Kalahari Desert soils and climate change

“We discovered that even after light rainfall, the gains and losses of carbon dioxide through the sands of the Kalahari Desert were similar in size to those reported for more organic rich grassland soils. Despite being short lived, these raised pulses of activity are a significant and previously unreported contributor to atmospheric carbon dioxide” says Dr Thomas. “Global climate change models have forgotten them”.

Dr Thomas with his colleagues, Dr Stephen Hoon and Dr Patricia Linton also of Manchester Metropolitan University, found that in some conditions, the cyanobacteria in the surface crust were taking net amounts of carbon dioxide out of the atmosphere as they photosynthesised. But after heavy rainfall other types of bacteria deeper in the subsoil became active and their activity masked the uptake of carbon by the surface cyanobacteria by consuming the organic matter in the soil, releasing large quantities of carbon dioxide.

“We also discovered that the fluxes of carbon dioxide from the soil were highly sensitive to temperature. Warmer air but similar soil moisture levels caused greater losses of carbon from the desert soils to the atmosphere”, says Dr Thomas. “These desert soils are contributing significantly to the global carbon dioxide budget. Until recently they have been ignored”.

“We need to know exactly what is happening as a better understanding of the factors controlling activity of the surface living soil cyanobacteria could help inform grazing policy. Millions of poor semi-subsistence pastoral farmers rely on the soils of the Kalahari to provide nutrients for grazing. The carbon produced by the cyanobacteria is a major contributor to the fertility of the soil and it is essential we understand how their metabolism is affected by environmental conditions”, says Dr Thomas.