Research on Value Evaluation and Impact Mechanism of Water Ecological Services in Mountainous Cities: A Case Study of Xiangxi Prefecture

Abstract

To have a more comprehensive understanding of the water ecological services of Xiangxi, the index system of water ecological service is constructed and the intensity of its influencing factors founded on the geographic detector model (GDM) is obtained in this paper. Then, the water ecological service index of eight cities in Xiangxi to evaluate the function level is determined. It is proved that: (a) The overall service value of water cultural function as a key factor in the construction of water ecological services, soil conservation value, and water supply value are relatively poor. (b) The value of the water ecological culture function type is the largest, with an overall value of 353.32 billion yuan. The value of water resources supply is the smallest, with a value of only 4.37 billion yuan, which indicates that human activities have a strong interference with the service function of the water ecosystem. (c) Based on GDM, four factors, including precipitation, resident population, sewage discharge, and water quality compliance rate, have a significant impact on water ecological services. Among them, per capita GDP(X7) > vegetation coverage (X6) > precipitation (X2) > resident population (X4), which further clearly explains the impact intensity of mountain climate basic conditions and human socio-economic activities on water ecological services. The results can offer a practical basis for the spatial development and protection of the water ecosystem to coordinate humans and the environment.

1. Introduction

Water ecology is the core element supporting the environmental life system and produces certain service functions through the energy effect [1]. Particularly, it is the basic resource for human survival and maintaining habitat structure. The service function of water ecology mainly includes direct service function for providing production function and indirect service function for providing life support function. Among them, the direct service functions mainly include aquatic products supply, water resources supply, etc. The indirect service functions mainly include soil conservation, carbon fixation, and oxygen release [2]. Meanwhile, with the increasing activities of economic and social, the ecological interference of human activities on water resources is gradually strengthened. Water ecology is constantly under threat and is showing a deteriorating trend [3]. Thus, at present, in-depth analysis and discussion of the current water ecological service function are highly concerned by scholars. Also As well, there have been many pieces of research on it [4].

The value evaluation of water ecological services began in the 1970s. Holdren et al. proposed the impact of biodiversity on ecological services. In China, the value evaluation of ecological service began with the value accounting of forest resources carried out by the China Forestry Society in the early 1980s. Subsequently, Daily, Costanza (1997) and other scholars systematically conducted relevant research on the value evaluation of ecological service [5]. As one of the important types of ecosystems, water ecology not only maintains the natural conditions for human survival, but also lays a good foundation for the economic development of human society. To evaluate the value of water ecological service function in different types of regions, scholars mainly discuss it based on the following aspects: Firstly, to establish ecosystem service value evaluation system and reveal the regional characteristics and differences of water ecosystem services from different types of scales, many scholars have researched the value evaluation of ecological services such as watershed [6], offshore [7], reservoir [8], lake [9] and wetland [10] based on the hydrodynamic characteristics. For instance, focusing on the regional identification of water ecological protection level, Su Chong, Jenkins, Kumar, and other scholars established the important source and security pattern of ecological services [11,12,13]. Secondly, from the perspective of water ecological function and evaluation methods [14], many scholars had deeply analyzed the connotation of water ecological function, and deeply discussed the evaluation methods for different functional values, aiming to make the evaluation results more accurate by modifying different methods [15,16]. Zhao Tongqian and other scholars evaluated the land surface water ecological types and various types of service functions [17] Also, Ouyang Zhiyun and other scholars discussed the value accounting methods of different ecosystem types [18]. In addition, the impact of service value intensity on water ecology is explained by the interaction effect with land use change [19], climate change [20], and spatial performance [21]. Also some scholars also found that the value of the water ecological service system was affected by the area of different land types [22]. Liu binyi et al., guided by water ecological service, established an interactive model from water ecology and human settlements space mode and put forward the planning and design strategy of water network reconstruction [23]. Although scholars have highly paid attention to the evaluation of water ecological service value, most of the findings focused on the perspectives of different scales [24], functional connotation [25], and technical methods [26,27,28], due to the great differences in the service connotation, action mode and intensity of water ecological types in different regions.

Combining with the issues raised above, the following aspects are focused on: (a) Select essential indicators on the scale of mountainous cities and build a water ecological services index system, while there is a lack of extensive analysis about it. (b) Existing research mainly focuses on the entire water ecological services in the scale of Dongting Lake [29] and Taihu Lake [30] et al., ignoring the spatial differences in county scale. Spatial difference can not only supervise land spatial planning, but also lay the foundation on the reference of urban spatial land layout [31]. (c) The research are mostly concentrated on the value of the entire water ecological services [32]. Few studies have been reported on driving factors that affect the type of water ecological service.

Xiangxi Prefecture is an important part of the ecological conservation and ecological function support in the upper reaches of Yuan River Basin. A perfect ecological compensation mechanism is an important content for the rational allocation of land resources and the virtuous cycle of the ecosystem. In view of this, from the scale of mountainous cities and based on the service structure of water ecological, this paper the evaluation index system of water ecological service function in mountainous areas is constructed and the value classification method to evaluate the economic value of water ecology in Xiangxi Prefecture is selected. Finally, the geographic detector method is constructed to analyze the characteristics of water ecological service value and potential influencing factors in Xiangxi Prefecture [33].

2. Materials and Methods

Xiangxi Tujia and Miao Autonomous Prefecture (referred to as Xiangxi Prefecture hereinafter) is located in the northwest of Hunan Province, between 109°10′–110°22.5′ E and 27°44.5′–29°38′ N. Xiangxi Prefecture is used as a case study to illustrate the spatial variability of water ecological service value (Figure 1). This is performed for two reasons: One is due to access to data. The second is the Xiangxi Prefecture with a typical mountain city with abundant water resources.

Xiangxi Prefecture is the middle and upper reaches of the Yuan River Basin. There are a total of 7 counties and 1 county-lever city with many rivers. The main tributaries are Youshui and Wushui. The total length of the river course is 2869 km. The total area of the river lake ecological buffer zone is 86.07 square kilometers (Figure 2). Among them, Youshui is the mainstream of the state, with a length of 233 km, and a drainage area of 9099 square kilometers. The main stream of Wushui is 141 km, with a drainage area of 3625 square kilometers. It belongs to a typical subtropical monsoon humid climate, with an annual average temperature of 15.8~19.5 °C. The average annual rainfall is 1400 mm, which plays a decisive role in water supply and ecological services in the middle and lower reaches. At the same time, it belongs to the water conservancy center of the Yuan River Basin.

Under the action of the mountain natural environment, karst groundwater resources are rich, with a total water volume of 21.37 billion cubic meters. The theoretical reserve of water energy resources is 1.68 million KW, of which 1.04 million KW can be developed ranking third in Hunan Province. It is an area with rich types of water ecological services and relatively significant service functions.

The water resources land, mainly includes drinking water protection sources and aquatic product protection, reflects the active degree of water resources (Figure 3 and Figure 4). However, water shortages related to engineering also exist in certain areas.

2.1. Data Source and Processing

The data selection was driven by availability, which needs to have similar indicators across the county. The socioeconomic data of this study comes from the statistical yearbook 2020, and the statistical bulletin 2020 of national economic and social development of Xiangxi Prefecture. The ecological environment data comes from the water ecological environment protection of key basins of Xiangxi Prefecture, which was provided by relevant departments. The water resources data comes from the hydrological statistical yearbook 2020 of Xiangxi Prefecture.

The phytoplankton report collected the investigation data of aquatic organisms in the Longshan main stream section of Youshui and Hunan snout mandarin fish National Aquatic germplasm resource protection area of Yongshun Sicheng river. According to the investigation results of the current situation, 27 species of fish were found in the water area from the hero power station to the Wantang power station in Longshan section of Youshui main stream, belonging to 4 orders and 6 families. The number of fish species decreased significantly compared with the past, especially Xianghualing, sand loach, eel, and other precious fish have been basically extinct in this area. Therefore, a loss in biodiversity could be contributed to water insecurity.

2.2. Methodology

Due to the availability, quantification, and objectivity of the data [34], the evaluation index system of water ecological services in Xiangxi Prefecture is constructed according to the existing research results [35]. It is divided into three categories: supply service, cultural function, and regulation function [36]. The specific classification is shown in Table 1.

2.3. Evaluation Index and Value Calculation of Water Ecological Function

There are some differences in the assessment methods and means of different water ecosystem service functions. Based on the consideration of the composition characteristics, ecological process, and development and utilization methods of the mountain city water ecosystem, the research results of foreign assessment theories and methods and domestic scholars are drawn on. Also, market value method, equivalent factor method, alternative cost method, and factor parameter method are adopted to evaluate the service value of water ecology in the study area.

The market value method focuses on water ecosystem service functions that are assessed at market price or have market value but do not require corresponding expenses. The alternative cost method can adapt to the change process of the aquatic environment diversification index. The factor parameter method can handle content that cannot be calculated by market value [37,38]. A full calculation formula as shown in Table 2.

2.4. Geographic Detector

Geo detector analysis methodology is employed, which means that the driving factors affecting the features can be detected. For analysis, the factor detector is selected to detect the heterogeneity of service functions of different water ecosystems. In addition, the Q value is used for measurement. The algorithm is as follows:

$q=1-\frac{{{\displaystyle \sum }}_{h=1}^L{N}_{h{Q}_h^2}}{N{o}^2}=1-\frac{SSW}{SST}$

where: H = 1,2,..., l is the stratification of Y and X; NH and N are the number of units in layer h and the whole area, respectively; Q_h² is the variance of layer h values of the whole region, respectively; SSW and SST respectively represent the sum of intra layer variance and the total variance of the whole region. If the independent variable x is generated by stratification, the greater the value of Q, the stronger the explanatory power of independent variable x to attribute y, and vice versa [39].

3. Results

The calculation method of index value and the occupation or consumption degree of socio-economic development play a decisive role in the value of water ecological service function. In Table 3, it is shown that the function value of water ecological culture service is the largest in the study area indicating that Xiangxi Prefecture. As a mountain tourism city, it has great potential for its cultural and tourism industry. It is expected that with the promotion of Rural Revitalization and tourism development, the cultural value of water ecological will increase year by year.

Rivers and reservoirs are important places for the storage and maintenance of water resources in Xiangxi Prefecture. They provide drinking water for human beings and habitats, metabolic water for plants, environmental water for Industry, and irrigation water for agriculture. The total water supply of Xiangxi Prefecture is 87.43 million cubic meters, which is mainly distributed in Changtangang, the water source of Fenghuang Tuojiang River, the main stream of Yuanjiang River, Youshui main stream, Wushui main stream and the tributaries of Donghe River, Wanrong River, Tuojiang River, Guoli River, Mengdong River, Huayuan River and Guyang river. Taking the regional water resources fee as 0.05 yuan/T, it is calculated that the total value of the water supply function of Xiangxi Prefecture is about 4.37 billion yuan. The results indicate that the precipitation is the key factor of water supply value.

Hydropower generation is a process in which the potential energy of water is transformed into mechanical energy and then into electrical energy. The reservoir hydropower station has the functions of irrigation, water supply, shipping and tourism development, which can create economic value and social benefits for it. According to the field survey, the water prices of various industries in Xiangxi Prefecture can be obtainedAlso, the value of hydropower generation in Xiangxi Prefecture can be calculated. Presently, the developed hydropower stations are mainly rural hydropower stations, mainly concentrated in Baojing County, Longshan County and Huayuan County. The total power generation of hydropower stations in the study area is 2.546 billion kwh, of which Jishou City has the strongest development and the lowest hydropower value, only 37 million yuan. It is indicated that the highly sensitive ecological security area is rich in hydropower reserves. As an important part of the Hunan ecological conservation area, it should not be overdeveloped.

The value of water ecological culture is the continuous development of the historical process, which reflects its bearing and reflection of historical and cultural information. Water ecological culture is the value embodiment of its water body space transformation. Xiangxi Prefecture is a city with profound traditional culture in Hunan. Wetland is the key factor of water ecological culture system, and also the ecological carrier of hydrological regulation ability [40]. Taking the average cultural and scientific research value of wetlands per unit area in China is 382 yuan/hm² [41]. The total area of wetlands in the study area is 26,284.16 hectaresAlso, the total value of water ecological culture and education is 353.32 billion yuan, which provides a strong material guarantee for the future water ecological restoration and the development of the tourism industry. Among them, Yongshun County, with a high ecological sensitive area, has the highest value of water ecological service function, which is consistent with the tourism development of this region. The lowest is Huayuan County with high altitude. The value of water ecological service function is not considerable. It can be seen that the natural environment has a certain impact on the water ecosystem. While there are conflicts and contradictions between the water’s ecological cultural value and the construction process, the surface flow constructed wetland should be built at the river inlet to purify the water quality, speed up the water circulation time and further improve the water’s ecological cultural value.

Aquatic ecosystems are rich in aquatic plants and animals, including high-quality carbohydrates. Xiangxi Prefecture is a typical mountainous city. The production of ecological conservation aquatic products is one of the most important contents. The water quality of key rivers and lakes (reservoirs) in the study area is in good condition. There has been basically no eutrophication. It is dominated by fish aquatic biotaAlso, a total of 27 species of fish have been found, which is significantly reduced compared with the past, especially the precious fish such as xianghualeng, sand loach and eel have been basically extinct. Meanwhile, from the horizontal comparison of the result data, the service value of this type of function is relatively low for building fish habitats, improving the fish living environment, perfecting biological chain, and increasing the stability of the aquatic ecosystem. The data results point out that, due to a large number of reservoirs in Baojing County and its proximity to Jishou City, the production value of aquatic products is relatively high. It also indicated that the largest amount of aquatic products is concentrated in Baojing County with 6469 tons, and the lowest is in Jishou City with 339 tons. The lowest is 339 tons in Jishou City with frequent human activities. According to the breeding area and output in the water resources division and the average market price of 7 yuan/kg, the value of aquatic products in Baojing County is the highest, with 4.53 billion yuan, which builds fish habitat, improves fish living environment, perfects biological chain and increases the stability of the aquatic ecosystem.

3.1. Indirect Use Value

Soil conservation service refers to the storage and conservation capacity of an aquatic ecosystem to prevent soil loss and reduce the risk of flood disasters. It is very important to protect soil diversity. The soil conservation value of the water ecological service function is second only to the water ecological culture value. As a mountainous city, the cultivated land in the study area is the main way of land use. The spatial pattern of ‘mountain building field water’ is an important agricultural production mode. The planting environment determines the diversity of land use and planting types. The soil conservation value in the study area is 100.51 billion yuan calculated by the equivalent factor method developed by Xie Gaodi et al. [42,43]. Where, Yongshun and Longshan have the highest value of soil conservation services, with 2.472 billion yuan and 2.448 billion yuan respectively. However, because most of the land use in Jishou City is construction land and economic activities are more active, the value of soil conservation services is the lowest, which is 2.19 billion yuan. It is founded that different vegetation structures have a certain impact on agricultural production. Furthermore, in order to avoid soil erosion, enhancing soil function and optimizing vegetation structure is the important connotation of water ecosystem restoration.

A large number of agricultural, industrial and domestic sewage are discharged. Then, a variety of pollutants is purified through organisms in the river to make them recycled. Water purification belongs to the function of ecological regulation service. By calculating the efficiency of COD, NH₃-N and TP of the water body, the total discharge of wastewater in Xiangxi Prefecture are 102.6609 million tons. The total service value of water purification in the study area is calculated to be 18.46 billion yuan. The chemical oxygen demand in the study area is the highest, 4982.83 tons, of which Guzhang wastewater discharge is the lowest, mainly in non-polluting industries of agricultural products such as tea. Accordingly, the value of the water purification service is the highest, which is 4.467 billion yuan. Jishou has the lowest value of water purification because of its high per capita GDP and faster industrial development than other cities. It can be seen that providing different green growth environments and improving the water network pattern will further improve the water quality purification function and achieve the optimal water living environment.

Through the calculation of various service function types, the total value of water ecological service function in the study area is 648 billion yuan. The direct use value of them is 431.79 billion yuan, indicating that the value of water ecological culture accounts for a prominent proportion. It belongs to the type of efficient water ecological service. Also, a large area of wetland also plays an important role in water purification. The indirect use value is 256.88 billion yuan, which shows that the value of soil conservation and aquatic products production accounts for a large proportion. It is mainly reflected in Guzhang, Yongshun, Longshan and other areas where tea, kiwi fruit, and tea oil are the main agricultural products. The data of spatial differentiation shows that the differences in economy, society and nature in different regions will promote the differences in the functional efficiency of water ecological services. In future planning work, the coordination between human activities and the self-regulation ability of the water ecosystem should be strengthened, so as to improve the diversity of water ecological types and the value of water ecological services. Especially for areas with frequent human activities, the value of water culture and education should be increased, the value of aquatic products and other aquatic ecosystems should be improved, and the balance of aquatic ecosystems should be maintained.

3.2. Analysis of the Type and Intensity of Factors Affecting the Value of Each Service

In the process of new urbanization, there are many types of factors affecting the water ecosystem. The degree of impact is complex. In order to further explore the influencing factors of water ecological service function in Xiangxi Prefecture, nine main influencing factors are selected: surface runoff (X1), precipitation (X2), urbanization level (X3), resident population (X4), sewage discharge (X5), vegetation coverage (X6), per capita GDP (X7), average temperature (X8) and water quality compliance rate (X9) to detect the impact degree of water ecosystem service value in Xiangxi Prefecture. The Q value and p-value are obtained through the factor detector. The main effects of urbanization level, per capita GDP and average temperature are obtained, as shown in Table 4.

• (1). Precipitation (X2): The multi-year average rainfall is identified as the key factor affecting the service function of the water ecosystem. It is shown that the regional natural environment is not only an important factor in water ecosystem, but also the leading factor determining its spatial difference. The terrain differentiation characteristics of Xiangxi Prefecture are obvious. The high-altitude areas are concentrated in the Wuling mountains with more than 1000 m. It is rainy and abundant in spring and summerAlso, the multi-year average rainfall is about 20 billion cubic meters. Rainfall is the main driving factor and limiting factor of soil respiration. Too dry soil will inhibit the progress of respiration. Based on the relevant data of each county, it can be seen that the obvious characteristics of undulating mountains, more precipitation, and humid climate in high-altitude areas is the decisive factor affecting water ecosystem services.

• (2). Resident population (X4): According to the factor detection model, there is a significant correlation between the number of the resident population and the maintenance of the water ecosystem. From the perspective of positive influencing factors, for example, the educational value of water ecological culture in Jishou City ranks second, which is closely related to wetland education based on frequent human activities. From the perspective of negative impact, in the process of new urbanization, the resident population is the key driving factor of industrial agglomeration and expansion. The socio-economic system produced by its human activities has a certain impact on the service value of the water ecosystem. Such as, due to the frequent impact of human activities on water quality, the value of aquatic products and services in Jishou City is relatively low. 0 = As the permanent population directly leads to land expansion, it changes the exchange relationship between surface and groundwater resources and finally leads to the service value of water ecosystem.

• (3). Water quality compliance rate (X9): Leading to the environmental quality report of Xiangxi Autonomous Prefecture and the environmental quality status report of Xiangxi Prefecture in 2020, the water quality compliance rate and excellent rate of centralized drinking water source water quality monitoring section above the county level in Xiangxi Prefecture are 100%. Moreover, a high-quality water source is an important element to support regional agricultural production such as rice, vegetables, and fishery breeding, and an important guarantee for the energy service function of the water ecosystem. In accordance with the spatial data, the value of aquatic products in Jishou City is the lowest, which matches the contradiction of regional social and economic development.

• (4). Per capita GDP (X7): The per capita GDP of Xiangxi reached 14.826 billion yuan, and agricultural water consumption accounted for 70.54%, which is the main discharge source. As a region with significant development of mountain agricultural industry, the agricultural industry increases the development degree of biological and landscape resources (industrial water consumption and Tourism Development), also leading to a sharp increase in industrial sewage discharge and waste discharge, especially wastewater discharge. Industrial, agricultural and domestic water use leads to the surge of wastewater discharge, the decline of water self-purification capacity and ecological imbalance. For instance, per capita GDP is the highest in Jishou City, but the value of water purification is the lowest, and also the value of soil conservation. Therefore, the upgrading and transformation of urban sewage treatment plants should be accelerated. The first-class discharge standard should be implemented strictlyAlso, after treatment, the secondary utilization of its water ecology should be carried out and converted into organic carbon storage body and soil to improve the material circulation of the water ecosystem.

4. Discussion and Conclusions

The overall value of water ecology is mainly composed of three services: water ecological culture, soil value, and water supply. There is a certain spatial heterogeneity. Precipitation, resident population, sewage discharge, and water quality compliance rate are the main influencing factors.

• (1). From the county level, this study evaluates the service value of water ecology in Xiangxi Prefecture, and quantifies the material flow process of water ecology in the study area. It is indicated that the driving factors in different regions lead to the spatial differences in aquatic system service functions. Calculated from the total value of regional aquatic ecosystem services, it is as follows: Guzhang County > Jishou City > Baojing County > Luxi County > Longshan County > Yongshun County > Fenghuang County > Huayuan County. The water ecological service function of Guzhang county is a high-value area. Its water ecology is less disturbed by the outside world, with good water quality and high water levelsAlso, there is a certain contradiction between the water conservation function and economic development opportunities. But there is a synergistic relationship between soil conservation and cultural value. This conclusion has formulated a scientific basis and reference scale for ecological compensation in mountainous cities.

• (2). Comprehensive use of relevant quantitative models is made in the research. It can provide a systematic method for ecological service value evaluation in mountainous areas, where basic data are relatively scarce, and improves the scientificity and reliability of the evaluation results. The evaluation results can be used as a reference scale and decision-making basis for regional water environment management. Water ecological culture and education, soil conservation, water supply, hydropower, aquatic product production, and water purification. Under the condition that the water conservation and cultural services in the rural areas of Hunan Province are the most important ecological barriers. The development of water conservation and cultural services in the rural areas of Hunan Province can be gradually improved. Consequently, with water conservation as the main goal, water conservation and cultural services in the rural areas of Hunan Province can be gradually improved.

• (3). Based on the quantification of the factor detector, the influence intensity of each influencing factor is as follows: per capita GDP(X7) > vegetation coverage (X6)> precipitation (X2) > resident population (X4). It can be seen that the natural environment and human activities are the key factors affecting the value of water ecological services. In future construction activities, the coordinated development of human and natural environment should be emphasized, the balance of the water regional ecosystem should be promoted and the service value of the water ecosystem should be enhanced. Meanwhile, the self-purification capacity of sewage discharge and the standard rate of water quality are also important preconditions affecting the value of water ecological services, because they have a good fit with the production of aquatic products and the value of soil. The industrial concentration areas with heavy metal pollution still existing in the city shall be intensively renovated to reduce the sources of heavy metals in water bodies and increase sewage treatment facilities.

In view of the difference in the value of water ecosystem services, it is necessary to strengthen water environment supervision in different regions and establish maintenance and regulation suggestions for early warning mechanisms of water ecosystem services [44]. In the study, six water ecological values of counties in Xiangxi Prefecture were calculated by integrating the relevant water ecological value method. At the same time, based on the simulation results of the main impact factors by the geographic detector, the occupation process and impact intensity of the nine factors of human activities on the service value of water ecological are analyzed. However, there are still some thoughts on relevant research:

The service functions of the water ecosystem are divided into three categories and six subcategories: water ecological supply, water ecological culture, and water ecological ontology functions, which basically cover their service functions, but new changes will occur with the development of cities [45].

From the research data and methods, there are some disputes about the market price quantification of water ecological value calculation. The calculation formula and related parameters are differentAlso, the results are also different. For example, although the existing research results are used as a reference for the parameter value of agricultural product price, it is limited to determining the parameter value only from the average price of the local market. The selection of water types, the selection of specific service values and the screening process of influencing factors need to be further refined. Because the assessment of the value of water v services not only requires a large amount of data, many types of data, but also involves multiple sectors, it is difficult to obtain comprehensive data.

The next step is to build water ecological security and integrate the fragmented water system landscape in combination with water ecological service system. Combined with the interactive effect of water ecological service function and regional spatial water city reconstruction, the research on improving the bottom line of regional ecological security will be carried out. From the perspective of dynamic space-time comparison, the systematicness of the evolution of water ecological service function will be strengthened. Furtherly, the interaction between regional water ecological service degradation and social economy needs to be studied. From the time level, the characteristic data of mountainous regions should be obtained to distinguish the change evaluation of water ecological service value dynamically for providing a more scientific theoretical basis for the effective management and control of water ecology.

Author Contributions

Conceptualization, S.Z.; W.Z.; writing—original draft preparation, S.Z.; writing—review and editing, S.Z.; visualization, C.L.; supervision, W.Z. All authors have read and agreed to the published version of the manuscript.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

Footnotes

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Figures and Tables

Figure 1. Study area.

Figure 2. Land use type.

Figure 3. Water source protection area of drinking water.

Figure 4. Aquatic protection area.

Table 1

Connotation identification of water ecological service function.

	Target Layer	Criterion Layer	Index Interpretation
Direct use value (A)	Water ecological supply services (A1)	Water resources supply (A11)	Meet the needs of agriculture, ecology, and industry
		Production value of aquatic products (A12)	Provide rich aquatic products for mankind
		Hydropower (A13)	Utilization value of river hydropower resources
	Water ecological cultural function (A2)	Cultural value of scientific research education (A21)	It is an important medium for understanding the material cycle and energy transformation in nature
Indirect use value (B)	Water ecological regulation function (B3)	Soil conservation value (B31)	Grassland and forest slow down wind erosion to a certain extent
		Water purification (B33)	Produce ecological purification function in the flow of material and energy in water body

Table 2

Calculation formula of water ecological service function value and definition of relevant parameters.

Value Index	Calculation Formula	Parameter Meaning and Calculation Basis
A11	$W_s=S_{W}dn$	Regardless of water quality, WS is the annual available water supply (M3); SW is the water area (M2); D is the difference between the normal pool level of the river and the water level corresponding to the minimum eco-environmental water demand, both of which are taken as 0.4 m; N is the number of times of water body re storage, which refers to the frequency of repeated water storage and drainage in the river in a year, taking the year of flat water as n = 1.5
A12	$Y_f={\displaystyle \sum }{V}_{fi}$	$Y_f$ is the production value of aquatic products (yuan); $V_{fi}$ is the product value of each district and county.The sharing method is the basis to measure the proportion of water scenery income in the total tourism income in the study area. Using this method has a certain reference significance for areas where there is no water ecotourism classification
A13	$V_p={\displaystyle \sum }{Y}_p{W}_p$	$V_p$ is the Hydropower value (yuan); $Y_p$ is the Annual power generation of P power station(KW·h); $W_p$ is the Unit price(yuan/KW·h)
B31	$C=1/7{\displaystyle {\displaystyle \sum }_{i=1}^n}\frac{m_j{p}_j{q}_j}{M}\left(i=1,\dots ,n\right)$	C is farmland provides food value (yuan/hm2); I is types of ecosystem services; j is crop species; The main crops in the study area include grain, oil, vegetables, etc; pj is average price of J crops (yuan/t); qj is unit yield of J crops (t/hm2); mj is area of J crops (hm2); M is the total area of N crops (hm2)
B32	$V_J=C\times V$	Vj is the water purification value (yuan); C is the cost of treating each ton of sewage (yuan/t); V is the amount of pollution treatment (t)

Table 3

Value of various water ecological services in Xiangxi Prefecture.

	Types of Water Ecological Services (100 Million Yuan)	Jishou	Luxi	Fenghuang	Huayuan	Baojing	Guzhang	Yongshun	Longshan
Direct use value	Water resources supply	1.53	0.27	0.43	0.18	0.46	0.35	0.43	0.72
	Value of water conservancy and electricity	0.38	0.92	0.83	2.2	6.28	0.23	1.53	2.60
	Production value of aquatic products	0.24	2.59	1.64	2.80	4.53	1.39	2.38	2.89
	Educational value of water culture	91.22	54.91	26.11	19.22	36.91	79.99	16.37	28.59
Indirect use value	Soil conservation value	2.19	3.76	17.36	11.59	11.16	5.25	24.72	24.48
	Water purification	7.96	14.22	16.99	10.66	26.88	44.67	18.37	16.62
	Total (100 million yuan)	103.52	76.67	63.36	46.65	86.22	131.88	63.8	75.9

Table 4

Factor detection model.

	X1	X2	X3	X4	X5	X6	X7	X8	X9
Q value	0.125449	0.704948	0.249175	0.651263	0.402057	0.810543	0.879495	0.154809	0.002279
p value	0.989935	0.738573	0.928069	0.846717	0.39988	0.456865	0.408265	0.921919	0.926061

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