DEPTH DEPENDENT DRIVERS OF LAKE ECOSYSTEM METABOLISM

Major drivers of whole lake ecosystem metabolism include lake morphometry and watershed characteristics. However, less is known about relationships between ecosystem metabolism and environmental drivers at different depths. Here, we examined how nutrients, chlorophyll, and seston stoichiometry influence gross primary production, respiration, and net ecosystem production at different depths within the photic zone. Our focal lake was Treetop Pond, a small dimictic eutrophic lake with a deep chlorophyll maximum located in Southeast Michigan. We installed a vertical chain of eight dissolved oxygen loggers in the lake from April to October 2024 measuring oxygen and temperature dynamics at 15-minute intervals. We collected weekly grab samples every meter through the water column for dissolved and total nitrogen (N) and phosphorus (P), chlorophyll a, particulate carbon (C), N, and P. Shortly after the onset of stratification, the hypolimnion became anoxic; anoxia later extended into the metalimnion during the growing season. Above the thermocline, dissolved oxygen was often supersaturated. Generally, there was more chlorophyll, lower seston C:P and N:P in the metalimnion (3m) than the surface. However, between late June and early August, dissolved oxygen concentrations at 3m declined, likely caused by vertical diffusion to the deeper layers. This stopped once the thermocline deepened below 3m. Overall, our results highlight that even with a deep chlorophyll maximum, vertical oxygen diffusion can outpace production and cause hypoxic conditions.

Presentation Preference: Oral

Primary Presenter: Olivia Sowa, Oakland University (oliviasowa@oakland.edu)

Authors:

Olivia Sowa, Oakland University  (oliviasowa@oakland.edu)

Hailee Mersino, Oakland University  (hmersino@oakland.edu)

Ryan Andrews, Oakland University  (ryanandrews@oakland.edu)

Scott Tiegs, Oakland University  (tiegs@oakland.edu)

Nicole Wagner, Oakland University  (nicolewagner@oakland.edu)