Microelectrode measurement of ammonium profiles in freshwater sediments

Abstract Ammonium microprofiles in two dominant types of lake sediment were measured using ion-selective microelectrodes. These profiles enabled establishment of local fluxes and convensions. Comparison of ammonium profiles obtained from the analysis of sediment slices with those measured with microelectrodes showed the superior spatial resolution of the latter method. Flux measurements with microelectrodes were confirmed by laboratory incubation experiments. In both sediments ammonium consumption was restricted to the oxic surface layer. In sandy sediments ammonium was only consumed, while in silty sediment both ammonium production and consumption were observed. In silty sediment ammonium production by anaerobic mineralization was not balanced by ammonium consumption in the oxic surface layer.