Using Dual Isotopes of Nitrate to Identify the Source of Nitrogen Pollution in the Songhua River Basin, Northeast China

Round 1

Reviewer 1 Report

Dear Author,

the manuscript is well structured but needs some improvements before the next step.

Introduction

The authors may have already provided a good literature review. Please add the authors’ new contribution to the published knowledge here. Row 39 add somethings like: "Methodologies based on the use of isotopes in a full spectrum of hydrological problems encountered in water resource assessment, development, and management activities are already scientifically established and are an integral part of many water resource investigations and environmental studies (Isotopes in hydrology and hydrogeology, Water (Switzerland)Open AccessVolume 11, Issue 27 February 2019 Article number 291). 

Methodology

Please add quality control for the isotopic analyses;

Discussion and Conclusion

Please add some solutions to prevention and the early warning responses to nitrogen pollution.

Author Response

Reviewer 1:

Dear Author,

the manuscript is well structured but needs some improvements before the next step.

Introduction

The authors may have already provided a good literature review. Please add the authors’ new contribution to the published knowledge here. Line 39 add somethings like: "Methodologies based on the use of isotopes in a full spectrum of hydrological problems encountered in water resource assessment, development, and management activities are already scientifically established and are an integral part of many water resource investigations and environmental studies (Isotopes in hydrology and hydrogeology, Water (Switzerland)Open Access Volume 11, Issue 27 February 2019 Article number 291). 

Response/Action: “Methodologies based on the use of isotopes in a full spectrum of hydrological problems encountered in water resource assessment, development, and management activities are already scientifically established and are an integral part of many water resource investigations and environmental studies[9]” were added. (Please see in line 40-43)

 

Methodology

Please add quality control for the isotopic analyses;

Response/Action:

It was added. The Environmental Stable Isotope Lab of Chinese Academy of Agricultural Sciences was entrusted to determine the nitrate nitrogen isotope δ¹⁵N-NO₃ and the nitrate oxygen isotope δ¹⁸O-NO₃. The Lab has actively cooperated with seven stable isotope laboratories in Europe and participated in international comparison. The experimental results have been recognized and highly praised by international peers. The laboratory uses the reference materials of IAEA and USGS to calibrate the relevant results, and uses the international standard determination method to determine the stable isotopes of C, H, O, N and S, so as to ensure the accuracy of the results. (Please see in line 80-85)

Discussion and Conclusion

Please add some solutions to prevention and the early warning responses to nitrogen pollution.

Response/Action: The prevention responses to nitrogen pollution were added. “For the control of nitrogen in SHR, it is necessary to control the point source input of urban production and domestic sewage in low flow season based on the nitrogen source analysis results. In high and flat flow season, the source of nitrogen is complex, the use of chemical fertilizer should be controlled primarily”. (Please see in line 320-322)

Author Response File: Author Response.docx

Reviewer 2 Report

The paper “Using dual isotopes of nitrate to identify the source of nitrogen pollution in the Songhua River Basin, Northeast China” by Ye et al. presents the investigation results for the contribution of nitrate pollution sources to the Songhua River Basin, Northeast China. Although the topic is interesting and the results may help to manage the water pollution problems in the watershed are, the paper has significant flaws as listed below. These concerns should be addressed before consideration of publication in the Water journal.

 

General comments:

• Detailed descriptions of isotope analysis, instrumentation, reference materials, and uncertainties related to the analysis should be presented.
• Clear description for defining end members is critical for the isotope balance model, which is the key to this paper. However, currently there is no discussion about this.
• The paper presents only simple calculation results for the obtained data without in-depth interpretation. Also, most of description for the data are repetitive.
• No general implication of the study is presented, other than information about the study area.

 

Specific comments:

Line 12-14: “…the main sources of nitrogen in the water were qualitatively analyzed by combining the water chemistry data with isotope data for nitrate, nitrogen, and oxygen.” --> NO water chemistry data is presented in this paper.

Line 14: “isotope data for nitrate, nitrogen, and oxygen” --> “isotope data for nitrogen and oxygen of nitrate”.

Line 46: “accurate” --> “accurately”

Line 51: “the Iso Source mass balance model” --> Up to this point, readers don't have any information about the Iso Source mass balance model.

Line 61-62: “which was drawn by ArcGIS.” --> don't need this information.

Line 65-66: “The distribution of the 36 research sections is shown in Fig. 1(a).” --> Why explanation about Fig. 1(a) is appearing in the last, while Fig. 1(c) is appearing in the first?

Figure 1: Needs location for the study site in terms of the entire map of China.

Line 92: “The basic Iso Source model” --> The model seems to be a typical 3-components isotopic balance model. Why was it named specifically?

Line 96: “for the three pollution sources” --> Defining end members are critical to use this type of balance model. What are the three pollution sources? Do you have confidence for defining end members?

Line 104: “using Denitrifying Bacteria Method in the laboratory” --> Cite the reference. Also present instrument details, the reference materials, and uncertainties related to the analysis.

Line 113: “and drawn by Origin9.0.” --> don't need this information.

Line 135: “In conclusion” --> It's too early to conclude at this point.

All figures: For all figures, why not using colors?

Line 141-142: “The contribution rates of the three major pollution sources during the low flow season are shown in Fig.3” --> There is no information about how the contribution rates were calculated? How were the end members identified and defined?

Line 142: “which was drawn by Origin.” --> don't need this information.

Line 174-176: “During the sampling period in August 2019, the SHR was hit by serious flooding, among which the Yitong River and the Up reach of SHR were the most serious. The water level exceeded the river limits, and roads and farmland along the river were flooded.” --> Needs information about the weather conditions in the method section, including the source of weather information.

Figure 6: What the difference between Fig. 2 and Fig. 6?

Figure 7: What the difference between Fig. 3 and Fig. 7?

Author Response

 General comments:

General comment 1）Detailed descriptions of isotope analysis, instrumentation, reference materials, and uncertainties related to the analysis should be presented.

Response/Action: It was added. The Environmental Stable Isotope Lab of Chinese Academy of Agricultural Sciences was entrusted to determine the nitrate nitrogen isotope δ¹⁵N-NO₃ and the nitrate oxygen isotope δ¹⁸O-NO₃. The Lab has actively cooperated with seven stable isotope laboratories in Europe and participated in international comparison. The experimental results have been recognized and highly praised by international peers. The laboratory uses the reference materials of IAEA and USGS to calibrate the relevant results, and uses the international standard determination method to determine the stable isotopes of C, H, O, N and S, so as to ensure the accuracy of the results. (Please see in line 80-85)

 

 General comment 2）Clear description for defining end members is critical for the isotope balance model, which is the key to this paper. However, currently there is no discussion about this.

Response/Action: It was added. Isosource is based on the source analytical model and the principle of mass conservation of stable isotopes. It can be used to quantify different nitrate pollution sources [14,15]. (Please see in line 52-53)

 

 General comment 3）The paper presents only simple calculation results for the obtained data without in-depth interpretation. Also, most of description for the data are repetitive.

Response/Action: In this study, the isotope tracer technique was used to analyze the main source of nitrogen pollution in the SHR, and the Iso Source mass balance model was used to calculate the pollution contribution rate of the major pollutants in each water stage. Based on the source analysis of the low, high and flat seasons, the main sources of nitrogen in the SHR were comprehensively evaluated, providing scientific and technological support for nitrogen pollution control in the SHR. It can also provide reference for nitrogen source apportionment in other watersheds.

 

 General comments 4）No general implication of the study is presented, other than information about the study area.

Response/Action: It was added. “In recent years, nitrogen has become one of the main environmental pollutants in SHR, it affects the assessment of water quality of SHR. Analyzing the main source is very important for nitrogen pollution control in SHR”. Based on the source analysis of the low, high and flat seasons, the main sources of nitrogen in the SHR were comprehensively evaluated, providing scientific and technological support for nitrogen pollution control in the SHR. It can also provide reference for nitrogen source apportionment in other watersheds. (Please see in line 54-60)

 

Specific comment 1）Line 12-14: “…the main sources of nitrogen in the water were qualitatively analyzed by combining the water chemistry data with isotope data for nitrate, nitrogen, and oxygen.” --> NO water chemistry data is presented in this paper.

Response/Action: It was revised. “by combining the water chemistry data was cancelled. (Please see in line 13)

 

Specific comment 2）Line 14: “isotope data for nitrate, nitrogen, and oxygen” --> “isotope data for nitrogen and oxygen of nitrate”.

Response/Action: It was revised. (Please see in line 14)

 

Specific comment 3）Line 46: “accurate” --> “accurately”

Response/Action: It was revised. (Please see in line 49)

 

Specific comment 4）Line 51: “the Iso Source mass balance model” --> Up to this point, readers don't have any information about the Iso Source mass balance model.

Response/Action: It was added. “Isosource is based on the source analytical model and the principle of mass conservation of stable isotopes. It can be used to quantify different nitrate pollution sources [14,15]”. (Please see in line 52-53)

 

Specific comment 5）Line 61-62: “which was drawn by ArcGIS.” --> don't need this information.

Response/Action: It was cancelled. (Please see in line 70)

 

Specific comment 6）Line 65-66: “The distribution of the 36 research sections is shown in Fig. 1(a).” --> Why explanation about Fig. 1(a) is appearing in the last, while Fig. 1(c) is appearing in the first?

Response/Action: The order of Fig. 1(a) to Fig. 1(d) was adjusted. (Please see in line 65-78)

 

Specific comment 7）Figure 1: Needs location for the study site in terms of the entire map of China.

Response/Action: It was added. (Please see in Fig. 1(a), line 74)

 

Specific comment 8）Line 92: “The basic Iso Source model” --> The model seems to be a typical 3-components isotopic balance model. Why was it named specifically?

Response/Action: Yes, the References [14.15] were added. And the main 3 pollution sources were added. (Please see in line 103-110)

 

Specific comment 9）Line 96: “for the three pollution sources” --> Defining end members are critical to use this type of balance model. What are the three pollution sources? Do you have confidence for defining end members?

Response/Action: It was added. “In SHR, soil organic nitrogen, domestic and manure sewage, atmospheric deposition are the main three pollution sources in low flow season. soil organic nitrogen, nitrogen fertilizers, domestic and manure sewage are the main three pollution sources in flat and high flow season[2,5]”. (Please see in line 107~110)

 

Specific comment 10）Line 104: “using Denitrifying Bacteria Method in the laboratory” --> Cite the reference. Also present instrument details, the reference materials, and uncertainties related to the analysis.

Response/Action: It was revised. The Environmental Stable Isotope Lab of Chinese Academy of Agricultural Sciences was entrusted to determine the nitrate nitrogen isotope δ¹⁵N-NO₃ and the nitrate oxygen isotope δ¹⁸O-NO₃. “The δ¹⁵N-NO₃ and δ¹⁸O-NO₃ were measured by using Denitrifying Bacteria Method in Environmental Stable Isotope Lab of Chinese Academy of Agricultural Sciences” (Please see in line 117-118)

 

Specific comment 11）Line 113: “and drawn by Origin9.0.” --> don't need this information.

Response/Action: It was cancelled. (Please see in line 126)

 

Specific comment 12）Line 135: “In conclusion” --> It's too early to conclude at this point.

Response/Action: It was cancelled. (Please see in line 151)

 

Specific comment 13）All figures: For all figures, why not using colors?

Response/Action: All figures were changed to using colors. (Please see in Fig. 1~ Fig. 7)

 

Specific comment 14）Line 141-142: “The contribution rates of the three major pollution sources during the low flow season are shown in Fig.3” --> There is no information about how the contribution rates were calculated? How were the end members identified and defined?

Response/Action: The contribution rates of the three major pollution sources was referenced the References [14,15,27]. And the main 3 pollution sources were added. “In SHR, soil organic nitrogen, domestic and manure sewage, atmospheric deposition are the main three pollution sources in low flow season. soil organic nitrogen, nitrogen fertilizers, domestic and manure sewage are the main three pollution sources in flat and high flow season[2,5]”. (Please see in (Please see in line 103-110)

 

Specific comment 15）Line 142: “which was drawn by Origin.” --> don't need this information.

Response/Action: It was cancelled. (Please see in Line 156)

 

Specific comment 16）Line 174-176: “During the sampling period in August 2019, the SHR was hit by serious flooding, among which the Yitong River and the Up reach of SHR were the most serious. The water level exceeded the river limits, and roads and farmland along the river were flooded.” --> Needs information about the weather conditions in the method section, including the source of weather information.

Response/Action: It was added. “The SHR is located in Northeast China. It has distinct water periods, in which Jan., Feb., Mar., Apr., Nov., Dec. are low flow season (period of ice sealed), May, Sep., Oct. are flat flow season, Jun. Jul., Aug. are high flow season.” (Please see in Line 63-64)

Specific comment 17）Figure 6: What the difference between Fig. 2 and Fig. 6?

Response/Action: Fig. 2 shows δ¹⁵N and δ¹⁸O values of nitrate in SHR during low flow season. Fig. 6 shows δ¹⁵N and δ¹⁸O values of nitrate in SHR during flat flow season. The points are located in different intervals. It shows that the sources of nitrate nitrogen during flat flow season and low flow season are different.

 

Specific comment 18）Figure 7: What the difference between Fig. 3 and Fig. 7?

Response/Action: Fig. 3 shows the 3 main sources contribution rate of nitrogen to the SHR during low flow season. Fig. 7 shows the 3 main sources contribution rate of nitrogen to the SHR during low flat season. The contribution rates of the three main sources are different.

Author Response File: Author Response.docx

Reviewer 3 Report

Great fun article. Very relevant.

The introduction is very short and concise.
The purpose of the work is not formulated.

Lines 28-60 should be moved to Section 2.2 (Analytical procedures).

Methods, procedures, standards according to which chemical analyzes were performed are not specified.

There is no reference to Figures 2, 4, 6.

Author Response

Reviewer 3

Great fun article. Very relevant.

The introduction is very short and concise.

Response/Action: The introduction was enriched. “Methodologies based on the use of isotopes in a full spectrum of hydrological problems encountered in water resource assessment, development, and management activities are already scientifically established and are an integral part of many water resource investigations and environmental studies[9].” “Isosource is based on the source analytical model and the principle of mass conservation of stable isotopes. It can be used to quantify different nitrate pollution sources[14,15]” “In recent years, nitrogen has become one of the main environmental pollutants in SHR, it affects the assessment of water quality of SHR. Analyzing the main source is very important for nitrogen pollution control in SHR” (Please see in line 40-60)

 

The purpose of the work is not formulated.

Response/Action: The purpose of the work was added. “In recent years, nitrogen has become one of the main environmental pollutants in SHR, it affects the assessment of water quality of SHR. Analyzing the main source is very important for nitrogen pollution control in SHR”. Based on the source analysis of the low, high and flat seasons, the main sources of nitrogen in the SHR were comprehensively evaluated, providing scientific and technological support for nitrogen pollution control in the SHR. It can also provide reference for nitrogen source apportionment in other watersheds (Please see in line 55-60)

 

Lines 58-60 should be moved to Section 2.2 (Analytical procedures).

Response/Action: Lines 58-60 was moved to Section 2.2. (Please see in line 80)

 

Methods, procedures, standards according to which chemical analyzes were performed are not specified.

Response/Action: It was added. The Environmental Stable Isotope Lab of Chinese Academy of Agricultural Sciences was entrusted to determine the nitrate nitrogen isotope δ¹⁵N-NO₃ and the nitrate oxygen isotope δ¹⁸O-NO₃. The Lab has actively cooperated with seven stable isotope laboratories in Europe and participated in international comparison. The experimental results have been recognized and highly praised by international peers. The laboratory uses the reference materials of IAEA and USGS to calibrate the relevant results, and uses the international standard determination method to determine the stable isotopes of C, H, O, N and S, so as to ensure the accuracy of the results. (Please see in line 80-85)

 

There is no reference to Figures 2, 4, 6.

Response/Action: It was added. (Please see in line 126, 191, 255)

Author Response File: Author Response.docx

Reviewer 4 Report

This paper is well organised and written and it can be published in this version

Author Response

Thank you for your comments.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The authors followed my reviewer comments and now the extended abstract is significantly improved and appropriate for publication.

Reviewer 2 Report

The authors have responded relatively well to the reviewers’ comments and thus the paper has been improved. Now it is recommended to be accepted in its present form.