The measurement and analysis of denitrification rates obtained using soil columns from river marginal wetlands

Soil cores from river marginal wetlands from three sites in the UK (Torridg e and Severn catchments), sampled and restrained in PVC piping, were floode d with dilute aqueous potassium nitrate. Half of the cores were sterilized prior to flooding to destroy the denitrifying bacteria. The change in nitra te concentration in the flood-water was measured over time. I; is argued th at the observed nitrate depletion rates (from 1.2 to 5.7 kg ha(-1) d(-1)) i s the result of microbially-mediated denitrification. The results show the method to be a simple and direct procedure for the assessment of spatial va riation in nitrate- sink capacity: The depth of the denitrifying layer at t he soil-water interface was confirmed to be of the order of a few mm only: A one-dimensional model for the diffusive flux in the flooded soil was deve loped which, on differentiation, gave a predictive expression for denitrifi cation rate in terms of the effective soil diffusion coefficient for nitrat e, the flood-water depth and concentration, and the thickness of the microb ially active zone.