Erosion-related soil carbon fluxes in a pastoral steepland catchment, New Zealand

New Zealand is currently identifying and quantifying its carbon sources and sinks to develop a national carbon budget. This will enable it to set policy and targets to reduce greenhouse gas emissions in line with the Kyoto Protocol. While soil is a major carbon sink, New Zealand also has high sediment yields to the ocean, suggesting that erosion has a significant effect on soil carbon fluxes, through CO2 emission during transport of carbon in sediment, carbon burial and recovery of carbon on eroded areas. As a contribution to the national carbon budget, a mass balance approach was used to calculate soil carbon fluxes from landslide and sheetwash erosion in the Tutira catchment in the North Island of New Zealand. This soft rock hill country catchment represents the upper limit for landslide-related soil carbon losses. It contains a lake that acts as a highly efficient trap for sediment and nutrients, and has preserved a high-resolution record of storm-induced erosion. Information from previous studies of erosion and lake sedimentation was used to construct a carbon budget for the 114-year period of European pastoral farming. The budget assumes the gross transfer of carbon by geomorphological processes and does not include biogeochemical exchanges with the atmosphere. Results indicate that 0.94±0.23 Mg C ha−1 per year enter the lake (0.50±0.15 Mg C ha−1 per year from landslide erosion and 0.44±0.17 Mg C ha−1 per year from sheetwash erosion). On a national scale this equates to an anthropogenically induced loss of 2 112 000 Mg C per year from the 10% of similar terrain under pastoral land use. However, the net loss from the landscape is significantly less due to carbon recovery on eroded sites. Landslide scars have a carbon recovery rate (after oxidation) of ∼0.61 Mg C ha−1 per year. Carbon recovery on areas affected solely by sheetwash erosion was not measured, but is significantly lower. This information is being used to constrain models of erosion-related carbon fluxes developed for landslide-prone terrains, as part of the national carbon budget.