Modelling nutrient retention in the coastal zone of an eutrophic sea

Almroth-Rosell, Elin; Edman, Moa; Eilola, Kari; Meier, H. E. Markus; Sahlberg, Jörgen

doi:https://doi.org/10.5194/bg-13-5753-2016

Articles | Volume 13, issue 20

https://doi.org/10.5194/bg-13-5753-2016

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

https://doi.org/10.5194/bg-13-5753-2016

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

Articles | Volume 13, issue 20

Research article

|

18 Oct 2016

Research article |

| 18 Oct 2016

Modelling nutrient retention in the coastal zone of an eutrophic sea

Elin Almroth-Rosell, Moa Edman, Kari Eilola, H. E. Markus Meier, and Jörgen Sahlberg

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Final revised paper (published on 18 Oct 2016)
Supplement to the final revised paper
Preprint (discussion started on 26 Feb 2016)
Supplement to the preprint

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Review for Almroth-Rosell et al', Anonymous Referee #1, 25 Mar 2016
- AC1: 'Response to referee #1', Elin Almroth-Rosell, 20 May 2016
RC2: 'reviewer comment', Anonymous Referee #2, 29 Mar 2016
- AC2: 'Response to referee #2', Elin Almroth-Rosell, 20 May 2016

Peer-review completion

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

ED: Reconsider after major revisions (20 May 2016) by Katja Fennel

AR by Elin Almroth-Rosell on behalf of the Authors (01 Jul 2016) Author's response Manuscript

ED: Referee Nomination & Report Request started (04 Jul 2016) by Katja Fennel

RR by Anonymous Referee #1 (18 Jul 2016)

Suggestions for revision or reasons for rejection

P6L5: "transparency"

P12L9: section title suggestion: Nutrient load reduction scenario

P12L21 (and everywhere else in the manuscript, there are many occurrences): change “with” to “by”

P12L22: replace “to” by “in”

P16L1-3: change to something like “Permanent retention was relatively stable during the simulated period, while fluctuations in the temporal retention reflects the effect of varying riverine nutrient input (Fig. 10c,d).”.
Also, temporal retention of P has increased, Can you comment on that?

P17L11-16: This new part could be polish for clarity.

P17L14: change “has” to “have”

P18L23: change “parameters” to “processes”

P18L26: change “relation” to “relationship”

P18L27-28: replace to “… the filter efficiency. Nixon et al (1996) show that including the depth in the analysis of retention”

P19L1-31: This added text could be improved.

P19L1-4: suggested replacement for the first 2 sentences: “In the model, denitrification is an O2 dependent process that has a maximum rate at O2 concentration…”.
P19L5-9: Are you talking about the model here or in general? This is not described in the Methods so we don’t know if this relates to your results or not.

P19L9-12: What do you mean by manually? This is vague, you need to provides details on what you did. It could be mentioned in the Methods.

P19L17: Is this due only to denitrification? what about higher primary production due to more P available? You mention this later in the load reduction experiment. Did you compare the different effects and found that denitrification is the dominant process?

P19L17-25: Suggested changes for clarity: “Denitrification increased in magnitude and as a proportion of the permanent retention from 92% to 94%, while the proportion of burial decreased . The decreased in P retention was due to higher released of P from the sediment.
Denitrification has been shown to increase in areas with longer residence times (Nixon et al., 1996, Nielsen et al., 2001, Finlay et al., 2013). In the simulation the residence time was only six days on average and the filter efficiencies of N and P were estimated to be 10% and 9%, respectively, which were lower than in the Stockholm Archipelago…”
Also, I don’t see why the results L23-25 are included here. Can you be more explicit about the comparison with your system?

P19L29-31: This is true everywhere. Please clarify your statement.

P19-20L33-4: Algae uptake changes the pool of nutrients, please rephrase to something like this: Assimilation of nutrients by benthic algae does not directly change the inventory of N and P but transfers inorganic N and P into organic material...”
What is the expected effect on retention? You need to relate this to your results, this is part of the uncertainty of your results.

P20L13: suggested change to title: “Response to nutrient load reduction.

P21L11: suggested change: “is” instead of “becomes”

P21L14: Change “From these experiments it seems that” to “These results indicate that”.

P21L17-18: suggested change: “… concentrations might be expected locally. However, this effect largely depends on the water residence time and on which nutrient limits the seasonal phytoplankton production initially…”

P21L20-29: I don’t see the use of this paragraph.

P21L22-25: not sure what that means, please clarify.

P23L6: replace “to” with “in”.

P23L8-10: is that permanent or temporary? Can you indicate their ratio?

P25L1: journal names should be abbreviated

P25L16-18: add database title: “Baltic Environmental Database” and use the short url provided: http://www.balticnest.org/bed

P44: is there a reason to not start the x-axis at 0? It seems odd.

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ED: Reconsider after major revisions (30 Jul 2016) by Katja Fennel

Dear Authors,

Reviewer 1 provided a further detailed review of your revised manuscript. I encourage you to carefully consider these comments.

In addition I'm providing my own comments below. I encourage you to submit a revised manuscript for further consideration as well as detailed responses to each comment.

Page and line numbers refer to the revised manuscript with changes tracked.

Define what you mean by “coastal filter” (P1, L18; P1, L25 and L26). The definition provided on page 4, lines 6-8 is insufficient. Where do these nutrients ultimately go? Which processes are responsible?

P1, L24: “good quality” Do you mean “the simulated values agree well with observations”? Unclear otherwise. Please rephrase.

P1, L26: “take care of” is not a good word choice. Replace by “remove” or “retain” or similar.

Also, please explain where all the nutrients ultimately go. The Archipelago cannot infinitely continue to retain nutrients.

P2, L1-7: Denitrification does not “retain” nutrients. Denitrification removes nutrients from the system! This is different from retention.

P4, L8: “There are not enough estimates of nutrient retention in different coastal systems around the world…”
I note that you are not providing references of those that exist – something that was also criticized by Reviewer 1. Here are just three examples that I’m familiar with (I’m sure there are many more):

Xue, Z., He, R., Fennel, K., Cai, W.-J., Lohrenz, S., and Hopkinson, C., Modeling ocean circulation and biogeochemical variability in the Gulf of Mexico, Biogeosciences, 10, 7219-7234, doi:10.5194/bg-10-7219-2013 (2013)

Fennel, K., The role of continental shelves in nitrogen and carbon cycling:
Northwestern North Atlantic case study. Ocean Science 6, 539-548, doi:10.5194/os-6-539-2010 (2010)

Fennel, K., Wilkin, J., Levin, J., Moisan, J., O'Reilly, J., Haidvogel, D., Nitrogen cycling in the Mid Atlantic Bight and implications for the North Atlantic nitrogen budget: Results from a three-dimensional model. Global Biogeochemical Cycles 20, GB3007, doi:10.1029/2005GB002456. (2006)

Two other studies of some potential relevance as well as the references given within are:

Laurent, A., Fennel, K., Hu, J., and Hetland, R.: Simulating the effects of phosphorus limitation in the Mississippi and Atchafalaya River plumes, Biogeosciences, 9, 4707-4723, doi:10.5194/bg-9-4707-2012 (2012)

Laurent, A., Fennel, K., Simulated reduction of hypoxia in the northern Gulf of Mexico due to phosphorus limitation, Elementa 2:000022, doi:10.12952/journal.elementa.000022 (2014)

Please make an effort to properly place your findings in the context of the published literature.

P11, L13: Please see my earlier comment about the difference between removal and retention. Please be very clear what you mean. At present these two terms are lumped together which is not appropriate. Always be clear about the processes that are underlying your results. Just quantifying the difference between incoming and outgoing matter fluxes without explaining where the missing matter ended up is not sufficient.

P11, L16: Do not relegate important definitions to the supplement. Define retention in the main text.

P12: I question your calculation of “freshwater” residence time. As per the Monsen reference you provide, residence time is defined as the ratio of an inventory and it’s inflow or outflow rate. You talk about freshwater residence time and divide the volume by the freshwater inflow rate, but the volume is not the freshwater volume but the total volume. Perhaps you do not mean freshwater residence time? Please clarify.

P12, L9-22: This text and Table 2 are not very informative. It is not clear what the baseline load is. Without this it is not particularly useful to state a percentage reduction. Consider giving less detail about treatment plants and instead describe better what nutrient inputs were used in the different experiments.

P13, L4-6: “A clear relationship between river outflow and nutrient load is observed …”
This is not a result that can be observed, but something that is imposed!!! Does not belong in the results but in the Methods.

Fig. 9: Please separate input from land and atmosphere instead of providing one combined number.

The concept of temporary retention does not make much sense to me. Do you consider your system to be in a dynamic steady state? How do you distinguish between processes leading to temporary versus permanent retention? Do the N and P inventories in the water column differ between the beginning and end of the simulation period? Please clarify this in section 3.2.

Katja Fennel
Editor

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AR by Elin Almroth-Rosell on behalf of the Authors (10 Sep 2016) Author's response Manuscript

ED: Publish subject to technical corrections (21 Sep 2016) by Katja Fennel

AR by Elin Almroth-Rosell on behalf of the Authors (26 Sep 2016) Author's response Manuscript

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Short summary

Nutrients from land have been discussed to increase eutrophication in the open sea. This model study shows that the coastal zone works as an efficient filter. Water depth and residence time regulate the retention that occurs mostly in the sediment due to processes such as burial and denitrification. On shorter timescales the retention capacity might seem less effective when the land load of nutrients decreases, but with time the coastal zone can import nutrients from the open sea.