Natural Dose of Blue Restoration: A Field Experiment on Mental Restoration of Urban Blue Spaces

Round 1

Reviewer 1 Report

Please find a document with all my comments attached.

Comments for author File: Comments.pdf

The paper will need to be checked for spelling and phrasing errors before publication.

Author Response

We would like to thank you for careful and thorough reading of this manuscript and for the thoughtful comments and constructive suggestions, which help to improve the quality of this manuscript. Here is a point-by-point response to your comments and concerns. All page and line numbers refer to the revised manuscript file.

OVERALL IMPRESSION

This is an empirical study investigating the restorative blue space effects at 4 different sites in Japan. Overall, the study is very well designed, the methodology is very well justified and I believe the findings would be a valuable contribution to the field.

However, I have several issues regarding the positioning of the study within the current evidence and its presentation, mainly in the introduction and discussion sections. Regarding the methodology, I suggest that the authors mention in detail the instruments they used for measuring environmental factors, so that the study can be replicated, and proceed to an analysis of the effects of perceived greenness on the restorative measures. Several statements in the discussion do not directly derive from the findings of the study. The paper will also need to be checked for spelling and phrasing errors before publication.

Below is a section-by-section list of my comments.

 Point 1: Line 13: “It is widely known the health benefits of urban blue spaces (UBS) for urban residents.” It appears to me that this sentence is grammatically incorrect. I suspect that the authors meant to say “The health benefits of urban blue spaces (UBS) for urban residents are widely known.” However, if so, thinking about all the available current evidence and research gaps on the association between blue spaces and health, I believe this is a rather bold statement. I would suggest that this statement is moderated, mainly because of the research gaps in the field around the underlying physiological mechanisms of the blue space health benefits.

 Response 1:

Thank you for point this out. We apologize for this ill-considered statement. In response to this comment, we have changed this sentence to a more conservative statement.

Details as follows:

(Abstract) Urban blue spaces (UBS) have been found to be beneficial to people's mental health. Yet, the empirical evidence of how and why different types of urban blue spaces could promote the resident’s mental health is still limited.

 

Point 2: Line 18: What are the three UBS types of UBS under investigation? Adding the types of UBS in parenthesis would aid understanding.

Response 2:

Thank you for pointing this out. We had added three types of UBS in parenthesis of the current version.

Details as follows:

(Line 14-17) The effects of two exposure behaviors (15 min of viewing and 15 min of walking) on psychological recovery in three different urban blue spaces settings (the Urban River, Urban Canal, and Urban Lake) were investigated in a field experiment.

 

Point 3: Line 33: “built environment” rather than “environment built”.

Response 3:

Thank you for pointing this out. This error has been corrected.

Details as follows:

(Line 31-33) Rapid urbanization and unhealthy lifestyles are threatening human health and quality of life (Song et al., 2020). According to reports, there is a link between the built environment and health problems.

 

Point 4: Lines 63-64: “Although cross-sectional, these field-based empirical studies provide direct evidence and a knowledge base for regional/national level green space health outcomes.” This is a nice statement, but there is surely longitudinal evidence (which is considered stronger and I think this is what this statement implies) around the restorative effects of green spaces. I suggest that the authors acknowledge the longitudinal evidence here.

Apart from these, there is also great heterogeneity in the field in terms of study designs and the measures of exposure and outcomes between different studies. I believe the authors should at least acknowledge this in section 1.2. as a limitation within the evidence of the green space restorative effects.

Response 4:

Thank you for this insightful comment.

However, another reviewer felt that this subsection was not relevant to the study and strongly suggested that we remove it, and focus on the blue space debate. Therefore, we had to delete the Subsection 1.2 and discuss only the literature on blue spaces.

 

Point 5: Lines 92-94: The authors state: “In particular, empirical studies provide a more direct understanding of how blue space affects mental recovery than city/region level studies; and are more realistic and reliable relative to laboratory settings.” Surely empirical studies may be a better representation of reality, however, there is an evidence-base from other study designs as well. The authors should acknowledge this evidence base and justify their statement. Some potential references of other study designs:

Associations between growing up in natural environments and subsequent psychiatric disorders in Denmark (Engemann et al. 2020)

A population-based retrospective study of the modifying effect of urban blue space on the impact of socioeconomic deprivation on mental health, 2009–2018 (Georgiou et al. 2022)

The Application of Wearable Technology to Quantify Health and Wellbeing Co-benefits From Urban Wetlands (Reeves et al. 2019)

Physical and mental health effects of repeated short walks in a blue space environment: A randomised crossover study (Vert et al. 2020)

Health-Related Effects of Short Stays at Mountain Meadows, a River and an Urban Site-Results from a Field Experiment (Arnberger et al. 2018)

The impact of nature exposure on body image and happiness: an experience sampling study (Stieger et al. 2020).

Response 5:

Thanks for this helpful comment and the useful reference provided. We have rewritten this statement and added the relevant citations.

Details as follows:

(Line 91-99) Although previous studies at the city/regional level have a solid evidence base (e.g. Engemann et al., 2020, Georgiou et al., 2022, Stieger et al., 2022), however the empirical studies provide a more direct understanding of how blue space affects mental recovery; and are more realistic and reliable relative to laboratory settings (Reeves et al., 2019). Furthermore, the findings could provide urban planners/managers with important knowledge and insights on natural interventions that promote the health of urban residents.

 

Point 6: Lines 119-120: The authors state “The restorative outcomes of these indicators are usually measured using questionnaires”. This is indeed part of the equation, but as mentioned in the above comment, there are studies that also use clinical/administrative data or several types of sensors. The authors should acknowledge this and justify the need for more empirical studies along with this evidence.

Response 6:

Thank you for this helpful comment. We have added this potential limitation to the Limitations subsection.

Details as follows:

(Line 634-636) Eighth, outcomes such as clinical/administrative or sensor data could be used to reflect the psychological restoration in more empirical studies.

 

Point 7: Lines 136-137: The authors state that fountains are not considered water bodies based on Volker et al. 2016. However, Volker et al. 2016 states “Fountains and other artificial water features are included in one of the last three categories depending on their appearance. Urban blue elements can be permanent or impermanent and natural or artificial.” This is in line with research showing that fountains may in fact offer similar benefits to other types of blue space. I suggest that the reference to fountains as non-waterbodies is removed. For instance:

Investigating the Effects of Exposure to Natural Blue Elements on the Psychological Restoration of University Students (Amirbeiki et al. 2020)

The role of blue and green infrastructure in thermal sensation in public urban areas: A case study of summer days in four Czech cities (Lehnert et al. 2020).

Response 7:

Thank you for your careful examination of our manuscript, and we apologize for the error. However, in response to this comment and the Point 9, we have rewritten this paragraph and removed the citation regarding Volker et al. (2016).

The current version as follows:

(Line 140-152) The blue spaces with different characteristics were selected for field experiments, in the urban environment, for this study. Besides, owing to the study setting, we primarily selected freshwater blue spaces (i.e., coastal blue spaces such as harbors and water-fronts were not included). Although the spatial coverage of freshwater is much smaller than that of marine environments, investigating freshwater blue spaces is of great value in promoting broader urban health, as more than 50% of the global population lives within 3 km of freshwater (McDougall et al., 2020). Besides, Poulsen et al. (2022) highlighted that the health effects of non-coastal freshwater blue spaces remain underexplored. Moreover, little is known about the potential of different freshwater blue space types, such as lakes, rivers, and canals, to contribute to health and well-being (McDougall et al., 2022). Therefore, three freshwater UBS commonly found in urban environments (an urban river, urban canal, and urban lake) were selected as sites for investigation.

 

Point 8: Line 146: “What important” does not fit.

Response 8:

Thank you for point this out. We changed the term to "Moreover" in the current version.

Details as follows:

(Line 148-150) Moreover, little is known about the potential of different freshwater blue space types, such as lakes, rivers, and canals, to contribute to health and well-being (McDougall et al., 2022).

 

Point 9: Lines: 148-150: The authors have stated in lines 137-139 that the selection of the study sites was based on the 4 categories of blue space types by Volker et al. 2016. However, here the authors state “three freshwater UBS commonly found in urban environments (urban rivers, urban canals, and urban lakes) were selected as sites for investigation”. However, both rivers and canals are in category 2 of flowing inland water bodies from Volker et al. 2016. These are two contrasting statements. The authors should justify the selection of the sites based on one of these.

Response 9:

Thank you for this insightful comment. We agree that these are two distinct selection criteria and statements, so we removed the citation from Volker et al. (2016) and used the recommendation from McDougall et al. (2022) as the selection criteria for the sites in this study.

Details as follows:

(Line 140-152) The blue spaces with different characteristics were selected for field experiments, in the urban environment, for this study. Besides, owing to the study setting, we primarily selected freshwater blue spaces (i.e., coastal blue spaces such as harbors and water-fronts were not included). Although the spatial coverage of freshwater is much smaller than that of marine environments, investigating freshwater blue spaces is of great value in promoting broader urban health, as more than 50% of the global population lives within 3 km of freshwater (McDougall et al., 2020). Besides, Poulsen et al. (2022) highlighted that the health effects of non-coastal freshwater blue spaces remain underexplored. Moreover, little is known about the potential of different freshwater blue space types, such as lakes, rivers, and canals, to contribute to health and well-being (McDougall et al., 2022). Therefore, three freshwater UBS commonly found in urban environments (an urban river, urban canal, and urban lake) were selected as sites for investigation.

 

Point 10: Overall methodology: The methodology of the paper is well written and justified. However, I believe there is a missing section describing the instruments that were used to measure the environmental factors. This will allow for the study to be replicated. The authors need to add this section.

Response 10:

Thank you for this comment. In the last paragraph of the Subsection 2.3, we describe in detail the measurements for the natural elements of the environment (blue, green).

Details as follows:

(Line 198-206) Finally, different levels of perceived natural elements (i.e., green, blue) may lead to different psychological recovery effects (Kaplan, 2001, Ulrich et al., 1991, White et al., 2010). Therefore, based on previous studies (Jiang et al., 2021, White et al., 2010), two additional questions were set to ask participants about their perception of natural element levels in the three UBS: "To what extent can you perceive the level of green here? including various vegetation and aquatic plants", and "To what extent can you perceive the proportion of water bodies in the whole site here?" Participants were asked to respond to these two questions using a Likert scale of 1 (not at all) to 7 (very high). The overall perceived natural element level was the average of these two items.

 

Point 11: Line 286: “between for” one of the two words here.

Response 11:

Thank you for your careful examination of our manuscript, and the error has been corrected.

Details as follows:

(Line 290-292) One-way ANOVA results showed no statistically significant differences for four psychological indicators between males and females in T1 time point (Appendix Table A), indicating that it was acceptable to analyze females and males together.

 

Point 12: Lines 288-291: Sentence has no verb.

Response 12:

Thank you for your careful examination of our manuscript, and the error has been corrected.

Details as follows:

(Line 292-295) Besides, no statistically significant differences between sites for each psychological indicator before the intervention (T1) were found: SVS (F(3,160)=0.211, p=0.889), ROS (F(3,160)=1.120, p=0.343), PANAS POS (F(3,160)=0.907, p=0.439), PANAS NEG (F(3,160)=0.371, p=0.774).

 

Point 13: Section 3.4: Surely understanding the perceived greenness of each sites has some value. But did the authors also look at the potential effects that perceived greenness may have on their several mental restoration scales? I believe this is a missed opportunity to identify whether the effect comes indeed from the “blue space” rather than “green space” or the combination of these environments. I suggest that the authors do this and reflect upon the results.

Response 13:

Thank you for this helpful comment.

In fact, the discussion of restorative mechanisms for these spaces is precisely the topic we wish to discuss in Subsection 4.3 of the manuscript. In Subsection 4.3 we discuss an interesting result found in this study, that is, that differences in psychological restoration in these blue spaces may arise from differences in the dose of environmental natural elements (blue, green).

Details as follows:

(Line 528-547) Similarly, differences in the restorativeness of the three UBS were found in the results of this study: the urban river as well as the urban lake were the most restorative, while the urban canal was less restorative. Reviewing the components of these environmental settings, UR is a blend of natural and artificial environments, as many aquatic plants and street trees are planted; UL is a large artificial lake; and UC is an artificial waterway located in the built-up area, which has a smaller water body area compared to UL. According to previous studies, higher perceived blue space and perceived green space within settlements are significantly associated with higher restorative quality (Dzhambov et al., 2018); perceived restorativeness increases with increasing naturalness in green space (Carrus et al., 2013); and there is a positive correlation between restorativeness scores and the proportion of water in the scene (White et al., 2010). These findings all affirm that there is a positive relationship between the dose of natural elements in the scene and the intensity of the restorative experience (Jiang et al., 2014; White et al., 2010).

Along these same lines, arguably, the higher the overall dose of visible/accessible natural elements in an environment, the higher the restorative quality of the environment, whether these natural elements are green (vegetation) or blue (water bodies), which consistent with the Biophilia Hypothesis (Wilson, 1993). Accordingly, it appears possible to propose the concept of a "natural health dose" to emphasize the complementary effects of blue and green elements (Figure 9), which could explain why health outcomes may be different for different restorative environments.

However, on the other hand, as stated in this review, we did not separately discuss the potential effects of green elements on psychological restoration, as this was not the main purpose of this study and was limited by the current space. Nevertheless, we believe that the current results, as well as the discussion, are consistent with the purpose of this study: (Line 129-132) "Therefore, specifically, the aim was to investigate the effects of the two behaviors "viewing" and "walking" on psychological indicators (subjective vitality, emotions, and perceived restoration) in different UBS, and to discuss the reasons for the differences (if any exist) in the restorative effects of different types of UBS."

 

Point 14: Line 441: “is” does not fit in the sentence here. Same goes for lines 443 and 445 for “have”.

Response 14:

Thank you for your careful examination of our manuscript, and the error has been corrected.

Details as follows:

(Line 448-454) First, we investigated the effects of the four environmental settings on the subjects by using multiple psychological measures, which include Subjective vitality (SVS) as an indicator of well-being and has been conceptualized as a positive psychological state (Rouse et al., 2015), the Restorative Outcome Scale (ROS) as a reliable scale developed based on previous research and observations of the restoration phenomenon (Bielinis et al., 2018), and improvements in emotion (PANAS) that have been consistently linked to psychological well-being (Tugade et al., 2004).

 

Point 15: Line 453-454: It is apparent through the results of the perceived greenness that the sites with the highest restorative effects also had the highest perceived greenness. Therefore, can we really conclude that what the results reflect is only because of the existence of the water element in these places? Disentangling blue for green space is indeed a limitation in the entire field of environmental epidemiology and probably the only area where these two spaces can be separated may be a lab. However, having measured both exposures, I believe that in this case there is a missed opportunity to address this. The authors should at least acknowledge that the effects their study shows may also be explained through the existence of greenness in the study sites. Therefore, the statement “the results confirm that the restorative benefits of UBS are similar to those of other green environments (e.g., urban parks, urban forests).” should be moderated.

Response 15:

Thank you for this insightful comment. We would like to provide some explanation for this statement.

First of all, as mentioned in this comment that the site with the highest restoration effect has the highest perceived greenness (the urban river, where the perceived blueness is very low). However, in fact, the other site with the highest restoration had the highest perceived blueness (the urban lake, with low perceived greenness). Moreover, the overall perceived natural element levels were the same for both sites (no significant difference). Therefore, the conclusion we wish to propose here is that the mental recovery at these sites stems from the overall perception of natural elements (blue and green) and not merely from "green" or "blue".

Second, perhaps the reviewer misunderstood the implication of this statement. In fact, this statement serves to review similar previous studies.

Original text: (Line 459-463) "In sum, all three UBS increased vitality, feelings of restoration, positive emotions, and decreased negative emotions; while the opposite was true for the urban setting. Consistent with the results of previous related studies (Mattila et al., 2020; Simkin et al., 2020; Tyrväinen et al., 2014), the results confirm that the restorative benefits of UBS are similar to those of other green environments (e.g., urban parks, urban forests)."

In the present study, we found that the experience in UBS resulted in improved vitality, feelings of restoration, positive emotions, and reduced negative emotions of participants. This positive effect is consistent with previous findings from Mattila et al. (2020), Simkin et al. (2020), and Tyrväinen et al. (2014) in green spaces (the urban parks and urban forests). Therefore, as a review of these literatures, we wrote this statement.

 

Point 16: Lines 472-473: The authors state that “Therefore, for subjects, unlike lakes in the wilderness or rivers in the forest, blue spaces in urban areas are less likely to feel threatened.” This may indeed be the case, but none of the sites under investigation were in the wilderness. I find it difficult to see how this statement derives from the findings.

Response 16:

Thank you for this comment. Indeed, as stated in this comment, none of our survey sites were in the wilderness nor were such comparisons made. However, this statement serves as a discussion of the possibility of why UBS leads to mental restoration based on the previous research (Ulrich et al., 1991), rather than a current result-based discussion.

Here, we discuss four possible explanations.

Details as follows:

(Line 474-492) So far, there has been a great deal of discussion about the causes of the mental restoration of blue space.

One possible interpretation is from the perspective of evolutionary psychology, blue space provides humans with the natural space and resources (e.g., fresh water, food) they need to survive (Luo et al., 2023).

Second, according to Ulrich et al. (1991), if an individual encounters a natural environment that is not threatening, there will be stress-reducing and restorative effects. The three UBSs we selected are all common types of water bodies in Japanese cities and are used daily by local residents in these areas. Therefore, for subjects, unlike lakes in the wilderness or rivers in the forest, blue spaces in urban areas are less likely to feel threatened.

Third, similar to numerous discussions of the restorative nature of green space, unconscious attention or fascination can lead to restorative impacts (Ulrich et al., 1991; Kaplan, 2001). Thus, unlike the marine blue space, the freshwater blue space selected for this study was "soft" in that the water flow was, for the most time, gentle, with no rough waves to attract the subjects' voluntary attention, which allowing participants brains to relax and recover from mental fatigue. This can be particularly beneficial for individuals who are experiencing stress or mental exhaustion.

Finally, Subiza-Pérez et al. (2019) stated that the sublime, a sense of connection to something larger than ourselves, can also be experienced even in daily natural environments like urban blue spaces which can promote feelings of awe and wonder, which have been linked to positive emotions and well-being.

 

Point 17: Lines 475-479: The authors state that “Therefore, for subjects, unlike lakes in the wilderness or rivers in the forest, blue spaces in urban areas are less likely to feel threatened.” As in the above comment, this may indeed be the case, but the study does not compare between urban and marine environments. The authors need to justify how this statement derives from their findings.

Response 17:

Thank you for this comment.

Indeed, as stated in this comment, none of our survey sites were in the wilderness nor were such comparisons made. However, this statement serves as a discussion of the possibility of why UBS leads to mental restoration based on the previous research (Ulrich et al., 1991), rather than a current result-based discussion. The discussion of this comment is the same as the Point 6.

 

Point 18: Lines 480-483: The authors state that “Subiza-Pérez et al. (2019) stated that the sublime, a sense of connection to something larger than ourselves, can also be experienced even in daily natural environments like urban blue spaces which can promote feelings of awe and wonder, which have been linked to positive emotions and well-being.” The link of this statement to the findings of this study needs to be mentioned/discussed here.

Response 18:

Thank you for this helpful comment. In the revised version, we have added an explanation of the relationship between this statement and the results of this study.

Details as follows:

(Line 489-495) Finally, Subiza-Pérez et al. (2019) stated that the sublime, a sense of connection to something larger than ourselves, can also be experienced even in daily natural environments like urban blue spaces which can promote feelings of awe and wonder, which have been linked to positive emotions and well-being. For example, in this study, the urban lake has a large body of water, and this large natural element in an urban environment may have surprised the subjects and evoked a sense of sublimity, thus leading to mental restoration.

 

Point 19: Lines 496-501: The authors state that “the health effects of physical activity typically come from a reduction in blood pressure and heart rate. However, a previous study showed that no positive cardiovascular effects were observed for the walking behavior in the blue space (Vert et al., 2020). Therefore, we speculate that unlike the green space, the walking behavior in the UBS had a limited effect on physical health and therefore led to the same psychological recovery outcome as the 15 min viewing.” Yes, but the comparison between blue and green spaces is a bit far-fetched under the current justification. Is there evidence that walking in green spaces increases reduces blood pressure and heart rate? Also, there is compelling evidence that exposure to blue space environments increases physical activity. The authors should position their findings within the current literature and discuss their statement more here.

Response 19:

Agree with this comment. However, we would like to provide some explanation.

First, there are a number of papers that have demonstrated that walking in green space can lower blood pressure and heart rate.

For example:

-Pratiwi, P. I., Xiang, Q., & Furuya, K. (2020). Physiological and psychological effects of walking in urban parks and its imagery in different seasons in middle-aged and older adults: Evidence from Matsudo City, Japan. Sustainability, 12(10), 4003.

-Lin, W., Chen, Q., Jiang, M., Zhang, X., Liu, Z., Tao, J., ... & Zeng, Q. (2019). The effect of green space behaviour and per capita area in small urban green spaces on psychophysiological responses. Landscape and Urban Planning, 192, 103637.

-Song, C., Ikei, H., Kagawa, T., & Miyazaki, Y. (2019). Effects of walking in a forest on young women. International journal of environmental research and public health, 16(2), 229.

In response to this comment, we have now added these quotes to the discussion of green space in this statement.

Details as follows:

(Line 508-514) Second, the health effects of physical activity typically come from a reduction in blood pressure and heart rate. However, a previous study showed that no positive cardiovascular effects were observed for the walking behavior in the blue space (Vert et al., 2020). Therefore, we speculate that unlike the green space (Pratiwi et al., 2020; Lin et al., 2019; Song et al., 2019), the walking behavior in the UBS had a limited effect on physical health and therefore led to the same psychological recovery outcome as the 15 min viewing.

Second, the reviewer is right that there are indeed studies showing that blue spaces increase physical activity (e.g. Mechanisms of impact of blue spaces on human health: a systematic literature review and meta-analysis. International journal of environmental research and public health, 18(5), 2486). However, increased physical activity does not mean that walking in blue spaces leads to a significant reduction in blood pressure and heart rate. For example, a study by Vert et al. (2020) found that walking in blue space did not have a positive effect on cardiovascular data. In addition, due to space limitations, we were not able to expand the discussion any further, as this section is intended to provide three possible explanations for the non-significant difference between the results of T2 and T3 in this study.

 

Point 20: Section 4.3.: This is a nice section, but does it really discuss whether we should have more green or blue space? The title of the section would align better with the findings if there was indeed an analysis of the association between perceived greenness and the restorative effects. I suggest that the authors remove the “more green or blue?” from the section of the title, unless they add the respective analysis.

Response 20:

Thank you for this helpful comment. We followed this suggestion and removed the "more green or blue?" from the title.

 

Point 21: Lines 587-589: The authors state that “for the first time, the psychological recovery effects of short visits (15 min of viewing, 15 min of walking) in three different UBS settings through a field experiment, and our current results add to this research gap.” However, this is not entirely correct because there have been other similar studies looking at the effects of different types of blue spaces. For instance: https://pubmed.ncbi.nlm.nih.gov/32590148/ I suggest that the authors acknowledge existing evidence of similar studies, position the implications of their findings within the current literature, and moderate this statement.

Response 21:

Thank you for this helpful comment. We have changed this statement to a more conservative one.

Details as follows:

(Line 599-603) Finally, in terms of theoretical contributions, there is less direct health evidence on blue space (e.g. Vert et al., 2020), this study investigated the psychological recovery effects of short visits (15 min of viewing, 15 min of walking) in three different UBS settings through a field experiment, and our current results add to this research gap.

 

Point 22: Line 620: Similar to my comment in the introduction, this is contrasting to the statement the authors have made that fountains were not considered water bodies in this study.

Response 22:

Thank you for your careful examination of our manuscript, and the error has been corrected.

 

Additional clarifications

In addition to the above comments, all spelling and grammatical errors have been corrected. Besides, we checked the language of the manuscript again to ensure it was written correctly.

Once again, we thank you for the time you put in reviewing our paper and look forward to meeting your expectations. Since your inputs have been precious, in the eventuality of a publication, we would like to acknowledge your contribution explicitly.

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript covers an interesting topic, and the authors try to use a systematic framework to assess the mental restoration effects of three types of urban blue spaces across a 15-minute viewing and visiting. However, the method used by this study is not rigorous enough, and some sections should be revised. The detailed comments are as follows:

 

The section of Introduction
1. The study focused on urban blue spaces, in my opinion, the section of “1.2. Research on restorative effect of green space” is unrelated to the study. I suggest the authors to focus on the main aims and reviewing the literature to identify what is known and what is unknown about urban blue spaces.

 

The section of Methodology

2. The main concern in this section is that the visiting experiment is followed after the viewing procedure, so the third measurement of mental restoration (T3) is the cumulative outcome of two procedures of viewing and visiting. Therefore, it is not valid for the result “the mental restoration effects between walking and viewing among three UBS shown no significant differences”. This just indicates that after a 15 minute visit, there is no significant increase in mental restoration.

3. The second main concern is that, in the section of “2.4. Experimental procedure”, the authors conducted the experiments in autumn (October 10 to November 20) and spring (April 20 to May 20, 2022). You know, the area that the experiments are conducted has a distinct seasonality, yet, the authors do not consider the impact of seasons on the experimental results.

4. Resolution of all Figures in the text is very low.

5. Line 191-193: “Both scales consist of ten items (e.g., positive: enthusiastic, interested, excited; negative: distressed, upset, guilty).” Please list all items for both positive and negative aspects.

 

The section of Results

6. Although the author say “These findings all affirm that there is a positive relationship between the dose of natural elements in the scene and the intensity of the restorative experience” (Line 530-532), they do not check the relationship between the dose of natural elements and mental restoration in the section of results which just checks the difference in natural elements among the three types of urban blue spaces.

 

The section of Discussion

7. Line 450-451, “In sum, all three UBS increased vitality, feelings of restoration, positive emotions, and decreased negative emotions; while the opposite was true for the urban setting”, you mean the urban setting decrease the indicators of mental restoration. But in line 375, the authors say: “No significant effects were caused after viewing and walking in the urban setting”

8. Generally, the section of discussion should not include new figures or tables, I suggest the authors to delete Figure 9 or move it to the section of results.

9. Line 606-607, “Second, although we speculate that the effect of blue space on physiological health is limited, it is worthwhile to conduct more experiments to verify this”, this sentence is not clear.

10. I do not think the concept of natural health dose is a new finding, because, several existing literature has been discussed this issue, maybe different names, but similar meaning.

 

Author Response

We would like to thank you for careful and thorough reading of this manuscript and for the thoughtful comments and constructive suggestions, which help to improve the quality of this manuscript. Here is a point-by-point response to your comments and concerns. All page and line numbers refer to the revised manuscript file.

OVERALL IMPRESSION

The manuscript covers an interesting topic, and the authors try to use a systematic framework to assess the mental restoration effects of three types of urban blue spaces across a 15-minute viewing and visiting. However, the method used by this study is not rigorous enough, and some sections should be revised. The detailed comments are as follows:

 The section of Introduction

Point 1: The study focused on urban blue spaces, in my opinion, the section of “1.2. Research on restorative effect of green space” is unrelated to the study. I suggest the authors to focus on the main aims and reviewing the literature to identify what is known and what is unknown about urban blue spaces.

 Response 1:

Thank you for point this out. In response to this comment, we have removed subsection 1.2 and focused on the review of blue space.

 

The section of Methodology

Point 2: The main concern in this section is that the visiting experiment is followed after the viewing procedure, so the third measurement of mental restoration (T3) is the cumulative outcome of two procedures of viewing and visiting. Therefore, it is not valid for the result “the mental restoration effects between walking and viewing among three UBS shown no significant differences”. This just indicates that after a 15 minute visit, there is no significant increase in mental restoration.

Response 2:

Thank you for this comment. We agree with the reviewer's query about this description of the results. However, we would like to provide some explanation for this statement.

In fact, according to our experimental design (Figure 2), before conducting the walk session, the experimenter first rested in the waiting room for 2 min and then filled out the questionnaire (about 3 min). Thus, the total interval was 5 min, which was considered to be able to eliminate the effect of the previous viewing experiment. Therefore, after the implementation of such an experimental design, the walking session and the viewing session are usually considered as two separate recovery processes.

Accordingly, we wish to retain the current statement.

 

Point 3: The second main concern is that, in the section of “2.4. Experimental procedure”, the authors conducted the experiments in autumn (October 10 to November 20) and spring (April 20 to May 20, 2022). You know, the area that the experiments are conducted has a distinct seasonality, yet, the authors do not consider the impact of seasons on the experimental results.

Response 3:

Agree with this comment.

We did so because we did not recruit enough volunteers in the fall of 2021 and therefore supplemented with new volunteers in the spring of 2022. We admit that this could lead to potential bias, however, we had to do this in order to recruit enough volunteers and to complete the experimental data collection as soon as possible, otherwise we would have had to wait a whole year.

Although there were significant seasonal differences in the experimental regions, we chose the two seasons with the closest environmental conditions (humidity, temperature), i.e., spring and autumn, to conduct the experiment. We believe that this will reduce the negative effects of such seasonal differences to some extent.

 

Point 4: Resolution of all Figures in the text is very low.

Response 4:

Thank you for point this out. We are not sure if the graphics are compressed due to the format of the PDF, but we use high resolution images in our word documents.

 

Point 5: Line 191-193: “Both scales consist of ten items (e.g., positive: enthusiastic, interested, excited; negative: distressed, upset, guilty).” Please list all items for both positive and negative aspects.

Response 5:

Thank you for pointing this out. We have now listed all the items in the current version of the manuscript.

Details as follows:

(Line 194-197) The PANAS test contains two scales reflecting positive affect (PANAS POS) and negative affect (PANAS NEG). Both scales consist of ten items (Positive: Enthusiastic, Interested, Strong, Excited, Proud, Attentive, Inspired, Determined, Alert, Active; Negative: Distressed, Upset, Guilty, Scared, Hostile, Irritable, Ashamed, Nervous, Jittery, Afraid).

 

Point 6: Although the author say “These findings all affirm that there is a positive relationship between the dose of natural elements in the scene and the intensity of the restorative experience” (Line 530-532), they do not check the relationship between the dose of natural elements and mental restoration in the section of results which just checks the difference in natural elements among the three types of urban blue spaces.

Response 6:

Thank you for this thoughtful insight. Indeed, as stated in this comment, for reasons of space we did not further examine the relationship between natural dose and restorative intensity. However, this statement is actually intended to review previous studies (Jiang et al., 2014; White et al., 2010), which found that higher proportions of natural elements (green, blue) were associated with stronger perceived restorativeness. Therefore, we hope that a review of these two studies will support the findings of the present study that high levels of overall natural element (blue + green) doses lead to higher mental restoration.

Details as follows:

(Line 538-549) According to previous studies, higher perceived blue space and perceived green space within settlements are significantly associated with higher restorative quality (Dzhambov et al., 2018); perceived restorativeness increases with increasing naturalness in green space (Carrus et al., 2013); and there is a positive correlation between restorativeness scores and the proportion of water in the scene (White et al., 2010). These findings all affirm that there is a positive relationship between the dose of natural elements in the scene and the intensity of the restorative experience (Jiang et al., 2014; White et al., 2010).

Along these same lines, arguably, the higher the overall dose of visible/accessible natural elements in an environment, the higher the restorative quality of the environment, whether these natural elements are green (vegetation) or blue (water bodies), which consistent with the Biophilia Hypothesis (Wilson, 1993).

 

Point 7: Line 450-451, “In sum, all three UBS increased vitality, feelings of restoration, positive emotions, and decreased negative emotions; while the opposite was true for the urban setting”, you mean the urban setting decrease the indicators of mental restoration. But in line 375, the authors say: “No significant effects were caused after viewing and walking in the urban setting”.

Response 7:

I would like to thank the reviewer for the careful examination of our manuscript, and I apologize for not stating it clearly. What we wish to express here is that the urban environment did not significantly improve these mental indicators. In the revised version, we have rewritten this statement.

Details as follows:

(Line 459-461) In sum, all three UBS increased vitality, feelings of restoration, positive emotions, and decreased negative emotions; while the urban environment did not significantly improve these indicators.

 

Point 8: Generally, the section of discussion should not include new figures or tables, I suggest the authors to delete Figure 9 or move it to the section of results.

Response 8:

The reviewer is right. In general, the discussion section should not contain new images and tables, but this is generally for images and tables based on research data. Figure 9 in this manuscript is an image created to explain more clearly the concept of "Natural health dose", and this is common in many papers.

For example:

-Luo, S., Xie, J., & Furuya, K. (2023). Effects of perceived physical and aesthetic quality of urban blue spaces on user preferences–A case study of three urban blue spaces in Japan. Heliyon, 9(4).

-Wang, H., Xie, J., Luo, S., Ta, D. T., Wang, Q., Zhang, J., ... & Furuya, K. (2023). Exploring the Interplay between Landscape Planning and Human Well-Being: A Scientometric Review. Land, 12(7), 1321.

-Luo, S., Shi, J., Lu, T., & Furuya, K. (2022). Sit down and rest: Use of virtual reality to evaluate preferences and mental restoration in urban park pavilions. Landscape and Urban Planning, 220, 104336.

Therefore, we would like to keep Figure 9 in this subsection to explain the concept more clearly.

 

Point 9: Line 606-607, “Second, although we speculate that the effect of blue space on physiological health is limited, it is worthwhile to conduct more experiments to verify this”, this sentence is not clear.

Response 9:

Thank you for this comment.

This statement corresponds to the second speculation in Subsection 4.2:

(Line 508-514) 2) Second, the health effects of physical activity typically come from a reduction in blood pressure and heart rate. However, a previous study showed that no positive cardiovascular effects were observed for the walking behavior in the blue space (Vert et al., 2020). Therefore, we speculate that unlike the green space (Pratiwi et al., 2020; Lin et al., 2019; Song et al., 2019), the walking behavior in the UBS had a limited effect on physical health and therefore led to the same psychological recovery outcome as the 15 min viewing.

 

Point 10: I do not think the concept of natural health dose is a new finding, because, several existing literature has been discussed this issue, maybe different names, but similar meaning.

Response 10:

Thank you for this helpful comment.

Indeed, as mentioned in this comment, many similar concepts have been proposed. Therefore, we have deleted "as a new finding" to make the current statement more conservative.

Details as follows:

(Line 637-640) Finally, the concept of natural health dose is proposed. However, owing to space limitations, we did not discuss it in depth, and future studies could quantify the value of "dose" by using visual indices to discuss the complementary effects of green and blue.

However, we still wish to present this concept for following two purposes:

1) to summarize the current discussion on the overall natural elemental dose (blue and green);

2) to raise a new topic: (Line 607-612) Furthermore, the proposed "natural health dose" may raise an interesting discussion about whether there are other restorative elements in the urban environment other than green and blue elements. For example, some studies have found that cultural (Gallou et al., 2022) or man-made elements (Luo et al., 2022) can also trigger restoration, yet such restoration may need to be achieved through design methods or a degree of coherence with the environment.

 

Additional clarifications

In addition to the above comments, all spelling and grammatical errors have been corrected. Besides, we checked the language of the manuscript again to ensure it was written correctly.

Once again, we thank you for the time you put in reviewing our paper and look forward to meeting your expectations. Since your inputs have been precious, in the eventuality of a publication, we would like to acknowledge your contribution explicitly.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

I'd like to thank the authors for providing a revised version and building on the reviewers' feedback. The manuscript is now significantly improved and I'm happy to recommend it for publication. 

Reviewer 2 Report

All issues I concerned have been solved by the authors except for the seasonal problem. Although the authors say “we chose the two seasons with the closest environmental conditions (humidity, temperature), i.e., spring and autumn, to conduct the experiment. We believe that this will reduce the negative effects of such seasonal differences to some extent.” I still think that seasonal effects on landscapes are significant, especially autumn VS spring.