Riverine Particulate Matter Enhances the Growth and Viability of the Marine Diatom Thalassiosira weissflogii
Round 1
Reviewer 1 Report
Dear Editors;
In the present work, experiments were conducted on the growth of diatoms in artificial marine waters with different presences of nutrients, different flasks and with the presence or absence of suspended sediments of different compositions. The work is certainly very interesting but in my opinion the explanation on the interpretation of the data is rather controversial and not well understood, especially due to the large number of variables considered. It is not very clear to me what is meant by biotic control. The English form is also not very good and sometimes it is difficult to understand the sentences. In general, it is not very clear to me how diatoms can influence the carbon cycle, given that they are siliceous and non-carbonate organisms. Is it only for the possibility of aggregating particles around their bodies? I wonder if it would not be better to concentrate the work on only a part of the data, and the remaining part of the data to be used for other work. I believe that the working text should be revised in order to make it clearer and more understandable. It also seems too long to me and would benefit from a synthesis work. . Furthermore, the analytical strategies employed should be briefly explained in the introduction. I think it would also be appropriate to report some photos of the instrumentation used for the experiments. In the attached PDF file I report some corrections of the English and I underline some sentences that are unclear in my opinion.
With best wishes
Comments for author File: 
Comments.pdf
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Reviewer 2 Report
The presented manuscript is a methodically verified and thorough description of the results of several series of experiments by the authors with the growth of diatoms Thalassiosira weissflogii under the influence of riverine particulate material of different composition - the material of the Mississippi river, sampled in the vicinity of New Orleans, and material from a small river in East Iceland. As a result of the analysis of the obtained data, the authors claim that they were able to demonstrate “... a positive effect of riverine particulate material on the growth of the marine diatom Thalassiosira weissflogii. In Guillard´s f/2 cul-ture medium enriched Instant Ocean©, the presence of riverine particulates increased the total diatom concentration and slowed post-exponential net diatom death rates. In Instant Ocean© without additional nutrients, riverine particulates led to a linear increase in dia-tom concentrations as a function of particulate concentration, whereas diatom cultures died in controls without particulates. These results indicate a strong positive influence of riverine particulates on phytoplankton growth in coastal environments.” It's hard to disagree with this.
The data obtained by the authors also allowed them to consider that “…the presenceof particulates is suggested to facilitate organic burial carbon through the delivery
of surface area available for adsorption of organic compounds and through their role
in the aggregation and sedimentation of phytoplankton. These combined effects
suggest a major role of riverine particulates in the global carbon cycle, which becomes especially significant in view of the current major anthropogenic perturbations of global particle fluxes”. This is also a very important conclusion, which, it seems, will be in demand both when studying the current features of the global carbon cycle and when interpolating the results into the future (if it occurs under the current geopolitical situation in the world) and the geological past. Thus, it can be considered, without much exaggeration, that the submitted manuscript
will be in demand by a large number of readers of the journal, and its citation will
be significant. I have no fundamental comments on the text and illustrations. Those comments that
are shown in the margins of the manuscript are mostly editorial in nature.
There are, perhaps, two essential wishes to the authors. First, it would be good
to expand information about the results of similar or similar studies of predecessors.
Secondly, it would also be good to give a brief excursion into the geological past,
showing, if possible, where it is possible to assume the work of the mechanism
described by the authors, “embodied in stone”.
Comments for author File: Comments.pdf
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The work has certainly improved and the explanations given by the authors to my criticisms are quite satisfactory.
However, I have a few more requests:
It should be explained in more detail what is meant by the term "limiting nutrients": are they substances that limit or increase the development of diatoms? In my opinion this concept is not always very clear.
In the paragraph of method some additional explanations on what the Guillard f2 should be reported-
in the paragraph of Results in the part between lines 219 and 224, it should be reported that the experiments were also conducted using the suspended particulate.
I have also made some corrections to the English form in paragraph 4 of the discussions and in lines 159-160 which I reproduce in the attached PDF file.
Comments for author File: Comments.pdf
Author Response
It should be explained in more detail what is meant by the term "limiting nutrients": are they substances that limit or increase the development of diatoms? In my opinion this concept is not always very clear.
We agree that this issue should be clarified. In the context of the present study (increase of biomass during incubations with various substrates), the meaning of ‘limiting nutrients’ is that these substances increase the development of diatoms. We rectified the revised text accordingly.
In the paragraph of method some additional explanations on what the Guillard f2 should be reported-
As indicated in section 2.2, the chemical composition of modified Guillard´s f/2 culture medium [80] used in the culture are provided in Table 2 and 3, respectively
In the paragraph of Results in the part between lines 219 and 224, it should be reported that the experiments were also conducted using the suspended particulate.
We agree and added this information in the revised text.
I have also made some corrections to the English form in paragraph 4 of the discussions and in lines 159-160 which I reproduce in the attached PDF file.
We carefully incorporated all corrections to the English recommended by the Reviewer on his/her pdf file.
