The secrets of Lake Kivu
10/26/12

An international and interdisciplinary team of researchers has published a work synthesizing all current knowledge about Lake Kivu. A lake that has been the subject of great scientific and industrial desire for well over a decade. An ecosystem with chemical, biological and geological characteristics that makes it totally unique.

Carte_Kivu-ENSituated between the Democratic Republic of Congo and Rwanda, the peaceful waters of Lake Kivu lie wedged between a volcanic chain at an altitude of 1 400 metres. It currently covers a surface area of 2700 km2 and is 485 metres deep. From the first African legends up to current scientific research, not to mention the romantic reports of late 19th century explorers, the lake has been the subject of many stories. And yet, for a long time, it was of much less interest to people than the other African Great Lakes. Initially, its food chain didn’t appear to be very developed and, at first sight, the lake’s biomass wasn’t attractive enough to allow the development of a significant fishing industry.

However, studies revealed approximately 60 km3 of methane (CH4) and 300 km3 of carbon dioxide (CO2). The two gases are imprisoned in the lake’s deep strata. The extraction of this gas could be the first step in the massive production of electricity, equivalent to more than 100 billion kilowatt hours. Besides the economic aspect, another stake has pushed scientists to recommend exploiting the methane: an excessive concentration of this gas could provoke a catastrophic eruption.

At the same time, a biodiversity that remained unnoticed up until recently is evolving in the upper strata of the lake, allowing fishing on quite an extensive scale. In light of a massive extraction of CH4, an international multidisciplinary team of researchers, led by Jean-Pierre Descy from the University of Namur, Martin Schmid from the Institut Fédéral Suisse de Science et Technologie Aquatique, and François Darchambeau from the University of Liège, decided to bring together all the available knowledge on the lake in a reference work (1), dealing with its physical, chemical, geological and biological aspects. Besides aiming to anticipate the consequences of a disrespectful extraction of CH4 from the lake, the researchers give a complete portrait of its ecosystem resulting in what can be considered as a reference work of the study of tropical limnology

A permanent lid 250 metres down

Lake Kivu is a meromictic lake, i.e., a lake whose surface waters and deep waters never mix. There are two main reasons for this: first of all, its depth and low exposure to wind, preventing convection through the force of the wind, which would normally mix the waters several tens of metres down. “Although the surface waters are currently colder, they contain less salt than the deep waters", explains François Darchambeau, researcher at ULg’s Chemical Oceanography Unit and co-editor of the work. “The deep waters are approximately 2°C warmer than the surface waters but, above all, they are far richer in salt (up to 6 grams per litre). This high salt content affects the density of the water and considerably increases the energy required to make the waters of the lake mix together fully. Since it is located at altitude of 1 400 metres and wedged between a volcanic chain whose peaks exceed 4 000 metres, therefore partially blocking the wind, this energy doesn’t exist. Hence, only the first 60 metres of the lake mix regularly, during the dry season." 

(1) Jean-Pierre Descy, François Darchambeau, Martin Schmid and co., Lake Kivu, Limnology and biochemistry of a tropical great lake, Springer, 2012.

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