Introduction

The basin ecosystem is a huge composite one composed of social, economic, and natural characteristics. As a complete ecosystem, the watershed not only provides various resources for human survival and development, but also plays an important role in the dynamic balance of the environment and social needs (Pattanayak 2004). Ecosystem services (ES) refer to the basic resources and benefits provided to people and their communities directly or indirectly by ecosystems and ecological processes, such as providing food, clean water, a stable climate, effective waste treatment, and recreational activities (Costanza et al. 1997). The river basin ecosystem provides multiple resources for the residents in the river basin. In particular, the unique interconnected characteristics of terrestrial and aquatic features in the basin system make it a complete ecological unit with strong integrity and high spatial heterogeneity (Straton 2006). Watershed ecosystem services refer to the ecological functions that gradually form in within the watershed, and can function to conserve water sources, improve the environment, prevent soil erosion, and maintain energy exchange. With reference to relevant research and combined with the characteristics of the watershed (Lebel and Daniel 2009), the watershed ecosystem service functions mainly include water conservation, biological protection, water and soil conservation, and landscape recreation (Loomis et al. 2000; Wang et al. 2010b, c).

As a typical composite ecosystem, its structure enables the resources of the river basin to indicate significant fluidity and temporal and spatial heterogeneity (Tian et al. 2016; Zhao et al. 2018). Ecological services dynamically couple service supply and demand through the flow process of different spatial areas in the basin, and connect the natural ecosystem with human socio-economic realities, which has an important impact on the well-being of communities throughout the entire basin (Trabucchi et al. 2012). Watershed ecosystem services have the characteristics of temporal and spatial heterogeneity of supply, demand, and consumption. The difference in the types and quality of the services provided between different geographic locations enables these services in the river basin to indicate significant temporal and spatial effects. The variations and interdependence of services under different temporal and spatial patterns, in the context of varied natural resources, have led to an imbalance in the characteristics of services, leading to serious changes for the well-being of communities in this region (Liu et al. 2016; Liu 2017).

In the past few decades, along with the rapid growth of the basin’s population, economy, and society, dangers to the natural environment have also increased. Degradation of ecosystems and loss of biodiversity, destruction of ecosystem functions, and resilience all seriously threaten the ecosystem’s ability to continuously provide ecosystem services. Also affected is the change in the value of ecosystem services (ESV) (De Groot et al. 2002; Small et al. 2017; De Groot et al. 2012). In recent years, the evaluation of watershed ecosystem service value has generated much academic, government, and public attention. Most stakeholders evaluate ecosystem service value based on basin water resources, soil and water conservation, disaster mitigation and other aspects from the perspective of basin management, land/water resources utilization, economic policy formulation, public education, etc. (Costanza et al. 2006; Arowolo et al. 2018; Li et al. 2018). These views focus on the trade-off analysis of economic services and ecological services, the relationship between upstream protection and downstream economy, and the impact of agricultural development, land use change, and different policies and measures on the value of ecosystem services in river basins. For example, Costanza et al. (2006) evaluated and summarized 12 ES of 11 land use cover types in the New Jersey ecosystem (Costanza et al. 2006). Kozak et al. (2011) calculated the ESV in the Des Plaines and Cache basins in the USA and analyzed the relationship between the ESV and geospatial units. Chaikaew et al. (2017) examined the Monetized Marginal Value of ES in the Suwannee River Basin, Florida. Chinese researchers revised the unit value coefficient based on the findings of Costanza et al (Xie et al. 2008). A series of studies on changes in the ESV have been carried out in typical river basins that are economically developed, but densely populated and ecologically fragile. Hu et al. (2019) employed the InVEST model to explore the ESV and land use/cover change (LUCC) response mechanisms in the Pearl River Basin. Luo et al. (2017) explored the impact of land use on ESV throughout the entire Yangtze River Basin based on remote sensing interpretation data. Liu et al. (2017) calculated the ESV of the Poyang Lake Basin based on GIS.

We can see that there is no universal method for assessing the changes and impacts of ES. Most researchers focused on the spatial, regional, and comprehensive characteristics of river basin ecosystem services (Bhandari et al. 2016; Sherrouse et al. 2011). Researchers often use remote sensing (RS), land survey and geographic information system (GIS), and other methods like monitoring, statistics, modeling, or interviews to assess the value and changes occurring in ES at different time and space scales (Zhao et al. 2018; Yang et al. 2018). The service value of a watershed ecosystem is mainly analyzed from the perspective of ecology and economics (Wang et al. 2018). The ESV is estimated by the production cost theory, without considering consumer preferences. The economic value of ecosystem services mainly derives from the exchange value of ecosystem services, which is based on consumers’ preferences but does not fully take into account the ecological mechanism and public service within the ecosystem (Pueffel et al. 2018). These assessment methods guide people to use natural resources effectively and address the imbalance between economic development and state of the environment by quantifying the service value of a watershed ecosystem. Using GIS and RS technology to establish the corresponding evaluation model can simulate and analyze the distribution of ecosystem services in the whole watershed. Due to the special geographical characteristics of the river basin, people mostly choose to live and work in these regions where there are abundant water resources. Consequently, there are obvious spatial differences in the socio-economic forms of different geographical units, such as the upper and lower reaches of the river, the left and right banks, the countryside, and the city.

However, most of the basin-scale ecosystem service research applies the global or regional scale research methods; and the relevant evaluation methods, index systems, and evaluation criteria do not clearly reflect the characteristics of basin ecosystem service evaluation. Furthermore, human psychology and social economic factors are rarely considered (Zhou et al. 2018; Zhang et al. 2001). On the other hand, the forest, grassland, valley, and plain in the basin form a whole ecosystem through rivers, lakes, and reservoirs, which makes it possible to realize the transfer and circulation of material, energy, and information. Most ESV assessments do not subdivide the structure and status of the ecosystem. For example, natural grassland, other grassland, and artificial grassland in a grassland ecosystem are not treated differently. These neglects often make the final assessment results deviate greatly, and subsequently make it difficult for them to be directly applied to watershed management, ecological compensation, and other related policies. Therefore, how to integrate social and economic issues into an evaluation system and refine the ecosystem structure is a key point in the quantitative study of watershed ecosystem services (Pueffel et al. 2018; Zhang et al. 2001; Nie et al. 2017).

Currently, China is experiencing a phase of economic contradiction between development and trying to protect the natural environment. Research on ecologically sensitive areas in the western parts of the country has developed rapidly in recent years. The ecosystem services value of the Heihe, Yellow, Manas, Shiyang, and other river basins have been evaluated and reported (Zhang et al. 2016; Sun et al. 2017; Zhang et al. 2017). Tibet, as an important ecological security barrier in China’s “two screens and three belts” system, has been the subject of only a few studies on ecosystem services at the basin scale (Sharma et al. 2007; Pant et al. 2018). The Lhasa River Basin is the most important agricultural, population, economic, and industrial distribution area in Tibet Autonomous Region, accounting for only 2.7% of the entire Tibet area. It carries 15% of the region’s population and about 30% of the economic output (Hu et al. 2011). There are particular geographical features along the Lhasa River, leading to huge natural space and socio-economic differences in people’s livelihood patterns on the downstream river basin, specifically the rivers, rural, and urban areas, for example, different geographic units. On the one hand, affected by natural geographical and climatic conditions, the ecosystem of the river basin has an obvious distribution pattern, while the upper, middle, and lower reaches of the ecosystem reveal significant differences in how the ecosystem is structured and functions. On the other hand, the population distribution and economic development in the upper, middle, and lower reaches of the river basin and their imbalances will inevitably cause tensions in how ecological resources are used and allocated in the administrative regions of the river basin (Wang et al. 2010a, b, c).

Given the dual characteristics of the fragile and sensitive plateau ecological environment of the river basin and the extremely unbalanced population distribution and economic development in various regions of the river basin, it is necessary to scientifically evaluate the service value of the river basin ecosystem. Doing so will provide strong support for social progress and ecological protection mechanisms in this region. Special natural environmental factors, development, and unbalanced socio-economic factors will exert a great influence on the ecosystem services function and value of a river basin. For this reason, evaluating the ecosystem services provided by the river basin is not only useful for global- or regional-level research and evaluation methods, it also helps to understand the various natural and socio-economic factors that typically affect the value of ecosystem services (Wang et al. 2010a, b, c). The purpose of this study is articulated here. Firstly, it draws on the theory of regional entropy based on the “Service Value Equivalent Table of Unit Area of China’s Terrestrial Ecosystem” by Xie Gaodi and others. Secondly, it establishes a measurement model based on the impact of the differences in natural and socio-economic locations and how these affect the value and measurement of ecosystem services in the river basin. Thirdly, this paper discusses differentiated ecosystem services value enhancement measures and ecological compensation mechanisms based on spatial changes in the river basin’s ecosystem services value.

Materials and methods

Study area

Lhasa River is a first-class tributary of the Yarlung Zangbo River, which originates from the north side of the middle section of the Nianqing Tanggula Mountain (Lhasa Bureau of land and resources 1997). Lhasa River Basin is located in the middle of Tibet Autonomous Region (90° 05′ E-93° 20′ E, 29° 20′ N-31° 15′ N), with a drainage area of 32471 km2 and an average elevation of 4812.26 m (Department of land and resources of Tibet Autonomous Region 2016a, 2016b, 2016c). Administrative areas include Lhasa City, Linzhou County, Dangxiong County, Duilongdeqing County, Dazi County, Qushui County, Mozhugongka County, and Linzhou County (Fig. 1). The climate of the plateau can be described as a cold temperate semi-arid monsoon climate area, and the daily temperature changes greatly (Department of land and resources of Tibet Autonomous Region 2016a, b, c). According to the topographic and geomorphic characteristics and administrative division boundaries of the basin, Lhasa River Basin is divided into upper, middle, and lower reaches. These are the Lhasa River Source (including Naqu County and Jiali County, which are high-altitude areas at the source and upper reaches of Lhasa River), Dangxiong basin (including Dangxiong County), Lhasa River Valley (including Lhasa Chengguan area, Dulong Deqing area, Dazi area, Qushui County, and Mohe area) at the lower reaches of Lhasa River Zhugongka County, and Linzhou County (Wang et al. 2010a, b, c). From 1990 to 2015, the total population of Lhasa River Basin increased from 758,700 to 1,930,700, while the GDP rose nearly 47-fold. Lhasa, located in the valley area, is the political, economic, and cultural center of Tibet and the most densely populated and economically developed core area (Repetto 1992; Brouwere 2000). It is not only beneficial to the well-being of the basin residents, but also important to maintain the ecological security of the basin and Tibet as a whole.

Fig. 1
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Location map of Lhasa River Basin

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Data sources

This study used the 2015 Tibet Autonomous Region Land Use Status Survey Data (Department of land and resources of Tibet Autonomous Region 2016a, 2016b, 2016c) and Image of the second national land survey change data in 2016 (Department of land and resources of Tibet Autonomous Region 2016a, 2016b, 2016c). The land use survey data is classified into the second level, and the second-class land type can be further determined with the image. Meteorological data is from China Meteorological Science Data Sharing Service Network (http://data.cma.cn). The soil data originates from the Chinese soil dataset of the FAO World Soil Database (HWSD) (v1.1) (http://westdc.westgis.ac.cn). DEM data and geomorphological data (resolution 30m) come from the geospatial data cloud website (http://gscloud.cn). The geological hazard data originates from the Tibet Autonomous Region County (City) Comprehensive Survey Report on Geological Hazards and Regional Planning (Department of land and resources of Tibet Autonomous Region 2016a, 2016b, 2016c). The demographic and socio-economic statistics are sourced from the statistical yearbook data of Lhasa, Dangxiong, Lin Zhou, Mozhugongka, and Dazi County in 2015 (Bureau of statistics of Tibet autonomous region 2015).

Methods

Currently, many calculations on the value of ecological services in river basins ignore the spatial heterogeneity of the same type of ecological community. For example, the spatial coverage of the same vegetation type ecosystem is different, the services provided are different, and the ecological value per unit area is also different. Ecosystem services are linked to many factors such as the value of natural capital, scarcity of ecosystems and their services, and the dependence of economic and social progress on the ecosystem (Li et al. 2013; Wang et al. 2014a, b). Ecosystem service value cannot remain constant. Often only single factor variables or key factor variables are used to study the spatial changes in the ecosystem service value. Natural and socio-economic factors will significantly affect the value of ecological services. The Lhasa River Basin has unique geographical units, diverse ecosystem types, and fragile ecological environment; and there are huge social and economic disparities between the upper, middle, and lower reaches. To scientifically analyze the value of ecosystem services, it is necessary to fully consider the spatial differences of ecosystems and the impact of various factors on their value (Peng et al. 2008; Zhang et al. 2010).

This study refers to Costanza et al.’s (2006) and Xie et al.’s (2001a, b) methods for evaluating the ESV per unit area. Taking into account the different ESVs of different secondary classification systems in the ecological community, we introduce the correction coefficient of ecosystem service value (Xie et al. 2001a, 2001b; Li et al. 2006) to obtain the unit ESV of the secondary classification area (Formula 1) according to the second level classification system (Fig. 2). On the other hand, the ESV and natural capital are also affected by the scarcity of ecosystem services and the dependence of economic and social development on ecosystems (Su et al. 2006). Therefore, natural factors and socio-economic location factors are introduced to clarify the differences between natural and socio-economic conditions in the basin (Table S2) (Li et al. 2013). The location factor regarding natural issues mainly indicates that the difference in the location natural disaster index is caused by the different natural location conditions, and in turn creates the inherent inequality of the ecosystem service value in each region. The socio-economic location factor mainly reflects the variations in the development of the location due to the different economic and geographical conditions in each region. The consequence of this is a difference in the level of demand for ecosystem services. The specific method flowchart is shown in Fig. 3.

Fig. 2
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Spatial distribution of ecosystem types in the Lhasa River Basin

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Fig. 3
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Technical flow chart of ecological service value evaluation in the Lhasa River Basin

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Amendment of ESV of secondary classification units

$$ \mathrm{ESV}=\sum \limits_i^n\sum \limits_j^m{A}_{ij}{K}_{ij}{V}_{ij} $$
(1)

Aij is the area of type i primary ecological community and type j secondary ecological community. Kij is the correction factor of unit area ESV for type i primary ecological community and type j secondary ecological community. Vij is area ESV of type i primary ecological community and type j secondary ecological community unit. The results of revising the ecosystem service value per unit area are shown in Table S2.

Natural factor location factor calculation

  1. 1)

    Major natural risks and weights

In this paper, natural factor risk refers to the possible adverse effects of natural disasters and other uncertainties on the ecosystem and its composition in a certain location, including damage to the structure and function of the ecosystem (Zhang et al. 2010). The author establishes a comprehensive natural disaster measurement model through qualitative and quantitative analysis of the main natural disasters that occur in the basin.

According to the statistics of natural disasters by Lhasa Natural Resources Management Bureau and Lhasa Water Bureau, geological disasters, soil erosion, and seasonal floods are the high incidence of natural disasters in the Lhasa River Basin. Therefore, we carried out water and soil erosion, land desertification, and geological hazard sensitivity assessments to divide the sensitive areas of the basin. The evaluation methods are shown in Table 1. Various types of natural risks have different risk effects in different regions (Li et al. 2013). Therefore, AHP is used to determine the comprehensive weights of the three types of natural risks in different regions.

Table 1 Sensitivity evaluation methods for soil erosion and land desertification
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According to the frequency, intensity, and damage degree of natural risk types in the Lhasa River Basin, we determined the disaster index of the same disaster in the river basin and then determined the disaster weight of various disasters included in the natural disaster risk index. Finally, the product of the two is the comprehensive natural disaster risk index for the upper, middle, and lower reaches:

$$ {R}_i=\sum \limits_{j-0}^3{r}_{ij}\times {\omega}_j $$
(2)

Ri is the comprehensive natural disaster index in area i; rij is the index of type j disasters in area i; ωj is the weight of type j disasters in the river basin.

  1. 2)

    Ecological loss index

The ecological loss referred to in this article refers to the damage done to ecosystem functions caused by disasters in a certain area (Peng et al. 2008). Different ecosystem types have different anti-interference capabilities for the same kind of natural risks, which also results in a different Ecological Deduction Index (EDI) for various types of ecosystems (Stahl et al. 2005). We can use the Ecological Anti-interference Index (EAI) and Fragile Degree Index (FDI) of the ecosystem to reflect the loss of different ecological risks to different ecological types.

  1. 1)

    The Ecological Anti-interference Index (EAI) refers to the ecosystem’s self-sustainment, self-regulation, and its ability to resist various pressures and disturbances. The size of the ecosystem’s anti-interference index reflects the buffering and regulating capacity of a particular ecosystem. The calculation method is shown in Table 2.

  2. 2)

    The Fragile Degree Index (FDI) refers to the vulnerability of an ecosystem after being disturbed by external factors. Ecological sensitivity is the specific representation of the temporal and spatial changes of ecological environment vulnerability. When calculating the vulnerability of the ecological environment, we should consider the geographical spatial differences within the region. In this paper, when calculating the vulnerability index of the ecosystem, firstly, the environmental vulnerability of upper, middle, and lower reaches of Lhasa River Basin is included. Following this the vulnerability index of each ecosystem is obtained by integrating the vulnerability of each ecosystem. Six indexes—geological hazard, desertification, biodiversity, soil erosion sensitivity, water conservation, and farmland pressure—are selected, and their weights are determined via the entropy weight method (Peng et al. 2008). The calculation method is shown in Table 2.

  3. 3)

    Ecological deduction index (EDI)

Table 2 Calculation methods of natural location factors for ESV
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Facing the same environmental risks in the same area, the degree of ecological loss of different ecosystems differs. We can use the outcome of the anti-interference index of an ecosystem and the vulnerability of the region to reflect the EDI of different ecosystems in that region. The calculation method is shown in Table 2.

  1. 3)

    Comprehensive Ecological Risk Index of Natural Location

Based on the three frequently occurring types of natural disaster in the Lhasa River Basin, i.e., geological hazards, soil erosion, and seasonal floods. According to the three types of risk intensity distribution, ArcGIS was used in this study to add a map of the current state of land use in the Lhasa River Basin. The purpose was to form a risk zone division in the upper, middle, and lower reaches of the river basin and calculate the Natural Ecological Risk Index (NEI) (Table 2).

Socio-economic location factor calculation

ES and ESV are affected by the scarcity of ecosystems and services and the degree to which economic and social development depends on ecosystems (Li et al. 2006). The development of the Lhasa River Basin varies greatly. The middle and upper reaches have a backward economy and are sparsely populated. The lower Lhasa River Valley is the most densely populated and economically developed core area of the Tibet Autonomous Region. It is evident that the increase in demand for resources and pressures on the environment have increased the scarcity of resources and affected the value of natural capital. This study reflects the impact of the socio-economic location of the basin on the ESV through the socio-economic location entropy LEi and the regional socio-economic comprehensive strength Si (Johst et al. 2002).

  1. 1)

    Socio-economic factors regional entropy

Drawing on the definition of location entropy, introduced here is the socio-economic location entropy(LEi) to reflect the relationship between socio-economic factors and spatial changes in the ecological service value (Li and Bian 2008). According to the relative concentration of regional economic and natural factors in this region, the superiority or relative position of the region can be determined (Table 3).

  1. 2)

    Regional socio-economic comprehensive strength

Table 3 Calculation method of socio-economic impact factors of ecosystem service value
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We selected 16 indicators in 5 areas including regional economic development (gross regional product, industrial added value above designated size, local fiscal budget revenue, total retail sales of social consumer goods), social security level (GDP per capita, public fiscal budget expenditure, urban aid funds), living standards (rural control income, per capita consumption level, per capita savings), science and education level (education, culture and sports expenditure, number of primary and secondary schools), and amount of infrastructure (investment, effective farmland irrigation area, fixed asset investment). We employed the entropy weight method to measure the socio-economic strength of the region and especially that of the cities and counties in the river basin (Zhang et al. 2010). The calculation method is shown in Table 3.

Estimating the ESV

Based on the analysis of natural and socio-economic location factors, the ecological service value of the river basin is calculated. The calculation method is shown in Table 4.

Table 4 Calculation method of ecosystem service value
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Results

Comprehensive ecological risk assessment of natural factors

Ecological loss degree

According to the calculation results concerning the extent of ecological loss in Table 5, after the Lhasa River Basin suffers from the same ecological risk source, the ecological loss degree of different ecosystems in the upper, middle, and lower reaches is quite different. For example, the ecological loss degree of natural grassland is midstream > upstream > downstream, and for lakes, the order is upstream>midstream > downstream.

Table 5 Ecological loss index of ecosystem in Lhasa River Basin
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Comprehensive ecological risk value of natural factors

After the comprehensive risk value of natural factors in each risk area is normalized (Table S3), cluster analysis is carried out with SPSS 16.0, and each risk area is divided into three levels (Fig. 4). The first-level ecological risk areas of the Lhasa River Basin are mainly distributed in the northern and southern parts of Jiali County, the central part of Naqu County, and the northern and eastern parts of Dangxiong County in the upstream region. These account for 48.85% of the whole basin area, and the vegetation types in this area are mainly natural grassland and forest land. The characteristics of ecological risks are complex geological environment, steep terrain, frequent geological disasters, serious soil erosion, and fragile ecosystem. Therefore, the protection of the grassland-based ecosystem should be strengthened to reduce economic development activities. The secondary-level ecological risk areas are mainly distributed in the Lhasa River Valley, among which the southern part of Linzhou County in the middle of the river valley and the northern part of Chengguan District are most concentrated. Meanwhile, the eastern section of Mozhugongka County in the river valley’s eastern part and the central part of Duilongdeqing County in the western part of Lhasa River Valley are scattered, and the secondary ecological risk areas account for 30.38% of the whole basin area. The vegetation types in this area are mainly natural grassland and shrubbery. The characteristics of ecological risk are clearly affected by land desertification and soil erosion. Meanwhile, precipitation is concentrated in summer, which makes the summer floods frequent and other seasons prone to drought. The third-level ecological risk areas with poor anti-interference ability are mainly distributed in the northwest of Dangxiong County and the Lhasa River Source, accounting for 20.09% of the basin area. The main ecological types in this region are glaciers, permanent snow cover, and other grasslands, and the characteristics of ecological risks are as follows. The anti-interference ability of this region’s ecosystem is mainly affected by geological disasters, and the ecological risk areas are diverse and relatively scattered, some of which are distributed in densely populated areas.

Fig. 4
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Spatial distribution of natural ecological risk in Lhasa River Basin

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Calculation of socio-economic location factors

In order to compare the distribution trend of vegetation coverage and regional comprehensive strength in Lhasa River Basin, the ecosystem service values of the upper, middle, and lower reaches were normalized. Table 6 shows that the ecological environment of Lhasa River Basin is clearly inconsistent with the economic distribution in the region, and there are two obvious distribution relationships. Firstly, the area with low level economic development and vegetation coverage is the Lhasa River Source in the upper reaches and the Dangxiong basin in the middle reaches. The forest area of the Lhasa River Source is only 7.29% of the total area. Influenced by global warming and human factors, the Lhasa River Source has revealed ecological problems such as water source reduction, grassland degradation, and soil desertification in recent years. The grassland ecosystem accounts for 81.76% of the total area of Dangxiong basin, while the forest land only accounts for 4.64% of the total area. The average altitude of the Lhasa River Source and Dangxiong basin in the middle reaches is more than 4200m. The development of agricultural production and industry in the area is limited by natural factors such as high altitude and cold.

Table 6 Regional comprehensive strength and ecosystem service value index of Lhasa River Basin
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Secondly, the area with high level of economic development and vegetation coverage is mainly distributed in the Lhasa River Valley. Most of this valley belongs to Lhasa City which is the political, economic, and cultural center of Tibet and the most densely populated core area. The forest coverage in the valley area is relatively high, accounting for 20.66% of the total area. However, the ecology and economic development level of each county in Lhasa River Valley shows obvious spatial differences. For example, Chengguan District reveals typical characteristics of high economic development and low vegetation coverage. Linzhou County, Qushui County, and Dazi County betray characteristics of low economic development level and high vegetation coverage. Lastly, Deqing County and Mozhugongka County in Duilong indicate typical characteristics of low economic development level and low vegetation coverage.

Calculation of ecosystem service value per unit area

According to the difference coefficient of natural conditions for each type of ecosystem in Lhasa River Basin (Table 7), it can be stated that each ecosystem in the basin is significantly affected by natural conditions. Among them, water and forest ecosystems will be easily affected by natural conditions and have strong natural sensitivity. Farmland in the downstream is greatly affected by natural location factors. The forest ecosystem confirms that the upper and lower reaches are influenced by the natural factors of location. The grassland ecosystem in the middle and upper reaches is greatly affected by these factors. Wetland and desert ecosystems are greatly influenced by regional natural factors in the middle and lower reaches.

Table 7 Difference coefficient of regional natural conditions in Lhasa River Basin
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The ESV of the same ecosystem system varies significantly in different regions of the basin (Table 8). Especially, grassland, woodland, farmland, water body, and wetland ecosystems have higher ecosystem service value per unit area in the downstream than in the upstream and middle reaches. The unit ecosystem service value of natural grassland in the Lhasa River Valley is 5.6 times and 1.07 times larger than that in the Lhasa River Source and Dangxiong basin, respectively. The main reason is that the scarcity of ecological service supply in the upper and middle reaches is relatively low. The large area of forest land and grassland ecosystem and relatively less ecological demand make this area a typical ecological “output” area. However, the population and economy in the downstream areas are relatively concentrated, and the ecological demand is strong, so the value of ecosystem services rises due to scarcity. On the other hand, the cultivated land in the Lhasa River Basin is mainly distributed in the lower river valley. Farmland ecosystem is not only an important economic production system, but also an important ecological service system. Due to the tight supply of regional ecological services, especially the threat of desertification in the lower reaches of Lhasa River, the value of cultivated land ecosystem services is increasing.

Table 8 Ecosystem service value per unit area of each type of ecosystem in Lhasa River Basin (Yuan/hm2)
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According to the spatial distribution map of ecosystem service value per unit area of Lhasa River Basin (Fig. 5), ecosystems with a high level of ecosystem service value in the basin are mainly distributed in the middle of Lhasa River Valley and the areas near the two sides of Lhasa River. The ecosystem with a high level of ecosystem service value in the basin is mainly distributed in the middle of Lhasa River Valley and the two banks near Lhasa River. The distribution area of an ecosystem with high ecosystem service value (317799.255–1099055.576 Yuan/hm2) in the upper, middle, and lower reaches of each region is 0.47%, 13.2%, and 25.51%, respectively. The high ecosystem service value area of the Lhasa River Source is mainly distributed in Cuoduo Township, Jiali County. The high ecosystem service value area of the Lhasa River Source of Dangxiong basin area is mainly distributed in Gongtang Township in the northwest and middle of Dangxiong County. The high ecosystem service value area of the Lhasa River Source of Lhasa River Valley area is mainly distributed in the coastal area of Lhasa River, among which the central and western part of Mozhugongka County is relatively concentrated in the north of Linzhou County and the central part of Qushui County, while other areas are relatively scattered.

Fig. 5
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The spatial distribution map of ecosystem service value per unit area of Lhasa river basin

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The ecosystem service value of Lhasa River Basin is 140.503 billion yuan. The proportion of land area in the upper, middle, and lower reaches of the basin is 31.14%, 22.21%, and 46.65%, respectively, while the proportion of ecosystem service value is 4.17%, 21.48%, and 74.35%, also respectively. The service value of the ecosystem in Lhasa River Valley is obviously affected by the comprehensive strength of unit area and socio-economic location factors. The ratios of the comprehensive strength per unit area of the upper, middle, and lower basins to that of the Lhasa River Basin are 0.12, 0.22, and 3.10, respectively; and the regional entropies of social economy are 0.21, 0.63, and 2.15, respectively. From the perspective of natural ecological risk, the first-class ecological risk area in Lhasa River Source accounts for 79.55%, and the first-class ecological risk area in Dangxiong basin accounts for 70.11%. Lhasa River Valley is mainly a secondary ecological risk area, accounting for 58.91%. Therefore, the ecosystem service value of Lhasa River Valley is higher than that of Dangxiong basin and the Lhasa River Source.

Discussion

Scarcity of ecological resources has a significant impact on ecosystem service value

Most studies on the value of ecosystem services in high-altitude areas focus on the temporal and spatial changes of ecosystem services, focusing on the impact of natural factors on ecosystem supply, or on the correlation between land use and the value of ecosystem services through temporal changes. The value of ecosystem services obtained through the revised calculation of natural and socio-economic location factors confirms that different regions have varying degrees of scarcity of ecosystem services due to the specific level of economic and social development, thus affecting the changes in ecosystem service values. The Lhasa River Source is mainly stockbreeding, with small population density and lagging economic development, while the Dangxiong basin is the most important pastoral area in Lhasa River Basin. The population and economic development in the upper and middle reaches exert less pressure on the environment, and the scarcity of ecological services is relatively low. The population of Lhasa River Valley is relatively concentrated. According to the statistics, the total population of Lhasa River Valley in 2014 was 1,093,700, of which the total population of Lhasa City, which belongs to Lhasa River Valley, was 902,500 in 2014, accounting for 82.52% of the basin’s total population. The level of agriculture, industry, tourism, and other industries in the Lhasa River Valley is relatively high, and it is the most developed area in Tibet’s economy. In 2014, the total social and economic output value of Lhasa River Valley accounted for 87.25% of Lhasa River Basin.

There are great differences in the social and economic location entropy among the upper, middle, and lower reaches of the basin. The calculation results regarding the value of integrated ecosystem services show that the value of integrated ecosystem services in the upper, middle, and lower reaches accounts for 2%, 21%, and 74% of the total value, respectively. This data fully reflects the impact of the lack of actual ecological resources relative to the demand in the process of sustainable economic, social, and environmental development in the lower reaches on the value of ecological services. According to the social and economic data of Lhasa from 2010 to 2014, the 5-year average growth rate of regional GDP in Lhasa is 12.3%. The average growth rate of fixed assets in the whole society is 25.3%, while the average growth rate of per capita disposable income of farmers and herdsmen is 15.7%. Meanwhile, the average growth rate of per capita disposable income of urban residents is 10.2%; the average growth rates of tourist reception and total tourism income in Lhasa are, respectively, 27.35% and 38.73%. Social and economic prosperity is occurring at the same time as rising demand for ecosystem services. The rapid construction of all kinds of economic development zones in the Lhasa River Valley area has led to changes in land usage and the decline in ecosystem service supply in the short-term. As a result, the value of ecosystem services per unit has significantly improved. The huge demand for ecosystem services in the Lhasa River Valley region has led to increased scarcity and soaring value of ecosystem services.

Finding different ways to improve the value of ecosystem services from the differences in the ecological service contribution of the river basin ecosystem

According to research on the value equivalent of ecosystem services in China by Xie et al. (2008), there are differences in the value of ecosystem services of various ecosystems, such as forest land, wetland ecosystem services. These are higher than grassland and cultivated land ecosystems (Xie et al. 2008). According to the secondary classification system (Fig. 2) of land use status survey data in Tibet Autonomous Region, the service value of the secondary classification area’s unit ecosystem is obtained by introducing the correction coefficient of the service value of the ecosystem (Table S2). On this basis, natural and socio-economic location factors are considered as reflecting the spatial change of service value of different ecosystems (Table 8, Table S4). In the Lhasa River Basin with an average altitude of 4000 m, the same vegetation ecosystem is distributed in different spaces, with varied coverage and socio-economic locations on the alpine plateau, resulting in obvious differences in the ecological services and values provided. The grassland area of the Lhasa River Source accounts for 88.66% of the area and 79% of the value of ecosystem services. The grassland ecosystem and water ecosystem areas in the Dangxiong basin account for 81.75% and 6.94%, respectively, while the grassland and water are 52% and 37%, respectively, in terms of ecosystem service value.

The area ratios of grassland, forest land, wetland, and farmland ecosystem in Lhasa River Valley are 67%, 19.65%, 1.88%, and 3.45%, respectively, while the service value ratios of ecosystem are 29%, 55%, 7%, and 7%, respectively. There are significant differences in the value of ecosystem services in different locations of the same ecosystem. Therefore, it is necessary to determine differentiated ecological protection measures in the basin to consolidate the comprehensive management of the basin and correspondingly improve the value of ecosystem services. For example, we should strengthen water conservation and biodiversity protection in the Lhasa River Source and promote the moderate development of animal husbandry. The grassland shall be protected and improved by fencing, water diversion, and irrigation. On the other hand, in view of the high ecosystem service value of wetland, we should strengthen the protection of the wetland ecosystem, and especially refine the wetland protection measures represented by Maidika International Wetland Reserve in the Lhasa River Source. In Dangxiong basin, water conservation and alpine biodiversity conservation are emphasized, and the alpine meadow ecosystem is continuously restored by controlling over-grazing. With the rapid rise in the population, agriculture, industry, and tourism in Lhasa River Valley, we should pay attention to enhancing irrigation agriculture, flood control, windbreak, and sand fixation; increase the coverage of grassland; and protect and restore the wetland represented by Lalu wetland. Doing so will improve the value of ecosystem services in the Lhasa River Valley.

Analysis of the mechanism concerning ecological compensation based on the value of ecosystem services

Ecological compensation is an effective mean to coordinate the contradiction between regional environmental protection and economic development, and find a better balance between the profit and loss within the basin. The evaluation of ecosystem service function helps to realize ecological compensation and the basis of establishing compensation amount (Costanza et al. 1997; Daily 1997). For a long time, determining the basis and standard of ecological compensation only establishes the ecological compensation mechanism with difficulty (Wang et al. 2014a, b; Costanza et al. 2014). At present, the practice of ecological compensation in China is mainly based on the cost of ecological construction. The point of compensation is to improve environmental benefits, which means ignoring the opportunity cost of economic development lost by the region to maintain the ecosystem. In any case, the amount of compensation paid is low (Zhang et al., 2015). Ecosystem service functions reflect the value of various services obtained by people from the natural environment, and are the basis for generating ecological compensation (Xie et al. 2015a, b).

This study is based on the ecosystem service value evaluation system established by comprehensive natural and socio-economic location factors, fully considering the spatial differences of the ecosystem service value of the river basin. This provides a basis for determining the ecological compensation standard of the river basin differentiation. According to Table S4, the total value of ecosystem services in Lhasa River Basin in 2015 was 104.503 billion yuan. The level of ecological compensation corresponds to the value of ecosystem services. Among different ecosystem types, forest value is the highest, and the compensation amount accounts for 42.05% of the total compensation standard, which is the core of ecological compensation in Lhasa River Basin. Then grassland, water body, wetland, and farmland accounted for 35.78%, 10.96%, 6.27%, and 4.71% of the total value, respectively. The value of forest and grassland in Lhasa River Basin accounts for 77.83%, which plays an irreplaceable role in the value of ecological services. However, the weight of farmland in the ecosystem service value of the basin is relatively small, so returning farmland to forest and grass can be properly implemented. This will in turn greatly improve the overall ecosystem service value of the basin.

The spatial difference of ecosystem service value in the upper, middle, and lower reaches of Lhasa River provides a more accurate basis for “differential back feeding.” Through the value evaluation of ecosystem services, the order of priority order regarding regional ecological compensation can be determined, and the effect of ecological compensation can be maximized. Based on the evaluation of ecosystem service value, the regional ecological compensation standard can be estimated according to the intensity coefficient of regional ecological compensation demand and the conversion coefficient of ecological value (Xie et al. 2015a, b; Lai et al. 2015). The actual amount of ecology-based compensation for the nine districts and counties in Lhasa River Basin is 14.569 billion yuan, of which the maximum amount for Mozhugongka County is 4.301 billion yuan, accounting for 29.52% of the total. The second is Linzhou County and Dangxiong County, which are 3.357 billion yuan and 3.298 billion yuan, respectively, accounting for 23.04% and 22.64% of the total compensation. The minimum supplementary amount of Chengguan District is 19 million yuan, which is only 0.13% of the total compensation figure. There are great differences in economic development among the upper, middle, and lower reaches of Lhasa River Basin. According to the Gross Regional Product of each district and county in 2015 (Table 9), it can be concluded that the ECPs of each district and county (Cui et al. 2015), except Chengguan District, are all greater than 1 (Table 9). Furthermore, the priority compensation order is Dangxiong County, Mozhugongka County, Linzhou County, Jiali County, Qushui County, Dulong Deqing County, Naqu County, and Dazi County.

Table 9 Ecological compensation standard of Lhasa River Basin (billion yuan)
Full size table

Lhasa River Basin is located in an area characterized by much poverty. Over the years, the middle and upper reaches of the region have made great contributions to protect the local ecological system, but at the cost of development opportunities. Economic development is at a low level in the basin, and priority has been given to ecological compensation. Elsewhere, the economic development level of the downstream area-especially Chengguan District is relatively high, so ecological compensation receives only low priority. The counties of Naqu, Jiali, and Dangxiong are all national key poverty alleviation locales. Because the middle and upper reaches of the county belong to high-altitude mountainous areas, the construction of an ecological environment is of great significance. Therefore, although the total ecosystem service value of these areas is far less than that of the Lhasa River Valley, the priority of ecological compensation should be maintained, and the economic policy of limited animal husbandry development should be strictly implemented only on the premise of protecting the regional environment. In Lhasa River Valley, the overall ecosystem service value is much higher than that in the upper and middle reaches. Chengguan District, as an ecological benefitting area, should take the lead in paying compensation to other districts and counties. In order to enhance the effectiveness of ecology-based compensation, the next step should be based on the needs of the environment and economic development of the basin. What should be devised is a compensation implementation plan that is suitable for the economic level of the basin. In this scheme, the cost of ecological protection and restoration, the compensation willingness of both the supply and demand of ecosystem services, and the ability to pay compensation can be combined to further explore the amount of ecological compensation.

Conclusion

The river basin ecosystem provides many important services to communities. Quantitative assessment of the value of watershed ecosystem service functions and dynamic assessment of them changes when the conditions of social and economic progress also change. This is coupled with the scarcity of ecological resources and is of significance for making reasonable decisions on watershed ecosystem protection and economic development. The ecosystem service value per unit area proposed by Costanza et al. does not consider the spatial heterogeneity of ecosystem services, and the value of the ecosystem itself is related to the structure and function of the ecosystem. When practically applied to making decisions about the best allocations of water and soil resources, it is the scarcity of resources and the willingness to pay for ecological value that change with the level of socio-economic development. Socio-economic location factors can more accurately and quantitatively reflect the changing laws of ecological value and how these work in tandem with socio-economic development. The increase in resource demand and resource scarcity caused by socio-economic changes takes into account the evolution of regional ecological resources. Based on the two revised calculation methods, the service value of plateau watershed ecosystems can be more comprehensively understood, and it provides a strategy to improve how ecosystem service functions are used for plateau watershed ecosystem research.

The Lhasa River Basin is an important addition to the database on plateau biodiversity and ecosystem services. The ecosystem of the basin is sensitive and fragile, and maintaining its ecosystem services is vital. The upper and middle reaches of the basin are the areas where water resources form, while the downstream areas are where the water is consumed. According to this paper’s research results, it is evident that the lower reaches of the Lhasa River Basin are experiencing large resource shortages and stronger demand for ecosystem services. It also reflects the fact that the ecological value of the unit area of the ecological community is higher than that of the upper and middle reaches. This provides a practical guideline for ecological protection of plateau river basins and the rational allocation of resources in the upper, middle, and lower reaches, and the formulation of differentiated ecological compensation standards in the basin. Future research, in view of the huge social, economic, and population disparity between the upper, middle, and lower reaches of the river basin, should select more criteria and weight settings of social and economic factors, so that a more comprehensive evaluation of the value of the river basin’s ecosystem services can be carried out. At the same time, given the market nature of the economy, how to realize the value of the natural environment and perfect the ecological compensation mechanism is the next stage of research.