Abstract

The degassing systems installed in the early 2000s at lakes Nyos and Monoun, Cameroon, have been working well, resulting in significant removal of dissolved gas. However, the systems of both lakes started losing their capability due to a reduced CO₂ partial pressure in the bottom waters, especially after installation of additional pipes in 2011. After initiation of a degassing operation, changes in CO₂ profiles in the bottom layer of Lake Nyos over time showed that gas-poor shallow water has descended to the bottom, leaving little CO₂ in the bottom water. The degassing system at Lake Monoun has completely lost its gas self-lift capability as the reduced CO₂ partial pressure in the bottom water is too low to sustain the gas-lift system, and all the degassing pipes stopped working in 2010. This situation led to the accumulation of CO₂ due to continued natural recharge of magmatic CO₂. To compensate this recharge of gas, we installed a new deep water removal system that is driven by solar power at Lake Monoun in December 2013. This system does not need power lines, fuel or complicated maintenance, thus it is convenient for remote lakes such as lakes Monoun and Nyos.