137-7 Can Bomb 14 C Indicate Dynamic Replacement of Soil Carbon in Eroded Agricultural Landscapes?.



Monday, October 17, 2011
Henry Gonzalez Convention Center, Hall C, Street Level

Bert VandenBygaart, Agriculture & Agrifood Canada, Ottawa, ON, Canada, Edward Gregorich, Agriculture and Agri-Food Canada, Ottawa, ON, Canada, David Kroetsch, Agriculture & Agrifood Canada, ottawa, ON, Canada and David Lobb, University of Manitoba, Winnipeg, MB, Canada
Subsoil organic matter situated below 30 cm can represent over half of the total organic C in many areas of the world. In agricultural landscapes, water and tillage processes redistribute soil organic matter whereby upper slopes can lose a majority of their inherent C, and toeslope and footslope landscape positions can gain large quantities of soil C. This process can be an important mechanism in global C dynamics, but studies assessing the effect have not been conclusive. In this study we utilize radiocarbon measurements on eroded and redistributed soils, in order to better understand C dynamics in these landscapes. In general, Δ14C values decrease linearly or exponentially under normal or undisturbed conditions. Four of the five depositional profiles studied here contained inversions of Δ14C which deviated from the typical depth profile under natural conditions. These perturbations were a result of erosion of recently-assimilated bomb-sourced 14C due to thermonuclear testing in the 1950’s and 1960’s, and this was verified by 137Cs measurements on the same samples. We investigated if recent assimilation of 14C from bomb-testing could be indicatative of dynamic replacement of C in eroded landscape positions. Three of the five sites clearly showed a large contribution of young bomb-sourced C, suggesting dynamic replacement of eroded soil C.
See more from this Division: S06 Soil & Water Management & Conservation
See more from this Session: Agricultural Practices to Increase Nitrogen-Use Efficiency, Carbon Sequestration, and Greenhouse Gas Mitigation : II