Ecosystem Services Evaluation of Karst New Urban Areas Based on Net Primary Productivity of Guanshanhu District, Guiyang, Guizhou Province, China

Net Primary Productivity (NPP) is the basis of the material and energy transport calculation in ecosystem studies. NPP directly reflects the production capacity of plant communities under natural conditions. Ecosystem services are hot topics in the field of ecology. Many studies calculate ecosystem service value based on NPP. Taking Guanshanhu District of Guiyang City, Guizhou Province as the research object, using TM, ETM + , Gaofen2 and MOD17A3HGF.006 as data sources, this paper analyzed the change of ecosystem service value based on NPP in 2000, 2010 and 2020. The results showed that the area of forest ecosystem increased during 2000-2010 and decreased during 2010-2020. The artificial surface grew rapidly from 1146.82 hm 2 to 7544.29 hm 2 during 2000-2020. The farmland ecosystem decreased from 13308.29 hm 2 to 6342.33 hm 2 during 2000-2020. With the dynamic changes in ecosystem spatial distribution and component structure, the total NPP in 2000, 2010 and 2020 was 12.58 × 10 4 t, 11.90 × 10 4 t and 11.78 × 10 4 t, respectively, showing a decreasing trend. The total value of natural and semi-natural ecosystems services based on NPP showed an increasing trend, which was ¥ 6.938 × 10 8 in 2000, ¥ 8.052 tems and fulfill the growing ecological demands of residents.


Introduction
Vegetation net primary productivity (NPP) refers to the increments in biomass per unit of land surface and time, calculated as the difference between the energy fixed by plant photosynthesis and their respiration [1] [2]. As the core concept in studies of ecosystem material and energy transportation, NPP directly reflects the production capacity of plant communities under natural conditions. The production capacity of ecosystems is directly related to the ability of maintaining the dynamic balance of CO 2 and O 2 and nutrient cycling [3] [4]. Ecosystem refers to any geographic area that includes all of the organisms and nonliving parts of their physical environment. Ecosystem is divided into natural ecosystem, semi-natural ecosystem and artificial ecosystem based on the amount of human interference. Agricultural ecosystem can be regarded as semi-natural ecosystem [5]. Ecosystem services are the products and services obtained directly or indirectly by human through the functions of the ecosystem, which is crucial to the survival of mankind while being difficult to duplicate [6]. The evaluation of ecosystem service is to quantitatively study the value of various ecosystem services, and to calculate the monetary value of natural factors [7] [8]. NPP can effectively represent the ecosystem services of carbon cycle regulation and nutrient transportation, which is conducive to scientific management and rational utilization of natural resources, and applicable for the system of Environmental-Economic Accounting [9] [10].
To enhance the productivity and services of ecosystems in new urban area of Karst, mountains are the fundamental guarantee to ensure that the urban ecosystem can give full play to its social, economic and ecological benefits. This article, on the basis of MOD17A3HGF, using RS and GIS technology, and with the help of field sampling data, studied the spatial distribution and dynamic changes of ecosystems and their NPP from 2000 to 2020 in the new urban area of Guanshanhu District, Guiyang City, Guizhou Province, Southwest China. Based on NPP, the natural and semi-natural ecosystem's ecological service value of carbon cycle regulation and nutrient transportation are evaluated. Location and quantitative evaluation of the long time series ecosystem services based on NPP is the novelty of the study, which clearly reflect the future development trend of the ecosystem, and to rationally protect, develop and utilize biological resources, which is of great significance for creating a stable and high-yield ecosystem in karst urban new areas.

Study Area
Guanshanhu District is located in the central karst area of Qianzhong mountain, northwest of Guiyang, Guizhou Province, China. There are three towns under the jurisdiction of Guanshanhu District: Baihuahu Town, Jinhua Town, Zhuchang Town, and are divided into nine community service centers ( Figure 1).
As a pioneer area of ecological civilization in Guiyang city, Guanshanhu District shoulders the historical mission of building ecological civilization demonstration area in the future development.

Materials and Pre-Processing
The remote sensing interpretation data of different ecosystem types in Gua-   Open Journal of Ecology existing land cover/land use information and field survey sample data, the interpretation signs and sample database are established. The eCognition object-oriented image automatic classification technology is used to assist human-computer interaction interpretation, and the spatial distribution map of ecosystem types is extracted. The confusion matrix is established by random verification samples, and the accuracy of image classification is evaluated [13] [14].

Methodological Approach
2) Estimation method of ecological services physical quantities. It is a very important function of the ecosystem to synthesize organic matter by solar energy, which supports the whole life system and is the food basis for all consumers and restorers. The amount of organic matter production in the ecosystem can be calculated by NPP. The content of carbon in plant dry matter accounts for about 45%, that is, organic matter production = NPP ÷ 45%. Ecosystems exchange CO 2 and O 2 with the atmosphere through photosynthesis and respiration, absorb CO 2 in the atmosphere and release O 2 , which plays an important role in maintaining the dynamic balance of CO 2 and O 2 in the atmosphere. According to the photosynthetic equation: The production of 162 g dry matter can absorb 264 g CO 2 , in other words, 1 g dry matter needs 1.62 g CO 2 and releases 1.20 g O 2 . 1 g Carbon(C) fixed in the ecosystem can accumulate 0.025426 g Nitrogen(N), 0.00201 g Phosphorus(P) and 0.01012 g Potassium(K), thus the nutrient accumulation in the ecosystem can be calculated [15] [16].
3) Ecological service value method. The value of organic matter production service is calculated by energy substitution method, that is, the fixed Carbon in the ecosystem is converted into the standard coal weight of equal energy, and the value of organic matter production is indirectly estimated by the standard coal price. The calorific value of carbon is 0.036 MJ/g, and the calorific value of standard coal is 0.02927 MJ/g. Standard coal price is calculated by market price. Carbon fixation value = carbon fixation volume * unit carbon price, carbon fixation price is calculated according to Swedish carbon tax. Oxygen release value = oxygen release volume * unit oxygen price, oxygen release price is calculated according to market price. Nutrient accumulation value is the average price of fertilizer multiplied by the amount of pure fertilizer of nutrient N, P, K. In order to facilitate the comparison of the ecological service value in 2000, 2010 and 2020, the comparable price is used in the specific pricing process, and the comparable price is reduced by the price index.

Dynamic Changes of Ecosystem Spatial Pattern and Structure
According to the spectral characteristics and texture characteristics of the image combining with field survey sample data, the spatial distribution map of ecosys- According to the attribute statistics in Figure 3, the dynamic changes of ecosystem structure in Guanshanhu District are shown in Table 1.   Table 2 and Figure 5.

Physical Quantity of Ecological Service Based on NPP
According to the above estimation method of ecological service material quantity, the organic matter production, carbon fixation, O 2 release and nutrient accumulation were calculated. The changes of ecological service physical quantity based on NPP of Guanshanhu District are shown in Table 3.  The total amount of ecological services physical quantity based on NPP showed a decreasing trend in Guanshanhu District. The largest ecological service physical quantity in 2000 was farmland ecological system and the largest physical quantity in 2010 and 2020 both were forest ecological system. The ecological service physical quantity of forest showed an increasing trend, but the increasing trend was slow down, such as the organic matter production in 2000, 2010 and 2020 were 10.61 × 10 4 t, 16.25 × 10 4 t and 16.61 × 10 4 t, respectively. The ecological service physical quantity of farmland showed a significant decreasing trend, and the organic matter production in 2000, 2010 and 2020 were 12.33 × 10 4 t, 7.52 × 10 4 t and 6.60 × 10 4 t, respectively. The ecological service physical quantity of grassland and wetland was relatively small.

Ecosystems Service Value Based on NPP
According to the above ecological service value method, the ecosystem services value based on NPP in Guanshanhu District were calculated. The standard coal price used the market average price, which was 996.36 ¥•t −1 in year 2000. In 2020, Sweden's carbon tax value was 137 $•t −1 , and the RMB exchange rate was 6.90, and then the Carbon tax was 944.94 ¥•t −1 . Oxygen market price was 1400.00 ¥•t −1 . The average price of chemical fertilizer of diammonium phosphate is 2360.00 ¥•t −1 , potassium chloride is 2300.00 ¥•t −1 . In order to facilitate the comparison of the ecological service value in 2000, 2010 and 2020, the comparable price is used in the specific pricing process, and the comparable price is reduced by the con-Open Journal of Ecology  Table 4 and Figure 6.

Conclusions
This 2) With the dynamic changes of ecosystem spatial pattern and structure, the NPP per unit area showed an increasing trend, and the total NPP in 2000, 2010 and 2020 was 12.58 × 10 4 t, 11.90 × 10 4 t and 11.78 × 10 4 t respectively, also showing a decreasing trend. The total amount of ecological services physical quantity based on NPP showed a decreasing trend in Guanshanhu District. The ecological service physical quantity of forest showed an increasing trend, but the increasing trend was slow down. The ecological service physical quantity of farmland showed a significant decreasing trend. The ecological service physical quantity of grassland and wetland was relatively small.
3) The comparable price is used in the specific pricing process, and the compa- The ecological service value of grassland and wetland was relatively small, and the ratio of the wetland ecological service value showed a decreasing trend.
In the future, it is necessary to establish a strict pretrial system for the land use, so as to effectively protect the natural and semi-natural ecosystems and meet the growing ecological needs of residents.