Multiple Evidence for Climate Patterns Influencing Ecosystem Productivity across Spatial Gradients in the Venice Lagoon

Round 1

Reviewer 1 Report

Dear Authors,

The article is interesting and dealing with the effects of climatic changes in the Venice Lagoon combining available data and a published model.

In my opinion, the manuscript addresses an interesting topic and falls into the aims of the Journal. However, a minor revision is needed in order to improve it.

In M&M you should better explain the following technical details:

• How did you consider Water Bodies (WBs) with no buoys?
• I disagree with merging of PC1 and PNC2 as their hydrodynamics are quite different due to morphological structures, which divide the two WBs.
• Why did not you directly use Dissolved Oxygen (mg/l) provided by buoys instead of Oxygen saturation?
• It is well known that SAMANET buoys have had some problems and several of them did not supply data for a long time (not only one missing data point). How did you manage the lack of data?
• Generally, it is not clear when you talk about basin or WBs. And what do you consider as a basin. Please, explain better the considered areas of your study. Moreover, if you considered basins instead of WB, please highlight them in Fig1

Finally, discuss better your results comparing them with other similar areas and with previous years of the Venice Lagoon. It is not acceptable to talk about evidences of extreme climate with only 9 years and without comparing data with a longer time series.

Detailed comments and note to the text:

ll.33 and throughout the whole text: c.ca --> cca.

ll.51 and throughout the whole text: Salinity is adimensional. Avoid PSU or any other unit of measure

ll.52: Sea

ll.53: (632*106 m³)-->better report the surface, lenght and mean width rather than the mean water volume. If you prefer the volume, please indicate it along the number

1. 55: ranging from 1.12 to 39 m --> ranging from 1.52 to 39 m

ll74: Salinity PSU

ll 74-76:  Explain better the other merging of WBs, as some of them have not buoys.

ll 75: PNC2were --> PNC2 were

Table in Fig. 1: explicitate for each buoy which WB represent

legend in Fig 1: hourly or half hourly?

ll.98: "the oxygen (DO), data for each sub-basin were used to calculate respiration" -> check word order and commas

ll.98: Buoys were not present in each WB. Please, explain how did you use data to properly represent each sub-basin (or WB)

ll 104: Why did not you use DO directly?

ll.123: Explain why you did not use NO₂ data (and then DIN)

ll 127: I believe seasonally sampling were made on Feb (not March), May, August and November, but with some exceptions. Explain how exceptions did (or did not) affect your results. For example see data from 2012.

ll155: each box. . --> each box.

ll158: delete psu

fig.3: Align years and order them in cronologically order

ll166: each box. . --> each box.

ll171: PC1 is the WB influenced by Dese River. Probably you are talking about PNC1.

ll 173: Valle Averto is in VLCS. PNC1 is the water body you spoke above. Maybe are you talking about MILLECAMPI and TENERI (PC3/PC4)??

ll173-176: senteces are not clear and uncorrect. Please, write it better

ll 176: The northernmost basin () --> complete the sentence

ll 181: Oxygen saturation or Dissolved oxygen? Explain why you used both of them and when (e.g. for eq(1) you used DO, here you prefer %O₂)

ll 188 and tab.2: standard errors or standard deviations? Better to use SE throughout the whole text

ll 194 figure 4.correlation --> Correlation

ll 196: no stars or not significative?

1. 196: . <0.09 --> > 0.05

ll 201:  Temperature (A°C) --> Temperature (°C)

ll 202: pmax, ---> pmax.

Fig. 6: write years in chronologically order

ll 215: box.. --> box.

tab 4: what about the other WBs?

1. 231-232: Discuss better your results comparing them with other similar areas and with previous years of Venice Lagoon. It is not acceptable to talk about evidences of extreme climate with only 9 years and without comparing data with longer time series.

ll 249: 2010 was a generally warm --> 2010 was generally warm

ll289: check size characters of "North Atlantic Subtropical Gyre"

ll 335: see comments about discussion and time series comparing

ll349-341: Furthermore, this study further --> delete further

ll389: delete "Received"

ll 395: delete (

Author Response

Please see attached letter

Author Response File: Author Response.docx

Reviewer 2 Report

jmse-1132251

The manuscript “Multiple evidence for climatic changes in the Venice lagoon influencing ecosystem productivity across spatial gradients”, by Bertolini et al., analyze the temporal and spatial patterns of water temperature, salinity and productivity time-series in the Venice lagoon.

The work is interesting and focus in a topic that has general interest but needs to improve some aspects before to be published. With the current data analysis design, it is not possible to conclude that the observed changes are due to climate change.

There are also some considerations that authors could be take into account. In the introduction authors talk mainly of transitional estuarine areas as a reference, for example for heterogeneity of the system. It would be recommended to also focus on coastal lagoons as this is the subject of study. In fact, although coastal lagoons tend to be included among transitional waters, their behavior is not exactly the same as in estuaries, mainly in matters of heterogeneity (since coastal lagoons have much more complex spatio-temporal patterns) (see Pérez-Ruzafa et al., 2011), particularly in lagoons than by their nature or due to ancient human interventions, as in the case of Venice, they do not have permanent river mouths.

The authors acknowledge the great environmental heterogeneity of the Venice lagoon, and it should be put it in context of the scales of variation of hydrological and water column parameters and the main sources of variation that can be found in coastal lagoons (Pérez-Ruzafa et al. 2007) and the own Venice lagoon (Franco et al., 2009; Sigovini, 2011; Minicante et al., 2019).

In this context, the methods section, to assess similarities between the seasonal evolutions of water temperature in the 2008-2019 decade, data for 10 buoys were pooled together, and a median water temperature value for each fortnight was calculated. Having recognized the heterogeneity of the Venice lagoon, the problem with having calculated the median of the 10 buoys is that the information on this environmental heterogeneity is lost and it is not possible to discriminate whether the observed temporal changes are a consequence of climate change (which would affect more or less to the entire lagoon) or to local changes in some of the localities (due to operations in the communication channels with the sea (for example MOSES works? Cavalieri et al., 2020; Umgiesser, 2020), or due to changes in the water discharges from the drainage basin from a historical (Omodeo et al., 2020), actual and expected future scenarios point of view.

Therefore, the main weakness of the work is that with the current data analyses design it cannot differentiate the variability due to local changes due to the heterogeneity of each sub-basin or to human actions in the different areas of influence from what may be real trends due to climate change. For this reason, some of the main conclusions of the study are speculative and cannot be derived from the data as it has been analysed. For example, the discussion starts with the assessment “This study shows how the climate in the Venice lagoon is becoming more extreme: summers are becoming warmer and winters colder (2012, 2017, 2019) and in some years extreme high summer temperature can be observed ( 2008, 2013, 2015, 2018)”, but looking to the results, there is no a clear temporal trend in salinity or temperature and both can depend or the sub-basin considered or be affected by inlets dynamic (see García-Oliva et al., 2019 to see how intervention in the inlets can affect salinity and temperature ranges and spatio-temporal variability in another Mediterranean coastal lagoon).

Using the available data, authors should perform the same analyses including spatial heterogeneity (for example 3 to 5 subbasins including at least 2 buoys in each one) and comparing if the spatio-temporal variability at smaller scales is significantly larger or lower than the expected climate changes trends.

The discussion requires deeper discussion and taking into account other sources of variability. It includes interesting papers analysing the expected effects of climate changes on several lagoons (Ferrarin et al., 2014) but could also include more detailed analyses on spatial variability in a given lagoon (De Pascalis et al., 2012). By other hand, the discussion focuses mainly in the expected consequences on the biological production but only takes into account the balances in the water column, and ignores the benthic communities. In the case of the Venetian lagoon, like other Mediterranean lagoons, the seagrass meadows are important, and it is heterogeneous in space and time (Sfriso and Facca, 2007; Zharova, et al., 2008), without forgetting that the microfitobenthos can also play a decisive role (Brito et al., 2012) even greater than that of some macroalgae. Therefore, authors should put their observations and results in the context of the trophic networks in the Venice lagoon (Brigolin et al., 2011, 2014) and what happens in other lagoons in relation to what was commented above regarding the pelagic or benthic production dominating the system (Bocci 2016, Pérez-Ruzafa et al., 2020).

Finally, and perhaps the more important is that discussion should focus in discriminate what changes can be due to climate change from that can be related to natural dynamic and human activities. Trends in sea surface temperature in the Venice lagoon has been already analyzed (Amos et al., 2017) and from a general analyses and conceptual models for the Venice lagoon could be see Tagliapietra et al. (2012) and for analizing the effects on natural resources Ghezzo et al. (2018). The discussion should compare the predictions for the Venice lagoon with the expected in other lagoons (Brito et al., 2012, De Pascalis et al., 2012) discriminating these effects from the interaction with human interventions in the lagoon of Venice (Ferrain et al., 2012) or other human effects like artificial opening and closing inlets as studied in Venice (Teatini et al., 2017 ) and other lagoons (Coelho et al., 2015), and references cited above, putting into context of the expected effects of climate change also in the adjacent sea (Rizzi et al., 2016; Torresan et al. 2019).

Cited references in order of citation

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5. Habitat Heterogeneity and Connectivity: Effects on the Planktonic Protist Community Structure at Two Adjacent Coastal Sites (the Lagoon and the Gulf of Venice, Northern Adriatic Sea, Italy) Revealed by Metabarcoding

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Author Response

please see attachment

Author Response File: Author Response.docx

Reviewer 3 Report

shhortcoming above all the terms of dynamic of populations and species detected 

Author Response

rev3

shhortcoming above all the terms of dynamic of populations and species detected 

We do not understand what this reviewer intends. However we have hoped to have addressed some of the shortcomings by responding to reviewers 1 and 2.

Round 2

Reviewer 2 Report

The authors have improved the discussion and put the results in the context of other studies, mainly in their area of study. They have also reduced the possible confusion of the effects of their study due to environmental changes with respect to those that could be linked to climate change, including the title of the work, which makes the results more in line with reality and the possibilities of the study. I consider that the work can be published in its current form.