Dissolved Gaseous Mercury (DGM) in the Gulf of Trieste, Northern Adriatic Sea
Round 1
Reviewer 1 Report
This MS is dealing with the continuous monitoring of DGM during the warm period in the Gulf of Trieste. MS is written clear and concise, although I found some minor errors and a question that should be appropriately addressed.
Line 85: “2019),” should be deleted.
Line 335: “-“ in front of 22:00 should be deleted.
The authors discussed in detail the external influences on DGM concentrations, in order to explain computational models. What would be the results if local maritime transport (which is not negligible in the research area) and its impact on shallow sea, horizontal and vertical mixing of the water column and impact on shallow sediment, were taken into account?
If authors adequately answer all questions raised, revised MS can be published.
Author Response
Response to reviewer 1:
- Line 85: “2019),” should be deleted. – deleted
- Line 335: “-“ in front of 22:00 should be deleted. – deleted
The authors discussed in detail the external influences on DGM concentrations, in order to explain computational models. What would be the results if local maritime transport (which is not negligible in the research area) and its impact on shallow sea, horizontal and vertical mixing of the water column and impact on shallow sediment, were taken into account?
Response:
Measurements performed in the vicinity of the Port Koper showed increased turbidity behind larger vessels (length > 100 m) when manoeuvering in or out the port, the distance between the hull and the bottom there being less than 2 m. However, even in such conditions the turbidity peaks lasted only for a few (usually less than 10) minutes before settling. Therefore, even maritime traffic of such large ships cannot be held responsible for the observed DGM peaks that lasted for 24 hours or more. Furthermore, the routes of such large vessels are positioned about 3 nautical miles from the coast and the remobilised turbidity could reach the sampling sites only in extreme meteorological conditions. Smaller vessels (local maritime traffic) produce higher mixing in the near-surface layers and the turbulence can hardly reach the seabottom in the relatively deep (> 15 m) southern part of the Gulf. The traffic in the near shore zone is limited to tourist and fishing vessels, and again, even in the shallows, the impact of navigation could only result in short-time peaks of any pollution resuspended from the sea-bottom. Although we cannot exclude either extrusion and mixing of pore waters or desorption of various Hg species from resuspended sediment to the water column, we do not expect these processes to be of the same order of magnitude with the current-induced water-mass transport and to increase the DGM concentrations to the observed level at any of the sampling points.
Reviewer 2 Report
The manuscript presents the results of studying “Dissolved gaseous mercury (DGM) in the Gulf of Trieste, northern Adriatic Sea”. This study was conducted during the summer (May to September) in the Gulf of Trieste to measure continuous dissolved gaseous mercury. Manuscript has four sections: Introduction, Methods, Results and Discussion and Conclusion. This is interesting research for reader. After reviewing this manuscript, I feel analytical methods and results are fine and also reliable. Presentation is good throughout the manuscript . Overall in my opinion the paper current form is suitable for publishing in worthy journal
Author Response
No response needed
Reviewer 3 Report
The manuscript “Dissolved gaseous mercury (DGM) in the Gulf of Trieste, northern Adriatic Sea” by Kotnik et al. discusses water-air exchanges of mercury in different sites from the Mediterranean Sea, particularly in the Gulf of Trieste.
Overall, the manuscript is well written and well organized, but still minor revisions on these aspects should be considered. In particular, there are some aspects concerning the English that could be improved to make the manuscript easier to read and understand.
One drawback of the manuscript is the lack of a clear hypothesis to be tested and the goals for that purpose. I suggest the authors to reformulate the last paragraph in the Introduction (lines 114-123).
Another major drawback that can be pointed out concerns the statistical processing of the data. The authors need to clarify and complete the statistical analyses performed for the correlations, e.g., as well as for the comparison of Hg fluxes between sites. Therefore, a sub-section should be added in the Material and Methods addressing those issues. It should be mentioned the p-values for the correlations found.
Another major issue that the authors should clarify relates to the Lagrangian distribution of particles within the Gulf during June 15, Figure 3, which does not clearly depict the influence of Soca/Isonzo River on Hg apportionment to the buoy Vida.
The region in Figure 1 should be slightly enlarged so the reader can easily relate to the part of the discussion in lines 517-542. In addition, Po River location is not indicated in the figure. Figures 3, 4, and 7 need legends in the yy axis, figures would benefit from breaking or adding a separate yy axis to avoid superimposing many parameters, which turns the figures hard to understand. In addition, figures need to have an orientation (an arrow indicating the North).
Table 1 needs the statistics showing the significant differences between both sub-periods analyzed.
Table 2 needs the reference numbers near the reference, e.g. Tomazic et al., 2018 [42].
Acronyms need to be revised; some are not included in the text
Finally, the abstract should not be a repetition of sentences from the manuscript and it should reflect its overall content. I suggest the authors to revised it and included some values found in the study, both DGM concentrations and fluxes.
Specific comments are provided below. In the present form, I suggest the authors to perform a major revision of the article before its acceptance.
Line 141: it is not clear where the discrete samples were collected.
Line 187-188: the reference number is missing.
Line 216: acronym for NIB, please explain.
Line 218: acronym for EMEP, please explain.
Line 228: units need to be consistent (check line 142).
Line 230-231: which data was considered and from which meteorological stations? Are these indicated in Fig 1?
Line 306: despite the excellent agreement as stated by the authors, there are apparently two outliers in Figure 2, namely two points concerning the DGN manual buoy Vida. Did the authors test the data for outliers? Please, clarify this.
Line 307: ‘from tube’
Line 313: values are slightly higher, and considering the natural variation of DGM perhaps there is no significant difference. Did the author perform any statistical test to check this?
Line 331: no statistical methods were described. This information should be also added in table 1 for the two subintervals used in the calculations.
Line 362-363: no statistical methods were described.
Line 368-369: isn’t it the concentration >50 ng/m3 instead of >150 ng/m3? Furthermore, this sentence needs some clarification: in Figure 4 is shown that in July 2 (~22h) the wind is high and Hg is high as well; however, for July 3 (~22h) the wind is high but Hg is low, and from June 30 until July 2 the wind is relatively low (more or less constant) with Hg concentration increasing in this period. Can the authors explain better what they meant to say?
Line 386: no statistical methods were described.
Line 403: wasn’t it the sampler tube 0.3m above the sediment?
Line 403-407: Assuming the 20 m depth is correct (and not 0.3 m as in my previous comment), this paragraph seems a bit contradictory and should be revised.
Line 409-410: a reference should be added.
Line 427-439: It is not clear if both high DGM events (line 430-431) include July. Consequently, transport of DGM by the sea current from the vicinity of the Isonzo river (Lines 438-439) is not clear particularly from Fig 5. Otherwise, can the sediments be the Hg source, considering the sampler to be at 0.3 m above the bottom? I suggest the authors to revise this paragraph.
Line 455-457: This statement is not correct. Figure 7 shows as well around May 30 that relatively high DGM is coincident with wind speeds of ~10 m/s depicting a low evasion; whereas around August 15 is shown higher wind speed with a relatively lower DGM concentration but depicting higher Hg evasion.
Line 457: The word event in this sentence may cause confusion. I suggest the use of periods.
Line 460-461: expressing the flux as average±SD may induce negative values, as it is in this case, I suggest the use of the flux range, min-max, to avoid misconceptions.
Line 461: ‘a minimum of’ ‘a maximum of’
Figure 7 – Can wind data be integrated in a data set with less points? It seems very confusing, and hard to see any existing pattern.
Line 479: the same comment as line 460-461.
Line 483: please, check the commas.
Line 486: ‘…winter periods to be approximately…’
Line 512: please add (MBP) after the Piran station
Line 513-516: I think Po River appears here for the first time and it is not indicated its location in Fig 1. Please check.
Line 517-542: This paragraph needs a thorough revision; it is confusing. For example, there is a lot of detail regarding the methodology of [44] that for the sake of discussion is not necessary. Secondly, mentioning the geo position of the sites should be clear, i.e. after a while the paragraph is hard to read and understand which loses the message. In addition, part of this discussion is related to an area that is not represented in fig 1 and this issue may increase therefore the difficulty of understanding this part of the discussion.
Line 551: no statistical methods were described.
Line 554: if the authors mention the correlations as an important part of the work, the indication of p-values should be given.
Line 564-566: It is not evident from Fig 5 that in June there was a pronounced influence from the Isonzo river on Hg apportionment.
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Round 2
Reviewer 3 Report
I acknowledge the effort of the authors to improve the manuscript. Tough some aspects could be (re)worked to enhance the clearness and soundness of the article. I think, however, the authors misinterpreted some of my points. For example, if relevance is given to the statistical analysis throughout the manuscript, just a brief paragraph describing the analyses should be given in the Methods. Another example would be the phrase “with concentrations over 150 ng·m-3 (June 10–19 and July 1–4)” that leads the reader to a completely different idea of the figure. The dates in parenthesis point to a period of concentrations over 150 ng/m3.
The coordinates need to be consistent throughout the manuscript, e.g. line 248 of revised MS.
I do not have more comments and recommend the article for publication after a minor revision.
Author Response
Dear reviewer,
the authors acknowledge your revisions to improve our article. Please find comments and corrections below:
I acknowledge the effort of the authors to improve the manuscript. Tough some aspects could be (re)worked to enhance the clearness and soundness of the article. I think, however, the authors misinterpreted some of my points. For example, if relevance is given to the statistical analysis throughout the manuscript, just a brief paragraph describing the analyses should be given in the Methods.
- Used statistical analysis and methods used are now clearly explained either in Methods or Discussion
Another example would be the phrase “with concentrations over 150 ng·m-3 (June 10–19 and July 1–4)” that leads the reader to a completely different idea of the figure. The dates in parenthesis point to a period of concentrations over 150 ng/m3.
- Phrase was redefined to clearly express DGM peaks: A more detailed investigation was performed in the periods (June 10–19 and July 1–4) of both DGM peaks (June 14-15 and July 2-3) with concentrations over 150 ng·m-3.
The coordinates need to be consistent throughout the manuscript, e.g. line 248 of revised MS.
- Corrected to digital values that are used throughout manuscript
I do not have more comments and recommend the article for publication after a minor revision.
Author Response File: Author Response.pdf
