**1. Introduction**

The first explosion of industry in the late 18th century required a greater concentration and continuity of production. Factors of production such as capital, manpower and resources are highly combined in a limited space, driving the formation and development of cities. Currently, more than half of the world's people live in urban areas. Although urbanization is of great significance in promoting population transformation, industrial development, scientific and technological progress, and cultural exchange, it has also produced some negative effects, such as widening the urban–rural gap, tightening resources and energy, intensifying environmental pollution, and overwhelming the ecosystem [1]. In this context, the Third United Nations Conference on Housing and Sustainable Urban Development (Habitat III) and the "Future Earth" (FE) all emphasized that the regional urbanization process should be coordinated with the state of the ecosystem and matched with the carrying capacity of the resource and environment. The goals of building inclusive, safe, disaster-resilient and sustainable cities and human settlements, and protecting, restoring and promoting the sustainable use of terrestrial ecosystems were included in the 2023 Agenda for Sustainable Development as part of the next 17 global sustainable development

**Citation:** Zhao, W.; Shi, P.; Wan, Y.; Yao, Y. Coupling and Coordination Relationship between Urbanization Quality and Ecosystem Services in the Upper Yellow River: A Case Study of the Lanzhou–Xining Urban Agglomeration, China. *Land* **2023**, *12*, 1085. https://doi.org/10.3390/ land12051085

Academic Editors: Li Ma, Yingnan Zhang, Muye Gan and Zhengying Shan

Received: 1 April 2023 Revised: 12 May 2023 Accepted: 17 May 2023 Published: 18 May 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

priorities. How to reduce the negative impacts of rapid urbanization on ecosystems and promote the synergistic development of urbanization and ecosystem services has become a hot topic of widespread concern worldwide. At present, China's urbanization development is in a critical transition period from the medium-term rapid growth stage to the later stage of quality improvement. The report of the 20th National Congress of the CPC and the Central Urbanization Working Conference pointed out that we should plan for development at the height of harmonious coexistence between human and nature; focus on improving the quality of urbanization development; improve the diversity, stability, and sustainability of the ecosystem; and take a green, intensive and efficient high-quality urbanization road. Therefore, from the perspective of system coupling, it is of great theoretical and practical significance to scientifically and accurately evaluate the current situation of urbanization quality and ecosystem services, as well as the coupling and coordination relationship between them.

International research is abundant regarding the relationship between urbanization and ecosystems. The Organization for Economic Cooperation and Development (OECD) and the United Nations Environment Programme (UNEP) pioneered the "Pressure-State-Response" model in the 1980s. This model fostered a two-way perspective for studying the interplay between urbanization and ecosystems. Through the application of econometric methodologies, Grossman and Krueger discovered the renowned environmental Kuznets curve based on panel data from 42 developed countries in 1995. This curve uncovers an inverted "U"-shaped evolution law, correlating urban economic development with the quality of urban ecological environments, thus providing a basis for further research. Contemporary international research can be classified broadly into two categories from a research perspective. One category focuses on the quantitative relationship between urbanization and ecosystems on a global scale. For example, Li studied the coupling mechanism between urbanization systems and ecosystems [2]. Howard delved into the interaction mechanism between urbanization and environmental evolution [3]. On the other hand, Deosthali used simulation to assess the impact of urbanization on the local climates of cities [4]. Vester uncovered the mechanism linking urban economic growth and its environmental evolution [5]. Girmm explored the correlation between changes in urban landscape ecology and global change [6]. Berry identified the primary factors impacting urban ecology due to urbanization. As for research methods, current studies primarily employ disciplines such as economics, ecology, biology, and physics. Howard implemented a system dynamics model, Berry utilized ecological factor analysis, Deosthali leveraged bioclimatic indices, and Vester applied sensitivity models. Overall, the regional scale of foreign research is larger, focusing on exploring the general rules of urbanization and ecosystems in long-time serial variation.

The domestic research began in the 1980s. In 1979, Wu Chuanjun innovatively proposed the theory of regional system of the man–land relationship, underlining the importance of geographical studies focusing on the interaction and negative feedback between humanity and nature within the man–land system [7]. As articulated by Lu Daodao, studying regional human–earth systems requires an understanding of their dynamic changes across different stages of societal development, necessitating an integrated qualitative and quantitative approach and advocating for a harmonious relationship between humans and nature at varying scales [8,9]. Domestic research in this field has also yielded a wealth of findings. Concerning research content, scholars have deployed mathematical models to elucidate various relationships between urbanization and ecosystems, such as "positive", "negative", or "inverted-U" relationships [10–13]. Evaluations of urbanization are predominantly conducted from the perspectives of population movement [14,15], industrial agglomeration [16,17], expansion of construction land [18,19], and infrastructure development [20,21]. Assessments of ecosystem services typically rely on the value scale formulated by Costanza and others [22], with the value of ecosystem services determined by continuously refining the value equivalent factor [23]. As for research methodologies, most existing studies have employed mathematical and statistical models such as regression analysis [24,25], input-output models [26,27], system dynamics models [28,29], or spatial analysis models. Regarding study area selection, empirical studies have mainly concentrated on provincial or municipal levels, predominantly targeting economically advanced regions, such as the Yangtze River Delta, Pearl River Delta, Beijing-Tianjin-Hebei region, and Chengdu-Chongqing region. Overall, contemporary domestic research on the relationship between urbanization and ecosystems exhibits three key characteristics. Firstly, the assessment dimensions of urbanization tend to be somewhat singular, primarily encompassing population aggregation, economic growth, and construction land expansion, with inadequate attention given to the comprehensive benefits of urbanization. Secondly, an over-reliance on statistical data often overlooks the natural attributes of ecosystems, which may result in the assessment findings not accurately reflecting the actual regional ecosystem conditions. Thirdly, the limitations of one-way research remain unaddressed, lacking the analysis of factor relationships and subject behaviors guided by synergistic ideas. The research primarily centers around the ecological effects prompted by urbanization, with insufficient focus on the feedback mechanism and mode of action of the ecosystem.

Ecosystem services refer to the conditions and processes that ecosystems and their species can provide to humans to satisfy and sustain their needs [30]. It is a frontier area of research in ecology and geography, and a link and bridge that connects natural and hu-man processes [31]. For the purpose of identifying regional ecosystem service issues, preserving regional ecological balance, and advancing regional sustainable development, it is crucial to explore the intrinsic interaction mechanism between the external spatial and temporal evolution of ecosystem services and the economic society [32–34]. We introduced an exponential efficacy function model to quantitatively measure the development of economic and social systems based on pertinent studies. Meanwhile, we used multivariate data and the InVEST model to analyze the regional ecosystem services and explore the current development status and coupled coordination of the complex ecosystem of the LXUA. The purpose of this research is to clarify the synergistic evolution mechanism of the man–land relationship in the ecologically sensitive area of the Upper Yellow River and provide a reference for ecological protection and high-quality development.

#### **2. Materials and Methods**

### *2.1. Study Area*

The LXUA, with coordinates of 34◦260 N–37◦380 N, 98◦550 E–105◦550 E, is the westernmost town-dense region in the Yellow River basin. It is situated below Longyangxia, in the basin of the Yellow River and Huangshui River valley (Figure 1). The LXUA, which spans 97,500 km<sup>2</sup> , consists of 39 counties in 9 cities, including Lanzhou, Xining, and Haidong. Mountains and river valleys dominate the region's terrain, which is complicated and varied. With an average height of 2000 m or more, the elevation varies from 1258 to 5255 m. In 2020, the GDP of LXUA reached 61.4 billion RMB, accounting for 51% of the GDP in the two provinces. The population reached 12.19 million, accounting for 66.5% of the permanent population in the two provinces. The city group is rich in hydraulic resources; climate geographic distribution differences; thick soil; and complex and diverse vegetation types, among which the eastern agricultural area of Qinghai is located in the Huangshui and Yellow River basin triangle. It has fertile soil, a mild climate, and a wealth of natural resources that are advantageous for developing agriculture and animal husbandry. Lanzhou, Xining, Huangzhong, Datong, Xunhua, etc. are important towns on the ancient Silk Road transportation route. Lanzhou is known as the "heart of the land", Xining is the "Pearl City" on the Qinghai-Tibet Plateau, and the two cities are the "growth poles" to promote the population clustering and economic development of the urban agglomeration.

poles" to promote the population clustering and economic development of the urban ag-

**Figure 1.** Diagram of the study area. **Figure 1.** Diagram of the study area.

#### *2.2. Analysis Framework 2.2. Analysis Framework*

glomeration.

Urbanization and ecosystems together make up a complex system that is a synthesis of ecological processes brought about by the interaction of human social, economic, and cultural actions with the environment [35]. The two subsystems are connected and engage in interactions with one another in terms of amount, structure, order, quantity in space, and time. The quality of urbanization refers to a comprehensive concept with a rich connotation that reflects the quality of urbanization in the process of urbanization [36]. In this paper, evaluation indicators were primarily created in seven dimensions: economic development, people's lives, environmental protection, infrastructure, public services, urban vitality, and relationships between urban and rural areas [37–39] (Table 1). The regional ecosystem condition is an important basic condition for the smooth promotion of urbanization. The LXUA is an essential strategic support for maintaining China's ecological security and is situated in the crucial zone of transition from the first to the second terrain in China. It contains significant ecological security barriers such as the Source Region of Three Rivers, Qilian Mountains, and Gannan Plateau. Water provision services refer to the interception, infiltration, and storage of precipitation by ecosystems through their unique structures and water interactions, and the effective regulation of water circulation through evapotranspiration. The water provision services of the LXUA play an important role in mitigating surface runoff, supplementing groundwater, mitigating seasonal fluctuations in river water flow, and ensuring water source quality. Meanwhile, vegetation can effectively reduce the impact of precipitation on soil. Plant roots are intertwined with the soil, which can effectively fix the soil. The soil conservation services are crucial to reduce soil erosion, maintain soil fertility, prevent and control desertification, and reduce the occurrence of geological disasters such as landslides and debris flows. Carbon fixation services refer to the conversion of atmospheric carbon dioxide into organic carbon through photosynthesis, which are fixed in the plants or soil. Carbon fixation services can reduce the Urbanization and ecosystems together make up a complex system that is a synthesis of ecological processes brought about by the interaction of human social, economic, and cultural actions with the environment [35]. The two subsystems are connected and engage in interactions with one another in terms of amount, structure, order, quantity in space, and time. The quality of urbanization refers to a comprehensive concept with a rich connotation that reflects the quality of urbanization in the process of urbanization [36]. In this paper, evaluation indicators were primarily created in seven dimensions: economic development, people's lives, environmental protection, infrastructure, public services, urban vitality, and relationships between urban and rural areas [37–39] (Table 1). The regional ecosystem condition is an important basic condition for the smooth promotion of urbanization. The LXUA is an essential strategic support for maintaining China's ecological security and is situated in the crucial zone of transition from the first to the second terrain in China. It contains significant ecological security barriers such as the Source Region of Three Rivers, Qilian Mountains, and Gannan Plateau. Water provision services refer to the interception, infiltration, and storage of precipitation by ecosystems through their unique structures and water interactions, and the effective regulation of water circulation through evapotranspiration. The water provision services of the LXUA play an important role in mitigating surface runoff, supplementing groundwater, mitigating seasonal fluctuations in river water flow, and ensuring water source quality. Meanwhile, vegetation can effectively reduce the impact of precipitation on soil. Plant roots are intertwined with the soil, which can effectively fix the soil. The soil conservation services are crucial to reduce soil erosion, maintain soil fertility, prevent and control desertification, and reduce the occurrence of geological disasters such as landslides and debris flows. Carbon fixation services refer to the conversion of atmospheric carbon dioxide into organic carbon through photosynthesis, which are fixed in the plants or soil. Carbon fixation services can reduce the concentration of greenhouse gases such as carbon dioxide in the atmosphere, which plays an importantrole in maintaining the carbon oxygen balance and slowing down global warming. Integrated ecosystem services are the overall manifestation of various service functions and an important indicator reflecting the quality and condition of regional ecosystems. These

four types of ecosystem services have an important impact on the ecological security of the Upper Yellow River and the country as a whole. Therefore, the study was based on the InVEST model, and the four aspects of water provision, soil conservation, carbon fixation, and integrated ecosystem services were selected for assessment. The analysis framework is shown in Figure 2.

**Table 1.** Indicators of urbanization quality.


The process of urbanization is one of the most important manifestations of the development and evolution of human society. The ecosystem is a natural background and supporting system for the subsistence and multiplying of human beings. Urbanization is closely related to ecosystems, and both are important components of the regional man–land system. The impact of urbanization on the ecosystem is bidirectional, with both negative stress and positive promotion effects. The coercive effect of urbanization on the ecosystem refers to the phenomenon of environmental pollution, imbalance between resource supply and demand, reduction of biodiversity, and degradation of ecosystem functions when the amount and speed of waste discharged by cities into the hinterland environment through production and living reach or exceed the speed of ecological environment decomposition and digestion. The promoting effect of urbanization on the ecosystem refers to the investment of more resources such as technology, funds, and manpower into urban economic construction activities within the range of ecological environment capacity and carrying capacity. Through policy intervention and the promotion of clean production technology, the economic development mode is transformed, resource utilization efficiency is improved, pollution emissions are reduced, citizens' lifestyles are transformed, the low-carbon and green development of cities is achieved, and the quality of the living environment is im-

proved. The ecosystem also has a positive and negative impact on urbanization. On the one hand, resources such as water, soil, energy, and minerals mainly constrain urban scale, affect urban layout, limit urban industrial structure, and influence the speed of urbanization development, thereby exerting constraints on various aspects of urbanization; on the other hand, ecosystem services such as water provision, soil conservation, and carbon fixation are fundamental for supporting and guaranteeing conditions for urban development and residents' lives. functions and an important indicator reflecting the quality and condition of regional ecosystems. These four types of ecosystem services have an important impact on the ecological security of the Upper Yellow River and the country as a whole. Therefore, the study was based on the InVEST model, and the four aspects of water provision, soil conservation, carbon fixation, and integrated ecosystem services were selected for assessment. The analysis framework is shown in Figure 2.

concentration of greenhouse gases such as carbon dioxide in the atmosphere, which plays an important role in maintaining the carbon oxygen balance and slowing down global warming. Integrated ecosystem services are the overall manifestation of various service

*Land* **2023**, *12*, x FOR PEER REVIEW 5 of 20

**Figure 2.** Analysis framework.

#### **Figure 2.** Analysis framework. *2.3. Data Sources*

The process of urbanization is one of the most important manifestations of the development and evolution of human society. The ecosystem is a natural background and supporting system for the subsistence and multiplying of human beings. Urbanization is closely related to ecosystems, and both are important components of the regional man– This study created an ecosystem classification map of the LXUA using the 100 m × 100 m land-use remote-sensing monitoring data in 2000 and 2020 provided by the Resource and Environment Science and Data Center (https://www.resdc.cn accessed on 22 August 2022) (Figure 3). *Land* **2023**, *12*, x FOR PEER REVIEW 7 of 20

transformed, the low-carbon and green development of cities is achieved, and the quality

( )/( ) *s hs <sup>x</sup> x x xB d Ae* − − = (1)

is the theoretical minimum value, *xh* is the theoretical

( )/( )ln 0.6 60 *s hs xx x x d e*−− − = (2)

zation efficiency is improved, pollution emissions are reduced, citizens' lifestyles are **Figure 3.** Land-use types of LXUA in 2000 and 2020. weight. The specific calculation process is as follows: **Figure 3.** Land-use types of LXUA in 2000 and 2020.

ence Data Center (http://www.geodata.cn accessed on 12 September 2022).

development process and trend of the data. The formula is as follows:

*2.4. Methods* 

2.4.1. Exponential Efficacy Function Model

Where *d* is the efficacy score, *xs*

2.4.2. The Entropy Method

mum are the same, set *d* = 100, then *B* = −ln0.6 [40,41].

were sourced from the National Basic Information Center. Meteorological data, including temperature, precipitation, water pressure, etc., were obtained from the China Metrological Data Service Centre (http://data.cma.cn accessed on 28 August 2022), and the local 5 year average meteorological data were taken for the calculation considering the interannual fluctuation of the data. the soil data were sourced from National Earth System Sci-

In previous studies, the linear efficacy function model was usually used to standardize the data. The linear efficacy function model defines the change of indicators as "uniform change", which is a relatively simplified form of processing. However, in the normal course of economic and social development, if an indicator increases continuously and reaches a certain number and scale, the actual utility provided by it will typically decrease over time, much like the well-known law of diminishing marginal utility. It will then be more challenging to maintain the indicator's growth or progress. The derivative of exponential efficacy function model is a lower convex function about independent variable. In practical applications, the exponential efficacy function model is chosen to better fit the

maximum value. The parameters *A* and *B* can be determined by the critical points. When the index value and the theoretical minimum are the same, according to the linear efficacy function method, set *d* = 60, then *A* = 60. When the index value and the theoretical maxi-

The entropy method is an objective weighting method that determines the weight according to the dispersion degree of the indicator, which can deeply reflect the utility value of the indicator information and avoid the interference of human factors in the evaluation process. The greater the dispersion of the indicator value, the smaller its entropy value, the greater the amount of information provided by the indicator, and the greater the

The socio-economic data used in this study were mainly obtained from "China Statistical Yearbook", "Gansu Development Yearbook", "Qinghai Statistical Yearbook",

The socio-economic data used in this study were mainly obtained from "China Statistical Yearbook", "Gansu Development Yearbook", "Qinghai Statistical Yearbook", "Gansu Urban Yearbook", statistical yearbooks, and statistical bulletins of various cities. Basic geographic data, including roads, rivers, administrative boundaries of counties, were sourced from the National Basic Information Center. Meteorological data, including temperature, precipitation, water pressure, etc., were obtained from the China Metrological Data Service Centre (http://data.cma.cn accessed on 28 August 2022), and the local 5-year average meteorological data were taken for the calculation considering the interannual fluctuation of the data. the soil data were sourced from National Earth System Science Data Center (http://www.geodata.cn accessed on 12 September 2022).

#### *2.4. Methods*

2.4.1. Exponential Efficacy Function Model

In previous studies, the linear efficacy function model was usually used to standardize the data. The linear efficacy function model defines the change of indicators as "uniform change", which is a relatively simplified form of processing. However, in the normal course of economic and social development, if an indicator increases continuously and reaches a certain number and scale, the actual utility provided by it will typically decrease over time, much like the well-known law of diminishing marginal utility. It will then be more challenging to maintain the indicator's growth or progress. The derivative of exponential efficacy function model is a lower convex function about independent variable. In practical applications, the exponential efficacy function model is chosen to better fit the development process and trend of the data. The formula is as follows:

$$d = Ae^{(\mathbf{x} - \mathbf{x}^{\kappa})/(\mathbf{x}^{\hbar} - \mathbf{x}^{\kappa})\mathbf{B}} \tag{1}$$

where *d* is the efficacy score, *x s* is the theoretical minimum value, *x h* is the theoretical maximum value. The parameters *A* and *B* can be determined by the critical points. When the index value and the theoretical minimum are the same, according to the linear efficacy function method, set *d* = 60, then *A* = 60. When the index value and the theoretical maximum are the same, set *d* = 100, then *B* = −ln0.6 [40,41].

$$d = 60e^{-(\mathbf{x} - \mathbf{x}^s)/(\mathbf{x}^h - \mathbf{x}^s)\ln 0.6} \tag{2}$$

#### 2.4.2. The Entropy Method

The entropy method is an objective weighting method that determines the weight according to the dispersion degree of the indicator, which can deeply reflect the utility value of the indicator information and avoid the interference of human factors in the evaluation process. The greater the dispersion of the indicator value, the smaller its entropy value, the greater the amount of information provided by the indicator, and the greater the weight. The specific calculation process is as follows:

$$\mathcal{Y}\_{ij} = \mathbf{x}\_{ij} / \sum\_{i=1}^{m} \mathbf{x}\_{ij} \tag{3}$$

$$k = \frac{1}{\ln m} \tag{4}$$

$$e\_{\vec{j}} = -k \sum\_{i=1}^{m} \left( Y\_{i\vec{j}} \ln Y\_{i\vec{j}} \right) \tag{5}$$

$$D\_{\rangle} = 1 - e\_{\rangle} \tag{6}$$

$$\mathcal{W}\_{\dot{\jmath}} = D\_{\dot{\jmath}} / \sum\_{j=1}^{n} D\_{\dot{\jmath}} \tag{7}$$

$$dL\_d = \sum (D\_{\dot{\jmath}} \times \mathcal{W}\_{\dot{\jmath}}) (a = 1, 2, 3) \tag{8}$$

In the formula, m and n represent the number of samples and indicators, respectively, *Yij* is the *i* sample of the *j* indicators accounted for the proportion of the indicator of the total sample value. *e<sup>j</sup>* , *D<sup>j</sup>* and *W<sup>j</sup>* are the entropy value, variability coefficient and weight value of the *j* indicator, and *U<sup>a</sup>* is the subsystem orderliness. The specific weights of each index are shown in Table 1.

#### 2.4.3. InVEST Model

The InVEST model is based on the distributed algorithm of "3S" technology. The spatial representation, dynamic assessment and quantitative evaluation of ecosystem service functions can be carried out quickly and accurately.

#### a. Water provision

Water provision is equal to the difference between precipitation and evapotranspiration, which is obtained from the water yield module of the InVEST model. The model is based on the Budyko water and heat coupling equilibrium assumption, taking into account factors such as terrain, climate, soil layer thickness and permeability [42]. The calculation formula is:

$$Z\_{i\circ} = (1 - AETi\_{\circ}/P\_{\circ}) \times P\_{\circ} \tag{9}$$

where *Zij* denotes the annual water yield of land-use type *j* in grid *i* (mm). *AETi<sup>j</sup>* represents the annual actual evapotranspiration of land-use type *j* in grid *i* (mm). *P<sup>i</sup>* represents the average annual precipitation of grid *i* (mm).

#### b. Soil conservation

The modified general soil loss equation can be used to determine soil retention, which is equal to the difference between the amount of possible soil erosion and the amount of potential soil loss. The following is the calculation formula:

$$SD = R \times K \times LS \times (1 - \mathbb{C} \times P) \tag{10}$$

where *SD* denotes the amount of soil conservation (t·hm−<sup>2</sup> ·a −1 ). *R* is rainfall erosivity (MJ·mm·hm−<sup>2</sup> ·h −1 ·a −1 ). *<sup>K</sup>* is soil erodibility (t·hm<sup>2</sup> ·h·hm−<sup>2</sup> ·MJ−<sup>1</sup> ·mm−<sup>1</sup> ). *LS* is the gradient and slope length factor calculated by DEM. *C* is vegetation coverage and management factor. *P* is the engineering measure factor.

#### c. Carbon fixation

Carbon storage represents the carbon fixation capacity of terrestrial ecosystems. The calculation formula is:

$$\mathcal{C} = \mathcal{C}\_{\text{above}} + \mathcal{C}\_{\text{below}} + \mathcal{C}\_{\text{soil}} + \mathcal{C}\_{\text{dead}} \tag{11}$$

where *<sup>C</sup>* is the underground carbon storage (t·hm−<sup>2</sup> ·a −1 ). *C*above is the aboveground carbon storage (t·hm−<sup>2</sup> ·a −1 ). *<sup>C</sup>*below is the underground carbon storage (t·hm−<sup>2</sup> ·a −1 ). *C*soil is the density of soil organic matter (t·hm−<sup>2</sup> ·a −1 ). *<sup>C</sup>*dead is carbon storage of litter (t·hm−<sup>2</sup> ·a −1 ).

#### d. Integrated ecosystem services

We constructed the comprehensive index of regional ecosystem services by using the dispersion coefficient method, and the geometric average method was used for grid cells [43]. The calculation formula is:

$$ES\_{\bar{i}} = \frac{\sigma\_{\bar{i}k}}{\varkappa\_{\bar{i}k}} = \frac{1}{\varkappa\_{\bar{i}k}} \sqrt{\frac{1}{N} \sum\_{k=1}^{N} \left(\varkappa\_{\bar{i}k} - \overline{\varkappa\_{\bar{i}k}}\right)^2} \tag{12}$$

where *ES<sup>i</sup>* is the ecosystem services of the *i*-th grid cell. *σik* is the amount of the *k*-th ecosystem services on the *i*-th grid cell. *xik* is the normalized value of ecosystem services of the *k*-th category on the *i*-th grid unit in the region. *xik* is the average of normalized values of the *k*-th ecosystem services on the *i*-th grid cell. *N* is the main ecosystem service category.

#### 2.4.4. Coupling Coordination Degree Model

Originally a physical concept, coupling refers to the phenomenon of two or more systems affecting each other through various interactions. The coupling degree can describe influence between systems or elements. The coupling action determines the state and structure of the system when it reaches the critical region, which determines the trend of the system from disorder to order. The impact of urbanization quality and ecosystem services interaction is defined as the coupling degree, which reflects the order of the system and the interaction strength between subsystems. The calculation formula is:

$$\mathbf{C} = \left[ \frac{\prod\_{i=1}^{n} \mathbf{U}\_i}{\left( \frac{1}{n} \sum\_{i=1}^{n} \mathbf{U}\_i \right)} \right]^{\frac{1}{n}} \tag{13}$$

where *n* is the number of subsystems; *U<sup>i</sup>* is the value of each subsystem, *C* is the coupling degree, and the value of *C* is between 0 and 1. According to the value range of the coupling degree, it can be divided into four stages. When the CD is below 0.3, the system is in the low coupling stage; when the CD is between 0.3 and 0.5, the system is in the antagonistic stage; when the CD is between 0.5 and 0.8, the system is in the running-in stage; and when the CD is between 0.8 and 1.0, the system is in the high coupling stage. The measurement functions of urbanization quality and ecosystem services at stage *t* are *f* (*t*, *x*) and *g* (*t*, *y*), where *x* and *y* are the evaluation indexes of the two systems, respectively. The formula is as follows:

$$\mathcal{C} = \left\{ \left[ f(t, \mathbf{x}) \times \mathbf{g}(t, \mathbf{x}) \right] / \left[ \frac{f(t, \mathbf{x}) + \mathbf{g}(t, \mathbf{x})}{2} \right]^2 \right\}^{\frac{1}{2}} \tag{14}$$

$$D = \sqrt{\mathbb{C} \times T} = \sqrt{\mathbb{C} \times \left[ a f(t, \mathbf{x}) \times b g(t, \mathbf{x}) \right]} \tag{15}$$

The coupling degree can indicate the strength of interaction between urbanization quality and ecosystem services, but it is not possible to judge whether the coupling status is benign or not. When the development level of both systems is low, a high coupling degree can still be obtained. The degree of coordination adds a development coefficient to the degree of coupling, which is a composite reflection of the order of internal structure and the external scale of the system, where *D* is the coordination degree; *C* is the coupling degree; *a* and *b* are the weights. In this study, it is considered that both urbanization quality and ecosystem services are crucial to the evolutionary development of the composite system, and it was more beneficial to compare the actual conditions of different county subsystems horizontally by assigning the same pending coefficients to each system on the basis of the control variables [44], so *a* and *b* were each assigned weight of 0.5.

#### **3. Results**

#### *3.1. Status of Subsystem Development*

#### 3.1.1. Urbanization Quality Subsystem

The enhancement of the LXUA's urbanization quality is crucial for advancing the coordinated development of Northwest China and serving as a crucial assurance for the construction of a multiethnic demonstration area of shared prosperity. According to the seventh national census, the resident population of the LXUA was 12.47 million, accounting for 40% of the total population of Gansu and Qinghai, among which the urbanization rate of the resident population in Lanzhou and Xining was 83.1% and 78.63%, respectively. In terms of distribution pattern, the urbanization quality of the LXUA in 2000 was in the barbellshaped "double core" pattern, with areas higher than 0.4 mainly concentrated in Lanzhou and Xining urban areas, in the eastern and western cores of the urban agglomeration (Figure 4). At the same time, the urbanization quality of Baiyin and Linxia, the municipal and prefectural government locations, was also higher than 0.4. Compared with 2000, the number of medium- and high-value areas of urbanization quality in LXUA increased in

**3. Results** 

*3.1. Status of Subsystem Development* 

3.1.1. Urbanization Quality Subsystem

2020, including Haiyan of the Haibei urban area and Ping'an of the Haidong urban area, which had increased to more than 0.4; and the main urban areas of Lanzhou and Xining, and Baiyin increased to more than 0.6. It is worth noting that there were no counties with an urbanization quality higher than 0.6 in 2020 in Dingxi, Hainan or Huangnan urban areas within the city cluster. urban area, which had increased to more than 0.4; and the main urban areas of Lanzhou and Xining, and Baiyin increased to more than 0.6. It is worth noting that there were no counties with an urbanization quality higher than 0.6 in 2020 in Dingxi, Hainan or Huangnan urban areas within the city cluster.

creased in 2020, including Haiyan of the Haibei urban area and Ping'an of the Haidong

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the degree of coupling, which is a composite reflection of the order of internal structure and the external scale of the system, where *D* is the coordination degree; *C* is the coupling degree; *a* and *b* are the weights. In this study, it is considered that both urbanization quality and ecosystem services are crucial to the evolutionary development of the composite system, and it was more beneficial to compare the actual conditions of different county subsystems horizontally by assigning the same pending coefficients to each system on the

The enhancement of the LXUA's urbanization quality is crucial for advancing the coordinated development of Northwest China and serving as a crucial assurance for the construction of a multiethnic demonstration area of shared prosperity. According to the seventh national census, the resident population of the LXUA was 12.47 million, accounting for 40% of the total population of Gansu and Qinghai, among which the urbanization rate of the resident population in Lanzhou and Xining was 83.1% and 78.63%, respectively. In terms of distribution pattern, the urbanization quality of the LXUA in 2000 was in the barbell-shaped "double core" pattern, with areas higher than 0.4 mainly concentrated in Lanzhou and Xining urban areas, in the eastern and western cores of the urban agglomeration (Figure 4). At the same time, the urbanization quality of Baiyin and Linxia, the

basis of the control variables [44], so *a* and *b* were each assigned weight of 0.5.

**Figure 4.** Urbanization quality of the LXUA in 2000 and 2020. **Figure 4.** Urbanization quality of the LXUA in 2000 and 2020.

On the whole, the urbanization quality of the LXUA has fewer areas with medium and high values, and the development of sub-central cities in the urban agglomeration is relatively insufficient. At the same time, the average urbanization quality of all counties in Lanzhou in 2020 was only 0.536, while that of Xining was 0.539. As the leading and core of the urban agglomeration, its development potential has not been fully released, and the leading and driving effects of both on regional urbanization development need to be further strengthened. The urbanization quality of 25 counties in the urban agglomeration in 2020 was between 0.2 and 0.4, accounting for 64% of the total number of counties; among them, 10 counties had scores less than 0.3. The counties in the LXUA have a single level of economic development, insufficient development of secondary centers, and obvious characteristics of an extensive distribution of low-level counties. At present, Lanzhou and Xining are still in the stage of polarized development: the "siphon effect" is obvious, a large On the whole, the urbanization quality of the LXUA has fewer areas with medium and high values, and the development of sub-central cities in the urban agglomeration is relatively insufficient. At the same time, the average urbanization quality of all counties in Lanzhou in 2020 was only 0.536, while that of Xining was 0.539. As the leading and core of the urban agglomeration, its development potential has not been fully released, and the leading and driving effects of both on regional urbanization development need to be further strengthened. The urbanization quality of 25 counties in the urban agglomeration in 2020 was between 0.2 and 0.4, accounting for 64% of the total number of counties; among them, 10 counties had scores less than 0.3. The counties in the LXUA have a single level of economic development, insufficient development of secondary centers, and obvious characteristics of an extensive distribution of low-level counties. At present, Lanzhou and Xining are still in the stage of polarized development: the "siphon effect" is obvious, a large number of production factors are gathered in the core area, the development vitality of the secondary core areas around the provincial capital is insufficient, and the economic radiation and driving capacity of the central cities need to be strengthened.

> In terms of temporal changes, the average urbanization quality of the counties in the LXUA was 0.328 in 2000, rising to 0.404 in 2020, with an overall increase of 23.17% and an average annual increase of 1.16%. There were big differences in the improvement of each county, among which Gaolan, Yuzhong, Jingyuan, Weiyuan, Dongxiang, Jishishan and Ledu's urbanization quality increased by more than 40%; and that of Yongdeng, Anding, Longxi, Lintao, Yongjing, Huangyuan and Huangzhong increased by more than 30%, mostly in the eastern Gansu section of the urban cluster (Figure 5). The junction of Yongdeng and Gaolan, Lanzhou New, was established in 2010. With the gathering of population and industry, infrastructure construction and production, and living services enhancement, its urbanization quality has achieved obvious improvement. Lintao, Yuzhong and Yongjing, close to Lanzhou, are radiated and driven by the core of the provincial capital, and the urbanization quality is also improved at a faster rate. The number of counties with an increase in urbanization quality of 20% to 30% was the largest, accounting for one-third of the total number of counties, mainly distributed in the urban agglomeration Qinghai area. The counties with less than a 20% increase were concentrated in the main urban areas of Lanzhou and Xining, as well as Baiyin, Pingchuan and Linxia. The urbanization quality of such counties in 2000 was higher than other surrounding counties. In the case of the same absolute value of growth, the larger the previous base, the lower the increase will be; at the same time, the development of regional urbanization also conforms to the law of

marginal diminution, and the higher its development degree, the more difficult it will be to improve it. will be to improve it.

number of production factors are gathered in the core area, the development vitality of the secondary core areas around the provincial capital is insufficient, and the economic

In terms of temporal changes, the average urbanization quality of the counties in the LXUA was 0.328 in 2000, rising to 0.404 in 2020, with an overall increase of 23.17% and an average annual increase of 1.16%. There were big differences in the improvement of each county, among which Gaolan, Yuzhong, Jingyuan, Weiyuan, Dongxiang, Jishishan and Ledu's urbanization quality increased by more than 40%; and that of Yongdeng, Anding, Longxi, Lintao, Yongjing, Huangyuan and Huangzhong increased by more than 30%, mostly in the eastern Gansu section of the urban cluster (Figure 5). The junction of Yongdeng and Gaolan, Lanzhou New, was established in 2010. With the gathering of population and industry, infrastructure construction and production, and living services enhancement, its urbanization quality has achieved obvious improvement. Lintao, Yuzhong and Yongjing, close to Lanzhou, are radiated and driven by the core of the provincial capital, and the urbanization quality is also improved at a faster rate. The number of counties with an increase in urbanization quality of 20% to 30% was the largest, accounting for onethird of the total number of counties, mainly distributed in the urban agglomeration Qinghai area. The counties with less than a 20% increase were concentrated in the main urban areas of Lanzhou and Xining, as well as Baiyin, Pingchuan and Linxia. The urbanization quality of such counties in 2000 was higher than other surrounding counties. In the case of the same absolute value of growth, the larger the previous base, the lower the increase will be; at the same time, the development of regional urbanization also conforms to the law of marginal diminution, and the higher its development degree, the more difficult it

radiation and driving capacity of the central cities need to be strengthened.

*Land* **2023**, *12*, x FOR PEER REVIEW 11 of 20

#### 3.1.2. Ecosystem Service Subsystem 3.1.2. Ecosystem Service Subsystem

Water provision services refer to the ability of an ecosystem to intercept or store water resources from rainfall. From 2000 to 2020, the water provision services of the LXUA improved significantly. The area of the high-value area in the southwestern Sanjiangyuan region had increased most significantly. The Laji Mountains and the Lianhua Mountains in the southeast evolved from the median area to the higher-value area. At the same time, the proportion of low-value areas for water provision services had increased in Yongdeng, Gaolan and Yuzhong counties in the northeast of the urban agglomeration (Figure 6); in 2020, water provision services increased from the northeast to the southwest, and high-Water provision services refer to the ability of an ecosystem to intercept or store water resources from rainfall. From 2000 to 2020, the water provision services of the LXUA improved significantly. The area of the high-value area in the southwestern Sanjiangyuan region had increased most significantly. The Laji Mountains and the Lianhua Mountains in the southeast evolved from the median area to the higher-value area. At the same time, the proportion of low-value areas for water provision services had increased in Yongdeng, Gaolan and Yuzhong counties in the northeast of the urban agglomeration (Figure 6); in 2020, water provision services increased from the northeast to the southwest, and high-altitude mountains became the main area for improving water provision services. *Land* **2023**, *12*, x FOR PEER REVIEW 12 of 20

**Figure 6.** Water provision service of LXUA in 2000 and 2020. **Figure 6.** Water provision service of LXUA in 2000 and 2020.

Soil conservation services refer to the ability of the ecosystem to hold the soil in a given time, which is an important guarantee for regulating water and soil loss, preventing soil degradation, and reducing the risk of geological disasters. From 2000 to 2020, the overall change of soil conservation services was not significant, and the areas to be promoted were mainly concentrated in the west of urban agglomeration (Figure 7). The median area along the central Laji Mountains and the southern Xiqing Mountains increased, while the area of the low-value area decreased. In 2020, soil conservation services mainly Soil conservation services refer to the ability of the ecosystem to hold the soil in a given time, which is an important guarantee for regulating water and soil loss, preventing soil degradation, and reducing the risk of geological disasters. From 2000 to 2020, the overall change of soil conservation services was not significant, and the areas to be promoted were mainly concentrated in the west of urban agglomeration (Figure 7). The median area along the central Laji Mountains and the southern Xiqing Mountains increased, while the area of the low-value area decreased. In 2020, soil conservation services mainly served in lowand middle-value areas, with a single hierarchical structure and a lack of high-value areas, showing a differentiation pattern that was slightly higher in the middle and lower in the east and west.

Carbon fixation services refer to the capacity of terrestrial ecosystem to store carbon.

There are two common ways of carbon fixation in nature: one is the photosynthesis of green plants and the other is the chemosynthesis of microorganisms such as nitrifying bacteria. The former, as the main mode of carbon fixation, is closely related to regional vegetation coverage and land-use type. The high-value areas of carbon fixation service in LXUA were mainly located in Daban Mountains in the north, Laji Mountains in the middle, the southern Xiqingshan residual vein and around Xinglong Mountains in the east (Figure 8). The low-value areas were mainly concentrated in the desert, water area and urban built-up areas of municipalities in the southwest. In terms of spatial distribution, the carbon fixation services in 2000 were mainly in the median area, with a relatively single hierarchical structure. In 2020, with the accelerated transformation of land-use types, the spatial distribution of carbon fixation services became more complex. The high and the low values were staggered, and the trend of "fragmentation" and "fragmentation"

and lower in the east and west.

was obviously intensified.

**Figure 7.** Soil conservation service of LXUA in 2000 and 2020.

served in low- and middle-value areas, with a single hierarchical structure and a lack of high-value areas, showing a differentiation pattern that was slightly higher in the middle and lower in the east and west.

Soil conservation services refer to the ability of the ecosystem to hold the soil in a

given time, which is an important guarantee for regulating water and soil loss, preventing soil degradation, and reducing the risk of geological disasters. From 2000 to 2020, the overall change of soil conservation services was not significant, and the areas to be promoted were mainly concentrated in the west of urban agglomeration (Figure 7). The median area along the central Laji Mountains and the southern Xiqing Mountains increased, while the area of the low-value area decreased. In 2020, soil conservation services mainly served in low- and middle-value areas, with a single hierarchical structure and a lack of

**Figure 6.** Water provision service of LXUA in 2000 and 2020.

**Figure 7.** Soil conservation service of LXUA in 2000 and 2020. **Figure 7.** Soil conservation service of LXUA in 2000 and 2020.

Carbon fixation services refer to the capacity of terrestrial ecosystem to store carbon. There are two common ways of carbon fixation in nature: one is the photosynthesis of green plants and the other is the chemosynthesis of microorganisms such as nitrifying bacteria. The former, as the main mode of carbon fixation, is closely related to regional vegetation coverage and land-use type. The high-value areas of carbon fixation service in LXUA were mainly located in Daban Mountains in the north, Laji Mountains in the middle, the southern Xiqingshan residual vein and around Xinglong Mountains in the east (Figure 8). The low-value areas were mainly concentrated in the desert, water area and urban built-up areas of municipalities in the southwest. In terms of spatial distribution, the carbon fixation services in 2000 were mainly in the median area, with a relatively single hierarchical structure. In 2020, with the accelerated transformation of land-use types, Carbon fixation services refer to the capacity of terrestrial ecosystem to store carbon. There are two common ways of carbon fixation in nature: one is the photosynthesis of green plants and the other is the chemosynthesis of microorganisms such as nitrifying bacteria. The former, as the main mode of carbon fixation, is closely related to regional vegetation coverage and land-use type. The high-value areas of carbon fixation service in LXUA were mainly located in Daban Mountains in the north, Laji Mountains in the middle, the southern Xiqingshan residual vein and around Xinglong Mountains in the east (Figure 8). The low-value areas were mainly concentrated in the desert, water area and urban built-up areas of municipalities in the southwest. In terms of spatial distribution, the carbon fixation services in 2000 were mainly in the median area, with a relatively single hierarchical structure. In 2020, with the accelerated transformation of land-use types, the spatial distribution of carbon fixation services became more complex. The high and the low values were staggered, and the trend of "fragmentation" and "fragmentation" was obviously intensified.

**Figure 8.** Carbon fixation service of LXUA in 2000 and 2020.

Overall, the integrated ecosystem services of the LXUA showed an overall stepped distribution pattern from northeast to southwest (Figure 9). The highest-value areas were mainly located in Hainan and Huangnan in the southwest. The terrain was dominated by high mountain landforms, with towering terrain and continuous mountain systems. The highest-value areas in the eastern urban agglomeration were small, scattered in the Maxian Mountains at the boundary between Yuzhong and Lintao, and Lianhua Mountains in the south of Weiyuan urban area. Through comparative analysis, the high-mountain area with an altitude of more than 2500 m in the urban agglomeration coincided with the high-value area of ecosystem services, showing a strong correlation. The land-use types in mountainous areas were mainly forestland and grassland. Their vegetation coverage was high, their root system was developed, and their ability to conserve water and soil was

strong. Compared with 2000, the area of high-value ecosystem services in the southwest of urban agglomeration increased significantly in 2020. As an important part of the ecological barrier area of the Qinghai Tibet Plateau, Hainan and Huangnan are also the birthplace of the Yellow River and an important supply area of freshwater resources in China. Driven by the National Sanjiangyuan Ecological Protection and Construction Phases I and II, the forest coverage and wetland area in the region has increased significantly in the past two decades. The service level of regional integrated ecosystem had been significantly improved. the birthplace of the Yellow River and an important supply area of freshwater resources in China. Driven by the National Sanjiangyuan Ecological Protection and Construction Phases I and II, the forest coverage and wetland area in the region has increased significantly in the past two decades. The service level of regional integrated ecosystem had been significantly improved.

Overall, the integrated ecosystem services of the LXUA showed an overall stepped

distribution pattern from northeast to southwest (Figure 9). The highest-value areas were mainly located in Hainan and Huangnan in the southwest. The terrain was dominated by high mountain landforms, with towering terrain and continuous mountain systems. The highest-value areas in the eastern urban agglomeration were small, scattered in the Maxian Mountains at the boundary between Yuzhong and Lintao, and Lianhua Mountains in the south of Weiyuan urban area. Through comparative analysis, the high-mountain area with an altitude of more than 2500 m in the urban agglomeration coincided with the high-value area of ecosystem services, showing a strong correlation. The land-use types in mountainous areas were mainly forestland and grassland. Their vegetation coverage was high, their root system was developed, and their ability to conserve water and

southwest of urban agglomeration increased significantly in 2020. As an important part of the ecological barrier area of the Qinghai Tibet Plateau, Hainan and Huangnan are also

*Land* **2023**, *12*, x FOR PEER REVIEW 13 of 20

**Figure 8.** Carbon fixation service of LXUA in 2000 and 2020.

**Figure 9.** Integrated ecosystem services of LXUA in 2000 and 2020. **Figure 9.** Integrated ecosystem services of LXUA in 2000 and 2020.

In 2020, the higher-value areas of ecosystem services were distributed along the Huangshui River, showing a belt pattern from northwest to southeast. Topographically, it mainly included Huangshui Valley, Lanzhou Basin, Zhuanglang Valley and Yuanchuan Valley. The land usage in this area is primarily made up of arable land and forest land, with the arable land being primarily dispersed along the rivers. These areas of the region are relatively low in elevation and have plentiful inflow water supplies. Crops, herbs and shrubs in cultivated land and forest land can increase soil organic matter content. The climate is regulated through carbon fixation and oxygen production, so as to reduce sur-In 2020, the higher-value areas of ecosystem services were distributed along the Huangshui River, showing a belt pattern from northwest to southeast. Topographically, it mainly included Huangshui Valley, Lanzhou Basin, Zhuanglang Valley and Yuanchuan Valley. The land usage in this area is primarily made up of arable land and forest land, with the arable land being primarily dispersed along the rivers. These areas of the region are relatively low in elevation and have plentiful inflow water supplies. Crops, herbs and shrubs in cultivated land and forest land can increase soil organic matter content. The climate is regulated through carbon fixation and oxygen production, so as to reduce surface water and soil loss and effectively conserve water. The higher-value areas are strongly affected by human activities. So, the ecological environment of the valley basin should be effectively protected to reduce ecological damage and environmental pollution.

face water and soil loss and effectively conserve water. The higher-value areas are strongly The medium- and lower-value areas of ecosystem services were located in the northeast of the LXUA, including Baiyin and Yongdeng, Gaolan and Yuzhong of the Lanzhou urban area. Land use in this area was mainly farmland and grassland. This region is located at the northwest edge of the Longxi Loess Plateau and the transitional zone from the eastern extension of the Qilian Mountains to the Tengger Desert. In this region, the climate is relatively dry, the ground vegetation is sparse, and the ecosystem services are under great pressure. The lowest-value areas of ecosystem services were highly overlapped with the water area and unused and construction land. The western part of the urban agglomeration was scattered in the Mugetan Desert of Guinan, the Tala Beach of Gonghe, the sand island at the northeast of Qinghai Lake and the Longyang Lake at the boundary between Gonghe and Guinan. The lowest-value areas in the east were mainly located in the urban built-up areas of each city, including the main urban areas of Lanzhou, Lanzhou New Area, and Baiyin.
