Environmental Factors Controlling Zooplankton Communities in Thermokarst Lakes of the Bolshezemelskaya Tundra Permafrost Peatlands (NE Europe)

Round 1

Reviewer 1 Report

The authors provide an assessment of the summer 2016 zooplankton community of 29 shallow tundra lakes, an important update on these unique northern habitats very sensitive to climate change.  These lakes are shallow and include a range of productivity, pH, macrophyte coverage, and browning.  Importantly for zooplankton, they are void of fish.

A key positive aspect of this contribution is the high level and quality of taxonomic detail provided for zooplankton including rotifers. The mesh used (74 micron) and the volume (30-50 L) appears appropriate.  One question I had, lines 152-156 note both the use of a surface sample for quantitative and whole water column sampling for qualitative. These lakes are only 0.5-1.5 m deep, so I assume that the primary data used was the surface sample with a known volume that should be fine in assessing these shallow lakes. But It is unclear how the whole water column qualitative tows were used in this paper.

For the quantitative data, a large assortment of zooplankton indicators are used and reported in Table 2, with values averaged for the three geographic districts.  But for comparison to environmental variables, only the simplest (density and biomass) are used for identifying potential correlations. In Figure 4, environmental variables are presented in rank order on the horizontal axis, but correlation analysis would benefit from scatter plots.  Also note figure caption for panel c and d are misplaced.

Pie charts (3 pies for region, 3 slices for group) may be more visual instead of bar graphs of Figure 2 and 3. 

Set up the key conclusions for links to pH (zooplankton abundance, biomass, diversity) and mineralization (diversity)

The English language of the paper is generally smooth, but there are a few things that could improve delivery.  Avoid use of "peaceful" zooplankton, instead use nonpredatory or herbivorous?  Zoocenoses can be replaced by zooplankton community.  Instead of saying 17 species "not registered in other lakes" say species "unique" to these lakes.  Instead of "oligo-mesoprobes" use oligotrophic or mesotrophic.  Instead of hydrobionts say zooplankton.

Do you have a list of the 8 "trophic groups" used to describe the range of feeding relationships?  You could include that in the supplemental material with your species list.  You focus on the top three, curious what others there are.  But basic differentiation of filter feeders, substrate feeders, and active capture seems straightforward.

Comparison of this data to data from 60 years prior and concluding that they are at stable state seems tenuous.

Minor corrections

-Line 210 is redundant with line 196

-What is the bit/ind scale used for Shannon index? (line 261)

-Line 223  Species diversity was determined cladocerans.  Add "by'?

-Line 357  use observed rather than revealed

-Line 466  is cpastal peat abration coastal?

Is the acidic character resulting naturally from peatland or does it have an remote anthropogenic source?  Line 503 mentions absence of a signficant anthropogenic load but we know that these can act remotely (e.g. acid rain from air pollution).  Is this an issue in the Russian tundra?

 

 

 

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 2 Report

Dear Authors,

Please, add some description of analyses of physical and chemical parameters of water to the Materials and Methods. The ms needs careful English editing because it is abound with inadequate words and expressions. Below, you can find my specific comments:

1. Line 21 – ‘the level of zooplankton development’ – this expression is blurry. Do you mean species structure, abundance or size structure?

2. Line 45 – Actually, the air and water temperatures correlate, thus I suggest to rephrase the sentence: ‘The temperature is the most important factor affecting….’

3. Line 74-75 – Species predominance or abundance predominance? As far as I know, rotifers predominate both in species and density (sometimes biomass) in most of freshwater ecosystems. So, this is not a point especially specific for Arctic and subarctic ecosystems.

4. Line 154 – ‘network’ and ‘microns’? Do you mean plankton net and micrometers?

5. Line 167 – Please, change ‘predatory’ and ‘peaceful’ for ‘predacious’ and ‘non-predacious’.

6. Line 209 – This is very interesting information. Do you think that untypical structure of zooplankton (predominance of cladocerans or copepods over rotifers) in the lakes can result from absence of planktivorous fish?

7. Line 213 – There in an information in the Materials and Methods that there are short cool summers with temperature 6-12 C in the area of lakes’ location. Taking climate conditions under consideration, how is that possible that water temperature in these lakes is so high?

8. Line 222 – This sentence is senseless, since each zooplankton species is a hydrobiont. Please, rephrase (‘In total, 60 zooplankton species were observed in tundra lakes…’ or ‘In total, 60 zooplankton species were observed among hydrobiota of tundra lakes…’).

9. Line 254 – 256 – Ceriodaphnia quadrangula and Chydorus sphaericus are not phytophilic species, since they settle also macrophyte-free areas of lakes.

10. Line 260-262 – As far as I know, Shannon species diversity index has no units.

11. Line 266-267 – ‘Decrease’ and ‘increase’ suggest some changes in time. Please, rephrase.

12. Line 271-272 – Change ‘equalization index’ for ‘index of uniformity’ or ‘Pielou index’. ‘Stable and balanced’? Do you mean that they are similar?

13. Line 276 – Below, you mention three trophic groups: filter-feeders, scrapers and predators. I wonder what other 5 trophic groups you derived. Please, name them in the Results.

14. Line 283 – What is the difference between filter-feeders and filter-feeding animals?

15. Line 285-287 – Cladocerans that extract food from surface of the substrate are called scrapers. As you include Chydoridae to this trophic group, I suggest to call this group as scrapers and facultative filter feeders, since some chydorids have the ability of taking additional food by filtration.

16. Table 2 is not cited in the text.

17. Line 248 – ‘Fluctuations’ suggest some changes over time. I suppose you mean ‘differences’.

18. Line 453-454 – Gas concentration? Do you mean oxygen concentration?

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

I accept the paper in present form.