Reservoir Surfaces as Sources of Greenhouse Gases to the Atmosphere: A Global Estimate

Following flooding of landscapes to create any kind of reservoir, terrestrial plants die and no longer assimilate carbon dioxide (CO2) by photosynthesis (Figure 1), resulting in the loss of a sink for atmospheric CO2. In addition, bacteria decompose the organic carbon that was stored in plants and soils, converting it to CO2 and methane (CH4), which are then released to the atmosphere. All of the reservoirs examined to date emit CO2 and CH4 to the atmosphere (Table 1), but different landscapes contain different amounts of stored organic carbon in soils and vegetation (Schlesinger 1997), and so the potential for gas production and loss varies from site to site. For example, in the boreal region of Canada, a worst-case scenario is flooded peatlands because they possess a large store of organic carbon held in peat, which can decompose and be returned to the atmosphere as greenhouse gases over a long period (Kelly et al. 1997). Reservoirs that flood peatlands probably emit more greenhouse gases in the long term than reservoirs created over upland boreal forests, which have thin soil layers and no peat deposits.