-value areas of Pb are scattered and distributed in patches, which are affected by air dust deposition and vehicle exhaust emissions. The distribution of Cd, Cu, and Zn contents ranged from 0.0949 to 0.3694 mg/kg, 19.5017 to 30.6043 mg/kg, and 31.2754 to 110.862 mg/kg and were mainly concentrated in northern Xiuyan County, where vegetable farming may contribute to the contamination of Cd, Cu and Zn (Fig. 6). None of the heavy metal contents exceeded the National Soil Environmental Quality Standard (GB15618-2018).
According to the land use map, agricultural land, construction land, and unused land were extracted. Spatial interpolation of the heavy metals cadmium, chromium, arsenic, mercury, and lead was carried out, and agricultural land was managed and controlled according to the "Soil Environmental Quality Agricultural Land Soil Pollution Risk Control Standard", which is divided into priority protection areas for agricultural land and key pollution risk control areas for agricultural land. Through the Anshan City Industrial Enterprise Pollution Discharge Key Enterprise List, a key control zone for pollution risks of construction land will be established. The remaining areas are divided into general control areas (Fig. 8 (c)).
Important Ecological Space Assessment
The ecosystem services, including water source protection, wind and sand protection, and biodiversity maintenance, were estimated based on the recommended methods in the “ecological red line assessment standard” (Fig. 7). The raster values corresponding to 50% and 80% of the total value of ecosystem services were taken as the demarcation points for the evaluation and classification of ecosystem services.
Based on the results of ecosystem services and the distribution of natural protected areas, the ecological redline of Anshan city was determined. The importance of ecosystem services is divided into three levels, namely, extremely important, important, and moderately important. Among them, the most important area of the ecosystem service function is the ecological protection red line area (Fig. 8 (d)).
Ecological environment management and control division
Ecological environment management and control function zoning
There were five levels of area division of the atmosphere: 1) priority protection areas, including nature reserves, scenic spots, and forest parks; 2) high emission areas, including industrial parks and high-emission towns; 3) layout-sensitive areas, including urban upwind, diffusion channels, circulation channels, and other layouts that affect air quality; 4) receptor-sensitive areas, including urban centers, built-up areas, and concentrated residential, medical, and education areas; and 5) general control areas, which are the remaining area without special protection. (Fig. 8(a)).
The boundaries of township administrative districts were combined with the delineating units via the SWAT model then divided into a total of 84 control zones. These zones include 16 priority protection areas, accounting for 19.05%; 46 key control areas, accounting for 54.76%; and 22 general control areas, accounting for 26.19%. According to different sources of pollution, the key control areas can be divided into key control areas for industrial pollution, key control areas for urban domestic pollution, and key control areas for agricultural pollution (Fig. 8(b)).
The area of nonpolluting agricultural land accounts for 82.49%, making it a priority protection area. The agricultural land pollution risk control area and the construction land risk control area account for 1.52% of the total pollution risk control area. General control areas account for 15.99% (Fig. 8(c)).
The ecological protection red line area of Anshan city is 1147.38 km2, accounting for 12.41% of the city; the general ecological space covers an area of 2384.09 km2, accounting for 25.78% of the city's area; and the general control area accounts for 61.81% (Fig. 8(d)).
Eco-environmental unit management terms
The number of environmental management and control units is divided into 67 areas that focus on ecological environmental protection, such as ecological protection red lines and other ecological spaces, water environment priority protection areas, and atmospheric environment priority protection areas, which should be regarded as priority protection units; regions serve as key control units; and other regions serve as general control units (Fig. 9).
The priority protection units include the ecological protection red line, water environment priority protection area, atmospheric environment priority protection area, agricultural land priority protection area, etc. They focus on ecological environment protection and prohibit or restrict large-scale industrial development, minerals, other natural resource development, and urban construction. There are 37 priority protection units in Anshan city, with a total area of 3458.82 km2, accounting for 37.37% of the total area of the city. Key control units include other ecological spaces, towns, and industrial parks outside the ecological protection red line, densely populated areas with high resource development intensity, and high pollutant emission intensity. According to the quality objectives and control requirements of water, atmosphere, soil, ecology, and other environmental elements in the unit, as well as the control requirements of natural resources, the list of access and treatment is comprehensively determined. There are 29 key control units in Anshan, with a total area of 4165.77 km2, accounting for 45.01% of the total area of the city. The general control unit includes other areas except for priority protection and key control areas and implements the basic requirements for regional ecological environment protection. There is one general control unit in Anshan, with a total area of 1630.77 km2, accounting for 17.62% of the total area of the city.
For the atmosphere, the priority protection area prohibits any construction projects other than ecological protection and restoration; the existing enterprises and industrial land in the area are gradually being removed; and all units and individuals are prohibited from destroying or occupying the land in the area. The high emission area will promote the construction of eco-industrial parks, the efficient recycling of resources, and the technological transformation of energy conservation and emission reduction. The use of high-polluting fuels is prohibited except for urban heating and power plant boilers in receptor-sensitive areas, and the construction of nonpoint source projects with dust below 15 meters is restricted. Reconstruction and expansion projects in weak diffusion areas should raise the entry threshold for energy conservation and environmental protection and prohibit the construction of new projects in high-polluting industries. In layout-sensitive areas, projects involving the emission of toxic gases and high pollution are prohibited.
For water environmental zones, priority protection areas need to strictly protect the water area, strengthen water ecological construction, avoid the deterioration of water quality, and protect drinking water safety. In key agricultural pollution control areas, agricultural nonpoint source pollution should be rectified, and the impact of planting and livestock on the aquatic environment should be reduced. Key urban domestic pollution control areas should promote the construction of rain and sewage diversion, control the total amount of pollutant discharge, and improve green coverage. In key industrial pollution control areas, the construction of direct wastewater discharge projects must be prohibited, and the carrying capacity of the water environment must be rationally utilized to ensure that the environmental quality does not deteriorate. The management of the general control area should restrict the entry of high water-consuming industries, control the total amount of pollution, and discharge up to the standard.
Agricultural land priority protected areas should encourage the application of organic fertilizers, promote water-saving irrigation, and implement new farming models. Key agricultural land pollution control areas need to monitor the changes in soil environmental quality at fixed points and implement plans for returning farmland to forests and grasslands for severely polluted farmland. In the key control area for pollution risks of construction land, the land and surrounding soil environment of key regulatory industries and industrial parks should be monitored, and the prevention and control of heavy metal pollution need to be strengthened. The management of general control areas should prevent soil pollution and ensure the safety of the regional ecological environment.