PRACTICAL IMPROVEMENTS FOR REDOX POTENTIAL (E-H) MEASUREMENTS AND THEAPPLICATION OF A MULTIPLE-ELECTRODE REDOX PROBE (MERP) FOR CHARACTERIZING SEDIMENT IN-SITU

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 suit able indicator electrodes are properly cleaned and tested before use. We compared the performance of platinum and glassy carbon indicator el ectrodes, 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 spec ies. The most effective way to clean platinum electrodes was to use ab rasive polishing routinely and concentrated nitric acid to overcome lo ng term fouling. A 1:100 dilution of ZoBell's solution (while maintain ing the original electrolyte strength) was found to be a sensitive tes t solution for determining the condition of indicator electrodes. Whil e limitations to the interpretation of E-H will remain for most natura l systems, we have demonstrated various ways in which useful informati on could be obtained from redox potential measurements in sediment usi ng a multiple-electrode redox probe (MERP). These examples included ge neral characterisation of the redox conditions of sediment from a vert ical redox profile, highlighting zones of varying redox processes with in a profile, and obtaining evidence of temporal changes in redox cond itions that arise in estuarine sediment during tidal cycles. (C) 1998 Elsevier Science B.V. All rights reserved.