Seasonal characterization of CDOM for lakes in semiarid regions of  Northeast China using excitation–emission matrix fluorescence and parallel  factor analysis (EEM–PARAFAC)

Zhao, Ying; Song, Kaishan; Wen, Zhidan; Li, Lin; Zang, Shuying; Shao, Tiantian; Li, Sijia; Du, Jia

doi:https://doi.org/10.5194/bg-13-1635-2016

Articles | Volume 13, issue 5

https://doi.org/10.5194/bg-13-1635-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/bg-13-1635-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 13, issue 5

Research article

|

17 Mar 2016

Research article |

| 17 Mar 2016

Seasonal characterization of CDOM for lakes in semiarid regions of Northeast China using excitation–emission matrix fluorescence and parallel factor analysis (EEM–PARAFAC)

Ying Zhao, Kaishan Song, Zhidan Wen, Lin Li, Shuying Zang, Tiantian Shao, Sijia Li, and Jia Du

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Final revised paper (published on 17 Mar 2016)
Supplement to the final revised paper
Preprint (discussion started on 15 Apr 2015)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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- Supplement

SC C1351: 'Comments', Khan M. G. Mostofa, 17 Apr 2015
- AC C3018: 'Reply to comments (SC C1351) from Mostofa KMG', Kaishan Song, 23 Jun 2015
RC C2557: 'Referee comment on "Seasonal characterization of CDOM for lakes in semi-arid regions of Northeast China using excitation-emission matrices fluorescence and parallel factor analysis (EEM-PARAFAC)"', Anonymous Referee #1, 03 Jun 2015
- AC C3021: 'Reply to comments (RC C2557) from Anonymous Referee', Kaishan Song, 23 Jun 2015
SC C3088: 'Seasonal characterization of CDOM for lakes in semi-arid regions of Northeast China using excitation-emission matrices fluorescence and parallel factor analysis (EEM-PARAFAC).', Khan M. G. Mostofa, 24 Jun 2015
- AC C5292: 'Responses to the comments (bgd-12-C3088-2015)', Kaishan Song, 12 Sep 2015
RC C4015: 'Comments', Anonymous Referee #2, 31 Jul 2015
- AC C5295: 'Response to the comments (bgd-12-C4015-2015)', Kaishan Song, 12 Sep 2015

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

ED: Reconsider after major revisions (02 Aug 2015) by Gerhard Herndl

AR by Kaishan Song on behalf of the Authors (12 Sep 2015) Author's response Manuscript

ED: Referee Nomination & Report Request started (10 Oct 2015) by Gerhard Herndl

RR by Anonymous Referee #1 (29 Oct 2015)

Suggestions for revision or reasons for rejection

Review II
Zhao, Y. et. al
“Seasonal characterization of CDOM for lakes in semi-arid regions of Northeast China using excitation-emission matrices fluorescence and parallel factor analysis (EEM-PARAFAC)”

General comments
The revised version of the manuscript improved in terms of readability. Still I want to point out some major issues that should be reconsidered:
• Statistics. In order to rely on so many regression analyses I recommend using multivariate analyses: A principal component analysis (PCA) based on the four fluorescence components containing the different lakes, the four seasons and maybe salinity as factor in order to reveal the major controls on fluorescent component distribution, e.g. is the between-lake variability higher than the seasonal variability? In how far might salinity affect the distribution? Though the authors do not aim at extracting differences between freshwater and brackish water DOM fluorescent component composition it might still be interesting to mention in how far salinity could play a role and why it had/ had no effects in this study. Secondly, I suggest performing a model II-ANOVA using season and lake as random effect factors
• The absorption coefficients still lack explanations: why have these specific absorption values been used (a254, a350, a280)? What do they indicate and what conclusions can be drawn from finding correlations with other factors like DOC or salinity?
• The discussion part might need an adaptation to the findings of new statistics. Anyway, it needs more actual discussion. Implications of the main findings should be pointed out more clearly in the summary.
• Proof-reading of the manuscript from a native speaker is highly recommended

Specific comments
Introduction
line54: better use “its ability” instead of “this ability”
line 82: unclear what is meant with “…are distributed due to its geomorphology”.
line 93: better use “at different seasons”
line 97: state why exactly it is interesting to link all of these factors

Materials and Methods
line105: in how far do these lakes form two groups? Due to geographical position only or are there also other factors? Is there variation within both groups as well (e.g. differences in salinity, temperature…)?
absorption measurement: please state clearly the calculation step for a254 and a280 and a350. Why are these indices used? What are they supposed to indicate? References?
Statistical analysis: please try analyzing your data as suggested in the general comments
Results and discussion
line 246 ff: I do not understand this sentence.
line255ff: going into detail on this specific lake seems pretty unnecessary. Figure 2 might better belong to the supplementary. Furthermore, any discussions about seasonal variations should be done at the respective chapter later in the manuscript.
line264ff: Skip the details about the split-half analysis. Further Figure 3 should be left out, it does not contain relevant information.
line293: what is (B) referring to? (citation!)
line299: which lakes or seasons did not contain some of the fluorescent components? Are there any interesting patterns?
line322ff: Do these values represent the sum of the four components for each season? Maybe this Fmax-values for each of the seasons can be added to plot 5? How about the ice samples?
line353: biological activities might be highly reduced, but not prohibited completely. Maybe there might still be a bit of production of C3 and C1 which could explain the difference in behavior of the terrestrially imported C2 that did not display significant differences between august and february?
line371: I do not understand this sentence. how can lake-CDOM be dominated by all four components?
CDOM VS EEM PARAFAC extracted components
line390: obviously sunshine-induced evapo-condensed DOC concentration had no significant effects here, otherwise DOC concentration would be highest in summer and not in winter?! Please state, shortly, the observed patterns here (which hydrological, climate and landscape patterns like stated in line394?)
line404: The SR as calculated here merely represents DOM molecular weight (Helms, 2008)?
line 413 ff: As mentioned in the general comments, please adapt the statistics. Anyway, the correlations presented here lack interpretation (e.g. C1 and C2, why do they correlate though they derive from different sources?)
line 425: I do not understand this argument.
line428 ff: C3 might be useful to detect water pollution but a correlation with DOC solemnly does not necessarily indicate water pollution. Some other factors correlating with C3 (i.e. nutrients) might help to underscore the usefulness of C3 as a pollution indicator.
line432ff: The co-linearity of DOC and salinity could be explained by evapotranspiration but, as mentioned before, obviously some other factors play crucial roles in this study since both display highest concentrations in winter rather than in summer where higher evapotranspiration rates are expected. How can this pattern be explained?
line 438: I do not understand this argument.
Conclusions: might be adapted to potential new findings using multivariate statistics. Overall it should contain the important main findings and underscore the importance of this study and maybe provide an outlook for the future (e.g. how is the microbial degradability of these fluorescent components? what would be the effects on this ecosystem?)
Figure 6 should better be part of the supplementary

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RR by Anonymous Referee #2 (01 Nov 2015)

ED: Reconsider after major revisions (08 Nov 2015) by Gerhard Herndl

AR by Kaishan Song on behalf of the Authors (10 Dec 2015) Author's response Manuscript

ED: Referee Nomination & Report Request started (19 Dec 2015) by Gerhard Herndl

RR by Anonymous Referee #3 (17 Feb 2016)

ED: Publish subject to minor revisions (Editor review) (20 Feb 2016) by Gerhard Herndl

AR by Kaishan Song on behalf of the Authors (24 Feb 2016) Author's response Manuscript

ED: Publish subject to technical corrections (28 Feb 2016) by Gerhard Herndl

AR by Kaishan Song on behalf of the Authors (01 Mar 2016) Author's response Manuscript

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Short summary

Our results of this study show that two humic-like C peaks and two protein-like B and T peaks were identified from CDOM using PARAFAC for investigated lakes. The average fluorescence intensity of the components differed seasonally. Components 1 and 2 exhibited strong linear correlation (R² = 0.63). Significantly positive linear relationships, between aCDOM and F_max, and between DOC and salinity (R² = 0.93), were revealed.