Microbenthic chamber with microelectrode for in-situ determination of fluxes of dissolved S(-II), I-, O2, Mn, and Fe

A 2-mL microbenthic chamber was fitted with a microelectrode for the in-situ determination of benthic fluxes of S(-II), I-, O-2, Mn(II), and Fe(II). Detection was by voltammetry using a battery operated potentiostat and a gold microelectrode. The chamber was fitted on a Perspex plate to be placed on sediments. Because of the small chamber volume, benthic fluxes could be determined in a few hours rather than days, without the need for sample extraction. Tests on homogenized sediments in the laboratory showed fluxes of 17.1 +/- 1.8 nmoles cm(-2) min(-1) SHO and 1.3 +/- 0.2 nmoles cm(-2) min(-1) Mn. Benthic fluxes of oxygen and iodide were determined in situ in the field. The oxygen flux was negative (consumption) at a rate of -4.9 +/- 0.5 nmoles cm(-2) min(-1) O-2. The I- flux was initially negative in oxygenated waters at a rate of -30 +/- 3 pmoles cm(-2) min-' and subsequently turned positive to a rate of 12 +/- 1 pmoles cm(-2) min(-1) when the oxygen concentration dropped. The rate of change in the microbenthic chamber was sufficiently quick to complete a flux measurement within minutes.