redoximorphic features is important for a clear understanding of reductimorphic processes. The Jackson-Frazier wetland is a rare, relatively undisturbed wet-The Jackson-Frazier wetland is a rare, relatively unland in the Willamette Valley of Oregon that experiences repetitive disturbed wetland in the Willamette Valley of Oregon annual flooding and drying cycles. Redoximorphic features formed that experiences repetitive annual flooding and drying by these wetting and drying cycles have not been calibrated with cycles and serves as a model for natural wetland condisaturation and reduction. Long-term measurements of soil saturation and soil redox potential (E H ) were combined with measurements tions in the area. The development of hydric soils in of Fe and Mn concentrations to understand the formation of these the wetland is driven by the annual flooding, prolonged redoximorphic features in the wetland soils. The Jackson-Frazier wetperiods of soil saturation, abundant organic carbon, and land is underlain by three stratigraphic units that control its hydrology: mild temperatures that facilitate reductive dissolution Holocene alluvium (A and Bss horizons), Malpass clay (2Bt horizon), and segregation of Fe and Mn into redoximorphic conand Irish Bend silts (3BC horizon). All three units are saturated for centrations and/or depletions (Somera, 1967; Cogger up to 9 mo each year, leading to E H values that fall below the Fe reand Kennedy, 1992; Lovely, 1993; Miller et al., 1993; Veduction threshold. Extractable Fe and Mn in nodules, concretions, praskas, 1994). Three distinct stratigraphic units within and soft masses document substantial depletions from the matrix soil the Jackson-Frazier wetland all contain Fe-Mn concenin all three units. In the 3BC, diffuse halos of Fe accumulation and trations in the form of macroscopic concretions and matrix chromas from two to four indicate a source of Fe that can be nodules (Stewart, 1997). Similar concentrations were reduced, translocated, and concentrated in nodular form. In the Bss identified as early as 1940 by Drosdoff and Nikiforoff and 3BC horizons, soft masses surrounding concentrations and higher ratios of oxalate to dithionite-citrate-bicarbonate Fe (Fe Ox /Fe DCB ) in the (1940), and more recent work by Somera (1967) and larger concentrations suggest that nodules and concretions are cur-Seter and Baham (1994) has shown that the greatest rently forming by accretion of Fe. In the 2Bt, virtually all of the Fe amount of nodules occur in the wettest (poorly drained) and Mn is gone from the matrix, and concretion boundaries are sharp.

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Electrodes used continuously in the field for up to 5 yr were removed, examined visually, and tested in both a quinhydrone solution and a 1:5 soil–water slurry. Comparison with pre‐installation quinhydrone readings showed that all but 3 of 102 electrodes tested were still within ±10 mV of the standard value. Water observed inside more than half the electrodes had no apparent adverse impact on electrode performance. The post‐removal quinhydrone test correctly identified one electrode that developed faulty readings in the first year of field use. Test values for two other potentially defective electrodes fell within acceptable standards after rinsing them in an HCl–HNO3 solution and retesting. Platinum poisoning with coatings could not be detected visually, and we conclude that poisoning, though possibly present at minimal levels, did not significantly impair electrode performance after 5 yr. Post‐removal testing in a constantly stirred slurry gave readings that were a little more variable than quinhydrone readings but were much less variable than actual field readings. Anomalous slurry readings within replicated electrode sets suggest that, despite good quinhydrone readings, some electrodes may not have responded properly under actual field use. Field data from one such set confirmed the presence of a defective electrode. We conclude that the slurry test provides valuable information that complements the quinhydrone test and could be used as a pre‐installation test to help identify potentially faulty electrodes.

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The relationship between wetland soils and hydrology can be better understood by linking soil geomorphological features to the measurement of groundwater depths in the soil. Soil stratigraphic analysis and long‐term measurements of soil water levels in piezometers were used at the Jackson‐Frazier wetland in western Oregon to investigate the interaction between local geomorphological history and the hydrology of the wetland. Morphological descriptions confirm the presence of a recent smectitic alluvial deposit (80–180 cm) overlying Malpass clay (≈35 cm thick), which overlies Irish Bend Silt. X‐ray diffraction and isotope analysis support the conclusion of the presence of the Holocene alluvium and Irish Bend Silt, but are inconclusive regarding the Malpass clay. Piezometer data from 1992 to 1996 show that the smectitic alluvium controls saturation and drying of the wetland surface, and that a separate water table is present below the Malpass clay in the Irish Bend silt. The recent alluvium and Malpass clay act as an aquitard that restricts the vertical infiltration of surface water and helps restrict the groundwater table in the Irish Bend silt deposit. These stratigraphic relationships and associated hydrologic responses provide a means to identify wetlands and predict hydrologic conditions on similar wetland landscapes.