The role of surface-active carbohydrates in the formation of transparent exopolymer particles by bubble adsorption of seawater

Experiments were performed to examine the role of surface-active polysaccha rides in the formation of transparent exopolymer particles (TEP) by bubble adsorption in seawater. Filtered (1.0 Gem, 0.45 mu m) and ultrafiltered (0. 1 mu m, 100 kDa, and 10 kDa) seawater samples were bubbled in a glass foam tower. The neutral sugar composition, concentration of TEP, and concentrati on of surface-active carbohydrates in generated foam samples were determine d. Three different surface seawater samples (Monterey Bay, California; Shan non Point, Anacortes, Washington; and East Sound, Orcas Island, Washington) were used in the experiments. Significant concentrations of pre-existing a nd new TEP were extracted into foam by bubble adsorption. Newly generated T EP accounted for 28-52% of the TEP collected in the foam samples by bubblin g 1.0-mu m-filtered samples. Neutral sugar composition analyses of foam sam ples derived as a function of bubbling time indicated that two types of sur face-active carbohydrates were extracted by bubble adsorption: highly surfa ce-active carbohydrates, which were extracted initially, and less surface-a ctive carbohydrates. As in our previous mesocosm study (Mopper et al. 1995) , highly surface-active polysaccharides were enriched in deoxysugars (fucos e and rhamnose), whereas the less surface-active polysaccharides and residu al (bubble-stripped) water were glucose rich. In addition, the highly surfa ce-active fraction was strongly enriched in covalently bound sulfate. The c oncentrations of TEP and surface-active carbohydrates that were extracted i nto the foam both decreased sharply with decreasing filter size used to fil ter samples prior to bubbling, in agreement with theoretical considerations . The results of this study suggest that bubble adsorption of sulfate-rich surface-active carbohydrates is an important pathway for the formation of T EP in surface waters, especially during algal blooms.