The panorama alongside the Buffels River in South Africa’s Namaqualand area is dotted with hundreds of sandy mounds that occupy about 20% of the floor space. These heuweltjies, because the locals name them (the phrase means “little hills” in Afrikaans), are termite mounds, inhabited by an underground community of tunnels and nests of the southern harvester termite, Microhodotermes viator.
I am a part of a gaggle of earth scientists who, in 2021, got down to examine why the groundwater within the space, round 530km from Cape City, is saline. The groundwater salinity gave the impression to be particularly associated to the situation of those heuweltjies. We used radiocarbon courting; courting the mounds, we reasoned, would enable us to see when minerals that had been saved within the mounds had been flushed to the groundwater.
The assessments revealed way over we anticipated: Namaqualand’s heuweltjies, it seems, are the world’s oldest inhabited termite mounds. Some date way back to between 34,000 and 13,000 years. The oldest beforehand identified inhabited mounds had been 4,000 years outdated (from a distinct termite species from Brazil) and 2,300 years outdated (from central Congo).
That is extra than simply an attention-grabbing scientific discover or historic curiosity. It presents a window into what our planet regarded like tens of hundreds of years in the past, offering a dwelling archive of environmental situations that formed our world.
It’s also vastly essential at the moment: there’s rising proof that termites have a considerable, however nonetheless poorly understood, position within the carbon cycle. By finding out these and different termite mounds, scientists can achieve a greater understanding of how one can sequester (retailer) carbon. This course of removes CO₂ from the environment and is significant for mitigating local weather change.
Carbon storage
Namaqualand is a world biodiversity hotspot famend for its spring flowers, however it’s a dry space. Floor water is briefly provide and the groundwater is saline.
Learn extra: Southern Africa’s Namaqualand daisies are flowering earlier: why it is a crimson flag
Though most of Namaqualand receives little or no rainfall, there are uncommon, excessive depth rainfall occasions. When these do happen, the termite burrows on the mound surfaces function water circulation paths that may harvest rain and channel water into the mound. This causes the salts that constructed up within the mounds over hundreds of years to be flushed into the groundwater system through circulation paths created by the tunnelling motion of the termites, pushing the dissolved minerals ever deeper. This course of additionally pushes down the carbon that slowly constructed up within the centre of the mounds when termites collected plant materials and introduced it into the mound over millennia.
The flexibility of those mounds to sequester carbon is linked to the termites’ distinctive behaviour. The bugs transport natural materials – resembling small sticks about 2cm lengthy and some millimetres large from small woody vegetation – deep into the soil. This fashion, recent shops of carbon are constantly added at depths larger than one metre. Deep storage reduces the chance of natural carbon being launched again into the environment. So the mound acts as a long-term carbon sink.
Not solely do the termites take the natural carbon materials deep underground into their nests, however their tunnels additionally enable dissolved inorganic carbon (generally known as soil calcite or calcium carbonate) within the mound soil to transfer into the groundwater together with different soluble minerals. So the termite mounds additionally provide a mechanism to sequester carbon dioxide by dissolution and leaching of soil carbonate-bicarbonate to groundwater. It is a long run carbon storage technique that carbon storage corporations are attempting to duplicate to cut back atmospheric carbon.
The outcomes of our radiocarbon courting of each the natural and inorganic carbon on this soil present that the mounds have been accumulating natural matter and vitamins, together with carbon, for tens of hundreds of years. This enrichment is likely one of the causes that Namaqualand’s well-known wildflowers are so outstanding on the mounds in spring.
In the course of the mounds’ formation, the area skilled extra rainfall than it does at the moment. Learning the layers of the mounds and searching on the carbon, sulphur, and oxygen isotopes preserved within the mounds and within the groundwater confirmed that durations of upper rainfall within the area had been related to international local weather cooling. These cooler and wetter durations had been related to the leaching of amassed carbon and different minerals to the groundwater.
Tiny engineers
These findings are additional proof that termites absolutely deserve their fame as ecosystem engineers. They modify their soil environment to take care of superb humidity and temperature situations, and their foraging paths prolong many tens of metres.
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We argue that, given what we have uncovered in Namaqualand, termite exercise must be integrated into carbon fashions. These primarily deal with forests and oceans; together with termite mounds might help present a extra complete understanding of world carbon dynamics. In Namaqualand, mounds occupy 27% of the full space however contribute 44 % of the full soil natural carbon inventory. This highlights the disproportionate contribution termite mounds make to carbon shares in these semi-arid environments.
Public consciousness and coverage integration are key, too. Termite mounds are sometimes cleared for agriculture or termites are thought of pests. Elevating consciousness concerning the ecological significance of termite mounds and integrating these findings into environmental insurance policies might help promote practices that assist pure carbon sinks.
Michele Francis, Researcher, Division of Soil Science, Stellenbosch College
