Abstract
AbstractThe patterns of spatial and temporal variability in CO2 and CH4 emission from reservoirs are still poorly studied, especially in tropical regions where hydropower is growing. We performed spatially resolved measurements of dissolved CO2 and CH4 surface water concentrations and their gas‐exchange coefficients (k) to compute diffusive carbon flux from four contrasting tropical reservoirs across Brazil during different hydrological seasons. We used an online equilibration system to measure dissolved CO2 and CH4 concentrations; we estimated k from floating chamber deployments in conjunction with discrete CO2 and CH4 water concentration measurements. Diffusive CO2 emissions were higher during dry season than during rainy season, whereas there were no consistent seasonal patterns for diffusive CH4 emissions. Our results reveal that the magnitude and the spatial within‐reservoir patterns of diffusive CO2 and CH4 flux varied strongly among hydrological seasons. River inflow areas were often characterized by high seasonality in diffusive flux. Areas close to the dam generally showed low seasonal variability in diffusive CH4 flux but high variability in CO2 flux. Overall, we found that reservoir areas exhibiting highest emission rates (“hotspots”) shifted substantially across hydrological seasons. Estimates of total diffusive carbon emission from the reservoir surfaces differed between hydrological seasons by a factor up to 7 in Chapéu D'Úvas, up to 13 in Curuá‐Una, up to 4 in Furnas, and up to 1.8 in Funil, indicating that spatially resolved measurements of CO2 and CH4 concentrations and k need to be performed at different hydrological seasons in order to constrain annual diffusive carbon emission.
Highlights
Reservoirs are important components of the global carbon (C) cycle (Cole et al, 2007; Tranvik et al, 2009)
Estimates of total diffusive carbon emission from the reservoir surfaces differed between hydrological seasons by a factor up to 7 in Chapéu D'Úvas, up to 13 in Curuá-Una, up to 4 in Furnas, and up to 1.8 in Funil, indicating that spatially resolved measurements of CO2 and CH4 concentrations and k need to be performed at different hydrological seasons in order to constrain annual diffusive carbon emission
While the spatial variability in diffusive CO2 and CH4 emission in three of the four reservoirs has been described for one season in a previous publication (Paranaíba et al, 2018), we present here, for the first time, an analysis of the seasonal difference in the spatial variability of diffusive CO2 and CH4 emission in four contrasting tropical reservoirs
Summary
Reservoirs are important components of the global carbon (C) cycle (Cole et al, 2007; Tranvik et al, 2009). CO2 and CH4 emission from reservoirs can be highly variable in space due to the heterogeneity of flooded terrestrial habitats, hydrological gradients (e.g., across the longitudinal axis from river to dam), and variability in internal primary production (DelSontro et al, 2016; Linkhorst et al, 2020; Pacheco et al, 2015; Paranaíba et al, 2018; Teodoru et al, 2012). Even though ebullition is the dominant pathway of reservoir CH4 emissions (Deemer et al, 2016), ebullition and the relative quantitative importance of the different flux pathways are not considered here but treated in detail in a separate study (Linkhorst et al, submitted)
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