Friday, October 26, 2007

Good news-bad news on soil: erosion not contributing to global warming, but soil not serving as carbon sink

Terra Daily: Agricultural soil erosion is not a source of carbon dioxide to the atmosphere, according to research published online today (25 October) in Science. …The researchers developed a new method to establish the net effect of erosion on exchanges of carbon between the soil and the atmosphere.

They found that in landscapes subject to soil erosion, erosion acts like a conveyor belt, excavating subsoil, passing it through surface soils and burying it in hill-slope hollows. During its journey, the soil absorbs carbon from plant material and this becomes buried within the soil in depositional areas. Erosion, therefore, leads to more carbon being removed from the atmosphere than is emitted, creating what can be described as a 'sink' of atmospheric carbon.

The team found that these sinks of CO2 represent the equivalent of around 1.5% of annual fossil fuel emissions. This finding challenges previous assessments that erosion represents an additional source of carbon to the atmosphere equivalent to adding 13% to annual fossil fuel emissions. The finding also challenges the opposite notion that erosion is currently offsetting fossil fuel emissions by more than 10%.

Dr Kristof Van Oost of the Katholieke Universiteit Leuven said: "There is an on-going debate on the link between agricultural soil erosion and the carbon cycle. Academics on one side have argued that soil erosion causes considerable levels of carbon emissions and on the other that erosion is actually offsetting fossil fuel emissions. Our research clearly shows that neither of these is the case."

This new insight into the effect of erosion on the carbon cycle is essential for sound management of agricultural soils. If previous assessments that erosion causes a high level of carbon emissions to the atmosphere had been correct, then erosion control could have been used to offset fossil fuel emissions. If the assessment that erosion created a very large sink of atmospheric carbon had been correct then the environmental benefits of erosion control would have had to be set against the loss of the sink.

"Our results show that erosion control should be pursued for its environmental and agronomic benefits but should not be used to offset fossil fuel emissions," said Professor Tim Quine of the University of Exeter. "Soil erosion is not the silver bullet for offsetting the ever-increasing emission of CO2 to the atmosphere."…

2 comments:

Hugh Milner said...

This finding seems to relate to the erosion, movement and deposition of subsoil. Did the researchers consider if carbon was oxidised(and how much) during the processes of erosion and exposure of the topsoil to the air? Would not this depend on (i) the type of topsoil, and (ii) the process of erosion (eg water or wind)? If these issues were not considered, I suggest the issue of whether soil erosion results in a release or capture of CO2 is still open and probably depends on the type of soil and the erosion process.

graciela said...

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