The Influence of Groundwater Migration on Organic Matter Degradation and Biological Gas Production in the Central Depression of Qaidam Basin, China
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe paper is well written and despite some minor mistakes that do not affect the quality of the article, it can be published in this journal after these revisions.
- Lines 93-96: A figure would be better to clearly illustrate this deposition sequence.
The geology of this study area should also be better detailed to better enlighten the reader and facilitate the understanding of this lithology.
- Lines 113-114: Figure 1. The resolution of this figure is not good. the legend and the name of localities are unreadable; please improve the quality.
- Line 165: Table 1. The formula in table 1 is not clear.
- Liens 171-172: What are you basing this conclusion on? Has your data been projected into a diagram or this is a simple observation of your data.
- Lines 184-186: It would not be superfluous to clarify what the abbreviations HY, SB and TN represent in the title of Table 2. Why does this table not also contain the isotopic data which are presented and commented on in this work?
- Lines 191-193: “......consistent with previous studies on riverwater isotopic values.” Reference is needed here.
- Lines 195-197: Presentation of this data in a table is necessary.
- Lines 204-206: Improve the quality of this image to better allow reviews please.
- Lines 210-246: Please indicate in the preceding table or in another table the values ​​per sample of TOC, DOC, HIX, SUV254, E253/E203
- Lines 260-261: Enlarge this figure please
Lines 261 to the end: Why is the way of presenting references changing in the discussion section?
Author Response
Reviewer 1
The paper is well written and despite some minor mistakes that do not affect the quality of the article, it can be published in this journal after these revisions.
- Lines 93-96: A figure would be better to clearly illustrate this deposition sequence.
The geology of this study area should also be better detailed to better enlighten the reader and facilitate the understanding of this lithology.
Reply: Thanks for the suggestion. We have modified Figure 1 to make it clearer, annotated sampling locations, river and gas field locations, and added a stratigraphic map to better understand the geological features of the area.
- Lines 113-114: Figure 1. The resolution of this figure is not good. the legend and the name of localities are unreadable; please improve the quality.
Reply: Thanks for the suggestion. We have modified Figure 2 to make it clearer, and added isotope data to Table 2.
- Line 165: Table 1. The formula in table 1 is not clear.
Reply: Thanks for the suggestion. Table 1 provides clearer formulas and indicates the source of the formulas.
- Liens 171-172: What are you basing this conclusion on? Has your data been projected into a diagram or this is a simple observation of your data.
Reply: Thanks for the reviewer’s remind. The geochemical type of water samples was generated from the concentration of brief cations and anions, which is important information to analyze microbial bioactivity and biogas production.
- Lines 184-186: It would not be superfluous to clarify what the abbreviations HY, SB and TN represent in the title of Table 2. Why does this table not also contain the isotopic data which are presented and commented on in this work?
Reply: Thanks for the suggestion. We have deleted the introduction of the abbreviations and added the isotopic data in Table 1.
- Lines 191-193: “......consistent with previous studies on riverwater isotopic values.” Reference is needed here.
Reply: Thanks for the suggestion. It’s our mistake, the data were collected from the reference [11], and the reference number was added.
- Lines 195-197: Presentation of this data in a table is necessary.
Reply: Thanks for the suggestion. The isotopic data were added in Table 1.
- Lines 204-206: Improve the quality of this image to better allow reviews please.
Reply: Thanks for the suggestion. We offer a large size of figure 4 with large number size.
- Lines 210-246: Please indicate in the preceding table or in another table the values ​​per sample of TOC, DOC, HIX, SUV254, E253/E203
Reply: Thanks for the suggestion. Because of the word count limits, We chose to present these parameters by a figure which displayed the data variation directly. We shows detail data in the supplementary file and here as follows.
|
|
Type |
Depth (m) |
TOC (mg/L) |
DOC (mg/L) |
HIX |
SUV254 |
E253/E203 |
|
TD |
Brine |
0 |
5.21 |
3.34 |
1.49 |
1.16 |
0.032 |
|
XCDH |
Brine |
0 |
7.58 |
5.55 |
2.92 |
1.74 |
0.026 |
|
GEMH |
River |
0 |
4.08 |
1.92 |
1.77 |
0.59 |
0.015 |
|
YKH |
River |
0 |
3.29 |
3.84 |
1.00 |
0.019 |
0.0191 |
|
YH1 |
YH |
190 |
20.65 |
5.83 |
3.71 |
0.104 |
0.104 |
|
YH2 |
YH |
300 |
20.98 |
5.19 |
2.74 |
0.104 |
0.104 |
|
YH3 |
YH |
410 |
11.66 |
6.71 |
3.31 |
0.071 |
0.071 |
|
S1-1 |
SB |
600 |
724.01 |
3.20 |
0.34 |
0.367 |
0.367 |
|
S1-2 |
SB |
685 |
81.94 |
2.90 |
3.70 |
0.385 |
0.3857 |
|
S1-3 |
SB |
980 |
164.23 |
2.22 |
0.89 |
0.230 |
0.230 |
|
S1-4 |
SB |
1100 |
65.05 |
2.23 |
2.87 |
0.297 |
0.230 |
|
S1-5 |
SB |
1100 |
74.98 |
1.88 |
2.51 |
0.302 |
0.302 |
|
S2-1 |
SB |
1160 |
127.90 |
1.79 |
1.67 |
0.325 |
0.325 |
|
S2-2 |
SB |
1425 |
299.53 |
0.67 |
0.79 |
0.365 |
0.365 |
|
TN1 |
TN |
990 |
50.46 |
3.17 |
1.90 |
0.164 |
0.164 |
|
TN2 |
TN |
1215 |
46.29 |
2.57 |
2.17 |
0.170 |
0.170 |
|
TN3 |
TN |
1365 |
37.64 |
3.53 |
1.97 |
0.132 |
0.132 |
|
TN4 |
TN |
1500 |
421.35 |
4.10 |
0.16 |
0.126 |
0.126 |
|
TN5 |
TN |
1535 |
56.93 |
3.25 |
1.38 |
0.143 |
0.143 |
|
TN6 |
TN |
1740 |
93.14 |
2.08 |
1.02 |
0.169 |
0.169 |
- Lines 260-261: Enlarge this figure please
Reply: Thanks for the suggestion. We enlarged the number and figure size in the manuscript.
Lines 261 to the end: Why is the way of presenting references changing in the discussion section?
Reply: Thanks for the suggestion. We modified the citation counts to normal letter size.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThe authors try to explain the influence of groundwater flow on the possibility of organic mater degradation and hence on the gas production in the Qaidam Basin in China.
They use the stable isotopes of water, Deuterium and O-18 ratios, water chemistry and also different types of DOM characterization. The results are interesting and worth for publication. But in my opinion there is need for a clarification and improvements in many points. Also, the English language should be improved, as sometimes the sentences are very long and hard to understand what is the conclusion.
While reading, these questions come into my mind:
Abstract: explain CDOM-EEM already here or at least sooner than you did (page 6, line 223)
Introduction:
Please explain, what is the difference of "Bio" gas to normal a normal gas reservoir. This is not clear to me as a reader
You refer all the time to "stable isotopes". Explain what isotope ratios you measured. There are a lot more stable isotope as Deuterium and O-18.
Explain CDOM-EEM , at least write the full name.
The last sentence (line77-79) is already a result . I would skip it here.
Study area description could be improved with a additional survey map. Not everyone knows the Qaidam Basin.
You describe the geology as a Quarternary Basin. Later in the text you mention the importance of Teriary layers. To understand the geology better a at least schematic cross profile would be nice.
The quality of ALL figures in my pdf was very bad, so that I hardly couldn’t see the content which would be very important to understand your argumentation. For example I couldn’t see the location of the sampling points in Fig 1.
Sampling and Laboratory analysis section is ok. Perhaps the notation of isotopes could be better explained. Here also the CDOM-EEM method should be mentioned and explained.
Data Processing
Table 1 is not very good and could be improved, also the header is not very good understandable.
Results
Hydrochemical parameters: The text is not consistent with the data in table 2 ! is the data in the text ok „formation water between 206 and 884 mg/L ??? this is not a brine!!
Fig 2 would be especially for me very interesting and important for the following discussion, which is in part very questionable for me.
Also the next paragraph is not very clear: From where comes the DOC only from Quarternary Sediments or also from Tertiary sediments? The leaching from organic mater comes from where (plant origin or plankton origin in a fresh to saline lake?). This should be making a difference in the characterization of DOM.
I think an additional Figure with typical predominance fields of the indicators of the different sources together with the data point would make the text more understandable.
Figure 3 in the text could be hardly seen, a real pity.
Discussion:
Are the results really speaking for this interpretation or a pure assumption? Please be more precise, for example, not groundwater but the groundwater aquifer evolves to a multi layered structure…
Also “increasing isotpic values” is absolutely not precise. In this part also a lot of typos are occurring.
In the argumentation of organic matter degradation you mention the Lower Teriary formations for the first time (line 301 ff)The argumentation of “relatively long retention time” cannot be measured with stable isotopes of water, as you mean surely the reaction time for degradation is longer. But it could be also that the degradation is faster under these hydro chemical conditions…. Your argumentation is possible but it is not really supported by your data.
I would take Fig 4 to the results and not to the Discussion part.
Conclusion: This is very general and does not really refer to the interpreted results.
So all in all I recommend a thorough revision of the paper and an improvement of the discussion.
Comments on the Quality of English Language
Sometimes the language is a little bit complicated with long sentences. But beside the typos it is ok.
Author Response
The authors try to explain the influence of groundwater flow on the possibility of organic mater degradation and hence on the gas production in the Qaidam Basin in China.
They use the stable isotopes of water, Deuterium and O-18 ratios, water chemistry and also different types of DOM characterization. The results are interesting and worth for publication. But in my opinion there is need for a clarification and improvements in many points. Also, the English language should be improved, as sometimes the sentences are very long and hard to understand what is the conclusion.
While reading, these questions come into my mind:
Abstract: explain CDOM-EEM already here or at least sooner than you did (page 6, line 223)
Reply: Thanks for the reviewer’s valuable suggestion. CDOM-EEM is the Extraction-Emission Matrix (EEM) of Chromophoric Dissolved Organic Matter (CDOM) detected by a fluorescence spectrophotometer. We have added the full name of CDOM-EEM here as fluorescence excitation-emission matrix of Chromophoric dissolved organic matter
Introduction:
Please explain, what is the difference of "Bio" gas to normal a normal gas reservoir. This is not clear to me as a reader
Reply: Thanks for the suggestion. The introduction of biogas was added to the first sentence as follows: Biogas is a natural gas produced by the degradation of organic matter by microorganisms.
You refer all the time to "stable isotopes". Explain what isotope ratios you measured. There are a lot more stable isotope as Deuterium and O-18.
Reply: Thanks for the suggestion. We have modified the measurement method of δ18O and δ2H, The isotope ratios was introduced as follows:
Line 137-140: Hydrogen and oxygen isotopes were analyzed using the Piccaro 2140 ultra-high-precision water isotope analyzer (Piccaro, USA) with a testing precision of D < 0.1‰ and δ18O < 0.025‰. The isotopic ratios of δ2H and δ18O were expressed as a permil (‰) deviation from Vienna Standard Mean Ocean Water (VSMOW).
Explain CDOM-EEM , at least write the full name.
Reply: Thanks for the suggestion. CDOM-EEM is the Extraction-Emission Matrix (EEM) of Chromophoric Dissolved Organic Matter (CDOM) detected by a fluorescence spectrophotometer. We have added the full name of CDOM-EEM here as fluorescence excitation-emission matrix of Chromophoric dissolved organic matter.
The last sentence (line77-79) is already a result. I would skip it here.
Reply: Thanks for the suggestion. We have modified the sentence as follows:
Line 78-80: We try to explain the biogas formation and production mechanism from the groundwater and nutrition migration process in the Quaternary strata.
Study area description could be improved with a additional survey map. Not everyone knows the Qaidam Basin.
Reply:
You describe the geology as a Quarternary Basin. Later in the text you mention the importance of Teriary layers. To understand the geology better a at least schematic cross profile would be nice.
The quality of ALL figures in my pdf was very bad, so that I hardly couldn’t see the content which would be very important to understand your argumentation. For example I couldn’t see the location of the sampling points in Fig 1.
Sampling and Laboratory analysis section is ok. Perhaps the notation of isotopes could be better explained. Here also the CDOM-EEM method should be mentioned and explained.
Data Processing
Table 1 is not very good and could be improved, also the header is not very good understandable.
Results
Hydrochemical parameters: The text is not consistent with the data in table 2 ! is the data in the text ok „formation water between 206 and 884 mg/L ??? this is not a brine!!
Reply: Thanks for the reviewer’s remind. The geochemical type of water samples was generated from the concentration of brief cations and anions, which is important information to analyze microbial bioactivity and biogas production. But, the impacts of individual cations or anions are not specific in this research, so we explain the geochemical type and TDS variations to show the geochemical change instead of describing the details of all parameters. The TDS of formation data ranged from 84.4 to 206.3 mg/L, where we made a mistake and recorrected it.
Fig 2 would be especially for me very interesting and important for the following discussion, which is in part very questionable for me.
Also the next paragraph is not very clear: From where comes the DOC only from Quarternary Sediments or also from Tertiary sediments? The leaching from organic mater comes from where (plant origin or plankton origin in a fresh to saline lake?). This should be making a difference in the characterization of DOM.
Reply: Thanks for the reviewer’s valuable suggestion. As shown in Fig. 1 we have modified, the Quarternary Sediments in Qaidam Basin has a depth of more than 2000m, and our water samples were collected from a depth of less than 1800m. Thus, the organic matter in this research comes from the Quarternary Sediments but not Tertiary sediments. The previous research revealed that the hydrocarbon source rock in Qigequan formation originated from plant origin in the saline lake(reference [17]), and the plant sourced organic matter were easily degraded by microbes. Modification were made in the discussion section line 310.
I think an additional Figure with typical predominance fields of the indicators of the different sources together with the data point would make the text more understandable.
Figure 3 in the text could be hardly seen, a real pity.
Reply: Thanks for the suggestion. We enlarged the figure size in the manuscript.
Discussion:
Are the results really speaking for this interpretation or a pure assumption? Please be more precise, for example, not groundwater but the groundwater aquifer evolves to a multi layered structure…
Also “increasing isotpic values” is absolutely not precise. In this part also a lot of typos are occurring.
In the argumentation of organic matter degradation you mention the Lower Teriary formations for the first time (line 301 ff)The argumentation of “relatively long retention time” cannot be measured with stable isotopes of water, as you mean surely the reaction time for degradation is longer. But it could be also that the degradation is faster under these hydro chemical conditions…. Your argumentation is possible but it is not really supported by your data.
Reply: Thanks for the reviewer’s suggestion. As mentioned in the previous reply, all water samples were collected from the Quarternary Sediments, and the organic matter originated from Quarternary Sediments too. We have made a mistake in translation of “Lower Teriary formations”, which should be the lower layers of Qigequan Formation which is the third layer of Quaternary Formation.
The retention time of groundwater can be measured by the ratio of tritium but not δD and δ18O indeed. However, the values of δD and δ18O reveal the influence of precipitation and water cycling, which offers more valuable information on understanding groundwater migration and surface water recharge. The “relatively long retention time” indicated that the longer retention time induced to the stronger evaporative fraction and resulted in the higher δD and δ18O values. We modified the sentence as follows to make it precise:
Line 322-324: As described in section 4.1, high values of δD and δ18O indicated long-time retention, and the long-time retention caused the significant substance interaction between water and bedrock which generated to increase in water salinity and mineralization levels. Meanwhile, long-time substance interaction also caused organic matter dissolving and migration.
We agree that the hydro chemical conditions control the organic matter degradation in formation water. The hydro chemical conditions offer suitable environment for the microbes, and the microbes decompose organic matter quickly in suitable hydro chemical conditions. But, in the inhibited hydro chemical conditions, microbes can’t survive, and organic matter degradation will stop. The high TOC concentrations were observed with the high values of δD and δ18O, and the reason is long retention time and strong water-rock interaction induced both high value of δD , δ18O, salinity and organic matter concentration. However, the recharge of modern precipitation changed the hydro chemical conditions, which brings low δD, δ18O and fresh water mixing and creates a suitable hydro chemical conditions. The low δD and δ18O values were observed with the low value of TOC. The change of δD and δ18O values and TOC could not be simply explained by dilution because the CDOM characters were changed. the degradation index and function group were decreased in the low TOC concentration formation. In order to make the paragraph precise, wo modified the sentences as follows:
Line 329-335: Microbial degradation is the main factor of organic matter decomposition and biogas formation[19-20], but microbial activities would be inhibited by extremely high salinity [8,27]. Thus, the organic matter degradation is accomplished in the environment that is suitable for heterotrophic bacteria and methanogens to survive, which means lower salinity and δD and δ18O values. Conversely, the formation environment with high salinity and δD and δ18O values would inhibit microbial activity and organic matter decomposition, and remained high organic matter concentrations.
I would take Fig 4 to the results and not to the Discussion part.
Conclusion: This is very general and does not really refer to the interpreted results.
So all in all I recommend a thorough revision of the paper and an improvement of the discussion.
Reply:Thank you very much for the hard work of the reviewer. We has made detailed revisions to achieve the publication. Figure 4 is a cross plot based on the data in the previous table during the discussion, so it is appropriate to place it in that location.The conclusion section summarizes the core working methods and ideas of the article, which the author believes is appropriate and not suitable for major revisions
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsI think the paper is now in a state to be published.
Comments on the Quality of English Languageis ok
