Objective 7. Soil Carbon Dynamics
Soils play a central role in mediating the response of natural and managed land to change. One of the most important changes New Zealand faces is climate change. Improving understanding of soils is a critical aspect of climate change science. Soils represent a key source and sink of the greenhouse gas carbon dioxide, and contain more carbon than living plants and the atmosphere. While we often think of soils as unchanging, soils could release much of this carbon to the atmosphere over coming decades as a result of changes in climate or land management. This would exacerbate the climate change problem, but many soils may also be capable of mitigating climate change by storing additional carbon under altered land management. Perhaps more importantly to New Zealand, if soils lose carbon they also lose other critical functions including the ability to supply nutrients and water to plants, such as the pastures and forests which underpin New Zealand's economy. We are working with other scientists from New Zealand and around the world to develop new ways of using isotopes, particularly radiocarbon, to improve our fundamental understanding of soil carbon in New Zealand. 
Key questions include the following. How has soil carbon changed in New Zealand over recent decades and how is it likely to change as a result of increasing agricultural intensification combined with climate change? And, are some C loss mechanisms, such as erosion and dissolved carbon fluxes, more important for New Zealand than other nations?
The National Isotope Centre plays a key role in New Zealand's soil carbon research by providing access to the Accelerator Mass Spectrometer (AMS) at the Rafter Lab, measuring radiocarbon. We use radiocarbon as a tracer of soil carbon inherited from hundreds or thousands of years in the past, and therefore unlikely to be lost due to land use or climate change. Radiocarbon also reveals soil carbon built up over recent decades by detecting the small but significant increase in the radiocarbon content of the atmosphere/biosphere/ocean system caused by above-ground thermonuclear weapons testing. We are augmenting this radiocarbon based research by contributing to the development of models and using chemical and physical characterization methods to better understand how and why carbon is stabilized in New Zealand soils.