Linking Changes in Land Cover and Land Use of the Lower Mekong Basin to Instream Nitrate and Total Suspended Solids Variations
Round 1
Reviewer 1 Report
The authors present a review of the status of the Mekong River and discuss the basis for changes that were observed in nitrate and suspended solids concentrations across the basin. The information presented is timely and relevant, although the paper would benefit from a more focused approach to the results obtained from the data analysis. The drivers identified through the decomposition of the data sets should be the focus of the paper. There are some findings identified that seem to differ from those more commonly found in the literature. For example, the authors note that, in contrast to many studies where forested lands are considered as undisturbed baseline condition, forested lands seem to contribute to the enhanced loads of suspended solids and nitrates. These are significant findings that should be considered further; perhaps the issue is not so much undisturbed forest lands and actively managed/harvested forest lands? The manuscript should be reviewed for consistency between number (plural v singular) and tense (present v past). Generally, past tense should be used when discussing the findings discovered through the analysis, for example. On p 2, the footnote could be incorporated into the text (it is on p 6, which is duplicative). Acronyms should be spelled out on first use (e.g., DEM in Fig 2). On line 204-205, the title of the Standard Methods manual should be italicised. On line 232, the FAO is properly the Food and Agriculture Organization of the United Nations. Figures 6 and 7 could be more extensively discussed as these are critical to the basic message of the paper, and are an approach that could be transferred to other studies. The figures and tables are appropriate and the references are current and applicable.
In short, the paper is of significant interest but seems to be written more in the form of a technical report that a journal article. It would make a good book chapter! However, as a journal article it requires greater focus on the results obtained by the researchers versus a review of previous work.
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
The present study is rather long. It contains more than 600 rows. In my opinion, the introduction is too long, and the results are overinterpreted. Some findings are not necessarily accurate based on the results. The biggest flaw is about methodology. Water discharge data is missing. TSS and nitrate concentration are in close relationship with water discharge. Thus the interpretation without this aspect is not adequate. Moreover, water quality values are investigated regarding the landuse of the given subbasin. Nothing is known about the ratio of runoff from the subbasin and the water discharge from the upper sections. I presume, especially at the lower parts of the river, the entering water discharge has a significant effect on water quality measured at the outlet. Runoff connectivity within the subbasins (e.g. runoff from paddies? or the role of ditches) is not involved even though it plays a fundamental role in water quality. Besides, the role of urbanized areas, e.g., wastewater treatment and load is not taken into account. The authors investigated the only landuse, however, it does not mean there are no additional driving forces such as animal husbandry, industry, or wastewaters.
For me, r2=0.2 means that there is no linkage at all. If the authors would like to prove the relationship, they must provide the significance level for the correlations. These results in the abstract are not acceptable.
In conclusion, the authors simply repeat the results without concluding any further information.
My additional comments are in the text attached.
Comments for author File: Comments.pdf
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
The manuscript by Kongmeng and co-authors is an interesting analysis of the impact of land use change on water quality data. It evidences results which are not surprising but confirm and document a number of processes in act in the Mekong river basin as well as in many other region of the world.
The step by step data analysis is not always described, in particular, I would suggest to add a short description of the method used to decompose the time series.
Furthermore, instead of showing the correlation of TSS and land cover (Figure 8) only for the year 2010, I would suggest to show how the correlation changed with time, in order to validate the conclusions.
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
The paper is completely reorganized, however, the most methodological flaws mentioned in the first round are still present. For example, I still do believe that
The authors did not address all my comments taken in the text. Their responses to my questions are not always focused on the problem. In the revised version 12 figs are included, which are too many. Also, the text (and the conclusion) is still too long. Besides the overinterpretation, in many places, the paper is not clear. E.g. I guess some sort of PCA is included as a statistical method, but nothing is given about this in the methods. The results in Fig 12a-b are redundant and obscured. Why have the red dots the same pattern but different scales?; r=-54 in line 577 or 295; 13 references are invalid in the list, "7,986 to 12,599 MJ.mm/ha2" are given as rainfall-runoff in line 341, even though based on its unit it seems to be some rainfall energy-related property; etc.
Telling the truths, I did not recognize significant improvement.
Author Response
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Author Response File: 
Author Response.docx
Reviewer 3 Report
I appreciated the way the Authors addressed the comments of the Reviewes.
Author Response
Dear reviewer,
Thank you for your comments.
