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 develo ped for the measurement of dissolved O-2, S(-II), Fe, and Mn in the po rewaters of marine sediments. This electrode can provide more informat ion at (sub)millimeter depth resolution on all of the major redox spec ies found in the environment than membrane microelectrodes which usual ly can measure only one of these species per electrode. We describe th e construction, standardization, analytical validation, and applicatio n of a microelectrode to marine sediments. The use of the microelectro de takes advantage of the fast scan voltammetric methods for simultane ous measurement of all redox species during one potential scan. Electr ochemical conditioning of the solid-state microelectrode between volta ge scans while deployed in waters and sediments allows for repeated us e of the electrode. Finally, we demonstrate depth profiles at millimet er resolution for the redox species in a Delaware salt marsh. The prof iles observed are consistent with the known biogeochemical cycling of the target redox species. In addition, we provide evidence for H2O2, i ron(II) sulfide complexes, and iron(III) colloids or organic complexes in porewaters.