SG: Microbes promote ice formation in inland waters

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Recent results suggest that ice formation in northern lakes, where ice cover forms seasonally, may be assisted by the presence of filamentous diatoms (microscopic plankton). This project will explore the idea that such biological ice nucleation actually facilitates recruitment of these diatoms, which cannot swim, from lake sediments where they live through summer up to the overlying ice where they live in winter. The bottom of the ice surface is a favorable zone for them because of the light that penetrates the ice and illuminates the diatoms; that light doesn't reach the lake bottom. To test this idea, the distribution of diatoms in summer and winter will be examined across a range of lake sizes. Who, or what, is responsible for ice nucleation will be determined using both regular microscopes and modern genome sequencing. It is unclear whether the diatoms themselves are responsible for ice nucleation, or if it might rather be the result of bacteria growing on the diatoms. This will also be investigated. Finally, the implications of this ice nucleation activity will be investigated to see if a model can be developed that is generally applicable to ice formation in lakes around the world. This is one of the first studies of the role of microbes in the formation of ice cover in freshwater ecosystems, with most previous work done in high latitude oceans. The project could uncover a new stage of the life cycle of phytoplankton and help explain why sometimes they bloom in lakes during winter. The associated bacteria on the diatoms may also benefit from their association with the phytoplankton. Results of this study may change classical thinking about ice as important to lake biology. The broader impacts of the proposed research will include a partnership with the NSF program called iEvolve with STEM. Ice covered lakes, streams and rivers are uniquely familiar to students in northwestern Ohio, although most students probably do not realize that they are lively, even in winter. A central feature of iEvolve is the integration of students in a citizen science program that reaches across the curricula of two local school districts. Through this association, the project will involve middle school teachers as Qualified Data Collectors as part of the Ohio Credible Data Program. Under teacher supervision, students will collect samples for water quality analysis through the seasons and be directly exposed to the vitality of lakes in winter.