Abstract
Hydrolyzable amino acids were measured in cores and surface sediment samples collected over a 14 month period from the rapidly accumulating, anoxic sediments of Cape Lookout Bight, NC. The concentration of total hydrolyzable amino acids (THAAs) shows an exponential decrease with depth, in a manner similar to total organic carbon and total nitrogen. Carbon and nitrogen in THAAs averages 10–15% of the total organic carbon and 30–40% of the total nitrogen in these sediments (both on a mole/mole basis). In surface sediments the concentration of THAAs do not show strong seasonal variations, with the exception of a small apparent decrease during the winter months. Aspartic acid, glutamic acid, glycine and alanine are the most abundant individual amino acids in Cape Lookout Bight sediments. The distribution of individual amino acids in these sediments is very similar to that observed in the two major sources of organic matter, vascular salt marsh plants and marine plankton. The mole fractions of most amino acids show no depth variation in Cape Lookout Bight sediments. However the mole fractions of alanine and glutamic acid decrease with depth and the mole fraction of glycine increases with depth. These changes are attributed to the selective microbial utilization of alanine and glutamic acid, and the selective preservation of glycine in these sediments relative to other amino acids. Kinetic modelling of these data indicates that the deposition of amino acids to the surface of these sediments is 5.8 ± 1.0 mol· m −2· yr −1. Approximately 46 ± 16% of this input is remineralized in the upper 40 cm. The recycling of amino acids accounts for 82 ± 43% of the total nitrogen regeneration and 27 ± 11% of the regeneration of total organic carbon in these sediments. The mean residence time of metabolizable amino acids is approx. 9 months, a value which is comparable to the mean residence times of both metabolizable organic carbon and nitrogen in these sediments.
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