the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Reviews and Syntheses: Variable Inundation Across Earth’s Terrestrial Ecosystems
Abstract. The structure, function, and dynamics of Earth’s terrestrial ecosystems are profoundly influenced by the frequency and duration that they are inundated with water. A diverse array of natural and human engineered systems experience temporally variable inundation whereby they fluctuate between inundated and non-inundated states. Variable inundation spans from extreme flooding and droughts to predictable sub-daily cycles. Variably inundated ecosystems (VIEs) include hillslopes, non-perennial streams, wetlands, floodplains, temporary ponds, tidal systems, storm-impacted coastal zones, and human engineered systems. VIEs are diverse in terms of inundation regimes, water chemistry and flow velocity, soil and sediment properties, vegetation, and many other properties. The spatial and temporal scales of variable inundation are vast, ranging from sub-meter to whole landscapes and from sub-hourly to multi-decadal. The broad range of system types and scales makes it challenging to predict the hydrology, biogeochemistry, ecology, and physical evolution of VIEs. Despite all experiencing the loss and gain of an overlying water column, VIEs are rarely considered together in conceptual, theoretical, modeling, or measurement frameworks/approaches. Studying VIEs together has the potential to generate mechanistic understanding that is transferable across a much broader range of environmental conditions, relative to knowledge generated by studying any one VIE type. We postulate that enhanced transferability will be important for predicting VIE function under future, potentially non-analog, environmental conditions. Here we aim to catalyze cross-VIE science that studies drivers and impacts of variable inundation across Earth’s VIEs. To this end, we complement expert mini-reviews of eight major VIE systems with overviews of VIE-relevant methods and challenges associated with scale. We conclude with perspectives on how cross-VIE science can derive transferable understanding via a ‘continuum approach’ in which the impacts of variable inundation are studied across multi-dimensional environmental space.
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RC1: 'Comment on egusphere-2024-98', Cedric Laize, 21 May 2024
Review egusphere-2024-98
General comments
This is an interesting review/opinion paper, which I understand resulted from a workshop. I feel it would stimulate thinking around the concept of VIE systems introduced by the authors. They provide useful pointers and mini-reviews on various types of VIEs as well as so ideas on how to improve monitoring and modelling of those, as well as ways to study them more holistically.
As a paper capturing the proceedings of a workshop, its structure is more like a review/position paper than a research paper and I think it would be useful to present that structure more explicitly in the introduction to help the reader find their way. For example, some of the information in the section at lines 212-240 could be introduced earlier, thus giving more clarity.
I made specific comments, which revolve for the most part around adding citations where it felt needed, and clarifying some points by adding examples or figures.
Scientific comments
P2 Introduction paragraph 1; the authors define a number of basic concepts for this paper. Some are general hydrology and could have a few key citations to back them up.
P2 Intro para 2; the authors define term VIE, and the conceptualisation around it. It would be useful to include a few key references that most likely informed the authors for this part.
P3 para 2; the authors give some examples of VIEs (including Fig1); it would be useful to state more explicitly that a VIE could belong to different types (especially, there is a wide range of human interventions, from light touch to heavy engineering so some systems may not be seen as human-engineered but would not be fully natural either).
P3 line 98-109 interestingly, re point about intermittent rivers going permanent, there is a lot of research on how rivers are drying (so permanent rivers going intermittent), which looks like the opposite problem. It could be useful to reflect about which issue could be the worst in terms of impacts.
P3 line 106-109; that sentence is not clear, and “dynamics” is repeated 3 times. Maybe you could split it in 2 sentences and clarify what the citations were actually about.
Fig 1 is good but for the middle world map pic marked (e); there doesn’t seem to be an explanation for what VIE is (e).
P5 There is no citation in these 2 paragraphs. The first paragraph is a bit vague. First sentence mentions “models” but it is unclear of what. I guess it is models of impacts on VIEs. Some environmental variables are mentioned but without support from literature. Sentence on line 129-130 is a bit of a sweeping statement. The reference to VIE location in space is a bit confusing; at first, it is in terms of environmental variable space, then later it looks like the authors are talking about actual geographical location.
P6 Fig2 the caption is very long and looks like some should be part of the main text.
P6-7 Lines 160-177 add key references to support this section.
P7-8 I appreciate this section cannot cover every possible impact but I think it would be very useful to add a couple of sentences (maybe after line 211) about how flooding is actually part of the normal functioning of some ecosystems (eg river/floodplain connectivity for fish spawning, wetlands water level requirements for some bird species), in which case change in VIE regimes (timing, drying) can have huge impacts.
Hillslope section. Re Fig. 3, the difference between 3b and 3c is not obvious looking at the pictures. Could the authors explain a bit more in the text where appropriate?
Hillslope section. P10 lines 304-309 Is there any citations that could support the statement on measuring hillslope VIE with earth observation? (IE examples of using EO for that purpose).
Non-perenial streams section. On the topic of monitoring intermittent streams, and routes to improve on that (eg UAVs), Dugdale et al. (2022) is useful to cite here (eg in P12 first paragraph).
Dugdale et al. 2022. Looking to the skies: Realizing the combined potential of drones and thermal infrared imagery to advance hydrological process understanding in headwaters. Water Res Research 58
Non-perenial streams section. It could be useful to elaborate briefly why these are undermonitored. For example, like headwaters, with which they partly overlap, intermittent rivers are undermonitored to a large extent because there are small and numerous, so the limited monitoring is more due to practicality and resources than anything else.
Non-perenial streams section. In section lines 386-398, it would be pertinent to cite Thompson et al. (2021) and their worldwide global warming/river flow alteration study. Thompson JR, Gosling SN, Zaherpour J, Laizé CLR. (2021) Increasing risk of ecological change to major rivers of the world with global warming. Earth's Future 9 (11), e2021EF002048
Floodplain and fluvial section. Fig 5 On the biological drivers (left-hand side of main figure), beaver dams are listed; while it is relevant where there are beavers, it looks rather specific given the otherwise broad view taken for this paper.
Floodplain and fluvial section. Some paragraphs (eg 2nd) in this section doesn’t have many references compared to the other mini-reviews, or compared to the other paragraphs. Please can you review if a few more key refs can be added. If it is that the text refers to the ones cited several times, then, can it be clear (it’s fine citing them several times if needed).
Floodplain and fluvial section. Another Thompson et al. (2021) ref would be useful to add (eg in 4th paragraph).
Thompson JR, Laizé CLR, Acreman MC, Crawley A, Kingston DG. (2021). Impacts of climate change on environmental flows in West Africa's Upper Niger Basin and the Inner Niger Delta. Hydrology Research 52 (4), 958-974
Human-engineered VIE section. I was wondering whether nature-based solutions would fall within this (eg, re-connecting river to upstream natural floodplain to mitigate flooding downstream).
Inundation process and scale section (from P26 onward). Web links: the k26 weblink returns a dead link. Is there a primary source for the lake stats other than the Guinness? (ie a scientific source).
Inundation process and scale section. This section is covering the important theme of scale, which can be quite complex to describe. I feel that it would benefit from a summary figure illustrating example of the different scales of organisms/processes, etc. to help the reader visualise better as they go through the text.
Inundation process and scale section. Similarly to my point on intermittent river being undermonitored, it could be useful to elaborate briefly on why there is relative lack of monitoring or modelling at the finer scales, as there is probably some practical reasons, and if there are ways forward to improve (eg drones, Lidar).
Primary methods section. Re monitoring, I was expecting mention of UAVs as they have potential to bridge between scales (eg between in-situ observation and traditional airborne and satellite EO. The Dugdale et al. (2022) paper I suggested above could actually be cited here.
Primary methods section. The second part of this section, on models, and particularly on ModEx is too vague. Could a concrete example of a ModEx approach be used to illustrate it and thus guide readers through the process, and/or a figure added.
Cross-VIE transferrable knowledge section. Lots of interesting food for thought in this section. However, at times, it is a bit vague and would benefit from having concrete examples, or specific citations. For example, in the first 2 paragraphs, the authors elaborate on the idea of using continuum approach, then they cite the wetlands unified classification; this could be detailed a bit further so that readers have an explicit example of what a continuum approach may look like. In paragraphs 3 and 4, slope and return period are presented as key control variables but there is no citation to really back this up. With regards to the discussion about scale in the previous sections, how such an approach would capture different spatial scales (can slope do that? Or return period?) In addition, this section could be made clearer by shortening the text a bit (eg 1st paragraph could be more concisely worded).
Technical comments
P2 L68 “variety of factors influence” should be “influences”.
Citation: https://doi.org/10.5194/egusphere-2024-98-RC1 -
RC2: 'Suggestions for Discussion', Bree Whitehead, 24 May 2024
Initially I was skeptical of aggregating such complex and diverse systems into a model framework, but the eight VIE mini-reviews did an excellent job of showing similarities in ecosystem dynamics, microtopography, and modeling challenges. The mini-reviews seemed a little disjointed to me, it may help to organize these sections by discussing their components in a more connected way. For example, instead of stating fact after fact, discuss how "the knee bone is connected to the leg bone" throughout each of these ecosystems. I can now see how a broad continuum utilizing ICON and ModEX methods may assist general VIE understanding. There are several places (ex. line 238-240) where comprehensive VIE models are proposed, but then never fully developed (excluding fig. 12 and the discussion on lines 876-890). This work often felt like it was leading up to a big reveal of broad models such as the proposed topo/return interval model (fig.12), but then fell short at the end by stating a new encouraged perspective with some guidance. I think to address this head on it may potentially assist the paper to move the various model discussions (lines 992-1052) forward into the introduction. The two extent and granularity axes and examples (lines 876-891) discussed would benefit from a figure. There are also a few locations where the easily accessible term "climate change" is awkwardly substituted for distractingly complex language, the most notable instance occurs in the abstract. I suggest boldly using the term that is utilized throughout the rest of the writing. Thank you for the opportunity to review!
Citation: https://doi.org/10.5194/egusphere-2024-98-RC2 -
CC1: 'Comment on egusphere-2024-98: Invited referee', Robert Payn, 30 May 2024
General comments
I greatly appreciate the careful outlining and meticulous preparation of this manuscript. I would have made different choices about the organization of the logic, but I review so few papers that are this carefully written these days that I just want to acknowledge how easy the majority of this paper is to read.
While the logical progression of the paper is probably fine for some readers, my personal taste would suggest that the presented order of logic is missing a golden opportunity. Namely, I don’t think the concepts of working with a “continuum perspective” in “multi-dimensional environmental space” is sufficiently developed before the mini review sections are presented. Furthermore, I don’t think the mini review sections provide explicit enough references back to these themes to really let the paper fully illustrate the usefulness of the approach. I didn’t really understand what “continuum perspective” meant until the very end of the paper, and I very much would have appreciated that understanding to provide a broader perspective with which to contextualize the mini reviews. As a result, I felt like this paper is in danger of supporting reductionist habits that are clearly intended to be avoided. Many of my specific comments are tied to this general criticism.
Specific comments
Line 70-72: The long history of general conceptual models from watershed hydrology that define infiltration excess (Hortonian) and saturation excess (Dunnian) overland flows may be relevant here. These concepts are quite abstract and do not imply specific mechanisms other than categorizing “top-down” or “bottom-up” sources of water. I realize that this is intended to be a more broadly applicable model, but a review of how existing concepts map to a transferable framework might be illustrative of its value.
Line 75: While I suppose it is implied by preceding statements, this paragraph seems to imply that the control volume for the water budget terms used is strictly associated with surface water? That must be true for “export via infiltration” in this sentence to make sense. I wonder if the control volume should be more explicitly defined to avoid the reader having to guess at the interpretation of the water budget in this paragraph.
Line 76: Would it be accurate to say “… continuous aqueous barrier of surface water…” to clarify the control volume per the previous comment?
Line 130: I can only guess at what “multi-dimensional environmental space” means at this point. I didn’t really understand what it meant in the abstract, either. Does it reference simply the dimensions of space and time? If not, what other dimensions are implied? This seems like buzz-wordy jargon without a little more development.
Line 238: The term “continuum perspective” has been used a couple times but has yet to be explicitly defined. Is this in reference to the continuum of the flow of water mentioned in introducing the organization of mini-reviews, or some other sort of continuum? Without an explicit definition, I have a hard time agreeing that a “continuum perspective” will somehow bridge the conceptual models of variable inundation across many different types of these systems.
Lines 237 to 240: After reading the first 2 mini reviews, I have come back to make this comment. As of now, I have not seen any specific references to the “continuum perspective” or any specific references to the changes of the systems in “multi-dimensional environmental space”. So far, these terms have still not been defined, nor have specific examples of their application helped clarify how they are useful in promoting transferable concepts. I would highly recommend that the mini reviews use these terms directly and provide some specific examples of how the behavior of that specific system lends to the transferable perspective being promoted. Lines 232-235 seems to be asking the reader to figure out these connections for themselves, without any guiding vision for this exercise provided by the paper. I am deep in the paper and am still not really sure how it is promoting transferable conceptual models, other than I am supposed to somehow be thinking about a “continuum” or about a change in “multi-dimensional space”.
Line 504: More information here for those not familiar with the location of the Pantanal? If the goal is to encourage cross-domain thinking, less assumption of domain-specific knowledge is critical.
Line 611 to 613: The sentence “As inundation regimes may become more variable, increasing conservation and protection efforts for ephemeral and temporary ponds may become more essential to maintain these critical VIEs” seems circular. Perhaps “As inundation regimes may become more variable, increasing conservation and protection efforts for maintaining ephemeral and temporary pond VIEs may become more essential.”
Line 632: The “area of coastal inundation” rather than the “size of coastal inundation”? Not clear what dimension “size” means in this context.
Line 755-756: Is “three-dimensional physical space” part of “multi-dimensional environmental space”? This is the first mention of something approaching this bridging concept in the mini reviews.
Line 766 and Figure 9: I find this figure hard to follow other than the gradients at the bottom. Are the dashed arrows about groundwater or the distance of inundation? Showing them below the land surface may be misleading. The crab seems like a visual non-sequitur.
Line 781-785: This list is difficult to read and appears to mix punctuation with semicolons and commas.
Line 865: This paragraph is suddenly using lakes and rivers of endorheic basins as an example of large scale variably inundated areas when none of the mini reviews provides a description of this particular example. This lack of connection seems a bit awkward.
Line 1063: This is the first time the idea of a “continuum approach” has been revisited since being introduced (without being defined) before the mini reviews. Also, figure 12 is the first concrete example of what is meant by “continuum approach”, and none of the ideas in figure 12 are actually discussed in the narrative of the paper. Should those ideas for some sort of integrating model be relegated exclusively to a figure caption? If the reductionist habits of categorizations used for the mini reviews is something to be avoided, why isn’t that being reinforced with visions for how to avoid it through the whole paper? Why is the conceptual model of figure12 not presented sooner, such that we can think about where each type of system fits as we read each mini review? That would make the mini reviews much more interesting to read and less of a list of loosely categorized details.
Line 1080-1089: I would have loved to have been explicitly informed that these were hypothesized to be the foundation of at least one “continuum” concept before reading the mini review sections. Then I would have liked if the mini review sections to explicitly discuss how our current understanding of each type of VIE feeds these overarching ideas.
Technical corrections
Line 953: The phrase “...revealing the governing the processes…” appears to be missing some words?
Line 966: Suggest “…captured by a passive microwave radiometer as well as through C- and L-band radar backscatter…”
Citation: https://doi.org/10.5194/egusphere-2024-98-CC1 -
RC3: 'Comment on egusphere-2024-98', Robert Payn, 31 May 2024
General comments
I greatly appreciate the careful outlining and meticulous preparation of this manuscript. I would have made different choices about the organization of the logic, but I review so few papers that are this carefully written these days that I just want to acknowledge how easy the majority of this paper is to read.
While the logical progression of the paper is probably fine for some readers, my personal taste would suggest that the presented order of logic is missing a golden opportunity. Namely, I don’t think the concepts of working with a “continuum perspective” in “multi-dimensional environmental space” is sufficiently developed before the mini review sections are presented. Furthermore, I don’t think the mini review sections provide explicit enough references back to these themes to really let the paper fully illustrate the usefulness of the approach. I didn’t really understand what “continuum perspective” meant until the very end of the paper, and I very much would have appreciated that understanding to provide a broader perspective with which to contextualize the mini reviews. As a result, I felt like this paper is in danger of supporting reductionist habits that are clearly intended to be avoided. Many of my specific comments are tied to this general criticism.
Specific comments
Line 70-72: The long history of general conceptual models from watershed hydrology that define infiltration excess (Hortonian) and saturation excess (Dunnian) overland flows may be relevant here. These concepts are quite abstract and do not imply specific mechanisms other than categorizing “top-down” or “bottom-up” sources of water. I realize that this is intended to be a more broadly applicable model, but a review of how existing concepts map to a transferable framework might be illustrative of its value.
Line 75: While I suppose it is implied by preceding statements, this paragraph seems to imply that the control volume for the water budget terms used is strictly associated with surface water? That must be true for “export via infiltration” in this sentence to make sense. I wonder if the control volume should be more explicitly defined to avoid the reader having to guess at the interpretation of the water budget in this paragraph.
Line 76: Would it be accurate to say “… continuous aqueous barrier of surface water…” to clarify the control volume per the previous comment?
Line 130: I can only guess at what “multi-dimensional environmental space” means at this point. I didn’t really understand what it meant in the abstract, either. Does it reference simply the dimensions of space and time? If not, what other dimensions are implied? This seems like buzz-wordy jargon without a little more development.
Line 238: The term “continuum perspective” has been used a couple times but has yet to be explicitly defined. Is this in reference to the continuum of the flow of water mentioned in introducing the organization of mini-reviews, or some other sort of continuum? Without an explicit definition, I have a hard time agreeing that a “continuum perspective” will somehow bridge the conceptual models of variable inundation across many different types of these systems.
Lines 237 to 240: After reading the first 2 mini reviews, I have come back to make this comment. As of now, I have not seen any specific references to the “continuum perspective” or any specific references to the changes of the systems in “multi-dimensional environmental space”. So far, these terms have still not been defined, nor have specific examples of their application helped clarify how they are useful in promoting transferable concepts. I would highly recommend that the mini reviews use these terms directly and provide some specific examples of how the behavior of that specific system lends to the transferable perspective being promoted. Lines 232-235 seems to be asking the reader to figure out these connections for themselves, without any guiding vision for this exercise provided by the paper. I am deep in the paper and am still not really sure how it is promoting transferable conceptual models, other than I am supposed to somehow be thinking about a “continuum” or about a change in “multi-dimensional space”.
Line 504: More information here for those not familiar with the location of the Pantanal? If the goal is to encourage cross-domain thinking, less assumption of domain-specific knowledge is critical.
Line 611 to 613: The sentence “As inundation regimes may become more variable, increasing conservation and protection efforts for ephemeral and temporary ponds may become more essential to maintain these critical VIEs” seems circular. Perhaps “As inundation regimes may become more variable, increasing conservation and protection efforts for maintaining ephemeral and temporary pond VIEs may become more essential.”
Line 632: The “area of coastal inundation” rather than the “size of coastal inundation”? Not clear what dimension “size” means in this context.
Line 755-756: Is “three-dimensional physical space” part of “multi-dimensional environmental space”? This is the first mention of something approaching this bridging concept in the mini reviews.
Line 766 and Figure 9: I find this figure hard to follow other than the gradients at the bottom. Are the dashed arrows about groundwater or the distance of inundation? Showing them below the land surface may be misleading. The crab seems like a visual non-sequitur.
Line 781-785: This list is difficult to read and appears to mix punctuation with semicolons and commas.
Line 865: This paragraph is suddenly using lakes and rivers of endorheic basins as an example of large scale variably inundated areas when none of the mini reviews provides a description of this particular example. This lack of connection seems a bit awkward.
Line 1063: This is the first time the idea of a “continuum approach” has been revisited since being introduced (without being defined) before the mini reviews. Also, figure 12 is the first concrete example of what is meant by “continuum approach”, and none of the ideas in figure 12 are actually discussed in the narrative of the paper. Should those ideas for some sort of integrating model be relegated exclusively to a figure caption? If the reductionist habits of categorizations used for the mini reviews is something to be avoided, why isn’t that being reinforced with visions for how to avoid it through the whole paper? Why is the conceptual model of figure12 not presented sooner, such that we can think about where each type of system fits as we read each mini review? That would make the mini reviews much more interesting to read and less of a list of loosely categorized details.
Line 1080-1089: I would have loved to have been explicitly informed that these were hypothesized to be the foundation of at least one “continuum” concept before reading the mini review sections. Then I would have liked if the mini review sections to explicitly discuss how our current understanding of each type of VIE feeds these overarching ideas.
Technical corrections
Line 953: The phrase “...revealing the governing the processes…” appears to be missing some words?
Line 966: Suggest “…captured by a passive microwave radiometer as well as through C- and L-band radar backscatter…”
Citation: https://doi.org/10.5194/egusphere-2024-98-RC3
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