Soil erosion in New Zealand is a net sink of CO2

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Abstract

Soil erosion in New Zealand exports much sediment and particulate organic carbon (POC) to the sea. The influence of this carbon export on carbon transfers between soils and the atmosphere has been largely unknown. Erosion models are used to estimate the net carbon transfer between soils and atmosphere due to soil erosion for New Zealand. The models are used to estimate the spatial distribution of erosion, which is combined with a digital map of soil organic carbon content to produce the spatial distribution of carbon erosion. The sequestration of atmospheric CO2 by regenerating soils is estimated by combining carbon recovery data with the age distribution of soils since erosion occurrence. The North Island of New Zealand is estimated to export 1·9 (with uncertainty of −0·5 and +1·0) million tonnes of POC per year to the sea and to sequester 1·25 (−0·3 /+0·6) million tonnes of carbon per year from the atmosphere through regenerating soils. The South Island of New Zealand is estimated to export 2·9 (−0·7/+1·5) million tonnes of POC per year and to sequester approximately the same amount. Assuming exported carbon is buried at sea with an efficiency of 80% gives New Zealand a net carbon sink of 3·1 (−2·0/+2·5) million tonnes per year; which is equivalent to 45% of New Zealand's fossil fuel carbon emissions in 1990. The net sink primarily results from a conveyor belt transfer of carbon from the atmosphere to soils regenerating from erosion to the sea floor where carbon is permanently buried. The net sink due to soil erosion can be further increased by reforestation of those terrains where erosion is excessive and there is no carbon recovery in the soils. Copyright © 2010 John Wiley & Sons, Ltd.

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