Unveiling the Value of Nature: A Comprehensive Analysis of the Ecosystem Services and Ecological Compensation in Wuhan City’s Urban Lake Wetlands

: Urban lake wetlands play an essential role in providing ecological services, promoting urban sustainability, and enhancing the quality of urban life. This study quantitatively assesses the ecosystem services value (ESV) of the Zhangdu, East, and Ziyang urban lake wetlands in Wuhan, China, based on primary survey data and methodologies, including the market price, shadow engineering, and travel cost methods. The ESV is categorized into direct use value (DUV), indirect use value (IUV), and non-use value (NUV). Our ﬁndings reveal that the non-use value proportion is signiﬁcant, amounting to 1.569 × 10 8 CNY × yr − 1 for Zhangdu Lake, 1.527 × 10 8 CNY × yr − 1 for East Lake, and 1.060 × 10 8 CNY × yr − 1 for Ziyang Lake. This indicates a high willingness to pay among respondents, reﬂecting a recognition of the value of wetland services. In addition to the non-use value, this study underscores the considerable material production, water conservation, and leisure tourism value that these urban lake wetlands provide. The assessment of ESV delivers a scientiﬁc basis for the management and protection of urban lake wetlands. It also highlights the challenges faced, such as pollution and fragmented management approaches due to unclear property rights and insufﬁcient funding. This study concludes by emphasizing the need for future research to explore mechanisms that promote social participation in wetland management, with the aim of enhancing the overall ecological health of urban lake wetlands.


Introduction
Wetlands refer to natural or artificial, permanent or temporary swamps, wetlands, peatlands, or water areas with static or flowing, or fresh, brackish, or salty water bodies, including shallow waters with a depth of not more than 6 m at low tide [1]. Wetlands are distributed between terrestrial and aquatic ecosystems, but wetlands have many features that distinguish them from terrestrial and marine ecosystems. The most notable features include the appearance of stagnant water during parts of the growing season, unique soil conditions, vegetation tolerance, and adaptability to saturated soil [2].
Wetlands are one of the most critical environments for human survival, with biologically important habitats, ecosystem types, and natural landscapes with the richest biodiversity [3]. They have a variety of service functions, such as providing food and fiber, regulating floods, conserving water sources, improving climate, consolidating soil and fertilizing, purifying the environment, and maintaining biodiversity [4]. They are also the "gene pool of species" and "paradise for birds" [5].
(WTP), the per capita WTP value, and the total payment value. We also analyzed the characteristics of respondents' WTP and the correlation between WTP and societal factors. These findings will provide valuable insights into the development of strategies to manage and protect these crucial wetlands.

Study Area
This study focuses on Wuhan, the capital city of Hubei province, located at the intersection of the Yangtze River and the Han River. Wuhan's climate is subtropical monsoon with abundant rainfall and distinct seasons. Geomorphologically, the city is characterized by a flat center surrounded by hills and ridges in the south and low bristly mountains in the north (Figure 1) [19].  Wuhan city boasts a rich variety of wetland resources, including rivers, lakes, swamps, marsh meadows, pools, and paddy fields [20]. According to Pan [21], it mainly includes six types of wetlands: rivers, lakes, swamps, marsh meadows, pools, and paddy fields, among which shallow lake wetland systems (including lake wetlands, swamps, and marsh meadow wetlands). However, these wetlands have faced significant challenges due to erosion, reclamation, pollution, and residential encroachment, leading to a reduction in their area, biodiversity, and overall ecosystem function [22]. For this study, we chose three typical urban lake wetlands: Zhangdu Lake, East Lake, and Ziyang Lake, based on their size, location, and type. Surface water samples were collected from 11 sites across these lakes, with four in Zhangdu Lake, four in East Lake, and three in Ziyang Lake ( Figure 1 and Table 1).

Data Collection
Our study combined primary and secondary data collection with several analytical approaches.

Primary Data Collection
Primary data were collected through key informant interviews and observations through field research. The details are described below: Key Informant Interviews: Ten key informants (Table 2), including local government officials, local leaders, and general citizens, were interviewed to gain insights into the strengths and weaknesses of the study areas, the major threats to urban lake wetlands, and the benefits derived from them. Observation/Field Research: Fieldwork was conducted to observe and collect information on people's behavior; the actual condition of the field; the value of aquatic resources such as fish, crabs, and shrimp derived from the lakes; the benefits imparted by the wetlands; and the cost of living for the local populace.

Socio-Economic and Willingness to Pay (WTP) Surveys
We conducted a two-part survey from August 2021 to April 2022 to gather socioeconomic data and evaluate the non-use value of lake wetlands. It should be noted that the response rate for this survey was high, at 96%, emphasizing the reliability of the collected data.
A structured questionnaire was administered through face-to-face interviews at the household level in 13 administrative districts under the jurisdiction of Wuhan. Using the equation suggested by Yamane [25], we required a sample size of 372 households (Table 3). In this two-part survey, the first part focused on socio-economic data collection, while the second part was a willingness to pay (WTP) survey. For the WTP, we employed the Contingent Valuation Method (CVM) to evaluate the non-use value of lake wetlands. The pre-survey used an open-ended (OE) questionnaire to obtain core estimates for the second survey, which utilized a payment card (PC) approach.
The successful application of CVM depends on the accurate and reasonable design of the questionnaire. The core valuation guidance techniques of CVM include iterative bidding game (IB), open-ended (OE), payment card (PC), and dichotomous choice (DC) [26]. In this study, we used OE for the first pre-survey to obtain the core estimate and its interval for the second survey; thereafter, PC was used.
The questionnaire was comprised of seven parts: 1.
Description of non-use value of lake wetland resources.

2.
Respondents' survey on environmental awareness of Wuhan Lake wetlands. 3.
On-site photos and basic information introduction to Zhangdu Lake, East Lake, and Ziyang Lake.

4.
Survey of respondents' willingness to pay.

5.
Identification of non-use value components (existence value, heritage value, and option value) the respondents are willing to pay for. 6.
The respondents' gender, age, occupation, education level, technical title, and annual income, among other social characteristics. 7.
Guidance and suggestions for this CVM survey.

Secondary Data Collection
Secondary data were collected from various sources, including official documents, government reports, and data from organizations such as the Hubei Provincial Department of Water Resources Lake Division, the Hubei Environmental Monitoring Center, and the Hubei Statistics Bureau.

Ecological Service Value Assessment
Using the environmental resource value theory, we divided the wetland value into use and non-use value. The use value further included direct use value (DUV) and indirect use value (IUV) [27]. We computed DUV based on the market price of ecosystem products, which included components such as aquaculture production, water conservation, and leisure tourism. Each component was assessed via different techniques: aquaculture production was evaluated by looking at the yield per unit area, the area of the lake wetland, and the market price of these products. The water conservation value was estimated based on the volumes of the urban lake wetlands at constant water levels and the construction cost of storage capacity per unit area. The leisure tourism value was gauged using the travel cost method, supplemented with questionnaire survey data.
IUV and non-use value (NUV) were estimated based on the willingness to pay (WTP) for utilizing an ecosystem service function. This involved calculating the sum of the values of carbon sequestration and oxygen release, transpiration and endothermic, water quality purification, flood control, biodiversity maintenance, and scientific research and education. Each component had its unique method for estimation: carbon sequestration and oxygen release were obtained by measuring these quantities in the aquatic vegetation of each lake and then monetizing them using the shadow price method. The transpiration value was calculated through monetization and transformation of the heat absorption function index. Water quality purification, flood control, and biodiversity maintenance values were estimated through a combination of measurement and monetization methods. The research and education value was calculated using the result reference method. Tables A4-A6 in Appendix A provide a list of indicators and methods of ecosystem services valuation used in this study. Non-use value (NUV) was estimated as the sum of existence, heritage, and option values. These components were estimated using the Contingent Valuation Method (CVM), which involved creating an open-ended (OE) questionnaire in the pre-survey stage to capture respondents' willingness to pay, thereby indicating the perceived non-use value of the lake wetlands. A payment card (PC) approach was then used in the main survey to solidify these initial estimates.
Consequently, an array of methods, such as the market price, shadow engineering, travel cost, shadow price, efficiency alternative, pollution cost, result reference, and contingent valuation methods, were employed to evaluate various functional indicators of wetland ecosystems. The total economic value was calculated by the sum of direct, indirect, and non-use values.
Through the use of the Contingent Valuation Method (CVM), we established an index database to analyze respondents' environmental consciousness, the significance of the non-use value component, the frequency distribution of respondents' WTP, per capita WTP value, and total payment value. This method allowed us to directly measure respondents' willingness to pay (WTP) values [28]. Additionally, the survey analyzed the correlation between WTP and societal factors.
In the analysis of the degree of importance of non-use value (NUV) indicators, a 4-point scale [29] was used to grade their significance: very important (3 points), important (2 points), average (1 point), and not important (0 points). The scores were then multiplied by the frequency of respondents' evaluation of the importance of each non-use value component, and the average score was calculated to determine their order of importance. The total payoff value was calculated by multiplying the actual number of people WTP by the average total payoff value (Vwtp) of each lake [30]. The correlation analysis of respondents' social characteristics on WTP and WTP value was tested by the p value size [31].

Water Quality Assessment
The water quality of the three lakes in Wuhan was assessed by measuring the levels of total nitrogen (TN); total phosphorus (TP); and several heavy metals, such as copper (Cu), zinc (Zn), lead (Pb), cadmium (Cd), arsenic (As), and mercury (Hg). In March 2022, 11 surface water samples from the selected lakes were collected and sent to the laboratory of No. 6 Geological Team of the Hubei Geological Bureau for analysis. This analysis provided crucial data for estimating the water purification values of the lakes.
The determination of TN and TP was carried out according to HJ 636-2012 and GB 11893-89 standards, respectively, using an LH-25A intelligent multi-parameter digestion device and a TU-1810D UV-visible spectrophotometer [32][33][34][35]. These standards are suitable for surface water, groundwater, industrial waste water, and domestic sewage. The detection limit for TN is 0.05 mg/L, and for TP, it is 0.01 mg/L.
For the determination of TN and TP, water samples were first digested using reagents P1 and P2 and potassium persulfate (SP). After digestion, the samples were colored with specific reagents, and their absorbance was measured using a spectrophotometer at specific wavelengths: 220 nm and 275 nm for TN and 700 nm for TP.
For heavy metal analysis, the procedure varied depending on the metal. For Cu, Zn, Cd, and Pb, unacidified samples were filtered and then measured using Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) [36][37][38]. For Hg and As, the samples were subjected to acid digestion followed by measurement using an atomic fluorescence analyzer [39][40][41].
Quality control for total nitrogen (TN), total phosphorus (TP), copper (Cu), zinc (Zn), lead (Pb), cadmium (Cd), arsenic (As), and mercury (Hg) was conducted meticulously. Correlation coefficients of the calibration curves for all substances met the requirements. A parallel double sample was analyzed for each batch, ensuring the relative deviation was within the acceptable range. For each batch, a standard quality control sample was also tested, with results complying with the standard values. For Cu, Zn, Pb, Cd, Hg, and As, blanks were within standards, and certified standard samples were confirmed to fall within the uncertainty range. Intermediate point concentration was checked and met the requirements. All these steps ensured the precision and accuracy of our measurements.

Results of Ecological Service Value Assessment
The material production value of the urban lake wetlands, classified as natural, seminatural, or artificial, was assessed. The assessment involved evaluating all types of material products provided by these lakes, considering the yield per unit area, the area of the lake wetland, and the market price of these material products. The total material production value (Table 4) was determined to be 796.59 × 10 4 CNY × yr −1 . Among this total, natural lakes contributed 445.77 × 10 4 CNY × yr −1 , and semi-natural lakes contributed 350.82 × 10 4 CNY × yr −1 , while artificial lakes did not contribute. This indicates that natural lakes have the highest material production value, followed by semi-natural lakes, with artificial lakes not contributing to the material production value. Additional details regarding the formulae and definition of variables V1 to V9 are provided in Appendix A (Tables A4-A6). Table 4. Direct use value of urban lake wetlands in Wuhan (in 10 4 CNY × yr −1 ).

DUV Components
Zhangdu Lake East Lake Ziyang Lake Water conservation values were estimated based on the volumes of the urban lake wetlands at constant water levels and the construction cost of storage capacity per unit area. The total water conservation value (Table 4) was found to be 9702.35 × 10 4 CNY × yr −1 . Natural lakes contributed 2784.63 × 10 4 CNY × yr −1 , semi-natural lakes contributed 6905.28 × 10 4 CNY × yr −1 , and artificial lakes contributed 12.44 × 10 4 CNY × yr −1 . While semi-natural lakes had the highest overall water conservation value, a different picture emerged when looking at the value per unit area, with natural lakes surpassing both semi-natural and artificial lakes.
The leisure tourism value of the three different types of lakes was estimated using the travel cost method, supplemented with questionnaire survey data. The total leisure tourism value (Table 4) came to 73,821.00 × 10 4 CNY × yr −1 . The breakdown of this total shows that the semi-natural East Lake contributed the majority, 71,940.00 × 10 4 CNY × yr −1 , followed by the artificial Ziyang Lake, 1168.20 × 10 4 CNY × yr −1 , and the natural Zhangdu Lake, 712.80 × 10 4 CNY × yr −1 . When comparing value per unit area, however, the artificial lake surpassed both the semi-natural and natural lakes.
In sum, the direct use value per unit area of urban lake wetlands is influenced by the extent of human intervention. The more significant the artificial influence, the higher the direct use value per unit area per year, while less artificial influence corresponds to a lower direct use value. The carbon sequestration and oxygen release values were obtained by measuring these quantities in the aquatic vegetation of each lake and then monetizing them using the shadow price method. The total value of carbon sequestration and oxygen release (Table 5) for the three urban lakes amounted to 281.33 × 10 4 CNY × yr −1 . Zhangdu Lake, a natural lake, had the highest value, followed by the semi-natural East Lake and then the artificial Ziyang Lake. Table 5. Indirect use value of urban lake wetlands in Wuhan (in 10 4 CNY × yr −1 ).

IUV Components
Zhangdu Lake East Lake Ziyang Lake Transpiration Value (V5) The transpiration value, a key measure of the heat absorption function of urban lake wetlands, was calculated through monetization and transformation of the heat absorption function index. The total transpiration value (Table 5) across the three urban lake wetlands was 145,294.98 × 10 4 CNY × yr −1 . The semi-natural East Lake contributed the most, 120,090.39 × 10 4 CNY × yr −1 , followed by the natural Zhangdu Lake, 24,758.55 × 10 4 CNY × yr −1 , and finally, the artificial Ziyang Lake, 446.04 × 10 4 CNY × yr −1 .

Water Purification Value (V6)
Water purification values were estimated by analyzing three different indexes of the water purification function for each type of lake and then monetizing the results. The laboratory testing results showed that the total nitrogen in the water bodies of the three studied lakes was 3.10 mg/L, 1.02 mg/L, and 0.72 mg/L, and the total phosphorus content was 0.39 mg/L, 0.05 mg/L, and 0.14 mg/L. The total value of water purification (Table 5) for the three urban lake wetlands was 94.00 × 10 4 CNY × yr −1 . The semi-natural East Lake had the highest water purification value, followed by the natural Zhangdu Lake and then the artificial Ziyang Lake.

Flood Control Value (V7)
The flood control values were derived by quantifying the homogenized flood function indices of the three targeted lakes and then monetizing the results. The total economic value of the flood control function (Table 5) across the three lakes was 4893.97 × 10 4 CNY × yr −1 . The semi-natural East Lake contributed the most to this value, followed by the natural Zhangdu Lake and then the artificial Ziyang Lake.

Biodiversity Maintenance Value (V8)
The biodiversity maintenance values of the three lakes were obtained by following Costanza [42], and Chen and Zhang [43]. The total biodiversity maintenance value (Table 5) across the three lakes was 1845.88 × 10 4 CNY × yr −1 . Here, too, the semi-natural East Lake contributed the most to the total value, followed by the natural Zhangdu Lake, and lastly, the artificial Ziyang Lake.

Research and Education Value (V9)
The research and education values of the three lakes were also calculated using the result reference method. The semi-natural East Lake had the highest value, followed by the natural Zhangdu Lake and, finally, the artificial Ziyang Lake.
The comparison of indirect use value per unit area of the three urban lake wetlands showed little difference, ranging between 20 and 23 CNY × m −2 × yr −1 (Table 5). This underlines the importance of urban lake wetlands and the need to protect them to ensure their sustainable existence, which plays a key role in enhancing the urban ecological environment.

Non-Use Value (NUV) Respondents' Environmental Awareness
Our survey on the importance of the non-use value (NUV) of Wuhan urban lakes and wetlands revealed that 88.2% of the respondents consider the NUV of Wuhan urban lakes as highly important, 9.7% are indifferent, and 2.1% view it as not essential. In terms of the current environmental quality of urban lakes and wetlands in Wuhan, 58.8% of the respondents believe that it is deteriorating, 25.8% opine that the overall quality remains unchanged, and 15.4% assert that it is improving.

Importance of NUV Components
When asked to evaluate the importance of the three components of the NUV of urban lake wetlands-existence value, bequest value, and option value-the respondents, on average, assigned the highest importance to existence value (2.509), followed by bequest value (2.188) and, finally, option value (1.692) (as shown in Figure 2).
The biodiversity maintenance values of the three lakes were obtained by follow Costanza [42], and Chen and Zhang [43]. The total biodiversity maintenance value (Ta 5) across the three lakes was 1845.88 × 10 4 CNY × yr −1 . Here, too, the semi-natural East L contributed the most to the total value, followed by the natural Zhangdu Lake, and las the artificial Ziyang Lake.

Research and Education Value (V9)
The research and education values of the three lakes were also calculated using result reference method. The semi-natural East Lake had the highest value, followed the natural Zhangdu Lake and, finally, the artificial Ziyang Lake.
The comparison of indirect use value per unit area of the three urban lake wetla showed little difference, ranging between 20 and 23 CNY × m −2 × yr −1 (Table 5). This derlines the importance of urban lake wetlands and the need to protect them to ens their sustainable existence, which plays a key role in enhancing the urban ecological vironment.

Respondents' Environmental Awareness
Our survey on the importance of the non-use value (NUV) of Wuhan urban lakes a wetlands revealed that 88.2% of the respondents consider the NUV of Wuhan urban la as highly important, 9.7% are indifferent, and 2.1% view it as not essential. In terms of current environmental quality of urban lakes and wetlands in Wuhan, 58.8% of the spondents believe that it is deteriorating, 25.8% opine that the overall quality remains changed, and 15.4% assert that it is improving.

Importance of NUV Components
When asked to evaluate the importance of the three components of the NUV of urb lake wetlands-existence value, bequest value, and option value-the respondents, on erage, assigned the highest importance to existence value (2.509), followed by bequ value (2.188) and, finally, option value (1.692) (as shown in Figure 2).

Respondents' Willingness to Pay (WTP) Per Capita
The statistical analysis of the survey samples indicated that the mean WTP in Zhangdu Lake is 114.57 CNY× yr −1 . Applying the linear interpolation method to obtain the median value of 50%, the WTP per capita was found to be 48.4 CNY × yr −1 . Similarly, the mean WTP values of East Lake and Ziyang Lake were 108.71 CNY × yr −1 and 100.38 CNY × yr −1 , respectively, and the median WTP values obtained by the same method were 49.6 CNY × yr −1 and 44.0 CNY × yr −1 , respectively (Figure 3).
The statistical analysis of the survey samples indicated that the mean WTP in Zhangdu Lake is 114.57 CNY× yr −1 . Applying the linear interpolation method to obtain the median value of 50%, the WTP per capita was found to be 48.4 CNY × yr −1 . Similarly, the mean WTP values of East Lake and Ziyang Lake were 108.71 CNY × yr −1 and 100.38 CNY × yr −1 , respectively, and the median WTP values obtained by the same method were 49.6 CNY × yr −1 and 44.0 CNY × yr −1 , respectively (Figure 3).

Total Payment Value (Vwtp) and Its Decomposition
The median, as a positional mean, is often used to replace the arithmetic mean to calculate Vwtp to avoid large errors. According to the 2020 Wuhan Yearbook [19], the total population of Wuhan in 2018 was about 110,810,000 people. The Vwtp of each lake, as calculated with the median WTP of Zhangdu Lake, East Lake, and Ziyang Lake (70.78%, 70.09%, and 56.92%, respectively), was 2.85 × 10 8 CNY × yr −1 , 2.89 × 10 8 CNY × yr −1 , and 2.08 × 10 8 CNY × yr −1 , respectively. The respondents were willing to pay the highest proportion of existence value, which is more than 50% for each lake, followed by heritage value and option value (Figure 4). population of Wuhan in 2018 was about 110,810,000 people. The Vwtp of each lake, as calculated with the median WTP of Zhangdu Lake, East Lake, and Ziyang Lake (70.78%, 70.09%, and 56.92%, respectively), was 2.85 × 108 CNY × yr −1 , 2.89 × 108 CNY × yr −1 , and 2.08 × 108 CNY × yr −1 , respectively. The respondents were willing to pay the highest proportion of existence value, which is more than 50% for each lake, followed by heritage value and option value (Figure 4).

Correlation Analysis between Social Characteristics of Respondents and WTP
An X 2 analysis was conducted to examine the correlation between the respondents' social characteristics and their willingness to pay (WTP). The results, summarized in Table  6, indicate that for Zhangdu Lake, the age of the respondents showed a significant influence on WTP. In contrast, factors such as gender, occupation, professional title, annual income, and education level had no notable effect.

Decomposition of Vwtp
Zhangdu Lake East Lake Ziyang Lake

Correlation Analysis between Social Characteristics of Respondents and WTP
An X 2 analysis was conducted to examine the correlation between the respondents' social characteristics and their willingness to pay (WTP). The results, summarized in Table 6, indicate that for Zhangdu Lake, the age of the respondents showed a significant influence on WTP. In contrast, factors such as gender, occupation, professional title, annual income, and education level had no notable effect. The WTP for East Lake was significantly influenced by the respondents' age and annual income, whereas gender, occupation, professional title, and education level showed no significant impact.
For Ziyang Lake, the respondents' annual income and educational level had a considerable effect on WT#$P, while gender, age, occupation, and professional title had no significant influence. Furthermore, a higher proportion of respondents of older age, higher annual income, and higher education level expressed a willingness to pay.

Correlation Analysis between Social Characteristics of Respondents and Payment Value
Further analysis demonstrated that respondents' social characteristics significantly influenced WTP values (Table 7). The Vwtp of Zhangdu Lake and East Lake were significantly influenced by the respondents' annual income, professional title, and educational level. The factors that significantly influenced the Vwtp of Ziyang Lake were the respondents' annual income and educational level. Gender, age, and occupation had no significant effect on Vwtp in the three lakes. In addition, respondents with higher annual income, higher education level, and higher professional titles expressed a higher willingness to pay.

Results of Water Quality Assessment
The water quality analysis of the three targeted lakes in Wuhan (Appendix A, Tables A1-A3) reveals important insights into the respective water quality and purification values. The lakes exhibited varying nutrient levels, with Zhangdu showing the highest total nitrogen (TN) and total phosphorus (TP) concentrations, while East Lake displayed the lowest levels (Table A1). These differences in nutrient levels can significantly affect the lakes' biological productivity and overall water quality.
In terms of heavy metal concentrations, Ziyang Lake had the highest average arsenic (As) concentration (Table A2). Traces of copper (Cu) were also detectable in both Zhangdu and East Lakes. Notably, while none of the lakes exceeded any dangerous threshold levels for the metals tested (including Cu, zinc (Zn), lead (Pb), cadmium (Cd), mercury (Hg), and As), the presence of these elements underscores the importance of ongoing monitoring.
The water purification values, estimated based on nutrient levels and each lake's water volume, showed that East Lake exhibited the highest water purification value (Table A3). This is likely due to its larger water volume compared to the other two lakes. It is crucial to understand that the purification capacity of a lake is an invaluable ecosystem service, serving to naturally improve water quality.
These results shed light on the current state of these urban lakes in Wuhan, emphasizing the need for continued monitoring and management to maintain and improve their water quality and ecological health.

Discussion
Our findings have several implications for wetland management strategies and policy. The high non-use value (NUV) and willingness to pay (WTP) suggest that policies aimed at preserving and improving these wetlands would receive strong public support. Furthermore, this high non-use value points towards the importance of these wetlands in providing long-term, inherent benefits, such as biodiversity maintenance, carbon sequestration, and flood control. Therefore, management strategies should focus on the preservation of these inherent qualities of the wetlands. Finally, the issues related to pollution highlighted in our results suggest a need for policies and regulations that control and reduce pollution sources in and around these wetlands.
Another important finding of our study is the impact of current management issues on the ecological service function values and ecological compensation. Our research highlights that the lack of a well-established lake management system, fragmented approach to management, insufficient funding, and failure to involve beneficiary households have all contributed to the degradation of the wetlands. This degradation, in turn, reduces their ecological service function values, as the services they provide, such as water quality purification, flood control, and biodiversity maintenance, are diminished. As for ecological compensation, the aforementioned management issues make it difficult to maintain the wetlands and restore them if degraded, thus increasing the cost of ecological compensation. Therefore, improving the management of these wetlands would not only increase their ecological service function values but also reduce the cost of ecological compensation.
The water quality analysis revealed notable differences in the nutrient levels and heavy metal concentrations among the three lakes, emphasizing the need for ongoing monitoring and management. The higher concentrations of total nitrogen (TN) and total phosphorus (TP) in Zhangdu Lake and the detection of copper (Cu) in both Zhangdu and East lakes underline the importance of regulating sources of these pollutants. On the other hand, the higher arsenic (As) concentration in Ziyang Lake calls for a more thorough investigation into potential pollution sources.
The results of IUV provide valuable insights into the public's perception of the non-use value of urban lakes and wetlands in Wuhan. The considerable proportion of the non-use value, when compared to the direct and indirect use value, indicates a strong societal recognition of the inherent and long-term benefits of these wetlands, even when they are not directly used.
Interestingly, a high level of willingness to pay was observed among the respondents. This suggests strong public support for the preservation and improvement of these wetlands. However, it is also evident that there is a lack of practical understanding and concern about the current status and issues of urban lake wetlands. This calls for more extensive awareness campaigns to foster informed participation in conservation efforts.
A notable point of discussion is the role of social characteristics in shaping individuals' willingness to pay. The survey results suggest that higher income levels, advanced education, and professional titles are positively associated with a higher willingness to pay. This could potentially guide targeted educational and awareness initiatives.
The higher WTP per capita for East Lake, despite respondents' dissatisfaction with its development and degree of interference, is intriguing. It could be attributed to the lake's status as a national scenic area, which possibly raises its perceived value. Similarly, the relatively high payment values for the more natural lake, Zhangdu Lake, could be attributed to a preference for less-disturbed ecosystems.
However, it is also important to note that the size of the lakes did not significantly influence their Vwtp. This suggests that the perceived value of the lakes is not just about their size but other factors, such as their ecological health, accessibility, and amenity value. This finding underscores the importance of comprehensive lake management strategies that consider more than just the physical size of the water body.
The correlation between the paid value distribution and the importance evaluation of non-use value components of lakes underscores the consistency in respondents' perceptions of these values. This consistency could be leveraged in future communication and awareness initiatives to emphasize the importance of preserving these ecosystems for their inherent non-use values.

Conclusions
This study, grounded in the theories and methods of eco-economics and resource economics, evaluated the wetland resources' various functions, including resource, environment, and social functions. The water quality analysis of the three lakes in Wuhan revealed differences in nutrient levels and heavy metal concentrations, indicating the need for regular monitoring and targeted management strategies. The assessment of the value of ecosystem services also highlighted the significant role these lakes play in water purifica-tion. The findings also underscored the indirect use value (IUV) of wetlands as the most considerable, accounting for 43.47% of the total ecosystem service function value. This emphasizes the need to enhance the wetlands' ability to improve the ecological environment. Conversely, the direct use value (DUV) was the least at 23.61%, indicating that the wetlands' primary role is not merely human service.
The non-use value (NUV) of the wetlands, higher than both DUV and IUV and constituting 32.92% of the total value, demonstrated a willingness among people to invest in preserving wetlands for their environmental benefits. However, the absence of an efficient lake management system and the burden placed solely on industries have led to public pollution. This study underlines the need to consider the ecological and environmental benefits of urban lake wetlands in their preservation and management decisions. The results suggest that less human disturbance results in higher water conservation value in the wetlands.

Recommendations
Our findings underscore the need for several key strategies to ensure the sustained health and value of urban lake wetlands in Wuhan city. Chief among these is the continued monitoring and management of water quality. The variations in nutrient levels and heavy metal concentrations among the lakes highlight the necessity of regular monitoring and swift, targeted intervention when needed.
Moreover, public education and engagement are instrumental in preserving these natural resources. It is essential to foster an informed public that appreciates the importance of these wetlands and understands the role they can play in their conservation.
Regulations must be strengthened and enforced to control and prevent pollution in and around the wetlands. The introduction of stricter regulations for potential pollution sources, such as industrial activities, is of paramount importance.
Efforts to enhance the ecosystem services provided by these wetlands, such as increasing biodiversity and improving water purification capabilities, should be prioritized.
Finally, the insights derived from this study can inform policy decisions. Recognizing the economic value of these wetlands and society's willingness to contribute to their preservation can help shape policies that prioritize and secure their conservation. The integration of this knowledge into policymaking can foster an environment that supports the sustainable management of these critical urban lake wetlands.

Data Availability Statement:
The data presented in this study are available on request from the corresponding author.  [27] Primary data: field survey in 2022-aquaculture product name, aquaculture area Si (m 2 ), yield per unit area Yi (kg); secondary data: aquaculture company-market price P (CNY) V2: Water Conservation Value V2 = G = ΣXi (i = 1, 2, . . . n) Shadow engineering method [44] Primary data: field survey in 2022-the cost of storage ΣXi (CNY); secondary data: Wuhan Water Bureau-the average water level (m), the highest water level (m), the lowest water level (m), capacity per unit storage volume (m 3 )