In this paper, erosion models (including NZeem) are used to estimate the net carbon transfer between the atmosphere and soils due to erosion in New Zealand. 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. The models are used to estimate the spatial distribution of erosion rates, which are then combined with a digital map of soil organic carbon (SOC) content to produce the spatial distribution of carbon erosion.

Methodology

Assuming a high burial efficiency of erosion carbon at sea, suggested by recent research (Galy et al., 2007), the net transfer of carbon between the atmosphere and soils (due to erosion) is estimated for each erosion terrain. The budgets for each erosion terrain are amalgamated for the North and South Islands separately. For the North Island, both present-day erosion-carbon budgets and budgets for before and immediately after deforestation are calculated. The processes to be considered are removal of organic carbon by erosion, redistribution and burial on the landscape, transport to and burial by the sea or release to the atmosphere, and sequestration of atmospheric CO2 by soils recovering from erosion.

Nzeem 1

Outputs

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.

nzeem 2

Associated Models

References

Dymond, John R. (2010) Soil erosion in New Zealand is a net sink of CO2. In: Earth Surface Processes and Landforms 35(15), 1763–1772. (URL: http://onlinelibrary.wiley.com/doi/10.1002/esp.2014/abstract)