Redox Processes and Diagnostic Wetland Soil Indicators in Bottomland Hardwood Forests

Abstract The presence of unique hydrologic, vegetative, and soil characteristics separates wetlands from nonwetlands. The hydrophytic nature of bottomland hardwood forest vegetation emphasizes soil and hydrologic parameters that are often inferred from soil profile characteristics. Our objectives were to determine the relationships among hydroperiod, soil redox processes, and diagnostic wetland soil indicators. Five transects traversing nonwetland, transitional, and wetland habitat were established parallel to the natural moisture gradient in alluvial bottomlands with mature hardwood forest overstory in Louisiana and Mississippi. Soil redox potential and O 2 content at 15, 30, 60, and 120 cm were monitored monthly from September 1982 to August 1985 with permanently installed equipment. Water‐table depth in the upper 120 cm of the soil was also measured during this time. Oxygen and redox patterns at 30 cm were analyzed for each site. These patterns were conclusive enough to classify five sites as nonwetland and eight sites as wetland; however, additional data (hydric soils, soil profile descriptions) were needed to delineate the remaining 11 sites. The quantitative data supported the qualitative diagnostic wetland soil indicators, hydrologic regime, and wetland status of 18 of the 24 sites. Bottomland hardwood wetlands in the lower Mississippi River Valley that are seasonally inundated may be oxidized and aerobic throughout the root zone for 60 to 80% of the growing season. Many bottomland hardwood soils would be considered hydric by the current wetland delineation procedure. Hydrology is the determining factor for these sites and proper assessment of the current hydroperiod is critical.