DEVELOPMENT OF A GOLD AMALGAM VOLTAMMETRIC MICROELECTRODE FOR THE DETERMINATION OF DISSOLVED FE, MN, O-2, AND S(-II) IN POREWATERS OF MARINE AND FRESH-WATER SEDIMENTS

A solid-state voltammetric gold amalgam microelectrode has been developed for the measurement of dissolved O-2, S(-II), Fe, and Mn in the porewaters of marine sediments. This electrode can provide more information at (sub)millimeter depth resolution on all of the major redox species found in the environment than membrane microelectrodes which usually can measure only one of these species per electrode. We describe the construction, standardization, analytical validation, and application of a microelectrode to marine sediments. The use of the microelectrode takes advantage of the fast scan voltammetric methods for simultaneous measurement of all redox species during one potential scan. Electrochemical conditioning of the solid-state microelectrode between voltage scans while deployed in waters and sediments allows for repeated use of the electrode. Finally, we demonstrate depth profiles at millimeter resolution for the redox species in a Delaware salt marsh. The profiles observed are consistent with the known biogeochemical cycling of the target redox species. In addition, we provide evidence for H2O2, iron(II) sulfide complexes, and iron(III) colloids or organic complexes in porewaters.