Influence of Rainfall Seasonality in Groundwater Chemistry at Western Region of São Paulo State—Brazil

Round 1

Reviewer 1 Report

I have read with interest your paper on "Influence of Rainfall Seasonality in Groundwater Chemistry at Western Region of São Paulo State-Brazil". As you say, it is important to consider groundwater quality against its recharge patterns, especially in the populous state of Sao Paulo in Brazil. Moreover, something that has been quite overlooked, is the transboundary nature of groundwater resources, which adds another layer of complexity to groundwater management. Here are suggestions to improve the paper:

• In the introduction clearly state: 1) the relevant literature within which this paper is situated; 2) the gap and your original contribution to the literature.
• Explain again in the Methodological section why you have picked this case study; justify it in a more convincing way.
• Concerning Brazil, include the issue of transboundary waters and their relevance to the state of sau paulo, therefore the guarani aquifer (think of the different scales issue, and how waters are subject to different governance structures and dynamics in the case of shared groundwater - which are more locally used and decided upon - and surface waters; e.g. Guarani VS La Plata). I suggest reading and including the following two studies: 1)  da Silva, Luis Paulo Batista. "Production of scale in regional hydropolitics: an analysis of La Plata River Basin and the Guarani Aquifer System in South America." Geoforum 99 (2019): 42-53; 2) Hussein, H. (2018). The Guarani Aquifer System, highly present but not high profile: A hydropolitical analysis of transboundary groundwater governance. Environmental Science & Policy, 83, 54-62.

They should provide you and the readers with further information on the transboundary nature of the guarani aquifer system.

Author Response

Dear Reviewer 

We appreciate the considerations made by the reviewer.  However, we want to clarify that the studied system was the Bauru aquifer. The Guarani aquifer is located more than 400 meters deep, covered by the sandstones of the Bauru Group and the Diamantina Formation. We know that there are wells that use the water from the Guanari aquifer, but the effect of the rain seasonality has very little effect on this system. Despite the good contribution of the reviewer, the authors decided not to include the theme of the Guanari aquifer, considering it out of context about the effect of the pluviometric index and the seasonal behavior of the metals studied in the Santo Anastácio aquifer.

 

 

Reviewer 2 Report

The submitted study relates biweekly variation in concentration of lead, cadmium, and copper ions, detected for 17 months in 7 wells of an aquifer (named Santo Anastácio) belonging to a regional aquifer system, whit the changes of pluviometric index of the region (West of São Paulo, Brazil). Thus, on direct and inverse correlation, two different sources, natural and antropic respectively, are inferred. The main stated goal seems to be "to improve and comprehend hydrochemical processes of groundwater in the western region of São Paulo State" (lines 57-58).

Sections regarding "study area" and "methods" are inappropriately placed at the end of the manuscript. Nevertheless, "Instructions for Authors" of Water indicate to put "Materials and Methods" between "Introduction" and "Results". In the case of the submitted study, the publisher-required location is really necessary. The belonging of the aquifer to a complex system and the short monitoring time, as well as the small number of considered wells, require again to change the succession of the sections by moving the current section 4.Methods after section 1.Introduction.

Moreover, the description of the study area must be improve. Authors should provide a description of location/features of the Santo Anastácio aquifer in reference to the Bauru aquifer system. A new introduction figure with the location of the underground bodies of the West of São Paulo would be useful for readers. What portion of aquifer do the seven wells (they are placed in an area of a few square kilometers) represent with respect to the whole Santo Anastácio aquifer? How is the Santo Anastácio aquifer hydrogeologically connected to the regional aquifer system?

It must be emphasized that, in the submitted version, the state of the hydrogeological knowledge of the case study is not explicited. Only a rough indication of its transmissivity is given (line 346). This does not allow to understand the possible novelty of the study and not even its usefulness for water management purposes. The authors are therefore invited to indicate previous works on the Bauru Aquifer System (also with specific reference to Santo Anastácio aquifer) and to present the state of knowledge, with emphasis on the specific issues.

With regard to the provenance of cadmium and lead from minerals present in the aquifer itself, can the authors provide more evidences? For the origin of the copper ions, do the authors consider further investigation necessary or do they consider their hypothesis sufficiently proven?

With the order of the Sections in the first submission, the months of well monitoring are unknown for the reader up to page 19 (line 349). In fact, in Tables 1, 2, 4, 6, the years are generically indicated, XX and YY. This is another reason to review the order of the Sections.

The authors stated the seven wells have been monitored "over a period of 17 months from August 2010 to December 2012" (lines 348-349). If the monitoring was continuous, as it should be, from August to December two years later are 29 months. Therefore there should be some error in the dates. Please, check them.

Author Response

Dear Reviewer

Regarding comments, firstly I thank for the interest and suggestions on the manuscript. I apologize if any question was not answered completely or with relevance for the reviewer. But I tried to answer the questions with details necessary. 

1) The manuscript was reformulated according to the reviewer's suggestion to change the positions of descriptions.

2) We understand the need for a better presentation of the stratification of the Bauru aquifer system. However, it is difficult for us to create a profile for the Bauru Group because we are not geologists. Even so, we quote a reference that describes stratification.

3) The emphasis of our manuscript was to verify the seasonality and to have an indication of the difference in behavior between the quantified  metals during the entire study period. 

4)  In our research group, we have been studying the emanation of radon gas and its correlation to lead in soil in the region.  The presence of radon in the subsoil is an indication of the presence of these chemical elements. This manuscript is the result of a master degree. Currently, we are studying the origin of these elements, trying to better understand the transport of species in groundwater focused on the Santo Anastácio aquifer.

5) The correct period is August / 2017 to December / 2019. The text has been corrected.

 

Reviewer 3 Report

Dear authors,

The monitoring of potential toxic contaminants (PTC) in groundwater resources is very important to: (1) understand their origin (natural or anthropogenic); (2) to evaluate the risks for human health; and, (3) to evaluate the risks for dependent ecosystems.

The identification of influence of rainfall seasonality in groundwater chemistry is indeed important but requires more than the observation of the impact of seasonality in the groundwater chemistry.

According to my personal view, the research paper “Influence of rainfall seasonality in groundwater chemistry at western region of São Paulo State (Brazil)” fails to deliver an understanding of the geochemical processes that release the PTC in groundwater. I do not reject it because I think there is an important number of monitoring sites and data that can be used for further interpretation.

I believe the paper needs to be completely reviewed and submitted again and I leave here some recommendations for the authors:

[Comment 01]: Paper structure needs to be changed: Introduction – Study Area – Methodology – Results – Conclusions. It is not correct to leave the section on methods for the last chapter.

[Comment 02]: Introduction: it is so general that becomes very little relevant for the paper. Rewrite.

[Comment 03]: Study Area – should be a section separate from the methods more detailed information needs to be provided about local geology/hydrogeology and recharge processes. Map with groundwater level and flow directions. I suggest to draw a conceptualization of the water circulation from the rainfall to the soil, unsaturated zone and aquifer so that the readers understand the rapid response of the aquifer to rainfall events.

[Comment 04]: In the methods it should be justified the monitoring period (why this number of months) and the selection of monitoring points (why and how these points were selected). Limitations of the methods, problems faced should be pointed and discussed;

[Comment 05]: Information on the rainwater chemistry should be provided in a study that is analyzing the influence of rainfall seasonality. I suggest that if the authors have chemical analysis for the rainwater they can calculate the rainwater contribution for groundwater using chloride as a tracer (I recommend the reading of the chapter 2 – From rainwater to groundwater of the book on Geochemistry, Groundwater and Pollution by C.A.J. Appelo & Dieke Postma. ISBN 9780415364287).

[Comment 06]: It should be provided a general description of the hydrochemical background of the study area (major ions, pH, EC at least).

[Comment 07]: Once interpretation of the rainwater chemistry is identified, then the authors can calculate the contribution of water-rock interaction and try to identify the main geochemical processes that justify the temporal evolution of the observed concentrations of Cd, Pb and Cu.

[Comment 08]: Reduce the number of tables (some can go to annex). Graphs are much more easy to read and analyze.

[Comment 09]: Conclusions should include recommendations for rainfall monitoring in groundwater studies.

A good review of the paper and a reinterpretation of the data using a more ambitious methodology (than just simple statistical analysis that does go beyond increase/decrease conclusions about wet/dry season periods) should provide a nice paper for international dissemination.

Author Response

Thank you very much for reviewing this manuscript. Please find answers to all your comments in attachment. 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Given the Sau Paulo State is also served by transboundary waters of the Guarani, I thought mention of this aspect would have been useful. If the authors do not feel the same, this is up to them I believe.

Author Response

Dear Reviewer

Thanks for the comments. We know the importance of the Guarani Aquifer. By the way, we have a project to evaluate the presence of arsenic in this aquifer.

Reviewer 2 Report

The few changes made have slightly improved the text.
To refer the question of the Bauru Aquifer System to a literature article is a convenient expedient. However, it does not provide the reader with a vision of the general hydrogeological context, which on the contrary is forced to other readings.
In the revised version, there is a short final addition that gives, at least, a perspective for the continuation of the research. However, the authors did not make a great effort to amend the text of the first submission.
Overall, the revised manuscript is suitable for publication, although further work in Section 4 would make it better.

Author Response

Dear Reviewer

We appreciate the comments attributed to our manuscript. We know that the issues raised are to improve the work developed. We added a hydrogeological map. The aquifer system was highlighted in green on the map. In this new version, information about the saturation thickness and transmissivity of the aquifer in focus in the portion of the study area was added.

In addition, the study continues to be developed with the objective of obtaining better answers about the effect of seasonality observed in the aquifer. The difficulty in better interpreting the transport of species in the Santo Anastácio aquifer is in the absence of articles on the subject. However, we are motivated by the possibility that our work will be the first for this aquifer.