An alternative to sampling porewaters to evaluate fluxes of nutrients and contaminants at the sediment-water interface is the use of a benthic flux chamber. This type of device is essentially a container enclosing sediment and a small volume of overlying water that is incubated for periods lasting from a few hours to several weeks. During this time, concentrations of nutrients and contaminants in the overlying water are monitored at regular intervals, and changes indicate the direction and proportion of their fluxes; an increase in concentrations indicates a flux coming out of the sediment, while a decrease shows a flux into the sediment.
Although flux chambers provide a direct measure of nutrient and contaminant fluxes, they are not without their shortcomings. Two of the more salient being that (1) the enclosed water will over time become anoxic with contact with the sediment, and (2) the enclosed water is secluded from surrounding benthic currents that mix water and sediment. Unless artificially regulated, both of these phenomena will induce anomalous changes in the redox chemistry that will influence the measured fluxes.
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