Estimation of Water Resource Ecosystem Service Value inTarim River Basin—From a Full Value Chain Perspective

Abstract

The estimation of ecosystem service value of water resources in the Tarim River Basin is of great significance for resource allocation management and ecological protection. However, there is still no unified and complete evaluation method for the ecosystem service value of inland rivers in China. Based on the perspective of the whole value chain, this study classified its ecological service functions and divided 11 sub-categories into four categories (supply, regulation, culture, and support) as evaluation indicators to carry out the quantitative evaluation. The results showed that the total value of ecosystem services in the Tarim River Basin in 2018 was USD 96.0262 billion (10⁹), and the values of regulating function, cultural function, supporting function, and supply function were, successively from high to low, as follows: USD 38.7938 × 10⁹, USD 36.7204 × 10⁹, USD 19.6209 × 10⁹, USD 0.8911 × 10⁹, among which the value of regulation function was dominant.

1. Introduction

Ecosystem services, which are materials produced by the ecosystem and ecological processes and maintain a good living environment for human service performance [1], the water ecological system (the foundation of human survival and development) that is closely related to the people’s well-being [2], especially in arid northwestern China’s social economic development and ecological environment protection, are very important. As the most important oasis agricultural region in China, the Tarim River Basin is one of the most arid regions in China and even the world, with the largest gap between water supply and demand and the most vulnerable ecology, as well as one of the regions with the highest agricultural water consumption ratio and lowest water resource utilization efficiency. With the economic development and agricultural area expansion of the Tarim River Basin, the water system has been cut off and the service function of the water resource ecosystem has been declining. The lower reaches of the Tarim River Basin have become the disaster area of serious ecological degradation in recent years [3], and the problems of resource allocation management and ecological protection are prominent. The first document of the Central Government in 2022 pointed out that it is necessary to “implement water resources allocation projects such as major water sources and water diversion” and “implement major ecological protection and restoration projects to recover the ecological environment of rivers and lakes” in order to ensure the stable and smooth development of the country’s economic and social development. The 14th Five-Year Plan for Water Culture Construction once again proposed to “improve water culture services”. A comprehensive and systematic study and calculation of the value of the water resource ecosystem service system in the Tarim River Basin has become an urgent demand for policy implementation.

The concept of an ecosystem service system has been gradually defined since it was put forward, but the definition of a watershed ecosystem is still controversial [1,2,4,5,6,7,8,9,10,11]. There are few studies on the full value of domestic inland rivers [12,13,14,15,16,17,18,19,20,21,22], and the comprehensive system measurement and pricing of a watershed ecosystem service system value are also open to discussion [13,20,21,22,23,24]. Therefore, it is particularly important to study the ecosystem service value of the Tarim River Basin. The Tarim River Basin was the research object of this research, and through the United Nations, in a one thousand ecosystem assessment classification method combined with the actual situation of the development and utilization of the river and its ecosystem structure characteristics, its ecological service function was divided into four categories (supply, regulation, culture, and support) in class 11 and an evaluation index. The corresponding assessment method (monetization of evaluation, such as the market value method, replacement cost method) was selected to carry on the quantitative evaluation to aid with the allocation of resource management and ecological protection to provide the theory basis of a system, to ease the river basin water resource shortage, and to provide reference for the sustainable development of the social economy in the Tarim River Basin.

2. Research Status and Theoretical Review

2.1. Research Progress of the Ecosystem Service System Value

In 1911, the Russian Vladimir Vernadsky proposed the concept of the Biosphere and expanded the concept of ecological relations to include the whole world. The basic concept of an ecosystem was first elaborated by the British ecologist Tansley [4], which then formed the research system of modern ecology. The ecosystem service function can be traced back to Man and Nature (George Marshd), who realized the reaction of human beings to the environment and proposed that the ecosystem service function of forests should be managed scientifically, moderately transformed, and developed. Since the 1990s, studies on ecosystem services have been increasing. Natural Services: Natural Ecology Determines Society (Daliy) systematically summarizes the theories and methods of relevant scholars and the value measurement of ecosystem services [5]. The Millennium Ecosystem Services Assessment (MA) of the United Nations divides the value of ecosystem services into four categories: supply function, regulation function, cultural function, and support function [1], making the assessment of ecosystem services a hotspot in the field of ecological research. This paper evaluated the ecosystem services in the Tarim River Basin from this perspective. However, attention should also be paid to the unassessability of ecosystem services proposed by Serafy and Ayres [6,7]. Domestic studies on the ecosystem service value appeared later. Zhang used the substitution cost method and shadow engineering method to evaluate water conservation and the soil retention function of the Fugong forest [8], and Bi evaluated the service function of a specific forest ecosystem in Hebei province [9]. At the end of the 20th century, the evaluation of the value of regional ecosystem services was gradually improved. Ouyang et al. used the evaluation method of ecosystem services to calculate the value of six types of services, while clarifying the connotation and evaluation indicators of domestic terrestrial ecosystem services [10]. Xie et al. (2001) predicted six development trends of ecosystem services, while describing the relevant progress in this field [11], and then they improved the concept of ecosystem services while calculating the value of China’s ecosystem services based on the extended labor value theory (Xie et al.) [2]. Yang et al. used an emergy-based wetland ecosystem service assessment framework and the computational methodology created by Howard. T. Odum when evaluating the Pearl River Delta urban agglomeration [25]. Zhao Sheng also used emergy-based wetland ecosystem services assessment framework to measure the real value of the system when evaluating the emergy value of Zhoushan marine ecosystem services [26].

2.2. Research Progress on the Value of Water Resource Ecosystem Services

2.2.1. Theory of Water Resource Ecosystem Service Value

The measurement of the water ecosystem service function started from the wetland-type rapid evaluation model proposed by Larson [12]. Later, on the basis of ecosystem service function, Young proposed an evaluation model of the recreational value of water [13]. Wilson et al. took freshwater ecosystem service functions as a starting point to elaborate on previous studies, which mainly focused on the river recreational function assessment [14]. Lu et al. used the water footprint theory, water footprint evaluation system, and decoupling theory to explore the relationship between water resource utilization and economic growth in the Tarim River Basin from 2008 to 2019 [15]. Similar to the research on the value of ecosystem services in China, the evaluation of water ecosystem services in China has just started. Ouyang et al. defined river ecosystem services as the benefits it brings to human beings and divided them into four types of functions (supply, regulation, culture, and support) as an indicator system from the perspective of full value chain (MA project) [16]. Fan, when defining the concept of the river ecosystem, pointed out that it is not independent and closed ecosystems [17]. The comprehensive evaluation of the river ecosystem service function has not been carried out in the early stage, and most of the studies focus on the evaluation and measurement of a specific factor in a specific water area in China, such as alpine wetland grassland resources in western China (Li) and reed resources in Bosten lake wetland in Bazhou (Sun) [18,19]. In the later period, the comprehensive assessment of the ecosystem service function of the exorheic river and its tributaries gradually increased. For example, Yang et al. studied the ecological service function and value assessment of the Weihe river basin, Beijing section of the Yongding river basin, and the Chishui river basin in Shaanxi [20,21,22]. In recent years, the research on the value of water resource ecosystem services in Xinjiang has also received increasing attention. Scholars have studied the value of ecosystem services in the Ili River Basin, the Aibi Lake Basin, and the Ulungu River Basin [27,28,29,30,31,32]. The Tarim River has also become one of the focuses of research; the Bai et al. analysis on the feature of quantity and structure change of land utilization was conducted by using satellite remote sensing data in 2005–2010, and the methods were based on the correction ecosystem service value (ESV) by Xie et al. [33]. Zhang et al. took the Tarim River Basin as their research area and explored the spatial and temporal evolution trend of ecosystem services under land use change in the Tarim river basin [34]. Wang et al. evaluated the ecological service value of Populus euphratica in the lower reaches of the Tarim river based on biomass [35]. Lin et al. explored the effect mechanism of land use and land cover change on the ecosystem service value in a complex environment, and the land use structure was optimized based on ESV [36].

2.2.2. Types and Evaluation Methods of Water Resource Ecosystem Service System Values

Based on different research perspectives, domestic scholars have different cognitions of river ecosystem service types. Zhao et al. divided river ecosystem service types into direct use value and indirect use value, and they calculated four function types according to water ecosystem service system value. Five direct use values, such as aquatic products and hydropower generation, and seven indirect use values, such as environmental purification and carbon sequestration, were constructed [25]. Li divided water environmental purification into five categories based on the MA project based on the supply–demand balance assessment [37]. Xie et al. innovated the method of value equivalent assessment by expanding the six types of ecosystems and subdividing them into two levels, thus achieving high reliability of the measurement results [38].

Based on the choice of research methods, the measurement methods of the river ecosystem service system value can be divided into the physical evaluation method and monetary value method to quantify its ecosystem service value. At the end of the 20th century, Ma was involved in the field of economics when he studied the terrestrial ecosystem services [39]. Since the 21st century, the level of scientific research technology and education in China has been constantly improving, and the number of published studies in this field has entered the fourth place in the world (Gong), and the evaluation methods have also made continuous progress [26]. Gao defined the physical evaluation method through research, data statistics, and so on within the basin ecological service value in the form of physical measurement, suitable for hydroelectric power value and river water and sediment value (such as physical value), but for the value of water storage, water purification and other non-food are difficult to measure [40]. Hao in domestic river ecosystem service functions were reviewed, the research methods were summarized, the evaluation methods of the monetary value method was used, and the basin ecological service function (a quantitative measurement) for money was used (including shadow engineering method, the results of the reference method, etc.) [41]. Fan argued that monetary willingness to pay (WTP) can be generally reflected. However, it should also be recognized that some ecosystem services and products cannot be measured by price, and the existing evaluation methods are controversial [17].

2.3. Existing Problems in the Research on the Value of Water Resources Ecosystem Services in China

The number of papers published in the field of water resource ecosystem service value measurement is still increasing year by year. As an emerging interdisciplinary hotspot, China has made great achievements in recent years, but there are still some shortcomings in its research, which can be summarized as follows:

(1) The definition of a river ecosystem service system is still controversial. The concept of the ecosystem service system has been defined continuously since it was put forward at the beginning of the last century. However, the definition of river ecosystem is still controversial. For example, the river ecosystem is defined as the river flowing water ecosystem (Zhao; Hao) [23,41], it is different from the river flow ecosystem, it is not an independent or a closed ecosystem (Fan) [17], it should include the river and its watershed surrounding areas, sources, reservoirs, wetlands, etc., it should not be separated, and measured in the study.

(2) The neglect of inland river research. Domestic research mostly focuses on the Haihe river and its tributaries (Yang; Zhu; Tian) [20,21,22], and few estimates are made on the value of the inland river. As the longest inland river in China, the Tarim River has bred the Western civilization for thousands of years in its basin. With the social and economic development in the basin, the cultivated land area has increased, and the river salinization has gradually increased, causing serious damage to the ecosystem in the basin. River ecosystem restoration faces severe challenges, including how to construct an evaluation index system of ecological service value suitable for the Tarim River Basin according to the actual situation of the Tarim River Basin and how to quantify the ecological service value of the Tarim River Basin. These will provide basic theories for resource allocation, ecological compensation policy, and the construction of “two new and one important” (namely new infrastructure construction, new urbanization construction, transportation, water conservancy and other important projects construction. It comes from the report on the Work of the Chinese Government in 2020).

(3) There is a lack of comprehensive and systematic evaluations and measurements of the water ecosystem service value. With the continuous improvement of relevant research, domestic research on ecological services is no longer limited to a specific factor in a specific region, the indicator system is gradually improved, and the research and calculations can be conducted for various functions and values of ecological service systems from multi-dimensional dimensions, such as mountain forest, river to province, region, and country (Zhu; Xie) [2,21]. Although the value of water ecosystem services has been comprehensively described, the research perspective is still expanded based on four functional types (Zhao et al.; Ouyang et al.; Li) [23,37], and there is still a lack of comprehensive and systematic evaluations and measurements of the ecosystem service value of watershed water resources.

Based on the above problems, this study used the theory and MA in economics related to the ecosystem service classification method, based on literature reviews and data analyses, the composition of Tarim River Basin’s water resource ecological service value, and the corresponding index system to study its value evaluation method. In order to provide scientific basis for the exploitation and utilization of water resources and ecological compensation policy, the environmental problems in the basin need to be alleviated and the sustainable development of the economy in the western region needs to be promoted.

3. Overview of the Research Area and Research Methods

3.1. Regional Overview

The research area of this paper was the main channel of the Tarim River and its source, with a total length of 2421 km, an area of 1020 × 10³ km², and an average annual runoff of natural surface water of 39.83 × 10⁹ m³. The Tarim River is the longest inland river in the country. There are eight main water systems, namely the Kaidu River and the Konqi River, the Ugan River, the Aksu River, the Kaxkar River, the Yarkant River, the Hotan River, the Qarqan River, and the Keriya River, as shown in Figure 1. There are more than 140 rivers in the river system and the Cheerchen River system. Most of the rivers in the basin are mainly supplied by the snow and ice from the Kunlun Mountains and the Tianshan Mountains, which are purely dissipative inland rivers.

3.2. Evaluation Indexes and Methods of the Ecosystem Service Value of the Tarim River

The value chain perspective of ecosystem services can be divided into supply, regulation, and culture and can support four types of function, through the classification of the MA program method and combined with the actual situation of the development and utilization of the Tarim River channel and its ecosystem structure characteristic, the classification of the ecological service function of Tarim River Basin [1], divided in four kinds of functions, with 11 sub-types as the evaluation index. The physical evaluation method and monetary value method were used to carry out the quantitative evaluation; that is, the watershed ecological service function was quantified as money. The evaluation indicators and methods are shown in

Table 1. Evaluation indexes and methods of the ecosystem service value in the Tarim River Basin.

Function Value	Basic Meaning of Function	Evaluation Index	Evaluation Method	Explanation of the Method	Calculation Formula
Supply	Supply function refers to the factors that maintain people’s life and production activities and bring direct benefits to human beings by providing direct products or services.	Water supply	Market valuation method	The environment is regarded as a factor of production. Changes in environmental quality lead to changes in productivity and production costs. The market price of products is used to calculate the resulting changes in output value and profits, and the economic losses or economic benefits caused by environmental changes are estimated.	Water supply by industry × water price
		Aquatic products	Market valuation method		The total value of fishery output in all areas of the basin
		Hydraulic electrogenerating	Market valuation method		Total hydroelectric power × hydroelectric power price
Regulation	Regulatory functions refer to the service functions and benefits that humans obtain from the regulation of ecosystem processes.	Water resources are stored and regulated	Shadow engineering method	Refers to the artificial construction of a project to replace the original environmental function after a certain link of the ecosystem or environment is polluted or destroyed, and the cost of constructing the project is used to estimate the economic loss caused by environmental pollution or damage.	Basin potential water storage × cost per unit of storage capacity
		Water quality purification	Substitution costing	Calculated at the disposal cost of other measurable disposal measures.	River pollutant carrying capacity × cost of pollutant treatment
		Transportability of sediments	Substitution costing		Annual sediment transport × river clean-up costs
Culture	Cultural functions refer to the non-material benefits that humans obtain from natural ecosystems through cognitive developmental, subjective, recreational, and aesthetic experiences.	Tourist recreation	Market valuation method	Refer to the above.	Total tourism revenue × (tourist attractions in the Tarim River Basin/number of tourist attractions in the autonomous region).
		Scientific research and teaching	Achievement reference method	Use the existing evaluation results as a reference object to evaluate a new environmental item.	Total area of watershed × cultural and scientific research value of ecosystem per unit area
		Aesthetics	Achievement reference method		Basin area × aesthetic value of river per unit area
Support	Life support function refers to the function of maintaining natural ecological processes and regional ecological environment conditions, and it is the basis for the above-mentioned service functions.	Biodiversity	Achievement reference method		Basin area × biodiversity value per unit area of river
		Providing a habitat for living things	Substitution costing	Refer to the above.	(The area of Tarim River Basin∗the global wetland ecosystem habitat unit value + total value of Chinese government investment in the Tarim River Basin)/2
Whole value					Supply + regulation + culture + support

.

4. Evaluation and Analysis

4.1. Evaluation of the Supply Function Value

4.1.1. Value of Water Supply

The evaluation method of the supply value of the Tarim River was the market value method; that is, the water supply of various industries and the current water price of the Tarim River Basin were used as evaluation indexes to measure the supply value of the Tarim River Basin. The calculation formula is:

$$V_1={{\displaystyle \sum }}^{ }(Q_{1i}\times P_{1i})$$

(1)

where V₁ is the water supply value of the Tarim River (USD); Q_1i is the water supply (m³) of i uses in the Tarim River Basin; P_1i is the price (USD/m³) of “four sources and one trunk” of water of the Tarim River.

As shown in

Table 2. Water consumption in various regions of the Tarim River Basin.

Prefecture	Primary Sector /109 m3	Secondary Sector /109 m3	Tertiary Sector /109 m3
Aksu Prefecture	10.223	0.181
Bayangol Mongolia Autonomous Prefecture	4.106	0.133	0.015
Kizilsu Kirghiz Autonomous Prefecture	1.019	0.019	0.002
Kaxkar Prefecture	10.276	0.062	0.021
Hotan Prefecture	4.055	0.014	0.003

, the water consumption of the primary industry in Aksu Prefecture is 10.2230 × 10⁹ m³, according to the water price adjusted by the Xinjiang Tarim River Basin Authority in 2018 in No.1741 (2016). The comprehensive agricultural water price in Aksu Prefecture is 0.0022 USD/m³; the value of the agricultural water supply is calculated to be USD 0.0221 × 10⁹; the water consumption of the primary industry in the Bayangol Mongolia Autonomous Prefecture is 4.1060 × 10⁹ m³; and the price of comprehensive agricultural water is taken from the average value of the Kaidu River irrigation area and the Kongque River irrigation area 0.0101 USD/m³. The calculated value of agricultural water supply is USD 0.0416 × 10⁹; the water consumption of the primary industry in Kizilsu Kirghiz Autonomous Prefecture is 1.0190 × 10⁹ m³, the comprehensive agricultural water price is 0.0008 USD/m³, and the calculated value of agricultural water supply is USD 0.0008 × 10⁹. The water consumption of the primary industry in Kaxkar Prefecture is 10.2760 × 10⁹ m³, and the price of comprehensive agricultural water is 0.0023 USD/m³. The calculated value of the agricultural water supply is USD 0.0238 × 10⁹; the water consumption of the primary industry in Hotan Prefecture is 4.0550 × 10⁹ m³, and the comprehensive agricultural water price is 0.0010 USD/m³. The calculated value of the agricultural water supply is USD 0.0040 × 10⁹.

The total water consumption of the secondary industry is 0.4090 × 10⁹ m³, the industrial consumption water price is 0.0302 USD/m³, and the total value is USD 0.0818 × 10⁹. The total water consumption of the tertiary industry is 0.0410 × 10⁹ m³, the urban housing and business water price is 0.0756 USD/m³, and the total value is USD 0.0031 × 10⁹.

The water supply value V₁ of the Tarim River is USD 0.1077 × 10⁹.

4.1.2. Value of Aquatic Products

The evaluation method of the aquatic product value of the Tarim River Basin was the market value method. The calculation formula is:

$$V_2={{\displaystyle \sum }}^{ }{V}_{2i}$$

(2)

where V₂ is the value of aquatic products in the Tarim River Basin (USD); V_2i is the fishery output value of each region in the Tarim River Basin (USD). According to the 2019 Xinjiang Statistical Yearbook, the fishery output value of Bayangol Mongolia Autonomous Prefecture, Kashgar Prefecture, Hotan Prefecture, Aksu Prefecture, and Kizilsu Kirghiz Autonomous Prefecture was obtained. The output value is USD 0.7691 × 10⁹; that is, the value V₂ of the aquatic product in Tarim River Basin is USD 0.7691 × 10⁹.

4.1.3. Value of Hydropower Generation

The evaluation method of the Tarim River hydropower generation value was the market value method. The calculation formula is:

$$V_3=Q_3\times P_3$$

(3)

where V₃ is the value of hydropower generation in the Tarim River Basin (USD); Q₃ is the total amount of hydropower generation in the Tarim River Basin (KW·h); P₃ is the power generation price of the Tarim River (USD KW⁻¹ h⁻¹).

The average power supply to the power system of the Tarim River Basin for many years was 0.4511 × 10⁹ KM·h [42]. According to the national on-grid price of 0.0318 USD/KW·h, the power generation benefit of the basin is USD 0.0143 × 10⁹.

4.2. Regulation Function Value Evaluation

4.2.1. Value of Water Resource Storage and Regulation

The Tarim River not only has the functions of water supply, fishery, and hydroelectric power generation, but it also has the functions of storage, regulation, and storage to regulate drought and flood disasters. The evaluation method of water resource storage, regulation, and storage value of Tarim River Basin was the shadow engineering method. The calculation formula is:

$$V_4=Q_4\times P_4$$

(4)

where V₄ is the water storage value of the Tarim River Basin (USD); Q₄ is the total water resources of the Tarim River Basin (m³); P₄ is the unit cost of the storage capacity (USD T⁻³). According to the Xinjiang Statistical Yearbook, the total amount of water resources in the Tarim River Basin is 42.0410 × 10⁹ m³, and the unit cost of storage capacity is USD 0.9226 [43]. The value V₂ of the water storage value in the Tarim River Yes, I confirm.

Basin is USD 38.7870 × 10⁹.

4.2.2. Value of Water Purification

The cost substitution method was used to quantitatively evaluate the value of water purification of the Tarim River ecosystem from the salinization and alkalization prevention and control of the river basin to a certain extent. The calculation formula is as follows:

$$V_5={{\displaystyle \sum }}^{ }(Q_5\times P_5)$$

(5)

where V₅ is the purification value of the Tarim River Basin (USD); Q₅ is the sewage carrying capacity of the Tarim River Basin (t); P₅ is the cost of pollutant treatment (USD T⁻¹). Salinization is the main pollution in the Tarim River Basin, and its main pollutants are sulfate, chloride, etc. The salinity in the main stream is high, so it is not suitable for irrigation water [44]. Xu et al. calculated that the sewage carrying capacity of the Tarim River was 769,800 t [45]. Due to the limitation of water quality and quantity, the evaporation and desalting method was adopted for treatment. The total value of purification of Tarim River was calculated as USD 0.0035 × 109 by referring to the calculation of evaporation and the desalting method of the China Water Network, which cost about 4.5373 USD T⁻¹.

4.2.3. Value of Sand Transport Capacity

The sediment transport capacity of the Tarim River adopted the substitution cost method, and the calculation formula is as follows:

$$V_6=Q_6\times P_6$$

(6)

where V₆ is the value of sediment transport capacity of the Tarim River Basin (USD); Q₆ is the annual sediment transport of the Tarim River Basin (t); P₆ is the cost of river cleaning (USD T⁻¹). The Tarim River Basin is located in the northwest, and the cost of river cleaning in the north is 0.2269 USD T⁻¹ as the basis [20]. The average annual sediment transport in the Tarim River Basin is shown in

Table 3. Annual sediment transport of the Tarim River.

Year	Sediment Runoff/103 t
Mean 2001–2006	116.9500
Mean 2007–2012	162.9670
Mean 2013–2018	197.5830
Weighted mean	145.7280

Source: Ministry of Water Resources, PRC. Bulletin of River Sediment in China [47].

[46]. Considering the different influences of time distance and distance of data on the event, the calculation was based on the moving weighted average method, and the average annual sediment transport was adjusted with the weights of 3, 2, and 1, respectively. After the weighted average, the average annual sediment transport was 0.01457 × 10⁹ t. The annual sediment transport value of Tarim River Basin is USD 0.0033 × 10⁹.

4.3. Evaluation of Cultural Function Value

4.3.1. Tourism Entertainment Value

The tourism and entertainment value of the Tarim River Basin was calculated by using the market value method, and a total of 107 A-level tourist attractions were verified in the Tarim River Basin in Southern Xinjiang in 2018, including 4 5A tourist attractions, 22 4A tourist attractions, 47 3A tourist attractions, 32 2A tourist attractions, and 2 1A tourist attractions [47], as shown in Figure 2. In 2018, there were 317 A-level tourist attractions in the Xinjiang Autonomous Region. According to the sample survey conducted by the statistical company, the total tourism revenue of the Xinjiang Autonomous Region in 2018 was USD 38.14876 × 10⁹, up 40.82% year by year. Meanwhile, there are 107 A-level tourist attractions in the Tarim River Basin, accounting for 33.75% of the total number of A-level tourist attractions in the Autonomous Region. Therefore, the tourism and entertainment value of the Tarim River Basin in 2018 is conservatively calculated to be USD 12.87671 × 10⁹. It should be pointed out that, due to the price and geographical location difference of tourist attractions in northern and southern Xinjiang, their value results may be high, and with the development and progress of tourist attractions in the Tarim River Basin and the increase of people’s demand for tourism, the tourism and entertainment value of the basin will continue to improve.

4.3.2. Value of Scientific Research and Teaching

The formula of the cultural scientific research value of ecosystem per unit area is as follows:

$$V_7=Q_7\times P_7$$

(7)

where V₇ is the scientific research and teaching value of the Tarim River Basin (US), Q₇ is the area of the Tarim River Basin (km³), and P₇ is the value of ecosystem research and teaching per unit area in the Tarim River Basin (USD/km²). The research and teaching value of wetland ecosystem per unit area in China is 5777.5492 USD/km² [48]. Due to the different ecological service values provided by different regions, the data of Xie Gaodi were used to process it: Ecosystem research and teaching per unit area in the Tarim River Basin Value = average scientific research value of ecosystem per unit area in China* Ecosystem service value per unit area in Xinjiang/Ecosystem service value per unit area in China * 250/100 (100 is the average value of the ecosystem service system per unit area in Xinjiang, 250 is the ecological service per unit area of the Tarim River Basin system mean) [48]. Among them, the ecosystem service value per unit area in Xinjiang is USD 0.000012 × 10⁹, and the ecosystem service value per unit area in China is USD 0.0006 × 10⁹. The scientific research value per unit area of the Tarim River Basin is 489.4650 USD/km², and the area of the Tarim River Basin is 1020 × 10³ km²; it was calculated that the value of scientific research and teaching in the Tarim River is USD 2.8890 × 10⁹.

4.3.3. Aesthetic Value

At present, there are mainly two evaluation methods for the aesthetic value of wetland rivers, the willingness to pay method and the achievement reference method. The former is based on a questionnaire survey with strong subjectivity, while the latter is improved based on expert consultation. Although the differences between different rivers are ignored, the overall aesthetic characteristics of rivers are still retained. In this paper, the results reference method was used to evaluate the aesthetic value of the Tarim River Basin V₈, and the formula is as follows:

$$V_8={{\displaystyle \sum }}^{ }(Q_{8i}\times P_{8i})$$

(8)

where V₈ is the aesthetic value of the Tarim River Basin (USD), Q₈ is the different types of land areas in the Tarim River Basin (km²), and P₈ is the aesthetic value of different types of land unit area (USD/km²). Taking the research results of Xie et al. as reference [48], the land use type area and ecological service value of the Tarim River Basin are shown in

Table 4. Land use type area and ecological service value of the Tarim River Basin.

Item	Proportion/%	Provide Aesthetic Landscape/USD·hm−2	Maintaining Biodiversity/USD·hm−2
Woodland	1.25	141.2823	306.3372
Grasses	24.14	59.0943	127.0184
Waters	3.44	301.5820	232.9789
Construction land	0.22	-	-
Desert	67.26	16.3012	27.1696
Arable land	3.69	11.5475	69.2822

Source: Spatial and temporal analysis of LUCC and landscape pattern in the Tarim River Basin from 1990 to 2015 based on GIS and RS [27].

. The area of the Tarim River Basin is 1020 × 10³ km². The value of aesthetic landscape provided by Tarim River Basin was calculated to be USD 3.85520 × 10⁹.

4.4. Support Function Evaluation

4.4.1. Biodiversity Value

In this paper, the value of biodiversity in the Tarim River Basin was calculated using the results-referenced method, and the formula is as follows:

$$V_{9i}={{\displaystyle \sum }}^{ }(Q_{9i}\times P_{9i})$$

(9)

where V_9i is the biodiversity value of the Tarim River Basin (USD); Q_9i is the different types of land areas in the Tarim River Basin (km²); P_9i is the biodiversity value of different types of land unit area (USD/km²). In Tarim Populus euphratica National Nature Reserve, there are eight kinds of animals under state first-class protection, such as wild camel, Xinjiang balihead fish, and so on; there are 26 categories of national second-class protected animals, such as whooper swan and Buteo Rufinus. Due to the lack of various biostatistical data in the Tarim River Basin, this paper calculated the land use type area and its ecological service value of USD 6.4604 × 10⁹ based on the research results of Xie et al. [48].

4.4.2. Providing a Habitat Value

In this paper, the substitution method was adopted to calculate the value of habitat provided by the Tarim River Basin, and the formula is as follows:

$$V_{10}=(Q_{10}\times P_{10}+L)/2$$

(10)

where V₁₀ is the Tarim River Basin biological habitat value (USD). Q₁₀ is the area of the Tarim River Basin (km²); P₁₀ is the global wetland ecosystem habitat unit value (USD/km²); L is the total value of Chinese government investment in the Tarim River Basin. Referring to the calculation method of Wu Lingling [49], the substitution method was used to make a preliminary assessment of the habitat value, and the average value of this value and the global wetland ecosystem habitat value [50] was taken as the habitat value of the Tarim River Basin ecosystem. When calculating the initial habitat value by the substitution method, according to the investment quota of the Chinese government in the comprehensive management of the Tarim River Basin of USD 1.62437 × 10⁹ in 2001, according to the project period of 18 years, the project investment benchmark rate of return is 12%, and the total investment value was calculated as USD 12.49139 × 10⁹. The annual ecosystem service value of the biological habitat provided by lakes and rivers is 47087.0262 USD/km², and the area of the Tarim River Basin is 1020 × 10³ km². The average value of the biological habitat value of the watershed calculated by Costanza’s method and the total investment in the watershed was calculated to give a value of USD 30.26008 × 10⁹ for the biological habitat provided by the watershed.

4.5. Evaluation Results

Based on the perspective of the full value chain, the calculation results of water resources ecosystem services in the Tarim River Basin are as follows (

Table 5. Calculation results of ecosystem service value of the Tarim River Basin.

Function Value	Evaluation Index	Estimated Value
		Classified Assessed Value/109 USD	Subtotal Assessed Value/109 USD	The Proportion/%
Supply	Water supply	0.1077	0.8911	0.93
	Aquatic products	0.7691
	Hydroelectric power	0.0143
Regulation	Water resources are stored and regulated	38.7870	38.7938	40.40
	Water quality purification	0.0035
	Sediment ability	0.0033
Culture	Tourist entertainment	12.8767	19.6209	20.43
	Scientific research and teaching	2.8890
	Aesthetic	3.8552
Support	Biodiversity	6.4603	36.7204	38.24
	Providing a habitat for living things	30.2601
Total			96.0262

):

5. Conclusions and Discussion

5.1. Conclusions

(1) According to the calculation method and evaluation index of the ecological service function of the Tarim River Basin, the value of ecological service function from high to low was regulation function value, support function value, cultural function value, and supply function value, respectively: USD 38.7938 × 10⁹, USD 36.7204 × 10⁹, USD 19.6209 × 10⁹, and USD 0.89108 × 10⁹, with a total value of USD 96.0262 × 10⁹ (Table 5). The regulation function was the core function of the Tarim River Basin, accounting for 40.40% of the total value of ecosystem services of the Tarim River Basin, and the value was USD 38.7938 × 10⁹. Among the evaluation indexes, providing a habitat for living things, water resource regulation, and storage value were the highest, mainly because the Tarim River is located in the arid area of northwest China with a broad basin and abundant water resources, accounting for 42.80% of the total water resources in Xinjiang. The supply function of the Tarim River Basin accounts for a low proportion, but it also plays a basic role, such as urban agricultural water, fisheries, and hydroelectric power generation. Therefore, attention should be paid to the development of the Tarim River Basin. With the improvement of the compensation mechanism for ecological protection, the cultural industry and tourism, featuring natural scenery and ethnic customs, will become ecological, and the cultural and supporting functions of the Tarim River Basin will continue to improve.

(2) The Tarim River is the longest inland river in China and one of the world’s most famous inland rivers. It is famous for its distinctive regional characteristics. The relatively abundant natural resources in the basin are intertwined with the extremely fragile ecological environment, which has the dual characteristics of abundant natural resources and fragile ecological environment. The contradiction between ecology and economy in the process of water resource development is very prominent. The related ecological and environmental issues are the key factors restricting the economic and social development of the Tarim River Basin. Since 2000, the state has implemented the recent comprehensive treatment project of the Tarim River Basin, which has achieved remarkable results in “water increase”, “water saving”, and “water delivery” in the basin. The Green Corridor was protected, and the productivity of the oasis increased significantly. However, with the recent implementation of the comprehensive treatment project in the Tarim River Basin, the area of arable land in the basin has continued to increase, the irrigation area has continued to expand, the proportion of agricultural water use has been too high, the water demand of the ecological environment has been seriously squeezed, the groundwater level has dropped significantly, and ecological hidden dangers and crises have become increasingly common. It is highlighted that there is a long way to go to solve the ecological problems in the Tarim River Basin.

(3) From the perspective of the ecosystem service value, the value of ecosystem services in the Tarim River Basin in 2018 was the adjustment function, the branch function, the cultural function, and the supply function, among which the adjustment function and the support function accounted for more than 78%. Water resources being stored and regulated and providing a habitat for living things accounted for 99.90% and 82.40% of the two functional values, respectively. This showed that the regulation of water resources and ecological management should be the primary goals in the comprehensive management of the Tarim River Basin. In terms of basin ecological red line and ecological protection target determination, the important functions of natural desert vegetation in the Tarim River Basin were comprehensively considered in ensuring oasis ecological security, oasis urban civilization, regional biodiversity conservation, etc., according to the distribution pattern of the natural vegetation and water conditions, the determined ecological red lines, ecologically-sensitive areas, and ecological protection targets in the Tarim River Basin. In the construction of key ecological projects in the basin, following the principles of ecological importance, urgency of protection, scarcity of species, and feasibility of implementation, the key ecological projects in urgent need include ecological protection projects for lakes and wetlands, conservation and restoration projects for bromine riparian forests, and groundwater monitoring and management projects. Therefore, water resource management, ecological water rights, ecological compensation mechanisms, and institutional innovation are important contents of future research. Of course, the Tarim River Basin, with its unique natural features and profound historical feelings, has a unique tourism value and important scientific research value, which must be considered in the future comprehensive management of the basin.

5.2. Research Contributions

(1) In terms of research methods, the estimation of scientific research and teaching value takes into account the different scientific research and teaching values per unit area of ecosystems provided by different regions, and it improves the previous result-based reference method, which is more suitable for the Tarim River Basin. Estimates of the value of providing a habitat for living things were calculated, taking into account the time value of the investment. (2) Unlike the definition of water in a river ecosystem, this research recognized the United Nations’ one thousand ecosystem services assessment (MA) in the definition, using the Tarim River main channel and the origin of wetlands, the surrounding areas of the reservoir ecosystem services value system, to conduct a comprehensive system of research estimates. (3) At present, the Haihe river and its tributaries are mainly studied in domestic research, while the inland river was studied in this paper. The core value of the Haihe river tributaries is mainly its supply function, while the Tarim River Basin is dominated by its regulation function. (4) The study of the ecosystem service value of the Tarim River Basin is no longer limited to the calculation of a specific factor in the basin, but it integrates different research perspectives to establish a relatively complete ecosystem service evaluation system.

The quantification of this value provides a theoretical basis for the restoration of the Tarim River Basin ecosystem and the improvement of the ecological compensation policy, and it also provides a reference for the establishment of the value index of water resource ecosystem services in the autonomous region and other inland rivers. Two sessions in 2020, “the government work report,” “achieve pollution prevention completed stage”, “the construction of water conservancy and other major project” provided a more accurate scientific basis to implement the party central committee and the State Council for western development guidance on the concepts that “lucid waters and lush mountains are invaluable assets” to build a national ecological security barrier.

5.3. Limitations and Prospects of the Study

The limitation of the study is that the difference between the intermediate value and final value was not clear, and there was repetition between the evaluated values. Secondly, the estimation of the watershed ecosystem service value required a lot of data support, and the lack of data lead to the limitation of research methods, leading to some deviations in the results of evaluation value, such as the lack of annual tourism income of the watershed water conservancy tourist attractions and the number of state-level protected animals. In addition, the resulting reference method may cause some deviation in the calculation results due to the differences of geographical characteristics between basins; thus, the evaluation method still needs to be further improved.

The relevant data in this paper are based on the 2018 Xinjiang Statistical Yearbook and the research results of relevant scholars, and the evaluation results are the static value of the water resource ecosystem services in the Tarim River Basin. Since the time factor had a correlation with the value of ecosystem services, its value also changed with the change of time. The analysis of static value will lay a foundation for the subsequent dynamic analysis. Taking the time factor into consideration in the study will be more conducive to understanding the ecological service value and its change trend in different periods of the Tarim River Basin.