Reactive Transport of NH4+ in the Hyporheic Zone from the Ground Water to the Surface Water
Round 1
Reviewer 1 Report
The work presents an experiment that looks at potential geochemical remediation of ammonium contamination. This is is an important problem worthy of study but the current manuscript is not ready for publication. Furthermore, the work is described as biogeochemical but as a far, as I can tell the work is geochemical without microbiological components.
Methods - these are not described in enough detail to tell if the experiment was conducted to a high enough standard. Particular issues are highlighted below.
- More detail needed on synthetic water. What reagents were used (brands etc.) to make this up? What purity of DIW was used? Was the synthetic water sterilised? If so, how?
- More detail need on sediments. How was the sediment sourced? What was there composition?
- Remove “We should note that the used deionised water does not contain ammonium ions” – this is not needed.
Results - figures are nicely produced but the text needs to be more quantitative in its style. I.e. it talks about peaks and troughs but doesn’t say what these values are.
Discussion - Very brief and needs a lot more detail.
Author Response
Dear Editors and Reviewers:
Thank you for your letter and for the reviewers’ comments concerning our manuscript entitled “Reactive transport of NH4+ in the hyporheic zone from the ground water to the surface water” (ID: 1648336). Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully and have made correction which we hope meet with approval. Revised portion are marked in blue in the paper. The main corrections in the paper and the responds to the reviewer’s comments are as following:
Response to Comments of Reviewer #1
Reviewer #1 : The work presents an experiment that looks at potential geochemical remediation of ammonium contamination. This is is an important problem worthy of study but the current manuscript is not ready for publication. Furthermore, the work is described as biogeochemical but as a far, as I can tell the work is geochemical without microbiological components.
1.Methods - these are not described in enough detail to tell if the experiment was conducted to a high enough standard. Particular issues are highlighted below.
(1) More detail needed on synthetic water. What reagents were used (brands etc.) to make this up? What purity of DIW was used? Was the synthetic water sterilised? If so, how?
Reply: Thanks for your suggestion. The Recipe of Synthetic Ground Water was added and this part was revised in manuscript, table 1, which was highlighted in blue. The water was used with ultrapure water system by Millipore super-Q plus. The synthetic water was used immediately so it was not sterilised. This part was revised in manuscript, line 73, which was highlighted in blue.
(2) More detail need on sediments. How was the sediment sourced? What was there composition?
Reply: Thanks for your suggestion. The sediments collected from Shuangxikou reservoir HZ. Before use for the experiments, the sediment was homogenized after removed plant shatters and stones and then air-dried and was sieved in 2mm after that it was stored at 4℃. In this paper, we need to understand the transport of NH4+ in the hyporheic zone from the ground water to the surface water, so we carried out the experiments used the sediments sampled in the field. This part was revised in manuscript, line 67-69, 116-120,which was highlighted in blue.
(3) Remove “We should note that the used deionised water does not contain ammonium ions” – this is not needed.
Reply: Thanks for your suggestion. The sentence was deteled.
2.Results - figures are nicely produced but the text needs to be more quantitative in its style. I.e. it talks about peaks and troughs but doesn’t say what these values are.
Reply: Thanks for your suggestion. This part was revised in manuscript, line 136-142, which was highlighted in blue.
3.Discussion - Very brief and needs a lot more detail.
Reply: Thanks for your suggestion. This part was revised in manuscript, line 177-182, which was highlighted in blue.
Special thanks to you for your good comments.
We tried our best to improve the manuscript and made some changes in the manuscript. These changes will not influence the content and framework of the paper. And here we did not list the changes but marked in blue in revised paper.
We appreciate for Editors/Reviewers’ warm work earnestly, and hope that the correction will meet with approval.
Once again, thank you very much for your comments and suggestions.
Best regards,
Ailan Yan
Reviewer 2 Report
Thank you for the opportunity to review Reactive transport of NH4+ in the hyporheic zone from the ground water to the surface water (water-1648336). The provides an analysis of core tracer studies to assess the influence of anaerobic versus aerobic conditions on NH4+. The proper has the potential to provide insight into the transport and fate of NH4+ in the HZ, but the paper suffers from issues in the experimental design and the reporting of the data. I have documented my concerns within the pdf, but I highlight here my concerns with the methodology/experimental design:
Core development
- What is the geochemistry of the sediment? This has implications for cation exchange capacity.
- What is the particle size distribution of the sediment? Were the cores that were developed created to represent a similar orientation/packaging of the sediment?
- How well did the packing represent real conditions? What is the porosity and hydraulic conductivity of the cores (and how did this compare to the real-world)?
- What is the organic content of the sediment? Was it the same for both cores? The organic content will influence the biological activity.
Synthetic Groundwater:
- How was the determination of the SGW composition determined?
- How much Br was added? What was the cation associated with the Br? If it was NaBr, did this offset the concentration of Na within the synthetic groundwater?
Results:
- How were the Darcy Velocity values calculated - what was used for K and the what was the hydraulic gradient?
- First - without knowing the units it is hard to interpret the data. However, why is sorbtion the reason for 0 NH4? Could it be that the travel times precluded concentrations in the values? With residence times of ~1.8 hours it would seem that the NH4 would take time before reaching the outlet. Second, is there a possibility of transformation that occurs, reducing the concentration-evidence available to support or refute this idea?
- For both aerobic and anaerobic. is the increase in Na a result of the Br tracer, i.e. if it was NaBr?
Comments for author File: 
Comments.pdf
Author Response
Dear Editors and Reviewers:
Thank you for your letter and for the reviewers’ comments concerning our manuscript entitled “Reactive transport of NH4+ in the hyporheic zone from the ground water to the surface water” (ID: 1648336). Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully and have made correction which we hope meet with approval. Revised portion are marked in blue in the paper. The main corrections in the paper and the responds to the reviewer’s comments are as following:
Response to Comments of Reviewer #2
Reviewer #2 : Thank you for the opportunity to review Reactive transport of NH4+ in the hyporheic zone from the ground water to the surface water (water-1648336). The provides an analysis of core tracer studies to assess the influence of anaerobic versus aerobic conditions on NH4+. The proper has the potential to provide insight into the transport and fate of NH4+ in the HZ, but the paper suffers from issues in the experimental design and the reporting of the data. I have documented my concerns within the pdf, but I highlight here my concerns with the methodology/experimental design:
1.What is the geochemistry of the sediment? This has implications for cation exchange capacity.
Reply: Thanks for your suggeston. The geochemistry of the sediment was added in the paper. This part was revised in manuscript, line 116-120, which was highlighted in blue.
2.What is the particle size distribution of the sediment? Were the cores that were developed created to represent a similar orientation/packaging of the sediment?
Reply: Thanks for your question. Before use for the experiments, the sediment was homogenized after removed plant shatters and stones and then air-dried and was sieved in 2mm after that it was stored at 4℃. This part was revised in manuscript, line 67-69, which was highlighted in blue. The length of the column was used for mimicking the behaviour of NH4+ with 10.5~10.7cm, actually, the sediment of the HZ was thicker than 10.5cm. This part was revised in manuscript, line 116-120, which was highlighted in blue.
3.What is the organic content of the sediment? Was it the same for both cores? The organic content will influence the biological activity.
Reply: Thanks for your question and suggestion. The organic content of the sediment was 15.6g/Kg. Both cores were the same sediment. This part was revised in manuscript, line 120, which was highlighted in blue.
4.Synthetic Groundwater:
（1）How was the determination of the SGW composition determined?
Reply: Thanks for your suggestion. Based on literatures and the determination of experiment site of groundwater composition, we figured out the recipe of SGW. This part was revised in manuscript, line 71-72, which was highlighted in blue.
literature: Yan A , Liu C , Liu Y , et al. Effect of ion exchange on the rate of aerobic microbial oxidation of ammonium in hyporheic zone sediments[J]. Environmental Science and Pollution Research 2018, 25(2):8880-8887.
（2）How much Br was added? What was the cation associated with the Br? If it was NaBr, did this offset the concentration of Na within the synthetic groundwater?
Reply: Thanks for your suggeston. The content of Br was 37.2mg/L in KBr, This data was revised and added in the Table 1, which was highlighted in blue in Table 1 and line 97-100. It has offset the concentration of K within the synthetic groundwater.
5.Results:
（1）How were the Darcy Velocity values calculated - what was used for K and the what was the hydraulic gradient?
Reply: Thanks for your question. The Darcy Velocity values were calculated with flow rate (mL/h) dividing by A (cm^2) ,which was highlighted in blue in line 125.
（2）First - without knowing the units it is hard to interpret the data. However, why is sorbtion the reason for 0 NH4? Could it be that the travel times precluded concentrations in the values? With residence times of ~1.8 hours it would seem that the NH4 would take time before reaching the outlet. Second, is there a possibility of transformation that occurs, reducing the concentration-evidence available to support or refute this idea?
Reply: Thanks for your suggestion. The units of data is mM in all figures. With residence times of ~1.8 PV with Br run through the column, the NH4 would take time before reaching the outlet, but after that, it takes a couple of PV for NH4+ coming out from the column, NH4+ is supposed to take part in all kinds of reactions,which was highlighted in blue in line 127-128.
（3）For both aerobic and anaerobic. is the increase in Na a result of the Br tracer, i.e. if it was NaBr?
Reply: Thanks for your question. For both aerobic and anaerobic condition, it was KBr as the Br tracer and the K+ content has been offset in the ions exchange data.
Special thanks to you for your good comments.
We tried our best to improve the manuscript and made some changes in the manuscript. These changes will not influence the content and framework of the paper. And here we did not list the changes but marked in blue in revised paper.
We appreciate for Editors/Reviewers’ warm work earnestly, and hope that the correction will meet with approval.
Once again, thank you very much for your comments and suggestions.
Best regards,
Ailan Yan
Round 2
Reviewer 1 Report
The authors have addressed my original comments on the methods and results well. This was essential to bringing this paper up to publication standard. Personally, I still feel that the discussion is too brief - it reads much more like a conclusion than a discussion. In a discussion, I like to see the authors explain to the reader how the results explain the answers to their aims. This discussion leaves a lot of work for the reader to do.
Author Response
Dear Editors and Reviewers:
Thank you for your letter and for the reviewers’ comments concerning our manuscript entitled “Reactive transport of NH4+ in the hyporheic zone from the ground water to the surface water” (ID: 1648336) in round 2. Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully and have made correction which we hope meet with approval. Revised portion are marked in blue in the paper. The main corrections in the paper and the responds to the reviewer’s comments are as following:
Response to Comments of Reviewer #1
Reviewer #1 : The authors have addressed my original comments on the methods and results well. This was essential to bringing this paper up to publication standard. Personally, I still feel that the discussion is too brief - it reads much more like a conclusion than a discussion. In a discussion, I like to see the authors explain to the reader how the results explain the answers to their aims. This discussion leaves a lot of work for the reader to do.
Reply: Thanks for your suggestion. This part was revised in manuscript, line 177-189, 208-210 which were highlighted in blue.
Special thanks to you for your good comments.
We tried our best to improve the manuscript and made some changes in the manuscript. These changes will not influence the content and framework of the paper. And here we did not list the changes but marked in blue in revised paper.
We appreciate for Editors/Reviewers’ warm work earnestly, and hope that the correction will meet with approval.
Once again, thank you very much for your comments and suggestions.
Best regards,
Ailan Yan
Reviewer 2 Report
My original concerns have been addressed. As I read through the revision, I had some additional questions about the results and discussion based upon the revisions and the additional information provided.
As the flow rate and the concentration of NH4 added is know, what is the mass balance of N in the system? What is the recovery of N and how much of the N was transformed during the period of evaluation?
The discussion does not place the work in the context of the science. The discussion is a summary of the work. The paper could be strengthened by comparing the results with other work, highlighting the similarities and pointing out the new findings.
Author Response
Dear Editors and Reviewers:
Thank you for your letter and for the reviewers’ comments concerning our manuscript entitled “Reactive transport of NH4+ in the hyporheic zone from the ground water to the surface water” (ID: 1648336) in round 2. Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully and have made correction which we hope meet with approval. Revised portion are marked in blue in the paper. The main corrections in the paper and the responds to the reviewer’s comments are as following:
Response to Comments of Reviewer #2
Reviewer #2 : My original concerns have been addressed. As I read through the revision, I had some additional questions about the results and discussion based upon the revisions and the additional information provided.
1.As the flow rate and the concentration of NH4 added is know, what is the mass balance of N in the system? What is the recovery of N and how much of the N was transformed during the period of evaluation?
Reply: Thanks for your suggestion. According to literatures, there exist four reactions at least for ammonia nitrogen in sediments (figure 1), including ammoxidation ( nitrification and anammox); DNRA—Dissimilatory Nitrate Reduction to Ammonium; assimilatory (organic N) and adsorption (ion exchange). While in this paper, we didn’t test the reactions of DNRA and assimilatory, so we couldn’t give the value of transformed N for it may cause inaccuracy result to the mass balance of N in the system.
Figure 1. The paths for ammonia nitrogen in sediments
2.The discussion does not place the work in the context of the science. The discussion is a summary of the work. The paper could be strengthened by comparing the results with other work, highlighting the similarities and pointing out the new findings.
Reply: Thanks for your suggestion. This part was revised in manuscript, line 177-189, 208-210 which were highlighted in blue.
Special thanks to you for your good comments.
We tried our best to improve the manuscript and made some changes in the manuscript. These changes will not influence the content and framework of the paper. And here we did not list the changes but marked in blue in revised paper.
We appreciate for Editors/Reviewers’ warm work earnestly, and hope that the correction will meet with approval.
Once again, thank you very much for your comments and suggestions.
Best regards,
Ailan Yan
Author Response File: Author Response.pdf
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
