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 1 pH unit upon an oxidation event, which was reversible. Soil temperature at the 50-cm depth never dropped below 5° 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.
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Vol. 22 • No. 1