Geochemical behavior of metals–sulfide–phosphorus at SWI (sediment/water interface) assessed by DGT (Diffusive gradients in thin films) probes

• Combined DGT probes were used for measurement of labile metals, sulfide and P.
• The co-release of trace metals by Fe-redox process caused DGT peaks and increments.
• P release from Fe-bound P in anoxic sediments engendered “internal P loading”.
• Grayscale analysis for AgI gel verified the existence of sulfide microniches.

Element profiles/images in sediment porewater at five sites of Dianchi Lake (China) were measured by AgI/Chelex-100, ferrihydrite and Chelex-100 DGT (Diffusive gradients in thin films) probes for labile sulfide, metals and P. Based on DGT profiles, remobilization character and geochemical behavior of multi-elements at fine scale were assessed. Fe remobilization characters at five sites indicated the distinct Fe-reduction process. The correspondence of Fe and Cu/Al/Zn, and good linear correlation in profiles verified the co-release of them by Fe-redox process in some sites. The reduction of Fe (III) hydroxyoxide caused P-release from Fe-bound P in anoxic sediment and “internal P loading” character, which has been verified by the linear correlation (R = 0.77) in the whole DGT-profiles of Fe/P and the co-existence of Fe/P peaks at same depths. The peak flux (1.13 × 10− 6–1.10 × 10− 5 μg cm− 2 s− 1), niche area (3.6 × 10− 5–6.0 × 10− 2 cm2), circularity (0.204–1.0) and RJM (4.02–6.62%) derived by CID (computer image densitometry) have revealed the existence of sulfide microniche in sediments.