Estuarine nitrification: A naturally occurring fluidized bed reaction?

The rates of nitrification in the water column of the Tamar river estuary, southwest England have been measured using the incorporation of H¹⁴CO₃ in samples with and without the inhibitor of nitrification, 2-chloro-6-(trichloromethyl) pyridine (N-Serve). N-Serve proved successful in totally inhibiting NH₄-oxidizing bacteria but the activity of NO₂-oxidizing bacteria was inhibited by only 30%; other organisms were only slightly affected. Measurements of the nitrification rate made over the entire salinity range of the estuary (0-30‰) showed that maximum nitrification always coincided with the turbidity maximum. The field data suggest that the organisms responsible for nitrification were associated with periodically resuspended particulate material and that the turbidity maximum acts in a manner similar to a fluidized bed reactor. A dispersion model has been used to demonstrate that nitrification in the water column can account for 100% of the NO₂ maximum which is apparent down estuary from the turbidity maximum.