Dynamics simulation of ammonia nitrogen absorption in a rural–urban canal on the Northeast China Plain

To study dynamic laws of ammonia nitrogen retention in a typical rural-urban fringe canal, NaBr was selected as a conservative tracer agent, and NH 4 Cl as an additive nutritive salt to conduct an instantaneously added tracer experiment outdoors. On this basis, tracer additions for spiralling curve characterisation (TASCC) method and nutritive spiral indexes were used for the quantitative depiction of retention dynamics of NH 4 + -N. The Michaelis-Menten (M-M) model was used to simulate absorption dynamic characteristics of NH 4 + -N. Results showed that the variation range of absorption length of NH 4 + -N under background concentration was 93.94-295.54 m with an average value of 177.41 m, the variation range of mass transfer coefficient was 0.16-0.38 mm/s with an average value of 0.26 mm/s, and the variation range of absorption rate was 0.16-0.38 mg/(m 2 ⋅s) with an average value of 0.26 mg/(m 2 ⋅s). The maximum absorption rate of NH 4 + -N obtained via M-M equation simulation was 0.59-1.38 mg/(m 2 ⋅s), and the subsaturation constant was 1.10-5.03 mg/L. The variability of the dynamic absorption length, overall dynamic absorption rate, and overall dynamic mass transfer coefficient shown by NH 4 + -N within the range from background concentration to saturation concentration certified that TASCC could analyse the dynamic process of NH 4 + -N retention and absorption by the canal.