Ideas and perspectives: Land–ocean connectivity through groundwater

Arévalo-Martínez, Damian L.; Haroon, Amir; Bange, Hermann W.; Erkul, Ercan; Jegen, Marion; Moosdorf, Nils; Schneider von Deimling, Jens; Berndt, Christian; Böttcher, Michael Ernst; Hoffmann, Jasper; Liebetrau, Volker; Mallast, Ulf; Massmann, Gudrun; Micallef, Aaron; Michael, Holly A.; Paasche, Hendrik; Rabbel, Wolfgang; Santos, Isaac; Scholten, Jan; Schwalenberg, Katrin; Szymczycha, Beata; Thomas, Ariel T.; Virtasalo, Joonas J.; Waska, Hannelore; Weymer, Bradley A.

doi:10.5194/bg-20-647-2023

Articles | Volume 20, issue 3

https://doi.org/10.5194/bg-20-647-2023

© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/bg-20-647-2023

© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 20, issue 3

Ideas and perspectives

|

10 Feb 2023

Ideas and perspectives |

| 10 Feb 2023

Ideas and perspectives: Land–ocean connectivity through groundwater

Damian L. Arévalo-Martínez, Amir Haroon, Hermann W. Bange, Ercan Erkul, Marion Jegen, Nils Moosdorf, Jens Schneider von Deimling, Christian Berndt, Michael Ernst Böttcher, Jasper Hoffmann, Volker Liebetrau, Ulf Mallast, Gudrun Massmann, Aaron Micallef, Holly A. Michael, Hendrik Paasche, Wolfgang Rabbel, Isaac Santos, Jan Scholten, Katrin Schwalenberg, Beata Szymczycha, Ariel T. Thomas, Joonas J. Virtasalo, Hannelore Waska, and Bradley A. Weymer

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Final revised paper (published on 10 Feb 2023)
Preprint (discussion started on 08 Jul 2022)

Interactive discussion

Status: closed

CC1:
'Comment on bg-2022-148', Clara Ruiz González, 05 Sep 2022

Very relevant and timely article! The authors might consider including a recent review on the microbial dimension of submarine groundwater discharge by Ruiz-González, Rodellas and Garcia-Orellana (2021, FEMS Microbiology Reviews), which evidences the poor knowledge of the (micro)biological aspects related to submarine groundwater discharge, ranging from the microbially-driven chemical transformations of the groudnwater within coastal aquifers to the microbial responses to groundwater inputs once in the coastal ocean. Current challenges and future directions of the field are also highlighted, empashizing, as in the current article, the need for multidisciplinary collaborations. This review article was published slightly earlier than the one of Archana et al (2021), already cited in the text, but targets the entire groundwater-marine continuum by discussing the microbial implications of groundwater discharge in the ocean.
Clara Ruiz-González, Valentí Rodellas, Jordi Garcia-Orellana, The microbial dimension of submarine groundwater discharge: current challenges and future directions, FEMS Microbiology Reviews, Volume 45, Issue 5, September 2021, fuab010, https://doi.org/10.1093/femsre/fuab010

Citation: https://doi.org/10.5194/bg-2022-148-CC1
- AC1: 'Reply on CC1', Damian Leonardo Arévalo-Martínez, 05 Sep 2022
  
  Many thanks for your interest in our manuscript and the suggestion. The (micro)biological aspects of both freshened submarine water discharge and offshore freshened groundwater certainly need further investigation, and their role within future multidisciplinary approaches is of course a topic we would like to highlight with our contribution.
  
  Citation: https://doi.org/10.5194/bg-2022-148-AC1
- AC2: 'Reply on CC1', Damian Leonardo Arévalo-Martínez, 19 Oct 2022
  
  Many thanks for your interest in our manuscript and the suggestion. We have included now the suggested publication in the revised version of the manuscript (l. 251–252).
  
  Citation: https://doi.org/10.5194/bg-2022-148-AC2
RC1:
'Comment on bg-2022-148', Ana Silva, 13 Sep 2022

Overall this manuscript provides a short summarising view of groundwater as a linking element between land and sea. Its scope is adequate for the publication format and the argumentation is well made in several key points. The topic and scope are very timely and match a research area reaching a cumulative point of becoming useful in management contexts. Albeit of considerable utility to the target readers, the manuscript reads mostly as a summarising text, where the authors' own contributions appear very scattered and hard to find; summarising their original contributions at the end of the sections might be a simple solution to enhance the manuscript's uptake and impact. I made several annotations in the attached pdf to be considered by the authors. Most reflect a need to alter the document to become more reader-friendly and add some contribution ambition, which is somewhat limited in this version. The point made about the common language/proposed framework for existing methodologies would be a particularly desirable adding value.

Citation: https://doi.org/10.5194/bg-2022-148-RC1
- AC3: 'Reply on RC1', Damian Leonardo Arévalo-Martínez, 19 Oct 2022
  
  On behalf of the authors, I thank Reviewer #1 (Dr. Ana Silva) for the positive assessment of our manuscript, as well as the constructive comments and suggestions. In the attached document we provide a point-by-point response to the issues raised during the review process, and list/discuss the changes done to the revised version.
  
  Citation: https://doi.org/10.5194/bg-2022-148-AC3
RC2:
'Comment on bg-2022-148', Anonymous Referee #2, 04 Oct 2022

This article provides a summary of the important roles, ideas, and prospects of groundwater as an important link between land and sea. In particular, the authors classify meteoric groundwater into coastal runoff FSGD and offshore freshened OFG, and emphasize the role of each and the connectivity between the two. This manuscript is very timely and necessary as the definitions scattered in several papers were arranged, the latest research from around the world were cited, as well as a perspective or direction for groundwater study is provided. Nevertheless, some suggestions are annotated in the attached pdf to help the reader understand.

Citation: https://doi.org/10.5194/bg-2022-148-RC2
- RC3:
  'Annotated manuscript version', Anonymous Referee #2, 12 Oct 2022
  
  The comment was uploaded in the form of a supplement: https://bg.copernicus.org/preprints/bg-2022-148/bg-2022-148-RC3-supplement.pdf
  
  Citation: https://doi.org/10.5194/bg-2022-148-RC3
  - AC5: 'Reply on RC3', Damian Leonardo Arévalo-Martínez, 19 Oct 2022
    
    On behalf of the authors, I thank Reviewer #2 for the positive assessment of our manuscript, as well as the constructive comments and suggestions. In the attached document we provide a point-by-point response to the issues raised during the review process, and list/discuss the changes done to the revised version.
    
    Citation: https://doi.org/10.5194/bg-2022-148-AC5
- AC4: 'Reply on RC2', Damian Leonardo Arévalo-Martínez, 19 Oct 2022
  
  On behalf of the authors, I thank Reviewer #2 for the positive assessment of our manuscript, as well as the constructive comments and suggestions. In the attached document we provide a point-by-point response to the issues raised during the review process, and list/discuss the changes done to the revised version.
  
  Citation: https://doi.org/10.5194/bg-2022-148-AC4

Peer review completion

AR – Author's response | RR – Referee report | ED – Editor decision | EF – Editorial file upload

ED: Reconsider after major revisions (19 Oct 2022) by Ben Bond-Lamberty

AR by Damian Leonardo Arévalo-Martínez on behalf of the Authors (20 Oct 2022) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (31 Oct 2022) by Ben Bond-Lamberty

RR by Anonymous Referee #3 (20 Nov 2022)

Suggestions for revision or reasons for rejection

General Comments:

This manuscript provides a brief overview of coastal groundwater dynamics, which is an important, timely, and understudied topic. The main message of the manuscript seems to be that more synergy is needed between research studying fresh submarine groundwater discharge and offshore freshened groundwater discharge and techniques applied in each domain should be merged in future interdisciplinary efforts. This is a notable cause for the research community to take on.

Overall, the manuscript gives a nice high-level overview of the topic and is generally approachable to a general audience, though at first the frequent use of acronyms is a bit jarring. Having table 1 shown in the first several pages in the final version will help this, as I found myself needing to look up the difference between FSGD and OFG several times while reading the introduction and section 2.

This review details mostly conceptual information and highlights key methods used in this domain of research. The study could be substantially more impactful if some form of quantitative analysis or summarization was performed such as a table showing ranges in discharge yields by geological setting, etc. However, I understand that such analyses would require substantial effort and is probably outside the scope of this short perspective paper. Considering the intended purpose of this perspective (i.e., high level overview of the field of research and call to action) I only have several specific comments below. The authors have done a nice job responding to previous reviews and I’m supportive of its publication.

Specific Comments:

Figure 1: I like the simple figure, but there are some confusing details if you look closely beyond the fact that FSGD happens nearshore and OFG happens offshore. For example, should saltwater intrusion also be shown in this figure, or is that implied by the dark blue parts of FSGD and OFG and red arrows? On that note, with the current design, it actually doesn’t look like the light blue freshwater ever reaches the sea. I’m not sure what the solution is, perhaps more of a color gradient? Salt water intrusion can also occur in the shallower terrestrial subsurface while fresh groundwater is discharged deeper/further offshore. Also, perhaps a dashed line could also represent rising sea levels? There are just suggestions should you have ideas how to improve on these nuances. With some improvements, the figure would be very useful for conceptual and educational purposes. As noted in my general comments, considering this perspective paper provides a high level overview, a very nice conceptual figure that gets widely used and shared would elevate the paper’s impact and influence.

Line 40 and throughout: What is the reason for using parentheses for (bio)geochemists here and a few other places?

Line 201: The influence of pumping practices and local reservoir properties on saltwater intrusion are astutely pointed out in this paragraph. Not much is said about sea level rise impacts on SWI aside from broad discussion of global rates of in the introduction. It might be worth adding some content either in the introduction or this section pointing out that rates of relative sea level rise vary substantially due to local factors such as subsidence and sedimentation. Local relative SLR is what influences saltwater intrusion, not global average rates.

Line 430: This may be implicit in point #3 as well as others, but I wonder if a task related to scaling, specifically would be useful? For example, once these various tasks are achieved will we be able to understand submarine discharge impacts on global scale processes, or is an additional task needed such as representing these fluxes in global Earth system models?

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RR by Anonymous Referee #4 (26 Dec 2022)

ED: Publish subject to minor revisions (review by editor) (17 Jan 2023) by Ben Bond-Lamberty

AR by Damian Leonardo Arévalo-Martínez on behalf of the Authors (27 Jan 2023) Author's response Author's tracked changes Manuscript

ED: Publish as is (27 Jan 2023) by Ben Bond-Lamberty

AR by Damian Leonardo Arévalo-Martínez on behalf of the Authors (27 Jan 2023)

Short summary

Groundwater flows at the land–ocean transition and the extent of freshened groundwater below the seafloor are increasingly relevant in marine sciences, both because they are a highly uncertain term of biogeochemical budgets and due to the emerging interest in the latter as a resource. Here, we discuss our perspectives on future research directions to better understand land–ocean connectivity through groundwater and its potential responses to natural and human-induced environmental changes.