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Evaluation method of ecosystem service value under complex ecological environment: A case study of Gansu Province, China

Scientific assessment of regional ecosystem service value (ESV) is helpful to make scientific ecological protection plan and compensation policy. The evaluation method has not been established that is adapted to the complex and diverse characteristics of the ecological environment. This paper takes Gansu Province as an example, on the basis of fully considering the regional differences of ecosystem service function, the five correction index of value equivalent factor per unit area were constructed in the provincial scale, and the regional difference adjustment index of 11 kinds of ES was constructed in regional scale, in the way, the value evaluation model based on regional difference was established. The results show that in 2015, the total ESV reached 2239.555 billion Yuan in Gansu Province, ESV gradually increased from the northeast to the southwest, and the high-value areas of service function located in Qilian Mountain and Longnan Mountain, of which the forest and grassland ecosystem contributed the most to the value. From the perspective of value composition, local climate regulation and biodiversity maintenance function are the main service functions of Gansu Province. From 2000 to 2015, ESV increased by 3.426 billion Yuan in Gansu Province, the value of forest and urban ecosystem continued increasing, while the value of cultivated land ecosystem continue decreasing. From the spatial characteristics of service value change, the area of value reduction gradually moved from the central part of Gansu Province to the surrounding area. In general, although this study needs further improvement, the constructed evaluation method provides a relatively comprehensive evaluation scheme for the spatiotemporal dynamic evaluation of ESV in Gansu Province. This study provided a more overall research idea for the evaluation of ESV under complex ecological environment.


Introduction 24
Ecosystems can not only provide various raw materials or products directly for human 25 survival, but also have functions such as regulating climate, purifying pollution, conserving water 26 sources, maintaining water and soil, preventing wind and sand, reducing disasters, and protecting 27 biodiversity. All ecosystem products and services are collectively referred to as ecosystem 28 services (ES) [1,2].The evaluation of ecosystem service value (ESV) is the basis of regional

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At present, the research on the evaluation method of ESV can be roughly divided into two 39 categories: (1) A method based on the service function price per unit area. This method evaluates 40 some key service functions by means of a series of ecological equations, such as food production, 41 soil and water conservation, carbon and oxygen production, and habitat quality [11][12][13][14].The 42 functional value method can accurately measure the size of some service functions in the region.

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However, for different service functions, different ecological equations and parameter inputs are 44 often required, and the calculation process is more complicated [3]. Therefore, this method is

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Other geographic data 127 The annual average NPP data and the annual average water production data from 2000-2015

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were used in this study, which comes from the satellite application center of the Ministry of 129 ecological environment.

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Socio-economic data 131 The social and economic data were used in this study from 2000-2015, and come from Gansu 140      Table 1 below.

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Correction index of value equivalent factor per unit area The calculation method of crop supply correction index is as follows: 236 Where, y is the average output per unit area in Gansu Province, and Y is the national average -14 -238 output per unit area.

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The calculation of y is based on the following formula:

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The calculation method of Y is the same as that of y.

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The fresh water supply correction index is calculated as follows: 248 Where, w is the average water supply per unit area in Gansu Province (10000m 3 ), and W is 252 3)Air quality regulation correction index (K) 253 The air quality regulation correction index is calculated as follows: 254 Where, a is the average proportion of air quality standards of prefecture level cities in Gansu The calculation method of water purification correction index is as follows: Where, q is the average length proportion of class I-III water reach in Gansu Province, and Q 263 is the average length proportion of class I-III water reach in China. The length data of water 264 quality reach is from water resources bulletin (2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015) in Gansu Province and China. 265 The calculation method of entertainment aesthetics value is calculated as follows: Where, r is the average tourism revenue per unit area in Gansu Province, R is the average

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The calculation method of crop supply regulation index is as follows: Where, ai is the average yield per unit area in Gansu Province, A is the average yield per unit 276 area in Gansu Province, the calculation method of ai and A is the same as formula (1), a1 is the 277 high-yield area, a2 is the low-yield area. 292 2)Livestock supply adjustment index(A2)

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The livestock supply adjustment index is calculated as follows: 306 3)Fresh water supply regulation index(A3)

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The calculation method of fresh water supply regulation index is as follows: Where, ci is the average water yield per unit area of each area, c1 is the average water yield 310 per unit area in the high water area, c2 is the average water yield per unit area in the poor water 311 area, and c3 is the average water yield per unit area in the dry area.

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The distance between East and West, North and south is large in Gansu Province, and the 313 precipitation decreases from southeast to northwest due to the influence of water vapor and terrain.

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The calculation method of local climate regulation index is as follows:

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Where, di is the average NPP of each partition, d1 is the NPP value of high adjustment area, d2 is the mean value of NPP in the middle regulation area, and d3 is the NPP value of low 327 regulation area.

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A large number of observation data analysis shows that, as the underlying surface of the

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The air quality regulation index is calculated as follows: Where, ei is the average vegetation coverage in each area, e1 is the average vegetation 344 coverage in the area with good air quality, e2 is the average vegetation coverage in the area with 345 general air quality, and e3 is the average vegetation coverage in the area with poor air quality.

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Generally speaking, the better the air quality in a region, the greater the air quality regulation

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The calculation method of groundwater recharge index is as follows:

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Where, fi is the ratio of actual exploitation amount and exploitable amount of groundwater in 363 each zone, f1 is the ratio of actual exploitation amount and exploitable amount of groundwater in 364 over mining area, f2 is the ratio of actual exploitation amount and exploitable amount of 365 groundwater in non over mining area, assuming that the actual exploitation amount and 366 exploitable amount of groundwater in non over mining area are in balance, the ratio is set as 1.

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The overexploitation of groundwater results in the drainage of aquifer, the decrease of 368 groundwater level, the formation of funnel, and land subsidence. Therefore, when the rapid The calculation method of soil conservation regulation index is as follows: Where, gi is the average erosion modulus of each area, g1 is the average erosion modulus of 383 key prevention area, g2 is the average erosion modulus of key control area, and g is the allowable 384 amount of soil erosion.

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The calculation method of windbreak and sand fixation regulation index is as follows: Where, hi is the amount of windbreak and sand fixation in each zone, h1 is the amount of

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The calculation method of water purification regulation index is as follows: Where, ji is the target proportion of water quality in each zone; j1 is the length proportion of 409 class II and above water reaches in high water purification area; j2 is the length proportion of class 410 III and below water reaches in low water purification area.

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The value adjustment index of biodiversity maintenance is calculated as follows: Where, li is the habitat quality index of each region, l 1 is the habitat quality index of priority 449 area for biodiversity conservation; l 2 is the habitat quality index of other regions.

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According to the conservation plan of biodiversity priority area in Gansu Province, there are 451 seven biodiversity priority areas in Gansu Province. This paper considers that the areas located in 452 the priority areas have the highest biodiversity maintenance value, followed by other areas, so the 453 province is divided into two areas. In order to determine the adjustment index of different regions,  (Table 2).
459 will affect the benefits human beings get from the ecosystem, thus affecting the regional 472 differences and divisions of ESV. The ArcGIS spatial analysis tool is used to grid Gansu Province,473 and a complete grid of 1km×1km is extracted. Based on the calculation of ESV of grid unit, the 474 total ESV is calculated in Gansu Province by the following formula (Fig 2). The total ESV in 475 Gansu Province (V) can be expressed as: Where, is the value of ecosystem service function c, c is ecosystem service function, and 478 the value is 1, 2.... 11.
Where, D is the standard equivalent factor, is the value equivalent factor per unit area of 481 ecosystem type m, is the regional difference adjustment index of ecosystem service function c,

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is the area of ecosystem type m (ha), n is the grid number.

487
From the composition of ecosystem types in Gansu Province (Table 3)

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In general, ESV decreases from south to North and from east to west in Gansu Province (Fig   501  3), which is consistent with the spatial distribution of forest, grassland and desert ecosystem.

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There are contiguous desert areas in the north of Gansu

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From the spatial changes of ESV (Fig 4), over the past 15 years, the township with increased