Siltation caused by erosion from deforestation is another main threat to Lake Tanganyika. Photo: Catherine O’Reilly / National Geographic

By Lisa Borre
7 March 2013

(National Geographic) – Tropical lakes in East Africa don’t grab headlines the way polar bears do, but climate change is having an effect on them, too. Although the changes are not as visible as melting polar ice caps, they are no less real.

As in many lakes around the world, water temperature is on the rise in Lake Tanganyika. This and other climate-related factors are causing subtle but significant changes that threaten the ecological stability of the lake and the livelihoods of people who depend on it.

With air temperatures across tropical Africa expected to rise as much as 2–5 degrees Celsius (3.5–9 degrees Fahrenheit) over the next 50-100 years, warming lake trends are also expected to continue. The changes underway serve as early warning signs, not just for the lake region, but perhaps, for the planet as a whole.

Considered one of the African Great Lakes, Tanganyika is the world’s second largest lake (by volume) and second deepest, after Russia’s Lake Baikal. It contains 17 percent of the world’s surface freshwater – almost as much water as all five of the North American Great Lakes combined. At more than 10 million years old, Tanganyika is among an elite group of only 20 or so ancient lakes in the world.

Lake Tanganyika also ranks in the top tier of some 250 lakes found to have globally significant freshwater biodiversity.

Four countries border the lake: Burundi, Democratic Republic of Congo (DR Congo), Tanzania, and Zambia. This poses a major challenge for lake conservation and management efforts.

About 10 million people live in the lake’s drainage basin, and the population is growing rapidly (by a rate of 2.5 percent per year), according to a 2006 Brief about the lake. In the nearshore areas of the lake, the rate of growth is nearly double the national average at 4 percent per year. […]

Catherine M. O’Reilly, an assistant professor of geology at Illinois State University, talked with me last fall at a meeting of the Global Lake Ecological Observatory Network (GLEON).

O’Reilly began studying the lake as part of a team looking at the impacts of deforestation in the Tanganyika watershed, where an astounding 100 percent of the native vegetation has been cleared in the northern portion of the watershed. It might not seem obvious, but if you’re interested in learning more about historical land use changes in the lake’s watershed or about the biological communities that have lived in the lake, a good place to look is in the mud at the bottom of the lake. […]

O’Reilly found that water temperatures in Lake Tanganyika have warmed 0.1 degrees Celsius (0.18 degrees Fahrenheit) per decade or 1 degree Celsius (1.8 degrees Fahrenheit) over for the past 100 years. Not only is this affecting the ecological stability of the lake, it has resulted in a 20 percent reduction in biological productivity in the lake.

Scientists are concerned about how continued warming will affect fish stocks and the lake’s rich biodiversity. Reduced fish catches would impact millions of people living in the lake region, many whom live on less than a dollar a day and depend on the lake for basic human needs – the protein from fish and clean water to drink.

More recent global assessments show that the rate of warming in Lake Tanganyika is consistent with other lakes around the world. Although it is not warming as rapidly as some lakes in the northern hemisphere, O’Reilly told me that even small changes in lake temperature can cause major disruptions in the lake’s ecological stability. [more]

Warming Lakes: Climate Change Threatens the Ecological Stability of Lake Tanganyika

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