ANOXIC AND OXIC DEGRADATION OF C-14-LABELED CHLOROPIGMENTS AND A C-14-LABELED DIATOM IN LONG-ISLAND SOUND SEDIMENTS

Anoxic and oxic degradation pathways of sedimentary chloropigments were examined by spiking marine sediment with C-14-labeled algal cells and purified chloropigments from the diatom Skeletonema costatum. These experiments suggest that Chl a degrades through multiple pathways. Under oxic conditions, most bulk sedimentary Chl a degraded to various colorless compounds and only a minor fraction degraded to pheophytin a; added C-14-labeled Chl a also degraded quickly, but 30-40% of this Chl a was converted to pheophytin a. Under anoxic conditions, only a small fraction of bulk Chl a degraded, but added C-14-labeled Chl a continuously degraded and approximately 30-40% of it was converted to pheophytin a. Pheophytin a is relatively stable under anoxic conditions but degrades under oxic conditions, thus it is a potential end product of chloropigment degradation in anoxic environments. Degradation pathways are likely dependent on the relative proportion of unassociated Chl a to chlorophyll complexes present in the sediment. Only unassociated Chl a appears to be available for anoxic decomposition. Under oxic conditions, some colorless products were further degraded and solubilized; none of the C-14 label added as purified pigments was lost under anoxic conditions during the 1-month incubation. About 80% of the acetone-extractable C-14 in labeled cells was lost in 1 month from sediments under oxic conditions and approximately 30% under anoxic conditions.