Integrated Terrestrial and Marine Ecosystem Services Valuation and Result Variation Trends: A Case Study of Jiangsu Province, China

Abstract

Quantitative ecosystem services valuation (ESV) is the key to effective environmental protection and ecosystem restoration. Studies have focused on terrestrial ecosystems and are mainly based on static analyses, excluding marine ecosystem service values and their variability. In this study, we comprehensively evaluated terrestrial and offshore ecosystem service values in Jiangsu Province in 2010 and 2018 using a table of unit area value equivalence factors and a vertically generalized production model (VGPM) to estimate marine primary productivity. The results showed that the terrestrial ESV in Jiangsu Province was 322.740 and 477.798 billion yuan in 2010 and 2018, respectively. The ESV of hydrological regulation in water areas was the highest, whereas that of unutilized land was the lowest. The ESV in different prefectural-level cities exhibited significant spatial heterogeneity and were highly correlated with the proportion, protection, and rational utilization of urban water areas. The offshore ESV in Jiangsu Province was 426.011 and 460.438 billion yuan in 2010 and 2018, respectively; the farther from land, the lower the ecosystem service value. The value of ecological regulation services is the dominant factor in the comprehensive services of terrestrial and offshore ecosystems in Jiangsu Province (accounting for 80% of ESV). From 2010 to 2018, the overall terrestrial and offshore ESV in Jiangsu Province rose by 188.901 billion yuan, increasing by 25.28% from 2010. In future, boundaries of development in production activities should be controlled, the protection and restoration of the ecological environment promoted, and regulatory functions and cultural services of ecosystems rationally exploited.

1. Introduction

Ecosystems are an essential foundation for human survival and development and provide indispensable natural resources and services for human beings. However, with rapid social development, industrialization, and urbanization, the human demand on ecosystems has grown sharply. The impacts of human activity on ecosystems have become increasingly drastic, causing severe ecological problems [1]. The constant encroachment on and destruction of ecosystems have directly led to a continually increasing scarcity of ecological resources. Ecosystem services have long been regarded as inexhaustible natural resources and have been excessively utilized without conservation, resulting in their overconsumption. Therefore, it is necessary to conduct relevant research to protect them. The term “ecosystem services” refers to all benefits humans obtain from ecosystems, including provisioning, supporting, cultural, and regulating services [2]. The value of ecosystem services fully and clearly reflects their composition. Currently, questions remain regarding how to rationally utilize the services provided by ecosystems and protect them from destruction. This has become a critical global issue. Ecosystem service valuations (ESV) are urgently required to provide data support for solving these problems.

Research on ecosystem services began in the 1970s, and early studies mainly focused on the definitions and theoretical bases of ecosystem service functions. The term “ecosystem service” was first defined by Ehrlich et al. [3] and has developed into a multidisciplinary research topic [4]. Assessments of marine ecosystems require a definition of marine net primary productivity. Nielsen [5] first employed a radioisotope (¹⁴C) tracer technique to measure photosynthesis in marine plants. Subsequently, Eppley et al. [6] used an empirical algorithm to calculate marine net primary productivity to explore the relationship between temperature and photoperiod on chlorophyll concentration, and established an Eppley-VGPM model based on chlorophyll content.

The 1990s witnessed milestones in ESV research. Costanza et al. [7] made the first attempt to scientifically and systematically calculate global ESV. Additionally, the book Nature’s Services: Societal Dependence on Natural Ecosystems, edited by Daily [8], was published during the same period, proposing that ESV can be reasonably defined by the natural environmental conditions formed by an ecosystem and its processes that can sustain human existence, as well as the utility of the ecosystem, and discussion on ESV approaches. Costanza et al. and Daily et al. [9] provided scientific and novel ideas for ESV studies, pushing ESV research to unprecedented heights that have attracted wide attention in the academic community. Costanza et al. [7] classified ecosystem service functions into 17 categories and identified 12 types of marine ecosystem services. Chinese scholars have also been deeply influenced by Costanza et al., and have placed focus on the valuation of ecosystem service functions and conducted research on the concept, the classification of service functions, and methods for service value assessments based on China’s environmental context [10]. Behrenfel et al. [11] proposed a vertically generalized production model (VGPM) by normalizing the chlorophyll concentration, photoperiod, and optical depth, and, subsequently, modifying the VGPM model for different aquatic environments. They also used data from remote sensing products, such as moderate-resolution imaging spectroradiometer (MODIS), to estimate marine primary productivity.

Research on ESV has developed rapidly since the beginning of the 21st century. In 2001, the United Nations officially initiated the Millennium Ecosystem Assessment (MA) project [12], which classifies marine ecosystem services into four categories—provisioning, regulating, supporting, and cultural—to provide guidance for ESV studies in different countries [13]. Chen et al. [14] investigated the components of marine ecosystems and identified 14 specific services based on a framework for evaluating marine ecosystem services proposed by the MA (MA, 2003). Their classification system was soon recognized and referenced by many Chinese scholars, and has been widely applied in practical research and included in the national standard. Dugdale et al. [15] used the average sea surface temperature (SST) to estimate marine primary productivity. Xie et al. [16] constructed an ESV method combining expert knowledge and unit area value equivalence factors based on the classification of ecosystem functions proposed by Costanza et al. [7], which has been widely used in ESV studies at different scales, such as the sampling-site, regional, and national scales.

He et al. [17] obtained an ESV in China of 9.17 trillion/year based on the magnitude of ESVs, considering the dynamic spatial changes in ecosystems. Xie et al. [18] improved their previously proposed ESV method, developed a modified version based on unit area value equivalence factors (considering the spatiotemporal dynamic variation characteristics of the ecosystem), and obtained an ESV of 38.10 trillion/year. Shi et al. [19] considered changes across time and space. They retrieved the service values per unit area from the available literature, adjusted the spatiotemporal dynamic distribution of the values with NDVI data, and, finally, obtained an ESV in China of 6.57 trillion/year based on food prices in 1999. The estimation results of different studies suggest that China’s terrestrial ESV is in the order of trillions [20]. Additionally, the valuation of specific ecosystem services has gradually been conducted to address the specific circumstances representative of China. Su et al. [21] assessed the ESV of Xiamen’s coastal zone and proposed important policy suggestions, such as adjusting the charge of sea area utilization and implementing ecological compensation, while Wang et al. [22] conducted questionnaire surveys to investigate the value of ecosystem service restoration in Xincun Bay, Hainan Province.

ESV accounting has become a research hotspot because ESVs have significant implications for managing the relationship between humans and nature. Regional ESV accounting provides decision-makers with ESVs for various types of ecosystems that reflect the structural information of regional ecosystem services and indicate the diverse and complex services that ecosystems provide to humans. This approach allows people to recognize the importance of ESV and provides a basis for the rational development and utilization of ecosystem services. However, existing studies generally focus on terrestrial ecosystems [21,22,23,24,25,26,27] and are mainly based on static analysis, with a lack of exploration of marine ecosystem service values and the response trends between marine and terrestrial ecosystems.

This paper presents a case study of Jiangsu Province and its adjacent sea area to understand the distribution pattern of marine and terrestrial ecosystem services and the gradient response law between changes in marine ecosystem services and changes in terrestrial ecosystem services in the research area, in order to provide decision support for the construction of ecological civilization, ecological restoration, and ecological protection in the coastal areas of Jiangsu.

2. Study Area and Data Collection

2.1. Overview of the Study Area

The study area (Figure 1) comprises two parts: the terrestrial area covering the entirety of Jiangsu Province and the sea area adjacent to Jiangsu Province, which is China’s claimed exclusive economic zone within the Yellow Sea area. Jiangsu Province is located on the eastern coast of mainland China, with a latitude ranging from 30°45′ to 35°20′ N and a longitude ranging from 116°18′ to 121°57′ E. Jiangsu borders Shandong Province to the north and the Yellow Sea to the east, with a total area of 107,200 km². The examined sea area was within 200 nautical miles of the coastline of Jiangsu Province in the Yellow Sea, covering a total area of 176,400 km².

The Yangtze River and Huaihe River flow through Jiangsu Province and face the sea to the east. The terrain is relatively flat with many lakes throughout the province. The major landforms include plains, water areas, and low hills. The sea area is inhabited by many types and large quantities of organisms, and is rich in benthic faunal resources. The most important edible species are mollusks and crustaceans, with many optimal fishing grounds.

In 2022, the GDP of Jiangsu Province reached 12,287.56 billion yuan, with an increase of 2.8% over the previous year. The added value of the primary industries was 495.94 billion yuan, with an increase of 3.1%; that of the secondary industries was 5588.87 billion yuan, with an increase of 3.7%; and that of the tertiary industries was 6202.75 billion yuan, with an increase of 1.9%. Recently, the industrial structure of Jiangsu Province has been continuously optimized with flourishing emerging industries. Industrial restructuring has accelerated, economic vitality has increased, and co-ordinated regional development has been vigorously promoted [28].

2.2. Data Sources

The data used in this study included land-use-type data, MODIS images and products, and socioeconomic data. These data were mainly used to calculate the ESVs of the entire Jiangsu Province and the Yellow Sea area adjacent to Jiangsu Province, as listed in

Table 1. Data collection.

Data Type	Data Name	Data Format	Data Source	Data Usage
Land-use data	Raster map of land use/land cover in Jiangsu Province, 2010 and 2018 (1 × 1 km)	Raster	Resources and Environmental Science Data Center, Chinese Academy of Sciences. Available online: http://www.resdc.cn (accessed on 2 July 2018)	Calculating the ESV in a specific year based on the changes in land-use types and analyzing the temporal variations in service values.
Remote sensing images and products	MODIS monthly average data of SST, sea surface photosynthetically active radiation, diffuse attenuation coefficient of seawater, and oceanic chlorophyll concentration (4 × 4 km) in March, June, September, and December 2018.	Raster	Available online: https://oceandata.sci.gsfc.nasa.gov (accessed on 31 December 2018)	Calculating the marine net primary productivity of the sea area adjacent to Jiangsu Province, then calculating the quantities of carbon sequestration and oxygen production in the sea area, and, finally, calculating its ESV.
Socio-economic data	Jiangsu Statistical Yearbook of 2018	Text	Jiangsu Provincial Statistical Bureau. Available online: http://tj.jiangsu.gov.cn (accessed on 2 December 2019)	Calculating the ESV in the study area.
Other data	Raster-based digital elevation model of Jiangsu Province (90 × 90 m), vector shapefiles of the boundaries of Jiangsu Province	Raster and vector	Resources and Environmental Science Data Center, Chinese Academy of Sciences. Available online: http://www.resdc.cn (accessed on 1 January 2023)	Delineating the range of the study area.

.

(1)

Land-use-type data

The data included raster maps of land use/cover in Jiangsu Province for 2010 and 2018 (1 × 1 km). The available land use/land cover (LULC) maps are GIS raster datasets in which each cell is assigned a numerical LULC code (

Table 2. Classification of land use in Jiangsu Province.

Level 1 Land-Use Code	Level 1 Land-Use Category	Level 2 Land-Use Code	Level 2 Land-Use Category
1	Arable land	11	Paddy fields
		12	Dry land
2	Woodland	21	Woodland
		22	Shrubs
		23	Sparse woodland
		24	Other woodlands
3	Grassland	31	High-coverage grassland
		32	Medium-coverage grassland
		33	Low-coverage grassland
4	Water area	41	River channels
		42	Lakes
		43	Reservoirs and ponds
		45	Mudflats
		46	Beach land
5	Urban, rural, industrial, mining, and residential land	51	Urban land
		52	Rural settlements
		53	Other construction land
6	Unutilized land	63	Saline-alkali land
		64	Swampy land
		65	Bare land
		66	Bare rocky ground

). These data characterize the land-use type of each land parcel in the study area in different years and form the basis for this study.

(2)

Remote sensing images and products

The remote sensing image data mainly included the average SST (4 × 4 km), photosynthetically active radiation (4 × 4 km), diffuse attenuation coefficient of seawater (4 × 4 km), and monthly chlorophyll concentration data (4 × 4 km) from the MODIS Level 3 products (data for four periods; March, June, September, and December 2018 were retrieved for each type).

(3)

Socioeconomic Data

These data were collected from the Jiangsu Statistical Yearbooks and the Global Carbon Market Report of 2018.

(4)

Other data

We also referred to the raster-based digital elevation model of Jiangsu Province (90 × 90 m) and vector shape files of the boundaries of Jiangsu Province.

3. Research Methods

In this study, we combined land-use-status data and MODIS product data to comprehensively evaluate the service value of terrestrial and offshore ecosystems in Jiangsu Province in 2010 and 2018 using the unit area value equivalent factor table and the vertical generalized production model (VGPM), in order to estimate marine primary productivity (Figure 2).

3.1. Terrestrial ESV Method

3.1.1. Matching of Ecosystem and Land-Use Types

The spatial characteristics and functions of the land are differentiated under the joint influence of economic, natural, and social factors within a specific area. Several methods are available for classifying land-use/cover types. The land-use data used in this study were classified into 21 categories (Figure 3). In Jiangsu Province, the arable land area is the largest among all land-use types, accounting for 60.50% of the total area of Jiangsu. Jiangsu Province has a large water area due to its well-developed water systems.

Xie et al. [16] divided the ecosystem into six subsystems in their ESV research: forests, grassland, farmland, wetland, water area, and deserts; this classification scheme has been widely applied in other studies. In the present study, we used their theoretical results and modified the classification system to accurately represent Jiangsu Province (

Table 3. Correspondence between ecosystem and land-use types.

Ecosystem Type	Corresponding Land-Use Type	Major Ecosystem Services [6]
Farmland	Dry land and paddy fields	Soil conservation, biodiversity maintenance, and hydrological regulation
Forests	Woodland, sparse woodland, shrubs, and other woodlands	Biodiversity maintenance, climate regulation, and hydrological regulation
Grassland	Low-, medium-, and high-coverage grasslands	Biodiversity maintenance and climate regulation
Wetland	Mudflats, beach land, swampy land, and river channels	Water supply, hydrological regulation, biodiversity maintenance, and environmental purification
Water area	Lakes, reservoirs, and ponds	Water supply, environmental purification, hydrological regulation, and biodiversity maintenance
Deserts	Saline-alkali land, bare land, and bare rocky ground	Biodiversity maintenance and environmental purification

).

Farmland ecosystems were further divided into two subsystems of dry land and paddy fields; woodland, sparse woodland, other woodlands, and shrubs, all belonged to forest ecosystems; low-coverage grassland, medium-coverage grassland, and high-coverage grassland constituted grassland ecosystems; lakes, reservoirs, and ponds with strong water-storage capacity and vast water areas were classified as water ecosystems; mudflats, beach land, river channels, and swampy land were classified as wetland ecosystems; and saline-alkali land, bare land, and bare rocky ground with extremely low vegetation coverage and harsh conditions for organism habitation were all included in desert ecosystems. Because anthropogenic activities have severely damaged the original natural conditions of urban land, rural settlements, and other industrial construction land, the ESVs of these areas are low. Ecosystem services in these areas are highly dependent on the surrounding natural ecosystems. Hence, these land-use types were not analyzed in this study.

3.1.2. Determination of ESV Equivalence Factors

As research progresses, static research methods have been found to not accurately describe spatiotemporal differences in the types and quality conditions of ecosystems. Xie et al. [18] refined these original results, fully considering the spatiotemporal dynamic changes in ecological structures closely related to ecological functions, and modified the equivalence factors of the ESVs (

Table 4. Reference table for the ESV equivalence factors [18].

Ecosystem Type		Provisioning Services			Regulating Services				Supporting Services			Cultural Services
Level 1	Level 2	Food Production	Raw Material Production	Water Supply	Gas Regulation	Climate Regulation	Environmental Purification	Hydrological Regulation	Soil Conservation	Nutrient Circulation Maintenance	Biodiversity Maintenance	Landscape Aesthetics
Farmland	Dry land	0.85	0.40	0.02	0.67	0.36	0.10	0.27	1.03	0.12	0.13	0.06
	Paddy fields	1.36	0.09	−2.63	1.11	0.57	0.17	2.72	0.01	0.19	0.21	0.09
Forests	Coniferous	0.22	0.52	0.27	1.70	5.07	1.49	3.34	2.06	0.96	1.88	0.82
	Mixed coniferous and broad-leaved	0.31	0.71	0.37	2.35	7.03	1.99	3.51	2.86	0.22	2.60	1.14
	Broad-leaved	0.29	0.66	0.34	2.17	6.50	1.93	4.74	2.65	0.20	2.41	1.06
	Shrubs	0.19	0.43	0.33	1.41	4.23	1.28	3.35	1.72	0.13	1.57	0.69
Grassland	Grassland	0.10	0.14	0.08	0.51	1.34	0.44	0.98	0.62	0.05	0.56	0.25
	Shrub–grassland	0.38	0.56	0.31	1.97	5.21	1.72	3.82	2.40	0.18	2.18	0.96
	Marshy grassland	0.22	0.33	0.18	1.14	3.02	1.00	2.21	1.39	0.11	1.27	0.54
Wetland	Wetland	0.51	0.50	2.59	1.90	3.60	3.60	24.23	2.31	0.18	7.87	4.73
Deserts	Deserts	0.01	0.03	0.02	0.11	0.10	0.31	0.21	0.13	0.01	0.12	0.05
	Bare land	0.00	0.00	0.00	0.02	0.00	0.10	0.03	0.02	0.00	0.02	0.01
Water area	Water system	0.80	0.23	8.29	0.77	2.29	5.55	102.24	0.93	0.07	2.55	1.89
	Glacier and snow	0.00	0.00	2.16	0.18	0.54	0.16	7.13	0.00	0.00	0.01	0.09

) to establish a more comprehensive and objective ESV.

Table 4 must be modified because of the different classification schemes applied to the land-use-/land-cover-type data in Jiangsu Province. The dry land and paddy fields in the ESV equivalence factor table (Table 4) correspond to the dry land and paddy fields in the land-use-/land-cover-type classification scheme, respectively. Here, 97% of the forest area in Jiangsu Province is woodland, in which broad-leaved forests account for 91.88%, coniferous forests account for 5.66%, and mixed coniferous and broad-leaved forests account for 2.46%. The equivalence factors of the woodland’s ecosystem services were obtained by calculating the weighted average of the equivalence factors of different types of forests. The equivalence factors of sparse woodland, shrubs, and other woodlands were taken as the values of shrubs in Table 4. The equivalence factors of medium-, low-, and high-coverage grassland were the mean values of the equivalence factors of grassland, shrub-grassland, and marshy grassland. The equivalence factors of wetland were accounted as those of river channels, mudflats, beach land, and swampy land. The equivalence factors of lakes, reservoirs, and ponds were calculated according to the equivalence factors of the water system. The equivalence factors of saline-alkali land, bare land, and bare rocky ground were replaced with those of bare land. Additionally, the equivalence factors of urban land, rural settlements, and other construction land were set to zero. Therefore, the ESV equivalence factor table was revised according to the actual situation in Jiangsu Province (

Table 5. Modified ESV equivalence factors in Jiangsu Province.

Ecosystem Type		Provisioning Services				Regulating Services			Supporting Services			Cultural Services
Level 1	Level 2	Food Production	Raw Material Production	Water Supply	Gas Regulation	Climate Regulation	Environmental Purification	Hydrological Regulation	Soil Conservation	Nutrient Circulation Maintenance	Biodiversity Maintenance	Landscape Aesthetics
Farmland	Dry land	0.85	0.40	0.02	0.67	0.36	0.10	0.27	1.03	0.12	0.13	0.06
	Paddy fields	1.36	0.09	−2.63	1.11	0.57	0.17	2.72	0.01	0.19	0.21	0.09
Forests	Woodland	0.29	0.65	0.34	2.15	6.43	1.91	4.63	2.62	0.20	2.38	1.05
	Shrubs and other woodlands	0.19	0.43	0.22	1.41	4.23	1.28	3.35	1.72	0.13	1.57	0.69
Grassland	Low-, medium-, and high-coverage grasslands	0.23	0.34	0.19	1.21	3.19	1.05	2.34	1.47	0.11	1.34	0.59
Wetland	River channels, beach land, mudflats, and swampy land	0.51	0.50	2.59	1.90	3.60	3.60	24.23	2.31	0.18	7.87	4.73
Unutilized land	Saline-alkali land, bare land, and bare rocky ground	0.00	0.00	0.00	0.02	0.00	0.10	0.03	0.02	0.00	0.02	0.01
Water area	Lakes, reservoirs, and ponds	0.80	0.23	8.29	0.77	2.29	5.55	102.24	0.93	0.07	2.55	1.89

).

Standard equivalences are the basis for ESV, and one standard equivalence factor is defined as the economic value of the total grain yield per hectare of arable land. The economic value of the ESV equivalence factor of arable land is calculated as one-seventh of the market value of grain yield per unit area [29]. The economic values of the ESV equivalence factors of other land-use types were defined relative to the ESV equivalence factor of arable land. The economic value of one standard equivalent factor in Jiangsu Province is shown in Equation (1), and the ecological product value of the research area was calculated using Equation (3).

$$F=\frac{1}{7}\sum _{i=1}^n\frac{a_i{p}_i{y}_i}{T}$$

(1)

$$EPV=\sum _{i=1}^n\sum _{j=1}^n{A}_i\times V{C}_{ij}$$

(2)

$$V{C}_{ij}=E_{ij}\times F$$

(3)

F is the economic value of the equivalent factor of 1 hm² of ecological products (yuan/hm²), i is the type of food crop in the study area, n is the total number of categories of major food crops, a_i is the total area sown for the ith grain crop, p_i is the average yield per unit area of the ith grain crop, y_i is the average market unit price of the ith grain crop, T is the total sown area of all grain crops, EPV represents the value of ecological products in Jiangsu Province, A_i represents the area of the ith type of ecological product, and VC_ij represents the value coefficient of the jth service function corresponding to the ith ecological product.

3.2. Marine ESV Method

3.2.1. Determination of Evaluation Indicators

Provisioning services in the coastal ecosystem include fishing, aquaculture production, and genetic resource supply; regulating services include climate regulation, air quality regulation, water purification, disturbance regulation, and biological control; supporting services include material circulation and habitat provision; and cultural services include scientific research and tourism.

3.2.2. Calculating Marine Primary Productivity Based on the VGPM Model

Marine primary productivity in the study area was first calculated to prepare data for evaluating climate and air quality regulation, and water purification services. To obtain reasonable marine primary productivity data, we averaged the monthly average marine primary productivity over the four months in this study. We selected the monthly average SST, photosynthetically active radiation, diffuse attenuation coefficient of seawater, and oceanic chlorophyll concentration data from March, June, September, and December from MODIS Level 3 products to measure the annual average marine primary productivity in the sea area.

Among the models used to calculate marine primary productivity, physiological process models based on remote-sensing images have high accuracy and are widely used. In particular, the vertically generalized production model (VGPM) is characterized by high estimation accuracy and a wide application range. Therefore, the VGPM is adopted in this study [30].

The maximum carbon sequestration rate was first calculated based on SST in the study area as per the following equation:

$$P_{\mathit{opt}}^B=\left\{\begin{array}{c}1.13,T<-1.0;\\ 4.00,T>28.5;\\ 1.2596+2.749\times {10}^{-1}T+6.17\times {10}^{-2}{T}^2-\\ 2.05\times {10}^{-2}{T}^3+2.462\times {10}^{-3}{T}^4-\\ 1.348\times {10}^{-4}{T}^5+3.4132\times {10}^{-6}{T}^{26}-\\ 3.27\times {10}^{-8}{T}^7,-1.0\le T\le 28.5;\end{array}\right.$$

(4)

where $P_{opt}^B$ is the maximum carbon sequestration rate in mg/(mg·h) and T is the SST in °C. The depth of the euphotic layer was calculated using the relationship between the diffuse attenuation coefficient of seawater and euphotic depth:

$$Z_{\mathit{eu}}=\frac{2\mathit{ln}10}{K_{d490}}=4.605/K_{d490}$$

(5)

where $K_{d490}$ is the diffuse attenuation coefficient of seawater in ${\mathrm{m}}^{-1}$.

When calculating the photoperiod, for convenience, we assumed that the sun moves over the same latitude per unit of time between the Tropic of Cancer and the Tropic of Capricorn; that is, the sun travels a total of 94° in 365 days and moves 0.2575° per day. Thus, the average latitude of the subsolar point is –1.3° in March, 21.2° in June, 1.9° in September, and –21.2° in December (negative values indicate the southern hemisphere). The average latitude of the study area was 33° N. The photoperiods of the study area (

Table 6. Photoperiod in Jiangsu Province and its adjacent sea area.

Month	March	June	September	December
Average latitude of the subsolar point (°)	−1.3 *	21.2	1.9	−21.2 *
Photoperiod in the study area (h)	11.89	13.95	12.25	10.06

* Negative values indicate the southern hemisphere.

) were obtained as follows:

$${A(D}_{\mathit{irr}})=12\times 2\times \mathit{arccos}(\mathit{tan}\beta \times \mathit{tan}\alpha )÷180,$$

(6)

where ${A(D}_{irr})$ is the photoperiod in the study area, $\alpha$ is the latitude of the study area, and $\beta$ is the latitude of the subsolar point, whose value is negative when the subsolar point is in the hemisphere where the study area is located.

Based on the maximum carbon sequestration rate, photosynthetically active radiation at the sea surface, euphotic depth, and chlorophyll concentration data, the marine net primary productivity in the study area (

Table 7. Net Primary Productivity in the sea area adjacent to Jiangsu Province.

Month	March	June	September	December	Annual Average
Average primary productivity in 2018 (mg/(m2·d))	1263.22	2336.69	1718.33	1365.00	1670.81
Average primary productivity in 2010 (mg/(m2·d))	1182.12	2417.68	1882.01	1519.86	1750.42

) was calculated as follows:

$${\mathit{PP}}_{\mathit{eu}}=0.66125 \times P_{\mathit{opt}}^B\times \frac{E_0}{E_0+4.1}\times Z_{\mathit{eu}}\times C_{\mathit{opt}}\times D_{\mathit{irr}}$$

(7)

where ${PP}_{eu}$ is the marine net primary productivity in mg/(m²·d); $E_0$ is the photosynthetically active radiation at the sea surface in mol/(m²·d); $Z_{eu}$ is the euphotic depth in m; $C_{opt}$ is the oceanic chlorophyll concentration in mg/m³; and $D_{irr}$ is the photoperiod in the study area in h.

3.2.3. Calculating ESVs for Indicators Based on Marine Primary Productivity

Climate regulation in the sea area is mainly realized through the fixation of carbon dioxide through the photosynthesis of marine organisms, such as macroalgae, and the net primary productivity of the sea area can be calculated on this basis. The mass of carbon sequestered in the sea area was 108 and 113 million tons in 2018 and 2010, respectively, and the unit values of fixed carbon in 2018 and 2010 were 139 USD/t (USD/RMB exchange rate was 6.73) and 864.5 yuan/t, respectively. Thus, the value of climate regulation services in the coastal areas of Jiangsu Province was 100.662 and 94.758 billion yuan in 2018 and 2010, respectively.

Air quality regulation in the sea area is mainly realized by the production of fresh oxygen through the photosynthesis of marine organisms, such as macroalgae. Based on marine primary productivity, organic matter and oxygen are produced from carbon dioxide and water in chloroplasts under illumination during photosynthesis. The masses of oxygen produced in the sea area adjacent to Jiangsu Province were 287 and 301 million tons in 2018 and 2010, respectively. According to the average value of the afforestation cost (352.9 yuan/t) and industrial oxygen production cost (400 yuan/t), which is 376.45 yuan/t, the value of the air quality regulation services in the coastal areas of Jiangsu Province in 2018 and 2010 was estimated as 108.022 and 113.311 billion yuan, respectively:

$$6{\mathit{CO}}_2+6H_{2}O\to C_6{H}_{12}{O}_6+6O_2,$$

(8)

The uptake of N and P, reduction in chemical oxygen demand (COD), and degradation of petroleum hydrocarbons by seawater [31] form the basis of water purification in the study area. For the uptake of N and P by seawater, the C/N and C/P ratios are approximately 5.68 and 41.03, respectively [32]. According to the mass of fixed carbon, the mass of N absorbed by the sea area adjacent to Jiangsu Province was 18,944,700 and 19,894,400 tons in 2018 and 2010, respectively, and the mass of absorbed P was 2622,600 and 2754,100 tons in 2018 and 2010, respectively. Based on the cost analysis of China’s wastewater treatment industry [33], the costs of N and P removal from domestic wastewater in China are 1500.00 and 2500.00 yuan/t, respectively. Therefore, the total values of N and P absorbed by the sea area adjacent to Jiangsu Province were 34.974 and 36.729 billion yuan in 2018 and 2010, respectively.

According to the Seawater Quality Standard of China (GB 3097-1997) [34], seawater quality grades 1, 2, 3, and 4 correspond to COD levels of 2, 3, 4, and 5, and petroleum hydrocarbon concentrations of 0.05, 0.05, 0.30, and 0.50 mg/L, respectively. The proportions of seawater with Grade 1 quality in the sea area were 38.5%, 50.5% for Grade 2, 4.4% for Grade 3, and 1.1% for Grade 4. The volume of seawater in the study area is 7,763,712 billion liters. According to the Measures on the Collection of Pollution Discharge Fee (2003) issued by China’s State Council, the pollution fee for petroleum hydrocarbon discharge is 7000 yuan/t, whereas that for COD discharge is 4300 yuan/t. Thus, the values of COD and petroleum hydrocarbon removal by the coastal ecosystems in Jiangsu Province were calculated as 109.194 billion yuan (

Table 8. Chemical oxygen demand and petroleum hydrocarbon treatment values in the sea area adjacent to Jiangsu Province.

Pollutant Type	Grade 1 (10,000 Tons)	Grade 2 (10,000 Tons)	Grade 3 (10,000 Tons)	Grade 4 (10,000 Tons)	Total Mass (10,000 Tons)	Unit Cost of Treatment (Yuan/t)	Total Value (100 Million Yuan)
Chemical oxygen demand	597.81	1176.20	136.64	42.70	1953.35	4300	839.94
Petroleum hydro- carbons	149.45	196.03	10.25	4.27	360.00	7000	252.00
Total value (100 million yuan)							1091.94

). Water purification services in the sea area adjacent to Jiangsu Province were valued at 144.168 and 145.923 billion yuan in 2018 and 2010, respectively.

3.2.4. Calculating ESVs for Indicators Based on Statistical Data

According to the 2018 and 2010 Jiangsu Statistical Yearbooks, the output values of aquaculture and fishing in the sea area adjacent to Jiangsu Province were 47.839 and 20.777 billion yuan, respectively.

Jiangsu Province has more than 900 km of coastline, of which 700 km consists of mudflats with limited beach views. The recreational value of the coastal areas in Jiangsu is relatively low compared to that of other coastal regions. Based on the Jiangsu Statistical Yearbooks, we accounted for 10% of tourism revenue in the three coastal cities of Lianyungang, Nantong, and Yancheng in Jiangsu Province as the value of recreational services in the sea area, which were 13.673 and 4.549 billion yuan in 2018 and 2010, respectively.

3.2.5. Calculating ESVs for Indicators Based on the Result-Checking Method

De Groot et al. [34] proposed that the value of genetic resources provided by the ecosystem per unit area is 6–112 USD/(hm²·a). Based on the actual situation in the coastal areas of Jiangsu Province, the median value of 59 USD/(hm²·a) was used in this study. According to Costanza et al. [7], the value of disturbance regulation services is 88 USD/(hm²·a), that of material circulation services is 118 USD/(hm²·a), that of habitat provision services is 8 USD/(hm²·a), and that of scientific research services is 76 USD/(hm²·a). The value of biological control services was taken as the average of the results of Costanza et al. [7] (38 USD/(hm²·a)) and De Groot et al. [35] (40 USD/(hm²·a)), which is 39 USD/(hm²·a).

The USD/RMB exchange rate in 2018 was 6.73 (

Table 9. ESVs of various categories in the sea area adjacent to Jiangsu Province in 2018 and 2010.

Year	Exchange Rate (Yuan)	Resource Supply (100 Million Yuan)	Disturbance Regulation (100 Million Yuan)	Biological Control (100 Million Yuan)	Material Circulation (100 Million Yuan)	Habitat Provision (100 Million Yuan)	Scientific Research Services (100 Million Yuan)
2018	6.73	70.06	104.50	46.31	140.12	9.50	90.25
2010	6.82	71.00	105.90	46.93	142.01	9.63	91.46

). Thus, in 2018, the value of genetic resource supply services in the sea area adjacent to Jiangsu Province was 7.006 billion yuan, that of disturbance regulation services was 10.450 billion yuan, that of biological control services was 4.631 billion yuan, that of material circulation services was 14.012 billion yuan, that of habitat provision services was 950 million yuan, and that of scientific research services was 9.025 billion yuan.

The USD–RMB exchange rate in 2010 was 6.82. Thus, in 2010, the value of genetic resources supply services in the sea area adjacent to Jiangsu Province was 7.100 billion yuan, that of disturbance regulation services was 10.590 billion yuan, that of biological control services was 4.693 billion yuan, that of material circulation services was 14.201 billion yuan, that of habitat provision services was 963 million yuan, and that of scientific research services was 9.146 billion yuan.

4. Valuation Results and Analysis

4.1. Terrestrial ESVs in Jiangsu Province and Their Spatiotemporal Characteristics

4.1.1. 2018. ESV of Jiangsu Province

The 2018 Jiangsu Statistical Yearbook states that, in 2017, the main food crops grown in Jiangsu Province were wheat and rice, and the rice varieties were mainly middle rice and single-cropping late rice. The planting area of wheat was 2.18 million hectares, with a yield of 11.71 million tons, and the planting area of rice was 2.27 million hectares, with a yield of 19.24 million tons. In 2017, the minimum purchase price of wheat was 2.36 yuan/kg, and the minimum purchase price of middle and late rice was 2.72 yuan/kg. Based on the above data, we calculated the total market value of the two types of grains harvested in a year and obtained the market value of the grain yield per unit area in Jiangsu Province in 2018 as 17,948 yuan/ha. The ESV was calculated based on the area of each land use/cover type in Jiangsu Province in 2018, and the total ESV in Jiangsu Province in 2018 was as high as 477.798 billion yuan (

Table 10. ESVs of various categories in Jiangsu Province in 2018 (unit: 100 million yuan).

Major Category	Subcategory	Farmland	Forests	Grassland	Wetland	Water Area	Unutilized Land	Total Value	Proportion (%)
Provisioning services	Food production	182.74	2.03	0.67	6.23	21.09	0.00	212.77	4.45	5.96
	Raw material production	36.49	4.63	0.99	6.11	6.06	0.00	54.28	1.14
	Water supply	−235.30	2.38	0.55	31.64	218.57	0.00	17.83	0.37
Regulating services	Gas regulation	147.46	15.22	3.47	23.21	20.30	0.00	209.66	4.39	83.11
	Climate regulation	76.86	45.58	9.18	43.97	60.38	0.00	235.97	4.94
	Environmental purification	22.40	13.58	3.03	43.97	146.33	0.02	229.33	4.80
	Hydrological regulation	263.99	33.56	6.72	295.97	2695.62	0.01	3295.87	68.98
Supporting services	Soil conservation	74.00	18.57	4.23	28.22	24.52	0.00	149.54	3.13	8.23
	Nutrient circulation maintenance	25.62	1.40	0.33	2.20	1.85	0.00	31.39	0.66
	Biodiversity maintenance	28.13	16.90	3.85	96.13	67.23	0.00	212.25	4.44
Cultural services	Landscape aesthetics	12.36	7.43	1.70	57.78	49.83	0.00	129.10	2.70	2.70
Total value		634.73	161.32	34.69	635.42	3311.78	0.04	4777.98	100.00
Proportion (%)		13.28	3.38	0.73	13.30	69.31	0.00	100.00	/

).

From an ecosystem-type perspective (Figure 4), the ESV of water areas was the highest, reaching 331.178 billion yuan, accounting for 69.31% of the total value, whereas the ESV of unutilized land was the lowest, at only 0.04 billion yuan. Although the area of farmland ecosystems was the largest in the study area, paddy fields have an extremely high demand for water resources, thereby exerting a significant impact on the water supply. Therefore, the ESV of farmland was not the highest. In terms of the ecosystem service categories, the value of hydrological regulation services was the highest, reaching 329.587 billion yuan, accounting for 68.98% of the total ESV. The value of water supply services was 1.783 billion yuan, which was the lowest among all ecosystem service categories.

The values of the four major categories of ecosystem services (regulating, provisioning, supporting, and cultural) in Jiangsu Province in 2018 varied significantly. The ecosystem services in Jiangsu Province were dominated by regulatory services, with a total value of 397.082 billion yuan, accounting for 83.11% of the total ESV in Jiangsu Province. The total value of provisioning services was 28.488 billion yuan, accounting for 5.96%, the total value of supporting services was 39.318 billion yuan, accounting for 8.23%, and the total value of cultural services was 12.910 billion yuan, accounting for 2.70%. Water ecosystems contributed the most to provisioning and regulating service values, with proportions of 86.26 and 73.60%, respectively. Wetland ecosystems contribute the most to the cultural and supporting service values.

4.1.2. ESV of Jiangsu Province in 2010

According to the 2011 Jiangsu Statistical Yearbook, the main food crops grown in Jiangsu Province in 2010 were wheat and rice, and the main rice varieties were middle rice and single-cropping late rice. The planting area of wheat was 2.09 million hectares, with a yield of 10.08 million tons, and the planting area of rice was 2.23 million hectares, with a yield of 18.08 million tons. In 2010, the minimum purchase price of wheat was 1.8 yuan/kg, and the minimum purchase price of middle and late rice was 1.94 yuan/kg. Based on the above data, we calculated the total market value of the two types of grains harvested in a year and then obtained the market value of the grain yield per unit area in Jiangsu Province in 2010 as 12,746 yuan/ha. The ESV was calculated based on the area of each type of land use/cover in Jiangsu Province in 2010. The total ESV in Jiangsu Province in 2010 was as high as 322.740 billion yuan (

Table 11. ESVs of various categories in Jiangsu Province in 2010 (unit: 100 million yuan).

Major Category	Subcategory	Farmland	Forests	Grassland	Wetland	Water Area	Unutilized Land	Total Value	Proportion (%)
Provisioning services	Food production	142.99	1.55	0.58	4.62	13.50	0.00	163.26	5.06	5.19
	Raw material production	25.34	3.52	0.86	4.53	3.88	0.00	38.14	1.18
	Water supply	−199.68	1.82	0.48	23.49	139.96	0.00	−33.94	−1.05
Regulating services	Gas regulation	115.61	11.58	3.01	17.23	13.00	0.00	160.44	4.97	83.31
	Climate regulation	60.11	34.71	7.96	32.65	38.66	0.00	174.09	5.39
	Environmental purification	17.59	10.35	2.63	32.65	93.70	0.00	156.91	4.86
	Hydrological regulation	219.94	25.67	5.84	219.77	1726.06	0.00	2197.27	68.08
Supporting services	Soil conservation	48.33	14.13	3.67	20.95	15.70	0.00	102.79	3.18	8.54
	Nutrient circulation maintenance	20.04	1.07	0.28	1.63	1.18	0.00	20.04	0.62
	Biodiversity maintenance	22.02	12.87	3.34	71.38	43.05	0.00	152.67	4.73
Cultural services	Landscape aesthetics	9.64	5.66	1.48	42.90	31.91	0.00	91.57	2.84	2.84
Total value		481.91	122.94	30.11	471.84	2120.60	0.01	3227.40	100.00
Proportion (%)		14.93	3.81	0.93	14.62	65.71	0.00	100.00	/

).

From an ecosystem-type perspective (Figure 5), the ESV of water areas was the highest, reaching 212.060 billion yuan, accounting for 65.71% of the total value, whereas the ESV of unutilized land was the lowest, at only 0.01 billion yuan. The area covered by desert ecosystems was the smallest, and their service values for all categories were the lowest. In terms of ecosystem service categories, the value of hydrological regulation services was the highest, reaching 219.727 billion yuan, accounting for 68.08% of the total ecosystem service value. The value of water supply services was −3.394 billion yuan, which was the lowest among all the ecosystem service categories.

Similar to the pattern observed in 2018, the values of the four major categories of ecosystem services in Jiangsu Province in 2010 varied significantly. The total value of regulating services reached 268.871 billion yuan, accounting for 83.31% of the total ecosystem service value; the total value of provisioning services was 16.745 billion yuan, accounting for 5.19%; the total value of supporting services was 27.966 billion yuan, accounting for 8.54%; and the total value of cultural services was 9.157 billion yuan, accounting for 2.84%. Water ecosystems also had the highest contributions to provisioning and regulating service values, whereas wetland ecosystems contributed the most to cultural and supporting service values.

4.1.3. Assessment of Changes in Terrestrial ESVs in Jiangsu Province from 2010–2018

The ESV in Jiangsu Province changed significantly in recent years (

Table 12. Changes in ESVs from 2010 to 2018 (unit: 100 million yuan).

Category	Provisioning Services	Regulating Services	Supporting Services	Cultural Services	Total Value	Proportion (%)
Farmland	15.28	97.47	37.36	2.72	152.83	9.86
Forests	2.17	25.65	8.80	1.77	38.38	2.48
Grassland	0.30	2.96	1.11	0.22	4.58	0.30
Wetland	11.32	104.80	32.58	14.88	163.58	10.55
Water area	88.39	1051.22	33.67	17.92	1191.18	76.82
Deserts	0.00	0.02	0.01	0.00	0.03	0.00
Total value	117.43	1282.11	113.52	37.53	1550.58	100.00
Increase from 2010 (%)	70.12	47.68	41.21	40.99	48.04	/
Proportion of total increase (%)	7.57	82.69	7.32	2.42	100.00

). The total value increased by 155.058 billion between 2010 and 2018, a significant increase of 48.04%. An increase in food prices led to an increase in equivalence values, thereby raising the value of ecological services. In contrast, land-use types in Jiangsu Province were generally converted to those with higher ESVs (

Table 13. Changes in the area of each type of ecosystem in Jiangsu Province (unit: km²).

	Farmland	Forests	Grassland	Wetland	Water Area	Unutilized Land	Total Value
Area in 2010	67,343	3387	1373	4988	9284	17	86,392
Area in 2018	62,785	3091	1122	4764	10,283	74	82,119
Area change	−4558	−296	−251	−224	999	57	−4273

). The change in the provisioning service value of the paddy field ecosystems was negative. Paddy-field ecosystems are highly dependent on water resources and have a prominent impact on water supply services, thereby leading to a decrease in the ESVs of paddy fields.

The value of provisioning services increased by 11.743 billion yuan, an increase of 70.12% from 2010, accounting for 7.57% of the total ESV increase. The regulating service value reached 128.211 billion yuan, an increase of 47.68% from 2010, accounting for 82.69% of the total ESV increase. This establishes regulatory services as the dominant factor leading to an increase in total ESV. The value of support services increased by 11.352 billion yuan, an increase of 41.21% from 2010, accounting for 7.32% of the total increase in ESV. The growth in the cultural service value was the lowest at only 3.753 billion yuan, with an increase of 40.99% from 2010, accounting for 2.42% of the total ESV increase. The contribution of the cultural service value to the total increase in ESV was the lowest. Regulatory services have had the most rapid recent development in Jiangsu Province, while support and cultural service values have risen slowly.

4.1.4. Assessment of ESV Changes in Prefecture-Level Cities in Jiangsu Province from 2010–2018

The development of different prefecture-level cities in Jiangsu Province from 2010 to 2018 in terms of ESV was unbalanced (

Table 14. ESVs in the prefecture-level cities of Jiangsu Province.

Prefecture-Level City	Area (km2)	2018			2010			Change from 2010 to 2018
		Total Value (100 Million Yuan)	Proportion (%)	Value per Unit Area (100 Million Yuan/km2)	Total Value (100 Million Yuan)	Proportion (%)	Value per Unit Area (100 Million Yuan/km2)	Total Value (100 Million Yuan)	Proportion (%)	Value per Unit Area (100 Million Yuan/km2)
Suzhou	8629	943.47	19.75	1093.37	665.81	20.63	771.60	277.66	17.91	321.77
Nantong	9907	309.73	6.48	312.64	205.86	6.38	207.79	103.87	6.70	104.85
Wuxi	4630	350.65	7.34	757.34	245.60	7.61	530.46	105.05	6.77	226.88
Changzhou	4356	233.77	4.89	536.67	172.02	5.33	394.91	61.75	3.98	141.76
Zhenjiang	3847	114.07	2.39	296.53	74.60	2.31	193.91	39.47	2.55	102.62
Nanjing	6521	222.29	4.65	340.89	179.33	5.56	274.99	42.96	2.77	65.90
Yangzhou	6592	375.01	7.85	568.89	249.99	7.75	379.23	125.02	8.06	189.66
Taizhou	5795	187.21	3.92	323.05	123.11	3.81	212.44	64.10	4.13	110.61
Yancheng	15,971	554.48	11.60	347.18	262.99	8.15	164.67	291.49	18.80	182.51
Huai’an	9995	607.28	12.71	607.58	424.99	13.17	425.21	182.29	11.76	182.37
Lianyungang	7335	164.79	3.45	224.66	112.73	3.49	153.70	52.06	3.36	70.96
Suqian	8524	468.49	9.81	549.61	325.29	10.08	381.62	143.20	9.24	167.99
Xuzhou	11,064	209.99	4.39	189.8	154.09	4.77	139.28	55.90	3.61	50.52
Total value	103,166	4777.98	100.00	463.14	3227.40	100.00	312.84	1550.58	100.00	150.30

). The ESVs in Suzhou were 94.337 and 66.581 billion yuan in 2018 and 2010, respectively, accounting for 19.75 and 20.63% of the ESV in Jiangsu Province in the same years, respectively. Suzhou contributed the most to the ESV in Jiangsu Province in 2018 and 2010. The ESV in Zhenjiang was 11.007 and 7.460 billion yuan in 2018 and 2010, respectively, accounting for 2.30 and 2.31% of the entire province’s ESV in the same years. Its contribution to the total ESV in Jiangsu Province was the lowest. Nanjing, the capital city of Jiangsu Province, had ESVs of 22.229 and 17.933 billion yuan in 2018 and 2010, respectively, which were lower than the provincial average for the same years. Nanjing has experienced rapid development with a high level of urbanization, and the proportions of urban land and other construction land, whose ESVs are relatively low (not reported), are considerably high, thereby leading to a low total ESV.

The development and utilization of ecosystem services in Suzhou were at the leading level in Jiangsu Province. The total ESV and ESV per unit area were the highest in Suzhou. In 2010, the system service value per unit area in Suzhou was 7,716,000 yuan/km², which is significantly higher than the provincial average of 3,128,400 yuan/km². In 2018, the ESV per unit area in Suzhou was 10,933,700 yuan/km², which was, again, significantly higher than the provincial average of 4,631,400 yuan/km². These findings are closely related to the large area of wetlands and water bodies and the vigorous conservation and rational utilization efforts in Suzhou. In 2010 and 2018, the ESV per unit area was the lowest in Xuzhou, at only 1,392,800 and 1,898,000 yuan/km², respectively, which were both below the provincial average.

The changes in ESV in different prefecture-level cities in Jiangsu Province from 2010 to 2018 varied significantly. The ESV in Suzhou City changed, with a high total value and a high average value. The growth of the ESV per unit area was at the leading level in the entire province, with an increase of 3,217,700 yuan/km². The growth in total ESV in Yancheng was the highest, reaching 29.149 billion yuan, surpassing that in Suzhou. The total growth in Nanjing and Zhenjiang lagged behind that of other cities in the province; the increase in the total ESV in Zhenjiang (3.947 billion yuan) was the lowest in the province. The increase in ESV per unit area was the lowest in Xuzhou, at only 505,300 yuan/km².

4.2. Marine ESVs in Jiangsu Province and Their Spatiotemporal Characteristics

4.2.1. ESV of Sea Area Adjacent to Jiangsu Province in 2018

In 2018, the ESV in the sea area adjacent to Jiangsu Province was 460.438 billion yuan (

Table 15. ESVs in the sea area adjacent to Jiangsu Province in 2018.

Major Category of Ecosystem Services	Subcategory	Value of a Subcategory of Services (100 Million Yuan)	Proportion of Total Service Value (%)	Value of a Major Category of Services (100 Million Yuan)	Proportion of the Value of a Major Category of Services (%)
Provisioning services	Fishing and aquaculture production	478.39	10.39	548.45	11.91
	Genetic resources supply	70.06	1.52
Regulating services	Climate regulation	1006.62	21.86	3679.33	79.91
	Air quality regulation	1080.22	23.46
	Water purification	1441.68	31.31
	Disturbance regulation	104.5	2.27
	Biological control	46.31	1.01
Supporting services	Material circulation	140.12	3.04	149.62	3.25
	Habitat provision	9.5	0.21
Cultural services	Scientific research services	90.25	1.96	226.98	4.93
	Tourism and recreation	136.73	2.97
Total value		4604.38	100	4604.38	100

). The total value of regulating services reached 367.933 billion yuan, accounting for 79.91% of the total ESV; regulating services were the dominant factor among the ecosystem services in the sea area. The total value of provisioning services was 54.845 billion yuan, accounting for 11.91% of the total ESV; the total value of supporting services was 14.962 billion yuan, accounting for 3.25% of the total ESV; and the total value of cultural services was 22.698 billion yuan, accounting for 4.93% of the total ESV.

The values of seven types of ecosystem services—scientific research, tourism and recreation, habitat provision, material circulation, disturbance regulation, biological control, and genetic resource supply—were not outstanding in the study area. Water purification services contributed the most to the total ESV in the sea area, with values as high as 144.168 billion yuan, accounting for 31.31%. Owing to the abundance of photosynthetic organisms such as macroalgae, which actively conduct photosynthesis to fix carbon and release oxygen in the sea area, the values of air quality regulation and climate regulation services are relatively high. The value of climate regulation services was 100.662 billion yuan, accounting for 21.86%, while that of air quality regulation services was 108.022 billion yuan, accounting for 23.46%.

4.2.2. ESV of the Sea Area Adjacent to Jiangsu Province in 2010

In 2010, the ESV in the sea area adjacent to Jiangsu Province was 426.011 billion yuan (

Table 16. ESVs in the sea area adjacent to Jiangsu Province in 2010.

Major Category of Ecosystem Services	Subcategory	Value of a Subcategory of Services (100 Million Yuan)	Proportion in Total Service Value (%)	Value of a Major Category of Services (100 Million Yuan)	Proportion of the Value of a Major Category of Services (%)
Provisioning services	Fishing and aquaculture production	207.77	4.88	278.77	6.54
	Genetic resources supply	71.00	1.67
Regulating services	Climate regulation	947.58	22.24	3692.75	86.68
	Air quality regulation	1133.11	26.60
	Water purification	1459.23	34.25
	Disturbance regulation	105.90	2.49
	Biological control	46.93	1.10
Supporting services	Material circulation	142.01	3.33	151.64	3.56
	Habitat provision	9.63	0.23
Cultural services	Scientific research services	91.46	2.15	136.95	3.21
	Tourism and recreation	45.49	1.07
Total value		4260.11	100.00	4260.11	100.00

). The value of regulating services accounted for 86.68% of the total ecosystem service value and were the dominant factor among ecosystem services in the sea area.

4.2.3. Changes in ESVs in the Sea Area Adjacent to Jiangsu Province from 2010–2018

From 2010 to 2018, the total ESV in the sea area adjacent to Jiangsu Province rose by 34.427 billion yuan (

Table 17. Changes in ESVs in the sea area adjacent to Jiangsu Province from 2010–2018.

Major Category of Ecosystem Services	Subcategory of Ecosystem Services	Value Change of a Subcategory of Services (100 Million Yuan)	Value Change of a Major Category of Services (100 Million Yuan)
Provisioning services	Fishing and aquaculture production	270.62	269.68
	Genetic resources supply	−0.94
Regulating services	Climate regulation	59.04	−13.42
	Air quality regulation	−52.89
	Water purification	−17.55
	Disturbance regulation	−1.4
	Biological control	−0.62
Supporting services	Material circulation	−1.89	−2.02
	Habitat provision	−0.13
Cultural services	Scientific research services	−1.21	90.03
	Tourism and recreation	91.24
Total value		344.27	344.27

), an increase of 8.08% from 2010. Provisioning services contributed to the highest proportion of the increase, reaching 78.33%, whereas the values of regulating and supporting services exhibited declined.

4.2.4. Analysis of ESV Distribution Based on Functions of Carbon Sequestration and Oxygen Production

To investigate the distribution patterns of the values of air quality regulation, climate regulation, and water purification services, which account for a high proportion of the total ESV, we assigned the values of air quality regulation and climate regulation services and the values of N and P absorbed by seawater during water purification services to each raster cell according to the distribution of net primary productivity in the sea area. The values of other types of ecosystem services were equally distributed among the raster cells.

The basic distribution patterns in 2018 (Figure 6) and 2010 (Figure 7) showed that the ESV decreased with an increase in distance from the position in the sea area to the coastline. Welegedara et al. [36] reported that phytoplankton and benthic plants contributing to marine net primary productivity are mostly distributed in coastal regions with shallow water depths. In the study area, as the distance from the coastline increased, water depth increased proportionally, the number of benthic plants decreased, and the net primary productivity of the sea area declined. Thus, the values of air quality regulation and climate regulation services, which accounted for a high proportion of the total ESV, decreased, resulting in the above distribution patterns for the ESV in the study area.

4.3. Integrated Terrestrial and Marine ESVs in Jiangsu Province and Their Spatiotemporal Characteristics

There is constant material circulation and energy exchange between land and ocean [37]. Several marine ecosystem functions in the sea area adjacent to Jiangsu Province serve the land; similarly, terrestrial ecosystems serve the ocean. Integrated ESVs accounting for marine ecosystems and their adjacent terrestrial ecosystems and an analysis of the connections and differences between the two can provide new insights for future integrated regional ESV.

4.3.1. Integrated Terrestrial and Marine Analysis Method

The values of the corresponding types of terrestrial and marine ecosystem services in Jiangsu Province in 2010 and 2018 were added for a comprehensive analysis (

Table 18. ESVs in Jiangsu Province and its adjacent sea area.

Type of Services	Total Value in 2018 (100 Million Yuan)	Proportion (%)	Total Value in 2010 (100 Million Yuan)	Proportion (%)	Value Change from 2010 to 1018 (100 Million Yuan)	Proportion (%)
Provisioning services	870.33	9.28	446.23	5.96	424.1	22.33
Regulating services	7650.15	81.54	6381.46	85.28	1268.69	66.81
Supporting services	542.80	5.79	427.14	5.71	115.66	6.09
Cultural services	356.08	3.80	228.52	3.05	127.56	6.72
Total value	9382.36	100.00	7483.35	100.00	1899.01	100.00

).

In 2018 and 2010, the total ESV in Jiangsu Province and its adjacent sea area were 938.236 and 748.335 billion yuan, respectively (Table 18), close to a magnitude of one trillion yuan. The values of provisioning, regulating, supporting, and cultural services accounted for approximately the same proportion of the total ESV in the two years. The proportion of the regulating service value was the highest, reaching over 80%. The contribution of cultural services was the lowest among all categories of ecosystem services. From 2010 to 2018, the total ESV in Jiangsu Province and its adjacent sea area increased by 189.901 billion yuan, representing an increase of 25.28% from 2010. The change in the value of regulating services was the largest, accounting for 66.81% of the total variation, whereas the proportions of change in the values of supporting and cultural services were roughly the same.

4.3.2. Distribution of Integrated Terrestrial and Marine ESVs

Policymakers should focus on realizing more intense and rational development and utilization of the cultural services of ecosystems and protecting regulatory service functions from excessive consumption. Figure 8 and Figure 9 show the distribution of ESVs per unit area in Jiangsu Province and adjacent sea areas in 2018 and 2010, respectively. Overall, the terrestrial ESVs per unit area were higher than the marine ESVs. The ESVs per unit area were evenly distributed over the sea, whereas terrestrial values varied significantly. Additionally, terrestrial ESVs depend entirely on land-use type, whereas marine ESVs per unit area are strongly influenced by marine net primary productivity.

4.3.3. Distribution of Terrestrial and Marine ESVs

A transect is a linear region with regular variations along the gradient of a dominant driving factor, where consistency within the region is emphasized [38]. In this study, based on the distance from the coast of Jiangsu Province and its adjacent sea area, we selected 407 terrestrial and marine transects in Jiangsu Province and its adjacent sea area based on data from 2010 and 2018 to examine the relationship between terrestrial ESVs in Jiangsu Province and adjacent marine ESVs (Figure 10).

(1)

Overall, the ESV in the marine transects steadily decreased with increasing distance from the coast. Marine ESV per unit area was significantly affected by marine net primary productivity. As the distance from the coast increased, the marine net primary productivity decreased and the ESV showed a downward trend. In contrast, the ESV in the terrestrial transects in Jiangsu Province fluctuated significantly; the terrestrial ESV depended entirely on land-use type and did not show apparent variations with distance from the coast;

(2)

In terms of absolute differences, the ESV in the terrestrial transects of Jiangsu Province presented the most significant variations in 2018. The value peaked approximately 19 km from the coast and was relatively low between 20 and 150 km from the coast. The value then reached two local maxima between 150 and 300 km from the coast. The main reason for this pattern is that the ESV of water areas was significantly higher than that of other land-use types. The ESV in the transect increased significantly when it passed through the water area. The variation trend of the ESV in the terrestrial transects of Jiangsu Province in 2010 was similar to that in the terrestrial transects in 2018, whereas the ESV in the marine transects in 2010 and 2018 decreased slowly without major fluctuations.

In the future, we should: strengthen wetland protection and restoration, and promote the high-quality development of wetland protection; improve the legal system of water ecological civilization; speed up the implementation of water ecological red line management and the establishment of a systematic and complete system of water ecological civilization; and guide, plan and constrain all kinds of development, utilization, and protection of water resources and water ecology. Combined with the national main function zoning and ecological zoning, the positioning and spatial zoning of water ecological function should be clarified, the management and protection scope of rivers, lakes, and lakeside zones are delineated, the water ecological space effectively maintained, and the water ecological red lines of sensitive areas and fragile areas of water ecological environment delineated. To protect and restore wetlands, it is necessary to preserve their authenticity, integrity, and continuity, promote scientific research, reasonably utilize them on the basis of effective protection and restoration, and fully leverage their significance for ecosystem services.

(3)

In terms of relative differences, there were large differences between the ESVs in the transects of Jiangsu Province in 2010 and 2018, particularly in the coastal area, where the ESV in 2018 increased significantly from 2010, mainly because of the regulatory effect of the coastal water area. The differences between the ESVs in the marine transects in 2010 and 2018 were relatively small, both showing a gradually decreasing trend as the distance from the coast increased; however, the decreasing rate of the marine ESV in 2018 was higher than that in 2010;

(4)

Regarding the interactions between terrestrial and marine ecosystem services, the terrestrial and marine ESVs in Jiangsu Province in 2018 were higher than those in 2010, especially within 20 km of the coast, where terrestrial and marine ESVs in 2018 increased significantly. Owing to human activities, the connection between land and sea areas has become closer, fully reflecting the ESV of water areas.

5. Discussion and Prospects

This article takes the exclusive economic zones within the entire region of Jiangsu Province and the vicinity of the Yellow Sea as the research scope. Firstly, based on the unit area value equivalent factor, the land ESV value of Jiangsu Province is calculated; secondly, based on the VGPM physiological model, a detailed calculation was conducted on the value of climate regulation and air quality regulation in the research sea area to obtain the ESV values in the adjacent sea areas of Jiangsu Province in 2018, as well as the distribution of the functional value focusing on “carbon sequestration and oxygen emissions”; finally, a unified evaluation of the ESV values of Jiangsu Province and its neighboring areas will be conducted, and the ESV values of the marine ecosystem and its neighboring land will be uniformly calculated. The relationship and differences between the two will be analyzed, providing new possibilities for future comprehensive regional ESV.

In this study, the results were presented and visualized in an intuitive manner so that we could easily obtain information at different spatiotemporal scales. This study revealed structural information on regional ecosystem services, reflected the diverse and complex services of ecosystems to humans, emphasized the importance of ESV, and provided a basis for the rational development and utilization of ecosystem services. The results can also serve as a reference for ecological civilization construction in the coastal areas of Jiangsu Province, provide data support for the utilization of marine resources and planning of marine ecosystem management, and provide new ideas for future integrated regional ESV research.

In this study, we used remote sensing images and GIS technologies to calculate terrestrial and marine ESVs, carefully analyzed the results, and comprehensively investigated the terrestrial and marine ecosystem services. The results showed constant material circulation and energy exchange between land and the adjacent sea area. Both the terrestrial and marine ecosystems serve each other. These findings are innovative in the relevant fields. However, we must further discuss the calculation and estimation methods for the various types of ESVs. The calculation of the terrestrial ESVs is highly dependent on the equivalence factors in the table of unit area values [16,18,39,40,41,42,43]. Although the table of equivalence factors has been modified and adjusted, it largely reflects the results of previous research [20]. In particular, when the classification of land-use types in the study area is not consistent with the classification scheme of the equivalence factor table, the land-use types and ecosystem types were not precisely matched [21,43]; therefore, we must remeasure the local equivalence factor according to the actual situation to obtain more accurate results. Marine ESVs were determined using the result-checking method, which limited data accuracy; therefore, future studies must construct a more specific reference system with more input data. Therefore, further research is required to develop more effective marine ESV systems. The interconnections between sea and land were considered when calculating the integrated terrestrial and marine ESVs, but the terrestrial and marine values were directly added together. Therefore, a more applicable evaluation indicator for the total ESV must be constructed based on the actual situation.

6. Conclusions

The results of the integrated terrestrial and marine ESV in Jiangsu Province showed that the terrestrial ESV in Jiangsu Province were 322.740 and 477.798 billion yuan in 2010 and 2018, respectively. The ESV of water areas was the highest, whereas that of unutilized land was the lowest. Moreover, the ESV in different prefectural-level cities showed significant spatial heterogeneity and were highly correlated with the proportion of urban water areas and the protection and rational utilization of water areas. The offshore ESV in Jiangsu Province was 426.011 and 460.438 billion yuan in 2010 and 2018, respectively; affected by marine net primary productivity, the farther from land, the lower the ESV. During the study period, the value of ecological regulation services accounted for approximately 80% of the total ESV in Jiangsu Province, rendering ecological regulation the dominant factor among the integrated terrestrial and marine ecosystem services. The contribution of cultural services to total ESV was low. Therefore, we should strictly control the boundaries of development in production activities [44,45], promote the protection and restoration of the ecological environment (especially in water areas), and rationally exploit the regulatory functions and cultural services of ecosystems.