LAKE TANGANYIKA IS CHANGING , AND THE FATE OF MILLIONS LIE IN THE BALANCE lions of people rely on the lake ’ s riches .
But despite being a world class reservoir of biodiversity , food and economic activity , the lake is changing rapidly and may be facing a turbulent future .
Lake Tanganyika was recently declared the “ Threatened Lake of 2017 ” – adversely affected by human activity in the form of climate change , deforestation , overfishing and hydrocarbon exploitation .
The threats
Beginning in the late 1980s scientists studying the lake began to notice significant and concerning changes caused by human activity .
But at the time worldwide attention was focused on other African Great Lakes , particularly Lake Victoria where evidence was beginning to emerge of the enormous impact the Nile Perch – an introduced species – was having .
The problems in Tanganyika were somewhat different . Fortunately , no major exotic species introductions have occurred up to now . Instead , evidence shows that underwater habitat degradation is taking place adjacent to hill slopes . They are being rapidly deforested – converted to agricultural lands or for urban expansion – in the fast growing population centres around the lake . This activity has led to a rapid increase in the amount of loose sand and mud being washed into the lake which is smothering the lake floor .
Danger of sediment
The biodiversity of Lake Tanganyika can be imagined like a thin bathtub ring . It hugs the shallow zones around a deep and steep bottomed lake , up to 1470m in its deepest parts . The hundreds of species that inhabit the sunlit shallows give way to a dark expanse of water lacking oxygen and , so , animal life .
This narrow strip of extraordinary biodiversity is on the front line . Eroded sediments are being carried into the lake , affecting this strip .
Researchers have begun to document where the impact is being felt . They are also looking back in time by collecting sediment cores with fossils of the many endemic animals to see when the impact was first felt .
They have found that some heavily populated regions lost much of their diversity more than 150 years ago . Other regions , particularly in the more southerly past of the lake , are seeing these effects unfold only in recent decades .
Other pressures
Excess sedimentation is just one problem . Fishing pressure and climate change are also affecting the lake . Large scale fisheries for the lake ’ s small sardines started in the 1950s , quickly mushrooming into a major industry . They export up to 200,000 tons of fish per year and make up a very large portion of the average person ’ s animal protein intake in the surrounding regions .
In recent years this fishing yield has declined dramatically . This has been partially caused by the unsustainable growth in fisheries , and exacerbated by large numbers of refugees flooding into the region because of conflicts in Rwanda , Burundi and the DRC during the 1990s .
It ’ s now increasingly clear that another factor has also been at play .
Starting in the early 2000s , scientists began to document that the surface waters of Lake Tanganyika were warming rapidly . This is most likely because of global climate change related to an increase in greenhouse gas emissions . This warming has had serious consequences for the lake ’ s fragile ecosystems .
Warming lake
Warm water is relatively light and struggles to mix with the deeper layers of the lake . This in turn keeps the vast pools of nutrients from being churned back to the surface by waves . It cuts down on the growth of floating plankton , which is what the lake ’ s many fish populations eat .
Scientists have been able to show that the decline in fish populations began well before the onset of commercial fishery in the 1950s . This implicates climate change and lake warming as the probable cause for much of the fishery ’ s long-term decline .
Unfortunately , this trend is unlikely to be reversed as long as the climate in the region continues to warm .
A related consequence of the reduction of mixing in the lake , is a continuous shallowing of the transition from the oxygenated to deoxygenated waters on the lake floor . This means there ’ s less of an oxygenated ring , reducing the habitat area within the bathtub ring of biodiversity from below .
As if scientists and lake managers at Lake Tanganyika didn ’ t have enough on their plates , a new problem has emerged : the search for oil and gas deposits .
Rift lake sediments of the type found in Lake Tanganyika are well known among geologists as reservoirs of hydrocarbons , as over millions of years vast quantities of plankton have died and settled on the lake floor .
The consequences of actual production are still unknown . But the recent record of catastrophic oil spills , for example along the Niger River Delta , highlight the critical need for very careful study and environmental planning before production proceeds in fragile Lake Tanganyika .
The biological and economic riches produced by 10 million years of evolution could lie in the balance .
2017 | Business Times Africa 61