Abstract
A new method to measure the CO2 concentration in lakes Nyos and Monoun using sound speed (SS) and electrical conductivity (EC) of the lake water was developed. Limnic eruptions at lakes Monoun and Nyos in Cameroon, characterized by a risk related to possible sudden release of magmatic CO2 gas dissolved in the lake water, occurred in 1984 and 1986 respectively, killing about 1800 residents. CO2 monitoring of the lake waters was initiated to prevent further disasters. Classical methods of CO2 measurement, which require chemical analysis of water samples, are not suitable for frequent and multi-point monitoring. Inspired by the method of measuring salt concentration using SS, we obtained data for dissolved CO2 (CO2(aq)) assuming the following formula , where Δv is additional SS due to dissolved ions and k1 and k2 are coefficients determined through experiments. The coefficient k1 was determined with temperature T (°C) dependence as 0.0323–0.000523T [l m s−1 mmol−1]. k2 was estimated to be 0.132 at Lake Nyos and 0.0930 at Lake Monoun. Once k1 and k2 values are obtained, [CO2(aq)] and
are calculated using the SS, T and EC.
- © 2017 The Author(s). Published by The Geological Society of London. All rights reserved
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