Analysis of Blue Infrastructure Network Pattern in the Hanjiang Ecological Economic Zone in China

Round 1

Reviewer 1 Report

Review Report

This manuscript deal with a crucial part of urban development, Blue Infrastructure provides multi-ecosystem services. The Hanjiang Eco-economic Zone will be taken as the study area. Morphological Spatial Pattern Analysis and Minimum Cumulative Resistance Model are adopted to construct the potential BI network for three periods for assessing network structure.  The authors' claim means the changes in Blue Infrastructure network patterns are closely related to the changes in the area and number of Blue Infrastructure sources. This is an interesting manuscript. I think Water readers will be interested.

The presentation is adequate; anyway, I have detected some criticisms in the text that should be properly addressed.

The Authors can benefit from the comments below to improve their paper.

1. First, the paper remains rather vague with regard to key terms and concepts. This is also mirrored in a phrasing that could often be much more precise.
2. In the introduction section, more new related works of literature are suggested to be referenced, as follows:

Using Systems Thinking and Modelling: Ecological Land Utilisation Efficiency in the Yangtze Delta in China. https://doi.org/10.3390/systems10010016

An Empirical Study on the Ecological Economy of the Huai River in China. https://doi.org/10.3390/w12082162

Integrated Evaluations of Resource and Environment Carrying Capacity of the Huaihe River Ecological and Economic Belt in China. https://doi.org/10.3390/land10111168

3. The main constraints of the research should be discussed in the conclusion section.
4. The resolution of the figures in the manuscript is not enough, and the authors are advised to improve it.
5. Research limitations should be mentioned.
6. The proposed research and obtained results should be compared with some research that was conducted before. In this way, the research implications could be proposed.
7. In the Conclusions section, The authors are suggested to supplement future research recommendations.
8. It is recommended to summarize research contributions and reflections in the conclusion.
9. Future research direction should be indicated in the Conclusion.

Other suggestions

(1)  Please review the entire document for typographical errors and any other necessary corrections, check headings, tables, and figures.

(2)  Authors should check this manuscript for grammar.

(3)  Authors should follow the journal format as follow:

https://www.mdpi.com/journal/ijerph/instructions

See the Reference List and Citations Guide for more detailed information.

https://www.mdpi.com/authors/references

In the methodology section, authors must discuss methodology carefully. The paper needs major revisions or should be rejected.

Comments for author File: Comments.docx

Author Response

Modification Instructions of《Analysising of Blue Infrastructure Network Pattern in the Hanjiang Ecological Economic Zone in China》

Dear reviewer and editor,

We earnestly appreciate it that your patient guidance is of great significance to our article. These suggestions and guidance are very important for the promotion of this article. Although the current article still has some shortcomings, but under the guidance of reviewer and editor, I think we will be able to get the article promoted a lot. These time, after receiving your email, we made a modifying based on your suggestions. In addition, the modified version will be sent to you in the form of an attachment, and the particular modification instructions will be attached to the post.

Wish you have a really nice day!

Pengfei He

2022-03-30

The detailed modification instructions were listed blow:

1. First, the paper remains rather vague with regard to key terms and concepts. This is also mirrored in a phrasing that could often be much more precise.

Answer：I would like to thank the reviewer for your comment. According to the reviewer's request to clarify key terms and their related concepts. On the basis of clarifying the relevant concepts, the research implications of this paper are further elaborated. The details are as follows, and I hope they will meet the requirements of the reviewers.

In the context of rapid urbanization and global climate change, cities are facing many challenges such as rapid climate change, frequent flooding and increased water pollution. As a sustainable development strategy to address the urban environmental crisis and improve urban resilience, BI can play parts in such ecosystem services as supporting, regulating, provisioning and culture for cities and residents [1]. BI is a network of aquatic ecosystems consisting of spaces and corridors covered by water bodies, which includes natural or semi-natural water bodies and artificially constructed water-bond surfaces [2]. Such as Rivers, Lakes, Wetlands, Natural waters coast, Reservoirs, Artificial river embankment, Artificial water course, etc. BI contributes to water purification, flood protection and overall climate change adaptation as well as provides various kinds of cultural ecosystem services [3-6]. Apart from it, BI also play a key role in improving public health and people's well-being, promoting regional economic development and maintaining urban ecosystem services [7-9]. However, the installation and use of BI depending on the different development needs of the city, such as alleviating urban flooding [10,11], promoting physical and mental health [12,13], and enhancing biodiversity [14,15], which are ultimately reflected in the design of urban BI. The gray infrastructure such as hardened roads, constructions and drainage pipes which is common in the city is significant for urban development. So is BI.[3]. However, there is rare evidence proving the value and ability of BI to provide ecosystem services for cities and humans [16].

In the last two decades, the concept of green infrastructure has gained attention.  Apart from BI, Green infrastructure also refers to natural or artificial green spaces such as forests, grasslands, plant and animal habitats, and farms that provide a wider range of ecosystem services to better address environmental issues and support human well-being [17-19]. Therefore, BI is placed in the broader framework of green infrastructure research, called blue-green infrastructure [20,21]. However, as the urbanization is gaining momentum, human activities is more frequent and the urban construction space is increasingly expanding, the water pollution is more serious [22]. Against this backdrop, BI is exposed to fragmentation and the connection is weakening, and it also faces the difficulties that great area loss and quality degradation [23]. this phenomenon is hided in the framework of broad discussion of green infrastructure. Therefore, it is imperative to study the spatial and temporal changes of BI network patterns in the context of rapid urbanization in order to assess the current status of urban BI. Therefore, the targeted protection and restoration for the sustainable functions of BI ecosystem services can be carried out.

2. In the introduction section, more new related works of literature are suggested to be referenced.

Answer：Thanks to the reviewer for the reminder. In the introduction section, we refer to the relevant literature suggested by the reviewer, which enables us to have a more comprehensive understanding of the relevant results of ecological economic research in China at the watershed scale and provides theoretical guidance for the research in this paper.

With the high-quality development of China's economy, the increasingly prominent environmental problems have attracted political and academic circles. Especially under the guiding ideology of regional development integration proposed by the Chinese government, the research on ecological economy at the scale of river basins has become a frontier hotspot, such as the Yangtze River Delta [38] and the Huaihe River Ecological and Economic Belt [39,40]. However, the crucial strategic value of the Hanjiang Ecological Economic Zone as an important link between the economic development of the central and western regions of China has still not received sufficient attention.

• Zhang, C.; Feng, Z.; Ren, Q.; et al. Using Systems Thinking and Modelling: Ecological Land Utilisation Efficiency in the Yangtze Delta in China. Systems. 2022, 10, 16.
• Hsu, W.-L.; Shen, X.; Xu, H.; et al. Integrated Evaluations of Resource and Environment Carrying Capacity of the Huaihe River Ecological and Economic Belt in China. Land. 2021, 10, 1168.
• Zhang, C.; Wang, C.; Mao, G.; et al. An Empirical Study on the Ecological Economy of the Huai River in China. Water. 2020, 12, 2162.

3. The main constraints of the research should be discussed in the conclusion section.

Answer：Thanking the reviewers for their suggestions. We added the main constraints of the research in the discussion section. The details are as follows:

1. The choice of research scale is important when using MSPA to analyze raster images of the landscape, because the results of MSPA analysis are closely related to the variation in granularity. In addition, the edge width needs to be set during the MSPA landscape pattern analysis, and the setting of the edge width represents the size of the extent of the edge effect produced by the patches. However, the edge effect is pertinent and complex. The width of the edge effect varies with different landscape properties, patch shapes, and different research objects [56]. As a result, the width of the edge effect set in this study is not applicable to some specific species and the characteristics of the protected species and the nature and shape of the study area landscape also need to be considered when setting the edge effect width.
2. For the reasons that different connectivity distance thresholds will have different impacts on the important value of patches, the betweeness centrality and the landscape’s connectivity, it is necessary to set the connectivity distance threshold when calculating the landscape connectivity based on PC and IIC [57,58]. However, the setting of the connectivity distance threshold needs to take into account the dispersal distance of species, which often varies among species. Therefore, the scientific determination of this distance threshold needs more argumentation.
3. The selection of resistance factors is the basis of BI network construction, and the construction of the resistance surface system is still controversial [35]. Due to the lack of detailed research data, this paper does not take the influence of the living habits of different species and the distribution of settlements and other factors on the construction of the resistance surface into consideration. In addition, the weight of resistance factors is subjective because there is no data on the relationship between species dispersal and resistance factors [60]. it needs to be further studied and discussed in more detail in the follow-up.
4. The resolution of the figures in the manuscript is not enough, and the authors are advised to improve it.

Answer：Thanks to the reviewer for the reminder. The images have been saved as uncompressed versions in the article.

5. Research limitations should be mentioned.

Answer：Thanks for the reminder from the reviewer. According to the reminder from the reviewer, we added the Research limitations in the conclusion section.

This paper reveals the spatial and temporal evolution characteristics of the BI network pattern in the Hanjiang Ecological Economic Zone during 2010-2020, and the results can provide references for optimizing the BI network and formulating BI protection policies in the study area. However, there are still some limitations in this study.

Firstly, when adopting MSPA and landscape connectivity analysis, the thresholds has a large impact on the analysis results, and the scientific setting of thresholds still needs further exploration.

Secondly, although this paper provides a basic framework for resistance surface construction, it still needs to be optimized. The selection of resistance factors is not comprehensive enough, and the weight of resistance factors is also subjective.

 Lastly, there is no comprehensive analysis on the ecological network of the study area through combining other land use types.

6. The proposed research and obtained results should be compared with some research that was conducted before. In this way, the research implications could be proposed.

Answer：According to the request of the reviewer, we added the description in the conclusion section. Obviously, the research value of this paper is highlighted by comparing the results with previous studies. Add content as follows:

 In the context of the implementation of the Central Line Project of South-to-North Water Diversion and the cascade reservoir project, the downstream area of Danjiangkou Reservoir shows hydrological characteristics of reduced flow and lower water level during the dry period [61], and the water quality deteriorates sharply [41,42]. Subsequently, with the implementation of the Yangtze river diversion to Hanjiang project and ecological restoration projects, the water quality in the Hanjiang river’s middle and lower reaches transitioned from heavier pollution to moderate pollution and showes a trend of turning better [62]. This is consistent with the results of this study. From 2010 to 2015, the total BI area and core area decreased, the landscape connectivity decreased and the BI network simplified. From 2015 to 2020, the total BI area and core area increased, the landscape connectivity improved, and BI network tends to be complex. It indicates that the study on the change of BI network pattern integrating MSPA, Landscape Connectivity Index, MCR Model and Gravity Model can reflect the hydrological characteristics and landscape pattern of water bodies in the study area from the macroscopic perspective. The research results can provide a reference for BI network planning in the study area, and give a reference for the planning of BI network pattern in other regions.

7. In the Conclusions section, The authors are suggested to supplement future research recommendations.

Answer：At the end of the Conclusions section, mainly around the limitations of this paper's research, we have added to our recommendations for future research.

Firstly, when adopting MSPA and landscape connectivity analysis, characteristics of species and study area should be considered to determine the thresholds in an integrated manner.

 Secondly, Under the condition that the relevant data are available, the resistance factors should be included and the species dispersal characteristics should be considered to establish a more suitable resistance surface system.

Lastly, green infrastructure such as forest, grassland and cultivated land should be included in the construction of regional ecological network in order to provide comprehensive support for urban ecological development.

8. It is recommended to summarize research contributions and reflections in the conclusion.

Answer：In the conclusion section, we have summarized the main contributions by comparing them with some previously conducted studies, while adding the inadequacies of the studies. These are responded to in the above questions.

9. Future research direction should be indicated in the Conclusion.

Answer：Same as the 7th question.

10. Please review the entire document for typographical errors and any other necessary corrections, check grammar, headings, tables, and figures.

Answer：Thanks to the reviewer's reminder, we have checked and revised again according to the journal template format.

11. In the methodology section, authors must discuss methodology carefully.

Answer：We introduce the application of the method in the introduction section, describe the main process of threshold setting in the method section, and detail the rationale of the method and the principles of threshold setting in the discussion section. The details are as follows:

In the introduction section:

These years, some experts have made researches on ecological networks with different kinds and dimensions from the point of view of landscape ecology theory. Several methods and models were tried in the research process, in which Morphological Spatial Pattern Analysis(MSPA) and Minimum Cumulative Resistance(MCR) are widely adopted [33-35].

MSPA method is adopted to identify and extract the core area that are important for species migration and energy exchange. And then Landscape Connectivity Index is selected to assess the landscape connectivity of the core area, and patches in the core area with a high patch importance index is regarded as BI sources. Based on MCR Model, it simulates the potential corridors and adopts Gravity Model to identify important corridors for the purpose of constructing a potential BI network in the study area.

In the method section:

MSPA is a raster data handling method based on principles of mathematical morphological proposed by Vogt and other experts and scholars, which can accurately identify the type and shape of the landscape, and then visualize the spatial distribution of the landscape, offering a new basis for the choice of BI sources [44]. In order to give full play of MSPA method, ArcGIS is used to set the extracted water body as the foreground, and other sections as the background. Then, the data is converted into a 30m×30m Tiff format binary raster data file. Finally, based on Guidos Toolboxs software, seven types of non-overlapping landscapes are obtained by taking MSPA method with eight-neighbor connectivity and thirty-meter edge width for this analysis.

MCR (4) is a common method to simulate ecological corridors, which can evaluate the min cost path between sources to determine the optimal path for species migration and dispersal [49]. MCR Model has the characteristics of simple construction, extension of elements, and wide application. It can simulate the extent and direction of species dispersal by avoiding various external disturbances [50]. Choosing the source and establishing the ecological resistance surfaces are the keys to MCR Model. Therefore, for model construction, it is attached great importance to the selection of appropriate resistance factors to construct the resistance surface system. Considering factors such as natural conditions and human interference and the condition of the study area as well as referring to the suggestions from the experts and the results of the existing research, the comprehensive resistance surface system is established, which includes five resistance factors: elevation, slope, landscape use types, distance from road and distance from the construction land(Table 2). These factors are confirmed from the perspective of topography, the types of the landscape and human activities and so on. Besides, the grading index and resistance value of each resistance factor are also confirmed. Higher resistance values indicate more difficulty of species migration and diffusion. Furthermore, determination of resistance factor weights by AHP. Based on ArcGIS 10.8 software, the resistance factor is assigned attribute and converted into raster data, and the comprehensive resistance surface is obtained by using the raster calculator, so the key data of model is achieved.

Using the Cost Distance analysis tool in ArcGIS is applied to calculate the min cost distance between pixels by using BI source and resistance surface raster images, and then the min resistance path between sources is calculated by using cost path analysis tool, thereby the potential corridors between BI sources is generated.

In the discussion section:

1. The choice of research scale is important when using MSPA to analyze raster images of the landscape, because the results of MSPA analysis are closely related to the variation in granularity. Therefore, it is very important to choose an appropriate analysis scale for MSPA research [51,52]. Different image raster sizes in the same study area will change the analysis results accordingly [53]. For example, an increase in the image raster size of the study area may lead to the disappearance or classification of the original smaller area patches into other categories, like small Cores may be reclassified as Islets, some Bridges may become Branchs, and some Branchs may disappear. The study area in this paper is the Hanjiang Ecological Economic Zone. It means that the study range is large and larger image raster size can cause some small patches with good connectivity to be lost or change categories types [35,52]. This is why the particle size at the urban scale is set to 30m. After several tests of the threshold, this granularity can better maintain the original data characteristics, but the reasonableness of the scale still needs further study.

In addition, the edge width needs to be set during the MSPA landscape pattern analysis, and the setting of the edge width represents the size of the extent of the edge effect produced by the patches. the edge width affects the impacted range of the edge effect of the patch. For example, an extension of the edge width will result in the reduction of the core area of the landscape type and the increase of the non-core elements, so the size of the edge width has a greater impact on MSPA analysis results [54]. Edge effect is an important concept in ecology, which is of great significance to ecological process, species protection, and habitat protection. It must be considered in the functional planning of nature reserves [55]. In this study, Considering the area scale and data accuracy, the edge width threshold is set to 1. Since the input image raster size is 30m× 30m, the edge effect is 30m. However, the edge effect is pertinent and complex. The width of the edge effect varies with different landscape properties, patch shapes, and different research objects [56]. As a result, the width of the edge effect set in this study is not applicable to some specific species and the characteristics of the protected species and the nature and shape of the study area landscape also need to be considered when setting the edge effect width.

2. For the reasons that different connectivity distance thresholds will have different impacts on the important value of patches, the betweeness centrality and the landscape’s connectivity, it is necessary to set the connectivity distance threshold when calculating the landscape connectivity based on PC and IIC [57,58]. For example, a patch is considered connected only if the distance between patches is less than a set threshold, and the opposite is not connected. In this context, this paper determines the connectivity distance threshold by comprehensively analyzing the following factors. Namely, in the condition of different distance threshold, the changes in the area and number of patches, the quantity of components and the changes of patch area in the biggest component, the area of individual patch and the distribution of the area of a single patch and the important value of the patch [59]. When the connectivity distance threshold is 10000m, the area and number of connected patches vary greatly, and both large-area patches and small-area patches show higher important values. In addition, in order to ensure the comparability of data between years, the connectivity probability is set to 0.5. However, the setting of the connectivity distance threshold needs to take into account the dispersal distance of species, which often varies among species. Therefore, the scientific determination of this distance threshold needs more argumentation.
3. MCR Model is used to simulate the potential BI corridor. The selection of resistance factors is the basis of BI network construction, and the construction of the resistance surface system is still controversial [35], through the study on relative researches and consulting experts, the method of constructing resistance surfaces by selecting resistance factors from topography, landscape types and human activities in this paper is scientific. Due to the lack of detailed research data, this paper does not take the influence of the living habits of different species and the distribution of settlements and other factors on the construction of the resistance surface into consideration. In addition, the weight of resistance factors is subjective because there is no data on the relationship between species dispersal and resistance factors [60]. it needs to be further studied and discussed in more detail in the follow-up.

 

 

 

 

 

 

Author Response File: Author Response.pdf

Reviewer 2 Report

General overview:

The management and reflections about blue ecosystem services in cities involve the adoption of coordinated strategies at various spatial and temporal scales. In the long-term perspective, territorial planning must consider the evaluation of landscape connectivity, and the decision-makers and stakeholders need to be aware of how the future climate will affect people’s safety, economy, social life, and human needs. The abstract appropriately summarizes the manuscript. The introduction is concise. The purpose of the study left clearly defined. The authors provide a rationale for performing the study based on a review of the actual literature. The methodology was described correctly. Another investigator can reproduce the study using the methods as outlined. The results are clearly explained and are reasonable. The authors' conclusions are justified by the results found in the study.

 

Specific comments:

As a variety of factors could bias simulation results if not taken into account properly, the authors focused on resistance factor classification, weight, and assignment. In addition to simplifying simulation, the approach eliminates the need to evaluate every possible scenario, making the simulation model an effective tool for decision-making. It is, therefore, worthwhile to invest the time and effort. Here are only some thoughts for consideration:

 

1. Please shorten the title of this publication. I would not use this title.

    

2. This mode can be fine-tuned using new data, especially temperature-related factors, as global warming accelerates. This will help us understand the environmental impact in the long run. Could the authors elaborate on their future plans for BI? Could they please elaborate on the Introduction?

    

   3. In Table 1: ”. Resistance factor classification, weight and assignment table”. In surface water entities, such as local lakes, reservoirs, and wetlands, the resistance value of affected properties may help address knowledge gaps. In conjunction with a model, BI networks can improve the understanding of long-term variability and trends of rainfall water processes, as well as provide observations for monitoring and prediction, particularly in data-scarce regions. From 2010 to 2020, the MSPA was not applied effectively to the river basin. You need to identify and prioritize critical subwatersheds for BI conservation and management.

    

   4. Alternative management practices must be predicted using the MCR to achieve adequate water quality and quantity. As shown in Table 6, you identified nodes. Do you know how to interpret them? The interaction between vegetation and runoff generation, sediment yield, and soil column impact the parameters selected for calibration and the calibrated values. The mechanisms behind these processes, however, remain poorly understood at a regional to global scale. It is necessary to examine the influence of microstructural parameters and hydraulic conductivity on the properties of forests using a variety of land-use types. Do you agree? Would you be able to apply spatial and temporal variability of corridor and application within the growing season and its environment? To achieve the research objectives of this study, you need to estimate applications for the growing season and construct the research setups.

   5. Add more papers related to the study. Explore the principles, structure, and applications of the model. Specifically, the number of components and the change in the patch area in the largest component is important in conditions of different changes in the area and the number of patches. In addition, the distribution of the area within one patch as well as the significance of the patch is also important. Construction must follow distance threshold principles and procedures.

   6. Please add more papers connected with a study. Research on the principle, structure, and application of the model. Namely, in the condition of different the changes in the area and number of patches, the number of components and the changes of patch area in the largest component, the area of individual patch and the distribution of the area of a single patch and the important value of the patch are important. Principles and methods of distance threshold, construction must be completed.

 

Constructive feedback;

This manuscript describes generic assessment criteria for the management of scenarios in Zones. You should add a paragraph describing the limitations of the behavioral patterns and calibrating an agent-based model of human activity patterns using the network construction with a database. Are there any specific areas that we can not apply in your area? Which are the characteristics that could prevent the application of this method in the research area?

The paper clearly indicates that it is reporting preliminary results towards map of a critical prospective analysis of the spatial Variation Based on MSPA in the study area in 2010, 2015, and 2020. Efforts to develop an empirically justified way of characterizing vegetation” can be seen in this paper. Information gathering, in the Discussion section, is also somewhat ad hoc and seems to have many attributes related to factors influencing residents’ access to and use of a large BI patch in the foreground pixel. Although they may capture a lot of information, dimensionality may be a problem. The paper, however, presents a practically viable technique, which I think can be very useful.

Authors can establish an empirically sound set of networks attributes of Ecological Economic Zone and associated health status that can be used in different kinds of research. I think, at its present form, with improvements suggested in the previous section, the paper makes an acceptable case for publication. I think this will generate research interest in improving the two components mentioned above. Specifically, the research includes soil on the basic effects of land use on terrestrial and aquatic ecosystems. Moreover, you must reconsider these points in the Discussion section:

1. Developing a set of simulation models coupled to each other to describe the Morphological Spatial Pattern Analysis (MSPA) is and mathematical morphological principles with processes happening in the study.

2. Evaluating the field and watershed-scale effectiveness of vegetation conservation practices, including theoretical and experimental research based on events that are overpredicted.

3. Exploring alternative management practices and options for further effectiveness improvement.

4. Optimizing the application timings and locations of conservation practices for maximized overall plot/watershed-scale effectiveness for a high ecological service value.

 

Summary:

The paper is well-organized, containing all of the expected components. The methodology is effective in attaining the object of this work. The authors provided a research background discussing the current state of environmental problems. This paper synthesizes the results from several primary literature papers to produce a coherent argument about a topic or focused description of a field. The conclusion is supported by the results presented in this paper. The text requires a small editorial correction, for example, all References in the text should be cited.

Author Response

Modification Instructions of《Analysising of Blue Infrastructure Network Pattern in the Hanjiang Ecological Economic Zone in China》

Dear reviewer and editor,

We earnestly appreciate it that your patient guidance is of great significance to our article. These suggestions and guidance are very important for the promotion of this article. Although the current article still has some shortcomings, but under the guidance of reviewer and editor, I think we will be able to get the article promoted a lot. These time, after receiving your email, we made a modifying based on your suggestions. In addition, the modified version will be sent to you in the form of an attachment, and the particular modification instructions will be attached to the post.

Wish you have a lovely day!

Best regards！

Pengfei He

2022-03-30

The detailed modification instructions were listed blow:

1. Please shorten the title of this publication. I would not use this title.

Answer：Thank you for your advice. We have shortened and modified the original title to 《Analysising of Blue Infrastructure Network Pattern in the Hanjiang Ecological Economic Zone in China》.

2. This mode can be fine-tuned using new data, especially temperature-related factors, as global warming accelerates. This will help us understand the environmental impact in the long run.

(1) Could the authors elaborate on their future plans for BI?

Answer：At the end of the Conclusions section, mainly around the limitations of this paper's research, we present our future research plan.

Firstly, when adopting MSPA and landscape connectivity analysis, characteristics of species and study area should be considered to determine the thresholds in an integrated manner.

 Secondly, Under the condition that the relevant data are available, the resistance factors should be included and the species dispersal characteristics should be considered to establish a more suitable resistance surface system.

Lastly, green infrastructure such as forest, grassland and cultivated land should be included in the construction of regional ecological network in order to provide comprehensive support for urban ecological development.

(2) Could they please elaborate on the Introduction?

Answer：In the context of rapid urbanization and global climate change, there is rare evidence proving the value and ability of Blue infrastructure to provide ecosystem services for cities and humans. We clarify key terms and their related concepts. On the basis of clarifying the relevant concepts, a case study of the Hanjiang Ecological Economic Zone in China to explore the significance of constructing a BI network from the perspective of landscape ecology. The details are as follows:

Introduction

In the context of rapid urbanization and global climate change, cities are facing many challenges such as rapid climate change, frequent flooding and increased water pollution. As a sustainable development strategy to address the urban environmental crisis and improve urban resilience, BI can play parts in such ecosystem services as supporting, regulating, provisioning and culture for cities and residents [1]. BI is a network of aquatic ecosystems consisting of spaces and corridors covered by water bodies, which includes natural or semi-natural water bodies and artificially constructed water-bond surfaces [2]. Such as Rivers, Lakes, Wetlands, Natural waters coast, Reservoirs, Artificial river embankment, Artificial water course, etc. BI contributes to water purification, flood protection and overall climate change adaptation as well as provides various kinds of cultural ecosystem services [3-6]. Apart from it, BI also play a key role in improving public health and people's well-being, promoting regional economic development and maintaining urban ecosystem services [7-9]. However, the installation and use of BI depending on the different development needs of the city, such as alleviating urban flooding [10,11], promoting physical and mental health [12,13], and enhancing biodiversity [14,15], which are ultimately reflected in the design of urban BI. The gray infrastructure such as hardened roads, constructions and drainage pipes which is common in the city is significant for urban development. So is BI.[3]. However, there is rare evidence proving the value and ability of BI to provide ecosystem services for cities and humans [16].

In the last two decades, the concept of green infrastructure has gained attention.  Apart from BI, Green infrastructure also refers to natural or artificial green spaces such as forests, grasslands, plant and animal habitats, and farms that provide a wider range of ecosystem services to better address environmental issues and support human well-being [17-19]. Therefore, BI is placed in the broader framework of green infrastructure research, called blue-green infrastructure [20,21]. However, as the urbanization is gaining momentum, human activities is more frequent and the urban construction space is increasingly expanding, the water pollution is more serious [22]. Against this backdrop, BI is exposed to fragmentation and the connection is weakening, and it also faces the difficulties that great area loss and quality degradation [23]. this phenomenon is hided in the framework of broad discussion of green infrastructure. Therefore, it is imperative to study the spatial and temporal changes of BI network patterns in the context of rapid urbanization in order to assess the current status of urban BI. Therefore, the targeted protection and restoration for the sustainable functions of BI ecosystem services can be carried out.

Currently, for BI study, the main study focuses are on its ecological service functions [24-26], value estimation [26,27], protection and space optimization [28,29]. the perspectives are mainly from environmental science, land management, ecology and so on. According to the study results, BI is deeply affected by urbanization and its ecological function is weakening greatly. Besides, the number and quality of BI are dropping, which mainly attribute to the great need from Grey Infrastructure, the dramatic climate change and the serious pollution in organic and inorganic compounds. In this context, to build an urban BI network based on the natural capital is seen as the most profitable protection strategy for urban development and a key breakthrough to improve urban ecological service [30-32]. 

These years, some experts have made researches on ecological networks with different kinds and dimensions from the point of view of landscape ecology theory. Several methods and models were tried in the research process, in which Morphological Spatial Pattern Analysis(MSPA) and Minimum Cumulative Resistance(MCR) are widely adopted [33-35]. MSPA method identifies ecological regions with high landscape connectivity from the pixel level through land use raster data, thus, the selection of BI source can be more scientific. In the light of various resistance factors such as topography and human activities and so on, MCR model simulates the least cost path between sources by combining landscape connectivity index, graph theory and gravity model based on Geographic Information System (GIS). The existing studies have conducted in-depth explorations in source selection, resistance factor selection, corridor importance identification and network optimization [36,37], which provide an important reference for this study.

 With the high-quality development of China's economy, the increasingly prominent environmental problems have attracted political and academic circles. Especially under the guiding ideology of regional development integration proposed by the Chinese government, the research on ecological economy at the scale of river basins has become a frontier hotspot, such as the Yangtze River Delta [38] and the Huaihe River Ecological and Economic Belt [39,40]. However, the crucial strategic value of the Hanjiang Ecological Economic Zone as an important link between the economic development of the central and western regions of China has still not received sufficient attention. The Hanjiang Ecological Economic Zone in China has a developed water system with dense rivers and lakes. With the implementation of the Central Line Project of South-to-North Water Diversion in December 2014, the flow of the Hanjiang river’s middle and lower reaches is reduced and the water level is lowered during the dry period of the river. The ecological environment has been exposed to strong negative influence [41]. In order to ensure the water volume of the Hanjiang river’s middle and lower reaches, the plan of cascade reservoir and the Yangtze river diversion to Hanjiang river are also carried. In spite of it, the Hanjiang river’s middle and lower reaches are still in shortage of water resources, and the ecological environment is still facing continually deterioration [42]. Besides, In the background of rapid urbanization, the built-up areas are continuously expanding outward, which will inevitably lead to the conflict between Eco-environmental protection and economic development, and bring serious challenges to the development of the region.

In this study, the Hanjiang Ecological Economic Zone is taken as the study area. The software platforms such as ArcGIS, ENVI, Guidos and Conefor are applied. MSPA method is adopted to identify and extract the core area that are important for species migration and energy exchange. And then Landscape Connectivity Index is selected to assess the landscape connectivity of the core area, and patches in the core area with a high patch importance index is regarded as BI sources. Based on MCR Model, it simulates the potential corridors and adopts Gravity Model to identify important corridors for the purpose of constructing a potential BI network in the study area. Thus the temporal and spatial pattern variation of BI network in the Hanjiang Ecological Economic Zone from 2010 to 2020 is explored. The research results can provide an important reference and basis for the optimization of BI network pattern in the Hanjiang Ecological Economic Zone, and give a reference for the planning of BI network pattern in other regions.

3. From 2010 to 2020, the MSPA was not applied effectively to the river basin. You need to identify and prioritize critical subwatersheds for BI conservation and management.

Answer：The results of the MSPA analysis provided the basic data for the subsequent study. The core area patches obtained through MSPA also need to be synthesized by the landscape connectivity index to determine the priority BI source sites for protection; therefore, the relevant contents are in the landscape connectivity index analysis chapter. The details are as follows:

3.2. Analysis on the Landscape Connectivity of BI

As seen in Table 4, the integral connectivity index of the Hanjiang Ecological Economic Zone falls from 2010 to 2015, but the number of BI network links and components rises. It means that the landscape fragmentation goes up during this period, and the integral connectivity of BI network goes down. However, the integral connectivity of the landscape gradually has increased since 2015, and the number of BI network links and components has decreased, which means landscape fragmentation is well curbed. The degree of potential connectivity between patches continually increases from 2010 to 2020 and the growth speed accelerates year after year. It implies that the potential connection degree between patches continues to increase. However, the landscape connectivity of the Hanjiang Ecological Economic Zone is still at a low level in an overall view, and the core area with the functions of bridging or stepping stone accounts for a low proportion. In addition, The advancement of urbanization has led to the reduction of the core area around the city and the weakening of the connectivity between patches. The core patches with more important landscape connectivity are mainly distributed in the Hanjiang river’s middle and lower reaches, such as the Hanjiang river’s main stream, the Changhu Lake, the Tangbai River, the Danjiangkou Reservoir, etc. They are particularly important to improve the survival rate of biological species during the migration process and the improvement of ecological service value. As a whole, only a few key core area patches in the study area exert profound influence on landscape connectivity, so these patches are the priorities for BI network planning.

4. Alternative management practices must be predicted using the MCR to achieve adequate water quality and quantity. As shown in Table 6, you identified nodes. Do you know how to interpret them? The interaction between vegetation and runoff generation, sediment yield, and soil column impact the parameters selected for calibration and the calibrated values. The mechanisms behind these processes, however, remain poorly understood at a regional to global scale. It is necessary to examine the influence of microstructural parameters and hydraulic conductivity on the properties of forests using a variety of land-use types. Do you agree? Would you be able to apply spatial and temporal variability of corridor and application within the growing season and its environment? To achieve the research objectives of this study, you need to estimate applications for the growing season and construct the research setups.

Answer：(1) In this paper, the selection and ecological significance of BI nodes are explained in the method section. The content is as follows:

According to the results of the MSPA analysis, this paper selects the core area ≥20hm2 as the landscape connectivity evaluation object [48]. Based on the software of Conefor and the connectivity distance parameter is comprehensively determined through the statistical analysis of the calculation results under different distance thresholds. In this paper, the diffusion distance parameter is 10000m, meanwhile the probability of connectivity is 0.5. The large-scale patches connectivity was evaluated quantitatively from 2010 to 2020, and the patches with dPC ≥1 is taken as BI sources for ecological protection.

(2) I agree with your point, therefore at the end of the Conclusions section, we have added to the future research proposal an integrated analysis of the ecological network of the study area using various land use types.

Lastly, there is no comprehensive analysis on the ecological network of the study area through combining other land use types. so for this paper, green infrastructure such as forest, grassland and cultivated land should be included in the construction of regional ecological network in order to provide comprehensive support for urban ecological development. In the future, our team will conduct follow-up research from the above aspects.

(3) In this study, because the study area is subject to frequent precipitation in spring and summer under the influence of rainy season, it is easy to cause uncertainty in the boundary of water bodies, and the remote sensing images have large clouds, while the remote sensing data acquired in autumn and winter with less rainfall can effectively avoid these effects. However, the spatial and temporal variation of corridors in different seasons should also be the focus of research in the subsequent constructed woodland ecological network studies.

5. Add more papers related to the study. Explore the principles, structure, and applications of the model. Specifically, the number of components and the change in the patch area in the largest component is important in conditions of different changes in the area and the number of patches. In addition, the distribution of the area within one patch as well as the significance of the patch is also important. Construction must follow distance threshold principles and procedures.

Answer：Agree with your point of view, we introduce the application of the model in the introduction section, describe the main process of threshold setting in the method section, and detail the rationale of the method and the principles of threshold setting in the discussion section. The details are as follows:

In the introduction section:

These years, some experts have made researches on ecological networks with different kinds and dimensions from the point of view of landscape ecology theory. Several methods and models were tried in the research process, in which Morphological Spatial Pattern Analysis(MSPA) and Minimum Cumulative Resistance(MCR) are widely adopted [33-35].

MSPA method is adopted to identify and extract the core area that are important for species migration and energy exchange. And then Landscape Connectivity Index is selected to assess the landscape connectivity of the core area, and patches in the core area with a high patch importance index is regarded as BI sources. Based on MCR Model, it simulates the potential corridors and adopts Gravity Model to identify important corridors for the purpose of constructing a potential BI network in the study area.

In the method section:

MSPA is a raster data handling method based on principles of mathematical morphological proposed by Vogt and other experts and scholars, which can accurately identify the type and shape of the landscape, and then visualize the spatial distribution of the landscape, offering a new basis for the choice of BI sources [44]. In order to give full play of MSPA method, ArcGIS is used to set the extracted water body as the foreground, and other sections as the background. Then, the data is converted into a 30m×30m Tiff format binary raster data file. Finally, based on Guidos Toolboxs software, seven types of non-overlapping landscapes are obtained by taking MSPA method with eight-neighbor connectivity and thirty-meter edge width for this analysis.

MCR (4) is a common method to simulate ecological corridors, which can evaluate the min cost path between sources to determine the optimal path for species migration and dispersal [49]. MCR Model has the characteristics of simple construction, extension of elements, and wide application. It can simulate the extent and direction of species dispersal by avoiding various external disturbances [50]. Choosing the source and establishing the ecological resistance surfaces are the keys to MCR Model. Therefore, for model construction, it is attached great importance to the selection of appropriate resistance factors to construct the resistance surface system. Considering factors such as natural conditions and human interference and the condition of the study area as well as referring to the suggestions from the experts and the results of the existing research, the comprehensive resistance surface system is established, which includes five resistance factors: elevation, slope, landscape use types, distance from road and distance from the construction land(Table 2). These factors are confirmed from the perspective of topography, the types of the landscape and human activities and so on. Besides, the grading index and resistance value of each resistance factor are also confirmed. Higher resistance values indicate more difficulty of species migration and diffusion. Furthermore, determination of resistance factor weights by AHP. Based on ArcGIS 10.8 software, the resistance factor is assigned attribute and converted into raster data, and the comprehensive resistance surface is obtained by using the raster calculator, so the key data of model is achieved.

Using the Cost Distance analysis tool in ArcGIS is applied to calculate the min cost distance between pixels by using BI source and resistance surface raster images, and then the min resistance path between sources is calculated by using cost path analysis tool, thereby the potential corridors between BI sources is generated.

In the discussion section:

1. The choice of research scale is important when using MSPA to analyze raster images of the landscape, because the results of MSPA analysis are closely related to the variation in granularity. Therefore, it is very important to choose an appropriate analysis scale for MSPA research [51,52]. Different image raster sizes in the same study area will change the analysis results accordingly [53]. For example, an increase in the image raster size of the study area may lead to the disappearance or classification of the original smaller area patches into other categories, like small Cores may be reclassified as Islets, some Bridges may become Branchs, and some Branchs may disappear. The study area in this paper is the Hanjiang Ecological Economic Zone. It means that the study range is large and larger image raster size can cause some small patches with good connectivity to be lost or change categories types [35,52]. This is why the particle size at the urban scale is set to 30m. After several tests of the threshold, this granularity can better maintain the original data characteristics, but the reasonableness of the scale still needs further study.

In addition, the edge width needs to be set during the MSPA landscape pattern analysis, and the setting of the edge width represents the size of the extent of the edge effect produced by the patches. the edge width affects the impacted range of the edge effect of the patch. For example, an extension of the edge width will result in the reduction of the core area of the landscape type and the increase of the non-core elements, so the size of the edge width has a greater impact on MSPA analysis results [54]. Edge effect is an important concept in ecology, which is of great significance to ecological process, species protection, and habitat protection. It must be considered in the functional planning of nature reserves [55]. In this study, Considering the area scale and data accuracy, the edge width threshold is set to 1. Since the input image raster size is 30m× 30m, the edge effect is 30m. However, the edge effect is pertinent and complex. The width of the edge effect varies with different landscape properties, patch shapes, and different research objects [56]. As a result, the width of the edge effect set in this study is not applicable to some specific species and the characteristics of the protected species and the nature and shape of the study area landscape also need to be considered when setting the edge effect width.

2. For the reasons that different connectivity distance thresholds will have different impacts on the important value of patches, the betweeness centrality and the landscape’s connectivity, it is necessary to set the connectivity distance threshold when calculating the landscape connectivity based on PC and IIC [57,58]. For example, a patch is considered connected only if the distance between patches is less than a set threshold, and the opposite is not connected. In this context, this paper determines the connectivity distance threshold by comprehensively analyzing the following factors. Namely, in the condition of different distance threshold, the changes in the area and number of patches, the quantity of components and the changes of patch area in the biggest component, the area of individual patch and the distribution of the area of a single patch and the important value of the patch [59]. When the connectivity distance threshold is 10000m, the area and number of connected patches vary greatly, and both large-area patches and small-area patches show higher important values. In addition, in order to ensure the comparability of data between years, the connectivity probability is set to 0.5. However, the setting of the connectivity distance threshold needs to take into account the dispersal distance of species, which often varies among species. Therefore, the scientific determination of this distance threshold needs more argumentation.
3. MCR Model is used to simulate the potential BI corridor. The selection of resistance factors is the basis of BI network construction, and the construction of the resistance surface system is still controversial [35], through the study on relative researches and consulting experts, the method of constructing resistance surfaces by selecting resistance factors from topography, landscape types and human activities in this paper is scientific. Due to the lack of detailed research data, this paper does not take the influence of the living habits of different species and the distribution of settlements and other factors on the construction of the resistance surface into consideration. In addition, the weight of resistance factors is subjective because there is no data on the relationship between species dispersal and resistance factors [60]. it needs to be further studied and discussed in more detail in the follow-up.
4. This manuscript describes generic assessment criteria for the management of scenarios in Zones. You should add a paragraph describing the limitations of the behavioral patterns and calibrating an agent-based model of human activity patterns using the network construction with a database. Are there any specific areas that we can not apply in your area? Which are the characteristics that could prevent the application of this method in the research area?

Answer：Thanks for the reminder from the reviewer. According to the reminder from the reviewer, we added the Research limitations in the conclusion section.

This paper reveals the spatial and temporal evolution characteristics of the BI network pattern in the Hanjiang Ecological Economic Zone during 2010-2020, and the results can provide references for optimizing the BI network and formulating BI protection policies in the study area. However, there are still some limitations in this study.

Firstly, when adopting MSPA and landscape connectivity analysis, the thresholds has a large impact on the analysis results, and the scientific setting of thresholds still needs further exploration.

Secondly, although this paper provides a basic framework for resistance surface construction, it still needs to be optimized. The selection of resistance factors is not comprehensive enough, and the weight of resistance factors is also subjective.

 Lastly, there is no comprehensive analysis on the ecological network of the study area through combining other land use types.

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors carefully revised the manuscript. All my concerns have been properly answered. I recommend this manuscript for publication in the journal such as "Water".

Author Response

Dear reviewer，    

      We earnestly appreciate it that your patient guidance is of great significance to our article. These suggestions and guidance are very important for the promotion of this article. I think we will be able to get the article promoted a lot. 

      Wish you have a really nice day!

                                                                                           

Reviewer 2 Report

 The paper has been improved based on my suggestion. Thank you.

Author Response

Dear reviewer，    

      We are much obliged to you for your constructive suggestions and patient guidance in the previous version, these suggestions and guidance are very important for the promotion of this article. 

      Wish you have a lovely day!

      Best regards！