Application of the 14C Organic Mineralization Technique to Marine Sediments

Abstract

This research was designed to demonstrate the usefulness of the heterotrophic mineralization technique in marine sediments and to assess the temporal and spatial heterogeneity of the marine sedimentary microbial population. To do this, adaptation of the mineralization procedures using [14C]urea and [U-14C]-L-aspartic acid was made. Exact details outlining procedures, replicates, substrate concentration, incubation conditions, etc. are described. The turnover times and maximal uptake velocity (Vmax) of substrate utilization as well as the total colony-forming units (CFU) on various media were all calculated according to standard procedures. Temporal heterogeneity was examined during two cruises in August 1975 and August 1976 by repeated sampling at one or more stations during a 24- to 48-h cycle. From the measured parameters, there appears to be no significant diel periodicity in either the level of microbial activity or in the CFU. Calculated values for turnover times generally showed less variation than did the values for maximal uptake velocities. Spatial heterogeneity in the sediments was evaluated using a multiple corer, which took four cores within 1 m2. Although slight variations in the absolute activity levels do exist within a station, they do not appear to be significant at the p = 0.1 level. Interstation variability is significant at p = 0.1. At the continuously reoccupied station, August 1975, close correlation between the numbers of CFU on selective media and the utilization of that 14C-labeled substrate indicated that the technique is indeed measuring microbial activity. Therefore, it is possible to use the 14C heterotrophic mineralizaion method in marine sediments, provided replication and sufficient controls are included. Within a designated station, the rather large sample size required obscures any microheterogeneity and provides an index of the level of microbial heterotrophic activity.