New Methods for Measuring Terrestrial Denitrification.

This project is a National Science Foundation funded “proof of concept” effort to test two new methods to measure denitrification.  Denitrification is an anaerobic microbial process that leads to the production of the gases nitric oxide, nitrous oxide and dinitrogen.  There is great interest in the production of these gases as humans have more than doubled the global circulation of “reactive” nitrogen (N), leading to degradation of air and water quality and coastal ecosystems in many areas.  The development of solutions to N pollution problems has been hindered by large amounts of “missing N” that dominate N balances at all scales.  A major question is if the production of gases can account for a significant percentage of the missing N in balances.  However, the fluxes of these gases are difficult to quantify because of problematic measurement techniques (especially for dinitrogen), high spatial and temporal variability, and a lack of methods for scaling point measurements to larger areas.  The two new methods, a gas flow soil core incubation system and an in situ 15-N tracer method, have been developed and applied at eight sites in and around the Hubbard Brook Long Term Ecological Research site in New Hampshire.   Results from the gas flow soil core incubation system show that we can measure low rates of both dinitrogen and nitrous oxide production and that rates of dinitrogen production are significant in Hubbard Brook soils, much higher than rates of nitrous oxide production.  Results from the 15-N tracer method provide evidence for both abiotic and biotic mechanisms of N gas production.  Efforts to validate and develop standard protocols for both methods are ongoing.