Spatiotemporal patterns of dissolved organic matter in Boreal Shield lakes and ice of the Laurentian Great Lakes

Dissolved organic matter (DOM) plays a vital role in lake ecosystems, yet its temporal and spatial variations in lakes remain poorly understood. This study investigates DOM dynamics in boreal lakes during the warm season and the Laurentian Great Lakes ice during winter. Sampling 10 boreal lakes in early and late June 2022, revealed subtle changes in DOM in the epilimnion and hypolimnion related to factors such as water residence time and stratification strength. In ice from the Great Lakes, lower dissolved organic carbon concentrations and a higher proportion of protein-like DOM were found compared to water, which mostly contained terrestrial-like DOM. Ice DOM composition varied with factors such as ice thickness, water nutrients, and DOM concentration in ice and water. In addition, we found that the potential release of protein-like DOM from ice to the water during spring melt is considerable and may fuel heterotrophic microbial metabolism.