The effects of river inflow and retention time on the spatial heterogeneity of chlorophyll and water–air CO<sub>2</sub> fluxes in a tropical hydropower reservoir

Pacheco, F. S.; Soares, M. C. S.; Assireu, A. T.; Curtarelli, M. P.; Roland, F.; Abril, G.; Stech, J. L.; Alvalá, P. C.; Ometto, J. P.

doi:https://doi.org/10.5194/bg-12-147-2015

Articles | Volume 12, issue 1

https://doi.org/10.5194/bg-12-147-2015

© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/bg-12-147-2015

© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 12, issue 1

Research article

|

09 Jan 2015

Research article |

| 09 Jan 2015

The effects of river inflow and retention time on the spatial heterogeneity of chlorophyll and water–air CO₂ fluxes in a tropical hydropower reservoir

F. S. Pacheco, M. C. S. Soares, A. T. Assireu, M. P. Curtarelli, F. Roland, G. Abril, J. L. Stech, P. C. Alvalá, and J. P. Ometto

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Final revised paper (published on 09 Jan 2015)
Preprint (discussion started on 11 Jun 2014)

Interactive discussion

Status: closed

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

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RC C3217: 'Reviewer Comments for Pacheco et al. Biogeosciences Discussion (bg-2014-214)', Anonymous Referee #1, 03 Jul 2014
- AC C4932: 'Response to Referee #1', F. S. Pacheco, 05 Sep 2014
RC C3327: 'Comment on "River inflow and retention time affecting spatial heterogeneity of chlorophyll and water-air CO2 fluxes in a tropical hydropower reservoir"', Anonymous Referee #2, 07 Jul 2014
- AC C4942: 'Response to Referee #2', F. S. Pacheco, 05 Sep 2014

Peer-review completion

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

AR by F. S. Pacheco on behalf of the Authors (14 Oct 2014) Author's response Manuscript

ED: Referee Nomination & Report Request started (27 Oct 2014) by Tom J. Battin

RR by Anonymous Referee #1 (03 Nov 2014)

Suggestions for revision or reasons for rejection

General Comments

The manuscript entitled ‘River inflow and retention time affecting spatial heterogeneity of chlorophyll and water-air CO2 fluxes in a tropical hydropower reservoir’ by Pacheco et al. focuses the dynamics of spatial and temporal CO2 fluxes from a reservoir. Overall, the research presented in this manuscript is relevant in regards to how we think of reservoirs in regards to CO2 fluxes. The authors present compelling data on the variation and potential drivers of temporal and spatial CO2 fluxes from a eutrophic reservoir where CO2 fluxes seem to be driven by production and inflow river plume dynamics. The work presented in this manuscript also adds to the body of knowledge of how dynamic and variable reservoirs can be in regards to emitting CO2, where reservoirs are often thought of as CO2 sources instead of seasonal sources and sinks.

While the manuscript has great potential in regards to the science that is presented, major revisions in terms of manuscript presentation need to occur. I understand that English many not be the first language of the authors, however, editing for writing, grammar, spelling, and structure is needed. I addressed many of these writing/grammar issues within my specific comments – but stopped commenting on them in the discussion (for the most part).

Specific Comments

Page 3, Line 4: Re-cast sentence, perhaps ‘In tropical regions, high temperatures and the flooding of forests intensify GHG emissions.’

Page 3, Line 10: Clarify sentence. I’m assuming the authors are referring to different regions of the reservoir could impact CO2 dynamics because of flooded biomass, river input of organic matter, primary production and dam operations. The word ‘system’ is vague. I suggest re-casting sentence to make the point clearer.

Page 3, Line 12: I suggest re-casting this last sentence. I understand the point the author’s are attempting to make, but I find this sentence to be very vague and not convey very much information. Make the sentence more active and concise. Heterotrophic and autotrophic activity drives reservoir CO2 concentrations in subtropical, tropical, and temperate regions.

Page 3, Line 18: ‘habitat conditions linked to’ not needed

Page 3, Line 19: Re-cast sentence. Also, hydrodynamic factors, such as retention time and river inflow, may influence the phytoplankton communities and growth.

Page 3, Line 22: ‘budget’ should be ‘budgets’

Page 3, Line 23: should be either ‘tropical hydropower reservoirs’ or ‘a tropical hydropower reservoir’

Page 3, Line 30: ‘by river and the dynamic of river inflow’ unclear, re-cast

Page 4, Line 2: ‘….strongly influenced by river.’ River flow? Nutrients? Please clarify.

Page 4, line 6: ‘respective impact’. Unclear. Is ‘respective’ needed here?

Page 4, line 8: ‘in’ should be ‘on’

Page 4, line 12: ‘cycle’ should be ‘cycling’

Page 4, line 29: ‘the’ before sewage

Page 5, line 3: ‘affected’ should be ‘effected’

Page 5, line 9 - Please combine/re-write this paragraph and the one directly following. Within these two paragraphs, the authors describe methods for collecting pCO2 and chl samples. The first sentence of the 2nd paragraph (Page 5, line 14) is not a proper topic sentence for this paragraph. Most of this paragraph describes pCO2 methodology. Please re-cast accordingly.

Page 5, line 9 – “the’, not needed – ‘ start sentence with ‘Water samples for chl and PCO2 were taken’. ‘the determinations’ is not needed.

Page 5, line 14 – delete ‘the’ before Chl

Page 5, line 16 - ..’the water pumped’… ‘is’ needed before pumped

Page 5, line 19 – conduct should be conducts

Page 6, line 7 – ‘picks’ should be ‘peaks’

Page 6, line 14 – I suggest writing a topic sentence. A list of the data collected isn’t an appropriate first sentence. Please check this throughout the manuscript – especially the methods section.

Page 6, line 26 – similar to the comment above – this paragraph describes methods for pCO2 calculations and collection and analyses of inorganic nutrients, yet the first paragraph is on calculation of pCO2. Re-cast /re-write into two paragraphs

Page 7, Line 19 – Equation 3 does not exist. Check equation numbering and references to all equations within the text, there seems to be an equation missing.

Page 8, line 1 – SIMA da – I think should be SIMA data?

Page 8, line 3 – ‘the’ before riverine

Page 8, line 12 – delete ‘the’ before station; 2 meter should be 2 meters

Page 8, line 17 – Sentence is awkward. ‘Measured turbidity was 29 and 11 NTU….”

Page 9, line 6 – condition should be conditions

Page 9, line 8 – zone should be zones

Page 9, line 9 – ‘considered data’ , please re-cast or clarify (data used?)

Page 10, line 6 – M*D11A1 L3? Please clarify what is this product or products (also check singular vs plural when referencing this product). Is this a data set? If so, please reference it as such. At this time, it is unclear within the text.

Similarly in the following paragraph regarding cloud cover, ‘product’ is actually generated data using these different algorithms, correct? Please clarify, re-cast as needed throughout the text.

Page 10, line 27 – ‘a MATLAB program’ – seems vague. Clarify (i.e. is this a program the authors wrote? A known program? ), what kind of calculations were used?

Page 10, line 29 – This sentence should be included in the previous paragraph.

Page 11 – Likely more common to write the results section in the past tense. Please check and modify where needed.

Page 11, line 8 – delete ‘the’ before primary production

Page 11, line 13 – I suggest changing ‘showed to be’ to ‘was’

Page 11, line 14 – change ‘The spatial data showed’ to ‘There was’ (spatial is assumed given this result is regarding spatial variation)

Page 11, line 16 – re-cast sentence – maybe ‘The average spatial pCO2 was…”

Page 11, line 18 – ‘drastically’ should be ‘drastic’

Page 11, line 20 – ‘on’ should be ‘of’

Page 11, line 22 - … and higher values of pCO2… move to discussion

Page 11, line 23 – ‘The chl’ should just be Chl Or Chl data

Page 12, line 1 – include a ‘the’ before spatial data

Page 12, line 7 – ‘calculated by’ should be ‘calculated from’

Page 12, line 19 – re-cast sentence; ‘… we assumed the equations…’, I don’t think ‘assumed’ is the proper verb here, perhaps ‘used’. Also the sentence could be more concise.

Page 12, line 22 – ‘However,….’ – this sentence is unclear. What ‘estimates’ were compared? Also ‘changed’ should be ‘change’

Page 12, line 24 – delete ‘of’ before flux

Page 12, line 28 – ‘studied’ should be ‘study’

Page 13, line 1 – This paragraph needs to be re-organized/re-written. Topic sentence? Also why are the authors presenting results from the spatial data set here, and not in the previous results section?

Page 13, line 7 – re-cast sentence, not a topic sentence and too long

Page 13, line 20 – ‘were’ should be ‘was’

Page 14 – ‘buoyance’ should be ‘buoyancy’ throughout the manuscript

Page 15, line 27 – The carbon budget discussion in this paragraph is over-reaching, especially given the lack of data on sedimentation rates and CO2/CH4 outgassing directly from sediments. Furthermore, the 2nd sentence (line 29, ‘Although there is…) is unclear (i.e. ‘…composed by phytoplankton and methanogenesis…’ – I’m am unsure what the authors are attempting to convey).

Page 16, line 4 – Yes, it is common for reservoir residence time to be driven by dam operations. However, given figure 4b – did the retention times by season differ significantly? The mean difference in retention time between wet and dry seasons was around 10 days? Is this a big enough difference to drive significant changes in CO2? I believe I understand what the authors are trying to convey: Reservoir volume and retention time vary by season. Seasonal attributes such as river inflow and river plume location within the reservoir vary, which then drives chl and CO2. I suggest downplaying retention time, and focus more on river plume dynamics.

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RR by Anonymous Referee #2 (13 Nov 2014)

ED: Publish subject to technical corrections (01 Dec 2014) by Tom J. Battin

AR by F. S. Pacheco on behalf of the Authors (13 Dec 2014) Author's response Manuscript

Short summary

CO2 fluxes in Funil Reservoir (FR) is driven by primary production and river inflow dynamics. Our findings suggest that the lack of spatial data in reservoir C budget calculations can affect regional and global estimates. Our results support the idea that the FR is a dynamic system where the hydrodynamics represented by changes in the river inflow and retention time are potentially a more important force driving both the Chl and pCO2 spatial variability than the in-system ecological factors.

The effects of river inflow and retention time on the spatial heterogeneity of chlorophyll and water–air CO2 fluxes in a tropical hydropower reservoir

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Peer-review completion

The effects of river inflow and retention time on the spatial heterogeneity of chlorophyll and water–air CO₂ fluxes in a tropical hydropower reservoir