Spatial and temporal gradients in aquifer oxidation‐reduction conditions

Abstract

The study was undertaken to identify principal oxidizing and reducing chemical species in groundwater with the goal of determining the utility of platinum electrode (Eh) measurements to characterize subsurface redox conditions. Serial measurements of Eh and groundwater analyses were conducted in oxic and suboxic environments over more than a 2-year period for major ionic, oxidized, and reduced species. Vertical gradients in measured Eh values in the oxic groundwater environments can exceed -40 mV/m depth. In the poorly poised, oxic groundwaters, the Eh measurements correlated reasonably well with calculated values based on analytical determinations of 02 and H202 which was detected persistently in the 10 -8 to 10 -9 M range. The equilibrium calculated Eh values from this and other redox couples did not correlate well with measured Eh values over the 2-year study period. In the suboxic range, the average calculated values based on the Fe3+/Fe 2+ coupled correlated well with averaged measured values. The results support the need to determine redox pairs in groundwater as a supplement to either calculated "equilibrium" Eh values or Pt electrode Eh measurements.

Bioremediation of Mangroves Impacted by Petroleum

“…The importance of oxygen comes from the involvement of oxygenases and molecular oxygen in the main pathways of hydrocarbon degradation. Aerobic production processes possess a higher energetic efficiency per substrate unit and tend to occur much faster (Atlas 1981;Harbison 1986;Kuznetsov and Ulstrup 1988;Zehnder 1988; Barcelona et al 1989;Levett 1990;Burland and Edwards 1999;Coates and Anderson 2000;Lyimo et al 2002;Boopathy 2003;Hwang et al 2007;Barbier et al 2008;Li et al 2009;Tsai et al 2009) Unlike aerobic bacteria, anaerobic bacteria depend on different acceptors to survive. The most common electron acceptors in the natural environment are nitrates, manganese (Mn (IV)), iron (Fe (III)) and sulfate.…”

Redox: fundamentals, processes, and applications

“…: leachate from unsecured landfills) or biodegradable organic contaminants (e.g. : from airfield fuel storage) into shallow aerobic aquifers usually initiate the development of redox successions (BARCELONA et al, 1989;LYNGKILDE & CHRISTENSEN, 1992b). These successions occur in a reverse order compared to deep pristine aquifers (LOVELEY et al, 1994).…”

“…The general approach for the assessment of the redox status of aquifers are platinum electrode measurements or chemical equilibrium calculations based on the chemical analysis of the main redox species (BARCELONA et al, 1989;HOSTETTLER, 1984). Beside the widely discussed problems of measuring redox potentials in natural waters , additional problems occur in contaminated aquifers due to high reactivity, disequilibrium and the distribution of reduced species (e.g.…”

Modeling reactive transport of organic compounds in groundwater using a partial redox disequilibrium approach

“…An implicit assumption is that redox disequilibrium is entirely restricted to the organic compounds and that mutual equilibrium between inorganic redox species is achieved rapidly in comparison. This assumption is never really true because most natural systems, including those largely tYee of dissolved organic compounds, are generally not in redox equilibrium [e.g., Wole.ry, 1983 ' Lindberg and Runnels, 1984;Drever, 1988;Barcelona et al, 1989]. Nevertheless, redox conditions predicted by equilibrium models are often in reasonable qualitative agreement with observed phenomena in terms of the concentrations of major species NO.C, NH•', SO¬-, CH 4, etc.).…”