Review Reports - Nitrogen Cycling in Widgeongrass and Eelgrass Beds in the Lower Chesapeake Bay

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The article compares nitrogen fluxes from different seagrass meadows and unvegetated areas in the Chesapeake Bay in spring and summer, and discusses differences in the view of the effect of climate change on ecosystem services.

The article is very clear, well written and easy to read. I don't have much to suggest to improve it, apart from a few questions.

Firstly, it seems that the data is quite old (2014) and I understand that the authors are in the process of tidying up their drawers. I think it is worthwhile as the results are interesting. However, I'm concerned about the data analysis: the R version cited is from 2011, so either the Anova hasn't been redone since 2014 (then, why?), or the citation should be updated. This needs to be clarified.

In the same vein, I really doubt that the p-value of the Tukey tests between eelgrass and others is 0.04 from the figure and given that the p-values of the test for N2 between eelgrass and non-vegetated areas are lower, while the standard errors are relatively larger. This needs to be double checked.

Figure 1 (bottom) can be improved. If the intention is to emphasise the huge difference in magnitude of ammonium fluxes between eelgrass and others, then the figure is appropriate, but this is not what I understood from reading the text. If the aim is to compare fluxes, the Y axis should be log-scaled so that the differences between widgeongrass beds and areas without vegetation are visible.

Last, the text refers to figures 1a and 1b, but the letters are missing from the figure.

Author Response

Please see the attachment. Our responses are noted in blue.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The authors conducted intriguing research to investigate how changes in vegetation due to environmental shifts impact denitrification and sediment N-cycling. However, further clarification is required in many sections to ensure completeness.

Introduction

The authors mentioned various nitrogen (N) processes in the introduction, but clarity is needed, particularly in the last paragraph, regarding the specific processes they intend to investigate or measure.

Methods

Line 104. I am confused about how do you make the vegetation alive under dark conditions?

Line 120. Why do you need to collect SOM data and only from the top 2 cm of sediment cores?

Results

Table 1. Significant test is also needed to compare between treatment and different seasons for plant characteristics.

Line 183. What does the differences in ammonium flux suggest in the ecosystem?

Figure 1. Is it possible that Eelgrass sediment has such high ammonium flux and where it is from?

Discussion

It is advisable to compare the obtained results with existing literature to identify similarities and differences in findings.

Author Response

Please see the attachment. Our responses are noted in blue.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The paper compares nitrogen cycling in eelgrass and widgeongrass beds and in unvegetated sediments. This topic could be current and interesting for readers, even if the data were measured 10 years ago. Unfortunatelly, the methodology is poorly described and the results are discussed only superficially, without deeper understanding. All the interpretation is based on comparison of N2 fluxes. However, nitrogen cycling includes a lot of processes that have been neglected.

I have several specific comments:

L. 61 This definition of denitrification is too general, maybe even misleading.

L. 75 Please, explain the relationship between denitrification and ammonium flux.

L. 103 How long lasted the incubation, until the samples were taken?

L. 115 Are these the same analyses as those mentioned on l. 109?

L. 123 How was the sediment surface determined?

L. 180 The abbreviation DIN is not explained.

Chapter Results:

In the chapter Methodology you mention a lot of measurements, the results of which are not presented, such as dissolved oxygen, temperature and salinity in water column at the time of core collection (l. 96), NOx and O2 in inflow and outflow line (l. 109). I think these results are necessary for understanding the results of your experiments. Moreover, the temperature at which the experiments were performed, should be indicated.

Chapter Discussion:

The difference between the three habitats in NH4 flux (Fig. 1) is not discussed, although it can be important for explanation of the difference in nitrogen cycling. Also information on oxygen conditions during the experiment would help.