Origin of 14C and 32P labelled lipids moving to and from freshwater surface microlayers

The production and distribution of 14C and 32 labelled lipids were studied in laboratory model aquatic systems consisting of organisms, sediment and suspended particles. Using teflon impactor plates, transport of the lipids from the water to the atmosphere via jet drops from breaking bubbles in the surface microlayer was measured. Several solid materials were studied for recovery of artificial and natural surface microlayers. Hydrophilic teflon, which collects a layer 17-19 μm thick, showed the best recovery in both cases. 14C and 32P added in inorganic form to sediment and subsurface water of the systems were biologically incorporated into neutral and complex lipids. The 14C labelled lipids were enriched in the surface microlayer to about 3500-5400 times the concentration found in the subsurface water. The corresponding enrichment for 32P labelled lipids was 16000 to 200 000. The 32P lipid material produced within the systems was strongly associated to microorganisms, particulate matter and sediment. However, during 5 d 0.3 to 16% of the labelled lipids left the systems via jet drops produced by breaking bubbles. (author)