A WHOLE ECOSYSTEM EXPERIMENT TO ASSESS HOW WATER COLUMN MIXING FREQUENCY IMPACTS METHANE CONCENTRATIONS AND EMISSIONS

The frequency of mixing events within ponds may dramatically impact methane production. While stratified, it’s common for pond bottom waters to become anoxic, creating favorable conditions for anaerobic methanogenic archaea to produce methane.  Alternatively, when ponds mix frequently, oxygen is generally high throughout the water column so methane production is less likely. Although ponds have been recognized as a significant source of methane to the atmosphere, emissions estimates vary widely, potentially due to these mixing related differences between ponds. In this study, we manipulated pond mixing regimes in experimental ponds to quantify impacts on methane emissions. All ponds were identical in surface area (30 x 30 m) and depth (1.9 m) and were naturally intermittently mixing (e.g., mixing every few weeks). We altered the mixing dynamics of three ponds using underwater propellers to create daily mixing conditions. From March - October 2023, we collected weekly samples to track surface and bottom methane concentrations, ebullitive flux, diffusive flux, and water chemistry. Thermistor lines at the center of each pond continuously tracked mixing dynamics. Both methane concentrations and emissions increased as mixing frequency decreased. The results of this study indicate that mixing frequency can explain some of the variability in pond greenhouse gas emissions.

Primary Presenter: Kathy Stenehjem, Cornell University (kjs297@cornell.edu)

Authors:

Kathy Stenehjem, Cornell University  (kjs297@cornell.edu)

Meredith Holgerson, Cornell University  (meredith.holgerson@cornell.edu)