The research team in front of the main nest. (Michelle Francis)
The landscape along the Buffels River in Namaqualand, South Africa, is dotted with thousands of sand dunes, covering around 20% of the total area. HeuveltzisThe site, which locals call “Little Hill”, is a termite mound that means “little hill” in Afrikaans and is home to a network of underground termite nests and tunnels. Mikrohodotermes Viator.
I am part of a group of geoscientists studying why groundwater in an area about 530km from Cape Town is so saline in 2021. The salinity of the groundwater seems to be specifically linked to the location of these rocks. HeuveltzisWe used radiocarbon dating, because we thought that dating the mounds would tell us when the minerals stored in them had leaked into the groundwater.
The results of the investigation revealed far more than expected. Heuveltzishave been found to be the world's oldest habitable termite mounds, some of which date back between 34,000 and 13,000 years ago. The oldest known habitable termite mounds date back 4,000 years (from another termite species in Brazil) and 2,300 years (from central Congo).
This is more than just a fascinating scientific discovery or a historical curiosity: it offers a window into what Earth was like tens of thousands of years ago, providing a living record of the environmental conditions that shaped our world.
This remains extremely important today: There is growing evidence that termites play a key role in the carbon cycle, but that role is still not well understood. By studying these and other termite mounds, scientists can better understand how they sequester (store) carbon, a process that removes CO₂ from the atmosphere and is essential for mitigating climate change.
Carbon Storage
Namaqualand is a global biodiversity hotspot known for its spring flowers, but it is also arid: surface water is scarce and the groundwater is saline.
Most of Namaqualand receives very little rainfall, but on the rare occasions when heavy rainfall occurs, termite burrows on the surface of the mound act as channels to collect rainwater and drain it down the mound.
This allows salts that have built up in the mound over thousands of years to flow into the groundwater system through the channels created by the termites' tunneling, pushing the dissolved minerals ever deeper down. This process also pushes down the carbon that has slowly built up in the center of the mound as the termites collected plant matter and brought it down into the mound over thousands of years.
The ability of these mounds to sequester carbon is linked to the unique behavior of termites: they transport organic matter, including twigs about 2 centimetres long and a few millimetres wide, harvested from small woody plants deep into the soil.
In this way, new carbon is continually stored at depths of more than one meter. Deep storage reduces the chance of organic carbon being released into the atmosphere, so the mounds act as long-term carbon sinks.
Not only do termites bring organic carbon material deep underground to their nests, but their tunnels also allow dissolved inorganic carbon in the soil (known as soil calcite or calcium carbonate) to flow into groundwater along with other soluble minerals.
That means termite mounds also provide a mechanism for sequestering carbon dioxide by dissolving carbonates and bicarbonates in the soil and leaching them into groundwater — a long-term carbon storage method that carbon storage companies are trying to mimic to reduce atmospheric carbon.
Radiocarbon dating of both the organic and inorganic carbon in the soil has revealed that the mound has been accumulating carbon-bearing organic matter and nutrients for tens of thousands of years – one of the reasons why Namaqualand's famous wildflowers often bloom on the mound in spring.
During the formation of the hills, the region received more rainfall than it does today. By studying the hills' strata and examining the carbon, sulfur and oxygen isotopes stored in the hills and groundwater, researchers found that periods of higher rainfall in the region are associated with periods when the Earth's climate was cooling. These cooler, wetter periods are associated with accumulated carbon and other minerals leaching into the groundwater.
Little Engineer
These discoveries are further evidence that termites well deserve their reputation as ecosystem engineers: they modify the soil environment to maintain ideal moisture and temperature conditions, and their foraging trails can span tens of metres.
We argue that, given our findings in Namaqualand, termite activity should be incorporated into carbon models.
These have mainly focused on forests and oceans, and the inclusion of termite mounds helps provide a more comprehensive understanding of global carbon dynamics. In Namaqualand, termite mounds cover 27% of the total area but account for 44% of total soil organic carbon stocks. This highlights the disproportionate contribution of termite mounds to carbon stocks in these semi-arid environments.
Public awareness and policy integration are also important. Termite mounds are often cut down for agriculture, and termites are considered pests. Raising awareness about the ecological importance of termite mounds and incorporating these findings into environmental policies can promote practices that support natural carbon sinks.
This article was originally published on The Conversation.