Paleo-Geohydrology of Lake Chilwa, Malawi is the Source of Localised Groundwater Salinity and Rural Water Supply Challenges

Round 1

Reviewer 1 Report

Comments on the manuscript titled: Paleo-geohydrology of Lake Chilwa, Malawi is the source of localised groundwater salinity and rural water supply challenges by Rivett et al.

 

This paper represents a nice compendium about what we knew and what we did not know about the Lake Chilwa (Malawi). Basically, all you need to know about this lake is in here. I did appreciate the details with which the Authors described the groundwater systems in the Chilwa area and there is very few to say about this manuscript. It is basically ready for publication.

Nevertheless, I do have a few comments, as follows:

• I would add in the Supplementary Material the chemical composition of the selected waters. This would allow the reader to better understand what the Authors are referring to in their paper, although most data are from previous works.
• 9 is the same of Figure S12, isn’t it? I would only keep one of them.
• 5 is the same of Figure S6, isn’t it? I would only keep one of them.
• I have some concerns about the conceptual model. According to Authors, it seems we are in the presence of a syncline. I think that, despite the Authors are dealing with a conceptual model, a geological correspondence has to be found and, in my opinion, this is not the case. Considering that we are in a peculiar geological environment, no fault systems are reported in any of the figures; even in the conceptual model they are missing. Since there are hot springs in the area, there must be some faults that favor the uprising of deep-seated(?) fluids.
• My latter concern is related to the structure of the paper. The Authors have included in the Materials and Methods the geological and hydrogeological setting, the socioeconomic context, and other sections that actually do not belong to Materials and Methods. In my opinion, these sections should be moved after the Introduction.
• Finally, I would appreciate to understand (in the Introduction or in the new section of Materials and Methods) which are the original data and which are those from the literature.

 

In conclusion, I think that this paper fits very well the topics of the journal and can (almost) be ready for publication after minor revision.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The topic of the manuscript entitled “Paleo-geohydrology of Lake Chilwa, Malawi is the source of localised groundwater salinity and rural water supply challenges” is interesting and falls into scope of the journal.

Your manuscript is well discussed about the effect of the paleo-environments on current groundwater quality. My only concern is anthropogenic effects on groundwater quality. You have showed that Ca-HCO3 (young recharge water) water type is major in this region. In addition, I think many samples are data of shallow groundwater (hand-pumps). These results indicate the importance of discussion about local environment around the sampling points. I suggest that you have to discuss about the relationship between local land use and water quality.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

The manuscript by Michael O. Rivett and co-authors presents a detailed study on paleo deposition of lacustrine – fluvial sediments arising from former paleo Lake Chilwa and data about the current status of water supply and water-point functionality at Basin scale with specific reference to field assessment of groundwater quality within the Basin’s Phalombe District where quality issues are of local community concern. The main aim is to develop a detailed understanding and conceptualisation of groundwater quality constraints upon community water supply provision.

 

The authors present a reconstruction of the paleo-environment of Lake, the hydrology control and the geochemistry. All the dataset, the social-economic implication and the discussion on factor controlling geochemistry of groundwaters and surface water are valuable and useful for the scientific community.

 

Material and Methods.

 

I suggest the authors the methods for the analysis of water. How carbonate, total alkalinity, anion and cations were analysed? What are instruments used for these analyses? Standard Method lists several methods for, eg., the analysis of Chloride. So I suggest to better clarify the methods used.

 

Line 279: What means “good repeatability”? Could the authors give the precision and accuracy of analysis?

 

Results

 

Could the authors explain the isotopic composition of lake during wet season? Could they give references or data for rainwaters isotopic composition? Why are surface waters different from lake water isotopic composition during wet season?

 

Line 578-579: Could the authors give a number for residence time? Did they sample older groundwater and how they define older??

 

Line 624: Could the authors describe and characterize the possible end members?

 

Minor comments:

 

Line 113: “Agroundwater” replace with A groundwater

Line 194: “are” replace with “is”

Line 217: what means “34+10” and “13+9”? Is 34±10?

Line 312: Add a parenthesis: “observed).”

Line 323: this sentence “acknowledging some possible tectonic land movements since” looks incomplete

Line 330: Replace (Figure 1] with (Figure 1).

Author Response

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Author Response File: Author Response.pdf