Open‐channel estimation of denitrification

Estimates of denitrification based on standard methods often cannot easily be extrapolated to entire ecosystems because of high spatial heterogeneity in rates of denitrification. Diel changes in the concentration of dinitrogen (N 2 ) in running waters provide the basis for estimating denitrification by an open‐channel technique in much the same way that ecosystem metabolism can be estimated from diel changes in the concentration of dissolved oxygen. The open‐channel N 2 method was field tested at a site on the South Platte River downstream from Denver, CO; concentrations of N 2 were measured by membrane inlet mass spectrometry. For a date in November 1998, the rate of denitrification was estimated to be 0.19 mol N 2 m −2 d −1 and was similar to rates reported in previous studies based on mass‐balance analysis. The open‐channel N 2 method is the first method to provide direct, whole‐system estimates of denitrification in flowing waters and may help to expand our understanding of nitrogen cycling in running waters.