Dear Dr Schleppi and Dr Bär,

Thank you very much for uploading your detailed responses to the comments by the two anonymous reviewers.

The evaluation and comments by the reviewers were positive and it seems like you are willing to address these comments on a revised version of your manuscript.

I am particularly interested in seeing how you addressed the following important issues:

Reviewer #2 made a very pertinent comment on what would be the impact of temporal autocorrelations among trends of pH over time in different compartments of the hydrological system. This analysis is particularly relevant to your study given its long-term and large-spatial scale.

In addition, reviewer #1 raises important questions regarding the impact of N deposition on the ecosystem. Again, given the long-term nature of this study I believe that it is important to address how this process could have influenced your results.

Please upload a revised version of your manuscript so that I can advise on how to proceed with this manuscript.

I am looking forward to reading your revised version of the manuscript,

Kind regards,

Dr Teresa E. Gimeno

Dear Authors,
I agree with the comments of the handling editor and would ask you to carefully revise your manuscript according to the reviewers and editor's comments.
All the best,
Anja Rammig

Dear Drs. Bär and Schleppi,

Thank you very much for submitting a revised version of your manuscript addressing the comments by the two external reviewers. I believe that the manuscript has improved with respect to the original submission, although, in my opinion, there is still room for improvement. I do not deem it necessary to send this manuscript to be evaluated by the same or additional external, reviewers, but I provide some comments that I hope will be useful to improve the clarity of this manuscript.

As I said before and in line with the comments by the external reviewers, I believe that this manuscript presents the results of a very valuable experiment assessing the impacts of increased N deposition over a long-time scale (> 2 decades!) and at a large spatial scale (catchment). These types of studies are not common and are incredibly valuable to assess how our terrestrial and water ecosystems will evolve under future global change scenarios.

After reading and evaluating the manuscript for the second time, there are two things that are not clear to me yet. First, I am not sure whether the griding and felling treatment was an explicit part of the experimental design. It appears that this was an intentional treatment that was replicated in the control and in the experimental plots. Also, it seems like the results of this treatment were presented in detail in another study, but here it appears that this experimental treatment still had a very significant effect on the acidity of not only soil, but also of runoff water. However, this does not become clear until the reader finishes the discussion. Therefore, it might be necessary to add a section in the introduction explaining how reducing basal area would have a feedback mechanism on soil and runoff properties derived from decreased N demand from plant uptake and decreased litter input. These mechanisms are invoked in the discussion without having been introduced properly. In addition, the authors would need to consider incorporating this treatment explicitly in their experimental design and statistical analyses.

Second, the experimental design and measurement methodologies are not explained clearly. It is not clear why while there were two catchments, the experimental plots where rainwater (with or without extra N) were outside these catchments. The spatial details and chronology of the study are not explained clearly. Furthermore, there seem to be some inconsistencies in how water and soil samples were measured. The information regarding the analytical methodologies is hidden in different sections of the methods, but I think that in this study this is critical information and deserves a sub-section of its own. Also, in this sub-section, the authors should clarify potential changes in instruments or methodologies that were (understandably) implemented over the course of such a long-term experiment. Also, why are there experimental pairs of plots outside the monitored catchment? And why are there no experimental pairs of plots inside catchment two?

In line with these comments, one wonders whether the observed decrease in pH of runoff water in control plots would be simply due to the addition of extra rainwater, which already has a baseline concentration of N forms. How do these trends compare to similar measurements of pH in runoff water from similar catchments?

In addition, I provide some more comments that I hope they will improve the clarity of the language, which can still be polished. Comments that I consider are more relevant are separated by an extra line space. Line numbers (L) refer to the version with track changes.

L11 N deposition is not exclusive to forests. Also “forest ecosystems” can be shortened to “forests”.
L12-13 what do you mean by “sensitive receptors of the environment”.
L20 name these “soil acidification processes”.
L20-21 I do not understand the addition of the clause “while previous reports…” I think you could remove this from the abstract.
L23 the sentence “In spite of…” is repetitive, this same idea is given in the previous sentence.
L23 Remove “First”.
L25 what does “they” refer to here?
L31 Close your abstract with a brief conclusion or future perspective derived from your study.
L33 remove “more than”.
L36 more concise language: remove “are a” and change “of” by “from”
L38 more concise language: “and deposited in dry or wet form”.
L40 New paragraph starting with “As large regions…”
L54 provide a citation for this.
L62-64 I am not sure this is very relevant for this study and you could consider removing it.
L116 “at a site”
L125 “a deeper water table” instead of a “lower laying water table” (unless you meant a “more shallow water table”, which is not entirely clear here).
L130 specify the net rate of which process.
L136 remove “their”.
L146 & 179 provide manufacturer details.

L141 Here is where you should present the experimental design in detail and how the treatments were applied (currently L180-191)

L140 I assume these values of N deposition refer to the levels at the beginning of the experimental treatment, please clarify this.

L142 According to the responses to the reviewers’ comments, one of the catchments was not delimited by a trench, could you clarify this?


L166-167 Can you provide the maker, model and manufacturer details of the rain gauges. Also, how did these gauges collected and measured precipitation? Were the two rain gauges located in the same open area? Where was this area with respect to the experimental and control plot?

L174-177 How consistent were measurements taken more than two decades apart? How can you relate potential drifts with changes in measurement instruments, technology and their precision?

L190 what does “it” refer to here?
L192 what do you mean here by “in general”?
L214 provide the corresponding package citations for this function.
L215-216 This belongs to the results section, also, what are “periods” here?
L232 I do not understand this, I thought the variable “treatment” was included as a fixed factor on the models testing for the trends of soil acidity.
L245 remove “highly” and “atmospheric” (precipitation is by definition atmospheric).
L246 what do you mean here by “at the beginning of the project”? Maybe use instead “at the start of the experimental treatment” or “pretreatment measurements”?
L247 remove “almost”.
L247 & 250 These rates of change should be accompanied by an error estimate.
L248 what do you mean here by “weather events”?
L251 where do you show this result? Please refer to the corresponding table or figure.
L263-269 replicates instead of replications. Also, consider writing your results in past tense.
L269 “were the most acidic” instead of “have the highest acidity”.
L307 add “of precipitation water” after NO3-.
L319 pH instead of “it”.
L325 remove “likely”
L333-334 I am not sure I understand this, soil acidification has to be intrinsically linked to the concentration of H+.
L339 remove “in greater detail”.
348-349 I am not sure I follow how decreased N demand by the trees has a feedback effect on the concentration of Ca+, could you explain this?
L349 But I thought the felling resulted in a decrease in N demand, this is contradictory.
L350-351 Please provide a citation to support this claim of low nitrification rates.
L364 what soil property is buffered?
L371 provide citations and examples. Also consider “lack” instead of “don’t contain”.
L376 how would deeper rooting help buffer acidification due to increased N deposition?
L376-379 This line of argumentation linking plant litter, denitrification and cation transport between moulds and depressions is not clear.
L383 “peaked”
L416 “emissions of N and S oxides”

Figure 1. Add a legend indicated what are the blue and red circles.

Figure 2-6. Please, increase font size of all labels and axes.

Dear Authors,
I agree with the comments of the associate editor.
Best wishes,
Anja Rammig

Dear Drs. Schleppi, Bär,

Thank you very much for addressing all of my comments in such a diligent manner. I believe that the manuscript has gained in clarity and, in my opinion, it is now -nearly- suitable for publication in Biogeosciences. While reading your manuscript one more time, I only found the following issues that still could be fixed (line numbers refer to the latest uploaded version with tracked changes):

L115-136 Consider mentioning here the felling experiment, when it took place and how this treatment did not have any significant impacts on the current study.
L138 "A" instead of "An"
L415-417 I know that you added the results on the pH trends of this other nearby catchment to address one of my comments. However, I think that in this revised version, the new explanations on how the pH of rainwater and runoff evolved over time are sufficient and this statement could be removed.

I hope you do not mid that I make this additional and very minor comments and I look forward to seeing your manuscript published in Biogeosciences.

Kind regards,

Dr Teresa E. Gimeno

Dear Authors,
Thank you for the careful revisions of your manuscript. I agree with the comments of the associate editor and suggest that the manuscript can be published after the corrections. Please make sure that Fig. 1 is readable for colorblind (red-green blind) persons.
Thank you & all the best,
Anja Rammig