Extraction and distribution of free amino-acids and ammonium in sediment interstitial waters from the limfjord, Denmark

Abstract

RESUME N. O. G. Jy;rgensen a, P. Lindroth b, K. Mopperc * a Institute of Ecology and Genetics, University of Aarhus, Ny Munkegade, DK-8000 Aarhus C, Denmark. b Department of Analytical and Marine Chemistry, Chalmers University ofTechnology and University of Goteborg, S-412 96 Goteborg, Sweden. · c College of Marine Studies, University of Delaware, Lewes, Delaware 19958, USA. • to whom correspondance should be adressed. Received 11/6/80, in revised form 16/3/81, accepted 10/5/81. Dissolved free amino acids and ammonium were extracted by centrifugation from four diverse sediments from a Danish fjord. Analyses were performed by precolumn fluorigenic labelling followed by HPLC separation and on-line fluorescence detection. The most abundant amino acids found were glutamic acid, serine, glycine, alanine and leucine. Glutamic acid and possibly ~-aminoglutaric acid were especially important in the anoxie sediments. At sorne of the localities, a close resemblance of the amino acid spectra in the overlying sea water to that of the sediment interstitial water was observed, which supports the idea that free amino acids can diffuse into bottom sea water. The concentrations of sediment interstial amino acids were found to decrease in the extracts with an increase in duration of centrifugation. In addition, the amino acid spectra of the ex tracts changed to varying degrees with increasing centrifugation time. These results are discussed in terms of: (1) rapid and selective microbial degradation during sediment storage and extraction; (2) stress induced excretion of intracellular amino acids, and (3) physiochemical processes. It was tentatively concluded that physiochemical processes were dominant. Oceanol. Acta, 1981, 4, 4, 465-474. Extraction et repartition des acides amines libres et de l'ammonium dans les eaux interstitielles des sediments du Limfjord, Danemark. Les amino-acides libres dissous et l'ammonium sont extraits par centrifugation de quatre sediments differents provenant d'un fjord danois. Les analyses comportent un marquage prealable par formation de derives fluorescents suivi d'une separation par HPLC et detection des composes fluorescents sur la courbe d'elution. Les amino-acides les plus abondants sont l'acide glutamique, la serine, la glycine, l'alanine et la leucine. L'acide glutamique et, peut-etre, l'acide ~-amino glutarique, apparaissent particulierement importants dans les sediments anoxiques. Dans quelques sites, on observe une forte analogie entre le spectre des amino-acides de l'eau sus-jacente et celui de l'eau interstitielle du sediment, ce qui conforte l'idee que les amino-acides libres peuvent diffuser dans l'eau du fond. Les concentrations en amino-acides des extraits interstitiels decroissent lorsque augmente la duree de la centrifugation; de plus,le spectre des amino-acides evolue de facon variable avec le temps de centrifugation. Ces resultats sont discutes en fonction : (1) d'une ·degradation microbienne rapide lors de la conservation du sediment et de l'extraction; (2) d'une excretion d'amino-acides intra-cellulaires causee par les phenomenes de stress; et (3) des processus physico-chimiques. On tente, en conclusion, de montrer que les processus physico-chimiques sont dominants. Oceanol. Acta., 1981, 4, 4, 465-474. 0399-1784/1981/465/$ 5.00/ (!:) Gauthier-Villars 465 N. O. G. J!l'>RGENSEN. P. LINDROTH. K. MOPPER