Date of Award


Document Type

Open Access Master's Thesis

Degree Name

Master of Science in Biological Sciences (MS)

Administrative Home Department

Department of Biological Sciences

Advisor 1

Trista J. Vick-Majors

Committee Member 1

Amy M. Marcarelli

Committee Member 2

Michael R. Gretz


Ice-covered lakes are vulnerable to environmental change, especially those in the Northern Hemisphere where ice cover is rapidly declining due to global warming. These changes can alter metabolic processes and disrupt carbon cycling driven by primary producers who form the base of the food chain and are key to sustaining ecosystem function. Photosynthetic primary production and dark carbon fixation under the ice in the Keweenaw Waterway, a temperate freshwater system that is ice-covered for ~3 months out of the year, were studied using a carbon isotopic labeling (14C-bicarbonate) technique. Water samples were collected weekly during ice cover and monthly during summer from winter 2021 into 2022. Environmental conditions were also measured at the time of sampling. Results revealed photosynthetic primary production was substantially reduced during ice cover, however, there was a relatively high abundance of chlorophyll-a present during the ice-covered periods suggesting photoadaptation. Dark carbon fixation was also suppressed during the ice covered period compared to the open water period. Extracellular release of dissolved organic carbon was substantially higher in dark carbon fixation compared to photosynthetic primary production suggesting dark carbon fixation may be an important source of dissolved organic carbon. Together, these findings give insight into the relative importance of photosynthetic primary production and dark carbon fixation to aquatic carbon production and its response to changing environmental conditions.