|Review of first revision of ‘Dynamic Responses of DOC and DIC Transport to Different Flow Regimes in a Subtropical Small Mountainous River’ by Shi et al.|
I reviewed the original version of this manuscript and the authors’ modifications/additions in response to those comments greatly improved the clarity and completeness of the methods section. In fact, the additional information provided in the Supplementary Information illustrated a considerably more thorough assessment of the modeling results, both the hydrology and water chemistry, than was evident in the original draft.
My previous summary of the research remains accurate in the updated version and I have copied it from the original review ‘This research makes a useful contribution to the understanding of the hydrologic controls on DOC and DIC streamwater export in a humid tropical region, and by quantifying the annual fluxes and DIC/DOC ratios, define these systems as end-members or ‘hot spots’ within the context of global measurements. While there has been evidence that sub-tropical regions were important with respect to both DOC and DIC fluxes due to high productivity and rainfall, the detailed long-term measurements of concentrations and evaluation of relationships with flow had not been previously studied in any detail. By consistently sampling during a range of flow conditions (including frequently during typhoons) over a relatively long period (2 1/2 years) and using the data in conjunction with measurements of flow, flow simulation and end-member mixing analysis, they are able to evaluate the relationship between concentration and flow, estimate the relative contribution of different hydrologic flow paths to the DOC and DIC fluxes and quantify the importance of the typhoon events relative to non-event flow conditions.’
Although the work appears very thorough, and the majority of the figures present the data clearly and from a variety of perspectives, the grammar and scientific writing needs considerable improvement throughout the text. In many cases the errors in writing made the point of the sentence or paragraph difficult to understand or appear incorrect as written. I have indicated numerous examples within the specific comments. The dataset is unique and robust and the methods are very thorough, but the consistent grammatical/writing/wording errors throughout the manuscript and especially within the discussion, made it difficult to read and therefore difficult to critically evaluate the findings and discussion.
(l. 49): delete second ‘transport’ in sentence
(l. 53): correct grammar, ‘DOC is mainly originated’
(l. 54/55): the phrase which includes ‘…organic matter is closely associated with different organic sources…’ is redundant, I would delete the last half of the sentence or state the organic sources and describe more clearly how bacterial degradation and redox impact organic carbon.
(l. 61): list a few important ‘direct effects’ on downstream ecosystems.
(l. 77-79): The citation Mei et al., 2014 relates to DOC, so I’m not sure why DIC transport is included in this sentence. The sentence needs clarification or DIC should not be included.
(l. 82-83): In the sentence ‘This has become important’, clarify what ‘This’ referring to. I would assume the understanding of shifts in the quantity and DIC:DOC ratio with different flow conditions.
(l. 92-93): correct sentence grammar/punctuation 1) comma after HBV, 2)‘a’ before 3 end-member, 3) correct ‘during in different flow regimes’
Material and Methods
(l. 100-102): correct grammar
(l. 104): correct grammar, replace ‘ones’ with air temperatures
(l. 112-113): the discharge station at M3 doesn’t correspond with the map, which indicates a discharge station only further downstream, and not at M3.
(l. 115): correct grammar, should be ‘patterns’ not ‘pattern’
(l. 117-119): Not sure why only agricultural land is quantified in the text, perhaps because the rest is forest in those 3 watersheds. Please state the relative percent forest as well and indicate that the ‘bare land’ and ‘built up’ land use is a minor component (if that indeed is the case). Also, I’m am not familiar with the term ‘built-up’, please clarify. I assume ‘bare land’ refers to landslide scars, but please clarify in text, i.e. landslide scars are indicated by the ‘bare land’ land use category in Figure 1.
(l. 126/127): correct grammar, ‘another bottle water samples’, perhaps ‘Water samples collected from the remaining 3 bottles’. Is this correct? Were the other 3 bottles filtered for major cations, anions and DOC?
(l. 134): Indicate that the water evaluated in this paper is in fact in the ‘neutral to alkaline’ range such that the ion balance method is appropriate. I don’t believe pH is presented in the paper for the reader to evaluate, though it was evaluated in-situ.
(l. 137/138): Indicate which samples were evaluated for DIC in the laboratory, how many, when and where were they collected, did they represent different concentrations and hydrologic conditions?
(l. 139): correct grammar, suggestion along the lines of ‘the strong relationship between calculated and measured DIC for the subset of samples (n=?) gives confidence in the accuracy in the values derived from the ion balance method’
(l. 147): ‘F, Q, and dtime are the flux’ doesn’t make sense. Isn’t Q discharge, and dtime change in time all of different units. Please clarify/correct.
(l. 149): correct grammar, delete ‘the’ in ‘the colinearity’.
(l. 150): redundant/rewrite, ‘The coefficient, a1 and a2, are coefficients’
(l. 151/152): the sentence ‘the other coefficients which regulate the seasonal variation can mimic the seasonal change…’ is awkward, coefficients themselves don’t’ mimic change but are optimized so that the model can account for measured seasonal change. Rewrite.
(l. 153-156): multiple areas where grammar/punctuation needs to be corrected, change ‘in LOADEST program’ to ‘into the LOADEST program’, ‘indicator’ should be pluralized, comma after measure should be period, ‘measure’ should be pluralized.
(l. 160): correct grammar, ‘The zero and the unity presents the performance is equivalent to expected value and perfectly matches between estimations and simulations’ is very confusing. Is the author trying to state an NSE value equal to ‘0’ or ‘1’ indicates that the estimated values are equal to the observed values? Please clarify.
(l. 161): similar to NSE, write out the Bp as an equation and define variables.
(l. 162-164): I understand what the author is trying to communicate here, but improvement in clarity and grammar is needed. Add the word ‘the’ between ‘by’ and ‘flow weighted’. ‘The fluxes for typhoon events are estimated by the flow-weighted method directly’ please explain this method, how were fluxes between sampling periods determined? LOADEST can compute fluxes at an hourly timestep, so indicate why it was not used for event-based fluxes. Of note, the R LOADFLEX package (Appling et al., 2015 http://dx.doi.org/10.1890/ES14-00517.1) may be of interest to the authors in the future as it can incorporate high frequency event data into annual fluxes.
(l. 172): after ‘its components’ list and define the three components, QRSR, QSSR, QDG.
(l. 181): correct grammar, ‘All the details and modeling works’
(l. 192): After the equations, indicate which terms are known and which are being solved for since the application of EMMA here is not the typical one. I realize that the information requested here is clarified by reading the Supplementary Information II, but it should also should be articulated clearly, though briefly, within the manuscript as well. Simply, the Q terms have been determined previously from the HBV model and the subsequent use of EMMA was non-traditional, as in you already had the relative fractions of Q in each of the three components and are using that information, along with measured streamwater concentrations, to calculate the DOC and DIC concentrations in those end-members given.
(l. 207): correct grammar, suggested change ‘concentrations varied widely from 1500 to 3500 uM presented the distinct seasonality’ with ‘concentrations varied widely from 1500 to 3500 uM during bi-weekly, non-typhoon events, illustrating a distinct seasonality.’
(l. 211/212/214/222/230): correct grammar for ‘were satisfactorily’, ‘good performance in flux’, ‘concentrations…were not well’, ‘attributed by that the low rainfall’, ‘without typhoon invasion’, ‘as rainstorm begins’
(l. 223/224) incomplete sentence.
(l. 234/235) last sentence is a discussion point, does not belong in results.
(l. 243/245) correct grammar, ‘model accompanying with’, ‘details could be referred to’
(l. 274-276) correct grammar/wording ‘the high DIC concentration superimposing the high streamflow lead the extremely high DIC export…’
(l. 280-284) The introduction of new SOC data is a bit confusing, is the Schomakers et al. ,(2017) paper for the area studied in this paper? How does SOC data after a landslide relate to this paper? What is the SOC content of the region and Oceania, to which it is being compared?
(l. 289/290) correct grammar/wording, not clear what is being communicated here ‘The a little SOC, but high productivity could result in consistent DOC supply and high flow velocities leads to low productivity of lotic systems’
(l. 316) Stated that ‘main carbon export from Oceania and SMR”s is from DIC and that is different than the global large rivers, but Table 4 indicates global large rivers are also dominated by DIC. Is the error in the sentence or the table?
(l. 319/321) Not clear how the prior discussion on DIC/DOC ratio’s is related to the sensitivity of DOC export to environmental change. Correct grammar ‘accounting for the small relative to global land mass’
(l. 334-335) It states the DOC concentrations in SSR and DG were 1-2 orders of magnitude lower than in RSR, does not appear to be true, concentration estimates based on figure 6 indicate RSR=108, SSR=206 and DG=86 microMole.
(l. 336-337) Where did Schomakers et al., (2018) measure SOC in top soil?
(l. 338-340) Unclear how measurement technique ‘ultrasonic-induced soil breakdown method’ related to lower estimated DOC concentrations? Assume wording is incorrect here.
(l. 356-357) several typos and/or grammatical errors
(l. 360-361) DOC quality introduced here, but not measured correct? The sentence makes it appear as if it was measured and changed with flow.
(l. 372-280) Need to provide citations to back up hypothesis about future climate impacts including ‘autotrophic production is favorable during longer dry seasons’, ‘DOC changes heterotrphic microbes and increases humic acid, decreasing pH’ and the impact it has on dissolution of carbonate minerals. What is meant by ‘reset the aquatic ecosystem’?
Table 2/Figure 3. Indicate fluxes are excluding typhoon events, if that is correct.
Figure 1. M3 is not denoted as a discharge site in the map
Figure 5. Define RSR, SSR and DG within caption.
Figure 6. Does high flow represent mean typhoon metrics for the two events?
Supplemental Information I
Figure S1 and S2. The (a) and (b) designation are in the incorrect location. Add r2 value for relationships. Add the term ‘hourly’ in the caption for Figure S2.
Supplemental Information II
(l. 2) Should the reference be equation 3 and 4, not 2 and 3?
(l. 3-4) Please clarify, ‘over 6 observations could be used to identify the end-members’, do you mean 6 samples in time?
(l 15) NSE was previously defined in the main text as it relates to discharge, but here it is relating to concentration of tracers. Is that correct? Please indicate the difference from the initial definition and what the NSE values represent with respect to confidence in the results.
(l 22) The phrase ‘on the other hand’ is not appropriate here.
(l 23) Table S5 is referenced after the presentation of the values for the three Q components, but that is not what is presented in the Table (only QSSR and QDG) so either present the estimated values for the 3 components in a separate table or do not reference a table at this location in the text.
Table S5. Indicate the first row, hillslope/subsurface, is representing the QSSR component and the second and third are both representing the QDG component. Correct Toe with T1, T2, as illustrated in map. Indicate how many samples the observed values represent (1?).