Abstract
Many freshwater environments experience dramatic seasonal changes with some systems remaining ice-covered for most of the winter. Freshwater systems are also highly sensitive to environmental change. However, little is known about changes in microbial abundance and community composition during lake ice formation and times of persistent ice cover. The goal of this study is to characterize temporal dynamics of microbial communities during ice formation and persistent ice cover. Samples were collected in triplicate, five days per week from surface water in the Keweenaw Waterway between November and April. Environmental conditions along with microbial abundance and microbial community composition was determined. Distinct community composition was found between ice-free and ice-covered time periods with significantly different community composition between months. The microbial community underwent dramatic shifts in microbial abundance and diversity during the transitions into and out of ice cover. The richness of the microbial community increased during times of ice cover. Relatives of microbes involved in nitrogen cycling bloomed during times of ice cover as sequences related to known nitrifying taxa were significantly enriched during ice cover. These results help to elucidate how microbial abundance and diversity change over drastic seasonal transitions and how ice cover may affect microbial abundance and diversity.
Highlights
Microbes in aquatic environments are drivers of many biogeochemical cycles
Molecular techniques and generation sequencing provided a detailed survey of the microbial community in the Keweenaw waterway through a period of ice cover
Our results suggest that ice formation may cause shifts in the microbial community composition
Summary
Microbes in aquatic environments are drivers of many biogeochemical cycles. Many temperate freshwater ecosystems experience dramatic seasonal variation with some environments remaining ice-covered for most of the winter[1]. Changes in microbial activity during ice-covered periods have implications on the ecosystem function and biogeochemical processes in these settings[2,3,4] Factors such as temperature, salinity, and dissolved oxygen may all act as limiting constraints on microbial activity and impact microbial diversity. Higher resolution variability on a day-to-day basis has been more finely investigated in marine settings[15,20] with a few time series studies in freshwater systems[21] These studies in the oceans have shown that there were dramatic and rapid shifts in the marine microbial community composition following seasonal change and in the days following phytoplankton blooms[15,20]. Despite our growing knowledge of temporal variation in freshwater microbial communities, very little is known about the stability of freshwater microbial communities on daily timescales, especially during the formation and persistence of lake ice
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