Hourly and Daily Variation of Sediment Redox Potential in Tidal Wetland Sediments

摘要

Variation of electrochemical oxidation-reduction (redox) potential was examined in surface salt marsh sediments under conditions of flooding and tidal simulation in mesocosms and field sites. Time series were generated of redox potential measured in sediment profiles at 2-10 cm depth using combination Pt-Ag/AgCl (ORP) electrodes. Redox potential data were acquired at rapid rates (1-55 samples/h) over extended periods (3-104 days) along with similar times series of temperature (water, air, soil) and pH. It was found that redox potential varied as a result of water level changes and was unrelated to diurnal changes in temperature or pH, the latter of which changed by < 0.5 units over the tide cycles. In closed, hydrostatic microcosms isolated from atmospheric oxygen, development of negative redox potentials proceeded rapidly (> 370 mV redox potential decrease in under 48 h). Attenuation of microbial activity by gamma-radiation and toxic chemicals eliminated this response. In tidal salt marsh mesocosms where the sediment-plant assemblages were exposed to a simulated diurnal tide, redox potential oscillations of 40-300 mV amplitude were recorded that had the same periodicity as the flood-drain cycle. Periodic redox potential time series were observed repeatedly in sediments receiving tidal pulsing but not in those sediments exposed to static hydrological conditions. Data collected over 12 days from a coastal marsh site experiencing diurnal tides showed similar fluctuations in redox potential. Data from these experiments indicated that: (a) redox potential can be a dynamic, nonlinear variable in coastal and estuarine wetland sediments over hourly and daily scales, and the designs of biogeochemical experiments should reflect this, and (b) redox potential can change rapidly and significantly in coastal wetland sediments in response to flooding and draining.