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Ecological compensation for inundated habitats in hydropower developments based on carbon stock balance
Journal of Cleaner Production xxx (2015) 1e9
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Ecological compensation for inundated habitats in hydropower developments based on carbon stock balance Bing Yu, Linyu Xu*, Zhifeng Yang State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, No. 19, Xinjiekouwai Street, Haidian District, Beijing 100875, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 14 July 2014 Received in revised form 9 June 2015 Accepted 13 July 2015 Available online xxx
Hydroelectric power reservoirs have been identified as potentially important sources of greenhouse gas (GHG) emissions due to the large areas of habitat which are inundated, leading to doubts as to whether hydropower is actually a net low-carbon energy source. In this study we propose a ‘service-to-service’ ecological analysis of inundated habitats from the viewpoint of carbon stock balance compared with the carbon stock loss from hydropower reservoirs. We consider whether the lost ecological service of carbon sequestration by inundated farmland, grassland and woodland could be offset by an increased ecological service provided by a grassland rehabilitation project. We also establish an integrated ecological compensation accounting methodology for inundated habitats by combining habitat equivalency analysis and estimates of carbon stock loss. This ecological compensation framework is illustrated by calculations from a case study of the Pondo hydropower project in Tibet, China. The results estimate that the total carbon stock losses from the construction and operation of this reservoir was 124,662 tons; requiring a compensatory restoration of areas of slightly, moderately, or severely degraded grasslands of 17.80, 8.90, and 5.93 thousand hectares, in a lump-sum payment mode. By means of such ecological compensations, carbon stock balance could be realized at the watershed scale, and the advantages of low-carbon hydropower developments could be fully realized. © 2015 Elsevier Ltd. All rights reserved.
Keywords: Ecological compensation Habitat equivalency analysis Carbon sequestration Grassland rehabilitation Tibet
1. Introduction 1.1. Inundated habitats and carbon emission The low-carbon advantages associated with hydroelectric power development are increasingly being called into question due to the multiple environmental impacts of these facilities (Li et al., 2015a; Zhang et al., 2014; Chen et al., 2015; Zhang et al., 2015). Zhang and Xu (2013) showed that the low-carbon status of large hydropower projects is currently overestimated. The Cary Institute of Ecosystem Studies reported that hydropower reservoirs are potentially important sources of greenhouse gas (GHG) emissions (Barros et al., 2011). When a hydroelectric reservoir is built it inundates an extensive area, destroying the terrestrial ecosystem on the site. As a result, ecosystem services such as CO2 sequestration and O2 release, and soil and water conservation are lost. Moreover, the newly flooded biomass decays, resulting in a gradual release of greenhouse gases (Varun et al., 2009).
* Corresponding author. Tel./fax: þ86 (0)10 58800618. E-mail address: [email protected] (L. Xu).
Globally, more than two-thirds of the world's rivers have been interrupted by dams and reservoirs, and the area of formerly terrestrial habitat inundated by large reservoirs in the 1990s was the size of California or France (Dynesius and Nilson, 1994). Previous calculations have indicated that the global GHG emissions from reservoirs may be equivalent to 7% of the total potentially global warming emissions (Louis et al., 2000). In tropical areas, GHG emissions per megawatt of electricity produced could be as high as those from fossil-fuel power plants (Rosa et al., 2004). In this context, the Intergovernmental Panel on Climate Change (IPCC) included emissions from artificially flooded regions in its National Greenhouse Gas Inventory Programme (Graham-Rowe, 2005). In 2006, it also developed guidelines for national GHG inventories which include a method for estimating changes in carbon stock due to land conversion to permanently flooded land (IPCC, 2006). 1.2. Importance of ecological compensation to carbon stocks Carbon emissions from reservoirs reduce the low-carbon advantages of hydropower development, and may even contribute to global climate change, such as global warming (Mendonça et al.,
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Please cite this article in press as: Yu, B., et al., Ecological compensation for inundated habitats in hydropower developments based on carbon stock balance, Journal of Cleaner Production (2015), http://dx.doi.org/10.1016/j.jclepro.2015.07.071
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B. Yu et al. / Journal of Cleaner Production xxx (2015) 1e9
2012; Li et al., 2015b). It is therefore necessary to take measures to improve degraded areas or to create new habitats with similar ecological functions and qualities to offset the resulting carbon stock loss. Such measures, referred to as ecological compensation (Allen and Feddema, 1996), are defined as the substitution of ecological functions or qualities that have been impaired by human activities (Cuperus et al., 1996). In practice, ecological compensation is referred to as ‘in-kind’ compensation when the ecosystem is restored using the same items that were lost, and ‘out-of-kind’ when the lost factors are replaced with different items (Cuperus et al., 1999) . Ecological compensation measures have been taken in many countries to compensate for environmental impacts on both terrestrial and aquatic habitats (Trussart et al., 2002; Xu et al., 2014). Habitat restoration projects and payments for ecosystem services (PES) are the two main methods of mitigation that have been used to compensate for the damage caused by hydropower development. Restoration measures have generally included the reduction of reservoir sedimentation, the modification of water quality, the regulation of hydrological regimes, and the removal of barriers to fish migration and river navigation (Trussart et al., 2002). Furthermore, some dams have even been decommissioned and removed in some developed countries (Anderson et al., 2006). PES schemes for hydropower involving payment in the form of planted forests have been conducted in Costa Rica (Rojas and Aylward, 2002) and Cambodia (Arias et al., 2011), although these methods have not been widely applied. Although current ecological compensation measures have been generally beneficial to hydropower development, there have been too few related studies geared toward understanding their effectiveness. As global warming proceeds, it has become increasingly important to pay attention to carbon stock loss from inundated habitats as a result of hydropower development. Further ecological compensation measures should probably be taken to offset carbon stock losses and improve the advantages of low-carbon hydropower development. This study was conducted for just this purpose. Notwithstanding the existing studies of ecological compensation, it is still unclear as to how much restoration work is required to offset the ecological losses caused by dams and reservoirs. The habitat equivalence analysis (HEA) was proposed by the United States National Oceanic and Atmospheric Administration (NOAA), which calls for properly scaled compensatory restoration (Burlington, 1999). Using the HEA, effective levels of compensation for damaged habitats can be realized on a service-to-service basis, but selection of the appropriate ecological metrics is difficult. In this study, we attempt to establish an ecological compensation approach for inundated habitats through a combination of HEA and carbon stock loss estimation. 2. Materials and methods 2.1. Study area and data collection In recent years hydropower has developed rapidly in China, especially in Tibet. The middle reach of the Yarlung Zangbo River is
to be the main source of new hydropower according to the 12th Chinese Five-Year Energy Development Plan (National Energy Administration, 2013). Tibet provides an important ecosystem service in supplying fresh water to most of Asia (Immerzeel et al., 2008). Therefore, determining how to compensate for natural ecosystems damaged during hydropower development in Tibet is essential. The Lhasa River is one of the larger tributaries in the middle reaches of the Yarlung Zangbo River, and originates in the southern ^ntanglha Mountain, on the Tibet Plateau foothills of the Nyainqe (Yang et al., 2007). The main stream of the Lhasa River is rich in water, and is capable of providing 1.715 million kW of electricity. With the increasing demand for electricity, hydropower projects have developed rapidly on the Lhasa River in recent years, and there are currently five hydropower projects on its main stream (Table 1). Among these the Pondo hydropower project is the most important engineering development affecting the flow of the Lhasa River, with the largest inundated area. We therefore selected the Pondo hydropower station as a case study to establish the ecological compensation required for habitats inundated by hydropower developments in Tibet, China (Fig. 1). We set out to examine the required ecological compensation, in the form of degraded grassland rehabilitation upstream, to restore carbon stock balance and improve ecological services at the watershed scale. The construction phase of the Pondo project lasted for 7 years (2008e2014) and the scheme will be operational for 50 years. The main characteristics of the Pondo hydropower station are shown in Table 2, and its land expropriation plan is shown in Table 3. In addition to text-based data, researchers investigated the Pondo hydropower plant and monitored some indicators of the reservoir in July over a 3-year period (2012e2014) to avoid the problem of stale data. The results revealed that in July the average dissolved oxygen (DO) in the reservoir was 5.86 mg/L and the average water surface temperature was 12.6 C. 2.2. Research framework This study was conducted to provide a method for estimating the required ecological compensation for habitats inundated during hydropower development to improve water basin resource management and ecological protection. Since the impacts of hydropower projects differ in terrestrial and aquatic habitats, the required compensation can be measured from different points of view. The ecological compensation approach proposed in this study was established from the point of view of overall carbon stock balance in the watershed (Fig. 2). During the process of hydro dam and reservoir construction and subsequent operation, the carbon stock losses at Site A (the dam and newly formed reservoir) mainly came from conversion of dry land to reservoir. To compensate for these losses, a restoration project was set up at Site B (an upstream grassland area) to improve ecological services through grassland rehabilitation and carbon sequestration. In this way, the carbon balance would be restored at the watershed scale. To determine the amount of restoration needed to compensate for the Site A, we established a service-to-service ecological
Table 1 Hydropower projects on the main stream of the Lhasa River, Tibet. Hydropower project
Type
Location
Installed capacity (MW)
Condition
Pondo Zhikong Pingcuo Najin Xianduo
Storage dam Storage dam River diversion Run-of-river diversion Run-of-river diversion
Linzhou county, upper reaches of Lhasa River Mozhugongka county, middle reaches of the Lhasa River Dazi county, lower reaches of the Lhasa River Chengguan district, lower reaches of the Lhasa River Chengguan district, lower reaches of the Lhasa River
120 100 6 7.8 2.6
Under construction Operational Operational Operational Operational
Please cite this article in press as: Yu, B., et al., Ecological compensation for inundated habitats in hydropower developments based on carbon stock balance, Journal of Cleaner Production (2015), http://dx.doi.org/10.1016/j.jclepro.2015.07.071
B. Yu et al. / Journal of Cleaner Production xxx (2015) 1e9
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Fig. 1. The location of Pondo hydropower station in Tibet, China. In this figure, the Site A and Site B stand for the inundated habitat and compensatory restoration area.
compensation framework for the inundated land following the concept described above (Fig. 3). The various restoration plans could be classified into four classes according to the type, quality, and value of natural resources and compensatory services provided relative to the natural resources and services lost due to inundation (NOAA, 1997). If the compensatory projects could provide the same or comparable services, the service-to-service approach could be used to scale the required compensation; otherwise, the value-to-value approach would be used to quantify it, which means that a variety of economic methods can be used to assess the socio-economic welfare implications of ecological damage and compensatory remediation
(Martin-Ortega et al., 2011). In this study, the service used in the framework was ecological carbon sequestration. Thus, the restoration of degraded grassland should provide comparable services (type, quality and amount of carbon sequestration) to those lost in the inundated habitats. The carbon stock losses could then be used as a basis for establishing the habitat equivalence analysis in terms of the service-to-service approach. That means the ecological compensation to be measured based on the calculated carbon stock loss and the equivalence of the local habitat. In this case, the project at Site B could offset the carbon sequestration loss at Site A; thus, the HEA method was used to determine the area of restoration at Site B required for compensating Site A.
Table 2 Key data for the Pondo hydropower station. Location
(30 N, 90 E)
Average flow (m3/s)
Runoff (108m3)
Dam height (m)
Available reservoir capacity (108m3)
Installed capacity (kW)
Inundated land (ha)
198
62.48
72.3
11.74
120,000
3251.36
Data source: Pondo hydropower project environmental impact assessment reports.
Table 3 Area inundated by the Pondo hydropower project during the construction period. Inundated area (ha)
1st year
2nd year
3rde4th year
5th year
6the7th year
Farmland Grassland Woodland
0 0 0
13.43 132.31 0
203.73 1035.32 3.26
101.87 517.66 1.63
203.73 1035.32 3.26
Data source: Pondo hydropower project environmental impact assessment reports.
Please cite this article in press as: Yu, B., et al., Ecological compensation for inundated habitats in hydropower developments based on carbon stock balance, Journal of Cleaner Production (2015), http://dx.doi.org/10.1016/j.jclepro.2015.07.071
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B. Yu et al. / Journal of Cleaner Production xxx (2015) 1e9
Fig. 2. A sketch map of inundated habitat site and compensatory restoration project site.
measures to offset these losses (Roach and Wade, 2006). The method uses an ecological metric to measure changes in ecological habitat services while focusing on quantifying the area involved and the level of impact over time. The gains and losses are quantified in units of “hectare-service-years” and “discounted service acre years (DSAYs)”, so that changes in past and future years are re et al., 2013). Using this comparable (Scruton et al., 2005; Vaissie method, the amount of compensation required can be calculated at a habitat scale (Zafonte and Hampton, 2007). The formula for the HEA can be summarized as:
AI
TI X t¼T0
ð1 þ rÞt It ¼ AR
TR X
ð1 þ rÞt Rt
(1)
t¼T1
where AI is the inundated area (ha) and AR is the compensatory area (ha); T0 is the time at which the injury occurs (yr) and TI is the time at which the injured area recovers to its baseline level (yr); T1 is the time at which the habitat restoration project begins to provide services (yr) and TR is the time at which the habitat replacement stops yielding services (yr); r is the discount rate (%); It is the intensity of impact, over AI at TI(%); and Rt is the intensity of compensation, over AR at TR(%). This method is primarily appropriate for use in situations involving the loss of ecological services with relatively little or no loss of direct human use (Natural Resource Trustees for Pearl Harbor, 1999). The main steps in the HEA can be summarized as follows. Fig. 3. ‘Service-to-service’ ecological compensation framework for inundated habitat during hydropower development.
2.3. Methods The methodology for estimating ecological compensation for inundated habitats in this study combined the HEA method and carbon stock loss estimation methods. 2.3.1. Habitat equivalency analysis Based on the service-to-service method, the HEA was adopted by the NOAA (1997) during the 1990s as part of the Natural Resource Damage Assessment procedure. The HEA estimates the lost ecological services associated with an environmental injury and then scales restorative ecological
(1) Quantification of the interim ecological loss due to inundation by the reservoir. The damage is measured as a combination of the area of habitat damaged and the degree of damage (in terms of the percentage reduction in the ecological services typically provided at baseline levels). (2) Selection of one or more ecological metrics as indicators of the service provided by natural ecosystems. (3) Identification of a range of compensatory restoration projects that provide a present value of service gain equal to the present value of the service losses from the natural resource injury. (4) Calculation of the size of compensatory area AR required to quantify the gains obtained from the compensatory area. In this study, carbon sequestration was the ecological service used to quantify the interim ecological loss, namely the carbon
Please cite this article in press as: Yu, B., et al., Ecological compensation for inundated habitats in hydropower developments based on carbon stock balance, Journal of Cleaner Production (2015), http://dx.doi.org/10.1016/j.jclepro.2015.07.071
B. Yu et al. / Journal of Cleaner Production xxx (2015) 1e9
stock loss, and thus Net Primary Productivity (NPP) was selected as its ecological metric. Alternative compensatory restoration projects were designed comprising various types of upstream grassland rehabilitation. The carbon stock loss from the inundated habitats was first estimated using the following methods.
2.3.2. Carbon stock loss estimation methods The gases produced in the reservoirs of these dams are primarily nitrogen, carbon dioxide and methane. According to the IPCC Guideline (2006), nitrous oxide emissions from flooded lands are typically very low, and there is currently insufficient information available regarding CH4 emissions because they are highly variable, both spatially and temporally, relative to CO2. In this study, we therefore focused on the emission of CO2, and its sequestration, to estimate the carbon stock loss caused by reservoir flooding. These losses come mainly from the conversion of the original dry land to reservoir flood (Part I) and from the new permanent reservoir itself (Part II). For part I, we calculated the carbon stock loss according to the following equations:
CLWfloodLB ¼
n X
CLWfloodLBðj1Þi þ DCLWfloodLBðj1Þi
(2)
j¼1
" DCLWfloodLB ¼
X
# Ai $ BAfteri BBeforei $CF
(3)
i
CO2
LWflood
44 ¼ DCLWfloodLB $ 12
(4)
where CLWfloodLB is the total carbon stock loss during reservoir construction; j is the construction period in years (7 in the case of Pondo); DCLWfloodLB is the annual change in carbon stocks as biomass on the land converted to reservoir, t C/yr; Ai is the area of land converted annually to reservoir from its original land use i, ha/ yr, (shown in Table 3); BAfteri is the biomass immediately following conversion to reservoir, t d.m./ha (default ¼ 0); BBeforei is the biomass immediately before conversion to reservoir, t d.m./ha, (shown in Table 4); CF is the carbon fraction of dry matter, t C/ t d.m.; and CO2_LWflood is the annual CO2 emissions on land converted to reservoir, t CO2/yr. For part II, experimental measurements were used to determine the amount of gas emitted from the reservoir via diffusion, bubbles and degassing. Presently however, two important gaps in our knowledge hamper integration of these emissions into national anthropogenic GHG inventories. Specifically, there is an obvious lack of data describing the emission patterns for reservoirs in several regions of the world. Additionally, the emission rates of reservoirs are highly variable. Due to a lack of full field data in Tibet, we used a simplified approach to estimate CO2 emissions from reservoirs using default emission factors and highly aggregated area data. The only CO2 emission pathway is diffusion during the ice-free period, and CO2 Table 4 NPP and biomass of farmland, grassland, woodland and water in the middle reaches of Yarlung Zangbo River. Land use type a
NPP (tC/ha yr) Biomass (t/ha yr) a
Farmland
Grassland
Woodland
Water
2.43 5.40
1.13 2.51
1.37 3.04
0.65 1.44
Adapted from Zhou et al. (2008).
5
diffusive emissions related to ice-cover period are assumed to be zero.
CO2 EmissionsLWflood ¼ P$EðCO2 Þdiff $Aflood;total
surface $fA $10
6
(5) where CO2EmissionsLWflood is the total CO2 emissions from the reservoir, Gg CO2/yr; P is the number of days without ice cover during a year, days/yr; E(CO2)diff is the average daily diffusive emissions, kg CO2/ha day; Aflood,total_surface is the total reservoir surface area, ha; and fA is the fraction of the total reservoir area that was flooded within the last 10 years.
3. Results and discussion 3.1. Carbon stock loss from Pondo Reservoir 3.1.1. Carbon stock loss from land conversion As shown in Table 4, the biomass of the local farmland, grassland and woodland could be estimated based on the NPP, namely Biomass ¼ NPP/CF, where CF ¼ 0.45 (Shi et al., 2008; Potter et al., 2010). Therefore, the carbon stock loss during the construction and operation of the Pondo reservoir were calculated according to equations (2)e(4) and are shown in Table 5. The annual loss of carbon stock during the Pondo reservoir construction period depended on the proportion of the annually inundated area during this period (Table 3). Moreover, the carbon stock was still falling during its period of operation because the NPP could not recover. Thus, the total loss over the long term ¼ sum [annual loss during construction] þ annual loss during operation the operating period in years (50 years for Pondo). Thus, the total carbon stock loss due to land conversion for the Pondo hydropower station throughout its life cycle would be 119,377 tons.
3.1.2. Carbon emissions from the Pondo Reservoir Calculation of carbon emissions from reservoirs is difficult, and reports of the intensity of these emissions vary widely in previous studies. Table 6 shows the changes in CO2 emissions with respect to water pH, temperature, reservoir age, latitude, and dissolved oxygen. Due to the location of Pondo (30 N, 90 E), we selected the data reported by Wang et al. (2012) to determine the CO2 emissions. According to historical meteorological data, the upstream portion of the Lhasa River freezes from November to March; thus, P was 214 days/yr (April to October). The total reservoir surface area (Aflood,total_surface) was 3788 ha, and fA was about 0.86. Additionally, the field survey revealed that CO2 emissions from the Pondo reservoir in July was about 2.78 kg/ha day. It was found that there was no obvious difference between the monitoring DO data (5.86 mg/L) and text-based data (6.2 mg/L, annual average DO data of Pondo segment of Lhasa River, cited from Pondo hydropower project environmental impact assessment reports). Thus, we adopted our field monitoring data to estimate the CO2 emission. According to equation (5), the CO2 emissions from the reservoir were about 1938 tons/year. It was assumed that CO2 emissions were limited to the first 10 years after flooding took place, and that any subsequent CO2 emissions were a result of carbon entering the reservoir from the surrounding land (IPCC, 2006). The total CO2 emission from the Pondo Reservoir was therefore about 19,380 tons, so that the carbon stock loss was 5285 tons. In total, the carbon stock loss as a result of reservoir construction and operation would have been 124,662 tons.
Please cite this article in press as: Yu, B., et al., Ecological compensation for inundated habitats in hydropower developments based on carbon stock balance, Journal of Cleaner Production (2015), http://dx.doi.org/10.1016/j.jclepro.2015.07.071
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Table 5 Carbon stock loss due to the Pondo hydropower's land conversion throughout its life cycle. Item
CO2 sequestration loss (tCO2) Carbon stock loss (tC)
Annual loss during construction 2009
2010
2011
2012
2013
2014
321.35 87.64
1905.20 519.60
3489.05 951.56
5072.91 1383.52
6656.76 1851.48
8240.61 2247.44
Annual loss during operation
Total loss over the long-term
8240.61 2247.44
437,716.55 119,377.24
Table 6 Previously reported CO2 emissions and correlations with related variables. Location
Dependent variable
Variables
Correlation
Source
United States (37 Ne47 N)
CO2 flux emission
Water pH
Soumis et al., 2004
Global estimations
CO2 emission
Reservoir age and latitude
Shuibuya Reservoir, China (30 Ne31 N)
CO2 flux emission
Dissolved Oxygen
Y ¼ (27085772x) þ 21952306 R2 ¼ 0.81, P < 0.001 Log(y þ 400) ¼ 3.06e0.16log xage 0.01xlat þ 0.41logxDOC R2 ¼ 0.40, P < 0.001; y ¼ 10.366x þ 123.98 R2 ¼ 0.8633
These results show that the inundated land provided a sink for an average of 0.64 t C/ha yr of carbon before the Pondo reservoir flooding, while after flooding it added 0.14 t C/ha yr of carbon. Since the life cycle of the Pondo hydropower project is 57 years, the total carbon stock loss of the habitat inundated by it was 124,662 tons, comprising 119,377 tons from land conversion and 5285 tons from reservoir emissions. It can be concluded that the wholesale ecosystem flooding caused by the Pondo hydro development changed the area from a relatively large GHG sink to a small source of greenhouse gases released to the atmosphere. However, in contrast to previous estimates that average fluxes from reservoirs worldwide range between 220 and 4460 mg m2 d of CO2 (Louis et al., 2000), the CO2 emissions from the Pondo reservoir (278 mg m2 d) were very low.
Wang et al., 2012
compensation scenarios for varying degrees of grassland degradation and rehabilitation over specific compensatory periods, as shown in Table 8.
3.2.2. Scale of compensation calculation (1) Ecological metric Considering the carbon stock changes in damaged habitats, we took the NPP as the ecological metric in the HEA of inundated lands. The NPP value-injured was defined to represent the carbon stock loss in inundated habitats, while the NPP value-restored was used to represent the carbon stock increase due to the restoration projects. (2) Restoration ratios in different ecological compensation scenarios
3.2. Results of ecological compensation study for inundated habitats 3.2.1. Alternative ecological compensation schemes According to a field survey and literature research, grassland is the main ecosystem type in Tibet, especially in Naqu Prefecture which consists of 286,900 km2 of native grasslands (Wei and Chen, 2001). The grasslands in Naqu Prefecture form the hinterland of the QinghaieTibet plateau and play an important role as windbreaks and in soil and water conservation. However, in recent years overgrazing has resulted in increasing grassland degradation, and over the last 20 years the area of grassland in Naqu Prefecture has decreased to 43.1% of the total land area (Mao et al., 2008). We therefore selected Nagqu County in Naqu Prefecture as a compensatory area (Site B) in which to develop a compensation scheme based on grassland rehabilitation (Fig. 1). According to the service-to-service principle, increasing the grassland ecological services by rehabilitating degraded grassland at Site B could offset the loss of ecological services at Site A caused by the Pondo development. We devised nine ecological
Barros et al., 2011
The restoration ratio (value-injured/value-restored) depends on the selected ecological metric and varies in different ecological compensation schemes. In this study, we set three types of grassland restoration for HEA based on the local conditions in Naqu Prefecture. Based on the above calculation, the carbon stock losses due to land conversion and reservoir emissions from the Pondo hydropower project per unit NPP were estimated to be 0.64 t C/ha yr and 0.14 t C/ha yr, respectively. The grasslands in Naqu Prefecture consist of alpine meadows. According to their biomass loss, the degraded grasslands could be divided into three classes; slightly, moderately, and severely degraded. Assuming that the compensation scheme would restore all the degraded grasslands to their original condition before degradation, restoration ratios could be calculated based on increases in NPP in the compensatory area under different ecological compensation scenarios. The results are shown in Table 7.
Table 7 Restoration ratios in three ecological compensatory scenarios. Ecological compensatory scenarios
Slightly degraded grassland restoration Moderately degraded grassland restoration Severely degraded grassland restoration
0.135 NPP increasea (tC/ha) Restoration ratios for land conversion 4.74 Restoration ratios for reservoir emission 1.04 a
0.27 2.37 0.52
0.405 1.58 0.35
NPP increases were cited from Li and Liu (2007).
Please cite this article in press as: Yu, B., et al., Ecological compensation for inundated habitats in hydropower developments based on carbon stock balance, Journal of Cleaner Production (2015), http://dx.doi.org/10.1016/j.jclepro.2015.07.071
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Table 8 Results of compensatory scale in various scenarios. Scenarios
Compensation period (yr)
Compensatory scale for land conversiona (ha)
Compensatory scale for reservoir emissionb (ha)
Total compensatory scale (ha)
Slightly degraded grassland restoration
1 5 10 1 5 10 1 5 10
17411.32 18455.54 19816.88 8705.66 9227.77 9908.44 5803.78 6151.85 6605.63
389.20 412.54 442.97 194.60 206.27 221.49 130.98 138.84 149.08
17800.52 18868.08 20259.85 8900.26 9434.04 10129.93 5934.76 6290.69 6754.71
Moderately degraded grassland restoration
Severely degraded grassland restoration
Note: the discount rate is 3%; the claim year in this study is 2015, i.e. the discount rate in this year is 1.0. a 100% loss of the inundated land and 100% full services of compensatory area continue in perpetuity. b 100% loss of the inundated land not in perpetuity and 100% full services of compensatory areas continue in perpetuity.
(3) Compensation scale under different scenarios In this study, the Visual_HEA software was chosen to calculate the compensatory area in each compensation scenario. This software provides a computer program which uses user-defined parameters representing HEA assumptions to determine the amount of compensatory resource services required. It was therefore useful to examine the sensitivity of results to a range of parameter values (Kohler and Dodge, 2006). We can use this software to compare the alternative compensation results, to determine the most appropriate compensatory action. It can also generate an injury and recovery curve to show the results more clearly. The specific program parameters used in single, and multiple time period compensatory scenarios were as shown as below, and the related results are shown in Table 8. C The extent of injury and loss of services of the Pondo Reservoir inundated habitats: the habitat injury begins in 2009; 4% of the 3251 ha (145.74 ha) was lost in 2009, and 23%, 42%, 62%, 81%, 100% of the 3251 ha was lost in 2010e2014. The total loss of the 3251 ha continues in perpetuity. C The services gained by the compensatory project (degraded grassland restoration). It was assumed that the compensatory action began in 2015. For a 1-year compensatory project, 100% of full services could be achieved by 2016. For a 5-year (or 10-year) compensatory project, 100% of full services could be achieved after 5 years in 2020 (or 2025); 100% full service continues in perpetuity. During the calculation process using the Visual_HEA software, a linear recovery function was used to represent the level of services provided by any compensatory action at a given time, as shown in Fig. 4. These results show that the compensatory area varies according to the compensatory period and degradation class. Due to the discount rate, the compensatory area required was larger when the ecological compensation was conducted over a longer compensation period. Because of the ‘service-to-service’ method, the compensatory area required was smaller when applied to the severely degraded grassland type. In terms of a lump-sum payment, in order to complete the compensation in 1 year, the required compensatory areas of slightly, moderately, and severely degraded grasslands were 17.80, 8.90, and 5.93 thousand hectares; for an ecological compensation period of 5 years, the compensatory areas of the slightly, moderately, and severely degraded grassland restoration scenarios were 18.87, 9.43, and 6.29 thousand hectares; and over a 10-year compensatory program, the compensatory areas in the slightly, moderately, and severely degraded grassland
restoration scenarios were 20.26, 10.13, and 6.75 thousand hectares. 3.3. Discussion In this study, degraded grassland restoration was considered as a method for ecological compensation for inundated land based on a service to service exchange. It is important to note that the following factors may lead to uncertainty in implementation of this design. In this study, we assumed the ecological compensation design with degraded grassland restoration could provide comparable services in terms of type, quality and carbon sequestration using the habitat equivalency analysis. As the habitat loss due to inundation during hydropower development is inevitable and irreversible, the on-site restoration was not practical. Thus, we selected NPP as the ecological metric and assumed that the relationships between NPP and the ecological service provided by grassland, farmland and woodland were equivalent. It aims to put forward an ecological compensation approach for inundated habitats from the aspect of the watershed. The restrictive assumptions may lead to some differences between HEA results and the actual compensation for losses. According to the ecological compensation scenario analysis, the scale of compensation for inundated habitats mainly depends on the compensation periods for any given type of grassland restoration. The results show that the longer the time period that the services took to reach full maturity, the larger the scale of compensation that was needed. However, in reality, the discount rate significantly affects these results, as it reflects the relative value of present versus future service levels. Because of this, a sensitivity analysis of the discount rate was conducted and the results are shown in Fig. 5. The sensitivity analysis showed that the discount rate had a significant impact on the DSAYs gained per unit area in different compensatory periods. In this study, the discount rate was set at a historical value of 3% (Kohler and Dodge, 2006). However, when the discount rate is increased to 0.1%, the gained DSAYs decrease by 4%. 4. Conclusion This study established a ‘service-to-service’ ecological compensation framework for inundated habitats in hydropower developments through measures to restore degraded grasslands upstream. It also demonstrated how the carbon stock losses from reservoir construction and operation could be combined with habitat equivalency analysis to determine the required levels of
Please cite this article in press as: Yu, B., et al., Ecological compensation for inundated habitats in hydropower developments based on carbon stock balance, Journal of Cleaner Production (2015), http://dx.doi.org/10.1016/j.jclepro.2015.07.071
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Fig. 4. The time history shape functions of lost and gained services used in the inundated area and compensatory area.
University (NCET-13-0064), and the State Environment Protection Commonweal Special Program, China (No. 201209032).
References
Fig. 5. The sensitive analysis to discount rate parameter (r).
ecological compensation. Through this ecological compensation, the carbon stock loss due to reservoir construction and operation could be compensated for and the eco-environmental status could be improved at the watershed scale. The results showed that the carbon stock loss of the Pondo reservoir project would be 124,662 tons, and that 97.7% of that loss arose from habitat inundation originating from land conversion. The restoration of about 5935 ha of severely degraded grasslands would be needed to compensate for the carbon loss, and the required compensatory area would be larger if the compensatory period was longer or if the improved compensatory grassland was less degraded. It should be noted that this study estimated the carbon stock based on CO2 sequestration, and therefore produced conservative estimates of the carbon stock exchange and the ecological compensation area in terms of GHG.
Acknowledgments This work was funded by the National Science and Technology Pillar Program, China (No. 2012BAC05B02), the Fund for Innovative Research Group of the National Natural Science Foundation of China (Grant No. 51121003), the New Century Excellent Talents in
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Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro
Ecological compensation for inundated habitats in hydropower developments based on carbon stock balance Bing Yu, Linyu Xu*, Zhifeng Yang State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, No. 19, Xinjiekouwai Street, Haidian District, Beijing 100875, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 14 July 2014 Received in revised form 9 June 2015 Accepted 13 July 2015 Available online xxx
Hydroelectric power reservoirs have been identified as potentially important sources of greenhouse gas (GHG) emissions due to the large areas of habitat which are inundated, leading to doubts as to whether hydropower is actually a net low-carbon energy source. In this study we propose a ‘service-to-service’ ecological analysis of inundated habitats from the viewpoint of carbon stock balance compared with the carbon stock loss from hydropower reservoirs. We consider whether the lost ecological service of carbon sequestration by inundated farmland, grassland and woodland could be offset by an increased ecological service provided by a grassland rehabilitation project. We also establish an integrated ecological compensation accounting methodology for inundated habitats by combining habitat equivalency analysis and estimates of carbon stock loss. This ecological compensation framework is illustrated by calculations from a case study of the Pondo hydropower project in Tibet, China. The results estimate that the total carbon stock losses from the construction and operation of this reservoir was 124,662 tons; requiring a compensatory restoration of areas of slightly, moderately, or severely degraded grasslands of 17.80, 8.90, and 5.93 thousand hectares, in a lump-sum payment mode. By means of such ecological compensations, carbon stock balance could be realized at the watershed scale, and the advantages of low-carbon hydropower developments could be fully realized. © 2015 Elsevier Ltd. All rights reserved.
Keywords: Ecological compensation Habitat equivalency analysis Carbon sequestration Grassland rehabilitation Tibet
1. Introduction 1.1. Inundated habitats and carbon emission The low-carbon advantages associated with hydroelectric power development are increasingly being called into question due to the multiple environmental impacts of these facilities (Li et al., 2015a; Zhang et al., 2014; Chen et al., 2015; Zhang et al., 2015). Zhang and Xu (2013) showed that the low-carbon status of large hydropower projects is currently overestimated. The Cary Institute of Ecosystem Studies reported that hydropower reservoirs are potentially important sources of greenhouse gas (GHG) emissions (Barros et al., 2011). When a hydroelectric reservoir is built it inundates an extensive area, destroying the terrestrial ecosystem on the site. As a result, ecosystem services such as CO2 sequestration and O2 release, and soil and water conservation are lost. Moreover, the newly flooded biomass decays, resulting in a gradual release of greenhouse gases (Varun et al., 2009).
* Corresponding author. Tel./fax: þ86 (0)10 58800618. E-mail address: [email protected] (L. Xu).
Globally, more than two-thirds of the world's rivers have been interrupted by dams and reservoirs, and the area of formerly terrestrial habitat inundated by large reservoirs in the 1990s was the size of California or France (Dynesius and Nilson, 1994). Previous calculations have indicated that the global GHG emissions from reservoirs may be equivalent to 7% of the total potentially global warming emissions (Louis et al., 2000). In tropical areas, GHG emissions per megawatt of electricity produced could be as high as those from fossil-fuel power plants (Rosa et al., 2004). In this context, the Intergovernmental Panel on Climate Change (IPCC) included emissions from artificially flooded regions in its National Greenhouse Gas Inventory Programme (Graham-Rowe, 2005). In 2006, it also developed guidelines for national GHG inventories which include a method for estimating changes in carbon stock due to land conversion to permanently flooded land (IPCC, 2006). 1.2. Importance of ecological compensation to carbon stocks Carbon emissions from reservoirs reduce the low-carbon advantages of hydropower development, and may even contribute to global climate change, such as global warming (Mendonça et al.,
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2012; Li et al., 2015b). It is therefore necessary to take measures to improve degraded areas or to create new habitats with similar ecological functions and qualities to offset the resulting carbon stock loss. Such measures, referred to as ecological compensation (Allen and Feddema, 1996), are defined as the substitution of ecological functions or qualities that have been impaired by human activities (Cuperus et al., 1996). In practice, ecological compensation is referred to as ‘in-kind’ compensation when the ecosystem is restored using the same items that were lost, and ‘out-of-kind’ when the lost factors are replaced with different items (Cuperus et al., 1999) . Ecological compensation measures have been taken in many countries to compensate for environmental impacts on both terrestrial and aquatic habitats (Trussart et al., 2002; Xu et al., 2014). Habitat restoration projects and payments for ecosystem services (PES) are the two main methods of mitigation that have been used to compensate for the damage caused by hydropower development. Restoration measures have generally included the reduction of reservoir sedimentation, the modification of water quality, the regulation of hydrological regimes, and the removal of barriers to fish migration and river navigation (Trussart et al., 2002). Furthermore, some dams have even been decommissioned and removed in some developed countries (Anderson et al., 2006). PES schemes for hydropower involving payment in the form of planted forests have been conducted in Costa Rica (Rojas and Aylward, 2002) and Cambodia (Arias et al., 2011), although these methods have not been widely applied. Although current ecological compensation measures have been generally beneficial to hydropower development, there have been too few related studies geared toward understanding their effectiveness. As global warming proceeds, it has become increasingly important to pay attention to carbon stock loss from inundated habitats as a result of hydropower development. Further ecological compensation measures should probably be taken to offset carbon stock losses and improve the advantages of low-carbon hydropower development. This study was conducted for just this purpose. Notwithstanding the existing studies of ecological compensation, it is still unclear as to how much restoration work is required to offset the ecological losses caused by dams and reservoirs. The habitat equivalence analysis (HEA) was proposed by the United States National Oceanic and Atmospheric Administration (NOAA), which calls for properly scaled compensatory restoration (Burlington, 1999). Using the HEA, effective levels of compensation for damaged habitats can be realized on a service-to-service basis, but selection of the appropriate ecological metrics is difficult. In this study, we attempt to establish an ecological compensation approach for inundated habitats through a combination of HEA and carbon stock loss estimation. 2. Materials and methods 2.1. Study area and data collection In recent years hydropower has developed rapidly in China, especially in Tibet. The middle reach of the Yarlung Zangbo River is
to be the main source of new hydropower according to the 12th Chinese Five-Year Energy Development Plan (National Energy Administration, 2013). Tibet provides an important ecosystem service in supplying fresh water to most of Asia (Immerzeel et al., 2008). Therefore, determining how to compensate for natural ecosystems damaged during hydropower development in Tibet is essential. The Lhasa River is one of the larger tributaries in the middle reaches of the Yarlung Zangbo River, and originates in the southern ^ntanglha Mountain, on the Tibet Plateau foothills of the Nyainqe (Yang et al., 2007). The main stream of the Lhasa River is rich in water, and is capable of providing 1.715 million kW of electricity. With the increasing demand for electricity, hydropower projects have developed rapidly on the Lhasa River in recent years, and there are currently five hydropower projects on its main stream (Table 1). Among these the Pondo hydropower project is the most important engineering development affecting the flow of the Lhasa River, with the largest inundated area. We therefore selected the Pondo hydropower station as a case study to establish the ecological compensation required for habitats inundated by hydropower developments in Tibet, China (Fig. 1). We set out to examine the required ecological compensation, in the form of degraded grassland rehabilitation upstream, to restore carbon stock balance and improve ecological services at the watershed scale. The construction phase of the Pondo project lasted for 7 years (2008e2014) and the scheme will be operational for 50 years. The main characteristics of the Pondo hydropower station are shown in Table 2, and its land expropriation plan is shown in Table 3. In addition to text-based data, researchers investigated the Pondo hydropower plant and monitored some indicators of the reservoir in July over a 3-year period (2012e2014) to avoid the problem of stale data. The results revealed that in July the average dissolved oxygen (DO) in the reservoir was 5.86 mg/L and the average water surface temperature was 12.6 C. 2.2. Research framework This study was conducted to provide a method for estimating the required ecological compensation for habitats inundated during hydropower development to improve water basin resource management and ecological protection. Since the impacts of hydropower projects differ in terrestrial and aquatic habitats, the required compensation can be measured from different points of view. The ecological compensation approach proposed in this study was established from the point of view of overall carbon stock balance in the watershed (Fig. 2). During the process of hydro dam and reservoir construction and subsequent operation, the carbon stock losses at Site A (the dam and newly formed reservoir) mainly came from conversion of dry land to reservoir. To compensate for these losses, a restoration project was set up at Site B (an upstream grassland area) to improve ecological services through grassland rehabilitation and carbon sequestration. In this way, the carbon balance would be restored at the watershed scale. To determine the amount of restoration needed to compensate for the Site A, we established a service-to-service ecological
Table 1 Hydropower projects on the main stream of the Lhasa River, Tibet. Hydropower project
Type
Location
Installed capacity (MW)
Condition
Pondo Zhikong Pingcuo Najin Xianduo
Storage dam Storage dam River diversion Run-of-river diversion Run-of-river diversion
Linzhou county, upper reaches of Lhasa River Mozhugongka county, middle reaches of the Lhasa River Dazi county, lower reaches of the Lhasa River Chengguan district, lower reaches of the Lhasa River Chengguan district, lower reaches of the Lhasa River
120 100 6 7.8 2.6
Under construction Operational Operational Operational Operational
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3
Fig. 1. The location of Pondo hydropower station in Tibet, China. In this figure, the Site A and Site B stand for the inundated habitat and compensatory restoration area.
compensation framework for the inundated land following the concept described above (Fig. 3). The various restoration plans could be classified into four classes according to the type, quality, and value of natural resources and compensatory services provided relative to the natural resources and services lost due to inundation (NOAA, 1997). If the compensatory projects could provide the same or comparable services, the service-to-service approach could be used to scale the required compensation; otherwise, the value-to-value approach would be used to quantify it, which means that a variety of economic methods can be used to assess the socio-economic welfare implications of ecological damage and compensatory remediation
(Martin-Ortega et al., 2011). In this study, the service used in the framework was ecological carbon sequestration. Thus, the restoration of degraded grassland should provide comparable services (type, quality and amount of carbon sequestration) to those lost in the inundated habitats. The carbon stock losses could then be used as a basis for establishing the habitat equivalence analysis in terms of the service-to-service approach. That means the ecological compensation to be measured based on the calculated carbon stock loss and the equivalence of the local habitat. In this case, the project at Site B could offset the carbon sequestration loss at Site A; thus, the HEA method was used to determine the area of restoration at Site B required for compensating Site A.
Table 2 Key data for the Pondo hydropower station. Location
(30 N, 90 E)
Average flow (m3/s)
Runoff (108m3)
Dam height (m)
Available reservoir capacity (108m3)
Installed capacity (kW)
Inundated land (ha)
198
62.48
72.3
11.74
120,000
3251.36
Data source: Pondo hydropower project environmental impact assessment reports.
Table 3 Area inundated by the Pondo hydropower project during the construction period. Inundated area (ha)
1st year
2nd year
3rde4th year
5th year
6the7th year
Farmland Grassland Woodland
0 0 0
13.43 132.31 0
203.73 1035.32 3.26
101.87 517.66 1.63
203.73 1035.32 3.26
Data source: Pondo hydropower project environmental impact assessment reports.
Please cite this article in press as: Yu, B., et al., Ecological compensation for inundated habitats in hydropower developments based on carbon stock balance, Journal of Cleaner Production (2015), http://dx.doi.org/10.1016/j.jclepro.2015.07.071
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Fig. 2. A sketch map of inundated habitat site and compensatory restoration project site.
measures to offset these losses (Roach and Wade, 2006). The method uses an ecological metric to measure changes in ecological habitat services while focusing on quantifying the area involved and the level of impact over time. The gains and losses are quantified in units of “hectare-service-years” and “discounted service acre years (DSAYs)”, so that changes in past and future years are re et al., 2013). Using this comparable (Scruton et al., 2005; Vaissie method, the amount of compensation required can be calculated at a habitat scale (Zafonte and Hampton, 2007). The formula for the HEA can be summarized as:
AI
TI X t¼T0
ð1 þ rÞt It ¼ AR
TR X
ð1 þ rÞt Rt
(1)
t¼T1
where AI is the inundated area (ha) and AR is the compensatory area (ha); T0 is the time at which the injury occurs (yr) and TI is the time at which the injured area recovers to its baseline level (yr); T1 is the time at which the habitat restoration project begins to provide services (yr) and TR is the time at which the habitat replacement stops yielding services (yr); r is the discount rate (%); It is the intensity of impact, over AI at TI(%); and Rt is the intensity of compensation, over AR at TR(%). This method is primarily appropriate for use in situations involving the loss of ecological services with relatively little or no loss of direct human use (Natural Resource Trustees for Pearl Harbor, 1999). The main steps in the HEA can be summarized as follows. Fig. 3. ‘Service-to-service’ ecological compensation framework for inundated habitat during hydropower development.
2.3. Methods The methodology for estimating ecological compensation for inundated habitats in this study combined the HEA method and carbon stock loss estimation methods. 2.3.1. Habitat equivalency analysis Based on the service-to-service method, the HEA was adopted by the NOAA (1997) during the 1990s as part of the Natural Resource Damage Assessment procedure. The HEA estimates the lost ecological services associated with an environmental injury and then scales restorative ecological
(1) Quantification of the interim ecological loss due to inundation by the reservoir. The damage is measured as a combination of the area of habitat damaged and the degree of damage (in terms of the percentage reduction in the ecological services typically provided at baseline levels). (2) Selection of one or more ecological metrics as indicators of the service provided by natural ecosystems. (3) Identification of a range of compensatory restoration projects that provide a present value of service gain equal to the present value of the service losses from the natural resource injury. (4) Calculation of the size of compensatory area AR required to quantify the gains obtained from the compensatory area. In this study, carbon sequestration was the ecological service used to quantify the interim ecological loss, namely the carbon
Please cite this article in press as: Yu, B., et al., Ecological compensation for inundated habitats in hydropower developments based on carbon stock balance, Journal of Cleaner Production (2015), http://dx.doi.org/10.1016/j.jclepro.2015.07.071
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stock loss, and thus Net Primary Productivity (NPP) was selected as its ecological metric. Alternative compensatory restoration projects were designed comprising various types of upstream grassland rehabilitation. The carbon stock loss from the inundated habitats was first estimated using the following methods.
2.3.2. Carbon stock loss estimation methods The gases produced in the reservoirs of these dams are primarily nitrogen, carbon dioxide and methane. According to the IPCC Guideline (2006), nitrous oxide emissions from flooded lands are typically very low, and there is currently insufficient information available regarding CH4 emissions because they are highly variable, both spatially and temporally, relative to CO2. In this study, we therefore focused on the emission of CO2, and its sequestration, to estimate the carbon stock loss caused by reservoir flooding. These losses come mainly from the conversion of the original dry land to reservoir flood (Part I) and from the new permanent reservoir itself (Part II). For part I, we calculated the carbon stock loss according to the following equations:
CLWfloodLB ¼
n X
CLWfloodLBðj1Þi þ DCLWfloodLBðj1Þi
(2)
j¼1
" DCLWfloodLB ¼
X
# Ai $ BAfteri BBeforei $CF
(3)
i
CO2
LWflood
44 ¼ DCLWfloodLB $ 12
(4)
where CLWfloodLB is the total carbon stock loss during reservoir construction; j is the construction period in years (7 in the case of Pondo); DCLWfloodLB is the annual change in carbon stocks as biomass on the land converted to reservoir, t C/yr; Ai is the area of land converted annually to reservoir from its original land use i, ha/ yr, (shown in Table 3); BAfteri is the biomass immediately following conversion to reservoir, t d.m./ha (default ¼ 0); BBeforei is the biomass immediately before conversion to reservoir, t d.m./ha, (shown in Table 4); CF is the carbon fraction of dry matter, t C/ t d.m.; and CO2_LWflood is the annual CO2 emissions on land converted to reservoir, t CO2/yr. For part II, experimental measurements were used to determine the amount of gas emitted from the reservoir via diffusion, bubbles and degassing. Presently however, two important gaps in our knowledge hamper integration of these emissions into national anthropogenic GHG inventories. Specifically, there is an obvious lack of data describing the emission patterns for reservoirs in several regions of the world. Additionally, the emission rates of reservoirs are highly variable. Due to a lack of full field data in Tibet, we used a simplified approach to estimate CO2 emissions from reservoirs using default emission factors and highly aggregated area data. The only CO2 emission pathway is diffusion during the ice-free period, and CO2 Table 4 NPP and biomass of farmland, grassland, woodland and water in the middle reaches of Yarlung Zangbo River. Land use type a
NPP (tC/ha yr) Biomass (t/ha yr) a
Farmland
Grassland
Woodland
Water
2.43 5.40
1.13 2.51
1.37 3.04
0.65 1.44
Adapted from Zhou et al. (2008).
5
diffusive emissions related to ice-cover period are assumed to be zero.
CO2 EmissionsLWflood ¼ P$EðCO2 Þdiff $Aflood;total
surface $fA $10
6
(5) where CO2EmissionsLWflood is the total CO2 emissions from the reservoir, Gg CO2/yr; P is the number of days without ice cover during a year, days/yr; E(CO2)diff is the average daily diffusive emissions, kg CO2/ha day; Aflood,total_surface is the total reservoir surface area, ha; and fA is the fraction of the total reservoir area that was flooded within the last 10 years.
3. Results and discussion 3.1. Carbon stock loss from Pondo Reservoir 3.1.1. Carbon stock loss from land conversion As shown in Table 4, the biomass of the local farmland, grassland and woodland could be estimated based on the NPP, namely Biomass ¼ NPP/CF, where CF ¼ 0.45 (Shi et al., 2008; Potter et al., 2010). Therefore, the carbon stock loss during the construction and operation of the Pondo reservoir were calculated according to equations (2)e(4) and are shown in Table 5. The annual loss of carbon stock during the Pondo reservoir construction period depended on the proportion of the annually inundated area during this period (Table 3). Moreover, the carbon stock was still falling during its period of operation because the NPP could not recover. Thus, the total loss over the long term ¼ sum [annual loss during construction] þ annual loss during operation the operating period in years (50 years for Pondo). Thus, the total carbon stock loss due to land conversion for the Pondo hydropower station throughout its life cycle would be 119,377 tons.
3.1.2. Carbon emissions from the Pondo Reservoir Calculation of carbon emissions from reservoirs is difficult, and reports of the intensity of these emissions vary widely in previous studies. Table 6 shows the changes in CO2 emissions with respect to water pH, temperature, reservoir age, latitude, and dissolved oxygen. Due to the location of Pondo (30 N, 90 E), we selected the data reported by Wang et al. (2012) to determine the CO2 emissions. According to historical meteorological data, the upstream portion of the Lhasa River freezes from November to March; thus, P was 214 days/yr (April to October). The total reservoir surface area (Aflood,total_surface) was 3788 ha, and fA was about 0.86. Additionally, the field survey revealed that CO2 emissions from the Pondo reservoir in July was about 2.78 kg/ha day. It was found that there was no obvious difference between the monitoring DO data (5.86 mg/L) and text-based data (6.2 mg/L, annual average DO data of Pondo segment of Lhasa River, cited from Pondo hydropower project environmental impact assessment reports). Thus, we adopted our field monitoring data to estimate the CO2 emission. According to equation (5), the CO2 emissions from the reservoir were about 1938 tons/year. It was assumed that CO2 emissions were limited to the first 10 years after flooding took place, and that any subsequent CO2 emissions were a result of carbon entering the reservoir from the surrounding land (IPCC, 2006). The total CO2 emission from the Pondo Reservoir was therefore about 19,380 tons, so that the carbon stock loss was 5285 tons. In total, the carbon stock loss as a result of reservoir construction and operation would have been 124,662 tons.
Please cite this article in press as: Yu, B., et al., Ecological compensation for inundated habitats in hydropower developments based on carbon stock balance, Journal of Cleaner Production (2015), http://dx.doi.org/10.1016/j.jclepro.2015.07.071
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B. Yu et al. / Journal of Cleaner Production xxx (2015) 1e9
Table 5 Carbon stock loss due to the Pondo hydropower's land conversion throughout its life cycle. Item
CO2 sequestration loss (tCO2) Carbon stock loss (tC)
Annual loss during construction 2009
2010
2011
2012
2013
2014
321.35 87.64
1905.20 519.60
3489.05 951.56
5072.91 1383.52
6656.76 1851.48
8240.61 2247.44
Annual loss during operation
Total loss over the long-term
8240.61 2247.44
437,716.55 119,377.24
Table 6 Previously reported CO2 emissions and correlations with related variables. Location
Dependent variable
Variables
Correlation
Source
United States (37 Ne47 N)
CO2 flux emission
Water pH
Soumis et al., 2004
Global estimations
CO2 emission
Reservoir age and latitude
Shuibuya Reservoir, China (30 Ne31 N)
CO2 flux emission
Dissolved Oxygen
Y ¼ (27085772x) þ 21952306 R2 ¼ 0.81, P < 0.001 Log(y þ 400) ¼ 3.06e0.16log xage 0.01xlat þ 0.41logxDOC R2 ¼ 0.40, P < 0.001; y ¼ 10.366x þ 123.98 R2 ¼ 0.8633
These results show that the inundated land provided a sink for an average of 0.64 t C/ha yr of carbon before the Pondo reservoir flooding, while after flooding it added 0.14 t C/ha yr of carbon. Since the life cycle of the Pondo hydropower project is 57 years, the total carbon stock loss of the habitat inundated by it was 124,662 tons, comprising 119,377 tons from land conversion and 5285 tons from reservoir emissions. It can be concluded that the wholesale ecosystem flooding caused by the Pondo hydro development changed the area from a relatively large GHG sink to a small source of greenhouse gases released to the atmosphere. However, in contrast to previous estimates that average fluxes from reservoirs worldwide range between 220 and 4460 mg m2 d of CO2 (Louis et al., 2000), the CO2 emissions from the Pondo reservoir (278 mg m2 d) were very low.
Wang et al., 2012
compensation scenarios for varying degrees of grassland degradation and rehabilitation over specific compensatory periods, as shown in Table 8.
3.2.2. Scale of compensation calculation (1) Ecological metric Considering the carbon stock changes in damaged habitats, we took the NPP as the ecological metric in the HEA of inundated lands. The NPP value-injured was defined to represent the carbon stock loss in inundated habitats, while the NPP value-restored was used to represent the carbon stock increase due to the restoration projects. (2) Restoration ratios in different ecological compensation scenarios
3.2. Results of ecological compensation study for inundated habitats 3.2.1. Alternative ecological compensation schemes According to a field survey and literature research, grassland is the main ecosystem type in Tibet, especially in Naqu Prefecture which consists of 286,900 km2 of native grasslands (Wei and Chen, 2001). The grasslands in Naqu Prefecture form the hinterland of the QinghaieTibet plateau and play an important role as windbreaks and in soil and water conservation. However, in recent years overgrazing has resulted in increasing grassland degradation, and over the last 20 years the area of grassland in Naqu Prefecture has decreased to 43.1% of the total land area (Mao et al., 2008). We therefore selected Nagqu County in Naqu Prefecture as a compensatory area (Site B) in which to develop a compensation scheme based on grassland rehabilitation (Fig. 1). According to the service-to-service principle, increasing the grassland ecological services by rehabilitating degraded grassland at Site B could offset the loss of ecological services at Site A caused by the Pondo development. We devised nine ecological
Barros et al., 2011
The restoration ratio (value-injured/value-restored) depends on the selected ecological metric and varies in different ecological compensation schemes. In this study, we set three types of grassland restoration for HEA based on the local conditions in Naqu Prefecture. Based on the above calculation, the carbon stock losses due to land conversion and reservoir emissions from the Pondo hydropower project per unit NPP were estimated to be 0.64 t C/ha yr and 0.14 t C/ha yr, respectively. The grasslands in Naqu Prefecture consist of alpine meadows. According to their biomass loss, the degraded grasslands could be divided into three classes; slightly, moderately, and severely degraded. Assuming that the compensation scheme would restore all the degraded grasslands to their original condition before degradation, restoration ratios could be calculated based on increases in NPP in the compensatory area under different ecological compensation scenarios. The results are shown in Table 7.
Table 7 Restoration ratios in three ecological compensatory scenarios. Ecological compensatory scenarios
Slightly degraded grassland restoration Moderately degraded grassland restoration Severely degraded grassland restoration
0.135 NPP increasea (tC/ha) Restoration ratios for land conversion 4.74 Restoration ratios for reservoir emission 1.04 a
0.27 2.37 0.52
0.405 1.58 0.35
NPP increases were cited from Li and Liu (2007).
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B. Yu et al. / Journal of Cleaner Production xxx (2015) 1e9
7
Table 8 Results of compensatory scale in various scenarios. Scenarios
Compensation period (yr)
Compensatory scale for land conversiona (ha)
Compensatory scale for reservoir emissionb (ha)
Total compensatory scale (ha)
Slightly degraded grassland restoration
1 5 10 1 5 10 1 5 10
17411.32 18455.54 19816.88 8705.66 9227.77 9908.44 5803.78 6151.85 6605.63
389.20 412.54 442.97 194.60 206.27 221.49 130.98 138.84 149.08
17800.52 18868.08 20259.85 8900.26 9434.04 10129.93 5934.76 6290.69 6754.71
Moderately degraded grassland restoration
Severely degraded grassland restoration
Note: the discount rate is 3%; the claim year in this study is 2015, i.e. the discount rate in this year is 1.0. a 100% loss of the inundated land and 100% full services of compensatory area continue in perpetuity. b 100% loss of the inundated land not in perpetuity and 100% full services of compensatory areas continue in perpetuity.
(3) Compensation scale under different scenarios In this study, the Visual_HEA software was chosen to calculate the compensatory area in each compensation scenario. This software provides a computer program which uses user-defined parameters representing HEA assumptions to determine the amount of compensatory resource services required. It was therefore useful to examine the sensitivity of results to a range of parameter values (Kohler and Dodge, 2006). We can use this software to compare the alternative compensation results, to determine the most appropriate compensatory action. It can also generate an injury and recovery curve to show the results more clearly. The specific program parameters used in single, and multiple time period compensatory scenarios were as shown as below, and the related results are shown in Table 8. C The extent of injury and loss of services of the Pondo Reservoir inundated habitats: the habitat injury begins in 2009; 4% of the 3251 ha (145.74 ha) was lost in 2009, and 23%, 42%, 62%, 81%, 100% of the 3251 ha was lost in 2010e2014. The total loss of the 3251 ha continues in perpetuity. C The services gained by the compensatory project (degraded grassland restoration). It was assumed that the compensatory action began in 2015. For a 1-year compensatory project, 100% of full services could be achieved by 2016. For a 5-year (or 10-year) compensatory project, 100% of full services could be achieved after 5 years in 2020 (or 2025); 100% full service continues in perpetuity. During the calculation process using the Visual_HEA software, a linear recovery function was used to represent the level of services provided by any compensatory action at a given time, as shown in Fig. 4. These results show that the compensatory area varies according to the compensatory period and degradation class. Due to the discount rate, the compensatory area required was larger when the ecological compensation was conducted over a longer compensation period. Because of the ‘service-to-service’ method, the compensatory area required was smaller when applied to the severely degraded grassland type. In terms of a lump-sum payment, in order to complete the compensation in 1 year, the required compensatory areas of slightly, moderately, and severely degraded grasslands were 17.80, 8.90, and 5.93 thousand hectares; for an ecological compensation period of 5 years, the compensatory areas of the slightly, moderately, and severely degraded grassland restoration scenarios were 18.87, 9.43, and 6.29 thousand hectares; and over a 10-year compensatory program, the compensatory areas in the slightly, moderately, and severely degraded grassland
restoration scenarios were 20.26, 10.13, and 6.75 thousand hectares. 3.3. Discussion In this study, degraded grassland restoration was considered as a method for ecological compensation for inundated land based on a service to service exchange. It is important to note that the following factors may lead to uncertainty in implementation of this design. In this study, we assumed the ecological compensation design with degraded grassland restoration could provide comparable services in terms of type, quality and carbon sequestration using the habitat equivalency analysis. As the habitat loss due to inundation during hydropower development is inevitable and irreversible, the on-site restoration was not practical. Thus, we selected NPP as the ecological metric and assumed that the relationships between NPP and the ecological service provided by grassland, farmland and woodland were equivalent. It aims to put forward an ecological compensation approach for inundated habitats from the aspect of the watershed. The restrictive assumptions may lead to some differences between HEA results and the actual compensation for losses. According to the ecological compensation scenario analysis, the scale of compensation for inundated habitats mainly depends on the compensation periods for any given type of grassland restoration. The results show that the longer the time period that the services took to reach full maturity, the larger the scale of compensation that was needed. However, in reality, the discount rate significantly affects these results, as it reflects the relative value of present versus future service levels. Because of this, a sensitivity analysis of the discount rate was conducted and the results are shown in Fig. 5. The sensitivity analysis showed that the discount rate had a significant impact on the DSAYs gained per unit area in different compensatory periods. In this study, the discount rate was set at a historical value of 3% (Kohler and Dodge, 2006). However, when the discount rate is increased to 0.1%, the gained DSAYs decrease by 4%. 4. Conclusion This study established a ‘service-to-service’ ecological compensation framework for inundated habitats in hydropower developments through measures to restore degraded grasslands upstream. It also demonstrated how the carbon stock losses from reservoir construction and operation could be combined with habitat equivalency analysis to determine the required levels of
Please cite this article in press as: Yu, B., et al., Ecological compensation for inundated habitats in hydropower developments based on carbon stock balance, Journal of Cleaner Production (2015), http://dx.doi.org/10.1016/j.jclepro.2015.07.071
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B. Yu et al. / Journal of Cleaner Production xxx (2015) 1e9
Fig. 4. The time history shape functions of lost and gained services used in the inundated area and compensatory area.
University (NCET-13-0064), and the State Environment Protection Commonweal Special Program, China (No. 201209032).
References
Fig. 5. The sensitive analysis to discount rate parameter (r).
ecological compensation. Through this ecological compensation, the carbon stock loss due to reservoir construction and operation could be compensated for and the eco-environmental status could be improved at the watershed scale. The results showed that the carbon stock loss of the Pondo reservoir project would be 124,662 tons, and that 97.7% of that loss arose from habitat inundation originating from land conversion. The restoration of about 5935 ha of severely degraded grasslands would be needed to compensate for the carbon loss, and the required compensatory area would be larger if the compensatory period was longer or if the improved compensatory grassland was less degraded. It should be noted that this study estimated the carbon stock based on CO2 sequestration, and therefore produced conservative estimates of the carbon stock exchange and the ecological compensation area in terms of GHG.
Acknowledgments This work was funded by the National Science and Technology Pillar Program, China (No. 2012BAC05B02), the Fund for Innovative Research Group of the National Natural Science Foundation of China (Grant No. 51121003), the New Century Excellent Talents in
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Please cite this article in press as: Yu, B., et al., Ecological compensation for inundated habitats in hydropower developments based on carbon stock balance, Journal of Cleaner Production (2015), http://dx.doi.org/10.1016/j.jclepro.2015.07.071