PATTERNS AND DRIVERS OF CARBON EMISSIONS VERSUS SEQUESTRATION IN SIX HYDROPOWER RESERVOIRS IN THE SOUTHEASTERN UNITED STATES

Reservoirs are a significant source of atmospheric C, but emission rates vary in space and time. Here, we compared C emissions via diffusion and ebullition pathways at several stations within six large hydropower reservoirs in the southeastern US that were previously sampled in summer 2012. We revisited the same stations and used similar methodology to compare emissions rates and predictors of emissions, and to compare with modelled emission estimates. Field data showed that CO₂ diffusion was the dominant flux pathway during 2012 and 2022 at > 95% of stations. However, the direction of the CO₂ diffusive flux shifted between 2012 and 2022; all but three stations were CO₂ sources in summer 2012, but every station was a CO₂ sink in summer 2022. In only two stations were CH₄ emissions high enough to result in net C emissions due to the strong negative CO₂ flux. Next, we explored drivers of spatial variation and found that indicators of greater algal production were associated with CO₂ sequestration (negative CO₂ flux), including chlorophyll-a concentration and dissolved oxygen saturation. Additional sampling outside the summer highlighted the importance of seasonal phenology in primary production on the direction of CO₂ diffusive fluxes, which shifted to positive CO₂ fluxes by the end of August as productivity decreased. Our results demonstrate the importance of capturing negative CO₂ diffusive fluxes in the field and models to improve understanding of the seasonal drivers of these fluxes when considering spatial and temporal upscaling.

Primary Presenter: Rachel Pilla, Oak Ridge National Laboratory (pillarm@ornl.gov)

Authors:

Rachel Pilla, Oak Ridge National Laboratory  (pillarm@ornl.gov)

Natalie Griffiths, Oak Ridge National Laboratory  (griffithsna@ornl.gov)

Chloe Faehndrich, University of California, Berkeley  (chloe_faehndrich@berkeley.edu)

Allison Fortner, Oak Ridge National Laboratory  (fortneram@ornl.gov)

Trent Jett, Oak Ridge National Laboratory  (jettrt@ornl.gov)

Michael Jones, Oak Ridge National Laboratory  (jonesmw@ornl.gov)

Nikki Jones, Oak Ridge National Laboratory  (jonesnj@ornl.gov)

Jana Phillips, Oak Ridge National Laboratory  (randolphjd1@ornl.gov)

Carly Hansen, Oak Ridge National Laboratory  (hansench@ornl.gov)

Bilal Iftikhar, Oak Ridge National Laboratory  (iranabilal122@gmail.com)

Henriette Jager, Oak Ridge National Laboratory  (jagerhi@ornl.gov)

Paul Matson, Oak Ridge National Laboratory  (matsonpg@ornl.gov)