A Preliminary Review of the Impact of Dam Reservoirs on Carbon Cycling

Payal Parekh
Monday, November 1, 2004


The International Hydropower Association (IHA) asserts that hydropower has a very low, or even positive impact on climate change because reservoirs (i.e., artificial lakes) sequester large amounts of carbon. The important question is whether reservoirs are important sinks for anthropogenic carbon. IHA uses an estimate indicating that reservoirs sequester 2.5% of global CO2 emissions. For several reasons this estimate gives a misleading indication of the climate impact of reservoirs. In some cases reservoirs will only be temporary sinks for carbon due to measures to mitigate reservoir sedimentation and dam decommissioning. Where reservoirs are permanent sinks their ability to sequester carbon will end once their storage capacity is filled with sediments. Furthermore, emissions of CO2 and CH4 from reservoirs may have a much higher negative climate impact than the positive impact due to carbon sequestration. In addition, reservoirs trap a significant amount of nutrients including silica that would otherwise have flowed to coastal waters. Silica is an important nutrient for diatom growth which plays an important role in the biological pump that transfers carbon to the deep ocean. A large amount of further research is needed to come up with any reliable estimates of the full climate impacts of reservoir construction.