In Situ Deployment of Voltammetric, Potentiometric, and Amperometric Microelectrodes from a ROV To Determine Dissolved O2, Mn, Fe, S(-2), and pH in Porewaters

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• 作者：George W. Luther ; III ; Clare E. Reimers ; Donald B. Nuzzio ; and David Lovalvo
• 刊名：Environmental Science & Technology
• 出版年：1999
• 出版时间：December 1, 1999
• 年：1999
• 卷：33
• 期：23
• 页码：4352 - 4356
• 全文大小：74K
• 年卷期：v.33,no.23(December 1, 1999)
• ISSN：1520-5851

文摘

Solid-state microelectrodes have been used in situ inRaritan Bay, NJ to measure pore water profiles of dissolvedO₂, Mn, Fe, and sulfide at (sub)millimeter resolution byvoltammetric techniques. The voltammetric sensor waspositioned with microprofiling instrumentation mounted ona small remote operated vehicle (ROV). This instrumentationand the sensor were controlled and monitored in real timefrom a research vessel anchored at the study site. Thevoltammetric analyzer was connected to the electrodes ofthe voltammetric cell with a 30 m cable which alsobridged receiver-transmitter transducers to ensure signalquality along the cable. Single analyte O₂, pH, andresistivity microsensors were operated alongside thevoltammetric sensor. We report on the technology of thesystem and the concentration changes of redox speciesobserved from 2 to 3 cm above to approximately 4 cm belowthe sediment-water interface during three deployments.O₂ measurements from both Clark and voltammetric electrodeswere in excellent agreement. The profiles obtained showthat there is no detectable overlap of O₂ and Mn²⁺ in thesediments which is similar to previous reports fromother continental margin sediments which were coredand analyzed in the laboratory. These data indicate thatO₂ is not a direct oxidant for Mn²⁺ when diffusive (ratherthan advective) processes control the transport ofsolutes within the sediment. Subsurface Mn²⁺ peakswere observed at about 2 cm and coincide with a subsurfacepH maximum. The data can be explained by organicmatter decomposition with alternate electron acceptorsand by the formation of authigenic phases containing reducedMn at depth.