MICROBIAL TRANSFORMATION OF LABILE DISSOLVED ORGANIC-MATTER INTO HUMIC-LIKE MATTER IN SEAWATER

Microbial transformation of labile, low molecular weight dissolved org anic matter (DOM) into dissolved humic matter (DHM) was studied in sea water. Surface water samples were amended with [C-14]glucose, and the partitioning of C-14 into (CO2)-C-14 (TOC)-C-14 (total organic C-14), and (POC)-C-14 (particulate organic C-14), was measured over time in c onfined samples. The humic and non-humic fractions of (DOC)-C-14 (diss olved organic C-14) were separated according to a common operational d efinition of DHM based on adsorption on XAD-8 macroporous resin. Both (TOC)-C-14 and non-humic (DOC)-C-14 decreased during the experiments. However, C-14-labelled DHM increased during the first week of the incu bations, to a level where it comprised 15% of the (TOC)-C-14 remaining in the samples, or 3% of the initially added C-14. Towards the end of experiments (ca 70 days), the humic fraction of (DOC)-C-14 gradually approached the background level of poisoned control samples. Provided that the XAD-8 operational definition of DHM is accepted, this study i ndicates that humic matter may be formed in seawater within days from labile monomers such as glucose.