Desorption kinetics of ammonium and methylamines from estuarine sediments: Consequences for the cycling of nitrogen

• Published in: Marine chemistry 2006-09, Vol.101 (1), p.12-26
• Main Authors: Fitzsimons, Mark F., Millward, Geoffrey E., Revitt, D. Michael, Dawit, Mekibib D.
• Format: Article
• Language: English
• Subjects: Ammonium; Brackish; Earth sciences; Earth, ocean, space; Exact sciences and technology; External geophysics; Geochemistry; Kinetics; Methylamines; Mineralogy; Physical and chemical properties of sea water; Physics of the oceans; Sediment resuspension; Silicates; Thames Estuary; Water geochemistry
• ISSN: 0304-4203; 1872-7581
• DOI: 10.1016/j.marchem.2005.12.006

Concentrations of dissolved and particulate NH 4 + and mono-, di- and trimethylamines (MAs) were determined in surface sediments and pore-waters collected from the Thames Estuary, United Kingdom, during July and November 2001. Dissolved NH 4 + was an order of magnitude more abundant than the MAs in the pore-waters, whereas in the solid phase each MA was more abundant than NH 4 +. Sediments were also used in controlled, time-dependent, desorption experiments, using indigenous, filtered seawater. Desorption of NH 4 + was more rapid than the MAs and the kinetics were interpreted using a reversible first-order mechanism. The mean response times (i.e. time taken to achieve 63% of the new equilibrium) of NH 4 + and MAs were about 15 and 25 min, respectively. Increases in the concentrations of dissolved NH 4 + and dissolved MAs, in the Thames Estuary over a tidal cycle, were coincident with the remobilisation of seabed sediments. Model calculations showed that desorption of NH 4 + from the remobilised sediments accounted for approximately 50% of increase, whereas for MAs it was > 90%. The results are proposed as a predictor for the sorption behaviour of other organic nitrogen compounds, such as basic amino acids, and emphasise the importance of sediment resuspension as a mechanism for the release of ON to the water column.