Effects of changes in nutrient loading and composition on hypoxia dynamics and internal nutrient cycling of a stratified coastal lagoon

Zhu, Yafei; McCowan, Andrew; Cook, Perran L. M.

doi:https://doi.org/10.5194/bg-14-4423-2017

Articles | Volume 14, issue 19

https://doi.org/10.5194/bg-14-4423-2017

© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/bg-14-4423-2017

© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 14, issue 19

Research article

|

06 Oct 2017

Research article |

| 06 Oct 2017

Effects of changes in nutrient loading and composition on hypoxia dynamics and internal nutrient cycling of a stratified coastal lagoon

Yafei Zhu, Andrew McCowan, and Perran L. M. Cook

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Final revised paper (published on 06 Oct 2017)
Preprint (discussion started on 11 Apr 2017)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Review of bg-2017-132', Anonymous Referee #1, 17 May 2017
- AC1: 'Response to Reviewer's Comments', Yafei Zhu, 28 Jun 2017
RC2: 'Review of Zhu et al. “Effects of changes in nutrient loading and composition on hypoxia dynamics and internal nutrient cycling of a stratified coastal lagoon”', Anonymous Referee #2, 23 Jun 2017
- AC2: 'Response to Reviewer’s Comments', Yafei Zhu, 28 Jun 2017

Peer-review completion

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

ED: Reconsider after major revisions (04 Jul 2017) by Caroline P. Slomp

AR by Yafei Zhu on behalf of the Authors (17 Jul 2017) Author's response Manuscript

ED: Referee Nomination & Report Request started (03 Aug 2017) by Caroline P. Slomp

RR by Anonymous Referee #1 (21 Aug 2017)

Suggestions for revision or reasons for rejection

General Comments :

The Authors clarified satisfactorily a number of essential points raised during the first round of review.
However I believe a little additional efforts in the redaction could largely enhance the manuscript's readability, which it absolutely deserves.

Specific comments :

* Altough it has been improved, the benthic model component has not yet been sketched clearly enough.
Please precise its structure, and mention burial in the description.
I understand a complete and detailed description is too heavy, but some aspects strongly constrain the nature and reach of this manuscript's conclusions
(ie. the range or classes of lability considered for benthic organic matter, the possiblity for burial, the possibility for delayed resuspension, etc..).
In answer to our comments regarding burial, the author mention the "total depth", without definition. I assume it refers to thickness of the accumulated sediment layer, but this is unsure.
In any case, any precision has to be done in the manuscript for readers, not just as answers to the reviewers.
The following sentence is ill formulated: " An accumulation of organic matter layer at the floor was formed due to settling. ".
The 2-layer topology of the benthic component comes last in the current desription, but should come first.

* The fact that sediment P stocks last longer than N is a consequence of modelling choices : the range of lablity considered and the presence of iron-bound P stocks.
Bearing several consequences in the study conclusions, the implications of those modelling choices should be stated more clearly (it adds to the already included conclusions regarding the need for a better description of OM lability).

* Rephrase P6L2 ".. and this confirmed that 60% of the particulate nutrient were labile was a reasonable assumption. "

* Rephrase P7L7 "On the other hand, the hypoxic area reduced more steadily when TN was reduced and decreased the most when TN and TP were reduced."

* P7L27 : " .. the deposition rate in Lake King was much higher than IN the rest of the lakes .. "

* The definition of total hypoxic area remains unclear.
The proposed definition ("the area with 24-hour-averaged bottom-water DO concentration < 2mg/L") defines a value that changes in time.
However, Fig 5. and the corresponding discussion consider a single number per simulation to characterize the hypoxic area.
Is the "total hypoxic area" the area where hypoxia (as defined above) occurs at least once during the simulation ?
Or the area where hypoxia occurs all the time ?
Or the maximum hypoxic area achieved during the simulation (ie, area simulataneously covered by hypoxia) ?
Please precise the definition.

* P10L7 : "simulated' -> "stimulated"

* P10L42 IF applying -> By Applying

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RR by Anonymous Referee #2 (24 Aug 2017)

ED: Publish subject to minor revisions (Editor review) (25 Aug 2017) by Caroline P. Slomp

AR by Yafei Zhu on behalf of the Authors (30 Aug 2017) Author's response Manuscript

ED: Publish as is (05 Sep 2017) by Caroline P. Slomp

AR by Yafei Zhu on behalf of the Authors (06 Sep 2017)

Short summary

We used a 3-D coupled hydrodynamic–biogeochemical water quality model to investigate the effects of changes in catchment nutrient loading and composition on the phytoplankton dynamics, development of hypoxia and internal nutrient dynamics in a stratified coastal lagoon system. The results highlighted the need to reduce both total nitrogen and total phosphorus for water quality improvement in estuarine systems.