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Hotspots of Diffusive CO 2 and CH 4 Emission From Tropical Reservoirs Shift Through Time
Author(s) -
Paranaíba José R.,
Barros Nathan,
Almeida Rafael M.,
Linkhorst Annika,
Mendonça Raquel,
Vale Roseilson do,
Roland Fábio,
Sobek Sebastian
Publication year - 2021
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1029/2020jg006014
Subject(s) - flux (metallurgy) , environmental science , seasonality , dry season , atmospheric sciences , wet season , inflow , spatial variability , hydrology (agriculture) , hydropower , chemistry , geology , geography , oceanography , ecology , statistics , cartography , mathematics , organic chemistry , geotechnical engineering , biology
The patterns of spatial and temporal variability in CO 2 and CH 4 emission from reservoirs are still poorly studied, especially in tropical regions where hydropower is growing. We performed spatially resolved measurements of dissolved CO 2 and CH 4 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 CO 2 and CH 4 concentrations; we estimated k from floating chamber deployments in conjunction with discrete CO 2 and CH 4 water concentration measurements. Diffusive CO 2 emissions were higher during dry season than during rainy season, whereas there were no consistent seasonal patterns for diffusive CH 4 emissions. Our results reveal that the magnitude and the spatial within‐reservoir patterns of diffusive CO 2 and CH 4 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 CH 4 flux but high variability in CO 2 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 CO 2 and CH 4 concentrations and k need to be performed at different hydrological seasons in order to constrain annual diffusive carbon emission.