Time Required for Anaerobic Conditions to Develop in Saturated Soils

Abstract

The amount of time required for a saturated soil to become anaerobic has been used to establish the regulations that define and protect wetlands in the U.S. Virtually no field data are available on the time or factors that control development of anaerobic conditions. The objectives of this work were to determine the amount of time required to develop anaerobic conditions in saturated wetland soils, and to determine the effect that soil organic carbon and temperature had on the time required. Anaerobic conditions were evaluated at a wetland restoration site in Robeson Co., and at three natural wetlands in Bladen Co. Seven automated sites were installed in the restoration site to record hourly soil redox potential at 25 and 61 cm and mean soil temperature. Manual measurements were made at the natural areas. Duration of anaerobic conditions was estimated from water table data by determining length of time needed for anaerobic conditions to develop once soils were saturated. The redox potentials and water table measurements showed that the time to develop anaerobic conditions for organic soil and mineral soils ranged from 1 to 45 d at both 25 and 61 cm. Soil organic carbon had a significant (p=0.009) effect on the time to develop anaerobic conditions. Soils containing >0.03 g/g of soil organic carbon required less time (1 to 3 d) to develop anaerobic conditions than soils with <0.03 g/g (3 to 45 d). Soil temperature had no significant (p>0.5) impact on development of anaerobic conditions in the soils studied, probably because soil temperature remained above 5 C.