Practical improvements for redox potential ( EH) measurements and the application of a multiple-electrode redox probe (MERP) for characterising sediment in situ

Abstract

Redox potential ( E H) measurements can provide qualitative information about sediment processes and conditions. However, there are problems associated with the measurement and interpretation of E H values. The measurement difficulties can be partly addressed by ensuring that suitable indicator electrodes are properly cleaned and tested before use. We compared the performance of platinum and glassy carbon indicator electrodes, and concluded that the former are preferred for application to natural waters and sediment. However, glassy carbon electrodes may be more suitable for measuring redox potentials involving organic species. The most effective way to clean platinum electrodes was to use abrasive polishing routinely and concentrated nitric acid to overcome long term fouling. A 1:100 dilution of ZoBell's solution (while maintaining the original electrolyte strength) was found to be a sensitive test solution for determining the condition of indicator electrodes. While limitations to the interpretation of E H will remain for most natural systems, we have demonstrated various ways in which useful information could be obtained from redox potential measurements in sediment using a multiple-electrode redox probe (MERP). These examples included general characterisation of the redox conditions of sediment from a vertical redox profile, highlighting zones of varying redox processes within a profile, and obtaining evidence of temporal changes in redox conditions that arise in estuarine sediment during tidal cycles.