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Review
Peer-Review Record

Biogeochemistry of Mediterranean Wetlands: A Review about the Effects of Water-Level Fluctuations on Phosphorus Cycling and Greenhouse Gas Emissions

Water 2021, 13(11), 1510; https://doi.org/10.3390/w13111510
Reviewer 1: Anonymous
Reviewer 2: Anonymous
Reviewer 3: Anonymous
Water 2021, 13(11), 1510; https://doi.org/10.3390/w13111510
Received: 15 March 2021 / Revised: 24 May 2021 / Accepted: 25 May 2021 / Published: 27 May 2021
(This article belongs to the Special Issue Advances in Mountain and Mediterranean Wetlands Conservation)

Round 1

Reviewer 1 Report

The paper reviews two prominent functions of wetlands, namely greenhouse gas balance and nutrient storage/release in/from the sediment, and how these are affected in meditarrenan wetlands specifically, as Mediterranean climate shifts towards more erratic preicipitation regime. The ensuing effects of precipitation are intermittent dryness and/or higher water level fluctuations are discussed.

The paper covers an important topics and hits on the major mechanisms. However, the paper could also benefit from a bit better organization. In places, it is not clear where the author is going with the paragraph, and how it links with the previous paragraph, and out it fits with the general goal of the review. Sometimes the paper would benefit from rearranging some of the paragraph and sometimes just connecting sentences or introductory sentences in a paragraph will do the trick. Most notably a motivation why focusing on P in the water column and on greenhouse gases is missing. I will point out several of potential organizational modification in the details below.

One of the most important features of a review is that it should be a bit more clear what can and must be tackled next. This is missing in the conclusion. What are next steps in research? What are effective management interventions? How would research/management in Mediterrenean wetlands differ from others?  What can we learn from studying wetland in general, what specific wetlands should be targeted to get a better handle on the issues raised? What experiments (laboratory or field) and which timescales should be addressed? What about modeling inquiries? This is unclear.

And finally, a disclaimer. I have limited knowledge of the literature in this field and cannot judge whether the review sufficiently encompasses the breadth of the research. However, the author has an included an impressive array of scientific work in this review.

 

Abstract: “future research is needed” This is too general: What kind of research can easily be done, should be done.  

L31: suggest substituting “sensibility” with “sensitivity”

L42: suggest to home in on Mediterranean region when talking about summer droughts – for example with “summer droughts, as they are projected for future Mediterranean climate, …”

L48: Mediterranean systems are not high latitude – but some high altitude? If not delete this sentence because less relevant to this study.

L65: Please specify proportional change – change in what?

L73: I think this paragraph should move up to before the previous paragraph so that it becomes clear early what motivates this review.

L85: Please elaborate why this makes these wetlands prone to land use change

L90+ this is a convoluted sentence, can it be broken apart and simplified?

L94: Many of the relationships are not intuitive, and picking only windspeed renders this paragraph out of context with the goal of the paper. I don’t think windspeed needs special consideration.

Figure 1: I like the figure! Can you indicate in the arrows the positive or negative effect one variable has on the next – for example with a + or – sign (instead of up/down arrows in boxes).

Figure 1: is solar radiation expected to increase or decrease with global climate change?

 

Paragraph starting with L122. For all the love of science, sediment preservation for future scientific studies may not be a marginal motivation to preserve Mediterranean wetlands. The case for benthic metabolism can be better made for water quality.

L139: similar – what has the BPN to do with wetland preservation? BPN is a scientific tool rather than a wetland function that needs to be preserved.

L83: Please specify whether increase or decrease

L86: typo “stoichiometric”

L202: This is the most general paragraph in this section – should be more towards the beginning

L222: last sentence of this paragraph is extremely vague, please delete or rephrase

In section 2 there is some reference to phosphorus, phosphorus cycle, yet the importance of P for wetland water quality is not discussed and/or introduced.

L238 and elsewhere: consider substituting “bacteria” with “microbe” to include fungi and archea, etc.

L246: This paragraph seems to be premature, as it is before the author organizes the major mechanisms that regulate phosphorus exchange with the surface water.

L301: In this paragraph a clear link between the organic matter concentration changes and P release should be made – this may be clear to some, but in my view it is better to explicitly state.

L314: not clear how temperature would change with drying. Also please state explicitly that oxygen supply is increased with drying because diffusion of oxygen is much faster in air filled than water filled pore spaces.

L317; not clear how this fits into this paragraph – this seems to be a physical/chemical mechanism? Does this refute the oxygen/temperature hypothesis – if yes, please state explicitly

Table 1: “degradation” better would be microbial transformation and/or mineralization. It is not clear how increased microbial activity decreases P adsorption capacity – this is not clearly discussed in text.

  L333+ Discussion of microbial activity and P release, that seems to be much better placed in the paragraph starting L301

 

L344 Disconnected from previous paragraph.

L428: CH4 in surface water or sediment?

L435/6: This is repeated information

L449: This is unclear: why this expectation?

L451: This may not be contradictory: The longer the time scale considered, the more influential CO2 becomes relative to N2O and CH4?

 

L457: release of CO2 and N is directly connected to changes in organic matter concentration in sediments as discussed earlier in this paper – worthwhile picking it up again.

L471: Not clear how this sentence fits into this paragraph

 

L473: This sentence should be way earlier in the review

L491: This contradicts an earlier statement that says that these wetlands are mostly heterotrophic.

L493: Please consider GWP as a metric when summarizing all greenhouse gases and carbon footprint when considering CO2 and methane (but do not weigh methane).

L502: What is “global” in this context?

L 555: Conclusion should be about the entire paper and not just about greenhouse gas emissions. A nice summary with path forward is missing.

Author Response

Reviewer #1: The paper reviews two prominent functions of wetlands, namely greenhouse gas balance and nutrient storage/release in/from the sediment, and how these are affected in meditarrenan wetlands specifically, as Mediterranean climate shifts towards more erratic preicipitation regime. The ensuing effects of precipitation are intermittent dryness and/or higher water level fluctuations are discussed.

The paper covers an important topics and hits on the major mechanisms. However, the paper could also benefit from a bit better organization. In places, it is not clear where the author is going with the paragraph, and how it links with the previous paragraph, and out it fits with the general goal of the review. Sometimes the paper would benefit from rearranging some of the paragraph and sometimes just connecting sentences or introductory sentences in a paragraph will do the trick. Most notably a motivation why focusing on P in the water column and on greenhouse gases is missing. I will point out several of potential organizational modification in the details below. One of the most important features of a review is that it should be a bit more clear what can and must be tackled next. This is missing in the conclusion. What are next steps in research? What are effective management interventions? How would research/management in Mediterrenean wetlands differ from others? What can we learn from studying wetland in general, what specific wetlands should be targeted to get a better handle on the issues raised? What experiments (laboratory or field) and which timescales should be addressed? What about modeling inquiries? This is unclear.

And finally, a disclaimer. I have limited knowledge of the literature in this field and cannot judge whether the review sufficiently encompasses the breadth of the research. However, the author has an included an impressive array of scientific work in this review.

 

Abstract: “future research is needed” This is too general: What kind of research can easily be done, should be done. 

Although we agree with the referee that more specific information may be included, it is relevant to consider that, in the abstract section, just brief information is adequate. Accordingly, we have included "... further research (considering a wide variety in sedimentary chemical composition)". Actually, it was already stated in the previous version of the review that there is a need for studying  "if the periodic exposure to dry-wet cycles, considering the extent and frequency of the cycles, will amplify the role of these especial ecosystems as a source of these gases and therefore, will act as a feedback mechanism for global warming". Then, we consider that the two main aspects to be considered in future research are the extent and the frequency of the dry-wet cycles on wetlands biogeochemistry.

 

L31: suggest substituting “sensibility” with “sensitivity”

We have considered the referee suggestion and replaced "sensibility" by "sensitivity".

 

L42: suggest to home in on Mediterranean region when talking about summer droughts – for example with “summer droughts, as they are projected for future Mediterranean climate, …”

We have modified the sentence according to the referee´s suggestion.

 

L48: Mediterranean systems are not high latitude – but some high altitude? If not delete this sentence because less relevant to this study.

As the referee suggested us, we have deleted this sentence as it is not relevant.

 

L65: Please specify proportional change – change in what?

According to the referee, we have specified that proportional change are referred to biodiversity.

 

L73: I think this paragraph should move up to before the previous paragraph so that it becomes clear early what motivates this review.

We have considered the referee´s suggestion and we have moved up this paragraph.

 

L85: Please elaborate why this makes these wetlands prone to land use change

As we stated in the text, the inherent characteristics of Mediterranean wetlands such as their shallowness and their typically high catchment area to lake area ratio, make them especially sensible to land use change.

 

L90+ this is a convoluted sentence, can it be broken apart and simplified?

We do not understand the referee´s comment as we think the sentence is difficult to be shorten.

 

L94: Many of the relationships are not intuitive, and picking only windspeed renders this paragraph out of context with the goal of the paper. I don’t think windspeed needs special consideration.

We still think that most of the relationships are intuitive and if readers are interested in a better explanation, it can be found in Nazari-Sharabian et al. (2018) as the figure caption mentions. However, and based on referee´s suggestion, apart from wind speed, we have also included some explanations about human activities.

 

Figure 1: I like the figure! Can you indicate in the arrows the positive or negative effect one variable has on the next – for example with a + or – sign (instead of up/down arrows in boxes).

We have considered the referee´s suggestion and accordingly, we have changed the figure.

 

Figure 1: is solar radiation expected to increase or decrease with global climate change?

As many studies have reported, global warming and solar radiation have mutual connections (i.e. Frey et al., 2011; Nazari-Sharabian et al., 2018; Ohunakin et al., 2015). In particular, we would like to stress the study by Nazari-Sharabian et al., 2018) who made a detailed explanation of the connection between both solar radiation and global change and the inherent implications.

 

Paragraph starting with L122. For all the love of science, sediment preservation for future scientific studies may not be a marginal motivation to preserve Mediterranean wetlands. The case for benthic metabolism can be better made for water quality.

We agree with the referee and accordingly, we have rewritten the paragraph.

 

L139: similar – what has the BPN to do with wetland preservation? BPN is a scientific tool rather than a wetland function that needs to be preserved.

We agree with the referee in the fact that the BPN index is a scientific tool but we do not understand his comment. We include the BPN in this subsection because, as we stated in the text, it is related to the fact that sediment reflects overlying water conditions and then it may represent an appropriate tool for assessing trophic state in Mediterranean wetlands.

 

L183: Please specify whether increase or decrease

We have considered the referee suggestion and make the corresponding modification in the text for including that it increases.

 

L186: typo “stoichiometric”

We have considered the referee suggestion.

 

L202: This is the most general paragraph in this section – should be more towards the beginning

We have considered the referee´s suggestion and accordingly, we have moved this paragraph up in this section.

 

L222: last sentence of this paragraph is extremely vague, please delete or rephrase

According to the referee´s suggestion, we have deleted this sentence.

 

In section 2 there is some reference to phosphorus, phosphorus cycle, yet the importance of P for wetland water quality is not discussed and/or introduced.

Considering the referee´s comment, we have rewritten the introductory paragraph for justifying the need for studying phosphorus.

 

L238 and elsewhere: consider substituting “bacteria” with “microbe” to include fungi and archea, etc.

We have considered the referee´s suggestion.

 

L246: This paragraph seems to be premature, as it is before the author organizes the major mechanisms that regulate phosphorus exchange with the surface water.

We disagree with the referee and we still think that the redaction of this paragraph is correct as we first explain that the absence of a clear pattern in the literature reflects the complexity of the chemical, physical and biological transformations involved and then, we explain in more detail each transformation.

 

L301: In this paragraph a clear link between the organic matter concentration changes and P release should be made – this may be clear to some, but in my view it is better to explicitly state.

We disagree with the referee in the need for including the relation between organic matter and P release as it is well know that during organic matter mineralization, P release occurs (see among others, Böstrom, 1982; Golterman, 2004).

 

L314: not clear how temperature would change with drying. Also please state explicitly that oxygen supply is increased with drying because diffusion of oxygen is much faster in air filled than water filled pore spaces.

Following referee´s suggestion, and in order to avoid any confusion, we have deleted the temperature from that sentence and we have included some data about the difusion in anoxic vs oxic conditions.

 

L317; not clear how this fits into this paragraph – this seems to be a physical/chemical mechanism? Does this refute the oxygen/temperature hypothesis – if yes, please state explicitly

We agree with the referee that it was a bit confusing and then, we have now included in page 8 a brief introductory sentence for explaining the methodology that is normally used for assessing the effect of water level fluctuations on P cycle: "Basically, in the literature, the analysis of the impact of sediment desiccation and re-flooding on phosphorus cycle is based on two different methodological approaches: adsorption experiments with differently dry sediment (wet vs dry sediment) and re-flooding experiments".  Then, this paragraph is referred to results reported in the literature for re-flooding experiments trying to simulate the effect of re-inundation conditions of dry sediment of P cycle.

 

Table 1: “degradation” better would be microbial transformation and/or mineralization. It is not clear how increased microbial activity decreases P adsorption capacity – this is not clearly discussed in text.

We have considered the referee´s suggestion and accordingly, we have replaced in Table 1, degradation by mineralization. In relation to the connection between the microbial activity and the reduction in P adsorption capacity, and as we explain in the text "The more plausible explanations for the positive correlation between sediment organic matter content and phosphate adsorption capacity in those study wetlands were the increase in amorphous minerals stabilization [111] and in caption bridging with compounds such as calcium and magnesium [112-114]. Even more, Darke and Walbridge [111] found that sediment organic matter can also inhibit re-crystallization of both iron and aluminum compounds, thus indirectly assisting phosphate sorption".

 

  L333+ Discussion of microbial activity and P release, that seems to be much better placed in the paragraph starting L301

We do not understand the referee´s comment as this discussion is mentioned before in the text.

 

L344 Disconnected from previous paragraph.

We understand the referee´s suggestion but we still consider that it is the best place for including this paragraph as it is related to additional factors to be considered such as the time exposure to desiccation conditions and also to management implications.

 

L428: CH4 in surface water or sediment?

We thank the referee´s suggestion as it is referred to emissions from surface waters and so we have specified it in the text.

 

L435/6: This is repeated information

We agree with the referee and we have deleted that sentence.

 

L449: This is unclear: why this expectation?

As we explain in the text, temporarily flooded wetlands are widely distributed in regions with alternating dry-wet seasons such as Mediterranean climates. Therefore, it is unexpected the lack of attention paid to the study of the effect of water level fluctuations on greenhouses gases emissions in Mediterranean wetlands.

 

L451: This may not be contradictory: The longer the time scale considered, the more influential CO2 becomes relative to N2O and CH4?

We are sorry but we do not understand this comment from the referee.

 

L457: release of CO2 and N is directly connected to changes in organic matter concentration in sediments as discussed earlier in this paper – worthwhile picking it up again.

We agree with the referee and accordingly, we have included this connection.

 

L471: Not clear how this sentence fits into this paragraph

We are sorry again but we do not understand this comment from the referee.

 

 

L473: This sentence should be way earlier in the review

We disagree with the referee as this sentence is related to the results obtained from Zhao et al. [168] in a coastal wetland in the Yellow River Delta.

 

L491: This contradicts an earlier statement that says that these wetlands are mostly heterotrophic.

We are sorry again but we do not understand this comment from the referee.

 

L493: Please consider GWP as a metric when summarizing all greenhouse gases and carbon footprint when considering CO2 and methane (but do not weigh methane).

We completely understand the referee´s suggestion and so we clarified in page 10.

 

L502: What is “global” in this context?

We referred to water level fluctuations induced by global change considering all major drivers of global change on Mediterranean wetlands represented in Figure 2.

 

L 555: Conclusion should be about the entire paper and not just about greenhouse gas emissions. A nice summary with path forward is missing.

We understand the referee´s suggestion but we think that the inclusion of a conclusion section would be very repetitive. In the present version of the revision, we have included some conclusions at the end of each section referred to the impact of water level fluctuations on P cycle and on greenhouse gas emission.

Author Response File: Author Response.pdf

Reviewer 2 Report

This paper is a review of the literature on the effects of oscillating water levels in wetlands (and other surface water bodies) on 1) phosphorous cycling in wetland systems and 2) emissions of carbon dioxide, nitrous oxide and methane from wetland systems.  The author implicitly assumes that climate warming in the Mediterranean region will results in greater variability in wetland water levels in the future with longer periods of sediment desiccation than in the past.  The objective of the review is to provide an understanding how the greater variability in wetlands will affect wetland water quality and greenhouse gas emissions.

The process affecting phosphorous dynamics are complex as are the processes affecting greenhouse gas emission from wetlands. The author concludes:

  • “All in all, it is clear the difficulties of predicting the ultimate effect of periodic sediment desiccation and re-flooding conditions on phosphorous cycle in Mediterranean wetlands as it depends on the exposure time to dry conditions, the frequency of dry/wet cycles but also on the sediment chemical composition, evidencing the need for ad hoc studies. However, we may expect that water level fluctuations induced by global change are likely to enhance phosphorous release from sediments to the overlying water, impairing water quality.” (lines 369-375)
  • There exists a gap of knowledge about the net effect of alternating water level fluctuations induced by global change on greenhouse gas emissions. Accordingly, further research is needed [sic] to assess if the periodic exposure of dry-wet cycles will amplify the role of these….as a source of these gases and therefore, will act as a feedback mechanism for global warming.”

 

The topics addressed in this paper are of interest to the readers of Water.  My recommendation is that the paper could be acceptable for publication after a major rewrite.  The paper in the current form is, in my opinion, not well structured, difficult to follow, and contains too much discussion of topics not relevant to the main thrust of the paper, and have many examples of redundant text.  Some major ways in which the paper could be improved are described below.

  • The paper uses the terminology throughout of “…global change..”. I think the author is referring to changes in climatic conditions, but I am not sure.  The author should be more precise.
  • The paper uses the terminology “Mediterranean wetland”. I think it would be useful for the reader if the author described the region of the world that contains Mediterranean wetlands, possibly with a map. Many readers are not that familiar with the Mediterranean region and it is not clear if the author is referring to wetlands in the Mediterranean region and/or to wetlands in areas with a Mediterranean type climate.
  • The author writes the paper with a focus on Mediterranean wetlands, but almost no details are provided of these type of wetlands except that they have large catchment areas and shallowness. Wetlands with these characteristics are found throughout the world and not only in the Mediterranean region or in regions with a Mediterranean type climate.  It seems that the effects that are described in this paper are valid for most wetlands in which climate change will increase water-level variability (and wet-dry cycles).
  • I think the author should consider revising as two separate review papers. The first would be a literature review of the effects of water-level changes on wetland dynamics, and the second would be a literature review of the effects of water-level changes on greenhouse gas emissions from wetlands. In my opinion, these are two separate topics with almost no overlap except that both concern changes caused by increased variability in water-level changes.
  • The introduction should be condensed to focus only on the main topic(s) of the paper. As I understand the paper, the introduction should introduce the theme that wetland water levels will become more variable as the climate changes, at least in some part of the world, and then focus on 1) how this will affect phosphorous dynamics and 2) how this will affect greenhouse gas emissions.  There may be many other processes affected by changes in wetland water levels, but they are outside of the scope of this paper. It would be useful to have some discussion of magnitude of changes in wetland level oscillations is expected with changing climatic conditions.
  • Several places in the paper there is language like “…we would have expected a much more profound consideration of Mediterranean wetlands...” [lines 45-451]. In my opinion, not appropriate to express an opinion about what should have been studied.  The literature contains what has been studied, and that should be described.  Also refer to lines 63 to 65.
  • The logic of the paper should be strengthened. For example, in the quote from the paper in the second paragraph above [lines 369 to 375] it is not clear why the author concludes that increased water-level variability will lead to enhanced phosphorous release from the sediments. The first sentence in this quote describes difficulties in understand phosphorus release and thus not clear how he can unequivocally conclude that it will lead to enhanced release.   Wetlands already have wet-dry cycles with sediment desiccation during some seasons (years).  What is not clear to me from this paper is how much more desiccation there will be with a changing climate and how new releases (if they occur) will compare to those that are already occurring as a result of existing conditions.  Thus, in the abstract [line 18] states “…water level fluctuations, will lead to the degradation of water quality in Mediterranean wetlands…”  without qualification. After reading this paper, the bases for this conclusion are not clear.
  • An overall conclusion regarding both phosphorous dynamics and greenhouse gas emissions under changing water-level conditions is that there is significant uncertainty regarding predictions/understanding. I think this uncertainty should be more clearly and concisely described and recommendations should be made regarding research topics to address this uncertainty.
  • Lines 80-82. “In fact, removing existing pressures on wetlands and improving their resiliency is the most is the most effective method of coping with the adverse effects of climate change.”  There are no bases in the paper for this conclusion, and in my opinion, is beyond the scope of the paper.
  • The paper needs to be carefully proofed.

Author Response

Reviewer #2:  This paper is a review of the literature on the effects of oscillating water levels in wetlands (and other surface water bodies) on 1) phosphorous cycling in wetland systems and 2) emissions of carbon dioxide, nitrous oxide and methane from wetland systems. The author implicitly assumes that climate warming in the Mediterranean region will results in greater variability in wetland water levels in the future with longer periods of sediment desiccation than in the past. The objective of the review is to provide an understanding how the greater variability in wetlands will affect wetland water quality and greenhouse gas emissions.

The process affecting phosphorous dynamics are complex as are the processes affecting greenhouse gas emission from wetlands. The author concludes:

  • “All in all, it is clear the difficulties of predicting the ultimate effect of periodic sediment desiccation and re-flooding conditions on phosphorous cycle in Mediterranean wetlands as it depends on the exposure time to dry conditions, the frequency of dry/wet cycles but also on the sediment chemical composition, evidencing the need for ad hoc studies. However, we may expect that water level fluctuations induced by global change are likely to enhance phosphorous release from sediments to the overlying water, impairing water quality.” (lines 369-375)
  • “There exists a gap of knowledge about the net effect of alternating water level fluctuations induced by global change on greenhouse gas emissions. Accordingly, further research is needed [sic] to assess if the periodic exposure of dry-wet cycles will amplify the role of these….as a source of these gases and therefore, will act as a feedback mechanism for global warming.”

 

The topics addressed in this paper are of interest to the readers of Water. My recommendation is that the paper could be acceptable for publication after a major rewrite.  The paper in the current form is, in my opinion, not well structured, difficult to follow, and contains too much discussion of topics not relevant to the main thrust of the paper, and have many examples of redundant text. Some major ways in which the paper could be improved are described below.

  • The paper uses the terminology throughout of “…global change..”. I think the author is referring to changes in climatic conditions, but I am not sure. The author should be more precise.

In the manuscript, we refer to both terms, climatic conditions and global change. Actually, as we mention in the text, water level fluctuations are typical of Mediterranean area and they are the result of both, changes in climatic conditions (evaporation and precipitation patterns) and global change (i.e. human activities promoting changes in land uses and aquifers overexploitation). Accordingly, Figure 2 (former figure 1) has been slightly changed to include the dependence of water level fluctuations on both precipitation and human activities.

 

  • The paper uses the terminology “Mediterranean wetland”. I think it would be useful for the reader if the author described the region of the world that contains Mediterranean wetlands, possibly with a map. Many readers are not that familiar with the Mediterranean region and it is not clear if the author is referring to wetlands in the Mediterranean region and/or to wetlands in areas with a Mediterranean type climate.

According to the referee, we have included a new figure (Figure 1) showing the geographic location of the Mediterranean climate around the world.

 

  • The author writes the paper with a focus on Mediterranean wetlands, but almost no details are provided of these type of wetlands except that they have large catchment areas and shallowness. Wetlands with these characteristics are found throughout the world and not only in the Mediterranean region or in regions with a Mediterranean type climate. It seems that the effects that are described in this paper are valid for most wetlands in which climate change will increase water-level variability (and wet-dry cycles).

We agree with the referee in the fact that the shallowness and the high catchment area are not exclusive characteristics of Mediterranean wetlands. However, apart from these intrinsic characteristics, it is clear that Mediterranean wetlands are exposed to a specific climate as it is now clarified in a better way in the first new paragraph " Accordingly, they suffer a strong seasonality in water supply outside the hot season and they also experience a longer vegetation period that made them quite distinct from the standard limnological paradigm [25]".

 

  • I think the author should consider revising as two separate review papers. The first would be a literature review of the effects of water-level changes on wetland dynamics, and the second would be a literature review of the effects of water-level changes on greenhouse gas emissions from wetlands. In my opinion, these are two separate topics with almost no overlap except that both concern changes caused by increased variability in water-level changes.

We understand the referee suggestion but we disagree as we have focused our attention in both topics (effects of water level fluctuations on phosphorus dynamics and on greenhouse gas emissions). In order to clarify the goals of this revision, we have included a new first paragraph as a way of introduction.

 

  • The introduction should be condensed to focus only on the main topic(s) of the paper. As I understand the paper, the introduction should introduce the theme that wetland water levels will become more variable as the climate changes, at least in some part of the world, and then focus on 1) how this will affect phosphorous dynamics and 2) how this will affect greenhouse gas emissions. There may be many other processes affected by changes in wetland water levels, but they are outside of the scope of this paper. It would be useful to have some discussion of magnitude of changes in wetland level oscillations is expected with changing climatic conditions.

According to the referee we have included a new paragraph for explaining briefly the structure of the revision. In relation to the different factors affecting water level fluctuations, figure 2 has been modified to consider that, apart from precipitation, human activities also play a key role in promoting changes of wetland water level and the text has been slightly modified (see page 4).

 

  • Several places in the paper there is language like “…we would have expected a much more profound consideration of Mediterranean wetlands...” [lines 45-451]. In my opinion, not appropriate to express an opinion about what should have been studied. The literature contains what has been studied, and that should be described. Also refer to lines 63 to 65.

We understand the referee consideration but we still think that the inclusion of some expectations/opinions is adequate in such type of manuscript (revision).

 

  • The logic of the paper should be strengthened. For example, in the quote from the paper in the second paragraph above [lines 369 to 375] it is not clear why the author concludes that increased water-level variability will lead to enhanced phosphorous release from the sediments. The first sentence in this quote describes difficulties in understand phosphorus release and thus not clear how he can unequivocally conclude that it will lead to enhanced release. Wetlands already have wet-dry cycles with sediment desiccation during some seasons (years). What is not clear to me from this paper is how much more desiccation there will be with a changing climate and how new releases (if they occur) will compare to those that are already occurring as a result of existing conditions.  Thus, in the abstract [line 18] states “…water level fluctuations, will lead to the degradation of water quality in Mediterranean wetlands…”  without qualification. After reading this paper, the bases for this conclusion are not clear.

We agree with the referee that it can be a bit confusing and accordingly we have included a new sentence: "Basically, in the literature, the analysis of the impact of sediment desiccation and re-flooding on phosphorus cycle is based on two different methodological approaches: adsorption experiments with differently dry sediment (wet vs dry sediment) and reflooding experiments". In the abstract section, the statement of "water level fluctuations, will lead to the degradation of water quality in Mediterranean wetlands" was based on results from reflooding experiments, which actually resemble better the last effect of reinundation of dry sediment. To clarify it, now we have included this information: "Major drivers of global change, and specially water level fluctuations, will lead (based on results from reflooding experiments) to the degradation of water quality in Mediterranean wetlands by increasing the availability of phosphorus concentration in the water column upon rewetting of dry sediment".

 

  • An overall conclusion regarding both phosphorous dynamics and greenhouse gas emissions under changing water-level conditions is that there is significant uncertainty regarding predictions/understanding. I think this uncertainty should be more clearly and concisely described and recommendations should be made regarding research topics to address this uncertainty.

We do not completely understand the referee comment as we have already stated in the abstract section (and as we have just mentioned), regarding to phosphorus availability, "...water level fluctuations, will lead (based on results from reflooding experiments) to the degradation of water quality in Mediterranean wetlands by increasing the availability of phosphorus concentration in the water column upon rewetting of dry sediment". In relation to greenhouse gases emission, "...data reported in the literature reflects that global CO2 fluxes are likely to be enhanced during desiccation, while inundation decreased cumulative CO2 emissions, and also N2O emissions, but increased CH4 emissions". Finally, we recognize that, however, "there exists a complete gap of knowledge about the net effect of water level fluctuations induced by global change on greenhouse gases emission. Accordingly, further research is need to assess if the periodic exposure to dry-wet cycles, considering the extent and frequency of the cycles, will amplify the role of these especial ecosystems as a source of these gases and therefore, will act as a feedback mechanism for global warming".

 

  • Lines 80-82. “In fact, removing existing pressures on wetlands and improving their resiliency is the most is the most effective method of coping with the adverse effects of climate change.” There are no bases in the paper for this conclusion, and in my opinion, is beyond the scope of the paper.

Again, we do not understand the referee´s comment and we think this sentence may be included as some recommendations are suggested.

 

  • The paper needs to be carefully proofed.

According to the referee, we have revised the manuscript in order to improve it.



 

 

Author Response File: Author Response.pdf

Reviewer 3 Report

This manuscript was focused on the biogeochemistry of Mediterranean Wetlands. This was a meaningful review about the potential effects of water level fluctuations induced by global change. However, the quality of this manuscript did not reach the requirements of the Journal. There were suggestions for revision as follows:

 

  1. In the introduction section, authors should reorganize the logic to clear the meaning and importance of this review, previous review reports, the gaps between previous reviewing reports, and the objective and contribution of this review.
  2. The body of review should also be described in the introduction section.
  3. Currently, the authors reviewed the sediment, phosphorus release, and GHG emissions. However, there were confusions about the title and the main body. The title was about the biogeochemistry of Mediterranean Wetlands under water level fluctuation conditions induced by global change. However, there were not a review of global change (e.g., climate change and human activities) in the Mediterranean region. What’s the relationship between global change and water level fluctuations in this region? In addition, characteristics of the biogeochemistry of Mediterranean Wetlands were still not adequate. Mechanisms of phosphorus release and GHG emissions have been reported in previous studies whether in arid or wet conditions. The authors should describe changes in elements C, N, and P in this region caused by water level fluctuations according to data analysis or review of previous studies to reflect the biogeochemical cycle of these elements in this region. Moreover, the effects of plants should also be reviewed except for biological, physical, and chemical processes. Consequently, characteristics of water level fluctuation induced by global change in this region, biogeochemical change of elements C, N, P in wetland caused by such fluctuation, and relation, reason, and complexity analysis should be reviewed according to previous studies. Furthermore, the authors discussed and predicted biochemical processes in Mediterranean wetlands, which are very important. These discussions and predictions could be combined to be as a discussion or perspective section.

There were many tables in this review. However, figures to illustrate the results, data, or mechanism of biogeochemical change in Mediterranean wetlands are more eye-catching. 

Author Response

Reviewer #3: This manuscript was focused on the biogeochemistry of Mediterranean Wetlands. This was a meaningful review about the potential effects of water level fluctuations induced by global change. However, the quality of this manuscript did not reach the requirements of the Journal. There were suggestions for revision as follows:

 

  1. In the introduction section, authors should reorganize the logic to clear the meaning and importance of this review, previous review reports, the gaps between previous reviewing reports, and the objective and contribution of this review.

As we have already stated, and according to both referees, we have included a new and introductory paragraph.

 

  1. The body of review should also be described in the introduction section.

We have considered the referee´s suggestion in the introductory paragraph.

 

  1. Currently, the authors reviewed the sediment, phosphorus release, and GHG emissions. However, there were confusions about the title and the main body. The title was about the biogeochemistry of Mediterranean Wetlands under water level fluctuation conditions induced by global change. However, there were not a review of global change (e.g., climate change and human activities) in the Mediterranean region. What’s the relationship between global change and water level fluctuations in this region?

We disagree with the referee and as it has been already explained, figure 2 show the connection among different drivers of global change. To avoid any confusion, we have now slightly modified this figure to include the dependence of water level fluctuations on precipitation but also on human activities.

In addition, characteristics of the biogeochemistry of Mediterranean Wetlands were still not adequate. Mechanisms of phosphorus release and GHG emissions have been reported in previous studies whether in arid or wet conditions. The authors should describe changes in elements C, N, and P in this region caused by water level fluctuations according to data analysis or review of previous studies to reflect the biogeochemical cycle of these elements in this region. Moreover, the effects of plants should also be reviewed except for biological, physical, and chemical processes.

Consequently, characteristics of water level fluctuation induced by global change in this region, biogeochemical change of elements C, N, P in wetland caused by such fluctuation, and relation, reason, and complexity analysis should be reviewed according to previous studies. Furthermore, the authors discussed and predicted biochemical processes in Mediterranean wetlands, which are very important. These discussions and predictions could be combined to be as a discussion or perspective section.

We understand the referee comment but unfortunately we recognize that it is impossible to discuss all processes affected by changes in wetland water level. As we clearly stated in the first paragraph, we focused our attention on two major aspect such as the impact of water level fluctuation on phosphorus dynamics and on greenhouse gas emission. As a review, we mentioned key references to be considered: "At this point, it is worth to consider that Batzer and Sharitz [96] gave an excellent overview of the relevance of wet/dry cycles for the biogeochemistry of wetlands" (page 6).

 

There were many tables in this review. However, figures to illustrate the results, data, or mechanism of biogeochemical change in Mediterranean wetlands are more eye-catching.

We disagree with the referee as there are only 2 tables in the whole manuscript and they can not be redrawn as figures due to the inclusion of many references.

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The paper has improved in this iteration, however there are still some organizational question marks. It is still difficult to discern the major objectives, and at times, the author seems to go out on a tangent and the relevance of some of the topics raised are not clear. From my reading of the paper, the major outline and discussion points are

  • Wetlands serve as kidneys, and one needs to care about the 1) quality of the water (i.e. the nutrient concentration of a wetland’s surface water) (true for all wetlands worldwide?) which also mitigates agriculture and land-use changes upstreams, and their ability to produce and sequester greenhouse gases 2). Greenhouse gas production/sequestration, and water quality are the two major ecosystem services.
  • Wetlands’ surface water are not only compromised by external nutrient (and sediment) load, but also by resuspension and recirculation from the sediments (true for all wetlands worldwide)
  • Mediterrenean wetlands are especially threatened to recirculation because a) low wetland to catchment area, high seasonal variability of water supply, shallow water conditions, and seasonal desiccation, these affect physical and biogeochemical sediment water interactions and greenhouse gas production.
  • Global change factors impale physical and biogeochemical mechanisms. having an effect on these two ecosystem services. Some of these factors are especially strong (precipitation and runoff changes)

So I feel that this should come out clearly throughout the manuscript. All parts, the abstract, the introduction, the main part, and the conclusion should follow this line of thought and organization. I think Figure 2 is very nice and illustrative and can be used to create a more effective roadmap of the paper and make the connections: for example, the author can highlight which effects are going to be emphasized and why, and where they are going to be discussed (which section).

Although the author did not take me up on the suggestion to include a few concluding remarks, it would help again to come back to the major points. 1) what are the major services wetlands and specific Mediterranean wetlands provide, 2) what global change factors are the most important ones regarding med. Wetlands, and finally, what are the next research steps to get a better handle on understanding med. wetlands.

I am also pointing out in my specific details where I feel the paragraph is misplaced or does not align with the goals the author states,  or where it feels more context needs to be given.

L9: I would use “wetland” instead of “freshwater system” so that it becomes clear right away what the review is about

L54: Suggest deletion, this is not the goal of the review. In my opinion, this is too broad. A question or a gap should be raised only in the context of the paper, and not in general.

L58: Rather than saying this is the first review for med. wetlands, point out what makes med. wetlands special and why do they need special consideration and sets them apart from other wetlands worldwide? Perhaps just deleting the first sentence of that paragraph is sufficient.

Fig 1: Could the author use a map projection that does not over-represent the high latitude area?

L84: I could not find the Gorham 1991 reference in your bibliography, however, the estimate of 20-25% of organic carbon in the world seems to be very high. For example: Bridgham, 2006, estimates a worldwide storage of about 215 Pg, which is <15 % of a 1500+ Pg Soil carbon storage worldwide.

L88: The end of this section may be a good place to lay out a roadmap of this review: What are you going to address in this review(and why), and what are the limits of this review?

L116+ I like this paragraph, pointing out the ecosystem services. A few sentences towards the end of the paragraph to highlight the services of Mediterranean wetlands may be good.

L130: Not clear why grasslands are mentioned here.

L142: suggest using “sensitive” instead of “sensible”

Figure 2: thank you for taking me up on the suggestion to add the pluses to the arrows: Can you carry this all the way through and mark every arrow? Also, this figure would be perfect to lay out what the focus of the review is (e.g. through highlighting some of the arrows), and laying out where med. systems connections (arrows) are different (stronger or weaker) than the average global one and why. You may even add numbers to tell the reader in which section you address which component.

L152: I still have a hard time to see why the author chooses to single out wind. I pointed out for example, that the effects of solar radiation are not clear altogether either. For example, solar radiation (does it increase or decrease, and when in the season), affects productivity, but also photo-degradation of organic matter. Similar, temperature has multitude of effects, some direct, some indirect. Wind just seems arbitrary. Again, it is OK to present figure 2 by indicating where the priorities are (and highlight in the text why).

L185+ and 204+. Preservation of sediment layer for science is a very small ecosystem service, so not really important to spend so many words on. Similarly, BPN is an index, not an inherent wetland value.   

L259: Add a brief sentence at the end of that paragraph to explain how med. wetlands are different or similar to global ones

L260: Several times “as an illustration” is used. I would rather see how important that mechanism is in the grand scheme of things, why using this specific illustration, what is its relevance?

L260: In fact this paragraph would fit thematically under the next section (flooding/desiccation), where there oxic/anoxic shifts can be discussed.

L304: bacterial -> microbial

L324: Why did these studies focus on Fe oxides transformation, are these important, and if yes,why?

L414 bacteria -> microbes

L533: Coming back to my original comment: There is net C gain because a 500 year time scale instead of a 100 year timescale is considered. On a longer timescale CO2 is higher weighted than other greenhouse gases. N2O and CH4 have a much shorter lifespan. This may be the cause of the apparent contradiction.

L642: I still believe a concluding paragraph with major research recommendation is valid and useful to the reader, addressing the following questions: What can and must be tackled next? What are next steps in research? What are effective management interventions? How would research/management in Mediterrenean wetlands differ from others?  What can we learn from studying wetland in general, what specific wetlands should be targeted to get a better handle on the issues raised? What experiments (laboratory or field) and which timescales should be addressed? What about modeling inquiries?

Bridgham, S. D., J. Patrick Megonigal, J. K. Keller, N. B. Bliss, and C. Trettin. 2006. The carbon balance of North American wetlands. Wetlands 26:889–916.

Author Response

Reviewer #1: The paper has improved in this iteration, however there are still some organizational question marks. It is still difficult to discern the major objectives, and at times, the author seems to go out on a tangent and the relevance of some of the topics raised are not clear. From my reading of the paper, the major outline and discussion points are

  • Wetlands serve as kidneys, and one needs to care about the 1) quality of the water (i.e. the nutrient concentration of a wetland’s surface water) (true for all wetlands worldwide?) which also mitigates agriculture and land-use changes upstreams, and their ability to produce and sequester greenhouse gases 2). Greenhouse gas production/sequestration, and water quality are the two major ecosystem services.
  • Wetlands’ surface water are not only compromised by external nutrient (and sediment) load, but also by resuspension and recirculation from the sediments (true for all wetlands worldwide)
  • Mediterrenean wetlands are especially threatened to recirculation because a) low wetland to catchment area, high seasonal variability of water supply, shallow water conditions, and seasonal desiccation, these affect physical and biogeochemical sediment water interactions and greenhouse gas production.
  • Global change factors impale physical and biogeochemical mechanisms. having an effect on these two ecosystem services. Some of these factors are especially strong (precipitation and runoff changes)

So I feel that this should come out clearly throughout the manuscript. All parts, the abstract, the introduction, the main part, and the conclusion should follow this line of thought and organization.

We thanks the referee´s suggestions and now we think that the structure of the manuscript has been generally improved.

 

I think Figure 2 is very nice and illustrative and can be used to create a more effective roadmap of the paper and make the connections: for example, the author can highlight which effects are going to be emphasized and why, and where they are going to be discussed (which section).

Although the author did not take me up on the suggestion to include a few concluding remarks, it would help again to come back to the major points. 1) what are the major services wetlands and specific Mediterranean wetlands provide, 2) what global change factors are the most important ones regarding med. Wetlands, and finally, what are the next research steps to get a better handle on understanding med. wetlands.

I am also pointing out in my specific details where I feel the paragraph is misplaced or does not align with the goals the author states,  or where it feels more context needs to be given.

L9: I would use “wetland” instead of “freshwater system” so that it becomes clear right away what the review is about.

Based on referee 2, we have deleted all this sentence.

 

L54: Suggest deletion, this is not the goal of the review. In my opinion, this is too broad. A question or a gap should be raised only in the context of the paper, and not in general.

As referee suggested us, we have deleted this sentence.

 

L58: Rather than saying this is the first review for med. wetlands, point out what makes med. wetlands special and why do they need special consideration and sets them apart from other wetlands worldwide? Perhaps just deleting the first sentence of that paragraph is sufficient.

We still think that it is important to remark that it is the first review focused on Mediterranean wetlands. We do not understand the referee comment in relation to the need for clarifying the relevance of Mediterranean wetlands as we have already stated that "... one of the most threatened ecosystems by climate change and natural habitat loss [Leberger et al. 2020]."

 

Fig 1: Could the author use a map projection that does not over-represent the high latitude area?

We have considered the referee´s comment and accordingly, we have made a new figure.

 

L84: I could not find the Gorham 1991 reference in your bibliography, however, the estimate of 20-25% of organic carbon in the world seems to be very high. For example: Bridgham, 2006, estimates a worldwide storage of about 215 Pg, which is <15 % of a 1500+ Pg Soil carbon storage worldwide.

As we specified to the editorial board when resubmitting the manuscript after the first revision, we did not yet update the reference list due to the lack of time (10 days). Anyway, we have considered the referee´s suggestion and we have included data from Bridgham et al. (2006).

 

L88: The end of this section may be a good place to lay out a roadmap of this review: What are you going to address in this review(and why), and what are the limits of this review?

We do not understand the referee´s comment as in the last paragraph, and based on his recommendation in the first revision, we already explained the structure of the review. Actually, we state "In this review...". However, for making easier to the reader understanding the main issue of the review, we have moved the first sentence of the last paragraph to the above paragraph.

 

L116+ I like this paragraph, pointing out the ecosystem services. A few sentences towards the end of the paragraph to highlight the services of Mediterranean wetlands may be good.

According to the referee, we have rewritten this paragraph to include some information about the effect of global change in ecosystems services of Mediterranean wetlands.

 

L130: Not clear why grasslands are mentioned here.

We have removed it.

 

L142: suggest using “sensitive” instead of “sensible”

We have done it.

 

Figure 2: thank you for taking me up on the suggestion to add the pluses to the arrows: Can you carry this all the way through and mark every arrow? Also, this figure would be perfect to lay out what the focus of the review is (e.g. through highlighting some of the arrows), and laying out where med. systems connections (arrows) are different (stronger or weaker) than the average global one and why. You may even add numbers to tell the reader in which section you address which component.

L152: I still have a hard time to see why the author chooses to single out wind. I pointed out for example, that the effects of solar radiation are not clear altogether either. For example, solar radiation (does it increase or decrease, and when in the season), affects productivity, but also photo-degradation of organic matter. Similar, temperature has multitude of effects, some direct, some indirect. Wind just seems arbitrary. Again, it is OK to present figure 2 by indicating where the priorities are (and highlight in the text why).

We have considered the referee´s suggestions and accordingly we have rewritten the paragraph. We have considered that instead removing the explanation related to the effect of global change on wind patterns, it is better to add a brief explanation about the effect of each driver.

L185+ and 204+. Preservation of sediment layer for science is a very small ecosystem service, so not really important to spend so many words on. Similarly, BPN is an index, not an inherent wetland value.  

Based on referees (both 1 and 2) comments, we have shorten this section but we still think that it is essential to outline the relevance of sediment (both affecting and reflecting the overlying water column) for understanding the functioning of Mediterranean wetlands.

 

L259: Add a brief sentence at the end of that paragraph to explain how med. wetlands are different or similar to global ones.

We have considered the referee´s suggestion and we have rewritten the sentence.

 

L260: Several times “as an illustration” is used. I would rather see how important that mechanism is in the grand scheme of things, why using this specific illustration, what is its relevance?

We understand the referee´s comment and we have decided just to removed it.

 

L260: In fact this paragraph would fit thematically under the next section (flooding/desiccation), where there oxic/anoxic shifts can be discussed.

Considering the referee´s suggestion, we have moved this paragraph to the next section.

 

L304: bacterial -> microbial

We have done it.

 

L324: Why did these studies focus on Fe oxides transformation, are these important, and if yes,why?

Iron oxides transformations, occurring along sediment desiccation, have been traditionally studied because of the close dependence on phosphorus and iron cycle and so, we have specified it in the text.

 

L414 bacteria -> microbes

We have done it.

 

L533: Coming back to my original comment: There is net C gain because a 500 year time scale instead of a 100 year timescale is considered. On a longer timescale CO2 is higher weighted than other greenhouse gases. N2O and CH4 have a much shorter lifespan. This may be the cause of the apparent contradiction.

We really appreciate the referee´s explanation and we have included it in the text.

 

L642: I still believe a concluding paragraph with major research recommendation is valid and useful to the reader, addressing the following questions: What can and must be tackled next? What are next steps in research? What are effective management interventions? How would research/management in Mediterrenean wetlands differ from others?  What can we learn from studying wetland in general, what specific wetlands should be targeted to get a better handle on the issues raised? What experiments (laboratory or field) and which timescales should be addressed? What about modeling inquiries?

We have finally included a concluding section with some questions proposed by the referee.

 

Bridgham, S. D., J. Patrick Megonigal, J. K. Keller, N. B. Bliss, and C. Trettin. 2006. The carbon balance of North American wetlands. Wetlands 26:889–916.

Author Response File: Author Response.pdf

Reviewer 2 Report

The author has not addressed a major comment in my original review which was that the review paper "contains too much discussion of topics not relevant to the main thrust of the paper, and has many examples of redundant text."  As a result, my opinion is that the paper still requires a major revision.

I note that the addition of Figure 1 adequately addresses an issue I had with my initial review.

Some editiorial comments I have with suggestions for condensing the text are the following:

Title – I suggest changing to “Biogeochemistry of Mediterranean Wetlands: a Review of Changes in the Magnitude of Water-Level Fluctuations on Phosphorous Cycling and Greenhouse Gas Emissions

Line 1  As “global change” in the context of this paper appears to refer to all changes caused by climate change, land use development, resource extraction, urbanization and sea level rise it is obvious that global changes is the greatest threat to functioning of freshwater ecosystems. In fact, the definition of global change seems to encompass all that could cause a change in freshwater ecosystem functions.  Also, global change, as defined, is not an emerging threat – it encompasses processes that have been ongoing for a long time. I suggest starting the section with “Mediterranean wetlands are ecosystems especially sensitive to changes in the magnitude of water-level fluctuations. Unexpectedly….”

Lines 11-12 delete parenthetical “(Mediterranean climate likely will experience the greatest proportional change)” as this parenthetical does not inform on “geographical location”.

Lines 18 and 25.  The parentheticals added on these lines, in my opinion, are not appropriate for an Abstract.  These issues are described in detail in the paper

Line 25 change “need” to “needed”

Line 58 change to “this review is the first one focused on Mediterranean wetlands…”

Figure 1 change title to “Geographic locations with a Mediterranean climate.

Line 75 delete “will”

Line 77 suggest deleting “drastic”

Line 78 delete “considered as”

Line 81 suggest replacing “in studying” with “is”

Line 89-125.  I suggest deleting this text as it is extraneous to the main topic(s) of the review.

Line 137 In this context “global change” should be “global climate change”.  I think the paper would be much easier to read if most instances of “global change” were modified as “global climate change” or “climate change”.  Most of what is discussed in this paper relates to changes in wetland ecosystems due to changing climatic conditions.  Certainly, other processes, as noted above, affect wetland ecosystems, but these can be mentioned as an aside as paper really focused on effects due to changing climate. 

Line 138 “shorten”

Lines 185 to 289.   This section in my opinion is much too long and could be deleted without changing the significance of the paper.

Line 312 suggest deleting “differently”

Line 342 change “conduct to” to “result in”

Line 375 delete “gets”

Line 404 delete “last”

Line 411 “enhance”

Line 633 delete “up”

Line 638 delete “last”

 

Author Response

Reviewer #2:  Referee 2

The author has not addressed a major comment in my original review which was that the review paper "contains too much discussion of topics not relevant to the main thrust of the paper, and has many examples of redundant text."  As a result, my opinion is that the paper still requires a major revision.

I note that the addition of Figure 1 adequately addresses an issue I had with my initial review.

Some editiorial comments I have with suggestions for condensing the text are the following:

 

Title – I suggest changing to “Biogeochemistry of Mediterranean Wetlands: a Review of Changes in the Magnitude of Water-Level Fluctuations on Phosphorous Cycling and Greenhouse Gas Emissions"

We have considered the referee´s suggestion and accordingly, we have changed the original title. However, the new title is not exactly that proposed by the referee and it is as follows: “Biogeochemistry of Mediterranean Wetlands: a Review of the Effects of Water-Level Fluctuations on Phosphorous Cycling and Greenhouse Gas Emissions".

 

Line 1  As “global change” in the context of this paper appears to refer to all changes caused by climate change, land use development, resource extraction, urbanization and sea level rise it is obvious that global changes is the greatest threat to functioning of freshwater ecosystems. In fact, the definition of global change seems to encompass all that could cause a change in freshwater ecosystem functions.  Also, global change, as defined, is not an emerging threat – it encompasses processes that have been ongoing for a long time. I suggest starting the section with “Mediterranean wetlands are ecosystems especially sensitive to changes in the magnitude of water-level fluctuations. Unexpectedly….”

We have considered the referee´s suggestion and therefore, the abstract have been rewritten.

 

Lines 11-12 delete parenthetical “(Mediterranean climate likely will experience the greatest proportional change)” as this parenthetical does not inform on “geographical location”.

Based on previous referee´s comment, we have deleted all this information.

 

Lines 18 and 25.  The parentheticals added on these lines, in my opinion, are not appropriate for an Abstract.  These issues are described in detail in the paper

We have done it.

 

Line 25 change “need” to “needed”

We have done it.

 

Line 58 change to “this review is the first one focused on Mediterranean wetlands…”

We have done it.

 

Figure 1 change title to “Geographic locations with a Mediterranean climate.

We have done it.

 

Line 75 delete “will”

We have done it.

 

Line 77 suggest deleting “drastic”

We have done it.

 

Line 78 delete “considered as”

We have done it.

 

Line 81 suggest replacing “in studying” with “is”

We have done it.

 

Line 89-125.  I suggest deleting this text as it is extraneous to the main topic(s) of the review.

Based on the referee´s comment, we have shorten this section but we still consider that the information that is provided here is essential for understanding the sensibility of Mediterranean wetlands to global change.

 

Line 137 In this context “global change” should be “global climate change”.  I think the paper would be much easier to read if most instances of “global change” were modified as “global climate change” or “climate change”.  Most of what is discussed in this paper relates to changes in wetland ecosystems due to changing climatic conditions. Certainly, other processes, as noted above, affect wetland ecosystems, but these can be mentioned as an aside as paper really focused on effects due to changing climate.

We have considered the referee´s comment and replaced "global change" by "global climate change".

 

Line 138 “shorten”

We have done it.

 

Lines 185 to 289.  This section in my opinion is much too long and could be deleted without changing the significance of the paper.

As the referee has suggested, we have shorten this section. However we would like to stress that we disagree with the referee as we consider that it is relevant to include this section because sediment play a key role in the functioning of all wetlands and specially of Mediterranean wetlands.

 

Line 312 suggest deleting “differently”

We have replaced "differently" by "different samples".

 

Line 342 change “conduct to” to “result in”

We have done it.

 

Line 375 delete “gets”

We have done it.

 

Line 404 delete “last”

We have done it.

 

Line 411 “enhance”

We have done it.

 

Line 633 delete “up”

We have done it.

 

Line 638 delete “last”

We have done it.

 

Author Response File: Author Response.pdf

Reviewer 3 Report

The quality of this manuscript was improved significantly after the authors' revision. However, it is also needed to be further revised to attract more attention as a review article.

  1. The figure of water qualify degradation updated by authors was still not adequate to reflect their motivation. The proportion of global-change factors were caused by climate change, and water quality and quantity were also impacted by human activities. However, the connections of each part were confusing. For example,  temperature, solar radiation, precipitation, and wind speed belong to climatic factors, which can be influenced by human activities, such as GHG emission. The fluctuations of such climatic indices are feedbacks of GHG emission increase. Therefore, on the one hand, water level can incline due to balance of increasing in precipitation and temperature. On the other hand, water level can also be impacted by run off, water discharging, geo-related distubance, which are caused by human activities. The  flowchart should be clear to reflect the interactions of climate change and human activities, and to express motivition the author described in body for this review article.
  2. It is necessary to prepare a figure to refeclt the geochemical processes the authors discussed, even it may relate to many references. The copyright of figure you drawn by yourselves is not an issue. In addition, there are many review articles containing figures related to many references, such as the meta-analysis of results. A mechanism figure of your work will provide more critical information of biochemical processes impacted by global change, and attract more citation for you.   

Author Response

Reviewer #3:  Referee 3

The quality of this manuscript was improved significantly after the authors' revision. However, it is also needed to be further revised to attract more attention as a review article.

 

The figure of water qualify degradation updated by authors was still not adequate to reflect their motivation. The proportion of global-change factors were caused by climate change, and water quality and quantity were also impacted by human activities. However, the connections of each part were confusing. For example,  temperature, solar radiation, precipitation, and wind speed belong to climatic factors, which can be influenced by human activities, such as GHG emission. The fluctuations of such climatic indices are feedbacks of GHG emission increase. Therefore, on the one hand, water level can incline due to balance of increasing in precipitation and temperature. On the other hand, water level can also be impacted by runoff, water discharging, geo-related disturbance, which are caused by human activities. The  flowchart should be clear to reflect the interactions of climate change and human activities, and to express motivition the author described in body for this review article.

We understand the referee concerns that climate change, and water quality and quantity were also impacted by human activities and that temperature, solar radiation, precipitation, and wind speed belong to climatic factors, which can be influenced by human activities. However we would like to stress that Figure 2, as it is specified in the figure caption, includes major drivers of global change, including both climatic factors and human activities.

Additionally, we have considered the referee´s comment and we have included new connections such as those between run-off and water level and air temperature and solar radiation with water level.

Lastly, we do not understand the last comment of the referee about "and to express motivation the author described in body for this review article" as we explain in the text and we marked in bold letters in the figure caption, what is the review focused on.

 

It is necessary to prepare a figure to refeclt the geochemical processes the authors discussed, even it may relate to many references. The copyright of figure you drawn by yourselves is not an issue. In addition, there are many review articles containing figures related to many references, such as the meta-analysis of results. A mechanism figure of your work will provide more critical information of biochemical processes impacted by global change, and attract more citation for you.  

We understand the referee but we disagree with he/she. The paper includes four figures and two tables and we consider that there are enough figures representing the more relevant geochemical processes. Additionally, the inclusion of tables help the readier to select the more important references and mechanisms involved in phosphorus cycling.

Author Response File: Author Response.docx

Round 3

Reviewer 1 Report

Thank you to the author for the changes in this iteration. I am pleased with the outcome of the paper.

Overall: The new additions have some minor issues with the English sentence structures - most likely due to the rapid turnover. The sentences seem sometimes a bit too long. I would appreciate if the author can take another look and reformulate some of the new text. I am far from judging, being myself a non-native speaker.

 A few minor touches:

Abstract: L12 – Isn’t it true that some wetlands are already experiencing dry/flood cycles (as opposed it will occur in the future)?

L13: suggest to delete “Doubtlessly”

L17: add “in Mediterranean wetlands” after “emissions”

L19: suggest deleting “In relation to greenhouse gases emission, data reported in the literature reflects that global” and start the sentence with “CO2 fluxes”

L50: “on a more specific context” this is vague

L75: suggest deleting “The reason for selecting” and start the sentence with “Phosphorus…

L77: suggest to break up the long sentence

L86: suggested title: “Sensitivity of Mediterranean wetlands to global change factors”

 

L118: Eastern and southern part of what – Europe? Please clarify

L154: I am not sure an explanation of water vapor change and atmospheric water holding capacity is needed – no obvious connection to wetlands

 Fig 1: I am wondering whether the boxes thermal stratification and water mixing can be merged into a single “surface water stratification”

Line 200: We’ve been going back and forth on the issue of preservation for science of being a sufficient ecosystem service. I could concede this point and let the author leave it in the manuscript. But could this be mentioned after the paragraph describing the influence of sediment on the water column (this 2nd argument is the more convincing and important in my view). Also, can the first aspect be shortened?

L282: suggest to delete “basically, in the literature”, and start the sentence with “The analysis of …”

L300: Can the author add low oxygen diffusivity of oxygen in water relative to air being as the other important factor for anoxic conditions

 

Author Response

Reviewer #1: Thank you to the author for the changes in this iteration. I am pleased with the outcome of the paper.

 

Overall: The new additions have some minor issues with the English sentence structures - most likely due to the rapid turnover. The sentences seem sometimes a bit too long. I would appreciate if the author can take another look and reformulate some of the new text. I am far from judging, being myself a non-native speaker.

 

 A few minor touches:

 

Abstract: L12 – Isn’t it true that some wetlands are already experiencing dry/flood cycles (as opposed it will occur in the future)?

We do not understand the referee´s suggestion as we already specified in the abstract the next:

"Although Mediterranean wetlands are characterized by extreme natural water level fluctuations in response to irregular precipitation patterns, global climate change is projected to amplify this pattern by shorting precipitation seasons and increasing the incidence of summer droughts in this area. As a consequence, a part of the lake sediment will be exposed to air-drying in dry years when the water table becomes low. This periodic sediment exposure to dry/wet cycles will likely affect biogeochemical processes".

Accordingly, water level fluctuations occurs in Mediterranean wetlands as a result of the natural climate forcing but the global climate change will amplify this natural pattern.

 

L13: suggest to delete “Doubtlessly”

We have considered the referee´s comment.

 

L17: add “in Mediterranean wetlands” after “emissions”

We have considered the referee´s comment.

 

L19: suggest deleting “In relation to greenhouse gases emission, data reported in the literature reflects that global” and start the sentence with “CO2 fluxes”

We have considered the referee´s comment.

 

L50: “on a more specific context” this is vague

Based on the referee´s comment, we have replaced "on a more specific context" by "under a regional context".

 

L75: suggest deleting “The reason for selecting” and start the sentence with “Phosphorus…

We have considered the referee´s comment.

 

L77: suggest to break up the long sentence

As the referee suggested us, we have break up the sentence.

 

L86: suggested title: “Sensitivity of Mediterranean wetlands to global change factors”

We have considered the referee´s comment.

 

L118: Eastern and southern part of what – Europe? Please clarify

It is specified that is the Eastern and southern part of the Mediterranean basin. It is written as follows: "However, not all Mediterranean wetlands are equally affected with the Eastern and Southern part of the basin being most heavily impacted already [42]".

 

L154: I am not sure an explanation of water vapor change and atmospheric water holding capacity is needed – no obvious connection to wetlands

We understand the referee´s comment as it is not exclusively to Mediterranean wetlands but we still think that this explanation can help the reader to see the connection between water vapor and evaporation and so, the effect on water level fluctuations.

 

 Fig 1: I am wondering whether the boxes thermal stratification and water mixing can be merged into a single “surface water stratification”

Although we understand the referee´s suggestion, we consider that it is easier to keep both boxes in a separate way for a better explanation of the single effect of each one.

 

Line 200: We’ve been going back and forth on the issue of preservation for science of being a sufficient ecosystem service. I could concede this point and let the author leave it in the manuscript. But could this be mentioned after the paragraph describing the influence of sediment on the water column (this 2nd argument is the more convincing and important in my view). Also, can the first aspect be shortened?

Based on the referee´s recommendation, we have rewritten the paragraph for a better introduction of the role of sediment when studying Mediterranean wetlands. However, we still think that it is better to explain first that sediment reflects processes occurring in the water column and then, we explain in more detail, because it plays a major role in Mediterranean wetlands, that sediment affects the water column. In relation to the referee´s comment for shortening the first aspect, we did it in the last revision and we think that it would be better to keep it as it is.

 

L282: suggest to delete “basically, in the literature”, and start the sentence with “The analysis of …”

We have considered the referee´s comment.

 

L300: Can the author add low oxygen diffusivity of oxygen in water relative to air being as the other important factor for anoxic conditions

We have considered the referee´s comment.

 

 

Author Response File: Author Response.docx

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