The challenge of denitrification

Abstract:

Understanding the nitrogen cycle at ecosystem, landscape, regional and global scales is a great current challenge in environmental science. Large amounts of “missing nitrogen” dominate nitrogen balances at all scales and have complicated efforts to address the effects of excess reactive nitrogen pollution on tropospheric ozone levels, coastal eutrophication and drinking water quality, and to determine “critical loads” for atmospheric nitrogen deposition. Uncertainty about nitrogen balances has led to increased interest in nitrogen gas fluxes as a fate of excess nitrogen. Denitrification, the conversion of reactive nitrogen oxides such as nitrate and nitrite into nitrogen gases, is a challenging process to study in terrestrial ecosystems. This process is difficult to quantify because of problematic measurement techniques, high spatial and temporal variability, and a lack of methods for scaling point measurements to larger areas. A particular challenge is that small areas (hotspots) and brief periods (hot moments) account for a high percentage of nitrogen gas flux activity. However, recent advances have yielded new methods capable of producing well constrained estimates of denitrification at the ecosystem scale, new ideas about the occurrence of hotspots and hot moments at ecosystem and landscape scales, and powerful new tools for extrapolation and validation. Progress on the challenges of denitrification suggest that we are poised for advances more generally across the genomes-to-ecosystems cascade.