The aerobic mineralization of organic compounds in the saline Lake Grevelingen (The Netherlands) (VI)

Summary During a one year period the uptake of aspartic acid and of a mixture of amino acids was determined using¹⁴C-labeled substrates as described by WRIGHT and HOBBIE (1966). By this technique the activity is analyzed of that part of the bacterial population which is able to utilize the added substrate. For comparison purposes the activity of the total heterotrophic bacterial population was determined by measurement of the oxygen consumption rate. From the oxygen consumption rate (mg O₂.l^–1.h^–1) the carbon mineralization rate (mg C.l^–1.h^–1) was calculated by applying a conversion factor of 0.29.Aspartic acid was respired for 80% and the amino acid mixture for 43%. From the maximum uptake rates, the potential yearly uptake of the substrate in question can be calculated. These data indicate the relative importance of the several subpopulations in the carbon mineralization process as a whole. The highest value of the potential yearly uptake was obtained for the amino acid mixture; the comparable value for the uptake of aspartic acid was slightly lower.The carbon mineralization rate as calculated from the oxygen uptake experiments was about 150–200 g C.m^–2.year^–1. The potential yearly uptake as determined with the¹⁴C-labeled amino acid mixture was only 2.8% of the amount of mineralized carbon, as calculated from the oxygen uptake experiments. This percentage is very low in view of the fact that 35–55% of the organic carbon of living phytoplankton and zooplankton consists of protein (HAGMEIER, 1961) and that the aerobic mineralization of amino acids is a very common property among the heterotrophic bacterial population (SEPERS, 1979). The value of the applied activity measurements was investigated in order to obtain information about the relation between the uptake process as measured with¹⁴C-labeled substrates and the activity of the bacterial population in situ. The results of this study have been published bij SEPERS and VAN ES (1979).