Effects of fluctuations in the Eh-pH environment on iron and or manganese equilibria.
About: This article is published in Soil Science.The article was published on 1970-08-01. It has received 85 citations till now. The article focuses on the topics: Manganese.
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TL;DR: In this article, the authors discuss the problems of field-measuring equipment and the Pt electrode that often lead to spurious results in the field and suggest some suggestions for improvement are discussed.
Abstract: Reduction and oxidation measurements create important data for analysis of wet soils. These measurements are actually recordings of voltage (EH) over time between a reference electrode and a sensor electrode inserted into a soil. The sensor electrodes are usually made of platinum wire (Pt electrode). Hydric soils require a period of reduction, and these measures can provide the length of time that the reduction process is occurring. The voltage results from an exchange of electrons between a redox couple such as ferrous and ferric iron during the process of reduction and oxidation. In soils that have fluctuating wet and dry conditions, wide fluctuations in Eh occur. Micro site differences complicate these measurements in that anaerobes may be active and at 1‐cm away they are completely inactive. The ferrous–ferric iron couple usually dominates these measurements but other couple often contributes complicating the measurements and interpretations of the data. Reference electrodes are often fine for laboratory work but are not rugged enough for the field. In this chapter, suggestions for improvement are discussed. Field‐measuring equipment and the Pt electrode are also sensitive and subject to problems that often lead to spurious results in the field. These problems are discussed at length. Iron‐coated tubes and other methods of establishing redox conditions are relatively recent and are discussed, also.
255 citations
TL;DR: In this article, it was shown by means of X-ray diffraction to be an Fe(II)-Fe(III)-Sulphate interlayered green rust, GRso4, which belongs to the pyroaurite-sjogrenite group of layered hydroxides.
232 citations
21 Apr 2016
TL;DR: In this paper, the chemistry of hydric soils is discussed by focusing on the oxidation-reduction reactions that affect certain properties and functions of the soil and form the indicators by which hydric soil are identified.
Abstract: Hydric soils are described in Chapter 2 as soils that formed under anaerobic conditions that develop while the soils are inundated or saturated near their surface. These soils can form under a variety of hydrologic regimes that include nearly continuous saturation (swamps, marshes), short-duration flooding (riparian systems), and periodic saturation by groundwater. The most significant effect of excess water is isolation of the soil from the atmosphere and the prevention of O 2 from entering the soil. The blockage of atmospheric O 2 induces biological and chemical processes that change the soil from an aerobic and oxidized state to an anaerobic and reduced state. This shift in the aeration status of the soil allows chemical reactions to occur that develop the common characteristics of hydric soils, such as the accumulation of organic carbon in A horizons, gray-colored subsoil horizons, and production of gases such as H 2 S and CH 4 . In addition, the creation of anaerobic conditions requires adaptations in plants if they are to survive in the anaerobic hydric soils. This chapter discusses the chemistry of hydric soils by focusing on the oxidation–reduction reactions that affect certain properties and functions of hydric soils and form the indicators by which hydric soils are identified (Chapter 7). Both the biological and chemical functions of wetlands are controlled to a large degree by oxidation–reduction chemical reactions (Mitsch and Gosselink 1993). The fundamentals behind these reactions will be reviewed in this chapter along with methods of monitoring these reactions in the field, and the effects of these reactions on major nutrient cycles in wetlands. In our experience, soil chemistry is probably the subject least understood by students of hydric soils and wetlands in general. Therefore, the following treatment is intended to be simple, and to cover those topics that can be related to the field study of hydric soils. Students wishing more detailed treatments are encouraged to consult the work of Ponnamperuma (1972) in particular, as well as the discussion of redox reactions in McBride (1994) and Sparks (1995).
187 citations
TL;DR: In this paper, the authors explain the lack of equilibrium between dissolved and reactive O2 and the presence of ionic Mn species on seafloor sediments by using surface adsorption and cation substitution within disordered birnessite-todorokite structure.
155 citations
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01 Jan 1976
TL;DR: In this paper, short-term and long-term chemical processes in periodically flooded acid sulfate soils in the Bangkok Plain and in various smaller coastal plains along the Gulf of Thailand, 16 acid sulfurate soils and one non-acid marine soil were examined for distribution of iron-sulfur compounds, elemental composition of soil and clay, clay mineralogy, redox potential, pH, and ionic activities in the soil solution.
Abstract: To study short-term and long-term chemical processes in periodically flooded acid sulfate soils in the Bangkok Plain and in various smaller coastal plains along the Gulf of Thailand, 16 acid sulfate soils and one non-acid marine soil were examined for distribution of iron-sulfur compounds, elemental composition of soil and clay, clay mineralogy, redox potential, pH, and ionic activities in the soil solution. The application of thermodynamics to mineral-water interactions enlightened various aspects of sulfate reduction, weathering and transformation of minerals (with emphasis on iron oxides, jarosite and clay minerals), and acid production and pH buffering reactions in the soils.
143 citations