| 10 Apr 2026
Experimental evidence that organo-mineral interactions regulate dissolved organic matter composition and lability across permafrost landscapes of northwestern Canada
Abstract. Increased land-water connectivity of northern landscapes driven by permafrost thaw is shifting the bioavailability of dissolved organic matter (DOM) in surface waters, with implications for northern food webs and regional and global carbon balances. However, sorption of DOM to previously frozen sediments has received little attention as a mechanism of regulating the bioavailability of organic matter in thaw-affected freshwater ecosystems. Using batch sorption experiments, we assessed sorption potential, water-extractable dissolved organic carbon (DOC) concentration, and the impact of sorption on DOM composition of six different permafrost sediment types common throughout northwestern Canada, reflecting variation in geologic and permafrost histories. A principal component analysis revealed that sediment biogeochemical characteristics reflected geologic origin, and past thaw increased within-type variation. Sorption was positively correlated with organo-reactive forms of Al and Fe and negatively correlated with sediment pH. Proportion of bulk sediment organic carbon released as water extractable DOC ranged from 1.0 % to 62.0 %, with yedoma sediments from the Klondike region releasing substantially more than sediments from other regions. Preferential sorption of larger, humic-like compounds and displacement of mineral-bound small, aliphatic molecules enriched the DOM pool in labile compounds. Bio-incubations verified that exposure to sediments increased rates of biodegradation, corresponding with shifts in DOM composition and increased nutrient concentrations. Our experiments demonstrate that organo-mineral interactions have the potential to decrease DOC concentrations while increasing DOM bioavailability following exposure to permafrost-origin sediments, but that the strength of this response varies with sediment characteristics that are reflective of landscape history.
General comments:
Thawing of permafrost is one of the most obvious and severe effects of global change and has the potential to fundamentally change ecosystems at higher latitudes and elevations. The release, subsequent transport and biological metabolization of soluble organic carbon entrapped in permafrost layers has drawn substantial scientific interest over the last decades but knowledge on controlling factors is still far from completeness. The present study investigates the role sediment mineral properties in the regulation of amounts, composition, and microbial consumption of soluble/dissolved organic matter at landscape scale.
The study addressed sorptive interactions between sediments and soluble/dissolved organic matter across large gradients in sediment mineral properties. Extensive sorption experiments were combined with incubation experiments and spectroscopic (absorption/fluorescence) analyses. The resulting comprehensive dataset was carefully evaluated and revealed that the fractionation during sorption and desorption control composition and, thus, the bioavailability of dissolved organic matter. Sorptive interactions with minerals in sediments seemingly are important in regulating the fate and ecological impacts of soluble organic matter within permafrost landscapes.
The entire manuscript is well structured. It starts with a focused, still extensive and comprehensive summary of the scientific background, a detailed presentation of the environmental settings in the study area that, and, based on that, a straight-forward justification of the presented study. The Method section is extremely detailed, providing all necessary information to fully understand the scientific approach. The presentation of results, in the manuscript as well as in the supplement, is very neat, comprehensive, and logic. The discussion, as the rest of the manuscript, is also well-structured, easy to follow, with the arguments well presented (I like much the artwork and the figures), and the conclusions/implications well supported/justified by data and literature evidence. I enjoyed the reading very much, likely because it is in line with my own way of thinking. However, other people might consider some of the detailed reflections as too lengthy (see comments below).
Overall, I think the manuscript presents a great contribution to the field of carbon research in permafrost regions, with novel and important findings on organic matter processing at landscape scale. Also, I think it fits very well the focus and style of the journal and therefore recommend acceptance for publication after minor revision.
Specific comments