Seasonal Groundwater Quality Status and Nitrogen Contamination in the Shallow Aquifer System of the Kathmandu Valley, Nepal

Lines 224-227: The inverse relationship between the nitrogen compounds during the dry and wet seasons suggests the site-specific nitrification of NH4-N into NO3-N triggered by the oxygen derived from the infiltrated rainfall.

Although other studies such as Dwivedi et al. (2018; see below) also showed the outsized impacts of short rainfall in contributing to groundwater nitrogen levels, it is not clear that soil organic matter contains significant NH4+ around Kathmandu valley. Second, NH4-N concentrations were similar in both seasons in the clay dominated area. How quickly different waters (clay and gravel dominated) mix?

Dwivedi, D., Arora, B., Steefel, C. I., Dafflon, B., & Versteeg, R. (2018). Hot spots and hot moments of nitrogen in a riparian corridor. Water Resources Research, 54, 205–222. https://doi.org/ 10.1002/2017WR022346

Response: Thank you very much for your suggestion. Using the reference, you have send, we have modified our discussion section where the redox condition in both the gravel and clay bearing aquifers.

Line 277: Rainfall is the primary means through which water returns to the groundwater system. How about the return flow from irrigation? For example, see the following papers Hot spots and persistence of nitrate in aquifers across scales; D Dwivedi, B Mohanty - Entropy, 2016 Hudak, P. Regional trends in nitrate content of Texas groundwater. J. Hydrol. 2000, 228, 37–47.

Response: Thank you very much for your valuable suggestion. From your suggestion we have removed the confusing statement in Line 277.

However, the possible discussion referring the above mentioned paper is added in the discussion sections. in Line no. 346-348, 480-484.

Lines 279-281: Consequently, dilution after rainfall is also an important mechanism of the attenuation of contamination in aquifer systems [40]. According to Lasagna et al. [41], the dilution potential is independent of the chemical conditions which are mostly dominated by the volumetric flow.

What are concentrations of nitrogen species in the rainwater?

Response: Rainfall concentration contains Cl of 1 mg/l whereas, NH4-N and NO3-N were 2.9 and 0.3 mg/L respectively (Shrestha et al., 2013), it is quite low concentrations compare with groundwater. They are presented in Line no. 344- 348.

Lines 294-296: The reduction of dissolved Fe2+ during the wet season indicates the effects of dilution and changes in the oxidation state of groundwater after rainwater infiltration.

This statement seems incorrect. Fe3+ might get reduced not, Fe2+? Please check? For more details on redox changes, see the following papers:

Influence of hydrological, biogeochemical and temperature transients on subsurface carbon fluxes in a flood plain environment

B Arora, NF Spycher, CI Steefel, S Molins, M Bill… - Biogeochemistry, 2016

Geochemical exports to river from the intrameander hyporheic zone under transient hydrologic conditions: East River Mountainous Watershed, Colorado

D Dwivedi, CI Steefel, B Arora, M Newcomer… - Water Resources Research, 2018

Response: Thank you very much for your suggestion and reference for the better discussion of our manuscript.  For the better understanding we have stated the sentence as “The deduction in the chemical concentration of dissolved Fe²⁺ during the wet season indicates the effects of dilution and changes in the oxidation state of groundwater after rainwater infiltration” in Line no. 363 -365.

1)     In the abstract, provide more important numerical values of the data collected.

Response: Thank you very much for your suggestion. We have now added the compared data in the abstract section for better understanding.

2)     In the entire results and discussion section, refer to more literatures on this topic and facilitate good (critical) discussion which has scientific basis. A lot of paragraphs merely look like a lab report and monitoring results. The implications of the result should be analyzed and discussed.

Response: Thank you very much for your suggestion. The discussion section is more clarified with scientific research paper as a reference added in Line no. 336 – 348, 354-361, 365-367, 374-382, 392-411, 416- 424, 429-432, 435-439, 467-474, 480- 487, 492-497, and 531- 535.

3)     What are the different legislation's pertaining to nitrogen compound, chloride and iron in Nepal and how does it compare with WHO, Japanese, Indian, EU and USEPA standards. Provide numbers and references.

Response: Thank you very much for the suggestion. In order to make more easy in comparing between other drinking water standards we have added the water quality standards from WHO, USEPA, Indian standard specification for drinking water in Line no. 171- 183.

4)     How does natural water purification occur?

Response: Sorry for the unclear statement in the manuscript. For more clarity we have added “Although natural purification of groundwater contamination occurs from natural filtration, absorption, chemical equilibrium, microbial degradation, dispersion” in Line no. 47-49.

5)     Provide a nice schematics (original) on N cycling in groundwater and explain the mechanisms involved. It is very important for the readers.

Response: Thank you very much for your suggestion. The schematic diagram is added as Figure 6 and placed in Line no. 349

Kind note: The authors should answer all the comments and implement them in the manuscript. Do not write ''this question was not within the scope of this work''. Please refer to recent literature and improve the scientific discussion.

6)     What factors caused heterogeneity of the groundwater contamination? Provide good examples and provide more new references.

Response: Thank you very much for pointing out the unclear expression. The expression has been changed to point source contamination in Line no. 181-183.

7)     What is the public perception about shallow dug wells? How much is the water polluted in different types of wells in Nepal. Please also provide values of other water quality parameters.

Response: Thank you very much for your suggestion. Referring to Warner et al., and Pant et al., the public perception on groundwater is added in Line no. 63 - 66 and Line no. 68- 69. Also, the health affect paragraph is added in Line no 531- 540.

8)     What are the other competing ions present in water and how does the ionic speciation affect the water quality. Provide good examples.

Response: Thank you very much for your comment. We have however, referred some of the reference in Line no. 67- 69.

9)     What are the biological and chemical reactions that occur in water where N, Cl and Fe are involved. Write all the possible reactions and facilitate more water chemistry based discussion.

Response: Thank you very much for your suggestion. We have added the equations in our manuscript and have used them Line no 368- 371 and 420- 424.

10)  How does temporal fluctuations affect the health of the people and the environment? Give good perspective by referring to manuscripts dealing with health and environment. Its very important.

Response: Thank you very much in pointing out the suggestion. We have added the explanation to your suggestion in Line no. 336 to 343.

Please: The journal WATER does not just publish reports. Its important to discuss the results and provide the authors own perspective to protect public health.

11)  Write some policy based recommendations for the Nepalese government based on the research outcomes.

Response: Thank you very much for your suggestion. We have added recommendation section in this manuscript based on the research outcomes in Recommendation section in Line no. 562-569.

12)  Provide more details on all the instruments and equipments used in this research, its model number and also country of manufacture.

Response: Thank you for your suggestions, we added the more detail information in the “2.3. Measurement Equipment “in Line no. 133-148.

13)  The effect of ORP and pH should be discussed with the help of chemistry based discussions. Refer to literatures.

Response: Thank you very much for your suggestion. The suggestions were used in the equations and a short description is included in discussion section Line no. 355-357, 365-367.

14)  What are the natural sources of Cl. Give good examples from Nepal.

Response: We are very sorry for the unclear statement. For clear understanding we have changed the statement from Line no. 374-382 and whole the paragraph is modified.

15)  Write the conclusions in line with the specific objectives. At present, it looks like a summary of results. Write the conclusions within 150 words.

Response: Thank you very much for your suggestion. We have now modified our conclusion section with the specific objectives.

16)  Write the novelty of this work in 5 sentences (in introduction section).

Response: Thank you very much for your suggestion. We have added our novelty of this study in the Kathmandu Valley in Line no. 84- 89.

17)  There are LOT of formatting mistakes with respect to the references. Unwanted upper case, lower case, author names are wrong (some with Latin names have accents), page numbers, issue number, etc. It has to be checked MANUALLY, word by word.

Response: We are very sorry for the errors. The mistakes have been rechecked manually and corrected.

18)  Use uniform font type and font size in the figures ...x and y axis. Many are wrongly formatted.

Response: We are very sorry for the font type mistake. The uniform font has been used in the manuscript.