The physical and microbiological processes governing nitrous oxide and methane fluxes to and from soil are highly variable in space and time and are controlled, directly and indirectly, by soil moisture content, which is largely governed by hydrologic processes. The goal of this project is to evaluate the impact of hydrological dynamics, in other words catchment scale water redistribution, on soil-atmosphere trace gas fluxes across a mountain landscape. A combination of nitrous oxide, methane and carbon dioxide flux determinations, soil water content and redistribution measurements, chemical assays of potential reactants, digital terrain analyses and hydrological monitoring will be used to assess the environmental controls on trace gas flux spatial and temporal dynamics in a forested Montana watershed. Relationships between trace gas sources and sinks and hydrologic properties in montane ecosystems will be uncovered. This project will test an existing topography analysis framework that uses hydrologic property based landscape units (slope position in relation to streams, aspect, drainage area, and so on) to translate point-scale trace gas measurements to the landscape scale. The project builds upon prior and ongoing NSF-funded research on hydrologic controls on carbon dioxide flux in montane ecosystems and uses existing field infrastructure and technical resources to advantage. Nitrous oxide and methane are, like carbon dioxide, radiatively active trace gases that contribute significantly to global warming. It is known that the montane forested ecosystems of North America are a significant carbon sink. However, the net impact of montane forested ecosystems on atmospheric warming potential is unclear because the net fluxes of other trace gases are not known. This is, in part, because effective approaches to translate point trace gas flux measurements to whole landscapes have yet to be developed for such systems. The approach that will be developed and tested in this project has the potential to improve net greenhouse gas emission estimates for montane forested ecosystems at the landscape scale ? the spatial scale considered in policymaking regarding greenhouse gas emissions. In addition, this research project will provide land-air carbon dioxide, nitrous oxide and methane flux data at multiple space and time scales that will be useful to scientists interested in benchmarking models. Hands-on field training opportunities in hydrology and biogeochemistry will be provided for graduate and undergraduate students from Montana State University.