A Chemical Analysis of Sediment Pore Water in Oxygen-free Atmosphere: Application to a Contaminated Area

Interstitial water chemistry has been widely studied to identify biological and chemical reactions in the sediment and to assess sediment-water exchange of dissolved chemical compounds (e. g. Sayles 1979; Froelich et al. 1979; Saager et al. 1990; van Raaphorst & Malschaert, 1996). However, sediment pore water sampling is tedious and requires the use of special equipment due to the possible effects and potential chemical alterations resulting from incorrect procedures. It is known that, with the exception of the uppermost sediment layers (of 1 to 3 cm thickness), most fine-grained deposits are anoxic but oxidize rapidly upon exposure to air. The oxidation of the sediments brings about rapid changes in the kinds of redox-sensitive chemicals dissolved in the sediment pore water. During pore water collection and sample processing the maintenance of an oxygen-free atmosphere is essential for the measurement of some of the original chemical constituents (Manheim, 1976; Kriukov & Manheim, 1982). Results from many studies indicate that nutrient concentrations of pore water may be much higher than those of the water column (Ohle, 1977; Esteves, 1988; van Raaphorst & Malschaert, 1996). Generally, glove bags or glove boxes should be used to handle the pore water samples that best represent the natural sedimentary environment. It is essential, to ensure these conditions, that any exposure of the sediment and sampled water to the atmosphere must be completely avoided by guaranteeing oxygen-free conditions during the entire process of sediment sample manipulation (Adams, 1991). This can be achieved by working in the inert atmosphere of such a gas as nitrogen, argon or, in some cases, helium or carbon dioxide.