Source and Mobilization Mechanism of Iron, Manganese and Arsenic in Groundwater of Shuangliao City, Northeast China

Round 1

Reviewer 1 Report

I like the manuscript contents.

The few suggestions on how to improve it are as follows:

consider the no of significant figures in table 1 be more precise; for example 'the red-ox state is a factor to dissolve..' ==> the reducing conditions limit language blunders eg. oxidation state ==> oxic Table 1 - provide units 'overage'- explain; I had to look the word in the dictionary Table 1; provide medians for TDS, TH, WLF line 160: remove 'strongly'  from strongly correlated for the platform samples

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

General comments: The study presents the results of a hydrochemical investigation of processes leading to elevated levels of iron, manganese and arsenic in groundwater in Northeast China. Arsenic especially is an important problem in groundwater worldwide and this study can contribute to a better understanding of the scope and causes. The authors use geospatial relationships and statistical correlation to interpret the sources and causes of the elevated arsenic, iron and manganese.  Nitrate and sulfide redox processes are completely ignored and should at least be considered in the introduction. While adequately written, there are many instances of incorrect terminology and other inconsistencies that need to be address before the article should be considered for publication. Reductive dissolution is mechanism that has been suggested as a cause for elevated levels of arsenic in other aquifers. Please incorporate results from addition recent investigations as part of the introduction and explanation of the mechanisms involved (see list below), and pay close attention to studies that have injected reactive carbon into shallow groundwater.

Specific comments:

Line 21: “results” do not “prove” conclusions

Line 46: This sentence must be rephrased. Iron and manganese dissolution/precipitation is not simply related to groundwater flow (e.g. dissolution happens without flow). Microbial activity, dissolved organic carbon, and oxygen or other terminal electron acceptor concentrations all control primary forms of iron and manganese minerals.

Line 88-89: What is meant by “overage rate”? I suggest this be rephrased.

Line 89-90: Phreatic aquifer is redundant. Eliminate “phreatic”

Line 94-95: Provide reference for soil salinization. Is it possible to highlight regions on Figure 1?

Lines 112-119: Were field blanks collected? How was pH, turbidity, alkalinity, and ammonia measured? Provide additional details for the analytical methods used, including instrumentation used, detection limits, and quality controls analyzed with samples.

Line 125: Explain “factor analysis”. Is this the same as principal component analysis? Provide some details of the methodology and contrast with regression analysis.

Line 128: How are the average Fe and Mn concentrations of soil types determined? What is the source of the data?

Line 130: Add legend and scale to figure. Include units for groundwater contours. How is the contour map generated?

Line 154: Add units to all parameters in Table 1. How is “WLF” determined?

Line 158: “Medium” correlation has no meaning. Suggest using correlation coefficient and confidence level. “Negative medium correlation” should be rephrased and qualified numerically.

Lines 164-165: The equations presented require organic carbon. Do the authors have data to support these reaction pathways? Are there related studies they can point to with similar processes that have been documented?

Line 170-175: I suggest you support the approach used for factor analysis with another study of groundwater chemistry.

Line 193: This appears to be speculation. Is there a previous study that can be cited for organic carbon availability in the aquifers?

Line 244: Figure 5 is misleading. The Fe and Mn concentrations are groundwater. Is the soil type from the areas the wells were sampled? Is there data on Fe and Mn in soils?

Line 282: Label each figure with the “groundwater dynamic” it is intended to depict. These all appear to have shallow water tables and would be expected to be hydrologically linked to surface. Are there data from deeper wells that could strengthen the observed concentrations and suggested processes?

Additional References

Biswas, A., Gustafsson, J.P., Neidhardt, H., Halder, D., Kundu, A.K., Chatterjee, D., Berner, Z. and Bhattacharya, P., 2014. Role of competing ions in the mobilization of arsenic in groundwater of Bengal Basin: insight from surface complexation modeling. Water research, 55, pp.30-39.

Kim MJ, Nriagu J, Haack S. Arsenic species and chemistry in groundwater of southeast Michigan. Environmental Pollution. 2002 Dec 1;120(2):379-90.

Neidhardt, H., Berner, Z.A., Freikowski, D., Biswas, A., Majumder, S., Winter, J., Gallert, C., Chatterjee, D. and Norra, S., 2014. Organic carbon induced mobilization of iron and manganese in a West Bengal aquifer and the muted response of groundwater arsenic concentrations. Chemical Geology, 367, pp.51-62.

Rawson, J., Siade, A., Sun, J., Neidhardt, H., Berg, M. and Prommer, H., 2017. Quantifying reactive transport processes governing arsenic mobility after injection of reactive organic carbon into a Bengal Delta aquifer. Environmental science & technology, 51(15), pp.8471-8480.

Shakoor, M.B., Bibi, I., Niazi, N.K., Shahid, M., Nawaz, M.F., Farooqi, A., Naidu, R., Rahman, M.M., Murtaza, G. and Lüttge, A., 2018. The evaluation of arsenic contamination potential, speciation and hydrogeochemical behaviour in aquifers of Punjab, Pakistan. Chemosphere, 199, pp.737-746.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

The authors have responded to comments and suggestions, improving the quality of the manuscript. However, I have a few final comments:

lines 120-133: Please check units and report all detection limits in same units used throughout the paper. Cite sources and methods used to determine detection limits. Cite chemistry for photometric ammonia detection method. It is unusual for spectrophotometry methods to specify part per trillion detection. At the very least, these should represent 3 times the standard deviation of the instrument noise level and there should be evidence provided that blanks did not contain  concentrations above these concentrations. 

 

line 333 - Please specify the units for turnover time. I suggest expanding the both the x and y-axis to illustrate the expected ages of groundwater and concentrations as predicted by this simple model (figure 6). Note this observation in the introduction

  

 

Author Response

Point 1:lines 120-133: Please check units and report all detection limits in same units used throughout the paper. Cite sources and methods used to determine detection limits. Cite chemistry for photometric ammonia detection method. It is unusual for spectrophotometry methods to specify part per trillion detection. At the very least, these should represent 3 times the standard deviation of the instrument noise level and there should be evidence provided that blanks did not contain  concentrations above these concentrations.

Response 1:

Thanks a lot for the kind suggestion. We are very sorry for the mistake in the last manuscript. Because of the novel coronavirus pneumonia in China, experimenters of the lab were off duty. An employee unfamiliar with the lab gave me the wrong information. After contacting again, we corrected the mistake. We rewrote it on lines 122-138 in the revised highlighted manuscript by saying that “The water samples were tested by Pony Testing International Group in Changchun (http://www.ponytest.com). The laboratory has CMA (China Inspection Body and Laboratory Mandatory Approval) certification. Temperature and pH were measured in situ using EC/pH meter (HANNA, HI99131) [22]. TDS was measured by an electric blast drying oven and an electronic analytical balance (vapor-drying method) [22]. Turbidity was determined via formazine scatterometer method (Xinrui, WGZ-200), the detection limit was determined to be 0.5NTU [22]. Total hardness (TH) was measured by Na₂EDTA titrimetric method, the detection limit was determined to be 1.0 mg/L [22]. HCO- 3 were measured by acid-base titration [23]. Fe and Mn were tested by inductively coupled plasma atomic emission spectrometry (Agilent, 5100ICP-OES), the detection limits were determined to be 0.0045 mg/L and 0.0005 mg/L respectively [24]. Total As was determined by atomic fluorescence spectroscopy (Jinsuokun, SK-2003A), the detection limit was determined to be 0.0010 mg/L [24]. Ammonia nitrogen was analyzed using ultraviolet-visible spectrophotometer (UNICO, UV-2800), the detection limit was determined to be 0.025mg/L [25]. Procedural blanks and replicate samples were also analyzed in a similar way to check the accuracy of analysis. The reliability of the water sample analysis data was checked by the relative error of the anion and cation milliequivalent, and the error of all water samples was less than 5%.” And we corrected other mistakes in the revised highlighted manuscript.

The added references are:

 

National standardization administration of China. Standard examination methods for drinking water: Organoleptic and physical parameters (GB/T 5750.4-2006), 1st ed.; China Standard Press: Beijing, China, 2007; pp. 1-11. (In Chinese) State Environmental Protection Administration. Methods for monitoring and analyzing water and wastewater, 4th ed.; China Environmental Science Press: Beijing, China, 2004; pp. 120-126. (In Chinese) National standardization administration of China. Standard examination methods for drinking water: Metal parameters (GB/T 5750.6-2006), 1st ed.; China Standard Press: Beijing, China, 2007; pp. 1-30. (In Chinese) National standardization administration of China. Standard examination methods for drinking water: Nonmetal parameters (GB/T 5750.5-2006), 1st ed.; China Standard Press: Beijing, China, 2007; pp. 30-35. (In Chinese)

Point 2:line 333 - Please specify the units for turnover time. I suggest expanding the both the x and y-axis to illustrate the expected ages of groundwater and concentrations as predicted by this simple model (figure 6). Note this observation in the introduction

Response 2:

Thanks a lot for the kind suggestion. As suggested, we added units for turnover time on line 335-337. In addition to those introduced in the introduction by saying that “With the increase of residence time, the groundwater gradually changes from oxic to reductive, and the reductive dissolution of Fe/Mn oxides increases the concentration of Fe and Mn in groundwater”, we added the observation on lines 80-81 by saying that “ In addition, a good correlation between the concentration of Fe/Mn and residence time was found in the study area.” The result of this study shows that there is a good correlation between residence time and the concentration of Fe/Mn. However, it remains to be seen whether such a good correlation will persist with the increase in residence time. Therefore, it is not recommended to expand the X-axis and Y-axis based on the existing research data.