| Abstract
| - The technique of diffusive equilibration in thin films (DET)was used to measure sediment pore-water concentrationsof dissolved iron and manganese at high-spatial resolution(1 mm). Measurements in a laboratory microcosm ofhomogeneously mixed sediment gave reproducibleconcentration-depth profiles with no fine scale features.By contrast, measurements in undisturbed surface sedimentsshowed fine structure that was only occasionallyreproduced in profiles from several replicate fielddeployments. Although redox-related features in theprofiles, indicative of processes traditionally consideredto occur with lateral uniformity, were generally present, thedetails observed in the replicate deployments weredifferent. DET was modified to allow horizontal as well asvertical measurement of pore-water solutes. The resulting2D images of the distribution of iron and manganeseconcentrations in pore-waters showed systematic verticaland horizontal structure. The individual componentvertical profiles of the 2D measurement were only 3 mmapart and yet they were sometimes quite different from oneanother. These findings suggest that (i) microniches playa major role in metal remobilization, (ii) results from singlevertical profiles may not be representative, and (iii)caution should be exercised when estimating exchangefluxes from vertical concentration gradients.
|
