What is the importance of distinguishing between net and gross emissions?
Ideally, a calculation of the warming impact of reservoirs should be based upon net emissions. This requires adjusting measurements of gross emissions at the reservoir surface and dam outlets to allow for whatever sinks and sources of greenhouse gases existed in the reservoir zone before submergence, the uptake of carbon through photosynthesis of plants and plankton in the reservoir, and the impact of the reservoir upon the pre-dam flows of carbon throughout the wider watershed. It is particularly difficult to assess the net impact of dams upon carbon dioxide fluxes, and net carbon dioxide emissions may be significantly smaller than gross emissions. However because reservoirs produce such huge amounts of methane relative to background fluxes, the difference between net and gross methane emissions is not likely to be significant. The INPE methane estimates are for gross emissions.
