Sampling anoxic pore waters in peatlands using “peepers” for in situ-filtration

Abstract

Equilibrium diffusion chambers (“peepers”) have been constructed to collect anoxic pore waters in bogs without degassing and/or oxidizing the samples. These samplers have been constructed of Plexiglass, either as a long board with a series of sampling chambers for close interval analyses near the surface of a bog, or as single chambers inserted at greater depths (1 to 6 m). Prior to installation, the chambers have been filled with deaerated, deionized water, and have been covered by a 0.2 μm membrane filter; this membrane allows the dissolved constituents in the waters to equilibrate with the deionized water in the chamber by diffusion. The samplers have been allowed to equilibrate in the bog for 4 to 6 weeks. Thereafter, they have been withdrawn into N₂-filled glove bags. Individual chambers have been sampled in the field by inserting a syringe through the glove bag; these syringes have been used immediately upon the arrival in the lab to analyze volatile and redox-sensitive species by ion chromatography. The effectiveness of this sampling approach has been demonstrated by measuring the concentrations of the dominant volatile acids in these waters (H₂CO₃) and two redox sensitive species (Fe²⁺ and HS^–). The procedure described here should be applicable also to trace metal speciation studies, provided that appropriate checks are made for all possible sources of contamination.