Environmental perturbations and anthropogenic disturbances determine mollusc biodiversity of Africa’s explosive Lake Kivu

Lake Kivu is one of the great lakes in the western branch of the East African Rift System and it is infamous as a dangerous “explosive” lake because of its limnological peculiarities and history of lacustrine volcanic eruptions (Jones, 2021). The lake hosts very substantial fisheries and other natural resources that support the livelihoods of millions of people in the two riparian countries, the Democratic Republic of Congo (DRC) and Republic of Rwanda (Rwanda) (Amisi et al., 2022). Lake Kivu is ancient, as it has existed since the middle Pleistocene, when it formed by uplift of the Virunga Mountains to the north (Degens et al., 1973). Previously, Lake Kivu drained to the north into Lake Edward. However, ∼20,000 years ago, volcanic eruptions and resulting lava flows in the Virunga Volcanic Province (VVP) impounded this outlet (Hecky and Degens, 1973, Ross et al., 2014). This barrier led to a lake level rise and a new outlet, the Ruzizi River, was formed in the South which drains to Lake Tanganyika (Degens et al., 1973, Ross et al., 2014). Since its formation, Lake Kivu has been heavily influenced by volcanic activity, particularly that within the VVP (e.g. Smets et al., 2010, d’Oreye et al., 2011, Ross et al., 2014). Lava flows from Nyiragongo and Nyamulagira, the two active volcanoes located north of Lake Kivu in the Virunga Mountains, have repeatedly entered Kabuno Bay and the main basin of Lake Kivu, particularly during the 1938–40 Nyamulagira and 2002 Nyiragongo eruptions (Balagizi et al., 2018). Beyond volcanic eruptions, Lake Kivu is exposed to earthquakes and degassing events, which may result in limnic overturns (Balagizi et al., 2018). The methane reservoir in Lake Kivu is a valuable energy resource for neighboring Rwanda and DRC, but also a looming threat to millions of people in the surrounding area if the stability of the lake is disrupted and the gasses are released into the atmosphere. Several researchers have suggested that methane gas exploitation could reduce the risks of dangerous limnetic eruptions due to supersaturation or subaqueous volcanic eruption (Balagizi et al., 2018, Ross et al., 2014, Schmid et al., 2021, Schmid et al., 2005).