Valuation of ecosystem services of rice–fish coculture systems in Ruyuan County, China

Ecosystem Services 41 (2020) 101054

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Valuation of ecosystem services of rice–fish coculture systems in Ruyuan County, China ⁎

T

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Duan Liua, , Runcheng Tanga, Jun Xieb, , Jingjing Tianb, Rui Shia, Kai Zhangb a b

Business School, Hunan University, Changsha, China Pearl River Fisheries Research Institute, Chinese Academy of Fishery Science, Guangzhou, China

A R T I C LE I N FO

A B S T R A C T

Keywords: Rice–fish coculture systems Ecosystem services Value assessment Sustainability China Economic value

Rice–fish coculture ecosystems have been designated a “globally important agricultural heritage system.” However, existing studies mainly focus on the provisioning services from these systems while ignoring the other valuable roles they play, such as in regulating and supporting services. To remedy this gap, this study constructs a new framework for classifying ecosystem services (ES) based on the Millennium Ecosystem Assessment and our analysis of rice–fish coculture ecosystem functions. Using our revised model, we found the ES value of rice–fish coculture ecosystems in the study area was 255,529 RMB/hm2/year and was 37.9% higher than that in rice monoculture, while the ES value increased by at least 6.74 times than direct economic value in rice monoculture. In addition, the ES value of rice–fish coculture increased by 2.31 times, as compared direct economic value with rice–fish coculture. These findings demonstrate the vitality of traditional ecological agriculture, which is not only conducive to enhancing the awareness of managers and the public regarding the protection of agricultural cultural heritage, but also provides data that will allow the government to formulate better compensation standards for rice–fish ecosystems.

1. Introduction Over the past 50 years, the application of modern agricultural techniques has hugely increased crop yields. However, such increased productivity comes at the cost of environmental pollution, pesticide resistance, and rising economic costs due to the necessary heavy application of chemical fertilizers and pesticides (Tilman et al., 2002). As a result, producing a sufficient amount of food while minimizing the negative environmental effects of crop cultivation has become a major challenge (Godfray et al., 2010). Some scholars and farmers are looking toward traditional ecological agriculture as a possible solution (Plahe et al., 2017). For centuries, traditional agricultural systems have supported human food and livelihood security. Today, such traditional models may allow farmers to successfully adapt to different environments while maximizing the use of limited resources and maintaining biodiversity and food security through species interactions (Altieri, 2004). Recognizing the ecological legacy of traditional agricultural systems may be conducive to the development of novel sustainable agriculture in the present. One such traditional model is the rice–fish coculture system. Rice–fish coculture has a long history in Asia, especially in China, where it can be traced back to the year 220 AD (Li, 1988). Rice–fish

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farming activities have also been reported from China, Egypt, India, Indonesia, Thailand, Vietnam, the Philippines, Bangladesh, Malaysia and part of West Africa (Halwart, 1998, Das and Uchimiya, 2002, Halwart and Gupta, 2004; Koide et al., 2015). In 2005, the United Nations (UN) Food and Agriculture Organization, the UN Development Program, and the Global Environment Facility designated rice–fish coculture model as a “globally important agricultural heritage system” (Xie et al., 2011), and the practice attracted additional attention after being highlighted as a major agricultural heritage practice in Qingtian County, Zhejiang Province, China. As compared with rice monoculture, the rice–fish coculture system can lead to more stable production and increase farmers’ incomes (Xie et al., 2011) due the reciprocal effects of rice, fish, and other organisms in balancing the levels of carbohydrates and animal proteins in the rice field (Ahmed and Garnett, 2011; Ahmed et al., 2007). Today, many areas view the rice–fish coculture model as a way to improve local ecosystems and alleviate poverty (Halwart and Gupta, 2004). Studies have found that the rice–fish coculture system can effectively reduce the use of chemical fertilizers and pesticides (Dwiyana and Mendoza, 2008) and decrease the amount of nitrogen (N), which is completely consumed and assimilated by both the rice and the fish (Xie et al 2011; Zhang et al., 2016; Frei and Becker, 2005). Although the rice–fish

Corresponding authors. E-mail addresses: [email protected] (D. Liu), [email protected] (J. Xie).

https://doi.org/10.1016/j.ecoser.2019.101054 Received 12 November 2018; Received in revised form 4 September 2019; Accepted 4 December 2019 2212-0416/ © 2019 Elsevier B.V. All rights reserved.

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24.78 N), Guangdong Province, South China. It is surrounded by mountains to the northwest and west and is one of the major sources of limestone in Shaoguan. To the northeast, the area is surrounded by a highly eroded plateau and hilly area. The terrain is gentle on both banks of the river. Ruyuan Yao Autonomous County has an area of 2299 km2 and has a population of approximately 230,000. The average altitude of the county is higher than 500 m above the sea level. The average annual sunshine time is 1500–1700 h. Because of karst topography, scorching heat, and uneven rainfall distribution, the region is prone to droughts and floods. Ruyuan is one of three minority autonomous counties in Guangdong Province and a recipient of government poverty alleviation and development programs. Such programs place particular emphasis on industrial poverty alleviation while also reforming agricultural supply, promoting the comprehensive planting of fields of Ministry of Agriculture, and focusing on field ecological breeding as an important technology for expanding freshwater fisheries. Such programs consider rice–fish coculture one of the best methods for poverty alleviation, and plans are in place to expand the program started in Ruyuan throughout the entire county. In 2016, Ruyuan included 533 hectares of rice–fish coculture land. The rice–fish systems in the research area of Ruyuan County plant one season of rice planting every year and simultaneously release carp by using small and simple agricultural machinery. In rice–fish systems, rice seedlings are transplanted; fish fingerlings are stocked in June every year and are harvested in September, the water is then drained, and rice is finally harvested. In addition, ridges in rice–fish systems must be designed at a high level to ensure that paddy fields can provide water storage for normal fish growth (Fig. 3). Note: A standard rice–fish coculture system extension pilot field has an area of 666 m2. The center of each field consists of a fish refuge, generally 1 m deep, with a total area 5–7% that of the entire field. For the purpose of this paper, we assumed the fish refuge to be 6% of the total and that each test field had a fish volume of 40 m3 (8.0 m × 5.0 m × 1.0 m).

coculture system has the aforementioned ecological advantages, the adoption rate of rice–fish cocultures systems is very low. For example, in Asia, the adoption rate is only slightly higher than 1% (Halwart and Gupta, 2004). Hence, the construction of a comprehensive and quantitative value evaluation system for rice–fish systems is urgently required. Ecosystem services (ES), which are defined as the ‘benefits that people receive from healthy ecosystems’ (MEA, 2005), have been utilized since the 1970s (Westman, 1977, Costanza et al., 1997). ES are generally classified into provisioning, regulating, supporting, and cultural services (Costanza et al., 2017). ES can evaluate the comprehensive and quantitative value of an ecosystem (Costanza et al., 2017; Costanza and Kubiszewski, 2012; Droste et al., 2018). ES in agricultural ecosystems have now been extended to satisfy public and private demands (Belt and Blake, 2014; Antle and Valdivia, 2006), have been utilized in aquaculture (Mathé and Rey-Valette, 2015; Weitzman, 2019) and rice-field ecosystems (Ondiek et al., 2016). An ES study was conducted for a prawn–rice rotational system in Vietnam, and the comparison indicates that although the comprehensive value of this system was higher than the rice monoculture system (Loc et al., 2017). However, the prawn–rice rotational system cannot be used as a suitable reference for the rice–fish coculture systems because of the difference ecological characteristics between the coculture and rotational systems (Dwiyana and Mendoza, 2006; 2008; Loc et al., 2017; Berg and Tam, 2018a,2018b; Xie et al., 2011). Berg and Tam (2018a,2018b) studies the rice–fish cocultures systems services and implies that the majority of the farmers were willing to reduce their rice yields slightly for an improved quality of the other ES by the rice–fish system in the Mekong Delta. However, its ES data only comes from the farmers’ perception on how their farming practices influence on ES. Therefore, the ES of rice–fish cocultures systems still need further studied to policy-makers, scientists, extension workers and farmers. Different ES models, including a pressure-state-response (PSR) model (Gerven et al., 2007) and driving force-state-response (DSR) model (European Environment Agency, 1998), are available for different ecosystems. A driver, pressure, state, impact, and response (DPSIR) conceptual model was first proposed by the Organization for Economic Co-operation and Development (OECD) when revising the PSR and DSR models (Borja et al., 2006). The DPSIR model emphasizes economic operation and its relationship with the environment, which reveals the causal relation between the environment and economy and can effectively integrate resource, developmental, environmental, and human health concerns (Maxim et al., 2009; Atkins et al., 2011). Fig. 1 shows the development of evaluation by using this model. Other scholars have found that economic evaluation can promote social learning and improve the relevance of ES for decision-making (Dendoncker et al., 2018). Such findings imply that ES values can increase sustainable practices. In this study, to fill the gaps in the research on the ES of rice–fish systems and help improve its consideration in decision-making and management, we used the DPSIR model for examining the value of rice–fish coculture systems and for establishing a comprehensive and quantitative evaluation method in partnership with Ruyuan County, Shaoguan City, Guangdong Province. The results of this study contribute to the understanding of considerable advantages of integrating conventional ecological and modern agriculture, of developing new ideas on sustainable development for modern agriculture, and of providing useful experience to reduce the impact of agriculture on the environment.

2.2. Value identification model Table 1 provides details on our model, which includes 21 ES. We divided 12 of the 21 indicators into 8 types of economic value based on data available and method feasibility and tested the model. This paper uses the classification of the Common International Classification of ES (CICES) V4.3 (2013) to develop an assessment system of rice–fish coculture systems. CICES, the latest classification of ecosystem service, is an internationally recognized ecosystem accounting system that aims to unify and standardize the description and evaluation of ES in an international context. It is based on the environmental accounting work carried out by the European Environment Agency and is currently led by the statistics division at the United Nations. The value of supply services focuses on rice and fish and regulation and maintenance of atmospheric composition, climate, soil formation, etc., while cultural values are concentrated on tourism development, agricultural heritage, and other cultural outputs. 2.3. The methods of valuation used According to the Economics of Ecosystems and Biodiversity (TEEB) method (Costanza et al., 1997; MEA, 2005, de Groot et al., 2012), the evaluation methods of ecosystem service value of rice–fish coculture system has been divided into three categories based on the market attributes: direct market method, replacement costs method and the equivalent factor method (Campagne et al., 2015; Christie et al., 2012). This study used the direct market approach in the valuation of “Provisioning services”, the simulated market approach to the valuation of “Tourism development”, and the rest were evaluated using the alternative market approach.

2. Materials and methods 2.1. Research area and the local method of agriculture Ruyuan Yao Autonomous County is located in a mid-subtropical mountainous region (Fig. 2) in the west of Shaoguan city (113.27E, 2

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Fig. 1. Framework that links ES assessment, social problems, and human well-being in the rice–fish coculture system.

the transpiration and osmosis of water in paddy fields impacts the water cycle of the entire ecosystem. In the rice–fish coculture system, the regulatory value of liquid flows is mainly reflected by the protection from farmland erosion. Surface runoff, such as stored irrigation water or rainwater, can be used to replenish groundwater. In order to achieve a good environment for the growth of rice and fish, it is usually necessary to reinforce a field’s ridge, widen or raise the height of the rice field dyke, and/or excavate fish ditches, pits, etc. Such changes may also improve fields’ water storage capacity and act as small reservoirs. The value of fields to store water can be represented by the cost of constructing reservoirs with the same water storage capacity (Liu et al., 2015).

The following is an overview of the estimates for the seven measurements obtained through the identification model, in addition to provisioning services. 2.3.1. Gas regulation Rice–fish coculture system regulates atmospheric gases through the photosynthesis of rice, which absorbs CO2 and releases O2 (Zhang et al., 2009; Sun et al., 2007). This paper also considers the effects of chlorophyll in water (Yang et al., 2009); we replaced the value of CO2 fixation and O2 release with the cost of carbon tax and industrial oxygen, respectively (Xie et al., 2005; Liu et al., 2015). 2.3.2. Temperature regulation Rice–fish coculture systems retain a large amount of water in the field during the growth process. Water transpiration absorbs a certain amount of heat and plays a role in regulating the temperature of the surrounding area. Scholars have found that the temperature on farms is 1.3 °C lower during the farming season than in surrounding towns (Yoshida, 2007). This temperature regulation can be calculated using replacement cost methods. Some scholars use hot summer days (above 35 °C) and other data to determine the total cooling effect of paddy fields using the heat of standard coal combustion (Liu et al., 2015) to obtain the temperature regulation of the rice–fish coculture system during the entire flooding process.

2.3.4. Organic accumulation Soil formation and maintenance functions include organic accumulation, reduction of waste and soil erosion, soil fertility, etc. We calculated soil organic accumulation based on the balance between organic input and output. The former is derived from organic fertilizers, the settling of rice roots, the straw left after harvest, and the underground part of the plants (Xiao and Xie, 2009). According to our field survey, the farmers in the study area basically did not use organic fertilizer and we have taken into account the characteristics of local farming in the selection of data such as organic matter content. Therefore, our results exclude the application of organic fertilizer.

2.3.3. Protection from farmland erosion Rice requires more water during its growth than other crops, and

2.3.5. Air purification and Improvement of environment Paddy fields have a purifying effect by eliminating the presence of 3

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Fig. 2. A map of study area showing topography with waterways.

2.3.6. Development of tourism The “rice–fish” culture has been formed around the “rice–fish system” in Ruyuan County, where the annual rice–fish culture festival attracts hundreds of tourists. Due to the difficulty in considering the daily passenger flow and tourism cost caused by the rice–fish culture, the evaluation of the tourism cultural value of the rice–fish system in this paper only refers to the expenditure of the tourists attending the rice–fish culture festival in Ruyuan so as to constitute the tourism cultural value of the rice–fish coculture system.

harmful substances such as SO2, NOx, HF, and dust in the air. The rice–fish system improves the environment mainly in three aspects: maintaining biodiversity, reducing greenhouse gas (GHG) emissions, and reducing pesticide use. The rice–fish system plays an important role in maintaining biodiversity and enhancing an ecosystem’s vitality. However, it remains difficult to obtain reliable data to determine the extent to which this actually occurs. Studies have shown that the rice–fish system can effectively prevent and control diseases, pests, and weeds. “Rice–fish system reduces the demand for pesticides, fertilizers and herbicides” from the authoritative Chinese journal. According to acceptance results of test, the reduction of chemical fertilizer use by 21.0% to 80.0%, and that of pesticide by 30.0% to 50.7% (Xie et al., 2009). According to the research results of Shanghai ocean university, Zhejiang University and other technical support institutions, the rice–fish system can reduce the use of fertilizer and pesticide by more than 50.0% on average (Xie et al., 2011).

2.4. Data collection Data for this study were collected in 2016 in Ruyuan County from interviews with local farmers, researchers, and government personnel. We began by interviewing members of the local technical section in order to gain some technical knowhow. Then, out of approximately 1000 integrated rice–fish farming adopting households, 95 households 4

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Fig. 3. Rice–fish coculture model and rice monoculture.

assets, integrated rice–fish farming activities and area cultivated as well as household income, expenditure, consumption. When required data could not be obtained through field research, the study relied on preexisting results with a wide range of application and used by many researchers. Value results are given in RMB as the currency unit. The data of rice monoculture system come from government agencies.

were selected randomly for interviews using a structured questionnaire. In addition, data were also collected from 100 questionnaires and expert consultation on the Internet. Interviews and investigations were conducted in stages between September and December 2016, by trained investigators with the help of the local Finance Ministry and NGO officials. There are three sources of follow-up parameters. Firstly, we obtained the yield and price of rice and fish products from the farmers under investigation, measured the physical structure of the rice–fish system, and mastered relevant geographic information. Secondly, samples were either taken from the study area and brought to the research institution for tests, such as the content of chlorophyll in water, or directly obtained from the local monitoring department and the official website, such as hot summer days, the days with the average maximum temperature, and the water price. Thirdly, the parameters of the ecological value of the rice–fish system, which included water evaporation, soil permeability and reservoir construction value, were extracted from relevant studies. The survey questionnaire included information on household composition and characteristics, ownership of

3. Results The median of economic value estimated for the contribution of rice–fish system to human well-being was 255,529 RMB/hm2/year, with a range of 232,000 to 279,000 RMB/hm2/year (Table 2) in 2016. This value includes eight categories (12 out of 21 ES), temperature regulation and provisioning were the highest, accounting for 33.6% and 30.2% of the total respectively (Table 2), followed by protection from farmland erosion (20.7%), gas regulation (7.7%), air purification (2.4%), organic accumulation (2.1%), cultural services (1.9%), and improvement of environment (1.4%). Considering the physical characteristics of the system, the impact of rice–fish coculture systems 5

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Table 1 ES and valued goods and benefits of rice–fish systems classified (According to CICES V4.3, Haines-Young and Potschin, 2013). CICES V4.3A Section

Division

Provisioning

Materials

Regulation＆maintenance

Regulation of physical, chemical, and biological conditions

Mediation of flows Mediation of waste, toxics, and other nuisances

Cultural

Physical and intellectual benefits

Spiritual, symbolic, other interactions

Ecosystem services of rice–fish system

Goods and benefits valued economically

1.Rice and fish are important source of food and nutrients 2.Straw used as material: organic fertilizer, animal feed 3.Carbon sinks and sequestration in the plants and the chlorophyll of water 4.Increase of oxygen production 5.Stabilization humidity owing to rice–fish system 6.Nutrient cycling and organic accumulation 7.Cooling effects of rice–fish system 8.Conservation of groundwater 9.Rock desert erosion protection by rice–fish system 10.Rice absorbs harmful gases and dust 11.Reduction of pesticides/herbicides 12.Increase of fauna diversity and micro-organisms 13.Reduction of greenhouse gas emissions owing to rice–fish system 14.Research subject 15.Education opportunities 16.Entertainment: ecological landscape tourism 17.Cultural value and heritage 18.Artistic inspiration: theatre, painting, sculpture 19.Experiential use of plants, animals, and land 20.Enjoyment of wild and charismatic existing farmland 21.Willingness to preserve for future generations

Agriculture and fishery contribution X Gas regulation

X Organic accumulation Temperature regulation Protection from farmland erosion Air purification Improvement of environment

X X Development of tourism X X X X X

Note: Groups, class, and class type of CICES are not represented; all subdivisions are not presented in the Table 1. Cases marked by X represent ecological services not economically valued because of missing or inaccessible data.

increased the protection from farmland erosion and gas regulation values by 36.6 % and 26.9 %, respectively, as compared with rice monoculture. In general, the ES value increased by at least 6.74 times than direct economic value in rice monoculture. In addition, the ES value of rice–fish coculture increased by 2.31 times, as compared direct economic value with rice–fish coculture.

measure the chlorophyll content in the water of rice–fish systems and use the research results of Yang and inflation coefficient to estimate the gas regulating value of the water in rice–fish systems in 2016. Therefore, the median value of gas regulation of rice–fish system in Ruyuan County was 19,777 RMB/hm2/year, with a range of 18,863–20,690 RMB/hm2/year after considering chlorophyll.

3.1. Provisioning services

3.2.2. Temperature regulation In this study, we calculated that there were 60 hot summer days. The average daily water evaporation in each paddy field is 6.89 mm/ day, and the amount of heat consumed in evaporating 50 mm water in a 1 hm2 paddy field is equal to the heat of burning 30.57 tons of standard coal. The evaporation per unit area for a period of 60 days in Ruyuan County is 413.4 mm, which is equivalent to burning 252.75 tons of standard coal. If the price of coal is 340 RMB per ton, the value of temperature adjustment per unit area is 85,935 RMB/hm2/year.

The basic function of rice–fish coculture is to provide primary products, including rice and fish. Given that there is an active market for both goods, we used market prices to evaluate their economic value. During our field research, we learned that the average transaction price of organic rice is 5–8 RMB/kg, and the price of fish is 90–100 RMB/kg. In 2016, rice–fish coculture produced approximately 7200–8250 kg/ hm2/year of rice and 250–300 kg/hm2/year of fish in the research area. Thus, the median value of primary products was 77,250 RMB/hm2/ year, with an estimated value range of 58,500 to 96,000 RMB/hm2/ year.

3.2.3. Protection from farmland erosion Value is calculated by multiplying the total storage in the field by the average price of water, or 3.14 RMB/ton, (http://www.gdwsa.com/ Price/North/5064.htm). To cultivate a proper habitat for the fish in the fields, the average height of rice field clams in Ruyuan County is often higher than in rice monoculture (after field research, it is about 0.4–0.46 meters). The fields also include a shelter for the fish in the center of the field (see Fig. 3) that takes up about 6% of the total area (about 1.0 meters deep pit). The unit price of the reservoir construction is 6.11 RMB/t in 2008 (adjusted to 7.34 RMB/t in 2016 based on the price index of the National Bureau of Statistics). We used a reference of 6 mm·d-1 as the average infiltration level of paddy soil (Lin et al., 2014). Through the calculation of the formula, the median value of protection from farmland erosion was 52,836 RMB/ hm2/year, with a range of 48,652–57,020 RMB/hm2/year.

3.2. Regulation & maintenance 3.2.1. Gas regulation In general, the economic coefficient of rice is 0.45–0.55 (Xie et al., 2005; Liu et al., 2015). According to the photosynthesis equation, one rice field can fix 1.63 g CO2 and produce 1.19 g O2 for every gram of rice dry matter. CO2 consists of 27.27% C. According to the forestry industry standard of the People’s Republic of China, the cost of industrial oxygen is 1000 RMB/t O2. Since this standard was issued in 2008, we adjusted this price from 1000 RMB/t O2 to 1200.67 RMB/t O2, according to the price index released by the National Bureau of Statistics of China. The results of an empirical study by Yang on the value of pond air-conditioning services indicate that when the average chlorophyll content in water was 1 g/L in 2009, the value of the fixed CO2 and released O2 in each hectare of water was 248 RMB and 335 RMB, respectively (Yang et al., 2009). Rice–fish systems have all attributes of freshwater fish farming systems. Thus, we can directly

3.2.4. Organic accumulation Due to the lack of data regarding rice and straw biomass and carbon content in Ruyuan County, this paper uses data measured by Jiang (2016) on early, middle, and late rice crops in Jingzhou City. Jingzhou 6

7.7

19,777

7 4,800

255,529 255.5 k

Total Total (rounded to the nearest unit)

100 100

1.9

2.1 2.4 1.4

5,291 6,079 3,561

Development of tourism

20.7

52,836

Protection from farmland erosion Organic accumulation Air purification Improvement of environment

33.6

30.2

77,250

Proportion of total value (%)

85,935

Agriculture and fishery contribution Gas regulation

Provisioning services Rice and fish are important source of food and nutrients Regulation ＆maintenance Carbon sinks and sequestration in the plants and the chlorophyll of water Increase of oxygen production Increase of oxygen production Cooling effects of rice–fish system Rice absorbs harmful gases and dust Conservation of groundwater Farmland erosion protection by rice–fish system Nutrient cycling and organic accumulation Rice absorbs harmful gases and dust Reduction of pesticides/herbicides Increase of fauna diversity and micro-organisms Reduction of greenhouse gas emissions owing to rice–fish system Cultural services Tout of rice–fish system: Ecological landscape tourism, rice–fish culture and arts festival

median

–

–

185,190 185 k

5,291 6,079 628

– – –

231,681–279,376 232 k–279 k

38,670

85,935

– 48,652–57,020

15,587

33,000

Rice monoculture system (RMB/hm2/year)

18,863–20,690

58,500–96,000

Interval values

Ecological Service Values of rice–fish systems (RMB/hm2/ year)

Temperature regulation

Goods and benefits

Ecosystem services valued ranged depending on goods and benefits valued

Table 2 Summary and comparison of valuation of rice–fish coculture systems and rice monoculture systems (2016).

70,339 70.3 k

4800

– – 2,933

14,166

–

4,190

44,250

Increased benefit (RMB/hm2/year)

38.0 –

– – 467.0

36.6

–

26.9

134.1

Increased proportion (%)

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insect, and grass damage control function in the rice–fish systems. The rice–fish systems contributed approximately 1000 RMB/hm2/year in reducing the use of pesticides. The total value of environmental improvement was approximately 3561 RMB/hm2/year.

City has fertile soil and high levels of organic matter, making it an appropriate estimate for Ruyuan County, which has a long history of cultivation and high levels of organic matter in soil as well. In addition, the promotion of ecological agriculture, such as straw returning and rice–fish coculture, also enhance the soil quality. Therefore, based on Jiang’s data, we estimated straw biomass to be 1.24 × 104kg/hm2, straw carbon content to be 41.4%, rice root biomass to be 0.21 × 104kg/hm2, and root carbon content to be 34.6%. Related studies have demonstrated that organic carbon deposition in a rice rhizosphere is approximately four times that of rice root biomass (Watanabe and Roger, 1985). Assuming conventional harvesting methods, the amount of straw remaining in the field after harvest is approximately 11% of the total straw biomass (Xu et al., 1998). Therefore, the input of organic carbon due to straw and rice roots was 4198 kg/hm2. The releases of CH4 in organic matter, mainly through paddy soils, in a flooded environment and the respiration of soil microorganisms consume organic matter. For the output of soil organic matter (OSOC), we referred to the experimental data in Jiang’s (2016) Master’s thesis and Yuan et al. (Yuan et al., 2019). The amount of CO2 released per acre of paddy field is 2124 kg/hm2, and the amount of annual emission of CH4 is 42.31 ± 12.67 kg/hm2 in a rice paddy wetland. We use 29.64 kg/hm2 for calculation. When CO2 and CH4 are converted to pure carbon with coefficients of 0.27 and 0.75, the amount of organic matter released from paddy fields per unit area was 595.61 kg/hm2, the net soil organic matter accumulation was 3602.09 kg/hm2, and the market price of organic fertilizer calculated by pure carbon amount was 1.47 RMB/kg C. Finally, the economic value of soil organic accumulation was 5291 RMB/hm2/year.

3.3. Cultural services 3.3.1. Development of tourism The statistics of the local tourism department revealed that in 2016, Ruyuan received 4.1 million tourists, and the tourism revenue reached 3.5 billion RMB. Approximately 3000 tourists were attracted by the rice–fish festival. Therefore, the tourism contribution value of the rice–fish system was 4800 RMB/hm2/year. 3.4. Valuation of rice monoculture systems The differences between the rice monoculture and rice–fish systems primarily have three aspects. First, difference in yields induced differences in provisioning services. Second, introducing rice–fish integrated ecosystems enhanced disaster resilience by improving the ecosystem’s capacity to retain water by 36.6% (Table 2), thus effectively reducing the negative impact of rocky desertification. Third, compared with rice–fish systems, although rice monoculture systems can increase diversity in fauna and micro-organisms, its environmental improvement and tourism cultural values are insignificant. According to field investigation data, rice yield in the rice monoculture systems in Ruyuan was constant at 8250 kg/hm2; however, the price of such rice was only 4 RMB/kg, and the average height of the field ridge was 0.27 m. Furthermore, we sampled the chlorophyll content in the water of rice monoculture systems, and the results showed that the chlorophyll content was 5 µg/L. Table 2 shows the values of each part of the system obtained by performing conversions based on similar formulas. Annex 2 presents the specific formulas and parameters.

3.2.5. Air purification Ma et al. (2004) examined the extent of this effect in different types of trees and rice fields. After comparing data recorded in 2002 and 2004, he determined that the rice field system had little change in its absorption of gases such as SO2 and NOx: the average SO2, NOx, HF, and dust absorbed by paddy fields is 45 kg/hm2/year, 33.3 kg/hm2/year, 0.57 kg/hm2/year, and 33,200 kg/hm2/year, respectively. According to forestry industry standards of the People’s Republic of China, the cost of purifying the air of SO2 is 1.44 RMB/kg, of NOx is 0.76 RMB/kg, of HF is 0.83 RMB/kg, and of dust is 0.18 RMB/kg. Based on this data, rice–fish coculture system in Ruyuan County is valued at 6079 RMB/ hm2/year due to its ability to purify the air.

4. Discussion 4.1. Economic evaluation approaches Ecosystems provide various services that are crucial for the wellbeing, health, livelihood, and survival of humans (Costanza et al., 1997; MEA, 2005; TEEB, 2010). With the development of ecological economics in the 1990s (Costanza et al., 1991), a proliferation of methods and frameworks have advanced the ES concept. ES valuation and assessment techniques can be the basis for interdisciplinary and holistic environmental decision-making by linking policy decisions to human benefits (Arkema et al., 2015,2017). The valuation of ES also can assist the analysis of policies and determination of payments for ES at multiple scales (de Groot et al., 2012; Costanza et al., 2014). The evaluation of ES in monetary units can serve different goals. An international study by The Economics of Ecosystems and Biodiversity (TEEB) (TEEB, 2010) assessed the economic significance of ES and biodiversity. By rendering a “valued” nature legible for key audiences, TEEB mobilized a critical mass of support by various groups, including modelers, policy makers, and bankers (MacDonald and Corson, 2012). This paper employed TEEB to evaluate the ES of the rice–fish system, and this evaluation is legible for scientists, extension workers and farmers, policy makers, and bankers.

3.2.6. Improvement of environment For this study, we referred to research by Xie et al. (2015). According to his findings, the value of biodiversity in each unit is 628 RMB/hm2. For measurement, global warming potential (GWP) is generally used to represent various GHGs at an emission level of CO2. The GWP of CO2 was set as 1, and other GHGs could be converted into CO2 with the same greenhouse effect based on their respective masses. Yuan (2019) compared and analyzed CH4 and N2O emissions between a rice field and rice–fish system and reported that the CH4 and N2O emission in the rice field and were approximately 49.5 and 6.01 kg/hm2/year, respectively. Because cultivated podocarps in this region primarily feed on floating podocarps and do not require frequent feeding, the CH4 and N2O emission in the rice–fish system were 29.64 and 2.29 kg/hm2/year, respectively. In the production of rice–fish systems, the reduction in fertilizer usage has a suitable inhibitory effect on GHG emissions. The negative ES value of rice–fish and rice monoculture systems, which was attributed to the release of GHGs, was 1432 and 3365 RMB/hm2/year, respectively. The rice–fish system contributed 1933 RMB/hm2/year to the reduction of GHG emissions. In the surveyed region, farmers spend approximately 1500 RMB/ hm2/year on pesticides for rice monoculture systems, whereas they use one-third of the previous value for the rice–fish systems. Therefore, the substitution price method was used to calculate the value of the disease,

4.2. The importance of ecosystem services value provided by rice–fish system The rice–fish system is related to a series of issues such as food supply, ecological environment, and social welfare (Berg et al., 2016). As compared with natural ecosystems, rice–fish systems are significantly affected by human activities. Due to the difference in the agricultural management level and the farming technology in different 8

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benefit method, which is relatively simple, while we comprehensively used the direct market method, the alternative market method, the cost method, and the travel cost method. On the other hand, the evaluation model used in the study in Vietnam is relatively conservative, which is from the angle of costs and benefits of the farmers’ land use, and has many limitations (Loc et al., 2017). However, our research was established on the basis of CICES, an international classification standard of ES. Although only 12 out of 21 functional values of ES were considered, it was far higher than other existing researches. In theory of Czúcz et al. (2018), our results should be closer to the ES value of ecological services of the rice–fish system.

regions, the level of productivity varies significantly, which has different effects (positive or negative) on the rice–fish system and the surrounding environment (Lightfoot et al., 1992). The inconsistency of this effect directly limited the development of the rice–fish system and affected the progress of agriculture. Therefore, it is necessary to continuously improve the cognition of rice–fish ecosystem and complete its value evaluation system. In this study, arable land and fresh water are essential resources to ensure sustainable global food supply. Effectively using the limited water and soil resources and reducing the negative impact of the agricultural production process on resources and environment while guaranteeing food supply is a major challenge agriculture facing globally economy (Foley et al., 2011). Rice plays an important role in global food security. The global rice field area is 163 million hm2 (Liesack et al., 2000; Monfreda et al., 2008) and is distributed mainly throughout East and Southeast Asian countries and regions (Frei and Becker, 2005). The rice–fish system, on the other hand, is just right to make the most of its cropland and fresh water. The rice–fish system plays an important role in improving people’s nutrition levels and alleviating poverty (Halwart and Gupta, 2004). Severe desertification and consequent water shortages have driven villages with low per capita arable land into a cycle of poverty. The introduction of a rice–fish coculture ecosystem has enhanced disaster resilience by improving the ecosystem’s capacity to retain water by 36.6% (Table 2), and reduced the negative impact of rocky desertification effectively. In addition, rice–fish coculture system has brought many other benefits to the area. Attributed to a high production value, air conditioning, and water regulating value, the overall value of the rice–fish system was higher than the rice monoculture system (Table 2). It indicated the advantage of the rice–fish coculture system in ecological environment maintenance and food supply. This study would also be a valuable start for building up a database if data and approach were to be available publicly.

4.4. Limits in economic values of goods and benefits valued Though this study took more indicators into consideration and attained more realistic and reliable results, there were also some limits in terms of the economic values of the goods and benefits valued. Firstly, we constructed a rice–fish system evaluation model composed of 21 indicators value according to the classification standard of CICES and divided 12 of the 21 indicators into 8 types of economic value. In spite of this, the other 9 indicators were not taken into account, including the spiritual impact of the rice–fish system (Table 1). Secondly, our study only briefly compared the negative value of the rice–fish system and the rice monoculture system to measure the value increment of the rice–fish system. We did not consider all the negative value that the rice–fish system may produce, which makes it difficult to fully understand how people bear the cost (Chris and Sandbrook, 2015). Thirdly, agricultural systems are also easily interfered with by human activities (Ku et al., 2017). For example, the rationality of tillage technology and the management exert an influence on the output of arable land and the resulting ecological effect. In this way, human behavior, in addition to the natural differences in the natural environment such as soil and climate, makes each agricultural system unique. This, in addition to the periodic and seasonal nature of rice–fish cultivation, means that the benefits may vary depending on the stage of rice growth (Nguyen et al., 2015). Determining the value assessment in such a dynamic cycle is complex and difficult. The traditional agricultural system has strong sustainability and ecological benefits, and its inheritance and vigorous development (such as the rice–fish system) are reasonable and inevitable. However, today, few people truly understand the implications of these systems, and traditional agriculture must compete with commercial and other agricultural systems to survive and thrive (Berweck et al., 2013). Our research on the value of the rice–fish system is still at the output level of ecological services, which cannot fully reflect the competitive advantages of the traditional agricultural system over commercial and other agricultural systems, and its potential advantages and commercial values are yet to be explored and analyzed.

4.3. Comparison of estimated value This paper establishes a model system of evaluation for rice–fish coculture systems using Ruyuan County as an example. Our results show the median of economic value estimated for the contribution of rice–fish system to human well-being was 255,529 RMB/hm2/year, with a range of 232,000 to 279,000 RMB/hm2/year in 2016. Loc et al. (2017) assessed the ES value of the rice–prawn rotational system by using an integrated approach. The average value is about 8000 RMB/ hm2/year. The evaluation values of the rice–fish system of Haney terraces and Qingtian County in China are about 33,100 RMB/hm2/year and 21,000 RMB/hm2/year, respectively (Liu et al., 2010; Liu et al., 2017). As compared with the results of Haney terraces and Qingtian’ studies, the evaluation value of the rice–fish system of Ruyuan County is higher for the following reasons. First, the fish in the rice–fish system of Hani Terraces and Qingtian County are fed artificial feed, whereas those in the rice–fish system of Ruyuan County only feed on natural food and are considered an “ecological product”; Moreover, the price of the fish in Ruyuan County is 3–5 times higher than of those in Hani Terraces and Qingtian County. Secondly, the data used in the study of the rice–fish system of Qingtian County and Haney terraces were from 2006 and 2011, respectively (Liu et al., 2010; Liu et al., 2017). As the price level has soared in recent years, it is understandable that their results differ greatly from ours. Thirdly, through field investigation and evidence collection, our study took more factors into consideration. For example, considering the special geographical structure of the rice–fish system and chlorophyll, the rice–fish system is more valuable than the rice monoculture system and about 8% and 20% of the same scale in terms of gas regulation and water regulation values. As compared with foreign studies, such as that of Vietnam, on the one hand, the evaluation method they adopted is mainly the cost-

5. Conclusion The rice–fish coculture system is related to a series of issues, such as food security, ecological and environmental health, and human wellbeing, etc. Each component of the ecosystem is interrelated and influenced by the other components. So it is necessary to maintain the integrity, continuity, relevance, logicality, openness and dynamics of the evaluation framework in the establishment of the assessment system, and then improve various evaluation indicators for the further assessment. This study estimated the ES value of the rice–fish coculture system from provisioning, regulating, and supporting services, and found this system could improve the comprehensive value of rice field and demonstrate the vitality of traditional ecological agriculture. Nonetheless, attributed to the lack of cultural service evaluation (Table 1), the ES value of rice–fish coculture system is still underestimated. Therefore, the assessment of the cultural service should be strengthen in the further study. 9

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