How to Assess the Ecological Status of Highly Humic Lakes? Development of a New Method Based on Benthic Invertebrates

Round 1

Reviewer 1 Report

The Water Framework Directive (WFD, EC 2000) introduced new challenges for the management of water bodies in the EU. Member states should assess and monitor the ecological status of surface waters primarily on the basis of biological elements (aquatic flora, benthic invertebrates and fish) supported by hydromorphological and physicochemical water quality elements. Dystrophic lakes, also known as humic lakes, are lakes that contain high amounts of humic substances and organic acids. Partly as a consequence of the high dissolved organic carbon (DOC)/concentration and high concentration of dissolved organic matter (DOM), humic lakes of the boreal zone share several features: a brown water colour, low penetration of light and predominance of the red part of the spectrum, acidity, low alkalinity, low conductivity and a low concentration of dissolved inorganic nutrients. In summer, the layer of epilimnetic water is thinner in humic lakes than in clear-water lakes and hypolimnetic oxygen depletion is a common occurrence, especially in small humic lakes. All these features have ecological consequences that can modify the structure and function of the food web. The biological communities differ considerably from those of clear-water lakes (phytoplankton; benthic invertebrates; macrophytes; periphyton; zooplankton; fish fauna]). These and other features make the determination of ecological status difficult dystrophic lakes. This study proposes a new approach suitable for the ecological status assessment of highly humic lakes impacted by hydrological modifications. Altogether macroinvertebrate samples from 15 raised bog lakes were used to develop the method.

In my opinion the article should be published. The abstract is informative enough. Keywords are informative and relevant. Defining the objectives of the article is adequate and appropriate to the subject. The methods are presented correctly and sufficiently informative to enable the repetition of tests, the work is research-specific. The statistical development of results does not raise any objections. Therefore, I can conclude that the purpose of the study was achieved and the results of the study were thoroughly discussed. The paper is well organized, and the Results and Discussion sections (highlighted in the text) are clearly and concisely written. The illustrations and tables all necessary, complete, clearly presented, and are the captions adequate and informative. The interpretations and conclusions sound, justified by the data and consistent with the objectives. Analyzing the results and discussing the support or rejection of hypotheses is properly documented and convincing.

MINOR COMMENTS

2.1. Study Sites/Figure 1. - only seven lakes are marked - should there be 15 right?

Line 105 - Are the tested lakes Natura 2000 habitats (Annex I habitat: 3160 - 3160 Natural dystrophic lakes and ponds?) , if so, has their conservation status been determined as part of the management of SACs?

2.4.3. Numerical Suitability

Line 184 - Altogether 14 metrics were selected for further investigation - which metrics have been rejected?

2.4.5. Correlations

Line 184 -190 - why the significance level was assumed - correlation coefficient ≥0.8 and not ≥0.5?

Author Response

We were pleased to receive the positive feedback. We have now revised the manuscript addressing the points raised. We would like to express our gratitude for valuable remarks. Our responses to the comments are given in the attachment.

Best regards,

Dāvis Ozoliņš, on behalf of all authors

Author Response File: Author Response.pdf

Reviewer 2 Report

The submitted article deals with using littoral benthic macroinvertebrate communities to assess lake health in highly humic boreal bog lakes. It is thus a timely and relevant topic and deserves attention.

In general, the manuscript is well written and to the point. Maybe you could add a comment in the introduction on the WFD – in the method section it becomes clear that you use the methods – so in my opinion you need to state already in the introduction what the WFD says about bogs and mires.

I suggest clarifying, what the paper is about – is it about comparing altered to natural systems? Or is it about defining the first multimetric index for humic bogs? Or both? The samples are limited, so it would be stretching it, if you addressed both points. However, if you concentrate on the difference between altered and natural lakes, in my opinion, you need to introduce that, to address this, you had to develop a new multimetric index, the test of which remains to be done in further studies. However, showing to what degree the communities differ between natural and altered lakes, would work even without the multimetric index, so you might even omit that from this paper, to make the analysis on differences between altered and natural humic lakes more concise.

You measure water quality and list the properties in Table 1 - but how does this relate to the difference between altered and natural? There is no hypothesis requiring Table 1, and the whole paper would work without physical and chemical properties.

line 32             I think this statement is too short – the low pH is rather caused by the degradation of the DOM.

line 102                       it might be interesting to point out with a third symbol those locations with 5 bog lakes each. Or better, number each dot and in the figure caption, give the names for each number.

line 121                       “Physical and chemical” – Physico-chemical refers in the stricter sense to the science where the physical properties are changed due to chemical reactions and vice versa – you are not observing changes to the physicochemical properties of a given substance, you are measuring variables that you hope are not changing during the observation. 

line 136                       “A hand net”

line 138                       how long was one sweep? 50 cm? 100 cm?

line 140                       “At the small lakes”

line 143                       since spring is the best season for sampling, why did you sample in October? Either comment on that or delete the spring sampling statement

line 155                       the last word is probably multimetric with a second t?

line 173 and SI Table 1            the Z value is from the Bayesian linear regression? So what about the table of the U tests? Please state in the Table caption.

Last line in SI Table 1 says “Anzahl Indiaktorarten”, probably a spelling error , probably Indikatorarten. However, that is the literal translation of the first line on this page 4 of Table 1 – in what way are they different?

line 179 f.        is this your own statement or general procedure? If the latter, please give a reference.

line 184                       is the selected in this sentence the same as the included in Figure 4? If yes, please use one of them conclusively.

line 185                       please state in the Figure caption what you mean by “included” / “not included”

                        please explain “OD”

line 188                       I am not a native speaker, but I think it should be “The group …”

line 189                       no classical statistics (if any) can give you causal relationships – I would replace by something like “non-explanatory” or similar. Also: weren’t all these indices created for ecoregions other than boreal? Or the other way around: which ones were? This is not major, but confusing ..

Table S2          The formatting is broken on my computer, therefore hard to read

                        Anzahl Indikatorarten is missing here.

                        There is only one BMWP score listed, but in Figure 4, the Greek, Hungarian, and Spanish version are marked as selected.

                        I cannot find ETCO in Figure 1?

line 201                       “As the selected .. ”

line 207                       “.. used the mean .. “

line 210                       “To ensure a multrimetic .. “ or probably better something like: “To ensure that the multrimetic index is limited between ....” – or maybe rather: “To ensure that the multrimetic index ranged from 0 to 1”

line 213                       Do you mean “impairment, too”? otherwise, I don’t understand what the “to” is relating to

line 220                       “each of the previous”

line 222                       since you are in the methods, I believe you did not suggest to use , but used it, correct? Thus: “We used the quality classes .. following the suggestion in Hering  ”

line 229                       “We consider an index to be best”, if this relates to single indices

line 232                       “We used the software”

line 239                       “observed in waterbodies”

line 242                       please add a column where you indicate which ones are the disturbed ones – e.g. with a “x”

line 244                       “presented in the Supplemental”

line 245/246   “recorded at the studied, … of which the orders”

line 247                       Mayflies ARE Ephemeroptera, therefore I suggest to write Ephemeroptera in brackets.

line 248                       replace “being only absent at” by “missing only in”

line 250                       replace “Both of these species” by “These two species”

line 252 & 253 replace “varying” by “ranging”

line 255                       replace “were dominant” by “dominated” … “The taxonomic structure”

line 256                       you don’t really have many data to talk about seasonal structure – I wonder whether you lose much of your data if you exclude the October samples. At the very least, indicate in the caption for Figure 5 that the 6 numbers at the end of the label stand for the date in format ddmmyy, where applicable. The differences between May versus October samples might be background variation – it would need many more samples to distinguish between background variation and seasonality.

line 265                       “natural water level”

line 283                       Diptera

line 286                       “We found the model … to be the best quality classifier” – don’t talk about suggesting it within the results section – suggestions are done in discussion and conclusion

                        Also – this model does not contain all 10 or 12 indicators that you deemed relevant in Figure 1 – why? How did you come up with this model, and how did it fare compared to alternative models?

line 294                       “The total number”

line 297                       delete “from bog lakes” – that’s already mentioned earlier in the sentence

line 303                       the first sentence of this paragraph is just repeating results – can be deleted.

line 306                       “an increased proportion”

line 307                       delete “at altered lakes” since that’s said at the beginning of the sentence

line 312                       replace “have” by “are”

line 312ff         the two paragraphs belongs into the introduction, in my opinion, and are also partly redundant

line 322                       either “most commonly” or “most common are”

line 327                       I have not looked it up, but the first PC of the mentioned PCA is most likely not a metric, but a site-specific outome and cannot be compared to your lakes – please delete the sentence

line 335                       “metric is” or “metrics are”

line 341                       “relatively”

line 345                       see line 327

line 346                       “a significant difference”

line 348                       delete however, and begin the sentence in line 345: “In contrast, we found”

line 354                       what is COP?

line 355                       “demonstrated relationships between”

line 356                       Coleoptera

line 358                       metric (Singular)

line 364                       delete the bracket, because you are in the middle of the sentence here

line 392                       addressed

line 394                       assessments (plural)

line 396 f.        either “assessment systems” or “an assessment system”

line 398 ff.       this was not the topic of this paper, and you cannot evaluate how the use of the common indices influenced your results – I would omit this whole section, and instead, compare your humic sites to non-humic sites in another project. Alternatively, state briefly in the introduction, with some of the sources you give here, that you used these common indices although they might not be appropriate.

Then, in the discussion, discuss briefly whether you believe this multimetric model of line 286 to be universal to humic bogs, and / or why (not).

Line 406          “phenomena and not”

line 413                       “system is based on”

line 415 – 418 in my opinion, this belongs to the introduction. And it might even become a second aim of the study, apart from showing how the indices differed for natural versus altered lakes. If you keep it here in end of the discussion, some conclusion or outlook is needed, I think, such as “Whether the multimetric index is applicable to further humic lakes, needs to be tested in future studies”.

Author Response

Thank you for the positive feedback. We have now revised the manuscript, carefully addressing each of the points raised. We would like to express our gratitude for the valuable remarks. Our detailed responses to the comments are given in the attachment and the changes made are visible in the manuscript file.

Yours sincerely,

Dāvis Ozoliņš, on behalf of all authors

Author Response File: Author Response.pdf