Tradeoff between Hydropower and River Visual Landscape Services in...

[Full title: Tradeoff between Hydropower and River Visual Landscape Services in Mountainous Areas]

sustainability Article Tradeo ff between Hydropower and River Visual Landscape Services in Mountainous Areas Bin Fu 1,2 and Naiwen Li 3, * 1 Institute of Mountain Hazards and Environment, Chinese Academy of Sciences, Chengdu 610041, Sichuan, China; fubin@imde.ac.cn 2 University of the Chinese Academy of Sciences, Beijing 100049, China 3 State Key Laboratory of Hydraulics and Mountain River Engineering, College of Water Resource & Hydropower, Sichuan University, Chengdu 610065, Sichuan, China * Correspondence: gxqlnw@163.com; Tel.: + 86-028-8546-1112 Received: 9 August 2019; Accepted: 25 September 2019; Published: 5 October 2019 Abstract: Water retention is one of the important services provided by ecosystems. Water retention is also the basis for multiple other services, such as hydropower development, river continuity, and biodiversity. However, there are clear tradeo ff s among these services. Tradeo ff s are already a hot topic in ecosystem services research, but the tradeo ff between hydropower and river visual landscape services (RVLS) has not yet been investigated. In this study, we used the Integrated Valuation of Ecosystem Services and Trade-o ff s (InVEST) hydropower model for spatial mapping of watershed services. The proportion of the inflow of power stations to annual flow was proposed as the indicator for RVLS. Finally, based on an evaluation of historical hydropower development, di ff erent flow recovery scenarios were set up, and the tradeo ff relationship between hydropower and landscape services was analyzed. The results showed that the tradeo ff between the hydropower service and RVLS in mainstream displayed obvious spatial and temporal changes. With the development of hydropower, the increase of hydropower services caused a rapid decline in RVLS. The di ff erence of two service scores fell from 1.0 in 1958 to 0.52 in 2015. The tradeo ff intensity showed a turbulent decline downstream, which was closely related to the cascades’ development. The tradeo ff was reversible. Through the flow scheduling of the reservoir group, the RVLS of each river section can be basically restored, while the hydropower service decline was only 29% Keywords: ecosystem services; spatial tradeo ff s; watershed management; ecological restoration; ecological flow; Zagunao River 1. Introduction Ecosystem services are the benefits that humans obtain from ecosystems [ 1 ]. The provision of ecosystem services depends on the structure and function of various ecosystems. Based on ecology and economics, di ff erent classifications of ecosystem services are developed. Among them, the four types of classification of supporting, provision, regulation, and culture service proposed by the Millennium Assessment are the most popular [ 2 ]. Rivers provide a variety of services in these four aspects, directly a ff ecting human wellbeing [ 3 ]. Rivers provide a habitat for aquatic animals, which is a supporting service for maintaining aquatic biodiversity [ 4 ]. Provision services are the most important services of rivers. For instance, many urban water supplies rely heavily on surface water delivered by rivers. About 16% of global electricity demand is also met by hydropower services [ 5 ]. Adjusting services are also prominent. In the process of transporting water and energy, rivers regulate the local climate along the river [ 6 ], and runo ff is purified due to the river self-cleaning e ff ect [ 7 ]. Compared to these services that are not easily perceived Sustainability 2019 , 11 , 5509; doi:10.3390 / su 11195509 www.mdpi.com / journal / sustainability

Sustainability 2019 , 11 , 5509 2 of 20 by the public, swimming, fishing, sightseeing, environmental education, and other activities are more common for people to enjoy rivers ecosystem services, reflecting the cultural ecosystem services of rivers [ 8 , 9 ]. The multiple services of the river interact with each other, resulting in tradeo ff s and synergies For example, the river a ff ects people’s activities such as walking or sightseeing by changing the temperature and humidity in the waterfront. This reflects the tradeo ff between climate regulation services and recreational services. In general, tradeo ff s usually occur between food production and water purification, while water quality regulation and fishery production are synergy [ 10 ]. Tradeo ff is the variation among multiple ecosystem services [ 11 ]. This topic is a hotspot in current ecosystem service research. Tradeo ff s can generally be divided into time tradeo ff s, spatial tradeo ff s, and reversible tradeo ff s [ 11 ]. Research focuses on the interaction of multiple ecosystem services, quantification of tradeo ff relationships, mechanisms, and scale e ff ects [ 12 – 14 ]. Case studies reflect an in-depth understanding of the interrelationships between multiple ecosystem services, confirming that tradeo ff s or synergies are common. They often involve tradeo ff s between supply services and regulation services [ 12 ], and there is a synergy between regulation and support services [ 15 ]. Tradeo ff research provides an important foundation for ecosystem-based management. Tradeo ff s can be used to analyze the preferences of multiple stakeholder groups for cultural services [ 16 ], or to assess the integration of traditional agriculture with modern agriculture [ 17 ], or to manage the grazing activities in pastures [ 18 ]. When designing wind power plants in the ocean, tradeo ff can be used to identify potential conflicts among the wind energy, commercial fishing, and whale watching industries [ 19 ]. For watershed management, tradeo ff s can be used to assess the benefits of increased hydropower relative to potential fishery production losses [ 20 ], or to discuss the relationship between energy production and flood protection [ 21 ]. The tradeo ff relationship can vary with the region. For example, vegetation carbon sequestration and freshwater supply services are synergy in the Baiyangdian watershed, China [ 22 ], while they are tradeo ff in the Urduba natural reserve area in Spain [ 23 ]. Coastal protection and tourism recreation services are synergy in Quebec, Canada [ 24 ], but tradeo ff s in Bonaire, the Netherlands [ 25 ]. Regional di ff erences suggest that ecosystem service space assessment is the basis for tradeo ff s The spatial and temporal characteristics of ecosystem services were explored through ecosystem services mapping [ 26 , 27 ], explaining the scale characteristics of ecosystem services [ 28 ]. The importance of spatial relationships in the assessment of ecosystem services is highlighted. A more complex integrated modeling approach that combines spatial and temporal changes in ecosystems with socioeconomic feedback can help to assess ecosystem services impacted by human activities [ 29 ]. River ecosystems have obvious multiscale characteristics, and it is hard to determine spatial boundaries. Therefore, ecosystem services assessment for a specific river or river section is rare. Most studies of river ecosystem services are carried out from the perspective of freshwater ecosystems or watersheds. Some studies analyze the spatial characteristics of rivers from a landscape scale [ 27 , 28 ], but lacking the combination of hydrological characteristics and landscape The European Landscape Convention defines landscapes as places that people perceive, and which are characterized by a natural and / or human factor [ 30 ]. Landscapes include not only natural and artificial elements perceived visually, but also through olfaction, taste, and even the historical and cultural values [ 31 ]. The river vision landscape service (RVLS) is an integral part of river cultural services, resulting from the shape, color, and flow of rivers. RVLS is di ff erent from the spatial landscape unit, which produces di ff erent ecosystem services from single ecosystems [ 32 ]. The indicators for landscape visual service evaluation vary with the objective. A comparison of the modeling methods of InVEST and ARIES found that di ff erent models have more similar carbon evaluation indicators, but it is hard to compare visual landscape evaluation [ 26 ]. Visual field indicators have a good application on the analysis of mountain landscapes. However, the main component of the river visual landscape is the water body, and the horizontal perspective does not fully reflect the

Sustainability 2019 , 11 , 5509 3 of 20 characteristics of the river vision. Runo ff is of paramount importance in water services [ 33 ]. Water quantity is a decisive factor a ff ecting the aesthetic and recreational functions of river ecosystems and their economic value [ 34 ]. The scientific assessment of the tradeo ff s of multiple services requires a study of the impact of multiple human activities and their associated stressors on the ecosystem [ 35 ]. Hydropower development is the main way to address energy demand and is especially important in developing countries. However, hydropower development, while meeting energy needs, also causes adverse environmental impacts such as biodiversity loss, river erosion, and water temperature changes [ 36 , 37 ], leading to a drop in ecosystem services [ 38 ]. Although the problem of river landscape change brought by hydropower is very prominent, the tradeo ff relationship between hydropower development and landscape services has rarely been studied. Darvill found that cultural ecosystem services are more important to participants than supply ecosystem services, especially aesthetics / landscape values [ 16 ]. However, there is no discussion of the tradeo ff between hydropower services and cultural services Southwest China is a hydropower enrichment area. The upper reaches of the Minjiang River are the earliest developed area in the region, where water retention and biodiversity are the two most concerned services. The rapid hydropower development process experienced before 2015 has exceeded the development limits in many river basins [ 29 ]. As the demand for energy has decreased in current, the demand for cultural services has begun to increase, but the tradeo ff between hydropower development and RVLS has not been reported. Based on a quantitative assessment of hydropower and RVLS, scenario analysis was used in this study to examine tradeo ff s with ecosystem services, following which proposals for corresponding management strategies were developed 2. Materials and Methods 2.1. Study Area The study area is located in the River Zagunao basin in Western Sichuan (Figure 1 ). The River Zagunao is a primary tributary of the River Minjiang with an area of 4300 km 2 and a length of 158 km The river basin belongs to Li County, Sichuan Province, and its economic center is located in Zagunao. This is the main area inhabited by the Yi people. In 2017, the registered population was 44,459, and the GDP was 245.92 million yuan. The county landforms are dominated by alpine valleys, with forests and grasslands widely distributed, accounting for 56.6% and 25.5%, respectively, of the total area. Natural ecosystems provide important ecosystem services downstream, the most important of which is water retention. The average annual runo ff of the river basin is 110.0 m 3 / s, and the large drop in elevation produces abundant water energy. In 1958, the first hydropower station on the upper reaches of the River Minjiang was built, and hydropower development became an important driving force for the region’s economy [ 39 ]. At the same time, rich natural and human resources have also formed the basis of important cultural services that attract many tourists. The main scenic spots include the Miyaluo Redleaf Scenic Area and Taoping Qiang Village.

Sustainability 2019 , 11 , 5509 4 of 20 Sustainability 2019 , 11 , x FOR PEER REVIEW 4 of 21 Figure 1. Hydropower development in the study area. 2.2. Research Framework The main method of ecosystem service tradeoff investigation is to compare the differences among various ecosystem services at different time and space scales through scenario analysis and spatial mapping using the InVEST model, the ARIES model, etc [40]. In addition, methods such as the Pareto curve, root mean square deviation, multiobjective decision making, redundancy analysis, and hierarchical cluster analysis have been used [41,42]. The InVEST toolset provides a variety of models for ecosystem services assessment and can be used to analyze the tradeoffs among different services effectively. The outstanding features of InVEST software are structured and have low data requirements, leading to wide application [40]. The ARIES model has powerful spatial analysis capabilities, but there have not been enough case studies in China [43]. The Pareto curve is derived from economics, also known as the production possibility boundary or the efficiency frontiers [44]. The point of the curve is that the tradeoffs of the two services can be visually reflected in graphs, but they do not reflect the quantitative relationship [45]. Scenario analysis is an effective decision support tool that assesses climate change, land use change, and changes in ecosystem services under different resource management models to identify their tradeoffs [46,47]. We combined the InVEST model, the Pareto curve, and scenario analysis to analyze the tradeoff between hydropower and landscape services. The main process is as follows (Figure 2): Step 1: Carrying field investigations to clarify the pattern and process of hydropower development. In May 2014, we conducted a survey of the hydropower station in the Zagunao watershed. We visited each power station along the mainstream and determined the location of dams and plants. We collected basic information on the power station, including the construction time, type, scale, inflow, and annual generated electrical energy. According to the distribution of dams and plants, the Zagunao watershed was divided into 18 sub-basins. The runoff amount of each dam was calculated according to the sub-watershed boundary. Figure 1. Hydropower development in the study area 2.2. Research Framework The main method of ecosystem service tradeo ff investigation is to compare the di ff erences among various ecosystem services at di ff erent time and space scales through scenario analysis and spatial mapping using the InVEST model, the ARIES model, etc [ 40 ]. In addition, methods such as the Pareto curve, root mean square deviation, multiobjective decision making, redundancy analysis, and hierarchical cluster analysis have been used [ 41 , 42 ]. The InVEST toolset provides a variety of models for ecosystem services assessment and can be used to analyze the tradeo ff s among di ff erent services e ff ectively. The outstanding features of InVEST software are structured and have low data requirements, leading to wide application [ 40 ]. The ARIES model has powerful spatial analysis capabilities, but there have not been enough case studies in China [ 43 ]. The Pareto curve is derived from economics, also known as the production possibility boundary or the e ffi ciency frontiers [ 44 ]. The point of the curve is that the tradeo ff s of the two services can be visually reflected in graphs, but they do not reflect the quantitative relationship [ 45 ]. Scenario analysis is an e ff ective decision support tool that assesses climate change, land use change, and changes in ecosystem services under di ff erent resource management models to identify their tradeo ff s [ 46 , 47 ]. We combined the InVEST model, the Pareto curve, and scenario analysis to analyze the tradeo ff between hydropower and landscape services. The main process is as follows (Figure 2 ): Step 1: Carrying field investigations to clarify the pattern and process of hydropower development In May 2014, we conducted a survey of the hydropower station in the Zagunao watershed. We visited each power station along the mainstream and determined the location of dams and plants. We collected basic information on the power station, including the construction time, type, scale, inflow, and annual generated electrical energy. According to the distribution of dams and plants, the Zagunao watershed was divided into 18 sub-basins. The runo ff amount of each dam was calculated according to the sub-watershed boundary.

Sustainability 2019 , 11 , 5509 5 of 20 Step 2: Using the InVEST water production model to assess water retention. Referring to the method proposed by Fu et al., the value of hydropower services is calculated based on the amount of electricity generated by the hydropower station. Flow proportion was used as an indicator to evaluate RVLS Step 3: Tradeo ff varied with time and space. The Pareto curve was used to analyze the tradeo ff direction between hydropower service and RVLS, and tradeo ff intensity was constructed to discuss the quantitative relationship of the two services. According to the development process of the mainstream, the number and size of new hydropower stations in di ff erent periods were analyzed, the changes in hydropower production value were calculated, as well as the RVLS, and then the time tradeo ff was analyzed. We compared the services between divided sub-watershed and conduct spatial tradeo ff analysis Step 4: Scenario analysis: We set up 2015 as the baseline since the mainstream hydropower development was completed, and six flow management scenarios were set according to the evaluated hydropower services and RVLS Sustainability 2019 , 11 , x FOR PEER REVIEW 5 of 21 Step 2: Using the InVEST water production model to assess water retention. Referring to the method proposed by Fu et al., the value of hydropower services is calculated based on the amount of electricity generated by the hydropower station. Flow proportion was used as an indicator to evaluate RVLS. Step 3: Tradeoff varied with time and space. The Pareto curve was used to analyze the tradeoff direction between hydropower service and RVLS, and tradeoff intensity was constructed to discuss the quantitative relationship of the two services. According to the development process of the mainstream, the number and size of new hydropower stations in different periods were analyzed, the changes in hydropower production value were calculated, as well as the RVLS, and then the time tradeoff was analyzed. We compared the services between divided sub-watershed and conduct spatial tradeoff analysis. Step 4: Scenario analysis: We set up 2015 as the baseline since the mainstream hydropower development was completed, and six flow management scenarios were set according to the evaluated hydropower services and RVLS. Figure 2. The framework for tradeoff in the hydropower service and river landscape service. 2.3. Water Retention Assessment The water retention service was evaluated using the InVEST water yield model. The InVEST tools is widely used for ecosystem service tradeoff analysis, land use assessment, watershed management, biodiversity conservation planning, and ecological compensation due to its clear concepts, intuitive results, and small data requirements [48,49]. Water retention has become a necessary assessment in most case studies. The water yield model was developed based on the water balance principle. The water yield is equal to the precipitation minus the actual evapotranspiration, the latter being related to climate, soil, and vegetation: Figure 2. The framework for tradeo ff in the hydropower service and river landscape service 2.3. Water Retention Assessment The water retention service was evaluated using the InVEST water yield model. The InVEST tools is widely used for ecosystem service tradeo ff analysis, land use assessment, watershed management, biodiversity conservation planning, and ecological compensation due to its clear concepts, intuitive results, and small data requirements [ 48 , 49 ]. Water retention has become a necessary assessment in most case studies. The water yield model was developed based on the water balance principle. The

Sustainability 2019 , 11 , 5509 6 of 20 water yield is equal to the precipitation minus the actual evapotranspiration, the latter being related to climate, soil, and vegetation: Y jx = 1 − AET x j P x ! P x (1) where Y jx is the water yield, P x is the precipitation, and AET xj is the actual evapotranspiration of the grid unit x on the land use type j The actual evapotranspiration is determined by the potential evapotranspiration and the crop coe ffi cient. The former is calculated using the Penman–Monteith approach. The model has high applicability because the theoretical basis includes the energy balance and water vapor di ff usion [ 50 ]. The data imported into the model include land use from local government departments. The average annual precipitation comes from the China Meteorological Data Network ( http: // data.cma.cn / ). We downloaded the yearly precipitation data of the meteorological stations within and surrounding the study area and carried out the Kriging spatial interpolation in ARCGIS software to create a 100 m x 100 m precipitation grid Other input parameters are soil saturated hydraulic conductivity, crop coe ffi cient (ETK), root depth (Root Depth) and flow coe ffi cient (Vel_coef). The crop coe ffi cient refers to the ratio of the actual evapotranspiration of plants to the evapotranspiration of open grassland with abundant growth, uniform coverage, high uniformity (8–15 cm), and su ffi cient soil water supply. The crop coe ffi cient is related to the species, growth period, and population of vegetation. We determined crop coe ffi cients by referring to the crop coe ffi cient from “Guidelines for Crop Evapotranspiration—Crop Water Demand Calculation” [ 51 ], and some Chinese cases studies [ 52 , 53 ]. The soil saturated hydraulic conductivity was calculated using NeuroTheta software developed by the University of Wales, Australia [ 30 ]. Other parameters are referenced in the user manual [ 54 ]. 2.4. Valuation Hydropower Services We used the catchment of the hydropower station as the evaluation unit, and the value for each power station was accumulated to obtain the final value. The electricity price was determined as 0.288 Yuan / Kwh according to the regulation from Sichuan Development and Reform Commission price, in which the method is consistent with the 2014 method of Fu et al. [ 39 ], but the land use patterns in 2015 were used here 2.5. River Visual Landscape Services We used flow rate as an indicator for RVLS evaluation. There are four reasons for this: First, runo ff is the top priority in the structure and function of the river ecosystem and is the decisive factor a ff ecting the aesthetic and recreational functions of river ecosystems and their economic value [ 33 , 34 ]. Second, river continuity is an important foundation for the creation of river visual landscape services [ 55 ], and flow is the material basis for river mobility. Third, runo ff is also a major controlling factor a ff ecting vegetation succession in the waterfront [ 28 ]. Fourth, landscape aesthetic evaluation usually considers the quality of the landscape itself or the subjective preferences of the visitors. The use of runo ff as an indicator can objectively reflect the objective quality of the RVLS and reduce the uncertainty of the tradeo ff analysis The RVLS was calculated as follows: ES landscape i = Q f Q n = 1 − Q in Q n , (2) where Es landscape is the score of RVLS for i -th power station. The average annual flow rate at the dam site when no hydropower development is carried out is Q n , the inflow of the hydropower station is Q in , and the actual flow rate Q f equal to Q n minus Q in .

Sustainability 2019 , 11 , 5509 7 of 20 When the inflow is zero, the river maintains its natural condition, and the RVLS is the maximum one. When inflow reaches the maximum at each dam site, the actual flow rate falls to zero, as does the RVLS. However, RVLS should be gradually increased downstream because of the recharge capacity downstream of the dam The method described above is applicable to a single power station. To evaluate the RVLS of the entire mainstream under cascade development, the RVLS in each river section was weighted and accumulated: ES landscape t = i X n = 1 Len i × ES landscape i , (3) where the total RVLS is ES landscape t , Len i is the weight, the ratio of the length of each river section to the total length of mainstream, and ES landscape i is the RVLS of each section. Depending on the degree of development, the mainstream landscape services have changed in di ff erent periods 2.6. Tradeo ff s Using the Pareto curve, the RVLS and the hydropower service were incorporated into a scatter plot in a two-dimensional coordinate system, and a curve was fitted by regression analysis. The tradeo ff relationship was qualitatively analyzed according to the classification of time tradeo ff s, spatial tradeo ff s, and reversible tradeo ff s, and changes in the curve were analyzed based on the production–possibility frontier (PPF) curve The Pareto curve refers to how to allocate resources to achieve overall optimality when resources are limited. This approach was introduced into ecology to explain ecosystem service tradeo ff s For example, Yang et al. used the Pareto curve to analyze the tradeo ff among carbon sequestration, water conservation, and soil conservation [ 56 ]. Ager analyzed the conflict between recovery policies and socioeconomic values in forest restoration [ 45 ]. We normalized the scores for hydropower services and RVLS, then ranked them in ascending order, using the landscape service on abscissa, and the hydropower service on ordinate, drawing a scatter plot. Regression fitting was performed using the binomial formula A quantitative expression of tradeo ff relationships was seldom reported. In this paper, a tradeo ff intensity index is proposed to discuss the quantitative relationship among tradeo ff s. The design of the tradeo ff intensity index can be considered in two ways. The first is the tradeo ff relationship for the entire basin, which can be expressed using di ff erent time periods of hydropower service and RVLS as: TI = ( ES power i + 1 - ES power i ) / ( ES landscape i + 1 - ES landscape i ) (4) The second is to analyze the tradeo ff relationship between di ff erent river sections based on the current status of hydropower development in 2015 2.7. Scenario Analysis Scenario analysis is very popular in ecosystem service tradeo ff studies. In this study, six scenarios were set up according to di ff erent flow control methods (Table 1 ), including unified recovery scenarios M 1–M 5 (all hydropower stations increase ecological flow by the same proportion) and the optimized recovery scenario M 6. Scenario M 6 is based on the analysis of the water use e ffi ciency of each power station. The specific process is to first calculate the power production value of each power station on unit flow and then sort all the stations. The lowest e ffi ciency power plant has the highest proportion of reduced flow.

Sustainability 2019 , 11 , 5509 8 of 20 Table 1. Reduction of inflow for each power plants in scenarios Power Station Scenario M 1 M 2 M 3 M 4 M 5 M 6 Lvganqiao 10 20 30 40 50 40 Shiziping 10 20 30 40 50 20 Hongye 2 nd 10 20 30 40 50 40 Lixian 10 20 30 40 50 50 Ganbao 10 20 30 40 50 10 Xuecheng 10 20 30 40 50 30 Gucheng 10 20 30 40 50 30 Xiazhuang 10 20 30 40 50 20 Weizhou 10 20 30 40 50 30 3. Results 3.1. Hydropower Service The ecosystem water retention service was assessed based on land cover in 2015. There was a gradual decrease from upstream to downstream, but there was a high-value zone between the mainstream and the main tributary, the River Mengtun (Figure 3 ). The water retention service averaged 800 mm, and the total water production was 3.44 billion cubic meters Sustainability 2019 , 11 , x FOR PEER REVIEW 8 of 21 Lvganqiao 10 20 30 40 50 40 Shiziping 10 20 30 40 50 20 Hongye 2 nd 10 20 30 40 50 40 Lixian 10 20 30 40 50 50 Ganbao 10 20 30 40 50 10 Xuecheng 10 20 30 40 50 30 Gucheng 10 20 30 40 50 30 Xiazhuang 10 20 30 40 50 20 Weizhou 10 20 30 40 50 30 3. Results 3.1. Hydropower Service The ecosystem water retention service was assessed based on land cover in 2015. There was a gradual decrease from upstream to downstream, but there was a high-value zone between the mainstream and the main tributary, the River Mengtun (Figure 3). The water retention service averaged 800 mm, and the total water production was 3.44 billion cubic meters. Figure 3. Distribution of water retention services. Figure 4 showed the hydropower service at different stages of development (Figure 4). Hydropower development in the study area took place early, and the first hydropower station in the basin, Xiazhuang Hydropower Station, was established in the last 50 years of the 20 th Century. This power station is still supplying electricity to the local area. However, in the following 30 years, no new power stations were added to the mainstream. This situation continued into the 1990 s. With the building of power stations such as those at Ganbao and Lixian, hydropower development in the basin Figure 3. Distribution of water retention services Figure 4 showed the hydropower service at di ff erent stages of development (Figure 4 ). Hydropower development in the study area took place early, and the first hydropower station in the basin, Xiazhuang Hydropower Station, was established in the last 50 years of the 20 th Century. This power station is still supplying electricity to the local area. However, in the following 30 years, no new power stations were added to the mainstream. This situation continued into the 1990 s. With the building of power stations such as those at Ganbao and Lixian, hydropower development in the basin entered a rapid

Sustainability 2019 , 11 , 5509 9 of 20 development stage. By 2010, the current new hydropower service had reached 400 million yuan. This growth continued until 2015, when the total value of water and gas services in the basin reached one billion yuan Sustainability 2019 , 11 , x FOR PEER REVIEW 9 of 21 entered a rapid development stage. By 2010, the current new hydropower service had reached 400 million yuan. This growth continued until 2015, when the total value of water and gas services in the basin reached one billion yuan. Figure 4. Historical hydropower service. Figure 5 a shows the total value of hydropower services in each watershed according to the upstream–downstream relationship. Clearly, the upstream ecosystem provided higher hydropower services than the downstream system. Among the power stations, the Luganqiao station provided the maximum of 232.89 million Yuan, and the Weizhou power station had the lowest, only 0.29 million Yuan. The elevation statistics showed more clearly that the high value area was in the area of 3500–4500 m altitude (Figure 5 b), but not in the highest altitude area. This showed that the value of hydropower services was related to the distribution of water retention services and power stations. Figure 5. Spatial distribution of hydropower values ( a ) Hydropower services in the sub-watershed of various power stations. The power stations are downstream from left to right; ( b ) hydropower services along altitude. 3.2. River Visual Landscape Services Figure 6 shows two typical river landscapes. Power stations in the study area were basically developed by diversion. Due to this diversion, river flow was greatly reduced, creating a water shortage. Although the river still maintains a certain base flow, the shortage causes severe damage to the river landscape, with the unpleasant visual impact of the exposed riverbed (Figure 6 a). Figure 6 b shows the river landscape downstream of the plant of the same power station, which is just 100 m away from the site in Figure 6 a. In this case, the runoff that was originally led through the turbine 0.00 200.00 400.00 600.00 800.00 1000.00 1200.00 1958 1990 1995 2002 2007 2010 2011 2015 Va lue (RMB m illio n Yua n ) Year Added Production Total Production Figure 4. Historical hydropower service Figure 5 a shows the total value of hydropower services in each watershed according to the upstream–downstream relationship. Clearly, the upstream ecosystem provided higher hydropower services than the downstream system. Among the power stations, the Luganqiao station provided the maximum of 232.89 million Yuan, and the Weizhou power station had the lowest, only 0.29 million Yuan. The elevation statistics showed more clearly that the high value area was in the area of 3500–4500 m altitude (Figure 5 b), but not in the highest altitude area. This showed that the value of hydropower services was related to the distribution of water retention services and power stations Sustainability 2019 , 11 , x FOR PEER REVIEW 9 of 21 entered a rapid development stage. By 2010, the current new hydropower service had reached 400 million yuan. This growth continued until 2015, when the total value of water and gas services in the basin reached one billion yuan. Figure 4. Historical hydropower service. Figure 5 a shows the total value of hydropower services in each watershed according to the upstream–downstream relationship. Clearly, the upstream ecosystem provided higher hydropower services than the downstream system. Among the power stations, the Luganqiao station provided the maximum of 232.89 million Yuan, and the Weizhou power station had the lowest, only 0.29 million Yuan. The elevation statistics showed more clearly that the high value area was in the area of 3500–4500 m altitude (Figure 5 b), but not in the highest altitude area. This showed that the value of hydropower services was related to the distribution of water retention services and power stations. Figure 5. Spatial distribution of hydropower values ( a ) Hydropower services in the sub-watershed of various power stations. The power stations are downstream from left to right; ( b ) hydropower services along altitude. 3.2. River Visual Landscape Services Figure 6 shows two typical river landscapes. Power stations in the study area were basically developed by diversion. Due to this diversion, river flow was greatly reduced, creating a water shortage. Although the river still maintains a certain base flow, the shortage causes severe damage to the river landscape, with the unpleasant visual impact of the exposed riverbed (Figure 6 a). Figure 6 b shows the river landscape downstream of the plant of the same power station, which is just 100 m away from the site in Figure 6 a. In this case, the runoff that was originally led through the turbine 0.00 200.00 400.00 600.00 800.00 1000.00 1200.00 1958 1990 1995 2002 2007 2010 2011 2015 Va lue (RMB m illio n Yua n ) Year Added Production Total Production Figure 5. Spatial distribution of hydropower values. ( a ) Hydropower services in the sub-watershed of various power stations. The power stations are downstream from left to right; ( b ) hydropower services along altitude 3.2. River Visual Landscape Services Figure 6 shows two typical river landscapes. Power stations in the study area were basically developed by diversion. Due to this diversion, river flow was greatly reduced, creating a water shortage. Although the river still maintains a certain base flow, the shortage causes severe damage to the river landscape, with the unpleasant visual impact of the exposed riverbed (Figure 6 a). Figure 6 b shows the river landscape downstream of the plant of the same power station, which is just 100 m

Sustainability 2019 , 11 , 5509 10 of 20 away from the site in Figure 6 a. In this case, the runo ff that was originally led through the turbine had been returned to the river, and the river had resumed normal flow, forming a mountain river landscape (Figure 6 b). Sustainability 2019 , 11 , x FOR PEER REVIEW 10 of 21 had been returned to the river, and the river had resumed normal flow, forming a mountain river landscape (Figure 6 b). Figure 6. ( a ) Riverbed appearance after runoff had been taken by the hydroplant; ( b ) restored river landscape after the runoff comeback from the power station. Figure 7 shows the relationship between distance to source (DTS) and flow of the power stations. As DTS increased, the catchment area of the river increased, and the flow rate increased. DTS and flow have a significant power relationship. By comparing the changes in flow before and after hydropower development, it can be seen that hydropower development led to a rapid decline in river flow. At 48 and 86 km, the hydropower station basically uses all the runoff of the river channel for power generation, resulting in the runoff flow tending to zero and the river channel basically breaking. Figure 7. Flows of different river sections before and after hydropower development. 3.3. Tradeoff of the Two Services Figure 8 a shows the changes in RVLS and hydropower services at different stages of development. Before 1958, the entire mainstream had low development intensity, hydropower services were less than 5% of their present value, and RVLS remained at one. The mainstream was basically in a natural undeveloped state. This state lasted until 1990, when hydropower services were y = 0.0103 x 1.6363 R² = 0.9785 0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00 45.00 0.00 20.00 40.00 60.00 80.00 100.00 120.00 140.00 160.00 180.00 runo ff (0 .1 b illio n m 3 p er y ea r) Distance to river source (km) Pre-development Post-development Figure 6. ( a ) Riverbed appearance after runo ff had been taken by the hydroplant; ( b ) restored river landscape after the runo ff comeback from the power station Figure 7 shows the relationship between distance to source (DTS) and flow of the power stations As DTS increased, the catchment area of the river increased, and the flow rate increased. DTS and flow have a significant power relationship. By comparing the changes in flow before and after hydropower development, it can be seen that hydropower development led to a rapid decline in river flow. At 48 and 86 km, the hydropower station basically uses all the runo ff of the river channel for power generation, resulting in the runo ff flow tending to zero and the river channel basically breaking Sustainability 2019 , 11 , x FOR PEER REVIEW 10 of 21 had been returned to the river, and the river had resumed normal flow, forming a mountain river landscape (Figure 6 b). Figure 6. ( a ) Riverbed appearance after runoff had been taken by the hydroplant; ( b ) restored river landscape after the runoff comeback from the power station. Figure 7 shows the relationship between distance to source (DTS) and flow of the power stations. As DTS increased, the catchment area of the river increased, and the flow rate increased. DTS and flow have a significant power relationship. By comparing the changes in flow before and after hydropower development, it can be seen that hydropower development led to a rapid decline in river flow. At 48 and 86 km, the hydropower station basically uses all the runoff of the river channel for power generation, resulting in the runoff flow tending to zero and the river channel basically breaking. Figure 7. Flows of different river sections before and after hydropower development. 3.3. Tradeoff of the Two Services Figure 8 a shows the changes in RVLS and hydropower services at different stages of development. Before 1958, the entire mainstream had low development intensity, hydropower services were less than 5% of their present value, and RVLS remained at one. The mainstream was basically in a natural undeveloped state. This state lasted until 1990, when hydropower services were y = 0.0103 x 1.6363 R² = 0.9785 0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00 45.00 0.00 20.00 40.00 60.00 80.00 100.00 120.00 140.00 160.00 180.00 runo ff (0 .1 b illio n m 3 p er y ea r) Distance to river source (km) Pre-development Post-development Figure 7. Flows of di ff erent river sections before and after hydropower development 3.3. Tradeo ff of the Two Services Figure 8 a shows the changes in RVLS and hydropower services at di ff erent stages of development Before 1958, the entire mainstream had low development intensity, hydropower services were less

Sustainability 2019 , 11 , 5509 11 of 20 than 5% of their present value, and RVLS remained at one. The mainstream was basically in a natural undeveloped state. This state lasted until 1990, when hydropower services were rated at only 0.1, whereas the RVLS remained close to one. In the following years, hydropower development began to grow steadily. By 2007, it had reached a high level. During this time, the RVLS gradually dropped to 0.85. After this, although the basin was a ff ected by the 2008 Wenchuan earthquake, more hydropower plants were built, and the development of the mainstream was basically complete by 2015. By this time, the RVLS had dropped to 0.48. The figure shows that in 2009, RVLS and hydropower services got the same score. The tradeo ff intensity reflected changes in the two services (Figure 8 b). From − 3.5 in 1990 to − 0.79 in 2015, the tradeo ff intensity gradually decreased, indicating that the relationship between hydropower service and RVLS was stabilized Sustainability 2019 , 11 , x FOR PEER REVIEW 11 of 21 rated at only 0.1, whereas the RVLS remained close to one. In the following years, hydropower development began to grow steadily. By 2007, it had reached a high level. During this time, the RVLS gradually dropped to 0.85. After this, although the basin was affected by the 2008 Wenchuan earthquake, more hydropower plants were built, and the development of the mainstream was basically complete by 2015. By this time, the RVLS had dropped to 0.48. The figure shows that in 2009, RVLS and hydropower services got the same score. The tradeoff intensity reflected changes in the two services (Figure 8 b). From − 3.5 in 1990 to − 0.79 in 2015, the tradeoff intensity gradually decreased, indicating that the relationship between hydropower service and RVLS was stabilized. Figure 8. Historical tradeoff analysis. (( a ) Hydropower service and river visual landscape services (RVLS) changed in different development periods, ( b ) tradeoff intensity during different development periods). The Pareto curve was plotted in Figure 9 using the scores of the two services. The tradeoff between hydropower service and RVLS was very obvious. As the hydropower services rose from zero to one, the RVLS decreased from 1.0 to 0.4, which showed a significant negative correlation. To ensure that the scattered points fall below the curve, the requirements of the Pareto boundary were met. A quadratic function was used to fit the points, resulting in a significant functional relationship. Figure 8. Historical tradeo ff analysis. (( a ) Hydropower service and river visual landscape services (RVLS) changed in di ff erent development periods, ( b ) tradeo ff intensity during di ff erent development periods) The Pareto curve was plotted in Figure 9 using the scores of the two services. The tradeo ff between hydropower service and RVLS was very obvious. As the hydropower services rose from zero to one, the RVLS decreased from 1.0 to 0.4, which showed a significant negative correlation. To ensure that the scattered points fall below the curve, the requirements of the Pareto boundary were met. A quadratic function was used to fit the points, resulting in a significant functional relationship Figure 10 shows that the tradeo ff intensity varied downstream and that the tradeo ff intensity decreased in an oscillating fashion. It was the highest ( − 0.3) in the upstream Luganqiao station and the lowest (0.003) in the downstream Weizhou station. The whole curve could be divided into three sections. The upstream section was above the Hongye 2 nd plant (more than 60 km to the outlet), showing a strong oscillation with an amplitude between 0.3 and 0.1. In the middle section between the Ganbao station and the Hongye 2 nd plant (45–60 km to the outlet), the amplitude dropped rapidly and remained below 0.05. The tradeo ff intensity downstream of the Ganbao station (less than 45 km to the outlet) suddenly increased to 0.1 and then rapidly dropped to zero. Actually, the hydropower service in the basin dropped to zero, but the RVLS still maintained a certain amount.

Sustainability 2019 , 11 , 5509 12 of 20 Sustainability 2019 , 11 , x FOR PEER REVIEW 12 of 21 −− Figure 9. Pareto relationship between hydropower and landscape services. The points in the figure represent the hydropower services and RVLS scores of the mainstreams in different years. Figure 10 shows that the tradeoff intensity varied downstream and that the tradeoff intensity decreased in an oscillating fashion. It was the highest ( − 0.3) in the upstream Luganqiao station and the lowest (0.003) in the downstream Weizhou station. The whole curve could be divided into three sections. The upstream section was above the Hongye 2 nd plant (more than 60 km to the outlet), showing a strong oscillation with an amplitude between 0.3 and 0.1. In the middle section between the Ganbao station and the Hongye 2 nd plant (45–60 km to the outlet), the amplitude dropped rapidly and remained below 0.05. The tradeoff intensity downstream of the Ganbao station (less than 45 km to the outlet) suddenly increased to 0.1 and then rapidly dropped to zero. Actually, the hydropower service in the basin dropped to zero, but the RVLS still maintained a certain amount. Figure 10. Variation of tradeoff intensity along the distance to the outlet. (This figure reflects the y = -1.062 x 2 - 0.3563 x + 1.4348 R² = 0.9991 0.00 0.20 0.40 0.60 0.80 1.00 1.20 0.00 0.20 0.40 0.60 0.80 1.00 1.20 ES power ES landscape Figure 9. Pareto relationship between hydropower and landscape services. The points in the figure represent the hydropower services and RVLS scores of the mainstreams in di ff erent years Sustainability 2019 , 11 , x FOR PEER REVIEW 12 of 21 −− Figure 9. Pareto relationship between hydropower and landscape services. The points in the figure represent the hydropower services and RVLS scores of the mainstreams in different years. Figure 10 shows that the tradeoff intensity varied downstream and that the tradeoff intensity decreased in an oscillating fashion. It was the highest ( − 0.3) in the upstream Luganqiao station and the lowest (0.003) in the downstream Weizhou station. The whole curve could be divided into three sections. The upstream section was above the Hongye 2 nd plant (more than 60 km to the outlet), showing a strong oscillation with an amplitude between 0.3 and 0.1. In the middle section between the Ganbao station and the Hongye 2 nd plant (45–60 km to the outlet), the amplitude dropped rapidly and remained below 0.05. The tradeoff intensity downstream of the Ganbao station (less than 45 km to the outlet) suddenly increased to 0.1 and then rapidly dropped to zero. Actually, the hydropower service in the basin dropped to zero, but the RVLS still maintained a certain amount. Figure 10. Variation of tradeoff intensity along the distance to the outlet. (This figure reflects the y = -1.062 x 2 - 0.3563 x + 1.4348 R² = 0.9991 0.00 0.20 0.40 0.60 0.80 1.00 1.20 0.00 0.20 0.40 0.60 0.80 1.00 1.20 ES power ES landscape Figure 10. Variation of tradeo ff intensity along the distance to the outlet. (This figure reflects the spatial variation of the trade o ff in the direction downstream. Red indicates a negative tradeo ff , and black indicates synergy in certain river sections.) 3.4. Flow Management Scenario To compare the e ff ects of di ff erent flow management scenarios, the value of hydropower services per unit of flow was calculated. Table 2 shows that the e ffi ciency of Shiziping Power Station was the highest, with a power generation output per unit flow of 0.26 yuan / m 3 . Xiazhuang Power Station was the lowest, with only 0.01 yuan / m 3 . This amounted to a twentyfold di ff erence between the two stations, which reflected the development of hydropower technology. Xiazhuang Power Station was

Sustainability 2019 , 11 , 5509 13 of 20 the earliest developed power station in the Zagunao basin, at 60 years old (built in 1958), and uses low dam diversion. Shiziping Power Station was built in 2010 and uses the high dam diversion method Table 2. Water use e ffi ciency of power stations No Station Annual Production (RMB Million Yuan) Annual Flow Extracted (10 8 m 3 ) E ffi ciency (Yuan / m 3 ) Rank 1 Luganqiao 37.47 5.25 0.07 5 2 Shiziping 238.46 9.22 0.26 1 3 Hongye 2 nd 134.21 13.66 0.10 2 4 Lixian 51.84 16.46 0.03 8 5 Ganbao 59.04 10.59 0.06 6 6 Xuecheng 167.04 17.13 0.10 3 7 Gucheng 218.88 27.58 0.08 4 8 Xiazhuang 37.78 26.96 0.01 9 9 Weizhou 95.27 29.14 0.03 7 Hydropower service and RVLS were assessed using the power plant watershed as a unit. As the flow rate increased, the river flow increased, and the RVLS of each sub-basin increased. The first to be considered was the Ganbao station. The development intensity of this power station was very small. Under the scenario of reducing the reference flow by 10% (Scenario M 1) (Figure 11 ), the river basically recovered continuously. At this time, except for the scenic score of Xuecheng Station, other power stations were still basically in a cuto ff state. In Scenario M 2, Xuecheng Station and Xiazhuang Station were also returned to a continuously operating state. In Scenario M 3, except for Luganqiao Station and Hongye Secondary Station, the other power stations resumed operation. In Scenarios M 4 and M 5, all the power stations resumed operation, and the landscape scores no longer changed. However, from Scenario M 1 to Scenario M 5, the hydropower services dropped from 1 to 0.5. The value of the lost hydropower services reached 50% To coordinate hydropower development and landscape restoration, the allocation of runo ff flow was optimized in Scenario M 6. We aimed at the basic recovery of each station RVLS (score greater than 0.4). We set the flow according to the power generation e ffi ciency. Low e ffi cient plants reduce inflow more. The inflow of each station was gradually adjusted in the range of 10%–50%, and the corresponding hydropower service and RVLS were calculated. Among the schemes that satisfied the requirement of RVLS reaching 0.4, the scheme with the smallest drop in hydropower service was selected as Scenario M 6 In Scenario M 6, the Lixian station reduced its inflow rate by up to 50%, followed by the Luganqiao station by 40%, and further followed by the Ganbao station, which reduced its inflow by only 10%. Under this scenario, both hydropower and RVLS were satisfactory. Except for the Shiziping station, the control sections of other power stations continuously recovered, with hydropower service scores of 0.7, which was higher than the 0.6 in Scenario M 4.

Sustainability 2019 , 11 , 5509 14 of 20 Sustainability 2019 , 11 , x FOR PEER REVIEW 14 of 21 than 0.4). We set the flow according to the power generation efficiency. Low efficient plants reduce inflow more. The inflow of each station was gradually adjusted in the range of 10%–50%, and the corresponding hydropower service and RVLS were calculated. Among the schemes that satisfied the requirement of RVLS reaching 0.4, the scheme with the smallest drop in hydropower service was selected as Scenario M 6. In Scenario M 6, the Lixian station reduced its inflow rate by up to 50%, followed by the Luganqiao station by 40%, and further followed by the Ganbao station, which reduced its inflow by only 10%. Under this scenario, both hydropower and RVLS were satisfactory. Except for the Shiziping station, the control sections of other power stations continuously recovered, with hydropower service scores of 0.7, which was higher than the 0.6 in Scenario M 4 Figure 11. Tradeoff analysis based on flow control. We set 2015 as a baseline. The cascade development of the river basin was completed that year. Hydropower services have reached their maximum. Hydropower service and RVLS under the six scenarios of M 1–M 6 are plotted with a radar chart. Since each power station of M 1–M 5 reduces the flow rate of the same ratio, the flow rate is a linear function of the power generation. Therefore, each power station shows a similar change. (a. Luganqiao, b. Shiziping, c. Hongye 2 nd, d. Lixian, e. Ganbao, f. Xuecheng, g. Gucheng, h. Xiazhuang, i. Weizhou). 4. Discussion 4.1. Tradeoff between Hydropower Service and RVLS Mountain rivers provide enormous ecosystem services. Among them, hydropower services have achieved economic value. From the 1950 s to the present, hydropower services have been valued Figure 11. Tradeo ff analysis based on flow control. We set 2015 as a baseline. The cascade development of the river basin was completed that year. Hydropower services have reached their maximum. Hydropower service and RVLS under the six scenarios of M 1–M 6 are plotted with a radar chart. Since each power station of M 1–M 5 reduces the flow rate of the same ratio, the flow rate is a linear function of the power generation. Therefore, each power station shows a similar change. (a. Luganqiao, b. Shiziping, c. Hongye 2 nd, d. Lixian, e. Ganbao, f. Xuecheng, g. Gucheng, h. Xiazhuang, i. Weizhou) 4. Discussion 4.1. Tradeo ff between Hydropower Service and RVLS Mountain rivers provide enormous ecosystem services. Among them, hydropower services have achieved economic value. From the 1950 s to the present, hydropower services have been valued 27.5 times and reached 1.04 billion Yuan in 2015. This represents an important source of ecological services in the mountains [ 32 ]. However, RVLS have declined as hydropower services have increased Considering the basin as a whole, there is a clear tradeo ff between hydropower services and RVLS (Figure 8 ). This is similar to the tradeo ff between hydropower and other services such as fisheries and biodiversity [ 38 ]. This situation exists primarily because the two services have a common source and because the ecosystem provides water conservation services. These services can produce a variety of benefits, with power generation and RVLS being the two most closely related services. Development, whether by damming or diversion, leads to a reduction in river flow, which will inevitably a ff ect the river landscape. The impact of diversion is particularly prominent. Because the distance of water diversion ranges from several kilometers to tens of kilometers (Figure 6 ), diversion results in long-distance dehydration of river courses, a ff ecting the quality of the river landscape. Therefore, the tradeo ff relationship between diversion and landscape is very obvious.

Sustainability 2019 , 11 , 5509 15 of 20 The tradeo ff s with other services are also di ff erent. For example, the impact of hydropower development on biodiversity is multifaceted, mainly because dams block the migration routes of aquatic animals, a ff ect habitats, change the structure of aquatic ecosystems, and a ff ect the catch of fisheries [ 20 , 57 , 58 ]. However, the impact of hydropower development on RVLS is more direct The landscape of the mountain river is characterized by rushing water, which gives people a huge visual and auditory shock. This is the core content of the RVLS and relies heavily on the huge flow of the river. Water diversion from dams directly reduces the amount of water in the river and has a significant impact on the river landscape The time tradeo ff means the service utilization of one period a ff ects the supply and demand of services in another period. As the watershed development began in the 1950 s, hydropower services continued to rise, while RVLS continued to decline. It reflects the change in the number of two services in two di ff erent periods. Since there is no direct correlation between the two periods, it is not a time tradeo ff in the strict sense With the completion of the cascade development of the basin, the hydropower and RVLS in the basin reached a stable state. This stability was determined with two reasons. First, new power plants were not an economic feasibility in the current development condition. Second, the Chinese government strengthened watershed management. The construction of new power stations in the study area is forbidden. The location and quantity of water taken by hydropower stations need to be issued by the water conservancy department The current state showed a clear spatial tradeo ff . Figure 10 illustrates that the tradeo ff intensity of hydropower and RVLS fluctuates downstream and is closely related to cascade development The farther upstream the development is, the greater the value of the hydropower service, but also the greater the impact on RVLS. As the river runs downstream, runo ff continues to be replenished, and there is a decrease in plants’ inflow. The value of hydropower service has declined as the impact on the landscape has decreased The spatial tradeo ff is not only reflected in the di ff erence in the strength of the upstream and downstream tradeo ff s, but also in the tradeo ff direction, resulting in more tradeo ff s and synergies This has been the focus of research on tradeo ff s in ecosystem services [ 22 , 35 ]. The spatial tradeo ff between hydropower and RVLS has spatial characteristics. The tradeo ff direction between adjacent catchments is often reversed. In other words, the tradeo ff direction of one sub-watershed is di ff erent from the tradeo ff direction of the next sub-basin downstream. The reason for this is that the RVLS increase and decrease regularly between two adjacent catchments. However, the hydropower services are di ff erent. Due to the size of the catchment area and the distribution of water production services, there is no obvious change for services in adjacent catchments. Changes in hydropower services may or may not have the same e ff ect as RVLS. Hence, tradeo ff s or synergies occur. Therefore, river cascade development creates regular changes in spatial tradeo ff s RVLS are also typical reversible tradeo ff s [ 11 ]. As shown in Figure 5 , behind a power plant, the tailwater returns to the river, and the RVLS can be e ff ectively restored. At the same time, based on the results of the scenario analysis, the RVLS can be significantly increased if the inflow into the plant is reduced. There have been numerous reports on river ecological restoration [ 28 , 59 ]. Examples of successes and failures are available [ 4 ]. However, whether the goal of recovery is water quality or biodiversity, the most basic considerations include flow recovery In the tradeo ff relationship, tradeo ff intensity is often overlooked [ 3 ]. Grazing intensity is comparable to hydropower development intensity. When grazing intensity increases from low to medium, grassland production services show significant tradeo ff s with biodiversity [ 18 ], but at high grazing intensity, production services and biodiversity decline and may cease to exist. This relationship needs to be weighed. The results of this study show that the tradeo ff strength between hydropower and landscape services is between 0.3 and 0. This shows that the two services experience moderate tradeo ff s. This situation is mainly determined by the characteristics of hydropower development The number of hydropower site locations suitable for construction in the basin is limited. Even in such high-intensity development basins as the study area, the length of the undeveloped river section of

Sustainability 2019 , 11 , 5509 16 of 20 the mainstream is still greater than the developed length. This means that the minimum value of the landscape service cannot be less than 0.5. It is then necessary to consider the economic and technical conditions of development and other factors. Hydropower development may be further limited, which is not the same as grazing 4.2. Policy Implications The environmental impact of hydropower development is already a global issue. Researchers have proposed various measures to reduce environmental impacts in di ff erent regions. Among these, the most representative ones include ecological flow systems, monitoring measures, and hydropower dispatching [ 60 ]. Most of these are technical measures that have a role in mitigating impact [ 61 , 62 ]. In developed countries, more extreme measures to demolish dams and restore the natural state of rivers have been proposed [ 63 ]. However, this entails a higher cost in lost power. For areas with less developed economies, hydropower is still needed to meet energy demand The findings of this study demonstrated that tradeo ff s between hydropower and RVLS could be used to optimize watershed management [ 64 ], especially for the ubiquitous cascade development of basins. The results of Scenario M 6 showed that the RVLS could be significantly restored after flow recovery in various river sections (Figure 10 ). For some sections of a river, only a small amount of flow will restore RVLS. From the perspective of the entire basin, di ff erent proportions of recovery could be used to avoid a rapid decline in hydropower services The tradeo ff between hydropower and RVLS is insignificant within a certain range. When hydropower development intensity is low, the continuity of the river will not be a ff ected. In Scenarios M 4 and M 5, a 40%–50% reduction in the flow rate taken could substantially restore RVLS, which reflected the elasticity of river ecosystems [ 65 , 66 ]. The whole of China is currently in a critical period of industrial restructuring. Sichuan Province, as an important hydropower base, is facing a serious water abandonment problem [ 59 ]. The main reason for this is adjustments in the regional industrial structure, in particular, the fact that existing high-energy-consuming industries are in a surplus state. Therefore, the hydropower services that provide energy for high-energy-consuming industries are facing problems of excess supply. However, this provides a good opportunity for restoration of river ecosystems. As income levels increase, the demand for urban cultural services by urban residents has also increased rapidly. Naturally flowing rivers can produce diverse cultural services such as rafting, photography, painting, and nature education [ 8 , 60 ]. These services depend on the recovery of river flows and landscapes The environmental impact of hydropower development must be mitigated through payment for ecosystem services. However, the loss of hydropower development can be o ff set by the development of ecotourism. Numerous studies have shown that ecological restoration does not always have a negative impact on the economy: It can bring about higher value with scientific management [ 67 , 68 ]. Scenario analysis indicates that river restoration is carried out in key river sections and that the development of hydropower services has not declined much. However, the value of tourism brought about by these changes is higher. According to the relevant literature, the study area is an important tourist destination for tourists from the surrounding areas because it is close to the Chengdu megacity. The red leaf landscape with the river and the human landscape are all attractive to foreign tourists. However, these landscapes do not form an organic connection with the river landscape. If the river flow landscape is restored by increasing the discharge flow of the hydropower stations, this will play an important role in enhancing ecotourism in the area We discussed the relationship between hydropower service and RVLS based on runo ff . In fact, there are many other environmental impacts in hydropower development. Using the tradeo ff analysis in this paper helps to e ff ectively assess the complex relationships of multiple services. For example, feedback relationships formed in energy–ecology (landscape)–climate regulation. Hydropower not only meets the energy demand for social and economic development, but more importantly, hydropower is the main clean energy, which can e ff ectively reduce carbon emissions [ 69 ]. However, hydropower

Sustainability 2019 , 11 , 5509 17 of 20 stations are also a potentially important carbo source with greenhouse gas emissions, as large areas of land submerged in the reservoir area could result in loss of carbon stocks [ 70 ]. Through ecological compensation for watershed land use, carbon pool balance can be achieved within the basin [ 71 ]. 5. Conclusions River development and protection are a common challenge worldwide. This study has evaluated RVLS and hydropower services using biophysical model and scenario analysis methods. Significant tradeo ff s between the two services were found, and tradeo ff s with hydropower development are gradually emerging. The main pattern of tradeo ff s was upstream and downstream of a dam, with the most obvious being the dam-to-plant section. Tradeo ff s can be used as a basis for optimizing watershed management, guiding the evolution of watersheds from hydropower to landscape utilization In particular, most river basins are developed as a cascade of dams and plants, which provides conditions for comprehensive utilization. Scientific assessment and analysis of the tradeo ff s between hydropower development and RVLS can provide an optimal solution. In a period of major changes in social demand, the original development and utilization model cannot adapt to new needs, and the utilization of di ff erent services can be re-evaluated to generate suggestions for river recovery. Such an evaluation can provide e ff ective advice for the protection and sustainable development of watersheds Rivers have multiple services, and cultural services, in particular, may be an important factor in supporting sustainable mountain development. Cultural services are closely linked to other services such as biodiversity conservation, water supply, energy, and climate regulation. We only analyzed the relationship between the two services from the hydrological and explained part of the tradeo ff relationship. However, the RVLS has richer connotations. It needs to be refined through further monitoring and evaluation. Hydropower development and complex issues such as energy, ecological protection, and climate change form complex feedback mechanisms. These issues require in-depth research in the future. A socioecological comprehensive analysis method provides a useful reference for exploring these issues [ 72 ]. Author Contributions: B.F. completed the data analysis and draft writing. N.L. designed research framework and participated the discussion Funding: This This research was funded by [the Major Scientific and Technological Special Program of Sichuan Province, China] grant number [2018 SZDZX 0027], [Natural Science Foundation of China project -Coupled relationship and regulation mechanism between rural livelihoods and ecosystem services in the Three Gorges Reservoir Area] grant number [41371539] and [Chinese Academy of Sciences project (Land Development Pattern Optimization of Mountainous Areas in Southwest China)] grant number [Y 7 K 2260263). And The APC was funded by [the Major Scientific and Technological Special Program of Sichuan Province, China] grant number [2018 SZDZX 0027]. The authors hereby would like to express their thanks Conflicts of Interest: The authors declare no conflicts of interest References 1 Daily, G.C Nature’s Service ; Island Press: Washington, DC, USA, 1997 2 MEA Millennium Ecosystem Assessment 2005. Ecosystems and Human Well-Being: Synthesis ; Island Press: Washington, DC, USA, 2005 3 Jianjia, Z. Characteristic of tradeo ff s between timber production and carbon storage for plantation under harvesting impact: Acasestudy of HuitongNational Research Station of Forest Ecosystem J. Geogr. Sci 2018 , 73 , 1085–1098 4 Fisher, W. Stream Ecology: Structure and Function of Running Waters Trans. Am. Fish. Soc 2010 , 125 , 5 [ CrossRef ] 5 Hamududu, B.; Killingtveit, A. Assessing climate change impacts on global hydropower Energies 2012 , 5 , 305–322. [ CrossRef ] 6 Leach, J.A.; Moore, R.D. Above-stream microclimate and stream surface energy exchanges in a wildfiredisturbed riparian zone Hydrol. Process 2010 , 24 , 2369–2381. [ CrossRef ] 7 Nayyeri, H.; Zandi, S. Evaluation of the e ff ect of river style framework on water quality: Application of geomorphological factors Environ. Earth Sci 2018 , 77 , 343. [ CrossRef ]

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Natural state, Basin, Diversion, Spatial distribution, Water shortage, Sustainable development, Developed countries, Cultural service, Negative correlation, Economic value, Environmental Impact, Aquatic ecosystem, Ecotourism, Energy demand, Spatial variation, Upstream and downstream, Clean energy, Developed economies, Catchment Area, Greenhouse gas emission, Water Retention, Ecological restoration, River ecosystem, Scenario analysis, Ecological health, Water use efficiency, Ecological compensation, Ecological protection, Carbon emission, Oscillation, Downstream, Hydropower, Power stations, Watershed management, Industrial restructuring, River basin, Regional industrial structure, Ecosystem service, Wenchuan earthquake, Water Diversion, Hydropower development, Hydropower station, Climate Regulation, River flow, Tradeoff, Technical measures, Ecological flow, Grazing intensity, Monitoring measures, River Channel, Spatial characteristic, Water retention service, Base flow, Payment for ecosystem service, Mainstream, River ecological restoration, Less developed economies, River development, Tradeo ff analysis, Cultural ecosystem service.