Deserts as Carbon Sinks

The sands of the desert are an important and forgotten storehouse of carbon dioxide taken from the world’s atmosphere, scientists heard today (Wednesday 2 April 2008) at the Society for General Microbiology’s 162nd meeting being held this week at the Edinburgh International Conference Centre.

“Desert soils are unusual because the sand grains at the surface are bound together into a crust by bacteria, reducing wind erosion and adding nutrients to the soil. Deserts cover over one third of the world’s land surface and yet our understanding of their contribution to the atmospheric carbon dioxide balance is poor”, says Dr Andrew Thomas of Manchester Metropolitan University.

Sands like those in the Kalahari Desert of Botswana are full of cyanobacteria. These drought resistant bacteria can fix atmospheric carbon dioxide, and together they add significant quantities of organic matter to the nutrient deficient sands.

“We know that globally there is a huge exchange of carbon between the atmosphere and the soil. As average global temperatures rise, scientists are concerned that bacteria will break down organic matter in soils more rapidly, releasing more carbon dioxide into the atmosphere”, says Dr Thomas. “However, there have been very few actual field studies of this carbon exchange through world soils and little information on how they respond to temperature and moisture changes. This is particularly true for deserts. Here the bacteria have to be able to cope with long periods without rain and extreme temperatures, so they lie dormant in the desert soil only springing to life when there is enough moisture”.

The exchange or flux of carbon between the soils and the atmosphere is much smaller over deserts than for areas with more organically rich soils, but the sheer size of deserts makes it globally significant. Even small changes in the carbon balance of desert soils will also be important locally, where soil organic matter underpins fragile ecosystems currently supporting millions of poor pastoral farmers.

“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”.

hmmmm. Must. Water. Desert. mmmm.