the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 29 Oct 2021
Pameterization of the responses of subarctic European vegetation to key environmental variables for ozone risk assessment
Abstract. The unique vegetation of the subarctic region acclimatized to extremes of cold and midnight sun are likely to be at threat from the combined impacts of climate change and increasing ozone concentrations [O3]. The atmospheric and climatic characteristics of the subarctic are known to lead to pronounced peak [O3] in spring. To date, only a few studies assessed the response of subarctic vegetation to variations in climate and air pollution. This study looks to fill this knowledge gap by examining essential climate variables, in particular ozone, over the past few decades. We evaluate the extent to which two recent years (2018 and 2019) deviate from climatic and [O3] norms and how these potentially more frequent future deviations may influence ozone damage to subarctic vegetation. We find that 2018 was an anomalously warm and bright year, particularly in spring and early summer. Higher than average [O3] was observed in April/May while frequent episodes of ozone volume mixing ratios (VMRs) above 40 ppb occurred in June–August. These episodes are in part attributable to forest fires in the Northern Hemisphere and warmer and sunnier conditions. We apply the integrated flux-metric Phytotoxic Ozone Dose (POD) to determine ozone risk and damage to vegetation as a function of [O3], environmental factors, and species-specific physiology. Our study suggests that using generic parameterizations in assessments likely leads to underestimating the risk of ozone damage in this region. We find that bespoke parameterizations of plant functional types (PFTs) for subarctic vegetation bio-types result in an ozone-induced biomass loss of 2.5 to 17.4 %. For some species, this loss is up to 6 % larger than projected from generic parameterizations. Efforts should be targeted towards accurately defining subarctic vegetations' physiological response to essential climate variables. Our method could help to improve regional and global scale biogeochemical cycling under current and future climates.
- Preprint
(12465 KB) - Metadata XML
- BibTeX
- EndNote
Status: closed
-
RC1: 'Comment on bg-2021-260', Anonymous Referee #1, 05 Nov 2021
GENERAL COMMENTS
The manuscript addressed a relevant issue related to the ozone risk assessment in the Subarctic.
However, the presented study is highly speculative and is not based on any experimental evidence (i.e. the parametrization of gstom is hypothetical and not obtained from any measurements made in the area).
The justification of some methodological choices is weak, for example the need to modify the gstom parameterization because in 2019 the gstom predicted with the MM parameterization would have been too low.
Many claims sound superficial to me, such as the one about the alleged deviation of the years 2018 and 2019 from the site’s climatology, and many statements are inaccurate (see the specific comments).
The manuscript is too long, and the organization is confused. The introduction is nice, but it’s too long and contains too many digressions to get to the point. The results are mixed in the methodology and there is no clear division between the methodological section and the results section (a purely results section does not exist at all). There are several repetitions, for example the section “Discussion and Conclusions” is over half a summary of the previous sections. The Appendixes contain inaccuracies and omissions.
The English should be carefully revised because some sentences are ambiguous.
In my humble opinion, though, the work is generally weak and the manuscript is not mature enough to be accepted for publication.SPECIFIC COMMENTS
Lines 51-52. “and leads to a build-up of ozone and its precursors during winter.”
Are you sure? How can BVOC accumulate in the atmosphere if the vegetation is covered by snow? Please add some citations to support this claim. Much more credible is the following explanation based on stratospheric intrusions.Line 63. “the time in which vegetation can accumulate ozone.”
It sounds very bad written this way: vegetation does not accumulate ozone because ozone it is not bioaccumulative. Did you mean the dose?Line 77. “(<[O3]> = 36−54ppb)”
Please explain the formalism. What do different brackets mean?Line 81. “A substantial body of evidence exists that suggests flux-based metrics, that relate stomatal ozone uptake to vegetation damage, are biologically more relevant for risk assessments than exposure-based metrics.”
Well, please cite at least some works of this “substantial body”Figure 1. This figure was never referred in the text.
Figure 2. It does not seem to me that the O3 concentrations of 2019 are different from those of 2018. The spring peak could even be identical (although unknown, because in 2019 O3 measurements started about 20 days after the spring peak)
Line 146. Please make clear the acronym PFT on first use
Line 165. “luftkvalitet.no”
What is it? And EBAS? Please make them clear.Line 182. “This indicates that the vegetation was more affected by ozone in 2018 than in 2019.”
Being affected by visible symptoms does not necessarily mean having suffered biomass or productivity reduction.Line 190. “high ozone concentrations ([O3] > 40ppb”
It is strange to read that O3 concentrations above 40 ppb are “high” concentrations.Line 194. “A method for gapfilling data has been presented in Falk et al. (2021).”
Ok, but was it then applied to this work? Please write it.Line 205. “We evaluate the statistical significance of divergences from the norm in these variables (referred to as anomalies) in 2018/19”
I suspect a misuse of the locution “statistical significance”. How was this significance assessed? Which statistical test was applied? What is the level of significance?Lines 206-208. I do not understand. Please, explicit the methodology.
Line 213. “Averaged monthly accumulated precipitation (blue bars) is shown with standard deviation”
It is not consistent to show SE once and STDEV the other time. The use of SE is more appropriate when estimating averages.Line 228. “Darker colors indicate higher probability to observe these values.”
Line 229. “On top of the density distributions, a 10 days average of daily mean (h[O3]i10d) is displayed together with 1sigma uncertainties and SE, respectively”
What does it mean? It is not clear to me. Why show a probability density if you are plotting a multiannual average? Or does the line represent the median instead?Line 232. “The decline in h[O3]i coincides with the average beginning of CO2 uptake by coniferous trees (Kolari et al., 2007; Wallin et al., 2013)”
I didn't know that evergreens only uptake CO2 starting in May. I was convinced they always did. Is it true? Doesn’t that contradict what you wrote in line 309 ("We base our temperature acclimation of coniferous trees on experimental results on Norway spruce which were found to be active already at rather low air temperatures and can reach 60% photosynthetic activity as early as doy 100 (Kolariet al., 2007; Wallin et al., 2013).")?
Here you state that photosynthesis is already active at DOY 100 and is at 60% of its maximum!Line 233. “In July–September (doy 182–273), ozone is occasionally almost completely depleted. This hints to ozone uptake by vegetation even at low light intensities during midnight sun conditions in combination with stable planetary boundary layer conditions preventing mixing of ozone rich air.”
I don't understand the connection. What does the night uptake have to do with the occasionally complete ozone depletion?Line 244. “if a normal distribution is assumed”
Are you sure that the distribution is normal and not lognormal or something else? There are some literature on the type of statistical distributions for variable such as Temperature, Rain, etc ...
Moreover, looking at your Figure 6b the distribution of the irradiance seems to be a Poisson distribution.Figure 5, caption. “dashed lines indicates statistical significance”
Statistical significance of what? By means of what test was it obtained, at what alpha level? And what are the numbers on the top right of each graph?Line 251. “deviated significantly from the climatology on the 1 sigma level.”
Here the standard deviation is used as reference for the significance. But the significance of the deviation should be statistically tested in another way.Line 262. “We use the bias-corrected and cross-calibrated ozone climatology (Falk et al., 2021) and assess the monthly significance of the ozone concentration anomalies in 2018/19.”
“Bias-corrected cross-calibrated” ozone? What is it? And what is the “significance” of the concentration anomalies? Please explain.Line 267. “Further, we presume that fVPD and fSWP suit our vegetation types and no acclimation is necessary for these.”
This statement is questionable, because in cold conditions VPD can be high (you also told it in the conclusions) and the water in the soil can be limiting because partially unavailable due to freezing or other.Line 272. “but a substantially higher number of peak [O3] were observed in 2018 than in 2019.”
How can you tell it if O3 measurements for all months of March, April and July are missing in 2019? I don't seem to see any differences between 2018 and 2019Line 291 “ Note, however, that these parameterizations are hypothetical and have yet to be verified by experiments.”
Figure 6a. Looking at the graph I understand that you assume an adaptation of the subarctic grasslands to the temperature distribution of the last decade (climate already changed) and not to the historical temperature distribution at your site. Is it reasonable to hypothesize such a rapid adaptation of vegetation to the new climate conditions?
Line 298. “We construct cold as representative for a species that is more tolerant to cold temperatures, but slightly less efficient at warm temperatures compared to MM. This is accomplished by moving Topt towards cooler temperatures while keeping the other parameters fixed to MM values”.
From Figure 6a and Table 1 I see that for the “cold” parameterization not only Topt was moved, but also Tmin for (e.g. for grassland).Figure 7. The gstom/gmax ratio in the subarctic parameterization with PPFD0.8 is greater in the morning than at noon. How then the choice of PPFD08 is explained? Please comment on this in the text.
Line 334. I don't understand how we can say that the differences are "substantial". I don't see much difference between deciduous trees (a) and grassland (c), sorry.
Line 336. Using net photosynthesis to calculate leaf emergence is not completely justified. Leaves are likely to be present and active well before gross photosynthesis equals heterotrophic respiration (eg. soil respiration). Gross photosynthesis should be used to calculate Astart and Aend instead.
Line 354. “A sample of downy birch leaves collected at Svanhovd had an average length of (3.0±0.5)cm”
Were top-canopy leaves sampled? How many leaves were collected to get +- 0.5 cm standard error?Line 355. “We used 13.5m height”
Why was this value chosen? What is the meaning of a height between the average tree height and the maximum tree heigh? Perhaps it would have been more reasonable to use the average height.Line 360 and following. POD1 was calculated by gap filling the data, right? Because there is a lot of data missing in the middle of the season. Or were POD1 compensated for missing data? If so, how? Please confirm it by writing it in the text.
Line 369. “Due to the shape of flight, a symmetric variation”.
Symmetric variation of what?Line 370. “We find that an opening of stomata at lower light intensities can cause higher sensitivity to drought conditions.”
Please, explain where we can see this. Graph 8 is not clear at all to me.
And then, “sensitivity” of what? Of plants? Of POD1?Line 373. “The magnitude of these effects varies between PFTs as well as years, but the predicted ozone uptake for the bespoke temperature parameterization is always larger than for the MM parameterizations and of the same order of magnitude as the variability between the years studied here.”
What effects?
“Of the same order of magnitude as the interannual variability…”: can you conclude it by comparing only two years?
The same for line 402Table 4. Have the percentage of reduction been calculated taking into account pre-industrial concentrations as prescribed by the MM?
What are meaning of the superscripts? And, above all, why some superscripts indicate a range (e.g. 1.9 ... 2.1)?
I did not understand how the stdev of the MM estimation was calculated, sorry.Line 416. “we have developed bespoke parameterizations”
it seems a bit strong statement to me, you have not developed any new tailored parameterization, you have only hypothesized one. There is no one experiment nor comparison with experimental results in your work.Line 417. “The comparison between meteorological conditions in 2018 and 2019 and their divergence from climatology allowed us to assess the influence of key environmental variables such as temperature, PPFD, and precipitation on vegetation susceptibility to O3 damage in light of future changes as may occur under climate change”
I did not understand where all this "divergence with the climatological average" of these two years alone lies, sorry.Line 432. “With respect to ongoing climate change, a clear positive trend emerged in length (5.2d decade−1) of the growing season that is almost equally distributed between earlier start (2.9 days decade−1) and later end (2.3d decade−1) (Appendix Fig. A1).”
How did you figure it out? Have you been doing retrospective MODIS analysis for 30 years? Or do you have a publication to quote?Line 435 and following. “visible damage”
Visible damage and POD can be totally unrelated, as demonstrated by some research conducted on agricultural species. I recommend caution in stating that the O3 peaks causing the visible symptoms can result in a biomass reduction (damage).Line 441. Does “damage” mean “visible leaf symptoms”? Or does it mean biomass reduction?
Line 456. “We found that soil water potential under 2018/19 meteorological conditions was negligible”
What does it mean? That there was no water in the soil (SWP were negligible) or that the effect on the POD of the presence or absence of SWP in the calculation was negligible? Please clarify.Line 461. “better suited”
Point 1 is questionable.
Also point 2 is questionable. How can you say that the MM parameterization does not capture the plant physiology of subactic vegetation if no comparisons with physiological measurements taken on subarctic vegetation are presented?Line 469. “However, the decline of this ozone spring peak is partly caused by the uptake of vegetation"
Are you sure? Please cite a reference.Line 491. “Automation of the here proposed PDF-based acclimation using machine learning techniques could overcome these issues in the future”
What does it mean? Please explain. Make an example.Figure A1. How was the length of the growing seasons in the various years identified? By satellite? Other method? What does the gray band represent?
Line 511. “with fmin, Dmin, Dmax describing the relative stomatal conductance to changes in vapor pressure deficit.”
It is not clear. Please, clarify what D and fmin are, and their units.Line 517. “The DO3SE model as described in Büker et al. (2012) is used to simulate SWP across a PFT specific root depth according to the Penman–Monteith energy balance method that drives water cycling through the soil–plant–atmosphere system”
I cannot understand how the P-M energy balance is used in DO3SE to derive the SWP. Please explain in detail.Line 525. “the concentration at the upper surface of the laminar layer for a sunlit upper canopy leaf”
At what height was the O3 concentration measured? If it was not measured at the top of the canopy (10m for trees or 10 cm for grassland), how was the O3 concentration at the top canopy calculated?
Please explain in detail.Line 526. What does rc represent? Is it the cuticular resistance or the bulk canopy resistance? What is its value?
Line 528. Can you explain where that formula for calculating the flux comes from? Why is there u(z1) in?
And what is the z1 height?Line 531. What is the z1 height? Where is it?
Line 535. Wind speed at 2 m: what is it used for? Please explain
Line 550. Please explicitly describe the method used to gap-fill O3 concentrations because it could be crucial.
Section B1. The description of fPHEN is missing. Please, provide it.
Again, how do you calculate the day-to-day SWP on your site? Please describe it in detail.Line 554. “From Fig. B1f) it is apparent that the mapping manual parameterized grassland would not have been able to grow in 2019.”
It does not seem to me that gstom has been reseted at all. If this is the case, the premises of the work appear weak.Citation: https://doi.org/10.5194/bg-2021-260-RC1 -
AC2: 'Reply on RC1', Stefanie Falk, 13 Jan 2022
We thank the anonymous referee #1 for their
comments. We will address all general comments raised regarding the structure and
readability of the manuscript in our next revision or resubmission. We consider sepa-
rating the manuscript in Introduction–Methods–Results–Conclusions and will improve
on the ”methods” Section to make our results more comprehensible. We will refine the
language to reduce ambiguity and supplement our statements with appropriate citations
that were indicated by the referee.
As the manuscript will, hence, undergo major structural changes, we will not address all
specific / technical comments in detail at this point. We will take all specific and
technical comments which are still relevant into consideration.
In the following, we shall give a brief response to all relevant issues.
-
AC2: 'Reply on RC1', Stefanie Falk, 13 Jan 2022
-
RC2: 'Comment on bg-2021-260', Anonymous Referee #2, 23 Nov 2021
General comments
This study has a novel motivation in studying the response of subarctic vegetation to ozone damage. It also raises potentially impactful takeaways based on the discussion and abstract, especially the potential underestimate in ozone risk. However, I found the current manuscript challenging to follow due to its organization and at times ambiguous or overstated language, so that it was difficult to identify and understand the supporting evidence or how to reproduce it. Along those lines, I would suggest using a more descriptive word or phrase than “bespoke” to distinguish your parameterization. Some equations appear to be described incorrectly in the text, and one of the main text figures is missing. Despite these issues that should be resolved, this paper investigates an interesting and potentially influential topic that I believe would be worthy of publication following major revisions.
Specific comments
Lines 62-63 – Please include a citation for the sentence “A longer growing season is prolonging…” It is not immediately intuitive that a longer growing season would lead to increased ozone accumulation.
Lines 83-84 – Please include a citation for the concept that soil moisture deficits are most influential in decoupling concentration and uptake.
Starting at line 90, the remaining paragraphs in the introduction could be separated into a methods section. I find the introduction to be a bit longer than would be most effective for conveying this information. At this length, it would be helpful to at least break it into subsections with informative headers. In particular, the content of the paragraph in lines 115 – 134 is important for contextualizing the somewhat extensive discussion of meteorological parameters, but it seems unconnected with the adjacent paragraphs and could be better emphasized as part of the introduction or as an opening paragraph for the text in section 2 that leads to Figure 2.
Line 102 – The concept of critical loads is much older than 2016 (eg for nitrogen or sulfur soil acidification for example), so please include an earlier citation or specify that this is specific to ozone damage.
Please correct the text in line 105, “The CL is calculated by:” This doesn’t seem to be a correct descriptor for Equation 2, which calculates the exceedance rather than the CL itself.
In general, the meteorological description and analyses could be improved to better connect with the paper’s focus of vegetation damage from ozone pollution. For example, it is not clear how the paragraph in lines 196 – 201 relates back to your objective.
Section 3.2, line 237-238: Please include a citation for the sentence that begins: “As weather extremes…” The word “extremes” in this manuscript needs clearer description or contextualization, as the definition for this word may vary between climatological studies.
In the paragraph that starts at line 241, the meaning of the word “significant” is unclear and varies within the paragraph. My understanding is that it is implied that “significance” is generally taken to be +/-1 sigma (or ½ sigma for precipitation) for this analysis, but in this case it should be stated clearly early on in this section. Ideally it will pertain to a significance test. In addition, “more than 40% of the days were significantly warmer” indicates a different result than “a significant number of warmer days,” and it needs to be clarified what is significant about either scenario. The latter part of this paragraph reads as a list of results relative to the anomalies, and it would be helpful to tie back what is said here to the objective of this paper (e.g. “March 2018 had many unusually cold days” is possibly too vague and detached to merit inclusion without additional context).
Line 265 – Please cite Falk et al. 2021 (I believe this is the appropriate reference) for the sentence “The star indicates the reconstructed data in July.”
Section 4 – Please expand the description of the DO3SE model and consider including a description of its structure as relates to the rest of the section. At present, section 4.1 reads as a list of parameters, but the relationship to your stated objectives and the common thread among this list is unclear. As a reader it is difficult to gauge whether the parameter adjustments described here are sufficiently comprehensive for the model’s intended application. Based on the current content, I believe it could be helpful, for example, to describe early in the section what are the high-level inputs and which of the species need to be adjusted for temperature acclimation.
Line 289-291, sentence “We identified…” – fT hasn’t been defined yet. Also, please clarify that this is the limiting factor of stomatal conductance in perennial grassland in this model (rather than in general).
Line 304 – Again “extreme” is ambiguous here and seems to differ in definition from previous use (e.g., at line 237 it seems to relate to periodic events, while here it is describing a climate zone).
Line 305 – Is fT = ftemp? Please clarify.
Lines 306 – 307 – Please clarify which timeframes are being compared related to what is meant by “subject to climate change.” In other words, are you comparing the 1990s to the 2000s? Or the 1990s + 2000s with implicit impacts of climate relative to the preindustrial era?
Please include a citation or support for the presumption stated in lines 316-317 that begins “Regarding the acclimation…”
Line 317-318 – Mention that this is PPFD 0.8 and 1.2 in parentheses after +/-20%? Where it is currently included (line 324) suggests to me that these configurations are specific to grassland.
Line 321 appears to substitute for flight in Equation 4, not for as described in the text.
Line 331 – Is the low standard deviation mentioned specific to nighttime?
Line 331 – I find the conclusion that the standard deviations indicate “higher robustness to variability in growing conditions” to be too sweeping relative to the evidence presented. Variability in growing conditions could include many different drivers, but the impetus discussed seems specific to sunlight. However, narrowing this conclusion to sunlight would still require an additional sensitivity test beyond what is presented here, so that I suggest cutting this sentence.
Line 332 – “subarctic-PPFD0.8” is “best” relative to what? Please clarify.
Line 360 – Is there a citation or justification for the 1 nmol/m2/s flux threshold?
Figure 8 appears to be missing from the document.
Lines 367-372 – “leads to” seems strong, given that there are many variables changing with respect to the climatic parameterizations or growing season variability. Consider “is associated with” or something similar that does not imply causation.
Line 372 – Where is it shown that temperature acclimation relates to the amplification of drought effects?
Minor or technical comments
Lines 35-36 – Sentence that begins with “Tropospheric background…” seems misplaced, consider moving to finish this paragraph with a concluding, summary or transitional sentence.
Paragraph starting at lines 68 - If possible, please consider adding context for which of the species mentioned here are expected to proliferate under Arctic amplification.
Note at line 81 (also 134, 314) there is an errant space, and this formatting inconsistency recurs later in the document.
Figure 3 – please increase the width of the precipitation error bars for readability.
Figure 4 – This is a very effective illustration of the data in this plot – well done! One minor suggestion is to use a different plot background color or a colorbar that does not start with white to make it easier to see what are now the light yellow points.
Figure 5 – Please include a description of the 5d star in the caption for this figure.
Lines 267-269 – This is an important and interesting contribution. Please consider breaking up this sentence for readability, eg by first mentioning that fire-based enhancements to peak ozone apparently did not result in anomalous monthly mean ozone.
Line 298 – 302 – Consider reminding readers that MM is specific to the subarctic class? I found the text from “We construct cold…” to “…most efficient at cold temperatures” to be a bit confusing because the cold definition is compared with MM values, while the subarctic category is not. It would be helpful to make their definitions parallel or analogous to one another, contextualizing using the MM parameterization as necessary.
Lines 337-339 – I haven’t previously seen this method for identifying the start and end points of photosynthesis, and (noting that I’m not an ecologist) it seems elegant in concept and approach.
Sentence in lines 339-340: “This value will be used for all PFTs alike.” Please specify – Aend? In this paragraph, please explain why it is acceptable to use the same Aend for all PFTs while Astart is specified with respect to the PFT.
Line 344 – “indicating” should be “indicate”
Line 352 – Two soil types seem to be described in this paragraph, but the sandy loam texture is only compared to one (unclear which one). Should “of this soil type” be “both of these soil types”?
Line 354-355 – Apologies if I missed it, but please clarify what leaf length you are using, given the observations are smaller than in the MM parameterization (this is specified for tree height later in the paragraph, so it seems odd this is not also described for leaf width.
Line 410 – I think “severer” should be “more severe.”
Line 456 – Consider expanding on the experimental data needed to verify these parameterizations.
Line 457 – do you mean the response to SWP, rather than SWP itself being negligible?
Lines 484-486 – Please consider breaking this into two sentences for readability.Citation: https://doi.org/10.5194/bg-2021-260-RC2 -
AC1: 'Reply on RC2', Stefanie Falk, 29 Nov 2021
To bg-2021-260-RC2 (23 Nov 2021): We thank the anonymous referee #2 for their very
constructive comments and useful suggestions. We will address all general comments
raised regarding the structure and readability of the manuscript in our next revision.
We will refine the language to reduce ambiguity and supplement our statements with
appropriate citations where indicated by the referee.
As the manuscript will, hence, undergo major structural changes, we can not address
all specific / technical comments in detail at this point. In the next revision of the
manuscript, we will take all specific and technical comments which are still relevant into
consideration.
In the following, we shall respond to all issues where reasonable
-
AC1: 'Reply on RC2', Stefanie Falk, 29 Nov 2021
-
RC3: 'Comment on bg-2021-260', Anonymous Referee #3, 30 Nov 2021
This paper presents an investigation of the sensitivity of subarctic vegetation to some assumptions concerning ozone uptake parameterizations. Although I think that it is important to highlight the potential weaknesses of the large-scale risk assessments being done in Europe, and to propose ideas for improvement, this paper is very difficult to read and confusing in many respects. I am also not convinced that the equations and results which are presented are correct. I cannot recommend publication at this stage, although I would encourage the authors to re-submit once the manuscript is in better shape.
Major comments
--------------Concerning the length of the paper, I really cannot see the benefit of all the work on long-term ozone and meteorology given in Sections 2-3. Isn't the main point of this paper to illustrate differences in vegetation characteristics between plants at nearly 70 degrees N and the Mapping Manual (MM)? That doesn't need a long analysis of climate differences or ozone trends.
Concerning the "default" growing seasons (from DOY 100 to 307) from the MM against which the "bespoke" are compared, these are just wrong for this latitude. The MM suggests a latitude function that gives DOY 129 to 268.
Some of the basic equations look wrong to me, see my comments on Appendix B below.
On p21 the author's first "key findings" state that their "bespoke parameterizations for subarctic species are better suited..." than the MM ones. This is a strong statement given that the authors admit on L293 that their bespoke suggestions are "hypothetical and have yet to be verified by observations".
Other comments
--------------
L14. one can ask if an underestimate of 6% is a significant problem. I would guess that the overall uncertainty of POD calculations is far greater than this!L22. Better to say "estimated" rather than reported. These numbers do not represent actual measured yield losses. Also, as this paper is mainly discussing DO3SE-type approaches to POD, it would have been relevant to cite the DO3SE-based estimates of the Mills et al 2018 paper (below) which also made yield estimates for four crops.
L29. A more recent citation would be Tarasick et al 2019.
L36. Are these numbers for tropospheric ozone relevant to this paper? Vegetation is affected by near-surface ozone, and levels of this are much lower than 50-65 ppb over the Nordic countries.
L39-40. Why "despite"? 22 days is a very long time! This time-scale is not so relevant though; it is the lifetime of ozone in the boundary layer that matters, and that is about 1 week (Hov et al., 1978, or as can be estimated by typical deposition velocities and boundary layer depths). Solberg et al. 2008 also show how residence times of less than 7 days are usual for ozone episodes.
L48. Spring peaks are seen across large swathes of the northern hemisphere, for example at Mace Head, caused by many factors (Monks et al., 2009). In fact, Monks et al cite Winkler (1988) that north of 60N, the maximum in ozone reduces in amplitude and shifts to later months.
L85. I don't think Simpson et al 2007 or Mills et al 2011, 2017 focused on the Mediterranean? These were pan-European studies, that also stressed that POD as a metric showed that risks in e.g. northern Europe were likely higher than the earlier AOT40 metrics showed. The ICP-vegetation type metrics have in fact been based upon data from countries across Europe, and with more data from central and northern than from southern European countries.
L89. Continuing the above, the studies from Karlsson et al have had a strong focus on Scandinavian vegetation.
L96. Define PLA
L97. I don't think you need this about typically exceeded under daylight hours. POD calculations follow DO3SE methods, and the flux is zero at night by definition.
L103. The Maas et al book isn't so easily available (and no web-access address is given anyway). It can be good to cite some of the other key papers behind ozone CLs, e.g. Fuhrer et al. (1997), Mills et al 2011 (below).
L105. "The CL is calculated by"? Do you mean exceedance of CL?
L110. "For our study...". This confused me. Are the authors reporting results from the present manuscript, or from some unpublished and uncited study? The sentences starting here seem to be out of place.
L127. Do you mean non-methane VOC (NMVOC)?.
L128. Why brackets in "[O3]"?
L131-132. I didn't quite understand "shall serve as a reference". Do you mean as an example or possible future?
L141. Why "sensu" here. I had to look up the word, and read that it is "used especially in technical taxonomic references". Use simpler English.
L141. In any case what does "(sensu World Meteorological Organisation)" mean in this sentence?
L165-167. Mangled sentences? Why "Last accessed"? There is no url here. Placement of (a) and (b) is strange.
L170-171. Why deal with data that may introduce a false trend at all? Why wouldn't the problems influence seasonality? I would guess that weather and climate conditions may well have influenced the frequency of quality-assurance checks.
L172. Here it says that agromet variables are available from 1992, so, again, why use problematic O3 data from the 1980s?
L214, Fig. 3. The stars are very small on the figure. Make these more obvious. Or just skip them - doesn't the temperature curve give enough information?
L215-224. Do we need to be told all of these details with plus/minus limits? These are just climatalogical values and can be seen well enough in Fig. 3. The numbers are not used for anything.
L255-256. Why "deduce"? Now the numbers given, 800 W/m2 and 200 W/m2, are very rounded - are these measurements or assumptions or limits?
L276. I would say hypothetical or local rather than bespoke.
L280. Again, why "deduce"?
L281-282. The better ref here for the generic PFTs is the 2017 Mapping Manual. Or what did you use from Simpson et al 2007 or Mills et al. 2011 that isn't in Mills et al 2017?
L286. First, what is Gstoleaf compared to gsto? On L553 it is stated that Gsto(leaf) is at leaf-level, which suggests that same as gsto in eqn (B1). Then, you claim that Fig. B1 shows low Gsto(leaf), but it shows enormous values! According to Fig. B1, Gstoleaf is ca. 100 mmole/m2/s, this is 1.0e5 nmole/m2/s! This makes no sense.
L292. The authors say that their fT system has not been verified, but haven't ecosystem models (e.g. JULES, CLM, LPJ-GUESS) parameterized such vegetation already? I would have thought that there was something to learn from such models.
L344. As noted above, why compare your Astart (129, 130) with the MM value of 100 which is valid for 50 degrees N? The MM suggests a latitude function, which gives a start date of 129 for your location - i.e. almost perfect, and your comment was misleading. Why would you consider an agricultural criteria for forests anyway? Why not apply the MODIS response for deciduous trees too?
Table 3: Again, the "Defaults" given here are incorrect for this latitude. The correct ref should anyway be the MM.
L345. "Due to the lack of quantitative field observation...". I didn't follow the logic here.
Table 4. Why average the MM but not the bespoke? Give the MM for both years - this is useful information.
L488. Give references for your statements that global land-surface models have problems in the Arctic regions.
L624-625. Mangled ref. And why source googlebooks, when this report is easily available from www.emep.int?
References: check upper-lower case, in e.g. AMBIO, grennfelt etc.
Appendix B: DO3SE modelThe equations used here, and especially around L524-532, have several problems:
- they do not account for differences between canopy and leaf-scale conductances
- they make no mention of how the ozone is calculated at the height of the vegetation from the 2m measured values.
- Equation B6 looks wrong. What is the u(z1) term doing here?
- What is "z1" in eqn. B7?
L531 the factor 1.3 accounts for the "difference in" diffusivity.
Figure B2 - does MODIS only respond to coniferous trees in this 1x1 km2 grid? No other vegetation?
References:Fuhrer, J., Skärby, L., Ashmore, M.R., 1997. Critical levels for ozone effects on vegetation in Europe. Environmental Pollution 97 (1–2), 91–106.
Hov et al 1978, Long range transport of tropospheric ozone, Nature, 273, 341-344.
Huang, M., et al., Air temperature optima of vegetation productivity across global biomes, Nature ecology & evolution, https://doi.org/10.1038/s41559-019-0838-x, 3, 772–779, 2019
Mills G et al. 2018 Closing the global ozone yield gap: quantification and cobenefits for multistress tolerance. Global Change Biol. 24, 4869–4893. (doi:10.1111/gcb.14381)
Mills, G, Pleijel, H, Braun, S, Büker, P, Bermejo, V, et al. 2011b. New stomatal flux-based critical levels for ozone effects on vegetation. Atmos Environ 45: 5064–5068. DOI: https://doi.org/10.1016/j.atmosenv.2011.06.009
Tarasick, D, et al. 2019. Tropospheric Ozone Assessment Report: Tropospheric ozone from 1877 to 2016, observed levels, trends and uncertainties, Elem. Sci. Anth., 7(1), http://doi.org/10.1525/elementa.376, 2019
Citation: https://doi.org/10.5194/bg-2021-260-RC3 -
AC3: 'Reply on RC3', Stefanie Falk, 13 Jan 2022
We thank the anonymous referee #3 for their
comments. We will address all general comments raised regarding the structure and
readability of the manuscript in our next revision or resubmission. We consider sepa-
rating the manuscript in Introduction–Methods–Results–Conclusions and will improve
on the ”methods” Section to make our results more comprehensible. We will refine the
language to reduce ambiguity and supplement our statements with appropriate citations
where those were indicated by the referee.
As the manuscript will, hence, undergo major structural changes, we will not address all
specific / technical comments in detail at this point. We will take all specific and
technical comments which are still relevant into consideration.
In the following, we shall give a brief response to all relevant issues.
-
AC3: 'Reply on RC3', Stefanie Falk, 13 Jan 2022
Status: closed
-
RC1: 'Comment on bg-2021-260', Anonymous Referee #1, 05 Nov 2021
GENERAL COMMENTS
The manuscript addressed a relevant issue related to the ozone risk assessment in the Subarctic.
However, the presented study is highly speculative and is not based on any experimental evidence (i.e. the parametrization of gstom is hypothetical and not obtained from any measurements made in the area).
The justification of some methodological choices is weak, for example the need to modify the gstom parameterization because in 2019 the gstom predicted with the MM parameterization would have been too low.
Many claims sound superficial to me, such as the one about the alleged deviation of the years 2018 and 2019 from the site’s climatology, and many statements are inaccurate (see the specific comments).
The manuscript is too long, and the organization is confused. The introduction is nice, but it’s too long and contains too many digressions to get to the point. The results are mixed in the methodology and there is no clear division between the methodological section and the results section (a purely results section does not exist at all). There are several repetitions, for example the section “Discussion and Conclusions” is over half a summary of the previous sections. The Appendixes contain inaccuracies and omissions.
The English should be carefully revised because some sentences are ambiguous.
In my humble opinion, though, the work is generally weak and the manuscript is not mature enough to be accepted for publication.SPECIFIC COMMENTS
Lines 51-52. “and leads to a build-up of ozone and its precursors during winter.”
Are you sure? How can BVOC accumulate in the atmosphere if the vegetation is covered by snow? Please add some citations to support this claim. Much more credible is the following explanation based on stratospheric intrusions.Line 63. “the time in which vegetation can accumulate ozone.”
It sounds very bad written this way: vegetation does not accumulate ozone because ozone it is not bioaccumulative. Did you mean the dose?Line 77. “(<[O3]> = 36−54ppb)”
Please explain the formalism. What do different brackets mean?Line 81. “A substantial body of evidence exists that suggests flux-based metrics, that relate stomatal ozone uptake to vegetation damage, are biologically more relevant for risk assessments than exposure-based metrics.”
Well, please cite at least some works of this “substantial body”Figure 1. This figure was never referred in the text.
Figure 2. It does not seem to me that the O3 concentrations of 2019 are different from those of 2018. The spring peak could even be identical (although unknown, because in 2019 O3 measurements started about 20 days after the spring peak)
Line 146. Please make clear the acronym PFT on first use
Line 165. “luftkvalitet.no”
What is it? And EBAS? Please make them clear.Line 182. “This indicates that the vegetation was more affected by ozone in 2018 than in 2019.”
Being affected by visible symptoms does not necessarily mean having suffered biomass or productivity reduction.Line 190. “high ozone concentrations ([O3] > 40ppb”
It is strange to read that O3 concentrations above 40 ppb are “high” concentrations.Line 194. “A method for gapfilling data has been presented in Falk et al. (2021).”
Ok, but was it then applied to this work? Please write it.Line 205. “We evaluate the statistical significance of divergences from the norm in these variables (referred to as anomalies) in 2018/19”
I suspect a misuse of the locution “statistical significance”. How was this significance assessed? Which statistical test was applied? What is the level of significance?Lines 206-208. I do not understand. Please, explicit the methodology.
Line 213. “Averaged monthly accumulated precipitation (blue bars) is shown with standard deviation”
It is not consistent to show SE once and STDEV the other time. The use of SE is more appropriate when estimating averages.Line 228. “Darker colors indicate higher probability to observe these values.”
Line 229. “On top of the density distributions, a 10 days average of daily mean (h[O3]i10d) is displayed together with 1sigma uncertainties and SE, respectively”
What does it mean? It is not clear to me. Why show a probability density if you are plotting a multiannual average? Or does the line represent the median instead?Line 232. “The decline in h[O3]i coincides with the average beginning of CO2 uptake by coniferous trees (Kolari et al., 2007; Wallin et al., 2013)”
I didn't know that evergreens only uptake CO2 starting in May. I was convinced they always did. Is it true? Doesn’t that contradict what you wrote in line 309 ("We base our temperature acclimation of coniferous trees on experimental results on Norway spruce which were found to be active already at rather low air temperatures and can reach 60% photosynthetic activity as early as doy 100 (Kolariet al., 2007; Wallin et al., 2013).")?
Here you state that photosynthesis is already active at DOY 100 and is at 60% of its maximum!Line 233. “In July–September (doy 182–273), ozone is occasionally almost completely depleted. This hints to ozone uptake by vegetation even at low light intensities during midnight sun conditions in combination with stable planetary boundary layer conditions preventing mixing of ozone rich air.”
I don't understand the connection. What does the night uptake have to do with the occasionally complete ozone depletion?Line 244. “if a normal distribution is assumed”
Are you sure that the distribution is normal and not lognormal or something else? There are some literature on the type of statistical distributions for variable such as Temperature, Rain, etc ...
Moreover, looking at your Figure 6b the distribution of the irradiance seems to be a Poisson distribution.Figure 5, caption. “dashed lines indicates statistical significance”
Statistical significance of what? By means of what test was it obtained, at what alpha level? And what are the numbers on the top right of each graph?Line 251. “deviated significantly from the climatology on the 1 sigma level.”
Here the standard deviation is used as reference for the significance. But the significance of the deviation should be statistically tested in another way.Line 262. “We use the bias-corrected and cross-calibrated ozone climatology (Falk et al., 2021) and assess the monthly significance of the ozone concentration anomalies in 2018/19.”
“Bias-corrected cross-calibrated” ozone? What is it? And what is the “significance” of the concentration anomalies? Please explain.Line 267. “Further, we presume that fVPD and fSWP suit our vegetation types and no acclimation is necessary for these.”
This statement is questionable, because in cold conditions VPD can be high (you also told it in the conclusions) and the water in the soil can be limiting because partially unavailable due to freezing or other.Line 272. “but a substantially higher number of peak [O3] were observed in 2018 than in 2019.”
How can you tell it if O3 measurements for all months of March, April and July are missing in 2019? I don't seem to see any differences between 2018 and 2019Line 291 “ Note, however, that these parameterizations are hypothetical and have yet to be verified by experiments.”
Figure 6a. Looking at the graph I understand that you assume an adaptation of the subarctic grasslands to the temperature distribution of the last decade (climate already changed) and not to the historical temperature distribution at your site. Is it reasonable to hypothesize such a rapid adaptation of vegetation to the new climate conditions?
Line 298. “We construct cold as representative for a species that is more tolerant to cold temperatures, but slightly less efficient at warm temperatures compared to MM. This is accomplished by moving Topt towards cooler temperatures while keeping the other parameters fixed to MM values”.
From Figure 6a and Table 1 I see that for the “cold” parameterization not only Topt was moved, but also Tmin for (e.g. for grassland).Figure 7. The gstom/gmax ratio in the subarctic parameterization with PPFD0.8 is greater in the morning than at noon. How then the choice of PPFD08 is explained? Please comment on this in the text.
Line 334. I don't understand how we can say that the differences are "substantial". I don't see much difference between deciduous trees (a) and grassland (c), sorry.
Line 336. Using net photosynthesis to calculate leaf emergence is not completely justified. Leaves are likely to be present and active well before gross photosynthesis equals heterotrophic respiration (eg. soil respiration). Gross photosynthesis should be used to calculate Astart and Aend instead.
Line 354. “A sample of downy birch leaves collected at Svanhovd had an average length of (3.0±0.5)cm”
Were top-canopy leaves sampled? How many leaves were collected to get +- 0.5 cm standard error?Line 355. “We used 13.5m height”
Why was this value chosen? What is the meaning of a height between the average tree height and the maximum tree heigh? Perhaps it would have been more reasonable to use the average height.Line 360 and following. POD1 was calculated by gap filling the data, right? Because there is a lot of data missing in the middle of the season. Or were POD1 compensated for missing data? If so, how? Please confirm it by writing it in the text.
Line 369. “Due to the shape of flight, a symmetric variation”.
Symmetric variation of what?Line 370. “We find that an opening of stomata at lower light intensities can cause higher sensitivity to drought conditions.”
Please, explain where we can see this. Graph 8 is not clear at all to me.
And then, “sensitivity” of what? Of plants? Of POD1?Line 373. “The magnitude of these effects varies between PFTs as well as years, but the predicted ozone uptake for the bespoke temperature parameterization is always larger than for the MM parameterizations and of the same order of magnitude as the variability between the years studied here.”
What effects?
“Of the same order of magnitude as the interannual variability…”: can you conclude it by comparing only two years?
The same for line 402Table 4. Have the percentage of reduction been calculated taking into account pre-industrial concentrations as prescribed by the MM?
What are meaning of the superscripts? And, above all, why some superscripts indicate a range (e.g. 1.9 ... 2.1)?
I did not understand how the stdev of the MM estimation was calculated, sorry.Line 416. “we have developed bespoke parameterizations”
it seems a bit strong statement to me, you have not developed any new tailored parameterization, you have only hypothesized one. There is no one experiment nor comparison with experimental results in your work.Line 417. “The comparison between meteorological conditions in 2018 and 2019 and their divergence from climatology allowed us to assess the influence of key environmental variables such as temperature, PPFD, and precipitation on vegetation susceptibility to O3 damage in light of future changes as may occur under climate change”
I did not understand where all this "divergence with the climatological average" of these two years alone lies, sorry.Line 432. “With respect to ongoing climate change, a clear positive trend emerged in length (5.2d decade−1) of the growing season that is almost equally distributed between earlier start (2.9 days decade−1) and later end (2.3d decade−1) (Appendix Fig. A1).”
How did you figure it out? Have you been doing retrospective MODIS analysis for 30 years? Or do you have a publication to quote?Line 435 and following. “visible damage”
Visible damage and POD can be totally unrelated, as demonstrated by some research conducted on agricultural species. I recommend caution in stating that the O3 peaks causing the visible symptoms can result in a biomass reduction (damage).Line 441. Does “damage” mean “visible leaf symptoms”? Or does it mean biomass reduction?
Line 456. “We found that soil water potential under 2018/19 meteorological conditions was negligible”
What does it mean? That there was no water in the soil (SWP were negligible) or that the effect on the POD of the presence or absence of SWP in the calculation was negligible? Please clarify.Line 461. “better suited”
Point 1 is questionable.
Also point 2 is questionable. How can you say that the MM parameterization does not capture the plant physiology of subactic vegetation if no comparisons with physiological measurements taken on subarctic vegetation are presented?Line 469. “However, the decline of this ozone spring peak is partly caused by the uptake of vegetation"
Are you sure? Please cite a reference.Line 491. “Automation of the here proposed PDF-based acclimation using machine learning techniques could overcome these issues in the future”
What does it mean? Please explain. Make an example.Figure A1. How was the length of the growing seasons in the various years identified? By satellite? Other method? What does the gray band represent?
Line 511. “with fmin, Dmin, Dmax describing the relative stomatal conductance to changes in vapor pressure deficit.”
It is not clear. Please, clarify what D and fmin are, and their units.Line 517. “The DO3SE model as described in Büker et al. (2012) is used to simulate SWP across a PFT specific root depth according to the Penman–Monteith energy balance method that drives water cycling through the soil–plant–atmosphere system”
I cannot understand how the P-M energy balance is used in DO3SE to derive the SWP. Please explain in detail.Line 525. “the concentration at the upper surface of the laminar layer for a sunlit upper canopy leaf”
At what height was the O3 concentration measured? If it was not measured at the top of the canopy (10m for trees or 10 cm for grassland), how was the O3 concentration at the top canopy calculated?
Please explain in detail.Line 526. What does rc represent? Is it the cuticular resistance or the bulk canopy resistance? What is its value?
Line 528. Can you explain where that formula for calculating the flux comes from? Why is there u(z1) in?
And what is the z1 height?Line 531. What is the z1 height? Where is it?
Line 535. Wind speed at 2 m: what is it used for? Please explain
Line 550. Please explicitly describe the method used to gap-fill O3 concentrations because it could be crucial.
Section B1. The description of fPHEN is missing. Please, provide it.
Again, how do you calculate the day-to-day SWP on your site? Please describe it in detail.Line 554. “From Fig. B1f) it is apparent that the mapping manual parameterized grassland would not have been able to grow in 2019.”
It does not seem to me that gstom has been reseted at all. If this is the case, the premises of the work appear weak.Citation: https://doi.org/10.5194/bg-2021-260-RC1 -
AC2: 'Reply on RC1', Stefanie Falk, 13 Jan 2022
We thank the anonymous referee #1 for their
comments. We will address all general comments raised regarding the structure and
readability of the manuscript in our next revision or resubmission. We consider sepa-
rating the manuscript in Introduction–Methods–Results–Conclusions and will improve
on the ”methods” Section to make our results more comprehensible. We will refine the
language to reduce ambiguity and supplement our statements with appropriate citations
that were indicated by the referee.
As the manuscript will, hence, undergo major structural changes, we will not address all
specific / technical comments in detail at this point. We will take all specific and
technical comments which are still relevant into consideration.
In the following, we shall give a brief response to all relevant issues.
-
AC2: 'Reply on RC1', Stefanie Falk, 13 Jan 2022
-
RC2: 'Comment on bg-2021-260', Anonymous Referee #2, 23 Nov 2021
General comments
This study has a novel motivation in studying the response of subarctic vegetation to ozone damage. It also raises potentially impactful takeaways based on the discussion and abstract, especially the potential underestimate in ozone risk. However, I found the current manuscript challenging to follow due to its organization and at times ambiguous or overstated language, so that it was difficult to identify and understand the supporting evidence or how to reproduce it. Along those lines, I would suggest using a more descriptive word or phrase than “bespoke” to distinguish your parameterization. Some equations appear to be described incorrectly in the text, and one of the main text figures is missing. Despite these issues that should be resolved, this paper investigates an interesting and potentially influential topic that I believe would be worthy of publication following major revisions.
Specific comments
Lines 62-63 – Please include a citation for the sentence “A longer growing season is prolonging…” It is not immediately intuitive that a longer growing season would lead to increased ozone accumulation.
Lines 83-84 – Please include a citation for the concept that soil moisture deficits are most influential in decoupling concentration and uptake.
Starting at line 90, the remaining paragraphs in the introduction could be separated into a methods section. I find the introduction to be a bit longer than would be most effective for conveying this information. At this length, it would be helpful to at least break it into subsections with informative headers. In particular, the content of the paragraph in lines 115 – 134 is important for contextualizing the somewhat extensive discussion of meteorological parameters, but it seems unconnected with the adjacent paragraphs and could be better emphasized as part of the introduction or as an opening paragraph for the text in section 2 that leads to Figure 2.
Line 102 – The concept of critical loads is much older than 2016 (eg for nitrogen or sulfur soil acidification for example), so please include an earlier citation or specify that this is specific to ozone damage.
Please correct the text in line 105, “The CL is calculated by:” This doesn’t seem to be a correct descriptor for Equation 2, which calculates the exceedance rather than the CL itself.
In general, the meteorological description and analyses could be improved to better connect with the paper’s focus of vegetation damage from ozone pollution. For example, it is not clear how the paragraph in lines 196 – 201 relates back to your objective.
Section 3.2, line 237-238: Please include a citation for the sentence that begins: “As weather extremes…” The word “extremes” in this manuscript needs clearer description or contextualization, as the definition for this word may vary between climatological studies.
In the paragraph that starts at line 241, the meaning of the word “significant” is unclear and varies within the paragraph. My understanding is that it is implied that “significance” is generally taken to be +/-1 sigma (or ½ sigma for precipitation) for this analysis, but in this case it should be stated clearly early on in this section. Ideally it will pertain to a significance test. In addition, “more than 40% of the days were significantly warmer” indicates a different result than “a significant number of warmer days,” and it needs to be clarified what is significant about either scenario. The latter part of this paragraph reads as a list of results relative to the anomalies, and it would be helpful to tie back what is said here to the objective of this paper (e.g. “March 2018 had many unusually cold days” is possibly too vague and detached to merit inclusion without additional context).
Line 265 – Please cite Falk et al. 2021 (I believe this is the appropriate reference) for the sentence “The star indicates the reconstructed data in July.”
Section 4 – Please expand the description of the DO3SE model and consider including a description of its structure as relates to the rest of the section. At present, section 4.1 reads as a list of parameters, but the relationship to your stated objectives and the common thread among this list is unclear. As a reader it is difficult to gauge whether the parameter adjustments described here are sufficiently comprehensive for the model’s intended application. Based on the current content, I believe it could be helpful, for example, to describe early in the section what are the high-level inputs and which of the species need to be adjusted for temperature acclimation.
Line 289-291, sentence “We identified…” – fT hasn’t been defined yet. Also, please clarify that this is the limiting factor of stomatal conductance in perennial grassland in this model (rather than in general).
Line 304 – Again “extreme” is ambiguous here and seems to differ in definition from previous use (e.g., at line 237 it seems to relate to periodic events, while here it is describing a climate zone).
Line 305 – Is fT = ftemp? Please clarify.
Lines 306 – 307 – Please clarify which timeframes are being compared related to what is meant by “subject to climate change.” In other words, are you comparing the 1990s to the 2000s? Or the 1990s + 2000s with implicit impacts of climate relative to the preindustrial era?
Please include a citation or support for the presumption stated in lines 316-317 that begins “Regarding the acclimation…”
Line 317-318 – Mention that this is PPFD 0.8 and 1.2 in parentheses after +/-20%? Where it is currently included (line 324) suggests to me that these configurations are specific to grassland.
Line 321 appears to substitute for flight in Equation 4, not for as described in the text.
Line 331 – Is the low standard deviation mentioned specific to nighttime?
Line 331 – I find the conclusion that the standard deviations indicate “higher robustness to variability in growing conditions” to be too sweeping relative to the evidence presented. Variability in growing conditions could include many different drivers, but the impetus discussed seems specific to sunlight. However, narrowing this conclusion to sunlight would still require an additional sensitivity test beyond what is presented here, so that I suggest cutting this sentence.
Line 332 – “subarctic-PPFD0.8” is “best” relative to what? Please clarify.
Line 360 – Is there a citation or justification for the 1 nmol/m2/s flux threshold?
Figure 8 appears to be missing from the document.
Lines 367-372 – “leads to” seems strong, given that there are many variables changing with respect to the climatic parameterizations or growing season variability. Consider “is associated with” or something similar that does not imply causation.
Line 372 – Where is it shown that temperature acclimation relates to the amplification of drought effects?
Minor or technical comments
Lines 35-36 – Sentence that begins with “Tropospheric background…” seems misplaced, consider moving to finish this paragraph with a concluding, summary or transitional sentence.
Paragraph starting at lines 68 - If possible, please consider adding context for which of the species mentioned here are expected to proliferate under Arctic amplification.
Note at line 81 (also 134, 314) there is an errant space, and this formatting inconsistency recurs later in the document.
Figure 3 – please increase the width of the precipitation error bars for readability.
Figure 4 – This is a very effective illustration of the data in this plot – well done! One minor suggestion is to use a different plot background color or a colorbar that does not start with white to make it easier to see what are now the light yellow points.
Figure 5 – Please include a description of the 5d star in the caption for this figure.
Lines 267-269 – This is an important and interesting contribution. Please consider breaking up this sentence for readability, eg by first mentioning that fire-based enhancements to peak ozone apparently did not result in anomalous monthly mean ozone.
Line 298 – 302 – Consider reminding readers that MM is specific to the subarctic class? I found the text from “We construct cold…” to “…most efficient at cold temperatures” to be a bit confusing because the cold definition is compared with MM values, while the subarctic category is not. It would be helpful to make their definitions parallel or analogous to one another, contextualizing using the MM parameterization as necessary.
Lines 337-339 – I haven’t previously seen this method for identifying the start and end points of photosynthesis, and (noting that I’m not an ecologist) it seems elegant in concept and approach.
Sentence in lines 339-340: “This value will be used for all PFTs alike.” Please specify – Aend? In this paragraph, please explain why it is acceptable to use the same Aend for all PFTs while Astart is specified with respect to the PFT.
Line 344 – “indicating” should be “indicate”
Line 352 – Two soil types seem to be described in this paragraph, but the sandy loam texture is only compared to one (unclear which one). Should “of this soil type” be “both of these soil types”?
Line 354-355 – Apologies if I missed it, but please clarify what leaf length you are using, given the observations are smaller than in the MM parameterization (this is specified for tree height later in the paragraph, so it seems odd this is not also described for leaf width.
Line 410 – I think “severer” should be “more severe.”
Line 456 – Consider expanding on the experimental data needed to verify these parameterizations.
Line 457 – do you mean the response to SWP, rather than SWP itself being negligible?
Lines 484-486 – Please consider breaking this into two sentences for readability.Citation: https://doi.org/10.5194/bg-2021-260-RC2 -
AC1: 'Reply on RC2', Stefanie Falk, 29 Nov 2021
To bg-2021-260-RC2 (23 Nov 2021): We thank the anonymous referee #2 for their very
constructive comments and useful suggestions. We will address all general comments
raised regarding the structure and readability of the manuscript in our next revision.
We will refine the language to reduce ambiguity and supplement our statements with
appropriate citations where indicated by the referee.
As the manuscript will, hence, undergo major structural changes, we can not address
all specific / technical comments in detail at this point. In the next revision of the
manuscript, we will take all specific and technical comments which are still relevant into
consideration.
In the following, we shall respond to all issues where reasonable
-
AC1: 'Reply on RC2', Stefanie Falk, 29 Nov 2021
-
RC3: 'Comment on bg-2021-260', Anonymous Referee #3, 30 Nov 2021
This paper presents an investigation of the sensitivity of subarctic vegetation to some assumptions concerning ozone uptake parameterizations. Although I think that it is important to highlight the potential weaknesses of the large-scale risk assessments being done in Europe, and to propose ideas for improvement, this paper is very difficult to read and confusing in many respects. I am also not convinced that the equations and results which are presented are correct. I cannot recommend publication at this stage, although I would encourage the authors to re-submit once the manuscript is in better shape.
Major comments
--------------Concerning the length of the paper, I really cannot see the benefit of all the work on long-term ozone and meteorology given in Sections 2-3. Isn't the main point of this paper to illustrate differences in vegetation characteristics between plants at nearly 70 degrees N and the Mapping Manual (MM)? That doesn't need a long analysis of climate differences or ozone trends.
Concerning the "default" growing seasons (from DOY 100 to 307) from the MM against which the "bespoke" are compared, these are just wrong for this latitude. The MM suggests a latitude function that gives DOY 129 to 268.
Some of the basic equations look wrong to me, see my comments on Appendix B below.
On p21 the author's first "key findings" state that their "bespoke parameterizations for subarctic species are better suited..." than the MM ones. This is a strong statement given that the authors admit on L293 that their bespoke suggestions are "hypothetical and have yet to be verified by observations".
Other comments
--------------
L14. one can ask if an underestimate of 6% is a significant problem. I would guess that the overall uncertainty of POD calculations is far greater than this!L22. Better to say "estimated" rather than reported. These numbers do not represent actual measured yield losses. Also, as this paper is mainly discussing DO3SE-type approaches to POD, it would have been relevant to cite the DO3SE-based estimates of the Mills et al 2018 paper (below) which also made yield estimates for four crops.
L29. A more recent citation would be Tarasick et al 2019.
L36. Are these numbers for tropospheric ozone relevant to this paper? Vegetation is affected by near-surface ozone, and levels of this are much lower than 50-65 ppb over the Nordic countries.
L39-40. Why "despite"? 22 days is a very long time! This time-scale is not so relevant though; it is the lifetime of ozone in the boundary layer that matters, and that is about 1 week (Hov et al., 1978, or as can be estimated by typical deposition velocities and boundary layer depths). Solberg et al. 2008 also show how residence times of less than 7 days are usual for ozone episodes.
L48. Spring peaks are seen across large swathes of the northern hemisphere, for example at Mace Head, caused by many factors (Monks et al., 2009). In fact, Monks et al cite Winkler (1988) that north of 60N, the maximum in ozone reduces in amplitude and shifts to later months.
L85. I don't think Simpson et al 2007 or Mills et al 2011, 2017 focused on the Mediterranean? These were pan-European studies, that also stressed that POD as a metric showed that risks in e.g. northern Europe were likely higher than the earlier AOT40 metrics showed. The ICP-vegetation type metrics have in fact been based upon data from countries across Europe, and with more data from central and northern than from southern European countries.
L89. Continuing the above, the studies from Karlsson et al have had a strong focus on Scandinavian vegetation.
L96. Define PLA
L97. I don't think you need this about typically exceeded under daylight hours. POD calculations follow DO3SE methods, and the flux is zero at night by definition.
L103. The Maas et al book isn't so easily available (and no web-access address is given anyway). It can be good to cite some of the other key papers behind ozone CLs, e.g. Fuhrer et al. (1997), Mills et al 2011 (below).
L105. "The CL is calculated by"? Do you mean exceedance of CL?
L110. "For our study...". This confused me. Are the authors reporting results from the present manuscript, or from some unpublished and uncited study? The sentences starting here seem to be out of place.
L127. Do you mean non-methane VOC (NMVOC)?.
L128. Why brackets in "[O3]"?
L131-132. I didn't quite understand "shall serve as a reference". Do you mean as an example or possible future?
L141. Why "sensu" here. I had to look up the word, and read that it is "used especially in technical taxonomic references". Use simpler English.
L141. In any case what does "(sensu World Meteorological Organisation)" mean in this sentence?
L165-167. Mangled sentences? Why "Last accessed"? There is no url here. Placement of (a) and (b) is strange.
L170-171. Why deal with data that may introduce a false trend at all? Why wouldn't the problems influence seasonality? I would guess that weather and climate conditions may well have influenced the frequency of quality-assurance checks.
L172. Here it says that agromet variables are available from 1992, so, again, why use problematic O3 data from the 1980s?
L214, Fig. 3. The stars are very small on the figure. Make these more obvious. Or just skip them - doesn't the temperature curve give enough information?
L215-224. Do we need to be told all of these details with plus/minus limits? These are just climatalogical values and can be seen well enough in Fig. 3. The numbers are not used for anything.
L255-256. Why "deduce"? Now the numbers given, 800 W/m2 and 200 W/m2, are very rounded - are these measurements or assumptions or limits?
L276. I would say hypothetical or local rather than bespoke.
L280. Again, why "deduce"?
L281-282. The better ref here for the generic PFTs is the 2017 Mapping Manual. Or what did you use from Simpson et al 2007 or Mills et al. 2011 that isn't in Mills et al 2017?
L286. First, what is Gstoleaf compared to gsto? On L553 it is stated that Gsto(leaf) is at leaf-level, which suggests that same as gsto in eqn (B1). Then, you claim that Fig. B1 shows low Gsto(leaf), but it shows enormous values! According to Fig. B1, Gstoleaf is ca. 100 mmole/m2/s, this is 1.0e5 nmole/m2/s! This makes no sense.
L292. The authors say that their fT system has not been verified, but haven't ecosystem models (e.g. JULES, CLM, LPJ-GUESS) parameterized such vegetation already? I would have thought that there was something to learn from such models.
L344. As noted above, why compare your Astart (129, 130) with the MM value of 100 which is valid for 50 degrees N? The MM suggests a latitude function, which gives a start date of 129 for your location - i.e. almost perfect, and your comment was misleading. Why would you consider an agricultural criteria for forests anyway? Why not apply the MODIS response for deciduous trees too?
Table 3: Again, the "Defaults" given here are incorrect for this latitude. The correct ref should anyway be the MM.
L345. "Due to the lack of quantitative field observation...". I didn't follow the logic here.
Table 4. Why average the MM but not the bespoke? Give the MM for both years - this is useful information.
L488. Give references for your statements that global land-surface models have problems in the Arctic regions.
L624-625. Mangled ref. And why source googlebooks, when this report is easily available from www.emep.int?
References: check upper-lower case, in e.g. AMBIO, grennfelt etc.
Appendix B: DO3SE modelThe equations used here, and especially around L524-532, have several problems:
- they do not account for differences between canopy and leaf-scale conductances
- they make no mention of how the ozone is calculated at the height of the vegetation from the 2m measured values.
- Equation B6 looks wrong. What is the u(z1) term doing here?
- What is "z1" in eqn. B7?
L531 the factor 1.3 accounts for the "difference in" diffusivity.
Figure B2 - does MODIS only respond to coniferous trees in this 1x1 km2 grid? No other vegetation?
References:Fuhrer, J., Skärby, L., Ashmore, M.R., 1997. Critical levels for ozone effects on vegetation in Europe. Environmental Pollution 97 (1–2), 91–106.
Hov et al 1978, Long range transport of tropospheric ozone, Nature, 273, 341-344.
Huang, M., et al., Air temperature optima of vegetation productivity across global biomes, Nature ecology & evolution, https://doi.org/10.1038/s41559-019-0838-x, 3, 772–779, 2019
Mills G et al. 2018 Closing the global ozone yield gap: quantification and cobenefits for multistress tolerance. Global Change Biol. 24, 4869–4893. (doi:10.1111/gcb.14381)
Mills, G, Pleijel, H, Braun, S, Büker, P, Bermejo, V, et al. 2011b. New stomatal flux-based critical levels for ozone effects on vegetation. Atmos Environ 45: 5064–5068. DOI: https://doi.org/10.1016/j.atmosenv.2011.06.009
Tarasick, D, et al. 2019. Tropospheric Ozone Assessment Report: Tropospheric ozone from 1877 to 2016, observed levels, trends and uncertainties, Elem. Sci. Anth., 7(1), http://doi.org/10.1525/elementa.376, 2019
Citation: https://doi.org/10.5194/bg-2021-260-RC3 -
AC3: 'Reply on RC3', Stefanie Falk, 13 Jan 2022
We thank the anonymous referee #3 for their
comments. We will address all general comments raised regarding the structure and
readability of the manuscript in our next revision or resubmission. We consider sepa-
rating the manuscript in Introduction–Methods–Results–Conclusions and will improve
on the ”methods” Section to make our results more comprehensible. We will refine the
language to reduce ambiguity and supplement our statements with appropriate citations
where those were indicated by the referee.
As the manuscript will, hence, undergo major structural changes, we will not address all
specific / technical comments in detail at this point. We will take all specific and
technical comments which are still relevant into consideration.
In the following, we shall give a brief response to all relevant issues.
-
AC3: 'Reply on RC3', Stefanie Falk, 13 Jan 2022
Viewed
| HTML | XML | Total | BibTeX | EndNote | |
|---|---|---|---|---|---|
| 717 | 273 | 43 | 1,033 | 37 | 33 |
- HTML: 717
- PDF: 273
- XML: 43
- Total: 1,033
- BibTeX: 37
- EndNote: 33
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1