Tuesday, November 14, 2006

Redoximorphic Feature Formation in Soils Subjected to Simulated Wetland Hydrology.

Rosalynd S. Orr and Martin C. Rabenhorst. Univ of Maryland, 1111 HJ Patterson Hall, College Park, MD 20742-0001

Soil redoximorphic features are commonly used to evaluate hydrologic conditions in soils. In addition to the hydroperiod, the nature and quantity of redoximorphic features observed can be affected by numerous factors including soil texture, mineralogy, temperature, organic carbon content, and vegetation. To evaluate the effects of soil properties and environmental conditions on hydromorphology, undisturbed soil cores lacking redoximorphic features in the upper part were subjected to simulated hydric conditions for varying lengths of time in both greenhouse and field settings over approximately two years.  In the greenhouse, water table dynamics were manipulated to mimic seasonal changes in wetland hydrology.  Water table levels, temperature, redox potentials, and pH were monitored in all experimental units.  Sets of soil mesocosms were periodically sampled and dissected and all “newly-created” redoximorphic features were documented through careful morphological descriptions.  Results from the greenhouse and field studies have shown that redoximorphic features may form in relatively short periods of time. After a single 16 week (wet-dry) hydrologic cycle in the greenhouse, cores that had been vegetated had formed less than 1% fine, faint concentrations as soft masses of iron.  In additional simulated hydrologic cycles, greater percentages of fine, distinct iron concentrations (soft masses of iron and pore linings) had formed, with variations apparently due to soil type and vegetation treatment. After 5 cycles (80 weeks) in the greenhouse, surface horizons of soil mesocosms had formed up to 10-15% in vegetated treatments, and 5-8% in non-vegetated cores depending on soil type.  Cores from the field setting were found to possess greater quantities of redoximorphic features than those from the greenhouse mesocosms (up to 10-15% after 52 weeks).  These data should assist in interpreting hydromorphology and hydric status for soils in problem settings such as those in disturbed areas or in wetland creation or restoration settings.