THE INFLUENCE OF SOIL ORGANIC MATTER STABILIZATION MECHANISMS ON CARBON MEAN RESIDENCE TIME WITHIN VARIOUS ECOSYSTEMS IN THE UNITED STATES

Some terrestrial ecosystems and soils serve as carbon sinks, partially offsetting rising atmospheric CO2 levels. Physiochemical mechanisms of soil organic matter (SOM) stabilization affect how carbon stocks respond to global warming. In order to clarify the variance in SOM stabilization mechanisms across different soil types, SOM abundance, distribution and mean residence time (MRT) were compared for thirty-two soil samples from six ecosystems across the United States. Soils were previously described, collected and archived by the United States Geological Survey. Samples were processed by LLNL at the Center for Accelerator Mass Spectrometry (CAMS) using density fractionation to separate particulate organics from mineral components. SOM abundance and distribution were compared among sites. Graphitization and radiocarbon analysis conducted at CAMS determined 14C/13C ratios which were used to evaluate differences in SOM MRT across the various ecosystems. Results confirmed SOM turnover varied among sites; therefore the response of SOM to global warming may vary among soils. Further work will explore how variance in SOM MRT is related to particular soil physiochemical properties such as mineral assemblage. Data from this investigation will be used in quantitative ranking of soil stabilization mechanisms and management of this important carbon sink. Initial investigation will allow for quantitative ranking of soil stabilization mechanisms and management of this important carbon sink.