The mobility and plant availability of many trace and toxic metals in wetland soils is often substantially different from upland soils. Oxidation-reduction (redox) and associated pH changes that occur in soils as a result of flooding or drainage can affect the retention and release of metals by clay minerals, organic matter, iron oxides, and, for coastal wetlands, sulfides. Except where a tlooded soil or sediment becomes strongly acid upon drainage and oxidation, as sometimes occurs, the processes immobilizing metals tend to be complimentary such that large-scale metal releases from contaminated soils and sediments do not occur with changing redox conditions. Metals tend to be retained more strongly in wetland soils compared with upland soils.

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Delineating wetlands from nonwetlands in seasonally inundated ecosystems is often difficult and requires data on soil functions and attributes. Techniques (including equipment design, construction, and installation) for assessing wetland soil attributes have been developed that allow direct field measurements of soil O2 content, oxidation‐reduction potential, water‐table depth, and presence of ferrous iron. Soil O2 content is measured from diffusion chambers with a specially fitted polarographic probe. Redox potential is measured with permanently installed platinum electrodes and a voltmeter. Determination of water‐table depth may require piezometers in addition to unlined observation wells. The presence of ferrous iron can be detected with α, α,‐dipyridyl and indicates anaerobic conditions, although interpretation and extrapolation of results must be carefully made. These parameters are particularly diagnostic and results of field studies reveal their dynamic nature and utility in wetland delineation efforts.

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