MEPS 307:59-68 (2006)  -  doi:10.3354/meps307059

ABSTRACT: High temporal–resolution fluctuations in oxygen concentration and vertical velocity were measured over an intertidal sandflat (water depth <69 cm) using an oxygen microelectrode and an acoustic Doppler velocimeter, in order to estimate oxygen flux across the sediment–water interface using the eddy-correlation method. The effect of flux estimate procedures, including noise removal and extraction of fluctuating components, was investigated. The estimated oxygen effluxes from the sediment ranged from –3.2 to 6.6 mmol O₂ m^–2 h^–1 in the light and from –14.5 to –6.6 mmol O₂ m^–2 h^–1 in the dark. The oxygen-uptake fluxes in the dark were markedly higher than those measured by a conventional enclosure technique. High-frequency turbulence and/or noise (>5 Hz) observed in the vertical velocity and oxygen concentration data made little contribution to the total oxygen flux (0 to 7%). However, trends (steady change over a longer time scale) caused significant artifacts in the estimated fluxes for several cases. Thus, removal of trends from raw time-series data is recommended. The co-spectrum of the fluctuating components of vertical velocity and oxygen concentration revealed that the oxygen flux at a frequency band between 0.3 and 1.4 Hz (at a period from 0.7 to 3.3 s) was a major contributor to the total oxygen flux. This frequency was consistent with the dominant frequency of vertical velocity, indicating that transport and exchange of porewater and overlying water by wind-induced waves may be crucial processes to dissolved oxygen flux between permeable sandy sediments and shallow waters.

KEY WORDS: Sedimentary oxygen flux · Microelectrode · Acoustic Doppler velocimeter · ADV · Permeable sediment · Banzu tidal flat