Turnover of tracer (14C,3H labelled) alanine in inshore marine sediments

✍ Scribed by D. Christensen; T. H. Blackburn

• Publisher: Springer-Verlag
• Year: 1980
• Tongue: English
• Weight: 629 KB
• Volume: 58
• Category: Article
• ISSN: 0025-3162
• DOI: 10.1007/bf00396120

✦ Synopsis

The turnover rate constants (k) of alanine in coastal marine sediments were measured using 3H-and 14Calanine in tracer amounts (less than in situ concentrations of alanine in the porewater). After incubation 14Clabel was recovered in free dissolved alanine, adsorbed alanine, volatile fatty acids and carbon dioxide pools. Alanine left the free dissolved pool by two processes: 1) adsorption (k = 0.06 min-a ) and 2) biological uptake (k = 0.16 min-1). Adsorption of alanine was deduced from the persistence of 14C-alanine, which was slowly metabolized after an initial rapid rate of degradation. Adsorption was confirmed in biologically inactivated sediments. The adsorbed 14 C-alanine was only partially exchanged by the addition of excess non4abelled alanine, indicating the existence of at least 2 different adsorbed pools. The rates of adsorption and desorption were equal, but the k-values were different, indicating that the adsorbed pool was 2500 fold greater than the free pool. From the biological turnover rate constant (0.16 rain -1 ), the mineralization percentage (80%) and the concentration of alanine (800 nmol 1-1 of porewater) a mineralization rate in the sediment of 75 nmol cm -3 d -1 was determined. This was in excess of the measured total NHz~ production. It is concluded that much of the dissolved alanine (800 nm) was biologically unavailable and a more realistic free dissolved pool would be ~10nM.