the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 23 Jun 2025
Temporal and vertical changes in biological communities within snowpacks during melting season in Northern Japan
Abstract. During the snowmelt season, diverse cold-tolerant microbes thrive within snowpacks. Snow conditions in forested areas change temporally with air temperature and budburst of trees. However, their effects on relevant biological communities are not well documented. Based on periodic sampling throughout the snowmelt season (March–May, 2021), this study describes the temporal and vertical changes in biological communities, including snow algae, microinvertebrates, and snow fungi, within snowpacks in Northern Japan. The melting season was divided into three periods: when the daily minimum air temperature was below the freezing point (Period A), when it was above the freezing point and before the budburst of beech trees (Period B), and after the budburst over the snow surface (Period C). During Period A, two types of algae and one of fungus were ubiquitously observed in the snowpack. During Period B, the abundance of microbes increased in the surface layer and green algal blooms visibly emerged. Later in this period, nutrients (NO3-, NH4+, and PO43-) depleted, likely inhibiting algal growth and consequently restricting the microinvertebrate population. Surface layer nutrient concentrations increased again during Period C, thereby increasing the abundance of algae and microinvertebrates. This increase in nutrients was likely due to the rainwater and tree-derived litter deposited on the snowpack. Analyses of snow pits and cores revealed that the active layers of microbes were distinct between snow algae/fungi (surface layer) and microinvertebrates (subsurface layers), probably because of their preferable conditions for the snowpack layers. This study highlights potentially important patterns in the dynamic interactions between microbial communities and environmental changes within snowpacks, revealing how tree phenology and snowmelt conditions jointly shape the vertical distribution and seasonal succession of snow-ice microbes.
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RC1: 'Comment on egusphere-2025-2617', Daniel Remias, 12 Aug 2025
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This is a fascinating study about seasonal dynamics of snow microbes during the melting season at a location below canopy. Despite much research has been performed with blooms in snowpacks above timerline or on glaciers, the special situation of snow algae blooms under decidous trees in Japan still deserves more attention. The authors did an outstanding work in repeatatly sampling the same site throughout the season, developing a picture about temporal changes and vertical shifts within the community. The data are about snow algae, microinvertebrates and snow fungi.The new insight of this work is that birch buds fertilize snow and support phototrophlic microbes.
Bacterial abundances were not assessed because no molecular protocols were applied to describe the communty by metagenomics. Snow chemistry was evalated well, but changes in the snow-water-content, which are expected to influence vitality and migragion capacity of organisms within the snow, were not recorded. Please regard this comment as a suggestion for future studies.
The results are very detailled and sufficient figures and literature is provided. The manuscript sometimes has repetitive elements in argumentation or conclusion and the text could be condensed here and there without effecting the scientific message.
I suggest to alter the title in a way like "Temporal and vertical changes in microbial snow communities during the melting season below canopy in Northern Japan"
My comments in detail:
Line 10, start sentence with "During snowmelt, diverse ...
Line 23, delete "for the snowpack layers".
Line 32, algae bloom "in" snowpacks, not only "on"
Line 38, delete "during the melting season". Moreover, nutrients are not only deposited by snowfall and rain, but also airborne by winds.
Line 45, 46: Here, a very important reference is not cited (though later in the discussion): Hoham et al. 2008, who described in detail that balsam fir litter supports the growth of snow algae. Tuhs, in general, it has already been known that leaches from vascular plants support algae blooms.
Line 55: delete "to the snow surface", because it was never observed that flagellates swim actively to the surface, they stopp their migration earlier in time to reach a favourable layer below.
Line 56, insert "sometimes" before "concentrated", because this situation described by Hoham 1975b does occur all the times.
Line 61, snow "particles", I guess you rather mean "crystals"?
Line 63, maybe you prefer to cite a much newer and well fitting reference about the swimming activity of snow algae instead? See: Détain, A., Suzuki, H., Wijffels, R. H., Leborgne-Castel, N., & Hulatt, C. J. (2025). Snow algae exhibit diverse motile behaviors and thermal responses. io, 16(5), e02954-24. https://doi.org/10.1128/mbio.02954-24
Line 66, add to sentence "during the season."
Line 97, start sentence probably with "First surface green algal blooms ..."
Line 101, start sentence probably with "The remaining snow depth ..."
Line 106, so the two snow surfaces sampled adjacent to the blooms were your controls? If yes, state them as "white snow" control or similar.
Figure 1: Were all the photos taken at the same time of the day?
Line 112, please state the brand/type of ice auger
Line 122, which mesh size had the sieve?
Lines 138 - 140: It is a flaw that the classes of snow algae (A-D) are not described here! Ok, the authors perform no morphological identification based on frozen and rethawn material, which is difficult, but still, which would have allowed a tendative taxonomical addressing by LM even without marker sequencing. In this context, it is wrong to say that vegetative cells could be determined from the material, because Matsuzaki describred his key using laboratorial strain material. Contrary, with field material, the identification of non-vegetative cysts or spores would have been easier, even from frozen material. The reader does not need the information about exact species ID to understand the reported communty dynamics, but stillt the 4 morphological classes (in fact stages, because it does not mean 4 different species!) should be briefly presented.
Line 149, elution "from" tree-derived litter?
Line 177, delete last word "season"?
Lines 195.196, here again, it is not acceptable just to cite a reference to describe which organisms were present. At least the supplement should provide a brief description of the snow algae stages A, B, C and D, ideally with a microphotograph. The tardigrada and the snow fungi information is clear.
Question: were any snow ciliates observed during the study?
Line 200, maybe you mean "at the first time of sampling" instead of "for the first time ..."
Line 215, maybe you mean "from which on" instead of "at which"?
Line 252, delite "chemical" in headline?
Line 306, microbial growth: of microinvertebrates? Because algae thrive already in the first month of snowmelt?
Line 315, "fatty acids and in the form of cysts", I guess you mean "fatty acids and other compounds like osmolytes, which increase during cyst formation" ? Another reference describes that the cyst morphology itself supports freezing tolerance: Ezzedine, J. A., Uwizeye, C., Si Larbi, G., Villain, G., Louwagie, M., Schilling, M., ... & Maréchal, E. (2023). Adaptive traits of cysts of the snow alga Sanguina nivaloides unveiled by 3D subcellular imaging. Nature Communications, 14(1), 7500.
Line 318, maybe insert "in the upper snow layer" after "growth"? The deeper snow pack is hardly influenced by air temperatures.
Line 322, the "upper" snowpack?
Line 326 - 329: this needs more explanation, are you talking about the local climatic conditions and composition of rainfall, which is here influenced by oceanic conditions? If yes, make this more clear to the reader and insert at line 328 "in this region" after "growth" and maybe give another reference about precipitation in Northern Japan?
Line 345, "was" instead of "is"
Line 346, which period? The study period?
Line 360, delete "forest" in the headline?
Line 375, 376: please discuss reference Hoham et al 2008 in more detail and compare your results. In their study, it was needle trees which fertilized, in your case buds of broadleaf trees. This reference should already be mentioned in the introduction.
Line 377: rather "below" instead of "in" the tree covered-area?
Line 378: here I dissagree with the authors. Why the increased shading in course of budburst should enhance algal growth due to decreased irradiation? In a low light scenario, photosynthesis is light limited. Flagellates have to overcome this by migration to the surface.
Line 381: But snow algae cope with high-light stress by the formation of astaxanthin and the bloom turns red. This does not happen below canopy?
Linie 382: I do not understand the argumentation. Wow can reduced light intensity contribute to the uptake of nutrients? In terms of physiology? Furthermore, increase in intracellular chlorophyll content is a side effect of long-term low light conditions, particuallary for chlorophyll b.
Line 407: insert "or from soil" after "layers"?
Line 417, use "support" instead of "have triggered"?
Line 426: too general sentence. Which activity should be monitored in future?
Citation: https://doi.org/10.5194/egusphere-2025-2617-RC1
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