Porewater Sulfide: The Most Critical Regulator in the Degradation of Mangroves Dominated by Tides

Round 1

Reviewer 1 Report

This is an important article in the field of mangrove dynamics and for mangrove restoration. In my place of research, I have a situation very similar to the one presented in this article, until then attributed only to hydrological factors.

Therefore, I would like to make some recommendations about the data presented:

a) Is it correct to affirm the death of the mangrove forest due to the appearance of sulfide? Isn't sulfide just a consequence of environmental change? particularly I didn't find the concentrations so high and the environment weakly reducing. Perhaps it would be better to record only the strong correlations found between sulfide concentrations and the death of plant species;

b) I suggest that the author(s) adopt the sulfide measurement unit in micromol/L or moles/L, as adopted for the other measured parameters;

Finally, I really liked the methods adopted in the research and the quality of the data obtained.

Author Response

a) Is it correct to affirm the death of the mangrove forest due to the appearance of sulfide? Isn't sulfide just a consequence of environmental change? particularly I didn't find the concentrations so high and the environment weakly reducing. Perhaps it would be better to record only the strong correlations found between sulfide concentrations and the death of plant species.

Comment. The alteration of the hydrology of mangroves leads to degradation, and the results were conclusive that areas with extreme mangrove mortality were associated with high values ​​of sulfide in the soil. It is also recognized that more abundant mangrove peat is released by mangrove dieback and combined with hydrological alteration, more biogeochemical cycles are altered.

Manuscript improvements. In figure 1 a photo of the flooded mangrove in the impaired site was attached.  

Comment. The manuscript explained that the soil potential redox (Eh) was measured with platinum electrodes and an Ag/AgCl reference electrode. Due to the reference electrode potential, a correction factor of 235 mV was added to each reading (Electrode register (mV) + 235 mV = Eh (mV)

Manuscript improvements. In conclusion “Increased hydrological connectivity through the hydrological tidal channel of areas affected by soil sulfides can contribute to the natural establishment and growth of mangroves. Our results can support decisions on mangrove management or restoration strategies.

b) I suggest that the author(s) adopt the sulfide measurement unit in micromol/L or moles/L, as adopted for the other measured parameters.

Manuscript improvements. We adopt the sulfide measurement unit in mg L^-1

Author Response File: Author Response.docx

Reviewer 2 Report

The content of the Introduction should be adjusted.

The structure and content of this article are sufficient for publication, and the results are valuable and indicative. I think it can be published with further revision. 

The scientific assumptions of this paper should be emphasized. The significance and purpose of the study should be explained in more detail.

The number of samples seems to be insufficient. The total number of samples should be stated, otherwise it is difficult to judge the repeatability of each sampling

Author Response

1. a) The scientific assumptions of this paper should be emphasized. The significance and purpose of the study be explained in more detail.

Comment. We accept the suggestions to improve the document.

Manuscript improvements. At the end of the introduction “This research aims to determine the effect of flooding time on the mangrove biogeochemical characteristics, such as salinity concentrations, sulfides, and nutrients. In addition, we determined which regulator of porewater was associated with the hydrological degradation and death of mangroves tidal dominated”.

 

1. b) The number of samples seems to be insufficient. The total number of samples should be stated, otherwise, it is difficult to judge the repeatability of each sampling.

Comment. Regarding the number of samples, there are enough statistical differences to support the results. We agree with the suggestion of having a larger number of samples, but we had logistical limitations that required a compromise in the experimental design and the optimal number of samples.

We are currently a monitoring program at other sites on Isla del Carmen, Campeche, Mexico; we are sampling other fringes, basins, and impaired mangroves. We have observed similar behavior in other impaired sites, where the mangrove dies by high sulfide in the soil.

The figure shows the flooding levels from March 2018 to January 2021 of another site identified Impaired_2, located in Isla del Carmen (18.686284° N: 91.661350°W). The conditions that we have recorded are long periods of inundation and the average concentration of sulfides is above 40 mg L^-1; even 180 mg L^-1 was recorded in October 2019. It has been observed that from August 2019 the water level increased and therefore the sulfides. We cannot include these data in the manuscript since the time of the data that was collected for the study does not coincide.

Author Response File: Author Response.docx