Dissolved gases in the deep water of lakes can be hazardous when extreme concentrations are reached. A sudden release of large amounts of gas can cost the lives of humans living in the neighbourhood, as it has happened at Lake Nyos in 1986. Since 2001, Lake Nyos gas risk has been mitigated by induced degassing, but the connection to the gas source is still in place and a regular survey needs to be implemented to guarantee safe conditions. Frequent sampling at the remote location of Lake Nyos requires an enormous effort and many analytical techniques are nearly impossible to run at the lake site. In this contribution, we combined a commercially available sound speed sensor with a CTD (electrical conductivity, temperature, depth) probe to gain an indirect but quantitative estimate of carbon dioxide concentrations at fine depth resolution (decimetre scale). Dissolved carbon dioxide increases sound speed but does not contribute to electrical conductivity. Hence the difference between measured and calculated (on the base of electrical conductivity, temperature and pressure) sound speed gives a quantitative indication of dissolved carbon dioxide. We highly recommend the implementation of the sound speed-CTD probe combination at Lake Nyos or at other gas-laden volcanic lakes as it could safeguard the people living in the area with acceptable cost and effort for the operators, as alarming CO2 concentrations in deep lake strata will be timely detected.

中文翻译：

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根据声速测量定量估计尼奥斯湖中的二氧化碳

当达到极端浓度时，湖泊深水中的溶解气体可能是危险的。大量气体的突然释放可能会导致附近居民的生命损失，就像 1986 年在尼奥斯湖发生的那样。自 2001 年以来，尼奥斯湖的气体风险已通过诱导脱气得到缓解，但与气源的连接仍然存在，需要进行定期调查以确保安全条件。在尼奥斯湖的偏远地区频繁采样需要付出巨大的努力，而且许多分析技术几乎不可能在湖区运行。在此贡献中，我们将市售声速传感器与 CTD（电导率、温度、深度）探测以获得精细深度分辨率（分米尺度）下二氧化碳浓度的间接但定量估计。溶解的二氧化碳会增加声速，但对导电性没有贡献。因此，测量和计算（基于电导率、温度和压力）声速之间的差异给出了溶解二氧化碳的定量指示。我们强烈建议在 Nyos 湖或其他富含气体的火山湖实施声速-CTD 探头组合，因为它可以以可接受的成本和操作员的努力保护居住在该地区的人们，因为深湖中的二氧化碳浓度令人担忧地层将被及时发现。因此，测量和计算（基于电导率、温度和压力）声速之间的差异给出了溶解二氧化碳的定量指示。我们强烈建议在 Nyos 湖或其他富含气体的火山湖实施声速-CTD 探头组合，因为它可以以可接受的成本和操作员的努力保护居住在该地区的人们，因为深湖中的二氧化碳浓度令人担忧地层将被及时发现。因此，测量和计算（基于电导率、温度和压力）声速之间的差异给出了溶解二氧化碳的定量指示。我们强烈建议在 Nyos 湖或其他富含气体的火山湖实施声速-CTD 探头组合，因为它可以以可接受的成本和操作员的努力保护居住在该地区的人们，因为深湖中的二氧化碳浓度令人担忧地层将被及时发现。