Analysis of Ecosystem Service Value Trends and Drivers in the Yellow River Delta, China

Comments 1: The introduction is quite extended and well documented.

Response 1: Thanks, we would like to express our sincere gratitude for your commendations and approval on the introduction of this manuscript.

Comments 2: Data and Methods. Data presentation and the overall methods are well elaborated and convincing

Response 2: Thank you very much. Your discernment in acknowledging the appropriate data expression and the robust methodological exposition is of immense significance to us. This acknowledgement will undoubtedly serve as a source of motivation, inspiring further enhancement of our research aptitudes.

Comments 3: 3.1.1. LUCC in Dongying 2000-2020. The dynamic changes of land use types are not really presented. You should present per land use category, the percentage of variation between 2000 and 2020 so that one can understand which land use types decreased or increased with time.

Response 3: This is a valuable comment, and we have appended a new pie chart in Section 3.1.1 (Figure 3). This figure provides a clear visualization of the percentage variation in the different land use types from 2000 to 2020. Each section of the pie chart corresponds to a specific land use type, and the scale of the pie chart represents the percentage change in the area of that type over a specific period of time. For further details, please refer to lines 289-290.

Comments 4: 3.1.2. LUCC in Reserve and Non-Reserve. Although the dynamic in land types is clearly presented, the interpretation of the changes is lacking. How can you explain the changes observed over time? The remaining results are quite innovative and well presented

Response 4: Thanks for your comments. The section has been rewritten, and the interpretation of the changes to explain the changes observed over time has been added. It reads as follows:

‘’A thorough examination of the LUCC of the Reserve and Non-Reserve (Fig. 3 and Fig.4) reveals a gradual decline in the area of cultivated land in both regions. This decline can be primarily attributed to the Chinese government's fallow policy and the ongoing process of urbanization. However, a more pronounced decrease has been observed in non-Reserve, with a decline of 10.58%, equivalent to 61307.09 ha, compared with the year 2000. Conversely, the decrease in Reserve was only 6.16%, a phenomenon that may be attributed to the stringent land protection policy in these areas, which strictly controls the development and utilization of arable land. At the beginning of the observation period, the grassland area in both regions was comparable, and the results of the changes were similar, with a nearly equivalent decrease in grassland area in both regions. The decline in the non-Reserve is substantially more pronounced, exhibiting a decrease of 729.36 ha, which is equivalent to 46.60% compared to the same period in 2000 and 21.65% relative to the same period in Reserve. Conversely, the area of water bodies in both regions exhibited a gradual increase on an annual basis, with an augmentation of 1336.86 ha in the Reserve and a substantial expansion of 46377.45 ha in the non-Reserve. The wetland landscapes in the two regions exhibited contrasting trends, with the wetland area in the Reserve increasing by 2385.45 ha and decreasing by 11692.80 ha in the non-Reserve. A statistically significant difference was identified in the changes in wetland area between the two regions, with an increase of 2385.45 ha in the Reserve and a decrease of 11692.80 ha in the non-Reserve. Furthermore, the non-Reserve area of construction land expanded significantly by 27151.56 ha, representing a year-on-year increase of 54%. Conversely, the Reserve exhibited a more than 100% year-on-year increase in new constructions, indicating a discernible expansion trend. The area of bare land has increased in both regions, exhibiting a comparable trend, although its share remains relatively small, not exceeding 0.1% of the total area. The marked difference between the changes in the area of water ecosystems and built-up land in the two regions may be related to factors such as protection policies, surrounding land use patterns, water recharge, level of economic development, industrial structure, population growth and distribution, transportation and infrastructure construction. The Reserve has demonstrated a consistent increase in watershed area and a gradual expansion of built-up land, attributable to the implementation of stringent protection policies, environmentally sustainable land use and industrial structure, and a moderate rate of population growth. In contrast, the non-Reserve area has undergone substantial expansion of the watershed area, but has been damaged in the early stages and undergone significant expansion of built-up land due to weak policy enforcement, high development intensity, rapid economic development, high population concentration, and high demand for infrastructure construction.” In lines 299-334.

Comments 5: In line 124 values related to longitude in geographic location of the study area is lacking.

Response 5: Thanks for your suggestion. We have added longitude and latitude in geographic location of the study area. “The YRD (118°33′E to 119°20′E, 37°35′N to 38°12′N),” In lines 118.

Comments 6: On Figure 1. Geographic setting and basic information of the YRD, details of legend telling about maps a), b) and, c) are lacking.

Response 6: Thank you very much. We have supplemented the details of legend telling about maps for Figure 1. The changes are as follows: “Note: (a) Dongying city, The YRD National Nature Reserve is designated as 'Reserve', whereas the remaining areas are designated 'Non-Reserve'; (b) China; (c) Shandong Province.” In lines 132-134.

Comments 7: 4. Discussion ;4.1. Changes in ESV and LULC ;4.2. ESV Driver Analysis. The two sections of discussion are quite consistent and analytic

Response 7: We would like to express our sincere gratitude for your acknowledgement of the contributions made to our discussion section.

Comments 8: Abbreviations. It is more useful to put the list of abbreviations before the introduction, then just after the abstract

Response 8: Thank you for pointing this out. It is acknowledged that the placement of the list of abbreviations after the abstract is believed to enhance readability. However, according to the journal's template, this list is to be positioned in a specific location. The formatting guidelines established by the journal have been meticulously adhered to, ensuring that the manuscript conforms to all the necessary submission requirements.

Comments 9: 5. Conclusion. It is consistent with the main results

Response 9: Thank you very much for your acknowledgement of the consistency of the ‘Conclusion’ section of the paper with the main results.

Response 1: We would like to express our gratitude for the comments that have been provided. The expression 'In said study' has been altered to 'In this study' in the abstract. This change can be found on line 18 of the revised manuscript.

Comments 2: Why direction has significant effect? Because it has not mentioned before.

Response 2: Thanks for your valuable suggestion. We have added the reason why direction has significant effect on ESV to make them clear.

 “Furthermore, disparities in the distribution of land use types gave rise to a discernible spatial distribution of overall ESV, with the northeast exhibiting significantly higher ESV levels in comparison to the southwest.” In lines 24-26.

Comments 3: How much the areas of each region?

Response 3: Thank you for pointing this out. We have added the areas of Reserve and non-Reserve. “This study focuses on Dongying City, which encompasses both Reserve (144473.76 ha) and Non-Reserve (843085.08 ha).” In lines 125-127.

Comments 4: What is a b c meaning? and which area is the reserve and non-reserve areas? How much areas in each site?

Response 4: Thanks for your suggestion. We have added the annotations for Figure 1. The changes are as follows: “Note: (a) Dongying city, The YRD National Nature Reserve is designated as 'Reserve', whereas the remaining areas are designated 'Non-Reserve'; (b) China; (c) Shandong Province.” In lines 132-134.

Comments 5: What is the E? Should add USD unit as well in order to compare with others.

Response 5: Thank you for pointing this out. E represents the Excel expression for scientific notation, a method that is not particularly suitable in this particular context. We have therefore corrected it to the standard expression. As you suggested, all units of economic value in the text have been converted to USD in order to facilitate comparisons with other studies.

Comments 6: ??? Regulation; ??? Provision. What is the dot line meaning? The resolution is low. It is difficult to see the number especially the increasing numbers with the arrows.

Response 6: Thanks for your suggestion. The terms 'value of reconciliation services' and 'value of supply services' are, respectively, representative of 'regulation' and 'provision'. We have updated Figure 5 in response to your suggestions by re-updating the legend to make it clear that the meaning of the dotted line represents a trend line. In addition, we have improved the resolution and font size of the image to make it easier to show the details of the image. In lines 366.

Comments 7: make it as the power of 10x

Response 7: Thank you for pointing this out. We have altered all scientific notation in our manuscript and made it in the form of 10 to the power of x. In lines 502-504.

Comments 8: GDP (X8) is still in the table 4. how importances are sorted? by the number of "q"??

Response 8: We would like to express our gratitude for your meticulous review and constructive recommendations. We regret to inform you that an error has occurred, resulting in the omission of a column of data. This has now been rectified. The missing column is labelled 'q', which stands for 'explanatory power'. We have added to Table 4 in the manuscript. In lines 521-522.

Table 4. Result of factor detector detection.

Comments 9: supporting? Please use the terms consistently throughout the manuscript

Response 9: Thank you for pointing this out. The term 'assisting' has been replaced by 'supporting' in the manuscript to ensure the uniformity of the terminology. In lines 574.

Comments 10: Missing % sign on line 582

Response 10: Thanks for your suggestion. We have added ‘%’ at line 619.

Comments 1: Line 46, ecosystem service value (ESV)

Response 1: Thank you for pointing this out. The term 'ecosystem service value (ESV)' has been shortened to 'ESV'. In lines 40.

Comments 2: Add a brief description for a, b and c

Response 2: Thanks for your suggestion. We have added the annotations to Figure 1. The changes are as follows: “Note: (a) Dongying city, The YRD National Nature Reserve is designated as 'Reserve', whereas the remaining areas are designated 'Non-Reserve'; (b) China; (c) Shandong Province.” In lines 132-134.

Comments 3: 30m spatial resolution

Response 3: Thank you for pointing this out. According to your suggestions, we have made more prescriptive changes to the presentation of the data descriptions in Table 1. “spatial resolution of 30m*30m.” In lines 145.

Comments 4: Fig.3 and Fig.4 add units

Response 4: Thanks for your suggestion. In light of the suggestions provided, Figures 3 and 4 have been revised to incorporate the unit of measurement ha, with the objective of enhancing the comprehensibility of the figures for the reader. In lines 337 and 339.

Comments 5: In Lines 336, this word “precent”

Response 5: Thank you for pointing this out. We have replaced ‘percent’ with ‘%’ to align with the full text. In lines 348.

Comments 6: “1.39513E10” and Fig. 5

Response 6: Thank you for pointing this out. We have redrawn Figure 5 and have correctly standardized the use of scientific notation throughout the text. In lines 366.

Comments 7: Line 423, Add a space

Response 7: Thank you for pointing this out. We have added spaces to all the missing spaces as you suggested. In line 435 and 454.

Comments 8: The discussion is too short, I suggest to improve this section, consider the subitems developed in results.

Response 8: Thanks for your valuable suggestion. An exhaustive analysis of the discussion section is provided, with a detailed comparative analysis of the findings with current relevant studies. Chapters 4.1 and 4.2 have been augmented, and a new sub-chapter, 4.3, has been added in lines 557-694.

“4.1. Changes in ESV and LULC

Most of the existing studies on the synergistic association between LUCC and ESV are limited to qualitative analyses based on spatial distribution maps [61–63], making it difficult to reveal their dynamic evolution. In addition, the extant literature on this subject typically focuses on a specific area, whether it is categorically protected [64,65] or unprotected [66,67]. However, a comparative analysis of temporal and spatial trends, as well as interactions between the two categories, is generally lacking in these studies. Therefore, this study used the centre-of-mass transfer method to conduct a comparative study of the transfer trends of ESV and major land use types in Reserve and Non-Reserve in Dongying City.

The spatial distribution map (Fig. 8) and the results of the spatial autocorrelation analysis demonstrate that the distribution of ESV exhibits a strong correlation with the categories of land use (Fig. 2). The Reserve is located in the northeastern part of Dongying City, and its water ecosystem area is 58.82% higher than that of the non-Reserve area (27.21%), while the area of artificial surface is 0.28%, which is significantly lower than that of the non-Reserve area (7.72%). This disparity in ESV per unit area between the two regions was found to be significant, with a ratio of approximately 0.023 and 0.011 (million/ha), respectively. Regulating services>Supporting services>Providing services>Cultural services in relation to the composition of ESV in both regions, which is consistent with the results of Lu [68]. The YRD is distinguished by its rich aquatic ecosystem, which possesses notable capabilities in terms of water purification, flood regulation, and climate regulation. Consequently, the regulatory services within this ecosystem are of paramount importance. In contrast, the supporting services are more susceptible to the impact of human activities. The development of the region has been accompanied by activities such as overfishing and irrational agricultural development, which have disrupted the supply balance of the natural ecosystem. This has led to a clear difference in the inter-annual trend of supply services between the two regions. Since 2005, the value of supporting services in Reserve has been on the rise (Fig. 6-a), while the decline in non-Reserve continued until 2015 (Fig. 6-b). The cultural services in the region are at their lowest level, indicating a lack of adequate cultural tourism facilities, professional cultural promotion teams, and other related infrastructure. It is evident that the value of cultural services is not fully reflected in the current system. In order to address this issue, it is essential that the management and planning in this area be strengthened in the future.

The results of the centre of gravity analysis demonstrate that the centre of gravity of ESV in Reserve shifted towards the southwest (Fig. 10-d), and that the centre of gravity of ESV in non-Reserve shifted towards the north-west (Fig. 11-d). While there were some differences in the trend of the centre of gravity of ESV within the two areas, they were all consistent with the trend of the centre of gravity of their respective water bodies shifting towards the urban centre. In relation to the configuration of land structures, cultivated land constitutes the primary source of water body and wetland transfer, in comparison with Reserve, with regard to both the distance of the centre of gravity transfer and the proportion of area. The alterations in land structures within non-Reserve are more substantial [69-71], A significant expansion in the area dedicated to construction, coupled with a substantial contraction in the area of cultivated land, has profoundly impacted ES, which is in alignment with the findings of studies conducted by scholars such as Wang [72]. The expansion of non-Reserve into large-scale urbanization and industrial development has been driven by the demand for economic growth, resulting in significant occupation of arable land and ecological space compression.

Notwithstanding the establishment of boundaries between Reserve and non-Reserve, the ESV remains predominantly shaped by human needs, thereby reflecting an inherent imbalance between ecological protection and economic development. In Reserve, the Development Plan for the YRD High-Efficiency Ecological and Economic Zone, implemented by the Shandong government in 2008, has provided policy support for the restoration of wetlands and water bodies, effectively enhancing ecological regulation services such as water supply, climate regulation and environmental purification. Conversely, non-Reserve have been found to be deficient in this regard, and the ESV is more susceptible to the urbanization process and industrial development. To enhance the sustainability of the region, it is imperative to promote a coordinated development of ecological protection and economic development according to the characteristics of the two regions.

4.2. ESV Driver Analysis

ESV is associated with vegetation distribution, climatic conditions and ecological structure [73,74]. The results of the GD indicate that the primary factor influencing ESV in the YRD region was NDVI, with an explanatory power of 62.51% and 73%. This indicates that vegetation distribution is the most critical feature influencing the spatial distribution of ESV, with an explanatory power of 89% in the two regions. These findings align with those of Kang Lei and colleagues' study conducted in the six-province region of Northwest China [75]. The distance factor from the railway is also a significant consideration. The influence of terrain differs considerably between Reserve and Non-Reserve. The explanatory power of climate is more stable in the two regions, and both factors play a non-negligible role. This is consistent with the conclusion of He [76] that climatic conditions have a significant influence on ESV. In Non-Reserve, the effect of economic and social variables, such as population and GDP, became evident, particularly the interaction between population and NDVI, which demonstrated a stronger explanatory power. This suggests that settlement density has a marked moderating and limiting effect on the geographical distribution of ESV in Non-Reserve, where the impact of anthropogenic activities is more pronounced [77].

Furthermore, it is imperative to consider the impact of policy factors on the ESV. The implementation of environmental protection and land planning policies in disparate regions has the capacity to directly or indirectly modify land use patterns. These alterations in turn exert an influence on the ESV. Since 1998, the Chinese government has proposed the policy of returning farmland to forest [78]. The initial implementation of this policy resulted in a significant decrease in the area of arable land, leading to a substantial decline in food production and the value of provisioning services provided by the production of raw materials. This decline also explains why the value of the four services changed the most significantly in the period of 2000-2005 (Fig. 6). Technological advances, such as more efficient agricultural technology, should also be considered, as they may reduce the pressure on arable land and the ESV to a certain degree. Concurrently, technological progress, exemplified by the enhanced efficiency of agricultural techniques, has the potential to mitigate the pressure on cultivated land to a certain extent, thereby enhancing the ESV. In terms of environmental protection policies [79], Reserve is usually subject to more stringent and comprehensive protection policies, such as restrictions on development activities, strict land use planning, and intense ecological monitoring and protection measures. The overarching objective of these policies is to preserve the integrity of ecosystems in their pristine state, whilst concurrently promoting the conservation of biodiversity and the stable performance of ecological functions. Conversely, environmental protection policies in non-Reserve are less stringent, often permitting a certain degree of economic development and human activities.

The results reveal that the variation in ESV across space is shaped by the complex interplay of environmental and economic factors. Notably, there are pronounced differences between Reserve and Non-Reserve. In natural Reserve, ecological factors exert a dominant influence, whereas in Non-Reserve, the impact of socio-economic factors gradually increases. This indicates that the necessity for the implementation of regionally targeted protection and restoration strategies, with consideration for inter-regional variability.

4.3. Recommendations and limitations

This study successfully revealed the spatial distribution characteristics and some key drivers of ESV in the YRD. This provides an important scientific basis for regional ecological protection and sustainable development. However, it is not without its limitations, which provide directions and ideas for follow-up studies.

Despite the identification of the primary drivers of ESV in the YRD region, including LUCC and NDVI, in this study, the complexity of the regional ecosystem precluded the consideration of all potential drivers and their interactions. Furthermore, micro factors such as changes in the soil microbial community, and socio-economic factors such as the awareness of ecological conservation and behavior of the local population, were not fully explored. This may result in an incomplete understanding of the mechanisms of ESV change. This may result in an incomplete understanding of the mechanisms underlying ESV change. The study primarily relied on public remote sensing data, which facilitates rapid acquisition of large-scale information, but lacks the capacity to accurately reflect the microscopic characteristics of the ecosystem and ecological processes. Additionally, it is deficient in complementing the findings from field research and integrating multi-source data, consequently impacting the study's precision and comprehensiveness. Furthermore, the present study focuses exclusively on Dongying City, the core area of the YRD, while disregarding the intricate material circulation and energy flow processes between the surrounding transition zone and the core area. This includes the water quality and quantity of the neighboring rivers, as well as the indirect impact of human activities on the ES and ESV of the delta wetlands. Consequently, this restricts the study's ability to comprehensively reflect the integrity of the ecosystems of the entire YRD and the dynamic changes of ESV.

The potential exists for the enhancement of future research in a number of ways. Firstly, the research scope of the drivers should be expanded to include more micro-ecological factors. Secondly, field research should be actively carried out, and multi-source data should be combined to improve the accuracy and reliability of the study. Furthermore, the scope of the study should be expanded to include the neighboring transition zones in the research system, and a more comprehensive regional ecosystem model should be constructed, so as to gain a deeper and more comprehensive understanding of the formation mechanism and dynamic change law of ESV in the YRD, and to provide a more solid theoretical support for regional ecological protection and sustainable development.”

Comments 9: Prior to the conclusions, I suggest adding the limitations of the study and future perspectives in the field of study…

Response 9: Thanks. The limitations and future perspectives of the field of study have been incorporated within the discussion section.

Comments 1: Provide concrete examples of how the findings could be used in environmental or economic management policies.

Response 1: Thank you very much for your suggestion. We have added the impacts of policy realization on ESV, including the policy of returning farmland to forests and the policy of environmental protection, in section 4.2 of the Discussion section, and added two new relevant references.

“Furthermore, it is imperative to consider the impact of policy factors on the ESV. The implementation of environmental protection and land planning policies in disparate regions has the capacity to directly or indirectly modify land use patterns. These alterations in turn exert an influence on the ESV. Since 1998, the Chinese government has proposed the policy of returning farmland to forest [78]. The initial implementation of this policy resulted in a significant decrease in the area of arable land, leading to a substantial decline in food production and the value of provisioning services provided by the production of raw materials. This decline also explains why the value of the four services changed the most significantly in the period of 2000-2005 (Fig. 6). Technological advances, such as more efficient agricultural technology, should also be considered, as they may reduce the pressure on arable land and the ESV to a certain degree. Concurrently, technological progress, exemplified by the enhanced efficiency of agricultural techniques, has the potential to mitigate the pressure on cultivated land to a certain extent, thereby enhancing the ESV. In terms of environmental protection policies [79], Reserve is usually subject to more stringent and comprehensive protection policies, such as restrictions on development activities, strict land use planning, and intense ecological monitoring and protection measures. The overarching objective of these policies is to preserve the integrity of ecosystems in their pristine state, whilst concurrently promoting the conservation of biodiversity and the stable performance of ecological functions. Conversely, environmental protection policies in non-Reserve are less stringent, often permitting a certain degree of economic development and human activities.” In lines 633-653.

Comments 2: Assess more directly the balance between environmental benefits and the impact on economic and social progress in the region.

Response 2: Thank you very much for your suggestion.  In Reserve, there is a high level of awareness of ecological protection, while in non-Reserve this awareness is lacking. In the future development process, the influence of socio-economic factors on the value of ecological services will gradually increase. It will therefore be more necessary to pay attention to the enhancement of ecological protection awareness, rather than blindly pursuing the high-speed development of economic benefits. Notwithstanding the establishment of boundaries between Reserve and non-Reserve, the ESV remains predominantly shaped by human needs, thereby reflecting an inherent imbalance between ecological protection and economic development. In Reserve, the Development Plan for the YRD High-Efficiency Ecological and Economic Zone, implemented by the Shandong government in 2008, has provided policy support for the restoration of wetlands and water bodies, effectively enhancing ecological regulation services such as water supply, climate regulation and environmental purification. Conversely, non-Reserve have been found to be deficient in this regard, and the ESV is more susceptible to the urbanization process and industrial development. To enhance the sustainability of the region, it is imperative to promote a coordinated development of ecological protection and economic development according to the characteristics of the two regions. You can see it on lines 567-615 of the manuscript.

Comments 3: I also think it is necessary to revise the wording, as some paragraphs are redundant or are too long and make the text difficult to read. In particular, I think the summary should be more concise.

Response 3: Thank you for pointing this out. We have revised the summary and delated some redundant paragraphs to make it more concise and easier to read. “Ecosystem service value (ESV) reflects ecosystem functions and benefits, but the factors influencing ESV and the mechanisms driving it in wetlands and non-wetlands are not yet fully understood. The Yellow River Delta (YRD) is distinguished by the presence of numerous wetland areas that are both Reserve and non-Reserve, and thus it was selected as the designated study area. In this study, the spatiotemporal structures of ESV in the YRD between 2000 and 2020 using land cover change analysis and the equivalent factor methodology. In addition, we analyze the drivers behind the geographical variability of ESV by applying the Geographical Detector method. The outcomes displayed that the land structure of the YRD National Nature Reserve is relatively stable, whereas the Non-Reserve exhibit greater fluctuations. The results showed that wetland in the YRD Non-Reserve decreased by 11.43%, compared with the more stable land structure in Reserve, where wetland decreased by 4.93%. Furthermore, disparities in the distribution of land use types gave rise to a discernible spatial distribution of overall ESV, with the northeast exhibiting significantly higher ESV levels in comparison to the southwest. Additionally, in the past two decades, the center of gravity of the ESV in both regions shifted towards urban centers, and wetlands migrated towards the coastline. Notably, the Normalized Difference Vegetation Index was identified as the main driver of ESV heterogeneity. The findings of this study are highly relevant to regional ecological conservation and the promotion of economic and social development. “You can see it on lines 14-30 of the manuscript.