| 12 May 2026
Permafrost conditions in peatlands govern riverine flushing of dissolved organic carbon, methylmercury, and nutrients
Abstract. Permafrost thaw and intensified droughts and floods threaten to alter the mobilization of dissolved organic carbon (DOC), nutrients and methylmercury (MeHg) from boreal peatlands, with cascading impacts on aquatic ecosystem functions and traditional food sources. Here we monitored 27 peatland-dominated (>30 %) catchments in western Canada (150 to 52,000 km2) over a five-year period (2020 – 2024) which captured extreme hydroclimatic conditions. These catchments spanned a climatic and permafrost gradient (mean annual temperature -0.2 to -2.8 °C), which provided a space-for-time framework to assess impacts of continued thaw and warming. Our results demonstrated that catchment climate, and thus permafrost conditions, strongly controlled the hydrological response of solute concentrations. Warmer catchments showed a pronounced flushing response where DOC and MeHg concentrations increased by 50 % and 80 %, respectively, as discharge increased from the 10th to 90th percentile. In contrast, colder catchments maintained a chemostatic response, where concentrations remained stable and low despite hydrological variability. Similar climate-hydrology interactions were found for total nitrogen, total phosphorous, and inorganic phosphorous, but not for inorganic nitrogen. It is likely that permafrost conditions in peatlands affect both the production of solutes and their hydrological connectivity to the stream network. The presence of permafrost in peatlands may act to both ensure connectivity during droughts but also preclude full connectivity during floods, yielding the observed patterns. Our findings suggest that ongoing peatland permafrost thaw will increase mobilization MeHg, DOC, and nutrients during high flow periods. This shift necessitates further monitoring to understand the long-term consequences for aquatic ecosystems and northern communities.
There is a reasonable study behind this
Needs a good re-read by an editor so that typos and poor English are sorted, eg. the opening sentence of the Abstract contains a typo and line 34, the opening sentence of the Introductions, does not make sense.
Line 21 – here and throughout the text the word strong or strongly is used. This word is a subject judgement and has no definition and so should be deleted on each occurrence.
Line 63 – that is ammonium not ammonia.
Line 72 – I think it should be important not importance
Line 78 – “… a major northern peatland region”, delete this sub-clause. What does broad permafrost gradient mean?
Line 100 – Here or in the Methodology, I would like to know what the real test of the study is – it turns out that the real test of the study is whether there is a significant interaction between FP and MAT.
Line 132 – Here and throughout the manuscript sentences that start with pronouns need to have the subject of the sentence stated.
Line 208 – I don’t understand the standardisation, it sounds like a partial z-transform.
Line 210 – what does cautiously mea? I would delete it.
Line 220 – It needs to be made explicit what are the random and fixed factors in the LMM. In reality the only random factor is SiteID and the key term is FP MAT interaction.
Line 255 – here and throughout the manuscript I would avoid the use of the word similar as it has no definition and is just a subjective judgement.
Figure 4 – too cluttered and should be split between panels.
Line 286 – the use of visual comparison and visually similar all seem too subjective and such comparison will tend to confirm unstated biases in the authors.
Line 301 – wildfire must be a binary variable and so how was it included in the modelling? I don’t think was made clear.
Table 2 – this is a mess, remove the asterisks and just state that only significant factors and variables are shown. When coefficient is negative then you don’t need the plus sign as well.
Line 329 – less apparent?
Line346 – chemostatic is never defined – seems arbitrary to me.
Line 349 – This sentence uses both strong and likely neither of which are defined or justified.
Line 391 – what is meant by unsaturated conditions?
Line 391 – here and throught the manuscript be careful to use significant only in the statistical sense.
Line 413 – high flow and rought are not opposite conditions, the opposite of high flow is baseflow. So I am not clear what is the contrasting being drawn here.
Line 414 – delete Ergo
Line 422 – “showed slight” – what does that mean?
Line 453 – what does chemodynamic mean?
Line 463 – what does concurrent behaviour mean here?
Line 467 - “… was only relevant within the context and interaction of hydrological conditions…” I don’t understand this.
Discussion – I had expected a section on the limitations of the study and the implications of the study.
Conclusion – this is not a conclusion section it is summary and interpretation – it needs a total re-write.