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 N 2 before use gave pore‐water concentration profiles of total Fe, Fe 2+ , dissolved reactive P, and SO 4 2− that were significantly different from those obtained with samplers in which only the aqueous dissolved O 2 had been removed by bubbling for 18 h with N 2 . The differences in concentrations are attributable to the loss of substantial amounts of O 2 by the plastic material and reaction of the liberated O 2 with reduced porewater constituents. Laboratory tests show that acrylic in equilibrium with atmospheric O 2 can store up to 1.6% (vol/vol) of O 2 that will be slowly lost (halftime, ∼5.7 d) once exposed to an anoxic environment. Oxygen solubility at 23°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 O 2 for more than a few hours.