Eco-environmental sensitivity evaluation is aimed at the possible eco-environmental problems in the region, combined with the existing natural environment characteristics and the degree of human interference, to determine the sensitivity evaluation index and evaluate the sensitivity of the eco-environment to human activities interference, that is, the possibility of ecological imbalance and eco-environmental problems. Through the comprehensive analysis of the main environmental indicators that affect the regional eco-environmental sensitivity, the level of eco-environmental sensitivity is determined and the geographical and spatial distribution of eco-environmental sensitivity is evaluated.

Ecological function evaluation is the ability and value evaluation of typical ecosystem service functions. Combined with the existing ecological environment and human interference, the importance evaluation index is determined to evaluate the importance of regional ecological environment. Through the comprehensive analysis of the main environmental indicators affecting the regional ecosystem function, the importance of ecosystem function is defined and the geographical and spatial distribution of the importance of ecosystem function is evaluated.

On the basis of eco-environmental sensitivity and ecological function evaluation, the eco-functional areas are divided, the main problems existing in each functional area are analyzed, and the corresponding eco-environmental protection measures are put forward, so as to realize the benign cycle of natural ecosystem, maintain the regional eco-environmental security and provide scientific basis for the sustainable development of social economy.

4.2.2 Evaluation content

The main indicators affecting the sensitivity of regional ecological environment were analyzed, and the sensitivity of soil erosion and biodiversity in the study area was evaluated. This paper analyzes the main indexes affecting the function of regional ecosystem, and evaluates the importance of ecological function to biodiversity, water conservation, soil conservation and nutrient cycle.

4.2.3 Evaluation method

Determine the evaluation index and scoring basis, use qualitative and quantitative methods to evaluate, and select the evaluation unit to the township level. According to the evaluation results, eco-environmental sensitivity is divided into five grades: extreme sensitivity, high sensitivity, moderate sensitivity, mild sensitivity and insensitivity. The importance of ecological environment is divided into four levels: extremely important, moderately important, relatively important and unimportant.

4.2.4 Eco-environmental sensitivity assessment

Sensitivity assessment of soil erosion

The factors such as rainfall erosivity (using runoff depth), soil texture, topography and vegetation are used as evaluation indexes of soil erosion sensitivity, and the classification basis is shown in Table 4.3.

Table 4.3 Classification of Impact of Soil Erosion Sensitivity

The evaluation results of soil erosion sensitivity are shown in Table 4.4. The results show that the water source area belongs to the moderately sensitive area of soil erosion, which accords with the actual situation of the study area.

Evaluation of biodiversity and habitat sensitivity in 4.2.4.2

According to the grade of national and provincial protected species in the evaluation area, the habitat sensitivity is evaluated, and the grading standard is shown in Table 4.5.

Table 4.4 Basic data of ecological environment and comprehensive evaluation of ecological environment sensitivity of water source area

sequential

Note: The data comes from 032 Report on Ecological Function Zoning of Nanyang City by Nanyang Environmental Protection Bureau.

Table 4.5 Classification of Biodiversity and Habitat Sensitivity

The comprehensive evaluation results of biodiversity and habitat sensitivity are shown in Table 4.6. As can be seen from the table, the regional distribution of biodiversity and habitat sensitivity in the water source area: the extremely sensitive area is 1782.38km2, accounting for 28% of the total land area of the water source area, mainly distributed in Xixia County; The highly sensitive area covers an area of 249 1.39km2, accounting for 39.2% of the total land area of the water source area, mainly distributed in Xixia County and Xichuan County. The moderately sensitive area is 1506. 13km2, accounting for 23.7% of the total land area of the water source, mainly distributed in Xichuan County and neixiang county. The lightly sensitive area covers an area of 582.04km2, accounting for 9. 1% of the total land area of the water source, and is distributed in neixiang county, Xichuan County and dengzhou city.

Table 4.6 Assessment of Biodiversity and Habitat Sensitivity in Water Source Area

4.2.5 Ecological function evaluation

4.2.5. 1 Importance Assessment of Biodiversity Maintenance Function

According to the sensitivity of evaluating regional biodiversity, the importance of evaluating regional biodiversity protection is determined.

The evaluation results of the importance of biodiversity maintenance function are shown in Table 4.7 and the comprehensive evaluation results are shown in Table 4.8. The extremely important area of biodiversity in the water source area is 4273.77km2, accounting for 67.2% of the total area, mainly distributed in all townships (towns) involved in Xixia County and some townships (towns) in the west of Xichuan County. Moderately important area 1506. 13km2, accounting for 23.7% of the total area, mainly distributed in the central area of Xichuan County. The important area covers an area of 582.04km2, accounting for 9. 1% of the total area, and is distributed in Xichuan, Neixiang and Dengzhou. Xixia County has a mountainous area of 80% and a forest coverage rate of over 70%. There is Laojieshan Nature Reserve in the area, which is rich in animal (plant) species and the overall biodiversity is extremely important.

Table 4.7 Evaluation on the Importance of Ecological Function in Water Source Area

Table 4.8 Importance Assessment of Biodiversity in Water Source Area

Evaluation on the Importance of Water Resources Protection in 4.2.5.2

According to the geographical position of the evaluation area in the regional urban watershed and its contribution to the water resources of the whole watershed, the importance of water conservation in the regional ecosystem was evaluated. See Table 4.7 for the evaluation results of the importance of water conservation function and Table 4.9 for the comprehensive evaluation results.

Table 4.9 Evaluation of Water Conservation Function in Water Source Area

As can be seen from Table 4.9, the importance distribution of water conservation function of water source area ecosystem: the extremely important area of water conservation is 237 1.2km2, accounting for 37.3% of the total area, mainly distributed in Xichuan County and Xixia County; Moderately important areas cover an area of 3485.46km2, accounting for 54.8% of the total area, mainly distributed in Xixia, Neixiang and Xichuan. The unimportant area covers an area of 505.28km2, accounting for 7.9% of the total area, and is distributed in Xixia, Xichuan and Dengzhou.

Xichuan county is not only the location of Danjiangkou reservoir area, but also the location of the head of the middle route of South-to-North Water Transfer Project. Therefore, it is an extremely important water conservation function area, and the area with extremely important water conservation function accounts for 77.3% of the total land area of the county.

Importance Evaluation of Soil and Water Conservation in 4.2.5.3

The evaluation of the importance of soil and water conservation is based on considering the sensitivity of regional soil and water loss, and analyzing the possible harm degree to downstream rivers and water resources. The evaluation results are divided into four categories: extremely important, moderately important, more important and unimportant.

See Table 4.7 for the evaluation results of the importance of soil and water conservation and Table 4. 10 for the comprehensive evaluation results.

Table 4. Evaluation of Soil and Water Conservation Function in10 Water Source Area

As can be seen from Table 4. 10, the area with extremely important soil and water conservation function is 1967.87km2, accounting for 30.9% of the total area, only distributed in Xichuan County. The functional area of moderately important soil and water conservation is1514.15km2, accounting for 23.8% of the total area, mainly distributed in Xixia, Neixiang and Xichuan. The area with important soil and water conservation function is 2862.3 1km2, accounting for 45.3% of the total land area in the study area, which is distributed in all counties (cities) in the study area, mainly in Xixia. In this study area, there is no area where the function of soil and water conservation is not important.

Evaluation on the Importance of Nutrient Cycle Function in 4.2.5.4

The importance of nutrient protection mainly depends on the consequences and severity of eutrophication caused by nitrogen and phosphorus loss in the evaluation area, and the importance of nutrient protection in the evaluation area is determined, that is, according to the position of the evaluation area relative to the river and the importance of the affected targets, the evaluation results are divided into four items: extremely important, moderately important, relatively important and unimportant.

The evaluation results of the importance of nutrient cycling function are shown in Table 4.7 and the comprehensive evaluation results are shown in Table 4. 1 1. From Table 4. 1 1, it can be seen that the importance distribution of nutrient cycling function in Nanyang City: the extremely important area is 1260.62km2, accounting for 19.8% of the total area, only distributed in Xichuan County; The moderately important area covers an area of 273 1.78km2, accounting for 42.9% of the total area, mainly distributed in Xixia and Xichuan. The relatively important area is 2369.54km2, accounting for 37.3% of the total area, which is distributed in counties (cities), mainly in Xixia.

Table 4. 1 1 Evaluation of Nutrient Cycle Function in Water Source Area

4.2.6 Study on Ecological Function Zoning

The ecological functions such as biodiversity, water conservation, soil conservation, nutrient cycle and mineral resources development are taken as indicators, and towns are taken as the smallest zoning units. See Table 4. 12 and Figure 4.7 for the zoning results.

Figure 4.7 Ecological Function Assessment Diagram

According to the National Outline of Eco-environmental Protection, the zoning implements rescue protection for severely degraded special ecological function areas, compulsory protection for key resource development ecological function areas and exemplary protection for good ecological function areas. On this basis, the water conservation area, Heyuan area, drinking water source area, hydrological storage area and soil and water conservation area are determined as special ecological function areas. The ecological destruction of resource development is a prominent problem of ecological destruction at present, especially in key resource development zones such as mineral resources development zones, eco-tourism resources development zones, forest and grassland resources development zones and land resources development zones, which are clearly marked, strengthened supervision and enforced protection; Implement demonstration protection in areas with coordinated economic and ecological development, as well as nature reserves, scenic spots, forest parks, special species-rich areas and ecological demonstration areas.

Table 4. 12 Ecological Function Zoning and Ecological Environment Protection Content of Water Source Area