Soil redox, pH, temperature, and water-table patterns of a freshwater tidal wetland

Knowledge of wetland hydrology, soil redox potential, pH, and temperature dynamics are key components required to understand the capacity of tidal wetlands to function, in particular to attenuate agrichemicals. In a freshwater tidal wetland along the James River in Virginia, USA, redox potential, pH, water-table level, and soil temperature were monitored continuously at two depths (20 and 50 cm) at three sites during a 12-month period from September 1, 1997 to August 31. 1998. Redox potentials were at or below - 150 mV (methanogenic or sulfate reducing conditions) at the 50-cm depth during the entire monitoring period. At the 20-cm depth. redox potentials remained highly reducing 95% of the time. The soil is continuously wet throughout the year, with the water-table level above the 20-cm soil depth for 95% of the time. Water-table level or hydrology was the primary factor controlling fluctuations in the redox state. Soil pH values were generally between 6 and 8, and they dropped I pH unit upon an oxidation event. which was reversible. Soil temperature at the 50-cm depth never dropped below 5degrees C, indicating a year-round biological activity season. This wetland supports a large diversity of plant species. Permanently reduced sub-surfaces, year-round biological activity, and large organic matter accumulations are characteristic features of this freshwater tidal wetland.