Influence of ice cover on bacterial community diversity and structure in remote arctic lakes

Arctic lakes are vital freshwater ecosystems that support wildlife, sustain Indigenous communities, and regulate regional biogeochemical cycles. These lakes experience prolonged periods of snow and ice cover, which shape their physical and chemical structure and profoundly influence microbial life. Rapid climate warming is disrupting these seasonal patterns by altering the duration, thickness, and extent of lake ice, with consequences for underwater light availability, stratification, mixing regimes, and nutrient dynamics. Among the most documented impacts is the progressive shortening of the ice-covered period, yet the biological consequences of these changes—particularly for microbial communities—remain insufficiently explored. Given that bacteria drive key ecological processes in Arctic lakes, including organic matter degradation, primary production, and nutrient cycling, understanding their responses to shifting ice conditions is essential for predicting ecosystem trajectories under climate change.

 

Recent exploratory work in Greenland has revealed that lake ice harbors unexpectedly abundant and metabolically active bacterial communities, often enriched in nitrogen species such as total nitrogen and ammonia compared to underlying waters. These ice-associated assemblages also differ taxonomically and functionally from those in the water column, including exhibiting an enhanced capacity to metabolize complex organic substrates. However, the mechanisms that lead to the development of these distinct microbial communities, their origin (including potential aerosol deposition), and their contributions to nitrogen cycling remain poorly resolved.

 

In this study, we investigated how ice cover structures microbial communities and nitrogen-transforming processes in lakes from both East and West Greenland. We combined environmental monitoring, ice and water chemistry, 16S rRNA gene sequencing, and metabolic assays to characterize microbial assemblages across ice, water column, and associated aerosol particles. Our findings show that lake ice forms a unique habitat enriched in nutrients and selective physicochemical conditions that promote distinct and active bacterial communities. The elevated nitrogen species and metabolic capacities observed in ice suggest that ice cover may act as both a reservoir and a seasonal pulse of microbial biomass and nutrients to the lake during melt. These insights highlight the ecological significance of ice-associated microbiomes and underscore the potential for ongoing shifts in ice phenology to reshape Arctic lake biogeochemistry in a warming climate.