the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 26 Jan 2024
Litter decomposition enhances volatile organic compound emission from a freshwater wetland: insights from year-round in situ field experiments
Abstract. Plant litter could be a potential source of atmospheric volatile organic compounds (VOCs). Previous studies are mostly restricted to forest litter, but VOC budget of wetlands, especially freshwater wetlands, resulting from litter decomposition remains largely unexplored. Here we performed in-situ VOC flux measurements in a freshwater wetland and three treatments including A (no litter addition), B (1.4 kg litter) and C (2.8 kg litter) were designed to investigate impacts of litter decomposition on wetland-atmosphere exchange of VOCs. During year-round litter decomposition, average fluxes of net VOCs for B and C were 5.93±3.13 μg m-2 h-1 and 8.30±4.00 μg m-2 h-1, respectively, significantly higher than that of A (2.90±2.74 μg m-2 h-1). These results suggested that freshwater wetland was a potential source of atmospheric VOCs and litter decomposition enhanced VOC release. Net VOC flux showed clear seasonal patterns and was highly correlated with ambient temperature (p<0.05). In general, higher positive VOC fluxes were observed in hot summer, while lower positive VOC fluxes or negative VOC fluxes were observed in cold winter. Moreover, the release (positive flux) or uptake (negative flux) of VOCs varied to chemical groups. Specifically, non-methane hydrocarbons (NMHCs) including alkanes, alkenes and aromatics showed positive net fluxes, and increased with added litter. Halocarbons showed a negative net flux in A, but positive net fluxes in B and C. While oxygenated volatile organic compounds (OVOCs) showed negative net fluxes in both A and B, and switched to a positive flux in C. Positive net fluxes of volatile organic sulfide compounds (VOSCs) were observed in three treatments. According to flux variations of specific VOC group, it has been suggested that temperature-driven biotic and abiotic processes co-modulated VOC release or uptake occurring in the freshwater wetland.
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CC1: 'Comment on egusphere-2023-2998', Zhigang Yi, 06 Mar 2024
Comments:
Fang et al. provide an interesting study of the biogeochemistry of volatile organic compounds in a freshwater wetland. The study measured the air-wetland exchange of VOCs through year-long in situ field experiments and investigated the impact of plant litter decomposition on these measured VOCs. Overall, this manuscript is well organized and most of results are clearly explained, and it fits within the scope of Biogeosciences. However, some issues in the current manuscript still need to be addressed. Thus, I recommend it for publication after a minor revision.
1. The abstract is well written but includes many abbreviations that are not needed in the abstract text and should be removed. Why do you include an abbreviation for a definition that you use one time only? These abbreviation explanations (NMHCs, OVOCs, VOSCs) should be moved to the manuscript text.
2. The references are outdated, especially in the Introduction section. Please replace with more recent studies.
3. In general, the experiment is designed comprehensively and the aim is clear. One question, however, is whether the authors measured the background VOCs of the chamber itself or whether these VOC concentrations were very low and could be neglected? I cannot find any relevant information in the manuscript.
4. I am a little interested in the AH emissions reported in the manuscript. As we know, AHs have traditionally been considered as anthropogenic VOCs. Are there any possible reasons or mechanisms for the emission of AHs from natural environments?
5. Line 179: volatile organic sulfide compounds (VOSCs)
6. Line 227-228. Monoterpene can be detected by GC/MSD method (Yuan et al. 2023. Emissions of isoprene and monoterpenes from urban tree species in China and relationships with their driving factors). The canister sampling used in the experiment may not be appropriate to capture these higher-molecular-weight species.
7. Line 398: Change abbreviations “VOSCs” as “Volatile organic sulfide compounds”.
Citation: https://doi.org/10.5194/egusphere-2023-2998-CC1 -
AC2: 'Reply on CC1', Ting Wu, 29 Jul 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2023-2998/egusphere-2023-2998-AC2-supplement.pdf
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AC2: 'Reply on CC1', Ting Wu, 29 Jul 2024
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RC1: 'Comment on egusphere-2023-2998', Arnaud P. Praplan, 06 Mar 2024
Fang et al., in their article "Litter decomposition enhances volatile organic compound emissions from a freshwater wetland: insights from a year-round in situ field experiment", present results from year-round VOC fluxes in a freshwater wetland located in southeastern Anhui Province in China for three different treatments: no litter addition, 1.4kg litter, and 2.8kg litter.
The manuscript is clear and the arguments easy to follow. The presentation of the results is clear, and they are discussed appropriately. I only found minor issues, which I trust the authors will be able to address. Therefore, I recommend accepting the manuscript with minor corrections.
Minor comments:
- ll. 128-131: An important element that is missing from the manuscript is an indication of naturally occurring litter. How much is it in treatment A? Are the authors able to give an estimate?
- ll. 134-136: Could the authors elaborate on when the Phragmites Australis above the roots were cleared in relation to the first samples being taken? In addition, could the authors briefly mention why roots were/could not be cleared up?
- ll. 213-214 (and Fig. S3): I wonder if Fig. S3 is necessary and if the authors should not instead refer to the literature to back their statement about this positive feedback loop. In addition, in Fig. S3 'arise' is the only intransitive verb and should be replace by 'increase', for instance, to be consistent with the two other (transitive) verbs.
- ll. 227-230: The authors only state that the 'technique used here failed to fully characterize higher molecular weight species, such as monoterpenes and lower molecular weight species, such as methanol'. Could the authors be more specific in relation to the limitations of the method? Does it have to do with the sampling? Also, do the authors mean 'higher molecular weight species, such as sesquiterpenes' as they include at least two monoterpenes in their results (Table S1).
- l. 232: The authors lead the discussion of seasonal pattern with a figure in the supplement material (Fig. S4). If the figure is important, it should be part of the main text. Also, I wonder if Fig. S4 is absolutely necessary given that the authors should be able to support their conclusions with Fig. 3 from the main text (mentioned later in this section), as well as with Fig. 5.
- Conclusions: I would like to again mention that it would be interesting and important for context to give the reader some information about the amount of litter naturally occurring at the wetland, potential changes in litter amount throughout the seasons, and how litter amounts are expected to change in a warming climate? Is more or less litter, expected to be found in the wetland? This information might also be included in the introduction and the discussion sections of the manuscript.
- Text S1: The authors seem to describe their laboratory blanks, but then mention that 'only when no targeted VOC were detected' the canisters were used for sampling. It is a little confusing. Why is only 10% of the evacuated canisters then analysed? Or have all the canisters been analysed earlier at some point for this project?
- Figure S2: I fail to understand the blue columns in this figure. I understand the numbers, but I don't understand their relation to the blue columns and if the blue columns have the same x-axis as the green bars. This should be made more understandable.
Technical/language comments:
- l. 245-247: Should the sentence end with 'in all three treatments' or 'in the three treatments'?
- l. 324: I would not use the turn of phrase 'ranked No. 1 contributor', which seems a little clunky compared to 'contributed most' or 'was the main contributor'.
- ll. 417 and 427: The conclusions include twice the acronym TVOC, which has not been defined.
- l. 430: While 'increasement' can be found in a dictionary, it is obsolete and can be replaced by 'increase'.
- l. 735: '11 campaigns': I would think that all the measurements in this study form a campaign, not each individual sampling time.
- Table S1: I noticed some small inconsistencies in the number of digits reported in this Table (e.g. sometimes ±0.1 and sometimes ±0.10).Citation: https://doi.org/10.5194/egusphere-2023-2998-RC1 -
AC1: 'Reply on RC1', Ting Wu, 29 Jul 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2023-2998/egusphere-2023-2998-AC1-supplement.pdf
-
AC1: 'Reply on RC1', Ting Wu, 29 Jul 2024
-
RC2: 'Methodology issues', Robert Rhew, 09 Jul 2024
-
AC3: 'Reply on RC2', Ting Wu, 29 Jul 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2023-2998/egusphere-2023-2998-AC3-supplement.pdf
-
AC3: 'Reply on RC2', Ting Wu, 29 Jul 2024
Status: closed
-
CC1: 'Comment on egusphere-2023-2998', Zhigang Yi, 06 Mar 2024
Comments:
Fang et al. provide an interesting study of the biogeochemistry of volatile organic compounds in a freshwater wetland. The study measured the air-wetland exchange of VOCs through year-long in situ field experiments and investigated the impact of plant litter decomposition on these measured VOCs. Overall, this manuscript is well organized and most of results are clearly explained, and it fits within the scope of Biogeosciences. However, some issues in the current manuscript still need to be addressed. Thus, I recommend it for publication after a minor revision.
1. The abstract is well written but includes many abbreviations that are not needed in the abstract text and should be removed. Why do you include an abbreviation for a definition that you use one time only? These abbreviation explanations (NMHCs, OVOCs, VOSCs) should be moved to the manuscript text.
2. The references are outdated, especially in the Introduction section. Please replace with more recent studies.
3. In general, the experiment is designed comprehensively and the aim is clear. One question, however, is whether the authors measured the background VOCs of the chamber itself or whether these VOC concentrations were very low and could be neglected? I cannot find any relevant information in the manuscript.
4. I am a little interested in the AH emissions reported in the manuscript. As we know, AHs have traditionally been considered as anthropogenic VOCs. Are there any possible reasons or mechanisms for the emission of AHs from natural environments?
5. Line 179: volatile organic sulfide compounds (VOSCs)
6. Line 227-228. Monoterpene can be detected by GC/MSD method (Yuan et al. 2023. Emissions of isoprene and monoterpenes from urban tree species in China and relationships with their driving factors). The canister sampling used in the experiment may not be appropriate to capture these higher-molecular-weight species.
7. Line 398: Change abbreviations “VOSCs” as “Volatile organic sulfide compounds”.
Citation: https://doi.org/10.5194/egusphere-2023-2998-CC1 -
AC2: 'Reply on CC1', Ting Wu, 29 Jul 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2023-2998/egusphere-2023-2998-AC2-supplement.pdf
-
AC2: 'Reply on CC1', Ting Wu, 29 Jul 2024
-
RC1: 'Comment on egusphere-2023-2998', Arnaud P. Praplan, 06 Mar 2024
Fang et al., in their article "Litter decomposition enhances volatile organic compound emissions from a freshwater wetland: insights from a year-round in situ field experiment", present results from year-round VOC fluxes in a freshwater wetland located in southeastern Anhui Province in China for three different treatments: no litter addition, 1.4kg litter, and 2.8kg litter.
The manuscript is clear and the arguments easy to follow. The presentation of the results is clear, and they are discussed appropriately. I only found minor issues, which I trust the authors will be able to address. Therefore, I recommend accepting the manuscript with minor corrections.
Minor comments:
- ll. 128-131: An important element that is missing from the manuscript is an indication of naturally occurring litter. How much is it in treatment A? Are the authors able to give an estimate?
- ll. 134-136: Could the authors elaborate on when the Phragmites Australis above the roots were cleared in relation to the first samples being taken? In addition, could the authors briefly mention why roots were/could not be cleared up?
- ll. 213-214 (and Fig. S3): I wonder if Fig. S3 is necessary and if the authors should not instead refer to the literature to back their statement about this positive feedback loop. In addition, in Fig. S3 'arise' is the only intransitive verb and should be replace by 'increase', for instance, to be consistent with the two other (transitive) verbs.
- ll. 227-230: The authors only state that the 'technique used here failed to fully characterize higher molecular weight species, such as monoterpenes and lower molecular weight species, such as methanol'. Could the authors be more specific in relation to the limitations of the method? Does it have to do with the sampling? Also, do the authors mean 'higher molecular weight species, such as sesquiterpenes' as they include at least two monoterpenes in their results (Table S1).
- l. 232: The authors lead the discussion of seasonal pattern with a figure in the supplement material (Fig. S4). If the figure is important, it should be part of the main text. Also, I wonder if Fig. S4 is absolutely necessary given that the authors should be able to support their conclusions with Fig. 3 from the main text (mentioned later in this section), as well as with Fig. 5.
- Conclusions: I would like to again mention that it would be interesting and important for context to give the reader some information about the amount of litter naturally occurring at the wetland, potential changes in litter amount throughout the seasons, and how litter amounts are expected to change in a warming climate? Is more or less litter, expected to be found in the wetland? This information might also be included in the introduction and the discussion sections of the manuscript.
- Text S1: The authors seem to describe their laboratory blanks, but then mention that 'only when no targeted VOC were detected' the canisters were used for sampling. It is a little confusing. Why is only 10% of the evacuated canisters then analysed? Or have all the canisters been analysed earlier at some point for this project?
- Figure S2: I fail to understand the blue columns in this figure. I understand the numbers, but I don't understand their relation to the blue columns and if the blue columns have the same x-axis as the green bars. This should be made more understandable.
Technical/language comments:
- l. 245-247: Should the sentence end with 'in all three treatments' or 'in the three treatments'?
- l. 324: I would not use the turn of phrase 'ranked No. 1 contributor', which seems a little clunky compared to 'contributed most' or 'was the main contributor'.
- ll. 417 and 427: The conclusions include twice the acronym TVOC, which has not been defined.
- l. 430: While 'increasement' can be found in a dictionary, it is obsolete and can be replaced by 'increase'.
- l. 735: '11 campaigns': I would think that all the measurements in this study form a campaign, not each individual sampling time.
- Table S1: I noticed some small inconsistencies in the number of digits reported in this Table (e.g. sometimes ±0.1 and sometimes ±0.10).Citation: https://doi.org/10.5194/egusphere-2023-2998-RC1 -
AC1: 'Reply on RC1', Ting Wu, 29 Jul 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2023-2998/egusphere-2023-2998-AC1-supplement.pdf
-
AC1: 'Reply on RC1', Ting Wu, 29 Jul 2024
-
RC2: 'Methodology issues', Robert Rhew, 09 Jul 2024
-
AC3: 'Reply on RC2', Ting Wu, 29 Jul 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2023-2998/egusphere-2023-2998-AC3-supplement.pdf
-
AC3: 'Reply on RC2', Ting Wu, 29 Jul 2024
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