The harmful effects of releasing water at surface level

There would be multiple and disastrous consequences if the water were to be wrongly reinjected. First of all, if the exploitation were to cause significant mixing of the waters and the physical destabilisation of the lake, bringing the deep waters to the surface, a considerable amount of methane and carbon dioxide would be released into the atmosphere, rendering it fatally toxic for the 2 million inhabitants around the lake. This type of disaster already took place at lakes Monoun and Nyos in Cameroon, in 1984 and 1986 respectively. Secondly, this water is very rich in ammonia and phosphates, nutrients that have accumulated for centuries in this anoxic area. If these waters were to be reintroduced too close to the surface, this would lead to a massive injection of these nutrients, the basic resource of phytoplankton, thus allowing the latter to proliferate. A sudden abundance of biomass, as well as the likely change in the dominant phytoplanktonic species would subsequently destabilise the lake’s entire food chain, leading to the degradation of the ecosystem following eutrophication. A disastrous biological impact that would have significant repercussions on local fishing, in particular. A third and final risk is linked to another unusable waste gas, H₂S, or hydrogen sulphide. This dissolved and highly reduced gas reacts with oxygen molecules. Discharged into the surface waters, it would make the (normally oxygenated) surface layer – where the lake’s aquatic life has developed – anoxic and therefore uninhabitable. “It’s an effect that was neglected in the methane exploitation scenarios”, Jean-Pierre Descy laments. “For the moment, there are no plans to reinject the hydrogen sulphide at depth, the idea being to release it on the surface.”

Besides the warnings issued by scientists, a voluminous biological database of the lake, concerning its current state, has been established thanks to a successful project funded by the Coopération Technique Belge (CTB). By means of comparison, it will be possible to assess the possible impacts of methane exploitation on the ecosystem in the future, and if necessary, take appropriate action.

The incredible discovery of a primitive ocean analog

An intellectually dishonest argument in favour of methane extraction is often put forward. Removing this gas would reduce the risk of an overturn, a natural disaster resulting from gas suddenly erupting from deep lake water following a dramatic change in the lake’s stratification. “In reality, the lake’s structure is so stable that unless a colossal amount of energy is released, such a risk is currently almost inexistent”, Alberto Borges argues. “Another risk would be that the deep waters would reach saturation point and the excess gas would naturally rise to the surface.” It is true that the methane seems to be continuing to accumulate at the bottom of the lake. But according to the estimations conducted within the framework of the project, the threshold would only be reached in a century and it is quite easy to measure its evolution. Therefore, the extraction of the methane isn’t an ecological emergency; it is above all dictated by strictly economic interests, with the exception of Kabuno Bay, to the north of Lake Kivu, the only potentially unstable place because the limit between the surface water and anoxic waters is relatively shallow and this bay is close to Nyiragongo, an active volcano. The waters could indeed overturn and release large amounts of CO₂, which would be fatally toxic for the local populations, especially in the nearby town of Goma. The bay is currently undergoing preventive degassing, a necessary process that is unfortunately destabilising the unique ecosystem which dates back to one of the great revolutions of primitive life on Earth. Today, all the world’s oceans have a much higher concentration of sulphur than iron. The opposite is true of Kabuno Bay, making it truly unique. It waters contain far more iron than sulphur. This distribution is due to the physical structure of the location as well as the volcanic composition of its watershed. A peculiarity that the bay shares with primitive oceans, dating back to a time when the Earth was deprived of oxygen. It is the subject of an article published by the EAGLES team, which Alberto Borges is thrilled about. “During the Precambrian period, the oceans were very rich in iron and were in addition anoxic. Specific bacterial communities, capable of photosynthesis combined with iron oxidation, started to produce oxygen in the oceans, which then transferred to the atmosphere. An essential process in the history of life on Earth. Kabuno Bay is the only place in the world where this type of bacteria still exists today. True living fossils that allow us to go back to Precambrian times, and whose existence we could only imagine up until now.”

Climate change and lake productivity

The other major section of the project concerned the estimation of the lake’s evolution and its productivity according to climate variations. It had already been noted that there were significant ecological responses to seasonal variations which influenced the lake’s relative poverty, especially in fish. The surface area containing sufficient oxygen for them to survive only ranges from 0 to a maximum of 60 metres during the dry season and approximately 40 metres during the rainy season. During the rainy season, the water becomes more stratified, and the nutrients necessary for algae to grow and the rest of the food chain are trapped in the very deep waters. It is necessary to wait for the dry season to return so that the surface water cools through evaporation and descends to a greater depth. This mixing is also encouraged by higher winds. The nutrients are then available again in the surface area allowing the production of biomass.