the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 08 Aug 2024
Estimates of critical loads and exceedances of acidity and nutrient nitrogen for mineral soils in Canada for 2014–2016 average annual sulphur and nitrogen atmospheric deposition
Abstract. The steady-state Simple Mass Balance model was applied to natural and semi-natural terrestrial ecosystems across Canada to produce nation-wide critical loads of acidity (maximum sulphur, CLmaxS; maximum nitrogen, CLmaxN; minimum nitrogen, CLminN) and nutrient nitrogen (CLnutN) at 250 m resolution. Parameterization of the model for Canadian ecosystems was considered with attention to the selection of the chemical criterion for damage at a site-specific resolution, with comparison between protection levels of 5 % and 20 % growth reduction (approximating commonly chosen base-cation-to-aluminum ratios of 1 and 10 respectively). Other parameters explored include modelled base cation deposition and site-specific nutrient and base cation uptake estimates based on North American tree chemistry data and tree species and biomass maps. Soil critical loads of nutrient nitrogen were also mapped using the Simple Mass Balance model. Critical loads of acidity were estimated to be low (e.g., below 500 eq-1 ha yr-1) for much of the country, particularly above 60° N latitude where base cation weathering rates are low due to cold annual average temperature. Exceedances were mapped relative to annual sulphur and nitrogen deposition averaged over 2014–2016. Results show that under a conservative estimate (5 % protection level), 10 % of Canada’s Protected and Conserved Areas in the study area experienced exceedance of some level of soil critical load of acidity while 70 % experienced exceedance of soil critical load of nutrient nitrogen.
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RC1: 'Comment on egusphere-2024-2371', Anonymous Referee #1, 30 Aug 2024
The manuscript Estimates of critical loads and exceedances of acidity and nutrient nitrogen for mineral soils in Canada for 2014–2016 average annual sulphur and nitrogen atmospheric deposition (egusphere-2024-2371) used national level input data and steady state mass balance model to determine a Canada wide critical load of acidity and nutrient nitrogen and determined exceedances. Although regional CL values had been developed this is the first CL values with currently available data calculated at such a scale. The values determined should facilitate environmental managers with sufficient information to further explore areas at risk. The authors have used a well-tested and recognized methodology and currently available to develop critical loads. Where used the assumptions have been declared for the most part. The data and method clearly explained but could benefit from additional information and clarifications in some areas as indicated in the detailed comments below. The manuscript is well written, equations are appropriately represented and for the most part the figures were informative and supported the results and discussion. All this being said, given that CLnutN exceedances are widespread and most noteworthy, however the authors have limited discussion of this component of the work.
Detail comments:
Lines 91-92: On average what is the soil depth for areas classified as barren where soil depth is indicated? As the purpose is to develop CLs to protect the ecosystem, what is the advantage of including these segments of the landscape?
Lines 92-94: What % of the land was classified as peat and wetland. Where data are available has the 30% organic matter == peat and wetland soil classification been tested?
94-96: The authors should include the average % of mineral soil for the Hudson Plain ecozone.
Figure 1: The authors should clarify the need for the classification in Figure 1a. Figure 1b the resolution does not permit the reader to see all the classifications in the ledged on the map. These areas can be grouped to simplify the legend and make the map useful for discussing the results.
Figure 2: The authors should indicate the relevance of the four different regions.
Lines 124-126: What value(s) of gibbsite equilibrium constant is used?
Lines 132-133: Significant figures when converting units. The authors should also explain why they selected the upper range value from Rosen et al (1992).
Lines 133-134: The authors should include what value was used for soil denitrification factor and how was the value obtained.
Lines 150 -151: The authors should site R version, and any libraries used as recommended by the software(s) developers.
Table 1: The authors should indicate their use of air temperature to approximate soil temperature when determining base cation weathering. Likely a good estimate given long term annual average data is used.
Lines 210-220: Would not a large amount of BC dep result in adding excess nutrient to the system? The authors should mention any other consequences of incorporating anthropogenic BC dep. This may proof important especially in areas that are exceeding nutrient N CL.
Lines 214-219: It is not clear the purpose of smoothing BC dep. It does not represent actual, nor does it represent non-anthropogenic BC dep.
Lines 217-219: The work could not consider forest fire impact, and the authors have mentioned the impact of this omission on BCdep. The authors should also indicate how not considering forest fires could affect other terms in their work.
Lines 242-243: Was the most sensitive species given priority in a grid cell irrespective of coverage, what were the range of coverage?
Table 3: It is not clear how V2.2 and V3.2 adds to the material presented in the section or elsewhere.
Lines 315-317: The authors should explain/define temperature correction in the method section.
Table 4: The results in the text is presented by administrative boundary and a few times by ecozones making reference to the table difficult. Because much of the discussion is by administrative boundary much of the results (Ecozones) presented are not discussed. What would be the takeaway for an international audience?
Lines 337-339: The average base cation deposition is higher after smoothing?
Lines 339-340: Where is the star on the map located presumably the entire region is not a source of BC deposition?
Section 3.5: Why does this section not include CLnutN results?
Lines 368-369: Which BC deposition is used to determine CLmaxS? Earlier when discussing the BC deposition (smoothed unsmoothed), the authors should indicate which of the two data sets is the primary data set.
Lines 379-382: Where are the isolated point sources and what are they due to? These seem to be in different areas of the province outside the previously mentioned AOSR.
Lines 382-384: The authors discuss Ndep by provincial average, but the most sticking observation is the north-south gradient. The authors should discuss what is driving the observed north-south gradient observed for much of the country.
Lines 393-395: Would not the CL values be lower for 5% protection?
Lines 425-426: It seems like a great many of the exceedances are less than 50 eq ha-1 yr-1 and probably within the uncertainty of the model. In addition to absolute exceedances the authors should comment on the various ranges.
Lines 486-489: The choice of level of protection for a managing agency is really a policy decision and not an ethical choice.
Line 491: Low CLnut N is more widespread than the Arctic, the authors should indicate what is driving the low values in other areas not just the arctic.
Lines 522:534: The comparison works presented seem to indicate the current work is under estimating CLnutN by a factor of 2, relative to the presented comparison work. What is the % of area with deposition greater than 2x CLnutN? See also comment on discussing various ranges of CLnutN exceedances.
Line 531-534: it looks like exceedance is largely driven by Ndep as CLnutN is very low in much of the area under study. Given the largest exceendance is of CLnutN what additional work or data do the authors recommend?
Citation: https://doi.org/10.5194/egusphere-2024-2371-RC1 - AC1: 'Reply on RC1', Hazel Cathcart, 11 Oct 2024
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RC2: 'Comment on egusphere-2024-2371', Anonymous Referee #2, 09 Sep 2024
An interesting paper describing the computation of critical loads of S and N for the whole of Canada, which is done here for the first time (earlier studies dealt with subregions only). The paper is well written, with some (minor) issues to be clarified, specially about Cl-deposition (see below). Thus, I suggest that the paper should be published with minor revisions. The corrections/amendments listed in the attached pdf-file should be addressed before re-submission
- AC2: 'Reply on RC2', Hazel Cathcart, 11 Oct 2024
Status: closed
-
RC1: 'Comment on egusphere-2024-2371', Anonymous Referee #1, 30 Aug 2024
The manuscript Estimates of critical loads and exceedances of acidity and nutrient nitrogen for mineral soils in Canada for 2014–2016 average annual sulphur and nitrogen atmospheric deposition (egusphere-2024-2371) used national level input data and steady state mass balance model to determine a Canada wide critical load of acidity and nutrient nitrogen and determined exceedances. Although regional CL values had been developed this is the first CL values with currently available data calculated at such a scale. The values determined should facilitate environmental managers with sufficient information to further explore areas at risk. The authors have used a well-tested and recognized methodology and currently available to develop critical loads. Where used the assumptions have been declared for the most part. The data and method clearly explained but could benefit from additional information and clarifications in some areas as indicated in the detailed comments below. The manuscript is well written, equations are appropriately represented and for the most part the figures were informative and supported the results and discussion. All this being said, given that CLnutN exceedances are widespread and most noteworthy, however the authors have limited discussion of this component of the work.
Detail comments:
Lines 91-92: On average what is the soil depth for areas classified as barren where soil depth is indicated? As the purpose is to develop CLs to protect the ecosystem, what is the advantage of including these segments of the landscape?
Lines 92-94: What % of the land was classified as peat and wetland. Where data are available has the 30% organic matter == peat and wetland soil classification been tested?
94-96: The authors should include the average % of mineral soil for the Hudson Plain ecozone.
Figure 1: The authors should clarify the need for the classification in Figure 1a. Figure 1b the resolution does not permit the reader to see all the classifications in the ledged on the map. These areas can be grouped to simplify the legend and make the map useful for discussing the results.
Figure 2: The authors should indicate the relevance of the four different regions.
Lines 124-126: What value(s) of gibbsite equilibrium constant is used?
Lines 132-133: Significant figures when converting units. The authors should also explain why they selected the upper range value from Rosen et al (1992).
Lines 133-134: The authors should include what value was used for soil denitrification factor and how was the value obtained.
Lines 150 -151: The authors should site R version, and any libraries used as recommended by the software(s) developers.
Table 1: The authors should indicate their use of air temperature to approximate soil temperature when determining base cation weathering. Likely a good estimate given long term annual average data is used.
Lines 210-220: Would not a large amount of BC dep result in adding excess nutrient to the system? The authors should mention any other consequences of incorporating anthropogenic BC dep. This may proof important especially in areas that are exceeding nutrient N CL.
Lines 214-219: It is not clear the purpose of smoothing BC dep. It does not represent actual, nor does it represent non-anthropogenic BC dep.
Lines 217-219: The work could not consider forest fire impact, and the authors have mentioned the impact of this omission on BCdep. The authors should also indicate how not considering forest fires could affect other terms in their work.
Lines 242-243: Was the most sensitive species given priority in a grid cell irrespective of coverage, what were the range of coverage?
Table 3: It is not clear how V2.2 and V3.2 adds to the material presented in the section or elsewhere.
Lines 315-317: The authors should explain/define temperature correction in the method section.
Table 4: The results in the text is presented by administrative boundary and a few times by ecozones making reference to the table difficult. Because much of the discussion is by administrative boundary much of the results (Ecozones) presented are not discussed. What would be the takeaway for an international audience?
Lines 337-339: The average base cation deposition is higher after smoothing?
Lines 339-340: Where is the star on the map located presumably the entire region is not a source of BC deposition?
Section 3.5: Why does this section not include CLnutN results?
Lines 368-369: Which BC deposition is used to determine CLmaxS? Earlier when discussing the BC deposition (smoothed unsmoothed), the authors should indicate which of the two data sets is the primary data set.
Lines 379-382: Where are the isolated point sources and what are they due to? These seem to be in different areas of the province outside the previously mentioned AOSR.
Lines 382-384: The authors discuss Ndep by provincial average, but the most sticking observation is the north-south gradient. The authors should discuss what is driving the observed north-south gradient observed for much of the country.
Lines 393-395: Would not the CL values be lower for 5% protection?
Lines 425-426: It seems like a great many of the exceedances are less than 50 eq ha-1 yr-1 and probably within the uncertainty of the model. In addition to absolute exceedances the authors should comment on the various ranges.
Lines 486-489: The choice of level of protection for a managing agency is really a policy decision and not an ethical choice.
Line 491: Low CLnut N is more widespread than the Arctic, the authors should indicate what is driving the low values in other areas not just the arctic.
Lines 522:534: The comparison works presented seem to indicate the current work is under estimating CLnutN by a factor of 2, relative to the presented comparison work. What is the % of area with deposition greater than 2x CLnutN? See also comment on discussing various ranges of CLnutN exceedances.
Line 531-534: it looks like exceedance is largely driven by Ndep as CLnutN is very low in much of the area under study. Given the largest exceendance is of CLnutN what additional work or data do the authors recommend?
Citation: https://doi.org/10.5194/egusphere-2024-2371-RC1 - AC1: 'Reply on RC1', Hazel Cathcart, 11 Oct 2024
-
RC2: 'Comment on egusphere-2024-2371', Anonymous Referee #2, 09 Sep 2024
An interesting paper describing the computation of critical loads of S and N for the whole of Canada, which is done here for the first time (earlier studies dealt with subregions only). The paper is well written, with some (minor) issues to be clarified, specially about Cl-deposition (see below). Thus, I suggest that the paper should be published with minor revisions. The corrections/amendments listed in the attached pdf-file should be addressed before re-submission
- AC2: 'Reply on RC2', Hazel Cathcart, 11 Oct 2024
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