FACTORS CONTROLLING THE FORMATION OF OXIDIZED ROOT CHANNELS - A REVIEW

Although root plaques and associated oxidized root channels are used f or wetland identification as field indicators of wetland hydrology, li ttle information is available concerning their reliability as related to the environmental and biotic factors controlling their formation. T herefore, this review describes and evaluates the current state of kno wledge of the factors controlling the formation of iron plaques and re commends research to address information gaps. Both abiotic and biotic factors control the presence and degree of iron plaque formation. The most important abiotic factor is the availability of soil iron. Howev er, the effect of site variation in soil physico-chemical characterist ics (e.g., texture, organic matter, pH, Eh, and soil fertility) on iro n availability and microbial activity can influence the formation and persistence of root plaques and oxidized root channels. Although the o xidizing capacity of the plant root is the most important biotic facto r controlling plaque formation, only a limited number of wetland speci es have been evaluated for this ability, so species-specific differenc es are generally unknown. Unlike some of the other hydrologic indicato rs used in wetland delineation (e.g., water marks on trees or sediment deposits) root plaques and oxidized root channels indicate soil satur ation for a sufficient period to produce anaerobic soil conditions. Ad ditionally, when found in conjunction with a living root, oxidized roo t channels indicate that the anaerobic conditions occurred within the life span of the plant root. Therefore, the presence of oxidized root channels and iron plaque surrounding living roots is a relatively good indicator of current wetland hydrologic conditions. However, research is needed to elucidate the relative abilities of different plant spec ies to produce oxidized root channels, the temporal persistence of the root iron plaque and the role that soil physico-chemical condition pl ays in controlling plaque formation. Without a better understanding of the controls on iron plaque formation and disappearance, the absence of oxidized root channels, in itself, should not be used to indicate t he absence of a wetland.