Spatial and Temporal Variability of Diffusive CO₂ and CH₄ Fluxes From the Amazonian Reservoir Petit‐Saut (French Guiana) Reveals the Importance of Allochthonous Inputs for Long‐Term C Emissions

Abstract

Variability in greenhouse gas emissions from reservoirs creates uncertainty in global estimates of C emissions from reservoirs. This study examines the temporal and spatial variability in CO2 and CH4 surface water concentrations and diffusive fluxes from an Amazonian reservoir using an original data set combining both a high temporal (1 central site × 22 years) and spatial (44 sites × 1 season) resolution monitoring. The gas concentrations at the central site decreased over time and suggested reduced bioavailability of C in the initial flooded soil but exhibited strong seasonal variation. Not accounting for this variability may result in uncertainties in estimates of annual concentrations (ranging from −68.9% to +260% for CH4 and from −71.5% to +156% for CO2) and thus in estimates of diffusive gas emissions. Gas concentrations and diffusive fluxes exhibited high spatial variability in the reservoir, 24 years after impoundment. In particular, diffusive fluxes were higher in littoral and transitional areas than in open areas, suggesting a large contribution of allochthonous C to current gaseous emissions. Not accounting for this spatial variability in diffusive fluxes may underestimate the total emissions expressed in CO2 equivalents from the whole reservoir by 50.7%. Our study stresses the importance of well‐resolved temporal and spatial monitoring to provide reliable estimated of C emissions and a comprehensive understanding of the processes involved; both of these inputs are needed to support decision‐making for developing energy strategies.

The tropical cookbook: Termite diet and phylogenetics—Over geographical origin—Drive the microbiome and functional genetic structure of nests

“…Nests from 28 termite colonies were collected during 2019 and 2020 at different sampling campaigns in South America and Africa ( Table 1 ). The first sampling site is located in French Guiana, Petit-Saut Dam area, which is located in the Sinnamary River (5°03′ N, −53°02.76′ E), and is characterized by hot and humid weather throughout the year with two dry seasons (February to March and July to November) and two rainy seasons (Colas et al, 2020 ).…”

Inland Water Greenhouse Gas Budgets for RECCAP2: 1. State‐Of‐The‐Art of Global Scale Assessments

“…Though some studies (Deemer et al., 2016; DelSontro et al., 2018; Raymond et al., 2013) have linked CO 2 variability in lakes and reservoirs to predictors such as waterbody size, mean annual precipitation, and ecosystem productivity, the controls on within‐system CO 2 spatial and temporal variations are not well understood and effective scaling relationships are still in need to better represent CO 2 evasion from lakes and reservoirs. Further, characterizations of spatial variability within water bodies are rather scarce, and the representativeness of the sampling site within an aquatic system is a large source of uncertainty (Colas et al., 2020). Finally, our estimates of reservoir CO 2 emissions do not account for fluxes from hydroelectric turbines and dam outlets, where deep, hypolimnetic water enriched in CO 2 is released (Figure 2a).…”

“…Such a well‐defined footprint is advantageous for studies of local flux regulation and for distinguishing variability in space versus time. Concurrently, the small size of the footprint leads to potentially high uncertainties in the extrapolation of flux chamber measurements to large areas, without numerous representative measurements (Colas et al., 2020). Eddy covariance towers, though less common and only applicable in standing water bodies of a certain size have the advantage of generating net fluxes (i.e., emission or uptake) from a larger surface area (depending on height, surface roughness and wind speeds, eddy covariance towers can have a footprint of up to 3‐km radius (Chu et al., 2021)), thus delivering a more representative emission rate (Podgrajsek et al., 2014).…”

Effect of river damming on nutrient transport and transformation and its countermeasures

“…Therefore, eutrophic reservoirs often have higher CH 4 emissions than oligotrophic reservoirs (Deemer et al, 2016). Tropical reservoirs typically emit more gaseous C than temperate reservoirs because of their larger surface area, higher soil organic C content, and warmer water temperatures (Fearnside, 2002;Abril et al, 2005;Kemenes et al, 2011;Colas et al, 2020). Over time, long-term sediment buildup in aging reservoirs may increase nutrients downstream, which could result in large-scale hazardous algal blooms (HABs) (Justic et al, 2002;Paerl et al, 2006;Fox and Ford, 2016;Fernandez-Alias et al, 2022;Liu et al, 2022).…”