Toward a Localized Water Footprint of Lithium Brine Extraction: A Case Study from the Salar de Atacama

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

1. The background information is too much in the abstract. Authors are suggested to focus more on the research results and main findings of the research in this section. At least 2/3 or 4/5 are needed to be used for the research results and main findings.
2. Do not divide several subsections in introduction section. Some paragraphs in the introduction section are too short. The introduction style is out of academic style and should be reorganized.
3. The writing style is poor. For example, line 120 figure 1 shows***.
4. The introduction of study area should be focused on the research aims rather than all information are listed there.
5. There are too many subsections in the results and discussion section. The logic of this section is not clear and should be improved.
6. The conclusion section is too long.

Author Response

Please see the attachment (Line numbers refer to attchaed tracked changes pdf)

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Please see the attached file.

Comments for author File: Comments.pdf

Author Response

Please see the attachment (Line numbers refer to attchaed tracked changes pdf)

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

This is a highly worthwhile study and very effectively communicated. It is rather lengthy, and the authors should try and be more concise. Is the discussion around Fig. 2 necessary for example. I have major comments regarding freshwater springs as important environmental assets and the absence of drawdown from the ALB abstraction. Perhaps there is a reason why there is little drawdown from the ALB well, but this needs to be explained. It is this drawdown that could impact on the critical springs.

 

Further definition of 'functional water quality' is required. Could this jargon be avoided altogether with potential for further space saving and a more directed story. The topic seems to be about drawdown impacts in relation to different zones. I think Functional units = zones. Functional units and functional water quality is confusing.

Comments for author File: Comments.pdf

Author Response

Please see the attachment (Line numbers refer to attchaed tracked changes pdf)

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Line 30: sub-section title 1.1 background is not needed for the introduction section.

Line 80: ten are too many.

Line 313: where is the content of section 3.1?

there are too many sub-sections in this part and more of them are too shallow and should be improved regarding the research depth.

Author Response

Dear reviewer, Thank you very much for your additional comments. Please find our answers below.

Comment 1: Line 30: sub-section title 1.1 background is not needed for the introduction section.

Response 1: Thanks for pointing it out. This subheading has now been deleted. 

 

Comment 2: Line 80: ten are too many.

Response 2: Thank you for sharing your impressions. However, as this is a follow-up to a previous publication in which these principles were introduced, we have stuck to the same structure to maintain consistency and familiarity. Unless you have a very specific suggestion of how we should rearrange, we would prefer to stick to the suggested structure.

 

Comment 3:  Line 313: where is the content of section 3.1?

Response 3:  Thank you. A formatting error occurred here, and the text from section 3.1 was accidentally shifted to section 3.2. We have corrected this. 

 

Comment 4: There are too many sub-sections in this part and more of them are too shallow and should be improved regarding the research depth.

Response 4: Some of the subsections are indeed short. However, we suggest keeping the structure relating to the different accounting themes and maintaining the same sub-numbering. For example, the same subheading (e.g. 2.3 and 3.3) in Method and Results/Discussion refers to the same sub-theme (here, groundwater level decline). Some sections, such as the mixing of low-salinity water with brine, are not very in-depth as there is currently no comprehensive ready-to-use data on this issue. While it is possible to explore such topics in more depth, this would most likely constitute basic research, potentially filling a separate publication if new insights can be gained. In this work, we focused more on ready-to-use data and how it could be used in a localised water footprint.

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have done an excellent job addressing a timely and relevant topic. The manuscript is now well-structured, methodologically sound, and clearly written. The localized water footprint approach applied to lithium brine extraction in the Salar de Atacama is innovative and provides valuable insights for sustainable water management. All previous comments have been addressed satisfactorily. I recommend the manuscript for publication.

Author Response

Dear reviewer,

We are happy to hear this. Thank you very much for your feedback and for the time you spent on the review. 

Kind regards and on behalf of all the authors, Andreas Link

Reviewer 3 Report

Comments and Suggestions for Authors

see attached

Comments for author File: Comments.pdf

Author Response

Dear reviewer, Thank you very much for your valuable feedback, which is much appreciated. Please find our response and the changes (-> marked red) we have made below. We hope that we could sufficiently adress your points and thank you for your time. Best wishes, and on behalf of all the authors, Andreas Link 

Comment 1: Can the authors include a paragraph clearly identifying why and how this study is different from Moran et al [62]. As far as I am aware Moran et al. is the most thorough and up to date study on the groundwater budget associated with Salar de Atacama. Is this study original because it focusses on impacts? If this is the case their should be a much more specific understanding of the environmental and cultural values of the groundwater systems. To do this the authors also improve on their loose identification of the lagoon systems that might be impacted. It does not seem possible to do this with Fig. 1. Where are ‘Soncor, Quelana, Peine, and Tilopozo’? Some of these ‘lagoons’ do not seem to be associated with the Salar. Furthermore Tilopozo is completely unrelated hydrogeologically from Quelana. The former is a spring fed wetland with relatively low salinity groundwater fed from the south by an independent aquifer [see Moran et al. Fig. 1]. According to Moran, any impacts on Tilopoza will be associated with extraction from the copper mining to the south with only modest impacts from the lithium extraction well immediately upgradient from the spring. These details seem to be left out of this study which leaves me wondering how it enhances our understanding beyond Moran et al.

Response 1: 

Thank you for this comment. Moran et al. provide a basin-wide assessment of anthropogenic water use and remain the most comprehensive study to date regarding the full water budget and varying users. It’s more on total water budgets. Our work focuses on leveraging local hydrogeological models to quantify the consequences of brine extraction on the hydrological system. A key focus is on separating and explicitly quantifying the effects of brine extraction activities. For example, we aim to determine what specific amount of groundwater drawdown can be exclusively linked to lithium brine extraction. This information is needed for methods such as water footprint assessments, where impacts are scaled relative to a unit of brine extracted (e.g., per ton of lithium). Such unit-linked impacts cannot be directly extracted from Moran et al. and require local numerical hydrolgeological models that simulate scenarios under natural conditions vs. lithium brine pumping vs. scenarios that include other overlaying human pressures. which helps to disentangle the various influencing factors.

Additionally, we explored other aspects, including:

• Changes in evaporation discharge due to mining, and
• Changes in lagoon surface areas resulting from brine extraction.
• etc.

In our work, we basically went through the list of potential effects induced by brine extraction and verified which of these could be quantified relative to a specified amount of lithium brine extracted. For example:

• X tons of lithium extraction lead, on average, to a spatially resoved decline in groundwater table depth of Y cm.
• X tons of lithium extraction lead, on average, to a decline in lagoon surface area of Y m².

We showed that for some aspects (e.g., changes in evaporation or groundwater table depth), we can link induced hydrological effects to a unit of brine extracted. For other aspects, such as for lagoon surface area, current data are insufficient because they have not yet been integrated into coupled local numerical groundwater models.

Regarding lagoons, we focused on displaying lagoons most closely attached to the Salar. While copper mining in the south was not the focus of this paper, we have excluded Tilopozo from the discussion. However, based on your comment, we have added a zoom-in map to the Appendix A to help readers locate the other for lithium mining more relevant lagoon systems (Peine, Quelana, Soncor).

We also emphasize in our work that to minimize risks for local lagoons, groundwater tables close to critical lagoon systems should be kept stable. While Moran et al. focuses on the water budget and sources, our study presents and discusses with respect to lagoons mainly the publications (Gutiérrez et al. [20] and Guzmán et al. [23]) that explicitly target the relationship between lagoon surface area decline and the amount of lithium brine extracted. However, we believe that quantifying this link more robustly will require future work coupling local numerical groundwater models with lagoon models under varying scenarios (natural, brine pumping, etc.).

Regarding cultural values of brine systems, this is indeed a valid point but pertains more to social assessment. We have addressed this in a separate study:

https://link.springer.com/article/10.1007/s11367-024-02378-8

With respect to the distinction from Moran et al., we have added several sentences in the manuscript to clarify differences:

Lines 527ff: This study tested localized water footprinting principles to assess the impact of lithium brine extraction on the SdA water balance. Unlike existing studies, which focus on basin-wide assessments of anthropogenic activities, total water and brine budgets, and their sources [62], this work aimed to analyze the feasibility of using ready-to-use models to establish the quantitative relationship between brine extraction and its induced hydrological effects. This is particularly relevant for localized, comprehensive water footprint studies, where information on changes in water table, lagoon area, or volume per unit of brine extracted is needed to characterize ecosystem impacts. When testing the applicability of previously defined accounting principles, it was found that they could not all be applied equally. However, several were feasible, including estimating the effects on evaporation, basin recharge and groundwater drawdown. In doing so, not all principles could be applied equally, but several proved feasible including estimating effects on evaporation, basin recharge, and groundwater drawdown. While mining has negligible effects on evaporation, precipitation, and basin recharge, continuous monitoring and modeling of groundwater levels are recommended. Existing numerical groundwater models suggest that current and near-future drawdown is expected to be confined to areas where it is unlikely to affect the local flora and fauna or nearby communities. However, they lack extraction scenarios needed to identify potential tipping points, critical thresholds beyond which ecosystems may undergo long-term or irreversible disturbance. In this context, an analysis of the sustainability implications of DLE technologies is needed to determine whether they could help minimize risks associated with brine extraction.

Moreover, we added the following changes with respect to local lagoons:

Lines 143ff: Figure 1 depicts the locations of mining companies’ freshwater wells, while additionally indicating the positions of relevant lagoons and surrounding communities. About the lagoons, Figure A1 of Appendix A provides an additional zoomed-in view of the main lagoon systems linked to the salt flat nucleus. 

Lines 394ff: Since there are conflicting results regarding the influence of lithium brine extraction on the evolution of lagoon surface area, we recommend that future research focuses more heavily on the development of numerical hydrogeological models that couple brine/groundwater dynamics with surface water behavior. However, the fact that groundwater levels around sensitive lagoon systems did not decrease significantly may indicate that the impact of brine extraction on these systems has been rather small so far. Assuming that lithium extraction is not the predominant driver of changes in lagoon surface area to date would also be consistent with the work of Moran et al. [62], who emphasized the importance of other influencing factors, such as climate and the full range of water users (e.g. the copper industry), in the basin.

 

Comment 2: Figure 1 I cannot make out the Lagoon systems using the symbology of the caption

Response 2: Thank you. We have rearranged Figure 1 to make it clearer. Regarding the lagoons, we have changed the hatched area in the legend to a solid pink colour, which is easier to spot. In addition, we have depicted the other lines in Figure 1, e.g., those relating to the hydrological models, somewhat more discreetly so that the lagoons are more clearly visible. Furthermore, in the supplementary information, we have provided a zoomed-in view of the lagoons east of the salt flat nucleus, as these are most likely to be affected by lithium mining. The Tilopoza lagoon system to the south was not included in our shapefile. However, as you pointed out, this lagoon has different hydrodynamics and may therefore be more susceptible to activities in the south.  

 

Comment 3: Figure 2 caption: ….zone hydrogeological model….

Response 3: Thank you. we have corrected the wording as follows (changes are highlighted in red):

Lines 236ff: Figure 2 Evaporation zones distinguished; the yellow dashed line refers to the delineation of the nucleus zone hydrogeolocial model of the nucleus zone [42], with which parallel modelling of the groundwater table depth took place.

Round 3

Reviewer 1 Report

Comments and Suggestions for Authors

It seems some of comments raised by me in last round did not addressed. Please carefully consider the comments in previous rounds.

Author Response

Dear reviewer,

Thank you very much for your feedback.

Regarding the previous review round (round 2), we have already addressed comments 1 and 3. We therefore assume that your current remarks primarily relate to comments 2 and 4.

With regard to comment 2 (the concern that the number of identified accounting issues is too high), we have provided an explanation as to why we kept it unchanged. However, we are unsure whether you have seen our response, as you did not refer to it. As this publication builds on a previous one, our preference is to stick to the structure of the previous publication to ensure consistency, unless you have a strong argument why we should leave the structure of the first paper.

With regard to comment 4 (unequal research depth between accounting topics), our objective was to determine which accounting themes could be analysed based on the available data in the Salar de Atacama. For some topics (e.g. the brine-freshwater mixing issue, which is relevant but not yet fully covered by existing data), the data remains insufficient. For others (e.g., groundwater level drawdown), we could built on available models. Naturally, therefore, the level of detail varies between topics.

However, we are, of course, happy to make improvements and would greatly appreciate any concrete suggestions on how we could refine these sections further. At present, your comments appear somewhat general and do not outline a very specific approach for improvement, which makes it a bit difficult for us to understand the precise changes you would like to see. Therefore, we haven't made additonal changes in this third review round. 

We thank you for your time and your constructive input. Kind regards and in behalf of all authors, Andreas Link

Reviewer 3 Report

Comments and Suggestions for Authors

I appreciate that the authors have carefully considered my comments and can now recommend this manuscript for publication. 

Author Response

Dear reviewer, we are very happy to hear this and thank you for your time you spent into the review. Kind regards and all the best, Andreas  

Round 4

Reviewer 1 Report

Comments and Suggestions for Authors

Do not cite references in the conclusion section.