Estimation of 14CO 2 flux at soil-atmosphere interface and distribution of 14C in forest ecosystem

Abstract

To realize the dynamical behavior of 14C among exchangeable carbon reservoirs in terrestrial environment, a method for in situ determination of 14CO 2 flux at soil-atmosphere interface and a high flow rate CO 2 sampler were developed. This method allowed us to collect integrated quantity of CO 2 for determining 14C activity over an extended time period under environmental conditions with minimal site disturbance. The 14CO 2 flux from ground surface was estimated to be 1.59×10 −5 Bq m −2 s −1 in a forest floor with the method. The specific activities of 14C in environmental materials such as some biological and air samples were also determined in the vicinity of the place, where the flux measurement was made, to discuss the behavior of 14C in the forest ecosystem. The results indicated that fresh pine needles had a similar 14C specific activity to the atmospheric CO 2 at the same height due to its fairly rapid equilibrium, 14C specific activity in the atmospheric CO 2 has a concentration gradient near the ground surface and, at least in this site, CO 2 with high 14C specific activity was generated by decomposition of soil organic matter which may be accumulated in soil as a result of former nuclear weapons tests.