USE OF DIFFUSION SAMPLERS IN OLIGOTROPHIC LAKE-SEDIMENTS - EFFECTS OF FREE OXYGEN IN SAMPLER MATERIAL

In the anoxic sediments of an oligotrophic lake, acrylic pore-water diffusion samplers conditioned by a 30-d exposure to N2 before use gave pore-water concentration profiles of total Fe, Fe2+, dissolved reactive P, and SO42- that were significantly different from those obtained with samplers in which only the aqueous dissolved O2 had been removed by bubbling for 18 h with N2. The differences in concentrations are attributable to the loss of substantial amounts of O2 by the plastic material and reaction of the liberated O2 with reduced pore-water constituents. Laboratory tests show that acrylic in equilibrium with atmospheric O2 can store up to 1.6% (vol/vol) of O2 that will be slowly lost (half-time, approximately 5.7 d) once exposed to an anoxic environment. Oxygen solubility at 23-degrees-C is highest in polycarbonate (3.7%) and Teflon (2.8%) and lowest in high-density polyethylene (0.6%) and polyvinylidene fluoride (0.8%). Samplers made of such materials should not be exposed to atmospheric O2 for more than a few hours.