In situ measurements of concentrations of Cd, Co, Fe and Mn in estuarine porewater using DGT.

Vertical profiles of metals were measured by the in situ application of DGT (diffusive gradients in thin films). Well-defined laboratory systems ensured the good reproducibility and precision DGT accumulated metals on a chelex resin after diffusional transport through a layer of hydrogel. Three kinds of DGT probes (with three thicknesses of diffusive gel: 0.40 mm, 0.80 mm and 1.92 mm) measured interfacial concentration and induced flux from solid to solution phase which had intricate variations with depth. The DGT induced flux and interfacial concentration of four metals belonged to "partially sustained" state, indicating a labile equilibrium of metals between solid phase and porewater. The concentration profiles showed the good correlation between Mn and Co and peak concentrations of Mn and Fe between -2.00 cm and -5.25 cm with depth.