Lake Tanganyika, the world’s second oldest and second deepest lake, is in the midst of unprecedented warming.
[social_buttons]Geologists led by Brown University have determined that the massive freshwater lake has warmed significantly during the last century, leading to its warmest surface temperatures on record. Such a change to the lake’s makeup will likely affect fish stocks which millions in the region rely upon for survival.
According to core samples taken in 2001 and 2004 the lake’s surface temperature has risen to 26 degrees Celsius (78.8°F), the warmest the lake has been for a millennium and a half.
“Our data show a consistent relationship between lake surface temperature and productivity (such as fish stocks),” said Jessica Tierney, a Brown graduate student who this spring earned her Ph.D. and is the paper’s lead author. “As the lake gets warmer, we expect productivity to decline, and we expect that it will affect the [fishing] industry.”
Lake Tanganyika borders four of the world’s poorest countries, Burundi, the Democratic Republic of Congo, Tanzania and Zambia, according to the United Nations Human Development Index, and supports an estimated 10 million people by providing drinking water and fish. Up to 200,000 tons of sardines and four other fish species are harvested annually from the lake which, according to a report in 2001 by the Lake Tanganyika Biodiversity Project, supports a large portion of the locals.
The Lake is dependent upon the wind to churn the waters so that the surface waters can acquire the nutrients that live much deeper. The majority of the animal species live in the upper 100 metres of the lake, with certain depths of the lake providing absolutely no oxygen at all. But as Lake Tanganyika warms the mixing of waters decreases which means that there is less food for animals in the upper reaches of the lake.
Data collected by the Brown University researchers points to a linkage between prolonged warming and cooling with low and high algal production, which in turn indicates a clear link between temperature changes and biological productivity in the lake’s history.
“The people throughout southcentral Africa depend on the fish from Lake Tanganyika as a crucial source of protein,” noted Andrew Cohen, professor of geological sciences at the University of Arizona and director of the Nyanza project. “This resource is likely threatened by the lake’s unprecedented warming since the late 19th century and the associated loss of lake productivity.”
Climate change models for the region show a general warming which, if proved accurate in time, would see a corresponding warming to Lake Tanganyika’s surface waters. Some researchers have attributed the decline in fish stocks to overfishing, which Tierney and her advisor James Russel agree could be a factor. However they add that the lake’s warming is exacerbating the stocks’ decline, if not causing it in the first place.
Source: Brown University