Contribution to the optimisation of an NH4+ extraction method for measuring remineralisation rates in marine systems
Chahid, A. (1999). Contribution to the optimisation of an NH4+ extraction method for measuring remineralisation rates in marine systems. MSc Thesis. VUB: Brussel. 44 pp.
As ammonium regeneration plays a major role in the pelagic food web by sustaining phytoplankton growth, and since most of ammonium is supplied to the euphotic zone from biological remineralisation via zooplankton excretion and metabolic processes of microheterotrophs, it is of great importance to estimate the remineralisation rate of ammonium usually by using isotope dilution method. The major problem surrounding the technique of isotopic dilution has been the extraction of dissolved ammonium for isotopic analysis. The aim of our study was to design an original experimental set-up that works for marine samples characterised by low ammonium concentrations (less than 5 pmoles) and that can be simple and fast. We used a modified diffusion procedure collecting ammonium dissolved in water by converting ammonium to ammonia under basic conditions and then trapping the ammonia gas on an acidified glass fibre filter. Nitrogen gas was used to enhance the diffusion rate and in order to obtain sufficient N- NH,' for analysis; large volume diffusions were used. While applying this protocol, we encountered contamination problems and we tried to discover the possible sources. From the possible contaminants we tested (nitrogen gas, sulphuric acid, the gas diffuser and the filter) we found that the gas diffuser and the filter could be the sources of ammonium contamination.
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