Award: OCE-2406176

Over the past few decades, the Great Lakes (containing ~ 20% of the freshwater on Earth) have been adversely impacted by anthropogenic stressors, and Lake Erie suffers from large scale, annually recurring cyanobacterial blooms in the summer months, while Lake Superior has experienced small cyanobacterial blooms in response to storm events. Understanding how lakes process nutrients in a nutrient-poor system (Lake Superior) vs. a nutrient-rich system (Lake Erie) will help us understand how to mitigate harmfuls algal blooms in both systems.

 

We investigated modern nitrogen cycling processes in the Great Lakes through seasonal incubations of sediment cores to measure rates of associated nutrient processes, including nitrogen removal through denitrification and anammox (pathways of N₂ gas production) and recycling through dissimilatory nitrate reduction to ammonium (DNRA).   We compared a system characterized by eutrophication and seasonal cyanobacterial blooms (Lake Erie) with one characterized by significant picocyanobacteria productivity but the near-absence of cyanobacterial blooms (Lake Superior). Our work shows that sediments perform an important ecosystem service in Lake Erie, removing excess nitrogen, while that service is hindered in Lake Superior by lack of organic carbon. We are evaluating the present and future impact of bloom formation on sediment ecosystem services, (i.e. nutrient removal vs. recycling within the lake system).  Our data will inform our collaborators’ work to use the nitrogen isotope composition of chloropigments as a molecular proxy of past cyanobacteria productivity in the Great Lakes through deep sediment core samples to address the history of blooms before European settlement.

Finally, this study contributed to the physical infrastructure resources available for future biogeochemical work in the Great Lakes. The sediment trap, time-series remote access water samplers, time-series particulate matter filter samplers, and mooring flotation purchased as part of this project has been added to the R/V Blue Heron’s shared use equipment pool and therefore the UNOLS shared use equipment pool and is available to the broader scientific community for future studies.   

 

Last Modified: 07/14/2025
Modified by: Silvia Newell