Baisden, W. Troy (Landcare Research, New Zealand Ltd, Private Bag 11052, Massey Univ Campus, Palmerston, North5300, New Zealand; Phone: +64 6-356 7145; Fax: +64 6-355-9230; Email: baisdent@landcareresearch.co.nz)

High Riverine Transport of Particulate Organic Carbon in New Zealand: Potential Significance of Soil Erosion to Carbon Accounting

D.T. Scott, W.T. Baisden*, N.J. Preston, N.A. Trustrum, R. Davies-Colley, R.A. Woods, D.M. Hicks, B. Gomez, M.J. Page, K.R. Tate

Tectonically active small island nations contribute a disproportionate amount of sediment to the world’s oceans-. For such nations, particulate organic carbon (POC) export associated with riverine sediment load can also be important compared with C fluxes reported under the United Nations Framework Convention on Climate Change (UNFCCC) and accounted for under the Kyoto Protocol. We quantified the total riverine export of particulate organic carbon (POC) from New Zealand’s landscape to the ocean. New Zealand comprises 0.1% of global land area, 0.2% of the world’s CO₂ emissions, and 1% of global riverine sediment flux. POC export was estimated at 3±1 Mt C yr^-1 (10±3 tC km^-2yr^-1). The total POC yield represents a movement of C equivalent to approximately one third of New Zealand’s total fossil fuel emissions, although this erosional flux cannot be treated as an emission to the atmosphere since a large proportion of POC may be sequestered in ocean sediments. Since elevated rates of erosion are associated with non-forested landcover, reforestation may contribute to changes in riverine POC fluxes. However, our calculations suggest that only 1.7% of New Zealand’s land area yields sufficient human-induced POC to rivers to be of concern in C accounting. Our approach of identifying ‘hot spots’ of erosion where significant uncertainties may interfere with C accounting potentially allows C accounting and trading to proceed based on existing rules in the vast majority of the landscape.