Greenhouse Gas Emissions from Freshwater Reservoirs: What Does the Atmosphere See?

Abstract

Freshwater reservoirs are a known source of greenhouse gas (GHG) to the atmosphere, but their quantitative significance is still only loosely constrained. Although part of this uncertainty can be attributed to the difficulties in measuring highly variable fluxes, it is also the result of a lack of a clear accounting methodology, particularly about what constitutes new emissions and potential new sinks. In this paper, we review the main processes involved in the generation of GHG in reservoir systems and propose a simple approach to quantify the reservoir GHG footprint in terms of the net changes in GHG fluxes to the atmosphere induced by damming, that is, 'what the atmosphere sees.' The approach takes into account the pre-impoundment GHG balance of the landscape, the temporal evolution of reservoir GHG emission profile as well as the natural emissions that are displaced to or away from the reservoir site resulting from hydrological and other changes. It also clarifies the portion of the reservoir carbon burial that can potentially be considered an offset to GHG emissions.

Estimating Carbon Dioxide (CO2) Emissions from Reservoirs Using Artificial Neural Networks

“…Recent study shows that the net carbon emissions from reservoirs are determined by different types of areas before flooding and provides a simple approach to quantify the net CO2 emissions [47]. Future studies are therefore necessary to simulate and predict …”

“…However, CH 4 is a more powerful GHG than CO 2 [12]. Unlike CO 2 emissions, CH 4 emissions from reservoirs are new and anthropogenic [47]. Therefore, CH 4 footprint should be simulated and the magnitude needs to be estimated based on various released pathways in the future.…”

The carbon footprint of a Malaysian tropical reservoir: measured versus modelled estimates highlight the underestimated key role of downstream processes

“…For each flux pathway, annual flux was estimated as the average of the sampling campaigns. Ecosystem-scale estimate of surface diffusion was calculated for each campaign as the average of measured flux rates applied to the reservoir area for N 2 O, and for CO 2 and CH 4 it was obtained by spatial interpolation of measured fluxes over the reservoir area based on inverse distance weighting with a power of two (a power of one yields similar averages, CV < 11 %) using package gstat version 1.1-6 in the R version 3.4.1 software (Pebesma, 2004;R Core Team, 2017). Ebullition at the reservoir scale was calculated as the average of measured reservoir ebullition rates applied to the littoral area (< 3 m deep).…”

Debating dams: The World Commission on Dams 20 years on

“…Globally, however, hydropower is still generally considered a “green” energy source (Käkönen & Kaisti, ), and (rightly or wrongly) many dams are funded for example, within the Kyoto Protocol's Clean Development Mechanism (CDM) explicitly to mitigate climate change (Erlewein & Nüsser, ; Rousseau, ). The most recent research on the relationship between dam reservoirs and greenhouse gas emissions suggests that the climate change impact of dams is not clear‐cut, and needs to be evaluated on a case‐by‐case basis, as for example, CH 4 emissions may vary with reservoir age, latitude, or productivity, among other factors (Deemer et al, ; Prairie et al, ). These issues are not completely new—some scholars had warned about the climate change impact of dams much earlier (e.g., Fearnside, ) and the WCD knowledge base discussed the relationship between dams and climate change extensively (WCD Secretariat, ).…”