Summer 2023 Greenhouse Gas Fluxes at Cedar Bog Lake, MN

Freshwaters are significant natural sources of greenhouse gasses (CO2, CH4, and N2O) to the atmosphere. Small freshwater bodies like Cedar Bog Lake, where Ray Lindeman did his classic work on the ‘Trophic dynamic concept in ecology’,  are increasingly being recognized as having large greenhouse gas emissions compared to their small size. Measured emissions can vary by orders of magnitude. To assess trends in greenhouse gas emissions at Cedar Bog Lake, concentrations and emissions of CO2, CH4, and N2O were measured roughly weekly over a two-month period from the middle of July until the middle of September in 2023. Over the two-month sampling period, Cedar Bog Lake was a net source of CH4 (mean 775.19 [se 556.00] mg CH4 m-2 d-1). CO2 fluxes varied more between being a source and a sink but was overall a source over the sampling period (mean 411.60 [se 696.29] mg CO2 m-2 d-1). N2O concentrations were measured in situ but average fluxes were not calculated since there was no appreciable difference between sample flux (floating chamber measurement) and in headspace concentrations at depth between the sample and the atmosphere. Both CH4 and CO2 concentrations were highest at the deepest measured depth (only 1.2 m) and concentrations peaked in mid-August which corresponded to the hottest part of the summer and the lowest concentration of O2 at the bottom. In general, there was a high degree of both spatial (within lake) and seasonal heterogeneity in the floating chamber measurements used to calculate the greenhouse gas fluxes from Cedar Bog Lake.

Primary Presenter: William Brown, University of Minnesota (brow6589@umn.edu)

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