MEPS 170:67-84 (1998)  -  doi:10.3354/meps170067

Seasonal variation of dissolved and adsorbed amino acids and ammonium in a near-shore marine sediment

Angela Landén*, Per O. J. Hall

Department of Analytical and Marine Chemistry, Göteborg University, S-412 96 Göteborg, Sweden

ABSTRACT: Dissolved free amino acids (DFAA) and ammonium in the pore water of a coastal sediment at a water depth of 40 m were investigated monthly for more than a year, to improve knowledge on how the concentrations and distributions of these dissolved compounds varied during an annual cycle. Seasonal changes in adsorbed amino acids and ammonium were also studied and adsorption coefficients were calculated. Ammonium distribution in the pore water showed clear seasonal trends. In the warmer period (August and September) there were high concentrations in the pore water, and in winter the lowest concentrations were measured. Pore water concentrations of DFAA were in general low, but showed seasonal trends during the year. At the end of summer when the bottom water temperature reached its maximum (about 14°C), the concentrations of DFAA were also at their maxima. However, a response to the input of organic matter to the sediment was also observed as increased pore water DFAA concentrations. The seasonal response was not strong, which probably was due to several processes (e.g. adsorption, degradation and bacterial assimilation) removing DFAA and thereby preventing large pools of DFAA from being built up in the pore water. Adsorption of ammonium followed the concentration of dissolved ammonium in the pore water and there was neither a relation with input of organic matter nor with temperature in the bottom water. The adsorption coefficient (the dimensionless K) for ammonium was 1.07 ± 0.11 and did not vary during the year. The adsorption coefficients for amino acids, which were all higher than K for ammonium, did show seasonal trends and the periods with high concentrations of adsorbed amino acids were related not only to high concentrations of DFAA, but also to recent input of organic matter and probably also to the stimulation of bioturbation as a result of high temperature in the bottom water at the end of summer. The results demonstrated a seasonal variation in K of amino acids, but not ammonium, indicating that the processes controlling dissolved concentrations were substantially different for these compounds.

KEY WORDS: Seasonality · Amino acids · Ammonium · Pore water · Coastal sediment · Adsorption · Adsorption coefficients

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