EN中文

Journal of Resources and Ecology >

2023 , Vol. 14 >Issue 1: 67 - 83

DOI: https://doi.org/10.5814/j.issn.1674-764x.2023.01.007

Soil Ecosystem

Research on the Suitability Evaluation of the Development and Utilization of Regional Selenium-rich Soil Resources and Spatial Zoning based on Niche Theory

  • CHEN Yi , 1, 2, 3 ,
  • CAI Haisheng , 1, 3, *
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  • 1. Poyang Lake Basin Key Laboratory of Agricultural Resources and Ecology, College of Land resources and Environment, Jiangxi Agricultural University, Nanchang 330045, China
  • 2. College of Public Management, Huazhong Agricultural University, Wuhan 430070, China
  • 3. Research Center of Selenium-Rich Agricultural Industry development, Jiangxi Agricultural University, Nanchang 330045, China
*CAI Haisheng, E-mail:

CHEN Yi, E-mail:

Received date: 2021-07-16

  Accepted date: 2021-12-01

  Online published: 2023-01-31

Supported by

The Land Development and Consolidation Center Project of Jiangxi Province(91312075474)

The Land Development and Consolidation Center Project of Jiangxi Province(9131207800)

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Abstract

Relying on the advantages of selenium-rich soil resources, the development of special selenium-rich agricultural industry is an effective measure to implement the rural revitalization strategy. This paper took Yuanzhou district as the research area, based on ecological niche theory, creatively determines the dominant and limiting factors of selenium-rich soil resources development and utilization from three aspects of natural resources endowment, land use conditions and ecological protection, constructed the evaluation index system of selenium-rich soil resources development and utilization and ecological niche suitability index measurement model, and explored the suitability of regional selenium-rich soil resources development and utilization and zoning. The research results show that: (1) The area suitable for exploitation of selenium-rich soil resources in the study area is 174658.4 ha, accounting for 68.83% of the total area, mainly distributed around Yuan River and in the central, northern, northwestern and northeastern areas of the study area. (2) Based on the evaluation results of the suitability of selenium-rich soil resources development and utilization and the development of related agricultural industries, the study area was divided into four functional zones of selenium-rich industrial development: core zone, key zone, development zone and radiation zone. The core zone and key zone are suitable for building selenium-rich agricultural industry demonstration area and selenium-rich products breeding production base, and the development zone and radiation zone can vigorously develop selenium-rich modern agriculture and selenium-rich recreation tourism, which will accelerate the development trend of multi-level and diversified selenium-rich industry in study area.This study can provide scientific, reasonable and feasible ideas and methods for the development and utilization of selenium-rich soil resources and the planning and development of selenium-rich industries in similar areas.

Key words： selenium-rich soil; selenium-rich agriculture; niche theory; suitability evaluation; soil use zoning; GIS

Cite this article

CHEN Yi , CAI Haisheng . Research on the Suitability Evaluation of the Development and Utilization of Regional Selenium-rich Soil Resources and Spatial Zoning based on Niche Theory[J]. Journal of Resources and Ecology, 2023 , 14(1) : 67 -83 . DOI: 10.5814/j.issn.1674-764x.2023.01.007

1 Introduction

First discovered in 1817 by Swedish chemist Berzelius, selenium is one of the essential trace elements in the human body. Selenium can maintain the activity of specific enzymes, and plays an active role in regulating hormone levels, improving immunity, anti-oxidative aging, and preventing cardiovascular diseases (Yuan et al., 2016; Chen et al., 2018; Duan, 2018). However, selenium cannot be synthesized by the human body and is mainly obtained through the daily diet. Organic selenium in soil migrates to crops and is processed into food for human consumption. Selenium- containing amino acids and proteins can play a beneficial role in the human body through digestion and absorption (Hatfield et al., 2014). According to statistics, more than 40 countries and regions in the world lack selenium in their soil. About 72% of China’s territory is internationally recognized as a selenium-deficient area (soil selenium content≤0.1 mg kg‒1), of which about 30% is seriously selenium-deficient (soil selenium content≤0.02 mg kg‒1), involving 22 provinces (municipalities and districts) and covering about 700 million people. In July 2009, the State Council issued the Healthy China Action (2019-2030) and other relevant documents, which proposed 15 major special actions such as the popularization of health knowledge, the promotion of nutritious diet, and the development of health industry, bringing the national health to an unprecedented height. These measures have important guiding significance to further accelerate the transformation of agricultural development patterns and promote the development of functional agriculture. At present, some regions attach great importance to the development potential of selenium-rich soil, and have been actively engaged in selenium-rich soil investigation and utilization of resources planning and relevant policies to support the development of se-enriched industry.
The development of selenium-rich soil, selenium-rich agriculture and the production of selenium-rich products highlight the characteristics of regional agricultural industry, conform to the needs of healthy China, and have a very broad development space and market prospects.
Scientific and green exploitation and utilization of the selenium-rich soil resources is the key premise for development of the selenium-rich agricultural industry. At present, there have been some studies on soil selenium resources. Related studies had found the best extraction method of available soil selenium, the influence of different crops on selenium uptake and operation, and the difference in selenium enrichment ability in different parts of crops (Zhou et al., 2014; Jiang et al., 2015). Some studies analyzed the distribution characteristics and influential factors of soil selenium resources in different regions from different research scales of provinces, cities and counties (Chen et al., 2015; Chi et al., 2016; Zou et al., 2018; Zheng et al., 2019). Some studies used the analytic hierarchy process, multi-factor comprehensive evaluation method, statistical analysis method, spatial analysis method and other methods to build an evaluation index system focusing on soil conditions, traffic location factors, topographic factors, hydrometeorology and other factors and carried out suitability evaluation for selenium-rich tea gardens, the cultivated land quality of selenium-rich areas and the development potential of selenium-rich tourism (Hou et al., 2015; Liang et al., 2017; Wan et al., 2019). These studies have reference value for the development and utilization of soil selenium resources. However, there is a lack of unified evaluation criteria for the development and utilization of soil resources and the formulation of industrial planning strategies in selenium-rich areas, and there are few theoretical studies and single research methods on the development and utilization of selenium-rich soil resources. The objective evaluation methods for the development potential of selenium-rich soil resources need to be further improved and expanded, and the research on the correlation between the evaluation of soil selenium resources and the selenium-rich industry should also be emphasized. In view of the deficiencies of existing studies, this study, based on the leading factors and limiting factors of selenium-rich agricultural production, introduces the niche theory to construct the suitability evaluation system for the development and utilization of selenium-rich soil resources, and provides effective decision support for the effective utilization of selenium-rich soil resources and the healthy development of selenium-rich agricultural industry.
The evaluation of regional land resources development needs to integrate the knowledge of geology, ecology and other disciplines in order to achieve the unity of the utilization mode and the natural property of land and to ensure the scientific rationality of the development and utilization mode. Niche theory is one of the important theories used to measure the suitability of biological habitat conditions in ecology. In this theory, the functional units of ecological processes such as material transformation and energy transformation in complex ecosystems are called ecological elements, and the ecological factors that can be utilized and adapted by ecological elements are called ecological niches (Liu, 1987). Based on the in-depth study of this theory, it has been widely used in the fields such as land reclamation, construction land suitability assessment, high-standard farmland construction suitability assessment, rural residential area suitability assessment, and land development suitability assessment (Meng et al., 2011; Qin et al., 2012; Nian et al., 2014; Zhao et al., 2016; Tan and Shao, 2018; Xu et al., 2018; Yu et al., 2018b; Zhang et al., 2018; Guo et al., 2019; Ye et al., 2019).
Yichun City in Jiangxi Province is a pilot city of the “ecology and the great health” industry in China. At present, the area of selenium-rich soil (selenium content≥0.4 mg kg‒1) has been proved to be 520000 ha. Taking Yuanzhou District as the study area, this study introduced the niche theory of ecology to construct the niche suitability index model, based on the endowment of selenium-rich soil resources and location advantages, clarified the leading factors, location factors and limiting factors for the development and utilization of selenium-rich soil resources from three aspects i.e., soil conditions, land use and ecological protection, and constructed an evaluation index system to evaluate the suitability of the development and utilization of selenium-rich soil resources, and put forward feasible suggestions for the development of selenium-rich soil resources from three aspects, namely, soil utilization improvement zoning, soil utilization functional zoning and selenium-rich agricultural production zoning. This will promote the study area’s advantages in terms of selenium-rich soil resources into capital advantages and industrial advantages and will provide effective decision support for the development of a modern selenium-rich agriculture industry with efficient output, product safety, resource conservation and environmental protection. This study can provide practical reference ideas and methods for the development and utilization of selenium-rich soil resources and industrial planning in similar areas.

2 Research methods

2.1 Research ideas

The suitability assessment for the development and utilization of selenium-rich soil resources is an effective method and means to maximize the advantages of selenium-rich soil resources in a region. It requires comprehensive consideration from multiple dimensions such as natural conditions, economic development and ecological protection. According to the suitability assessment results for the development and utilization, the green efficiency of agricultural production and the rationality and practicality of the agricultural industrial layout can be further improved. This study is based on niche theory and geographic information system technology to evaluate the suitability of the development and utilization of selenium-rich soil resources. The research ideas are as follows (Fig. 1): 1) Based on niche theory, a niche suitability calculation model and a comprehensive niche suitability index model were constructed for evaluating the suitability of development and utilization of selenium-rich soil resources. 2) Evaluation indexes were selected from natural resource endowment, ecological environment protection, agricultural environment quality, etc., and an evaluation index system was constructed for the suitability of the development and utilization of selenium-rich soil resources in the study area. 3) Relevant information and data were collected, and a basic database of the development and utilization of selenium-rich soil resources after data processing was built. 4) The evaluation unit was determined through spatial superpositions. 5) Based on the geographic information system software, the comprehensive niche suitability index of each evaluation unit was calculated based on the model to obtain the suitability evaluation result of the development and utilization of selenium-rich soil resources in the study area. 6) The evaluation results were divided into four suitability zones according to the natural break-point method, a suitability zoning map for the development and utilization of selenium-rich soil resources was generated, and the leading obstacles in each zone were analyzed. 7) Combined with the evaluation results and the current situation of industrial development, the development and utilization modes of selenium-rich soil resources in each region were determined, and suggestions for the development and utilization of selenium-rich soil resources in the study area were put forward from two aspects, namely, utilization improvement of selenium-rich soil and functional layout of the selenium-rich agricultural industry.
Fig. 1 Technology roadmap for the development and utilization of selenium-rich soil resources based on niche theory

2.2 Construction of the fitness index model based on niche theory

The niche concept was first proposed by Grinnell in 1917, and it refers to the spatial unit occupied by organisms in their habitat. Later, scholars added and expanded the connotation of niche and proposed the concept of a niche suitability, which was used to express the suitability of organisms with respect to their habitat conditions (Meng et al., 2011; Xu et al., 2018). When the actual resource conditions fully meet the demand, the niche suitability is 1, but when the actual resource conditions do not meet the demand, the niche suitability is 0 (Tan and Shao, 2018). Niche theory has not only been applied in animal ecology, but has also been widely used in the fields of resource evaluation, agricultural production, urban planning and so on. Many scholars in China have also conducted related research and further extended the application of ecological niche theory to the “nature-economy-society” composite ecosystem, in which the biological and other functional units that can carry out ecological processes such as material transformation, energy conversion, and information processing are called ecological elements, and the ecological factors that can be used and adapted by ecological elements are called ecological niche (Liu, 1987). Regional development depends on the support space composed of “natural-economic-social” and other multidimensional real resources, which is the most suitable ecological niche for regional development resources, and the coupling analysis of the real ecological niche provided by real resource conditions can measure the suitability of resource conditions for regional development (Liu, 1987; Ouyang et al., 1996).
As part of the land ecosystem, the selenium-rich soil ecosystem is a dynamic and open “natural-economic-social” composite ecosystem with material circulation, energy exchange and information transfer occurring all the time. It can be seen that the selenium-rich soil ecosystem is also an ecological element, and the utilization of selenium-rich soil resources also has its optimal ecological position. As a systematic and comprehensive project, the effect of development and utilization of land resources is closely related to the resource conditions in multi-dimensional space. If the development and utilization of selenium-rich soil resources are compared to biological behavior, the key to the suitability zoning of the development and utilization of selenium-rich soil resources is to find the most suitable comprehensive resource spatial location. Therefore, the concept of soil niches rich in selenium can be expressed as follows: In the region with rich soil selenium resources, the development and utilization of selenium-rich soil resources are taken into account comprehensively by resource endowment, land use conditions, soil environment and other restrictive factors, and the status and role of the ecological element of selenium-rich soil resources in the development and utilization process as well as the degree of correlation with other restricting elements in the region are the ecological niche of selenium-rich soil resources. The way of selenium-rich soil resources development and utilization of the resource requirements of multidimensional space is referred to as the way of the development and utilization of the resources demand niche, the actual resource space associated with soil resource development and utilization is referred to as the realistic ecological niche. The matching relationship between actual resource conditions and the development and utilization mode of soil reflects the degree of suitability of the actual resource conditions for soil development and utilization, namely, the niche suitability degree. The development and utilization of selenium-rich soil resources are mainly restricted by dominant factors and limiting factors, and the comprehensive index calculation model of the niche suitability of these two factors is as follows:
1) Dominant factors: The higher the value, the more favorable the factor for the development and utilization of selenium-rich soil resources. The calculation model is as follows:
$N_{i}=\left\{\begin{array}{lc} 0 & X_{i}<D_{i \min } \\ \frac{X_{i}}{D_{\text {iopt }}} & D_{i \min } \leqslant X_{i}<D_{\text {iopt }} \\ 1 & X_{i} \geqslant D_{\text {iopt }} \end{array}\right.$
where Ni is the niche suitability of each evaluation factor i, Xi is the real niche of evaluation factor i, Diopt is the optimal niche of evaluation factor i, Dimin is the minimum value of the niche of evaluation factor i.
2) Limiting factors: The smaller the value, the more favorable the factor for the development and utilization of selenium-rich soil resources. The calculation model is as follows:
$N_{i}=\left\{\begin{array}{lr} 1 & X_{i} \leqslant D_{i \min } \\ 1-\frac{X_{i}-D_{i \min }}{D_{i \max }-D_{i \min }} & D_{i \min }<X_{i}<D_{i \max } \\ 0 & X_{i} \geqslant D_{i \max } \end{array}\right.$
According to the Shefold Restrictive Law (Meng et al., 2011), the niche suitability composite index model for selenium-rich soil resources was constructed, and the formula is as follows:
$N=(\prod^{n}_{i=1} N_{i})^{1/n}$

2.3 Construction of the evaluation index system

2.3.1 Selection of evaluation indexes

For the evaluation of soil suitability, a multi-level and multi-objective evaluation method is usually used to conduct a comprehensive analysis based mainly on natural conditions such as geomorphology, climate, soil and vegetation type, the current situation of soil utilization and its characteristics, and the economic and social conditions of soil utilization. The focus of evaluation is to combine with the effective use of soil resources, analyze the significant inter-regional differences and relative consistency within the region in terms of the constituent elements of soil resources and their combined properties, the status and characteristics of soil utilization, and the vision of soil utilization direction. From the perspective of ecological niche, the key to the evaluation and zoning of suitable areas for the development and utilization of selenium-rich soil resources is to fully consider the role and status of multi-dimensional factors such as the status of selenium-rich soil resources, land use conditions, soil environmental quality, and man-made external interference, so as to balance and coordinate the leading and limiting factors of agricultural production in the utilization of selenium-rich soil resources. Through determining the optimum threshold value of each dimension factor for the development and utilization of selenium-rich soil resources, the niche space with different suitable degrees was obtained to provide basic support for selenium-rich agricultural production. In accordance with the principles of comprehensiveness, difference, scientific and data accessibility, and in combination with the current policies on ecological civilization construction, on the premise of providing basic conditions for the development of selenium-rich agriculture, considering resource endowment, land use conditions, ecological sustainability and other aspects, the soil selenium content, land use type and ecological protection were selected as the dominant factors in this study, and the topographic gradient, agricultural environmental quality and basic farmland were selected as the limiting factors to build a regional selenium-rich soil suitability evaluation index system of resources development and utilization.

2.3.2 Evaluation index data processing, grading and the determination of the most suitable value

Each evaluation factor has a different impact on the development and utilization of selenium-rich soil resources, so it is necessary to grade its suitability to determine the suitability degree of the development and utilization of selenium-rich soil resources in the evaluation unit. Through a combination of the expert scoring method and reference to relevant literature (Tang et al., 2014; Li et al., 2017; Xu et al., 2018; Yu et al., 2018a; Zhang et al., 2018), the data of each indicator were preprocessed and the suitability score of each indicator was determined. Considering the functional requirements for the development and utilization of selenium-rich soil resources and the basic conditions for the development of selenium-rich industry, each evaluation factor was divided into four grades according to the suitability of its application niche: grade I - highly suitable, grade II - moderate suitable, grade III - low suitable and grade IV - not suitable, and they were assigned the score of 100, 70, 40 and 0, respectively. The optimum niche index was assigned a value of 100, and the least suitable niche index was assigned a value of 0, as shown in Table 1. For the development and utilization of selenium-rich soil resources, each evaluation factor had an optimal niche value. The higher the niche value of the dominant factor is, the more suitable it is for the development and utilization of selenium-rich soil resources. Therefore, the optimal niche value of the dominant factor was 100. The smaller the niche value of the limiting factor is, the more beneficial it is to the development and utilization of selenium-rich soil resources. Therefore, the optimal niche value of the limiting factor was 10. Table 1 shows the classification of the ecological niche optimum and the actual niche suitability of each factor.
1) Soil selenium content: Referring to the “Atlas of Endemic Diseases and Environment of the People’s Republic of China” and the description of selenium-rich soil resources in the report "Environmental Quality of Surface Soil and Distribution of Selenium Resources in Yuanzhou District" by Jiangxi Geological Survey Research Institute in July 2018, the grading standard of soil selenium content in the study area was determined: selenium-rich soil (Se ≥ 0.4 mg kg‒1); potentially selenium-rich soil (0.4 mg kg‒1 > Se ≥ 0.3 mg kg‒1); sufficient selenium soil (0.3 mg kg‒1 > Se ≥ 0.175 mg kg‒1); and potential selenium deficiency (0.175 mg kg‒1 > Se ≥ 0.125 mg kg‒1). Then ArcGIS 10.2 software was used to vectorize the distribution map of selenium-rich soil resources in the study area, and vector data of the distribution map of selenium-rich soil resources in the study area was obtained. Different selenium contents were assigned different scores: selenium enrichment (Se ≥ 0.4 mg kg‒1) was assigned a value of 100, potential selenium enrichment (0.4 mg kg‒1 > Se ≥ 0.3 mg kg‒1) was assigned a value of 70, sufficient selenium (0.3 mg kg‒1 > Se ≥ 0.175 mg kg‒1) was assigned a value of 40, and potential selenium deficiency (0.175 mg kg‒1 > Se ≥ 0.125 mg kg‒1) was assigned a value of 0.
2) Land use types: According to the classification standards of land types and land planning for the third national land survey, eight land use types were designated: cultivated land, garden land, woodland, grassland, other agricultural land, construction land, water area and other land. Considering the degree of difficulty in agricultural planting and land development, the cultivated land was assigned a value of 100, the garden land was assigned a value of 70, the woodland, grassland and other agricultural land were assigned a value of 40, and the construction land, water area and other land were assigned a value of 0.
3) Terrain slope: A digital elevation image containing the study area was downloaded from the geospatial data cloud website (http://www.gscloud.cn/). Based on ArcGIS 10.2 software, the administrative boundary data of the study area were used to crop the digital elevation image to obtain the elevation data of the study area. The slope was extracted with the 3d analysis tool and converted into vector data by a transformation tool. Finally, the slope spatial distribution map of the study area was obtained. The slope was reclassified into four grades by the classification tool: less than 6°, 6°-15°, 15°-25°, greater than 25°, and the scores were 100, 70, 40, and 0 respectively.
4) Soil composite pollution index: The single factor pollution index method and Nemero comprehensive pollution index method were used to evaluate the heavy metals in soil samples by referring to the Soil Pollution Risk Control Standards for Agricultural Land, and the comprehensive evaluation results of each soil sample were obtained. The calculation formula is as follows:
$P_{i}=\frac{C_{i}}{S_{i}}$
P= $\sqrt{\frac{P^{2}_{I max}+\bar{P}^{2}_{i}}{2}}$
where Pi is the pollution index of single factor, Ci is the measured value of heavy metal content in soil, Si is the risk screening value of heavy metals in soil, Pimax is the maximum pollution index of single factor, P is the Nemero comprehensive pollution index.
After using ArcGIS 10.2 software to vectorize soil sample points and interpolate them in space, the soil pollution comprehensive evaluation results were divided into five levels according to the natural breakpoint method: no pollution, slight pollution, mild pollution, moderate pollution and heavy pollution. A value of 10 was assigned for no pollution and slight pollution, 40 for mild pollution, 70 for moderate pollution and 100 for heavy pollution.
5) Ecological protection: The spatial analysis tool of ArcGIS 10.2 software was used to overlay the ecological preservation area with the administrative boundary of the study area, and the area outside the ecological preservation area was assigned a value of 100, the area inside the line was assigned a value of 0. The outside of the ecological protection site was the optimum niche.
6) Basic farmland: The spatial analysis tool of ArcGIS 10.2 software was used to overlay the permanent basic farmland area with the administrative boundary of the study area, and the area inside the permanent basic field was assigned a value of 100, the area outside this range was assigned a value of 0.
The above pre-processed data were imported into ArcGIS software to build a database, and spatial analysis tools were used to overlay terrain slope, land use, soil selenium resources, ecological protection red line, basic farmland range line and agricultural environmental quality vector data with the administrative boundaries of the study area, as the basic data for the suitability evaluation index of the development and utilization of selenium-rich soil resources.
Table 1 Evaluation index system of suitability for the development and utilization of regional selenium-rich soil resources and optimal niche value
Evaluation factor Unit Evaluation index suitability score Most suitable value
Class I-100
(Highly suitable)		 Class II-70
(Moderate suitable)		 Level III-40
(Low suitable)		 Level IV-0
(Not suitable)
Soil selenium content mg kg‒1 Selenium enrichment
Se≥0.4		 Potential selenium enrichment 0.4>Se≥0.3 Sufficient selenium
0.3>Se≥0.175		 Potential selenium deficiency Se<0.175 Selenium enrichment
Se≥0.4
Land use type - Cultivated land Garden land Woodland, grassland Construction land, water areas and other land types Cultivated land
Terrain slope ° <6 6-15 15-25 >25 <6
Soil composite
pollution index		 - No pollution and slight pollution (P≤1) Mild pollution
(1<P≤2)		 Moderate pollution
(2<P≤3)		 Heavy pollution
(P>3)		 No pollution and slight pollution (P≤1)
Ecological
conservation		 - The area outside the ecological preservation area - - The area inside the ecological preservation area The area outside the ecological preservation area
Basic farmland - The area inside the permanent basic field - - The area outside the permanent base field The area inside the permanent base field

2.4 Spatial autocorrelation analysis

Spatial autocorrelation analysis can be used to verify whether the attribute value of spatial variables at a certain location has an obvious correlation with the attribute value in the adjacent location and can be divided into global spatial autocorrelation and local spatial autocorrelation. Global spatial autocorrelation can reflect the spatial characteristics of attribute values within the whole study area, while local spatial autocorrelation can reflect the aggregation and spatial heterogeneity of attribute values in the study area (Ye and Feng, 2013; Chen et al., 2016). In this study, local spatial autocorrelation analysis was used to reveal the spatial aggregation law characteristics of the appropriate degree of development and utilization of regional selenium-rich soil resources. Geoda 1.12 software was used to calculate the spatial weight matrix and univariate local Moran’s I index. Spatial autocorrelation analysis was conducted on the appropriate degree of development and utilization of regional selenium-rich soil resources, and ArcGIS 10.2 software was used to draw the local index spatial association diagram (LISA). According to the LISA aggregation map, the spatial distribution of the suitability for the development and utilization of selenium-rich soil was divided into “high-high”, “low-low”, “high-low” and “low-high” spatial aggregation types to analyze the spatial pattern of suitability for the development and utilization of selenium-rich soil resources in the region. “high-high” region and “low-low” region indicate that the evaluation unit itself and the surrounding ecological quality are both higher or lower, with little difference and high spatial correlation. “high-low” and “low-high” regions indicate that the quality of their own evaluation units differs greatly from the surrounding ecological quality, and the spatial correlation is relatively low. The calculation method of local Moran’s I index is as follows:
$I_{i}=\frac{n(x_{i}-\bar{x})\sum^{n}_{j=1}W_{ij}(x_{j}-\bar{x})}{\sum^{n}_{i=1}(x_{i}-\bar{x})^{2}}$
where Ii is the Moran index, which represents the correlation of two spatial properties, n is the total number of spatial samples, xi and xj are the attribute values of variables at positions i andj, $\bar{x}$ is the average value of the attribute values of spatial samples, and Wij is the weight value of the space.

2.5 Development and utilization of suitability partitions

In this study, the composite index layer superimposed on the evaluation index data and the administrative boundary space of the study area were used as the suitability evaluation base map. On this basis, the fishing net tool created in ArcGIS 10.2 software was used to divide the administrative boundary of the study area into the 1 km×1 km grid as the evaluation unit, and a total of 3189 evaluation units were obtained. Compared with the traditional method that takes the administrative district as the evaluation unit, such division of the evaluation unit will break through the boundary limit, and the evaluation result will be more accurate. According to formula (1) and formula (2), the raster calculator tool was used to obtain the single factor niche suitability index of each evaluation unit, and then the comprehensive niche suitability index of each evaluation unit was calculated according to formula (3). According to natural breakpoint method, the study area selenium-rich soil resources development and utilization suitability results were divided into four levels: class I (high suitability zone), class II (moderate suitability zone), class III (low suitability zone), class IV (unsuitable zone), and each level is shown in Table 2.
Table 2 The grading standard of the development and utilization suitability of selenium-rich land resources in the study area
Level Comprehensive index of niche suitability Develop and utilize suitability partitions
Class Ⅰ ≥ 0.8811 High suitability zone
Class Ⅱ 0.7500-0.8811 Moderate suitability zone
Class Ⅲ 0.4055-0.7500 Low suitability zone
Class Ⅳ ≤ 0.4055 Unsuitable zone

2.6 Obstacle factors analysis

To develop and utilize selenium-rich soil resources reasonably and efficiently, it is necessary not only to evaluate the suitability of the factors that affect development and utilization, but also to know the key obstacles that restrict its development and utilization, so as to carry out targeted planning and layout of relevant agricultural planting and breeding and enterprise setting. The higher the niche suitability of the evaluation index, the more suitable the actual conditions are for development and utilization. A lower value indicates that the actual conditions are not suitable for the development and utilization activities. At this time, the evaluation factors are obstacles to the development and utilization of selenium-rich soil resources. With reference to relevant literature (Chen et al., 2016; Xu et al., 2018), this study introduced the restriction factor model to conduct quantitative analysis of obstacles to the development and utilization of selenium-rich soil resources. The model is as follows:
$S=min{\bar{N}_{i}, \bar{N}_{i+1}, …, \bar{N}_{n}}$
where S is the leading obstacle of each partition and $\bar{N}_{i}$ is the mean value of the niche suitability index of each evaluation index in each zone. In combination with the selection of indicators, the three indicator factors with the lowest N values were taken as the leading obstacles to the development and utilization of selenium-rich soil resources in this region.

3 A case study on the development and utilization of regional selenium-rich soil resources

3.1 Introduction to the study area

Yuanzhou District, located in the southwest of Yichun City in Jiangxi Province, is the political, economic, cultural and information centre of Yichun City. It covers an area of 253752 ha. At the end of 2018, it had a total population of 1.1627 million, with an urbanization level of 39.96%, and has jurisdiction over 8 sub-district offices and 20 townships (Fig. 2). The study area is rich in water resources, including the Yuan river that goes from west to east through the area, and has many large and medium-sized reservoirs. The district has convenient transportation, the high-speed railway and the Zhejiang-Jiangxi electrified railway run parallel to the Yuan River. Since the implementation of the 13th Five-Year Plan, focused on the “Rural Revitalization Strategy” and on the premises of high yield, high quality, high efficiency and ecological security, the study area has vigorously promoted advanced and applicable agricultural technologies, carried out extensive experiments and demonstrations, and optimized the agricultural industrial structure. It has built pillar industries such as high-quality rice and oil tea, showing good momentum in agricultural economic development.
According to the multi-objective soil geochemistry survey conducted by the Jiangxi Geological Survey Research Institute in 2018, there are abundant selenium-rich land resources in the study area among which the selenium-rich soil covers an area of 191241 ha, accounting for 75.52% of the total land area. The study area has the resource advantages necessary for the development of a selenium-rich modern agricultural industry. At present, the study area has made full use of the advantages of selenium-rich soil and selenium-rich hot spring resources to encourage and support farmers to carry out large-scale production and processing of selenium-rich agricultural and sideline crops as well as selenium-rich mineral water, giving rise to successful selenium-rich brands such as “Zhuang Yuan Zhou”, “South of the Moon” and “Run Tian Cui Water”.

3.2 Source of indicator data

The data used in this study were derived from three categories: vector data, raster data and statistical data. The vector data included the permanent basic farmland database provided by The Bureau of Natural Resources of Yuanzhou District, the land use change data of Yuanzhou District in 2017, and the boundary data of village-level administrative divisions, as well as the boundary data of the ecological preservation area of Yuanzhou District provided by the Bureau of Environmental Protection of Yuanzhou District. The raster data included 30 m resolution digital elevation model data downloaded from the geospatial data cloud website (http://www.gscloud.cn/) and the distribution map of selenium-rich soil resources in Yuanzhou District provided by the Bureau of Agriculture and Rural Affairs of Yuanzhou District. The statistical data were those of the heavy metal content of the soil sample points in Yuanzhou District. In May 2019, the research team conducted a field survey in all towns and townships in the study area. According to the topography and landform and the size of the sampling area, a diagonal arrangement method was adopted. Soil samplers such as earth drills and spades were used to collect 0-20 cm surface soil, and 152 soil samples in total. After transport to the laboratory, soil samples were prepared through natural air drying, wooden rod grinding and nylon screening with a diameter of 2 mm; and 500 g was sent to the Jiangxi Geological Survey Research Institute for the detection of cadmium (Cd), mercury (Hg), arsenic (As), lead (Pb), chromium (Cr), copper (Cu), nickel (Ni), zinc (Zn), as well as the pH value, and then the soil sample point detection table was sorted out. Among them, Hg was determined by cold atomic absorption spectrophotometry, Cu, Zn, Ni and Cr by flame atomic absorption spectrophotometry, Pb and Cd by graphite furnace atomic absorption spectrometry, As by atomic fluorescence spectrometry, and the pH value was determined by a pH meter. Based on ArcGIS 10.2 software, the coordinates of soil sample points were vectorized to obtain the distribution diagram of soil sample points in the study area (Fig. 2).
Fig. 2 The administrative division and geographical location map of the study area

3.3 Measured data of evaluation indexes

The measurement results of each evaluation index are shown in Fig. 3. Soil selenium detection results showed that the selenium-rich soil in the study region covered an area of 187487.8 ha, accounting for 73.89% of the total land area. This region was mainly distributed in the central and northern part of the study area. The potential selenium-rich soil area was 41519.62 ha, accounting for 16.36%. The soil area of sufficient selenium was 24744.58 ha, accounting for 9.75%. There were various types of land use in the study area, among which the cultivated land area was 62316 ha, accounting for 24.61%. Area with a slope less than 25° covered an area of 180958.67 ha, approximately 93.17% of the selenium-rich soil area, mainly distributed in the central and northern areas, and this is a suitable area for the development of agricultural industry. The agricultural environmental quality of the study area was generally good, and a few areas had cadmium pollution phenomenon mainly caused by pesticide residues and industrial waste emissions. The ecological protection area of the study area was 29024.29 ha, mainly distributed in the southern and northwestern high- altitude areas, where the existing natural landscape was beautiful and the ecological environmental quality was good. The basic farmland area with good farming conditions in the study area covered 51527.39 ha and was widely distributed in the region.
Fig. 3 Spatial distribution diagram of suitability evaluation index data for the development and utilization of selenium-rich soil resources in the study area

3.4 Suitability evaluation results

The evaluation results of the suitability for the development and utilization of selenium-rich soil resources in the study area are shown in Fig. 4. According to the calculation, the mean value of the ecological suitability composite index for the development and utilization of selenium-rich soil resources in the study area was 0.5532, among which the proportion of the area where the ecological fitness composite index was greater than the mean was 60.33%, indicating that the selenium-rich soil resources in the study area have a relatively wide area for development and utilization. The result showed that in the study area, the area with a high soil resources development and utilization suitability index were mainly concentrated in the central, northeastern, northern and western areas; these areas were located near traffic networks, close to water, with the rich or within the potential rich selenium land resource and good farming conditions for developing selenium-rich agriculture. The low- value areas were mainly located in the main urban area and the ecological conservation areas in the northeast and south, with a small distribution in the east. These areas were at high altitude and had a low soil selenium content, which is not conducive to agriculture and cultivation.
Fig. 4 Evaluation results of the suitability for the development and utilization of selenium-rich soil resources in the study area

3.5 The spatial autocorrelation of the evaluation results

Local spatial autocorrelation can detect the clustering pattern of the appropriate degree space between adjacent ranges. In this study, Geoda 1.12 software was used to calculate the local Moran’s I index based on the spatial weight of k-neighbors, and the local spatial autocorrelation LISA map of the suitability results for the development and utilization of selenium-rich soil resources in the study area was obtained, as shown in Fig. 5 and Fig. 6.
Fig. 5 Moran’s I index distribution of the evaluation results of the suitability for the development and utilization of selenium-rich soil resources in the study area
Fig. 6 LISA spatial aggregation map of the comprehensive index of the development and utilization suitability of selenium-rich soil resources in the study area
The local Moran’s I index in the comprehensive evaluation of the suitability for the development and utilization of selenium-rich soil resources in the study area was 0.7578, indicating that the suitable results for the development of selenium-rich soil resources in the study area had a high spatial autocorrelation. The “high-high” region accounts for 20.76% of the study area. They were mainly distributed in the central, northeastern and southwestern parts of the study area, where the soil selenium content was above the standard of selenium enrichment, was close to the main urban area, the terrain was flat, the agricultural environmental quality was good, and the suitability for the development and utilization was relatively high. The “low-low” region accounts for 21.29% of the study area; these areas were mainly distributed in the main urban area, the south and some areas in the northwest of the study area. The other areas except the main urban area were relatively remote, mostly in high-altitude mountainous areas. Moreover, the soil selenium content only met the standard of sufficient selenium, and the suitability for development and utilization was relatively low. Only 33 grids were isolated areas of “high-low” and “low-high”, accounting for 1.03% of the study area.

3.6 Results of suitability grade partitioning

According to the calculation results of the niche suitability composite index, the development and utilization suitability levels were divided, as shown in Fig. 7. It can be seen from the result figure that the range of suitability zoning was highly similar to the “high-high”, “low-low”, “high-low” and “low-high” concentration areas mentioned above. The areas with good suitability for the development and utilization of selenium-rich soil resources were mainly distributed around the Yuan river and in the western, central and northeastern areas north of the river, with a relatively concentrated area. Among them, the total area of the high suitability zone was 38910.23 ha, the total number of grids in this area was 489, accounting for 15.33% of the study area, and the average value of the comprehensive index of niche suitability was 0.9301. The total area of the moderate suitability zone was 58325.56 ha, accounting for 22.99% of the study area; the total number of grids in this area was 733, and the average comprehensive index of niche suitability was 0.8146. The total area of the low suitability zone was 77422.61 ha, accounting for 30.51% of the total area of the whole district.
Fig. 7 Schematic diagram of the suitability distribution of the development and utilization of selenium-rich soil resources in the study area
The total area of the unsuitable zone was 79093.60 ha, accounting for 31.17 % of the study area. According to formula (7), the leading factors affecting the development and utilization of selenium-rich soil resources in each district were calculated, and the results are shown in Table 3.
Table 3 Evaluation results and obstacle factors of the suitability for the development and utilization of selenium-rich land resources in the study area
Partition Area (ha) Grid number Proportion (%) Main distribution area Major obstacles Mean niche
suitability index
Zone Ⅰ 38910.23 489 15.33 Zhaixia Town, Wujiang Town, Xintian Town, Jinrui Town Terrain slope 0.9315
Land use type 0.9486
Soil selenium content 0.9943
Zone Ⅱ 58325.56 733 22.99 Xintian Town, Jinrui Town, Hongtang Town, Zhuting Town Soil composite pollution index 0.6727
Terrain slope 0.7859
Soil selenium content 0.8745
Zone Ⅲ 77422.61 973 30.51 Xinfang Town, Binjiang Town, Xicun Town, Wentang Town Terrain slope 0.6281
Soil composite pollution index 0.6305
Ecological conservation construction 0.6945
Zone Ⅳ 79093.60 994 31.17 Hongjiang Town, Cihua Town, Feijiantan Township, Wentang Town Basic farmland 0.7188
Ecological conservation construction 0.7710
Soil selenium content 0.8002

3.7 Result analysis and planning recommendations

3.7.1 Result analysis

Zone I was the most suitable area. The region’s ecological niche suitability index for selenium-rich resource development and utilization was between 0.8811 and 1, the minimum niche suitability index was 0.8811, the mean was 0.9301, and accounted for 15.33% of the study area. This region was mainly distributed in towns such as Zhaixia, Wujiang, Xintian and so on, which are located at the intersection of the Hu-Kun Expressway, Wanyi Expressway and G320 National Highway, with convenient transportation. The soil selenium content met the standard of selenium enrichment, with a low slope, and the agricultural environmental quality is the best. During the investigation, members of the research team took samples of rice, bamboo fungus, sweet potato and other crops and sent them to the Geological Survey Research Institute of Jiangxi Province to measure the selenium content. The results showed that the selenium enrichment rate of the samples was as high as 73.5%. It could be seen that the resource endowment, land use conditions, ecological protection and other evaluation indexes in this region reached the optimal combination for the development and utilization of selenium-rich soil resources.
Zone II was the moderate suitable area. The niche suitability composite index of this region was between 0.7500 and 0.8811, accounting for 22.99% of the whole study area. In addition, the mean value of the niche suitability composite index of this region was 0.8146. This region was mainly distributed in towns such as Xintian, Jinrui, Hongtang and so on. The soil selenium content in this region reached the standard of selenium enrichment; the terrain is relatively flat, the distribution is concentrated and contiguous, and the agricultural infrastructure is perfect. Relying on resources and location advantages such as selenium-rich soil and selenium-rich hot springs, companies such as Jiangxi Xinghuo Agriculture and Forestry Development have been established, and tourist attractions such as the Zhuojiang Scenic Area have been built. However, the quality of the agricultural environment in this region is relatively weak, so it is necessary to strengthen environmental protection.
The ecological niche suitability index of zone III was between 0.4055 and 0.7500, accounting for 30.51% of the whole area, mainly distributed in the hills and mountain areas such as Xinfang, Binjiang and Xicun towns. The soil selenium content in this area reached the standard of selenium enrichment or potential selenium enrichment, but this area is far away from the main traffic lines and towns, with relatively steep terrain and fragmented landscape patches.
Zone IV was the most unsuitable region for the development of selenium-enriched agriculture, and the total number of grids in this district was 994, accounting for 31.17% of the whole study area, mainly distributed in the main urban areas and towns such as Hongjiang, Wentang, Cihua and Feijiantan. Compared with the other three regions, the soil selenium content in this region only reached the standard of potential sufficient selenium, the terrain fluctuated the most and the location advantage was the lowest, so it is not suitable to carry out the development and construction project of selenium-rich soil resources. In addition, there are National 5A-class scenic spots, the Mingyue Mountain Scenic Spot and Feijiantan Reservoir in this area, with a beautiful natural landscape and great potential for developing selenium-rich tourism.

3.7.2 Suggestions related to the development mode of industrial planning

The functional zoning of selenium-rich soil resources was based on the theory of regional differentiation; the suitability of the utilization function was adopted as the fundamental requirement, took the relative consistency of soil utilization improvement measures, utilization directions and approaches, and social and economic conditions were used as the basic principles, and land use safety, ecological suitability and output efficiency were defined as the goals. Functional zoning of regional soil resources is the key means to adjust the structure of land use, optimize the distribution of agricultural industry and promote the coordinated development of regions. Based on the suitability evaluation results for the utilization of selenium-rich soil resources in the study area and the development status of agricultural industry, this study put forward suggestions for the development and industrial development of selenium-rich soil resources in this study area from two aspects, namely, to improve the utilization quality of selenium-rich soil and the functional layout of the selenium-rich industry.
1) Improve the utilization quality of selenium-rich soil. In view of the obstacles in each region, improvement measures for selenium-rich soil comprehensive utilization were put forward, and this was the key measure to improve the ecological niche suitability evaluation and promote the rational and efficient utilization of selenium-rich soil resources. According to the result of the obstacle degree calculation, the main obstacle factors of each partition were slightly different, and the main influential factors of zone I, zone II, zone III and zone IV were the land use type, the agricultural environmental quality, the soil selenium content and the terrain slope. The redevelopment of urban land with low efficiency should receive attention in zone I to improve economic and intensive land use and to meet the requirement of improving the quality of urban green development, focusing on the development goals of urban industrial structure adjustment, functional upgrading and improvement of the living environment. In zone II, the agricultural environmental quality was the first problems solved, so the regional resources development and ecological environmental protection in this zone require attention. In addition, it is also necessary to strengthen the construction of the water conservation capacity, actively guide people to use clean energy, standardize the operation procedures of wastewater and sewage discharge from factories, ensure the cleanliness of local water sources, maintain the soil ecological barrier, and steadily improve the function of the farmland ecological system. The soil selenium content and the crop selenium-rich area of zone III were relatively low, i.e., this zone is not suitable for a selenium-rich agricultural planting industry. As this area is close to the main urban area, the construction of grain warehouses and other bases should be carried out in accordance with the principles of the intensive use of land and protecting the quality of the ecological environment so as to further improve the agricultural industrial chain. The zone IV is located in the ecological protected area within the scope of the area with a beautiful natural ecological landscape and high ecological benefit; those responsible should continue to improve the environmental protection and biodiversity conservation management system and mechanism so as to ensure the local ecological sustainable development.
2) Functional layout of the selenium-rich industry. Based on the natural conditions, the industrial base and the development potential of the selenium industry development in the study area, dominated by selenium-rich agricultural industry development, the study area was divided into four selenium development zones: the core zone, key zone, development zone and radiative zone. The model of the modern “agriculture + selenium-rich” industry was adopted to promote the economic development of characteristic leading industries such as selenium-rich rice, selenium-rich vegetables, selenium-rich fruits, selenium-rich oil tea, and the tourism service industry in the study area. The functional partition diagram is shown in Fig. 8.
Fig. 8 The schematic diagram of the function zoning of the selenium-rich agricultural industry in the study area
The core zone mainly includes the areas with good suitability for the utilization of selenium-rich soil resources, relatively concentrated contiguous areas, and relatively concentrated selenium-rich products, including Xicun, Xintian, Hongtang and other towns. The area is located in a low hilly area with relatively flat terrain, good ecological environment conditions and superior traffic conditions. The development of selenium-rich related agricultural industries and enterprise construction in the area are relatively mature. In this area, we suggest coordinating the construction of a variety of modern selenium-rich agricultural demonstration zones centered around Xicun Town.
The key zone mainly includes areas suitable for developing a selenium-rich planting and breeding industry, including Tiantai, Zhuting, Hutian and other towns. The area mainly surrounds the built-up area of Yichun City with rich selenium-rich soil resources, a large area and good industrial site conditions. We suggest building a selenium-rich planting and breeding base and some standardized production bases for selenium-rich products in this area.
The development zone mainly includes towns in the northwest of the study area, such as Shuijiang, Cihua, Feijiantan and Nanmu. This area has a good ecological environment, and has certain selenium-rich agricultural production conditions, and large-scale cultivation of selenium-rich fruits, Chinese medicinal materials and other agricultural products. We suggest developing the selenium-rich forest and fruit industry through land renovation projects, and a “selenium-rich + modern agriculture” industry should be built so as to promote the multi-level and diversified development trend of the selenium-rich industry in the study area.
The radiative zone mainly includes the main urban areas, Nanmiao, Xinfang, Wentang, Hongjiang and other towns. This region is rich in culture, tourism and hot spring resources, and the development of tourism resources is relatively mature. We suggest that tourism is adopted as the main industry, relying on tourism culture and the selenium-rich industry, following the “selenium and health care tourism” development model of the modern agricultural economy.

4 Discussion

To implement the rural revitalization strategy, prosperous industry is the key. Based on the resource endowment advantages of regional selenium-rich soil, transforming the advantages of selenium-rich resources into capital advantages and industrial advantages, vigorously developing selenium-rich agricultural industry, creating new features and new advantages of modern agricultural industry, are the new requirements, new tasks and new opportunities for implementing the rural revitalization strategy and health China strategy and building a well-off society in all aspects. Carrying out the evaluation and zoning research on the suitability of selenium-rich soil resources development and utilization, and realizing the green and efficient ecological utilization of selenium-rich soil resources, is the basic support and important guarantee for the development of selenium-rich special agricultural industry. At present, scholars mostly focus on the physical and chemical properties of selenium-rich soil, resource investigation, distribution characteristics and influencing factors, selenium-rich agricultural production, feasibility analysis of development and utilization.There are not many studies on the development and utilization of selenium-rich soils, and the studies on the suitability evaluation and utilization zoning of the comprehensive development and utilization of selenium resources are relatively weak, especially the qualitative and quantitative combined studies are relatively few.The innovation and objectivity of the theoretical method is slightly lacking, and the ecological protection, land use conditions and other relevant factors related to the industrial layout planning should be considered in order to improve the effectiveness and practicality of the evaluation results.The dominant and limiting factors of agricultural production combined with the development and utilization of selenium-rich soil resources are less discussed, and there are certain limitations in the selection of indicators.
With the progress of science and technology and the depth of interdisciplinary research, ecological niche theory and model methods have been widely applied. Based on the ecological niche theory, this study regarded the exploitation of selenium-rich soil as a biological behavior in the natural environment and discussed the matching problem between the demand ecological niche and the real ecological niche of the exploitation of selenium-rich soil. The space constituted by the resource demand for the development and utilization of selenium-rich soil to meet the development of selenium-rich agriculture is called the demand ecological position, and the realistic resource conditions for the development and utilization of selenium-rich soil in the region is called the realistic ecological position, and the suitability degree of the realistic conditions of selenium-rich soil resources for the production and utilization of selenium-rich agriculture was analyzed. Combining the dominant and limiting factors of selenium-rich agricultural production such as natural resource endowment, land use conditions, agricultural environment quality and ecological protection construction, the spatial location required for the development of selenium-rich agriculture is found through a combination of qualitative and quantitative methods. And further explored the functional zoning of selenium-rich soil resources utilization and selenium-rich agricultural industry zoning in the study area. This study can provide scientific, reasonable and feasible ideas and methods for the development and utilization of selenium-rich soil resources and the planning and development of selenium-rich industries in similar areas.

5 Conclusions

In this study, niche theory and relevant evaluation model methods were introduced into the suitability evaluation study of development and utilization of selenium-rich soil resources, the main conclusions are as follows:
(1) In this study, the niche theory was introduced into the suitability evaluation study of the development and utilization of selenium-rich soil resources. The leading and limiting factors of the development and utilization of selenium- rich soil resources were determined from three aspects of natural resource endowment, land use conditions and ecological protection, and an evaluation index system and niche suitability index measurement model of selenium-rich soil resources development and utilization were constructed. The evaluation results were divided into four suitability levels by the natural breakpoint method, namely, high suitability zone, medium suitability zone, low suitability zone and unsuitable zone. Based on selenium-rich soil using two aspects of the improved selenium-rich industry functional layout, we discussed the selenium-rich soil resource development and utilization of functional zoning and the industrial development pattern in the study area. This study further enriches the research methods and theories of the suitability evaluation of selenium-rich resources and can provide scientific and reasonable guidance and suggestions for the development planning of regional selenium-rich industries.
(2) According to the development and utilization results, the suitable area for development and construction in the study area covered an area of 174658.4 ha, accounting for 68.83% of the total area, mainly distributed in the territory of Yuan river surrounding and the west, central and north of the northeastern region of the river, with relatively flat terrain, regional road connectivity, the development of selenium-rich agricultural resource advantages and location advantages. According to the results of the leading obstacles, the main obstacles to the development and utilization of selenium-rich soil resources in the study area were the terrain slope and agricultural environmental quality. In the process of development and construction in the future, measures such as land levelling can be implemented to carry out agricultural planting and breeding and industrial planning according to local conditions. At the same time, attention should be paid to soil and ecological environmental protection to ensure the stability and sustainability of soil ecological functions.
(3) Based on suitability evaluation results and obstacle factor analysis results, suggestions were put forward to improve the utilization quality of selenium-rich soil in each zone. Considering the functional positioning of the planned development of the selenium-rich industry, the study was divided into four major selenium-rich industry development functional areas, namely, the core zone, key zone, development zone and radiative zone. Among them, the development of selenium-rich related agricultural industries in the core and key zones have been relatively mature, and the planting and breeding conditions are superior. We suggest building demonstration zones of selenium-rich agricultural industries and standardized planting and breeding production bases for selenium-rich products. The development zone and radiative zone are rich in selenium-rich fruits, vegetables and hot spring resources, with a good ecological environment and advanced tourism development. We suggest vigorously developing selenium-rich modern agriculture and selenium enriched tourism, as well as accelerating the multi-level and diversified development trend of the selenium rich industry in the study area.

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