the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 15 Apr 2024
Testing Ion Exchange Resin for quantifying bulk and throughfall deposition of macro and micro-elements on forests
Abstract. Atmospheric deposition is a major nutrient influx in ecosystems and high anthropogenic deposition may disrupt ecosystem functioning. Quantification of the deposition flux is required to understand the impact of such anthropogenic pollution. However, current methods to measure nutrient deposition are costly, labor intensive and potentially inaccurate.
Ion Exchange Resin (IER) appears a promising cost-and labor-effective method. The IER-method is potentially suited for deposition measurements on coarse time scales and for areas with little rainfall and/or low elemental concentrations. The accuracy of the IER-method is, however, hardly classified beyond nitrogen. We tested the IER-method for bulk deposition and throughfall measurements of macro and micro-elements, assessing resin adsorption capacity, recovery efficiency, and field behavior.
We show that IER is able to adsorb 100 % of Ca, Cu, Fe, K, Mg, Mn, P, S, Zn and NO3 and >96 % of P and Na. Loading the resin beyond the capacity resulted mainly in losses of Na, P, NH4 while losses of Ca, Cu, Fe, Mg, Mn and Zn were hardly detected. Heat (40 °C), drought and frost (-15 °C) reduced the adsorption of P by 25 %. Recovery was close to 100 % for NH4 and NO3 using KCl (1 or 2M) while high (83–93 %) recoveries of Ca, Cu, Fe, K, Mg, Mn and S were found using HCl as an extractant (2–4M). We found good agreement between the conventional and the IER-method for field conditions.
Overall, IER is a powerful tool for the measurement of atmospheric deposition of a broad range of elements as the measurements showed high accuracy. The IER-method has therefore the potential to expand current monitoring networks and increase the number of sampling sites.
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Status: final response (author comments only)
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RC1: 'Comment on amt-2024-46', Anonymous Referee #1, 14 May 2024
General Comments: Ion exchange resin precipitation collectors (IERs) have been used to quantify element/ion deposition in remote locations, but there remain questions about the reliability of IERs. This study examined different laboratory approaches (wet vs dry resins; drip vs drip-shake extraction; molarity of extraction) to processing IERs and also compared IERs to more traditional wet precipitation collectors in a forest with four different canopy covers. The study addresses important questions. However, the experimental design is a major weakness of the work. In both the laboratory and the field part of the work, complete statistical analyses are not shown. Given the unbalanced design and low replication (n=1 for some treatment combinations in the lab study), I read, but did not comment on the Discussion. I was not convinced that the laboratory study especially provided convincing new insights into questions about IER processing.
Lines 107ff – IER construction is not the same across all published IER studies. Please specify the diameter and length of the resin tubes themselves.
Line 115. Change weighted to weighed.
Line 127 – Existing deposition data for where?
Lines 128-135. This is a long sentence – and one that I do not fully understand. “…representative stations” – representative of what? What does “for the funnel surface” mean?
Lines 135-136 – Table S1 is referenced in text, but when I read Table S1 I had a hard time understanding what the Table was showing or how it related to the sentence in the manuscript.
Lines 138-142.This information could be put in to a small table. It would be useful to give the recipe for these solutions (how many grams of each salt?).
Line 145 – Should be column or column’s, not columns
Line 147 – Should be resin or resin’s, not resins
Lines 150-155 – Were the leachate and demineralized water samples filtered prior to analysis? Hopefully, yes.
Line 163 – “…previous studies…” but only one reference. I do not see in Fenn et al. (2018) a discussion of the molarity of the extraction solution. That paper does have a section of using solutions other than KCl or KI is a researcher wants to quantify K+ deposition.
Table 1 – These are very low sample sizes.
Line 185 - Table 2 – I think I can see why there is not an equal number of samplers in bulk deposition and throughfall in each treatment, but statistically, I do not see how the design presented in Table 2 would work.
Line 192 – What is a “common” deposition collector?
Line 193 – Maybe add “collectively” after “The 7 collectors per plot”
Line 222 – Change send to sent
Lines 222ff – Were the samples filtered?
Line 223 – Change contents to concentrations
Lines 246-254 – Calculating adsorption capacity and recovery efficiency based on analyte concentrations assumes that the volume of the added solution is the same as the volume of the extract solution. Was this always the case?
Lines – 263ff – The results section suffers from not considering results in light of the ANOVA and subsequent Tukey’s tests. As an example, statistical results are not considered at all regarding the results shown in Figure 3. And how can it be that overloading of the cation and/or anion exchange capacity results in 100% adsorption capacity?
Lines 290ff – Table 3 does not show statistical interactions. The bottom row shows mean recovery efficiencies for each element, but there were element interactions with pretreatment, molarity, and extraction type, so averaging element means across all treatments ignores the ANOVA interactions. Table 3 clearly illustrated the unbalanced ANOVA design and exceptionally minimal replication. Table S3 shows part of an ANOVA, but it only shows 2-way interactions (and not all of the 2-way interactions). A complete ANOVA would have 3-way interactions and one 4-way interactions. It is hard to tell what complete ANOVA would look like (it might not even run because of the unbalanced design with low replication).
Lines 310 ff – In Figure 4 and Table 5, if the goal is to compare corrected, blank corrected and recovery corrected regressions, it would be appropriate to use ANCOVA for homogeneity of slopes. This would be a better approach than simply showing the highest R2 value in bold. One cannot compare log-transformed regression coefficients to non-transformed regression coefficients (for S).
Line 326 – I do not see that Fig. S1 shows canopy openness results.
Citation: https://doi.org/10.5194/amt-2024-46-RC1 - AC3: 'Reply on RC1', Marleen Vos, 18 Jul 2024
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RC2: 'Comment on amt-2024-46', Anonymous Referee #2, 15 May 2024
The comment was uploaded in the form of a supplement: https://amt.copernicus.org/preprints/amt-2024-46/amt-2024-46-RC2-supplement.pdf
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AC1: 'Reply on RC2', Marleen Vos, 18 Jul 2024
The comment was uploaded in the form of a supplement: https://amt.copernicus.org/preprints/amt-2024-46/amt-2024-46-AC1-supplement.pdf
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AC1: 'Reply on RC2', Marleen Vos, 18 Jul 2024
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RC3: 'Comment on amt-2024-46', Anonymous Referee #3, 20 May 2024
I would like to congratulate the authors for a very thorough work. A multitude of variables have been taken into account and the experimental and field design are excellent. It is a very necessary work from the point of view of forest monitoring, since the use of methodologies based on ion exchange resins is not widespread despite being used for decades already, and it could be because of the scarcity of methodological approaches such as the one here it is presented.
I would like to recommend the publication of this manuscript, but not before suggesting some minor changes and raising some questions:
Line 108: First, the resin columns were cleaned using 0.2M HCl and demineralized water - Please add some few words to fully explain the cleaning method. Demineralized water was used for cleaning or for rinsing (as stated in the next sentence)?
Line 136: Thereafter, the deposition of the summer was multiplied by 2, which is an average correction factor to convert bulk deposition to throughfall (Table S1). - It is unclear how 2 is an average of what it is shown in Table S1. Moreover, Table S1 presents factors to convert bulk to total deposition, but in the text it is stated that the factor is used to convert to throughfall deposition values.
Line 151: Three loaded resin columns were thereafter flushed with demineralized water to test the stability of the adsorption. - Which three resin columns?
Line 152: Both the samples of the leachate and the demineralized water used to wash the loaded columns, were analyzed for N-NH4, and N-NO2 + N-NO3 content using a Segmented Flow Analyzer (SFA type 4000, Skalar Analytical B.V., the Netherlands), and the content of Ca, Cu, Fe, Mg, Mn, Na, total-P, S and Zn using the ICP-AES (Thermo-Scientific iCAP 6500 DUO, USA). - This sentence should be moved to end of the next paragraph, adding the extracted solution to the list of samples analysed.
Table S2: Please consider changing macro- and microfluid by "macro- and micro elements".
Table 1: Please consider changing here (and in the rest of the manuscript) extraction fluid by "extraction solution".
Table 2: The columns of Paired samples (Bulk deposition and Throughfall) seem to be switched.
Line 169: The extraction method was either drip, in which the extractant was slowly dripped over the resin, or a shake drip combination in which the resin was shaken in 50 mL of the extractant for 1 hour and the remaining extractant was dripped over the resin. - For the shake-drip method, how the resin was shaken? was the resin put into the column again after shaken it in a plate? Please, clarify.
Line 226: the resin columns were collected on January 14th, 2020, dried together with lab blanks to a constant weight at 28ºC and subsamples were taken for 2M KCl extraction followed by N-NH4 and NNO2 + N-NO3 content analysis using a Segmented Flow Analyzer (SFA 4000, Skalar Analytical B.V., the Netherlands) and for 3.5M HCl extraction followed by Ca, Cu, Fe, Mg, Mn, Na, P, S and Zn content analysis using the ICP-AES. - Why this methodology (drying and concentration of extraction solution) was selected for the field comparison? Also, what volume of extraction solution was used?
Line 265: The adsorption capacity was not influenced by the flushing of the resin with demineralized water. - I believe that this result corresponds to the text named before as “stability of absorption”. It is not well explained in the methodology section and some more words to clarify the implications of the results could be added here or in the discussion.
Line 272: Elemental adsorption within the resins exchange capacity was thus close to 100% for all elements except P which was underestimated under extreme conditions. - Please, consider adding to the sentence the following (or a similar one) particularization: “under the different simulated environmental condition”.
Line 291: The average recovery efficiency was highest (90-100%) following either 2M HCl extraction or 4-2-1M HCl extraction. - The average here is per element or per extraction combination. Looking at the table it is not clear where this range is extracted from. P is not this range, neither FW method is. It is possible that it refers only to DW method per extraction combination? Please, clarify.
Table 5: Please consider adding any error- or bias indicator, such as mean normalized error or/and mean normalized bias. Moreover, the acronym ORG is not explained here and it is missing from the rest of the text.
Line 335: First, the adsorption capacity of the IER when loaded within its capacity was generally high. - Consider clarifying here that the value was 70% of its capacity, as it is done at the beginning of the next paragraph.
Line 440: The lower deposition estimates of P can be caused by a better adsorption of inorganic P compared to organic P to the resin. - Have you consider measuring PO43- in addition to P? Could it be a further-research objective?
Line 460: Our results even imply a higher reliability of the IER-method than the water method since uncertainties related to biological reactions and the detection limit for lab measurements could be removed. - I strongly recommend adding a clarification to this sentence, such as “under certain circumstances”. In the field work of the present study, the IER funnels were cleaned weekly (if contaminated), which is something that cannot occur when collectors are only visited seasonally (or longer). Take into account that IER method is intended also for avoiding frequent visits to field, e.g. in locations with difficult access.
Finally, a common concern in the use of IER is the pH of the resultant extracted solution. This can pose a problem for the analysis of some elements or their conservation in the sample. Did you perform a pH test in the extracted samples? Do you have any comment on this?
Citation: https://doi.org/10.5194/amt-2024-46-RC3 -
AC2: 'Reply on RC3', Marleen Vos, 18 Jul 2024
The comment was uploaded in the form of a supplement: https://amt.copernicus.org/preprints/amt-2024-46/amt-2024-46-AC2-supplement.pdf
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AC2: 'Reply on RC3', Marleen Vos, 18 Jul 2024
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