Defining Dry Rivers as the Most Extreme Type of Non-Perennial Fluvial Ecosystems

Round 1

Reviewer 1 Report

An interesting paper that examines a landscape (dry rivers) that has received scant attention in the past.  I do not feel qualified to evaluate the biogeochemical sections of the paper, but find the geomorphic and management sections of the manuscript to be scientifically sound.  

Following are a few minor suggestions that are keyed to individual lines in the paper.

1. Page 1, Lines 30-32. The end of the abstract is rather vague and not very informative. A stronger sentence or two here presenting the main findings of the research would be more appropriate.
2. Page 2, Line 47. Word "evidenced" could be replaced with "shown".
3. Page 2, Line 62. Replace "needed of" with "need for".
4. Page 2, Line 64. Remove "During decades" and start the sentence with "Hydrologists".
5. Page 2, Line 75. Remove "and, however" and replace with "but".
6. Page 2, Line 84. This sentence notes that wet conditions replace dry conditions over a matter of "hours or days", but over what time period? Yearly? Every few months? Variable?  Some additional context here would be useful.
7. Page 7, Lines 178-179. This sentence notes that high discharges will convey long-stored sediment downstream. What are the downstream implications of these "sediment pulses"? At least some mention or short discussion of this would appear appropriate here.
8. Page 9, Line 204. I would recommend replacing the word "commonest" with "most common".

Author Response

Response to Reviewer 1 Comments

An interesting paper that examines a landscape (dry rivers) that has received scant attention in the past.  I do not feel qualified to evaluate the biogeochemical sections of the paper, but find the geomorphic and management sections of the manuscript to be scientifically sound.  

Following are a few minor suggestions that are keyed to individual lines in the paper.

Point 1: Page 1, Lines 30-32. The end of the abstract is rather vague and not very informative. A stronger sentence or two here presenting the main findings of the research would be more appropriate.

Response 1: According to the suggestions of the reviewer we have included the following sentence in the abstract:

Page 1, Lines 34-37: With this paper we ultimately expect to put in value Dry Rivers as non-perennial rivers with an own ecological identity with significant roles in the landscape, biodiversity and nutrient cycles and society, thus worth to be considered, especially in the face of exacerbated hydrological drying in many rivers across the world.

Point 2: Page 2, Line 47. Word "evidenced" could be replaced with "shown".

Response 2: Page 2, line 49: Done

Point 3: Page 2, Line 62. Replace "needed of" with "need for".

Response 3: Page 2, Line 64: Done

Point 4: Page 2, Line 64. Remove "During decades" and start the sentence with "Hydrologists".

Response 4: Page 2, Line 66: Done

Point 5: Page 2, Line 75. Remove "and, however" and replace with "but".

Response 5: Page 2, Line 77: Done

Point 6: Page 2, Line 84. This sentence notes that wet conditions replace dry conditions over a matter of "hours or days", but over what time period? Yearly? Every few months? Variable?  Some additional context here would be useful.

Response 6: The wet conditions in Dry Rivers are necessarily couple to rainfall events. Such events are highly variable over time and it does not strictly coupled to a temporal frequency, thus, a fixed time period is not possible to include in the definition since it is completely variable. Nevertheless,  we have polished the definition of Dry River to clarify this aspect. It has been done in several sections of the manuscript:

Page 1, Line 20

Page 5, Line 98

Page 6, Line 164

Point 7: Page 7, Lines 178-179. This sentence notes that high discharges will convey long-stored sediment downstream. What are the downstream implications of these "sediment pulses"? At least some mention or short discussion of this would appear appropriate here.

Response 7: According to this comment, we have included a brief review on the implications of the high downstream sediment discharge after heavy flooding.

Page 8, Lines: 182-184: Likewise, sediments deposited in channels can remain immovable for decades until a high energy flood shifts them and transports them downstream direction [e.g. 67, 69], which are key for the morphological and dynamic development of DRs, as well as for the maintenance of riparian habitats.

Point 8: Page 9, Line 204. I would recommend replacing the word "commonest" with "most

common".

Response 8: We agree and we have changed it. Page 10, Line 209: Done

Reviewer 2 Report

Review of a manuscript submitted to the Sustainability, entitled “DEFINING DRY RIVERS AS THE MOST EXTREME TYPE OF NON-PERENNIAL FLUVIAL ECOSYSTEMS”, by Maria Rosario Vidal-Abarca, Rosa Gómez, Maria Mar Sánchez-Montoya, Maria Isabel Arce, Nestor Nicolás, Maria Luisa Suárez.

From the scientific point of view but also for the restoration practice the work might miss any novelty, however still I would strongly support a publication of this study. Such detailed and comprehensive information as presented here can be usually only obtained with a rather high effort (really nicely accomplished by the authors) and/or are sometimes even not accessible or citable. Overall the manuscript is well organized and written and thus easy to read. However, in particular for the Introduction I would suggest a shortening (and some reorganization) which should be possible without losing any important information. Is an interesting paper with a clear enough purpose within its limited aims. The objective of the study has been met, and research findings have been thoroughly discussed. The article is an overview of the state of the art on temt dry rivers. This explains the lack of a chapter on research methods. The paper is well organized, and the Results and Discussion sections: 2. Contextualisation of Dry Rivers/ 3. Distribution, Geophysical and Hydrological Characteristics of Dry Rivers/ 4. Biota of Dry Rivers/5. Biogeochemical Processing in Dry Rivers/ 6. Ecosystem Services of Dry Rivers/ 7. Anthropogenic threats to Dry Rivers/ 8. Management challenges are clearly and concisely written. The paper title match its contents, the key words and the abstract characterize the contents of the paper sufficiently, the objective of the paper formulated correctly, the material presented appropriately and clearly, the assumptions formulated in the objective been achieved, the data contained in tables and figures represent the appropriate, understandable documentation of the contents of the paper, the discussion of results correct and sufficient, the items of literature included in the paper sufficient and adequate to the subject of the paper, the conclusions formulated correctly and justified by the contents and results of the study.

MINOR COMMENTS

Abstract

Line 10-15 (In recent decades, hydrologists, ecologists and geomorphologists have generated many terminologies to classify the universe of non-perennial rivers. As standard criteria are lacking among the proposed typologies, scientific evidence for the ecology of non-perennial rivers may be confusing, because not all structural and biogeochemical attributes can be generalised. Several knowledge gaps still exist, particularly for those rivers characterised by a dominant dry phase (herein referred to as Dry Rivers) - I consider it redundant and postulate that it be deleted

1. INTRODUCTION

I think the paper could be improved significantly through a reworking of the introduction section.

Line 39-63 - the information contained in this four paragraph can be significantly shortened.

Line 86-89 Table 1. - I suggest to include in the supplementary material

Line 90-96 it is necessary to fix the space between the lines

2. Contextualisation of Dry Rivers

Line 130-139 is a repetition of the text from the Introduction section (line 77-84)

Author Response

Response to Reviewer 2 Comments

Review of a manuscript submitted to the Sustainability, entitled “DEFINING DRY RIVERS AS THE MOST EXTREME TYPE OF NON-PERENNIAL FLUVIAL ECOSYSTEMS”, by Maria Rosario Vidal-Abarca, Rosa Gómez, Maria Mar Sánchez-Montoya, Maria Isabel Arce, Nestor Nicolás, Maria Luisa Suárez.

From the scientific point of view but also for the restoration practice the work might miss any novelty, however still I would strongly support a publication of this study. Such detailed and comprehensive information as presented here can be usually only obtained with a rather high effort (really nicely accomplished by the authors) and/or are sometimes even not accessible or citable. Overall the manuscript is well organized and written and thus easy to read. However, in particular for the Introduction I would suggest a shortening (and some reorganization) which should be possible without losing any important information. Is an interesting paper with a clear enough purpose within its limited aims. The objective of the study has been met, and research findings have been thoroughly discussed. The article is an overview of the state of the art on temt dry rivers. This explains the lack of a chapter on research methods. The paper is well organized, and the Results and Discussion sections: 2. Contextualisation of Dry Rivers/ 3. Distribution, Geophysical and Hydrological Characteristics of Dry Rivers/ 4. Biota of Dry Rivers/5. Biogeochemical Processing in Dry Rivers/ 6. Ecosystem Services of Dry Rivers/ 7. Anthropogenic threats to Dry Rivers/ 8. Management challenges are clearly and concisely written. The paper title match its contents, the key words and the abstract characterize the contents of the paper sufficiently, the objective of the paper formulated correctly, the material presented appropriately and clearly, the assumptions formulated in the objective been achieved, the data contained in tables and figures represent the appropriate, understandable documentation of the contents of the paper, the discussion of results correct and sufficient, the items of literature included in the paper sufficient and adequate to the subject of the paper, the conclusions formulated correctly and justified by the contents and results of the study.

Point 1: Abstract

Line 10-15 (In recent decades, hydrologists, ecologists and geomorphologists have generated many terminologies to classify the universe of non-perennial rivers. As standard criteria are lacking among the proposed typologies, scientific evidence for the ecology of non-perennial rivers may be confusing, because not all structural and biogeochemical attributes can be generalised. Several knowledge gaps still exist, particularly for those rivers characterised by a dominant dry phase (herein referred to as Dry Rivers) - I consider it redundant and postulate that it be deleted

Response 1: Page 1, Lines: 13-18. According to the reviewer, we have removed the first paragraph of the abstract.

Point 2: INTRODUCTION

I think the paper could be improved significantly through a reworking of the introduction section.

Line 39-63 - the information contained in this four paragraph can be significantly shortened.

Response 2: Accordingly, to the reviewer's suggestions, we have shorted the first paragraphs of the introduction and now it can be read as following:

Page 3, Lines: 69-84:

Non-perennial rivers are characterised by the presence of a dry phase (i.e. when surface water is lacking) of variable duration and spatial extent. Compared with perennial rivers they have been less studied [1-12], despite occurring in all continents and climates [13-14] and covering large geographical extent [15].

Valuable knowledge on their hydrology and ecology has been achieved recently [14, 16-18. and highlights the dry phase as one of the main factors that shape their structure and functioning [6, 19-22]. Drying is a fundamental to shape aquatic biodiversity by impacting some biological groups such as aquatic arthropods [23-26]. Besides, the tight influence of the terrestrial environment contributes to shape macro and microbial community structure and carbon and nutrient stocks [27-28] and biogeochemical aspects [29-31].  

Dry phase is variable in temporal duration, spatial extent and predictability [e.g. 11, 32-33]. While in some rivers it can be limited to 2-3 months (or even less) throughout a year, dry phase occurs on scales of years in others [e.g. 34]. Furthermore, drying may involve complete riverbed desiccation or takes place as isolated pools [35].

The duration of dry phase is critical in the ecology and functioning of these rivers, thus detailed information about their hydrology of non-perennial rivers is essential [33, 36-40]. Nowadays, there is a consensus on the need for of detailed hydrological information on dry phase to disentangle how drying affects the whole ecology of non-perennial rivers. 

Point 3: Line 86-89 Table 1. - I suggest to include in the supplementary material.

Response 3: Pages 3-4:  We understand this suggestion and in some instances, it would be a proper solution. However, since Table 1 is the basis for the contextualisation section, we believe that it is more useful for the reader if the table is included in the main text. If the editor agrees, we would rather to maintain the Table 1 in the main body of the manuscript.

Point 4: Line 90-96 it is necessary to fix the space between the lines

Response 4: Page 4, Lines 93-99. According to the reviewer we have corrected the space between lines.

Point 5: Contextualisation of Dry Rivers

Line 130-139 is a repetition of the text from the Introduction section (line 77-84)

Response 5: Although it seems repetitive, each paragraph indicated by the reviewer refers to a different context.

Thus, in the contextualisation section, the paragraph intends to differentiate and explicitly to define intermittent, ephemeral and dry rivers

Page 5, Lines 133-142.  Contextualisation of Dry Rivers:

Faced with this confusing framework, our intention is to analyse and to describe main biogeophysical and functional features of DRs to properly characterize their own entity as a particular type of ecosystem within the continuum described by non-perennial rivers. To do that, we compare DRs with intermittent and ephemeral rivers. Based on the widespread consideration of both terms in the literature, in our analysis, we consider intermittent rivers as those rivers experiencing flowing periods longer than dry periods year-round. On the contrary, we understand the ephemeral rivers as those experiencing flowing periods shorter than dry periods throughout the year, with surface water present for some months. Taking intermittent and ephemeral rivers as a framework, DRs would be located in the hydrological extreme of the gradient (Fig. 1) with surface water present only during hours or days always dependent of the rainfall event and its intensity.

On the contrary, the introductory paragraph describes the objectives of the manuscript and provides a definition of Dry River in the framework of non-perennial rivers (that is, intermittent and ephemeral rivers).

Page 2, Lines 79-86.  Introduction:

This article aims to highlight the singularity of a specific type of non-perennial rivers where aquatic conditions are anomalous, which we denominated Dry Rivers (hereafter, DRs). We pose that conceptually, DRs would represent the extreme of the hydrological continuum of increased flow interruption that typically characterizes the non-perennial rivers, thus being preceded by intermittent and ephemeral rivers that usually support longer flowing and/ or stagnant aquatic phases, respectively, as described in the literature (Table1). According to that, we define DRs as those whose usual habitat in space and time are dry channels where surface water may interrupt dry conditions for hours or few days…

Reviewer 3 Report

The manuscript entitled “Defining Dry Rivers as the most extreme type of non-perennial fluvial ecosystems” reviews the definitions used to refer to non-perennial rivers and provide an exhaustive overview for the existing knowledge about distribution, hydrological features, biota and biogeochemical attributes characterising Dry Rivers. I found the paper to be instructive and the topic interesting. In particular, I appreciate the integrate and multidisciplinary approach used by the authors and the combination of the limnological and terrestrial perspectives. The paper is well written and easy to follow. I just marked few typing errors.

As suggestion for the future, I believe that understanding the response of these peculiar environments to climatic changes could be a challenging path to take on, also considering Dry River systems from the geological and hydrogeological point of view.

Comments for author File: Comments.pdf

Author Response

Response to Reviewer 3 Comments

The manuscript entitled “Defining Dry Rivers as the most extreme type of non-perennial fluvial ecosystems” reviews the definitions used to refer to non-perennial rivers and provide an exhaustive overview for the existing knowledge about distribution, hydrological features, biota and biogeochemical attributes characterising Dry Rivers. I found the paper to be instructive and the topic interesting. In particular, I appreciate the integrate and multidisciplinary approach used by the authors and the combination of the limnological and terrestrial perspectives. The paper is well written and easy to follow. I just marked few typing errors.

Point 1: As suggestion for the future, I believe that understanding the response of these peculiar environments to climatic changes could be a challenging path to take on, also considering Dry River systems from the geological and hydrogeological point of view.

Response 1: We fully agree with the reviewer's comment. As we pointed out in the conclusions of the manuscript, an increase in the number of dry rivers is expected because of climate change. In this way, management policies should perform actions to ensure the ecological values of DRs and their contributions to human well-being, which requires a deeper knowledge of these ecosystems also from a geological and hydrogeological point of view.

Point 2: I just marked few typing errors.

Response 2: We thank the reviewer for such detailed revision and all typing errors detected have been corrected.

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