Aquatic ecosystems are a large but uncertain source of greenhouse gases (GHG) to the atmosphere. Managed aquatic ecosystems may be a disproportionately large source of emissions given their co-location with human activities and the influence of artificial water level management. The Intergovernmental Panel on Climate Change (IPCC) recently published a methodology for estimating anthropogenic GHG emissions from managed aquatic ecosystems (e.g., reservoirs, canals, ditches, farm ponds) and several countries now include this source in their national GHG inventory. National GHG inventories are used to track trends in GHG emissions, monitor compliance with emission-reduction commitments under international treaties, provide an important framework for incorporating aquatic systems into climate-relevant policy discussions, and highlight the need for accurate emission estimates. In this session, we solicit presentations that address challenges and recent advances in estimating GHG emissions from managed aquatic ecosystems. We encourage contributions focusing on 1) spatial and temporal patterns in emission rates, 2) biophysical drivers of GHG production and emission, 3) models (statistical or mechanistic) for predicting aquatic GHG emissions, 4) methods for upscaling and/or downscaling emission measurements to regional and/or national scales, and 5) identification and mapping of managed aquatic ecosystems. We welcome submissions by students, early career researchers, and researchers from BIPOC, LGBTQIA+, and other marginalized identities.

Lead Organizer: Jake Beaulieu, United States Environmental Protection Agency (Beaulieu.jake@epa.gov)

Co-organizers:

Bridget Deemer, U.S. Geological Survey (bdeemer@usgs.gov)

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

Rachel Pilla, Oak Ridge National Laboratory (pillarm1@ornl.gov)

Presentations

---

02:00 PM

Comparing atmospheric CO2 and CH4 exchange from a natural lake and a cascade reservoir in a boreal watershed across a seasonal cycle (8126)

Primary Presenter: Sajjan Heerah, Dalhousie University (sajjanh2@gmail.com)

Canada’s boreal landscapes are a globally important carbon sink. However, the majority of Canada’s hydroelectricity infrastructure is located in boreal landscapes and flooding disturbs their carbon cycle. Aspects of the aquatic boreal carbon cycle are uncertain and data on year-round, landscape-scale water-atmosphere carbon exchange are rare, limiting our understanding of hydroelectriy’s carbon budget impact. Here, we present CO₂ and CH₄ eddy flux data from the boreal La Romaine watershed in Québec, Canada. Parts of La Romaine were impounded for hydroelectricity starting in 2014. Since 2022, we have measured carbon fluxes at both the watershed’s oldest reservoir and a natural lake in the watershed. We estimated both water bodies’ atmospheric carbon flux and contrasted the fluxes’ drivers over the seasonal cycle by analyzing them in relation to atmospheric and hydrological measurements and with a biogeochemical model. We found that both water bodies were CO₂ sources, with the reservoir being a larger source. We observed a diel CO₂ flux cycle at both sites, indicative of algal photosynthesis or shoreline contamination and use a footprint model to assess this. The lake appeared to have near 0 CH₄ emissions while the reservoir was a small but significant CH₄ source. This may be related to pre-flood biomass and dissolved oxygen. Stratification and ice dynamics also appeared to play an important role in structuring emissions over the year. Our study contributes to our understanding of the boreal aquatic carbon cycle and will help constrain the carbon effect of hydroelectricity.

View Additional Details

---

02:15 PM

CONFIRMING THE C FOOTPRINT OF THE PAIX DES BRAVES (EASTMAIN 1) RESERVOIR 17 YEARS AFTER FLOODING (7792)

Primary Presenter: François Bilodeau, Hydro-Quebec (bilodeau.francois@hydro.qc.ca)

In the early 2000s, Hydro-Québec launched extensive research in the Paix des Braves reservoir watershed to study greenhouse gases (GHG) emissions at an integrative scale. This study presents the long-term GHG monitoring results for the reservoir and surrounding lakes. Diffusive emissions were measured directly on the reservoir during ice-free season and allowed to validate estimates obtained through gas concentration measurements made all year round using automated systems installed in the Eastmain-1 generating station. Degassing emissions were also calculated owing to this monitoring made in the water going through the turbines. The results indicate that despite a significant decrease in CO₂ dissolved concentration and emissions a few years after impoundment, CO₂ diffusive emissions still represented 90 % of the total emissions in CO₂eq in the 2018-2022 period. Despite a high spatial and temporal variability, CH₄ emissions represented only a small fraction of the total gross emissions (< 6.8 %). Total net reservoir emissions after 17 years are in the order of 438۰10³ tCO₂eq/yr, very close to the prediction made in 2012. Accordingly, current generation efficiency represents 76 gCO₂eq/kWh, number that could be further discussed considering natural CO₂ emissions that should not be attributable to the reservoir. The study confirms that hydropower in Quebec has a low carbon footprint.

View Additional Details

---

02:30 PM

PATTERNS AND DRIVERS OF CARBON EMISSIONS VERSUS SEQUESTRATION IN SIX HYDROPOWER RESERVOIRS IN THE SOUTHEASTERN UNITED STATES (7894)

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

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.

View Additional Details

---

02:45 PM

MONITORING BIOGEOCHEMICAL AND HYDROLOGICAL DYNAMICS IN A NEWLY CREATED INTERTIDAL WETLAND: IMPLICATIONS FOR GREENHOUSE GAS FLUXES AND MITIGATION STRATEGIES (7909)

Primary Presenter: Jasmin Dorinda, Plymouth Marine Laboratory (jaur@pml.ac.uk)

This study investigates the biogeochemical and hydrological factors controlling estimated greenhouse gas (GHG) fluxes in a developing intertidal wetland created during a flood defence improvement scheme in 2021. Through gas flux calculations, we assess whether the wetland located on the River Tamar, UK, has acted as a net source or sink of N2O and CH4 within the first two years since the wetlands creation. Additionally, we explore the application of remote sensing and high resolution drone imagery for mapping water inundation to understand hydrological factors contributing to GHG flux variability. Sampling 3 hours before and after high tide, our preliminary findings indicate significant (p < 0.05) seasonal variations in N2O and CH4 concentrations and estimated fluxes. Significant strong correlations were found between salinity, nitrite and GHG concentrations, indicating the importance of tidal and freshwater transport of material between the wetland and the river in driving microbial cycling of carbon and nitrogen. This study is actively taking place alongside the wetlands management plan and will continue to inform further wetland creation projects within the catchment. As nature-based solutions to flood risk, deteriorating water quality, habitat loss and climate change are implemented across the globe, understanding these dynamics is crucial for informing effective mitigation strategies to reduce GHG production in restored or created wetlands, thereby contributing to broader and achievable climate policies and mitigation efforts.

View Additional Details