the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 15 Jul 2026
Chronic environmental radioactivity suppresses microbial diversity and activity in threatened glacier surface ecosystems
Abstract. Environmental radioactivity can act as a chronic stressor not only in nuclear accident zones but also in ecosystems that capture atmospheric pollutants, yet its effects on organisms remain understudied. Using biologically active glacier sediments that concentrate natural and legacy radionuclides, this study provides the ecosystem‑scale test of how chronic radiation affects microbial life outside nuclear accident zones. Across a radioactivity gradient, higher levels corresponded to significant declines in microbial richness and phylogenetic diversity. Functional diversity decreased, with fewer KEGG Orthologs, indicating elevated radioactivity as a selection factor. However, showing strong redundancy in this ecosystem, as key functions remain in the higher radioactive habitat. Despite stable overall functional profiles, an essential DNA repair pathway (non-homologous end joining) was enriched. Metatranscriptomic revealed significant metabolisms and growth suppression, shown by reduced RNA transcripts per DNA copy for metabolisms pathways. These results show that chronic environmental radiation is a strong, underrecognized ecological factor that decreases the biodiversity of glaciers threatened by climate change.
Competing interests: Prof. Roberto Ambrosini serves as associate editor for the special issue to which this paper belongs.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.- Preprint
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2026-4043', Emily Louise Mary Broadwell, 30 Sep 2026
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RC2: 'Comment on egusphere-2026-4043', Anonymous Referee #2, 03 Oct 2026
This manuscript addresses an interesting and potentially important question: whether chronic environmental radioactivity associated with natural and legacy anthropogenic radionuclides can influence microbial communities in cryoconite ecosystems. The authors combine a relatively large-scale survey across Alpine glaciers with a within-glacier metatranscriptomic gradient analysis, which is potentially valuable. However, I have several major concerns regarding the attribution of the observed microbial patterns specifically to radioactivity. In particular, the main radioactivity gradient occurs among glaciers, making radioactivity potentially confounded with glacier identity and other glacier-specific environmental factors. In addition, the functional conclusions are largely based on PICRUSt2 predictions rather than directly measured metagenomic functional profiles, whereas the metatranscriptomic analysis is restricted to a single glacier. These limitations substantially affect the strength and generality of the causal conclusions currently drawn from the data.
Major comment
- The critical issue is the extent to which differences in radioactivity can independently explain variation in microbial communities among glaciers. Microbial communities across Alpine glaciers may differ for many reasons unrelated to radioactivity, including geographic location, climatic conditions, atmospheric deposition, substrate and mineral composition, organic matter content, nutrient availability, and other glacier-specific environmental characteristics. These factors have been documented as important drivers of glacier microbial communities in previous studies. However, the current manuscript controls only for glacier size and elevation, which is unlikely to be sufficient to exclude potential confounding effects. The authors should therefore clearly specify which environmental variables were measured or available for each glacier and assess whether the relationship between radioactivity and microbial diversity remains after accounting for relevant environmental and spatial variation.
- The functional analyses presented in Sections 3.3 and 3.4 rely on PICRUSt2 predictions derived from 16S rRNA gene profiles. Although PICRUSt2 is a useful approach for generating hypotheses regarding functional potential from marker-gene data, these predictions depend on the availability and phylogenetic relatedness of reference genomes and inevitably carry uncertainty associated with inferring genomic content from taxonomic composition. Therefore, predicted functional richness or pathway abundance should not be interpreted as direct measurements of functional capacity. This limitation is particularly important because the authors also have metatranscriptomic data. The rationale for relying primarily on PICRUSt2 to support conclusions regarding functional simplification and the enrichment of DNA-repair functions therefore requires further consideration. The authors should also consider whether the observed decline in predicted functional richness is simply a consequence of the decline in taxonomic richness, rather than evidence for an independent loss of functional potential.
- The within-glacier metatranscriptomic analysis is arguably one of the most valuable aspects of this study because it provides an opportunity to examine microbial responses along a local radioactivity gradient while reducing some of the confounding associated with comparisons among different glaciers. Although the results indicate an association between radionuclide activity and transcriptional profiles within Dosdè Glacier, this alone is insufficient to establish that the same relationship occurs across Alpine glaciers more generally. Furthermore, although all 15 metatranscriptomic samples were collected from the same glacier, the authors should examine whether radionuclide activity covaries with other local environmental characteristics. In particular, it would be important to evaluate potential associations with cryoconite organic matter content, mineral composition, particle size, nutrient availability, and other relevant physicochemical variables.
- The manuscript should more clearly distinguish among transcriptional activity, metabolic activity, and microbial growth. A decrease in RNA transcripts relative to DNA copies for selected pathways provides evidence for reduced transcriptional activity relative to genomic potential, but does not necessarily demonstrate reduced microbial growth or reproduction. More generally, the manuscript should consistently distinguish between correlation and causation and avoid interpreting observational associations along radioactivity gradients as direct evidence that radioactivity itself caused the observed ecological responses.
Citation: https://doi.org/10.5194/egusphere-2026-4043-RC2
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Buda et al., present a detailed assessment of microbial communities within the cryoconite holes across alpine glaciers and how they are impacted by ionising radiation. The broad geographical coverage and integration of community composition with a range of environmental variables provides valuable insights to how IR can impact glacier surface ecosystems. Overall, the study makes a useful contribution to our understanding of such environments. However, several aspects of the manuscript would benefit from minor revision. Find more detailed comments below.
Line 72: Perhaps expand on how these organisms drive the accumulation of such pollutants
Line 75-76: Include some references as to the impacts of climate change on these surface ice systems.
Line 86: Make clear in the introduction that this study is primarily focused on the glaciers of the Alps. Also maybe include a little more background to the studies of these environments specifically and how processes here differ from larger polar ice sheets.
Line 100: Could you include a figure with a map of the sample sites and some photos of the cryoconite holes that were sampled?
Line 111: Why use this data set from roughly 5-6 years before the sampling was taking place? Also then using another from a different time for one of the 16 glaciers. Would be better to estimate using satellite imagery from the time the samples were collected?
Line 136: Confused by the word ‘Total’ here. I imagine it was not a 100% DNA extraction yield?
Line 251: Again I wonder about using this older dataset for estimating the glacier surface area. Knowing how much glaciers are changing their extent, I feel that this value could have changed significantly in these years.
Line 291: Rephrase ‘we did sampling’ to ‘samples were collected’
Line 295 (Figure 1): Perhaps relabel Figure 1 as ‘Prokaryotes’ rather than ‘Bacteria’. Also why is one plotted to a ‘phyla’ resolution and one to a ‘Class’ resolution?
Line 313: Consider rephrasing ‘marginally non-significant’, it either is or isn’t statistically significant.
Line 363-366: I think this sentence
Line 380: Given that this is a key part of the results section, it would be beneficial to include a more comprehensive background to these pathways and the functions they serve within these communities in the introduction.
Line 392 (Figure 4): Please include the statistical analysis used in the Figure caption. I would also suggest including the full pathway names for the x-axis rather than acronyms.
Line 416-419: Again I feel like this section belongs more in the discussion.
Line 432: I would start here with a summary of the work done in this study and the findings rather than jumping straight into other studies.
Line 440: This would be better suited to the introduction.
Line 496: Although this section provides a detailed overview of the methods used in this paper, I think the manuscript would benefit from this being synthesised across the methods and discussions sections where relevant, rather than being presented as a separate section.