the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 21 Jan 2025
The response of small boreal catchments to extreme weather event: Hurricane Larry
Abstract. The boreal environment is high in dissolved organic carbon (DOC) and iron concentrations. This DOC is enriched in functional groups allowing it to bind strongly with iron and act as a significant source of iron to the coastal and marine environment. As climate change intensifies more extreme weather events will affect the northern hemisphere and boreal environment. These weather events can lead to massive fluxes of material from the environment but the impact it will have on the boreal environment is currently unknown. Hurricane Larry made landfall on Newfoundland (NL) in 2021 providing an opportunity to investigate how the boreal environment will react to extreme weather events. We sampled three rivers before and after the hurricane to see how DOC and iron concentrations, lability, and colour were affected by the hurricane. We found that a high percentage of forest and peatlands buffered against increases in DOC and colour, with wetlands buffering an increase in iron concentrations. This study represents one of the first to observe boreal catchment responses to extreme weather events such as hurricanes.
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RC1: 'Comment on egusphere-2024-3843', Anonymous Referee #1, 02 Mar 2025
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General comments: This manuscript was an interesting look at extreme weather (Hurricane Larry) on DOM in three small catchments in Atlantic Canada in 2021, a region which had not experienced such an event in about 10 years. The novelty here is that studies of hurricane effects on coastal ecosystems in this region of North America are rare but are valuable because of increasing frequency of intense Atlantic tropical cyclones that may reach the region. The coupling of DOM and Fe in this study was interesting. The streams were small such that even after passage of the hurricane, discharge <1 m3/s. Site information, methods all were good.
Specific comments: I found the results in Figure 3 and bore additional discussion. Though not significant in magnitude I wondered if the proportional increase in a350 was closer to the proportional increase in DOC or in Fe? This could indicate if the a350 is attributable to DOC or Fe or both.
L160 - approaching significance isn't useful to describe; remove. In fact the use of p values in this manner is not insightful and at times confusing. For example, Fe related to catchment properties - Why is p = 0.181 a relationship but p = 0.616 not a relationship? The relationship is evaluated by the strength of the correlation. While Fe had a high correlation with Wetland there was a lower correlation - not no relationship - to Peat.
L178 - Explain the last sentence in more detail.
L183 - What does "type of land cover increases" mean?
L184 - Connect this point about buffering to the present work.
L193 - "found to build in" - rephrase to clarify
L196 - what might happen to the Fe once it encounters oxygen in surface waters and does this have any implication for DOC or CDOM?
L201 - who is ignoring them? Rephrase to clarify.
L212 - Perhaps, it depends on the model. The systems here while having large DOC concentrations have small flows that offset their importance regionally. For South River, using average values reported here to upscale, I estimate the annual export of DOC is about 75,000 g C/yr. This is very small and probably not of regional importance, but obviously could be important for local biogeochemical models. So I would clarify that point.
L213 - the authors may wish to look at Nick Ward's work on terrestrial-aquatic interfaces to better consider these points.
Technical: L131: hurricane was misspelled; L222 - important in place of significant
Citation: https://doi.org/10.5194/egusphere-2024-3843-RC1 -
RC2: 'Comment on egusphere-2024-3843', Anonymous Referee #2, 05 Mar 2025
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The manuscript, entitled “The response of small boreal catchments to extreme weather event: Hurricane Larry” by Heerah et al. evaluated DOM and iron concentration after 2021 Hurricane Larry in Newfoundland, and found that the forests and peatlands may have capacities to buffer DOC and colour, while wetlands may buffer the increase in iron concentrations. The study provides insights into impacts of extreme weather events on water quality in boreal regions. However, I do have some concerns and suggestions for improvement, outlined below.
General comments:
1. This study may have a major issue of pseudoduplication, which affects the validity of the statistical analyses within each watershed. For each watershed, only one time sample collection was conducted before and after the hurricane, respectively. Regardless of the number of samples collected per event, applying statistical analyses to compare the changes in colour, DOC, iron etc., before and after the hurricane within a single watershed is problematic because these samples are not independent. To address this, the study could combine all samples into two groups: samples from three watersheds before the hurricane vs. samples from three watersheds after the hurricane. This approach would mitigate the pseudoreplication issue and ensure more robust statistical results.
2. Regardless of whether the above pseudoreplication issue is valid, another major concern is that some conclusions are not supported by statistically significant results. For instance, the study suggests that a high percentage of forest and peatlands buffered against increases in DOC and colour, with wetlands buffering an increase in iron concentrations. However, Table 2 does not indicate any statistically significant correlations supporting these statements. Similarly, the higher DOM properties observed in Figure 3 are not statistically validated.
Specific comments:
L47-50: Please briefly describe how forests and peat barrens regulate DOM and iron.
Section 2.1: How many samples were collected before and after the hurricane in each stream?
L84-85: Can you show the gauged sizes of those three watersheds?
Figure 1: Can you insert three sub-figures to show land use types of each watershed?
L104: Include the relevant equation. In addition, I did not see any analyses about this index.
Methods section:
(1) I would suggest adding a subsection to provide more information about the Hurricane Larry, for example, wind speed, amount the rainfall, etc. This information helps understand the severity of the hurricane and its consequence on water quality.
(2) What statistical methods were used?
L141: this should be Table 1.
Citation: https://doi.org/10.5194/egusphere-2024-3843-RC2
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