Smemo, K.A., G.P. Robertson, N.E. Ostrom, S. Bohm, M. Opdyke, and M.H. Ostrom
Presented at the All Scientist Poster Reception (2006-05-09 )
Microbial nitrogen transformations in soil represent the most significant source of atmospheric nitrous oxide (N2O), yet annual flux estimates are fraught with uncertainty due to limited measurements and high spatial and temporal variability. Moreover, the unknown contribution of specific microbial N2O production pathways to total flux limits our ability to model and predict soil fluxes. A robust and widely applicable method for measuring fluxes, therefore, is needed to constrain annual N2O budgets and to provide a process-based understanding of measurement variability. Here we discuss the development of an automated chamber system that will allow continuous measurement of N2O over a period of weeks to months. Such long-term measurements will improve the accuracy of flux estimates and allow collection of sufficient N2O for isotopomer abundance analysis to quantitatively apportion N2O sources. Our chamber design uses a conditioned molecular sieve trap to collect soil-derived N2O that is circulated from the chamber using a diaphragm pump. Prior to contact with the molecular sieve, chamber air is circulated through desiccant and ascarite traps to remove water vapor and CO2, which compete for N2O on molecular sieve. We can demonstrate that N2O is absorbed onto molecular sieve and removed efficiently without sample loss or isotopic fractionation. Currently, we are in the chamber-testing phase and addressing field deployment and automation issues, we expect to conduct field trials this summer. This new chamber system has the potential to become a new tool for soil trace gas measurements that can be easily deployed in a variety of managed and natural ecosystems.
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