High resolution evidence of iron phosphorus sulfur mobility at hypoxic sediment water interface: An insight to phosphorus remobilization using DGT induced fluxes in sediments model.
The deterioration of reservoirs in southern China due to the kinetics of Iron (Fe) Phosphorus (P) and sulphide (S) at the sediment water interface (SWI) is a major problem that needs urgent attention. Studies on the biogeochemistry of Fe, P, and S using high resolution profile techniques in reservoirs in this region are limited. The diffusive gradient in thin films (DGT) technique, high resolution dialysis, DGT computer imaging densitometry (CID) DGT induced fluxes in sediments (DIFS) and planar optode (PO) device were used to describe the dynamics Fe P S in SWI during hypoxia. The results showed the release of Fe P S in SWI was due to sulfate reduction and iron reduction influenced greatly by hypoxia. Positive apparent fluxes were recorded indicating that the sediments release Fe P S to the overlying water. High positive correlations (r2 0.7) for DGT labile Fe and DGT labile P in sediments revealed that iron bound P controlled the release of P at SWI during reductive dissolution. The low correlation between DGT labile Fe and DGT labile S (r2 0.4) disclosed the combative nature between sulfate reduction and iron reduction process. The low correlation occurred because of the co precipitation between Fe and S, forming black materials such as monosulfide (FeS) and pyrite (FeS2) in a hypoxic environment. The DIFS model showed the resupply ability (R values) of P in sediments belonged to the partially sustained case with a steady state case of resupply at TB3 (Tc 1088s, Kd 1005.61 cm3/g R 0.72, K 1 0.19 day 1) and TB4 (Tc 712 s, Kd 712.53 cm3/g, R 0.78, K 1 0.46 day 1) The resupply rate belonged to the non steady state case at TB1 (Tc 10,990 s, Kd 396.3 cm3/g, R 0.35, K 1 0.07 day 1) and TB2 (Tc 6097 s, Kd 578.5 cm3/g, R 0.45, K 1 0.10 day 1) The DGT CID PO DIFS provided a deep insight on the mechanism of Fe P S and remobilization of P at SWI leading to Blackwater events and eutrophication.
The Science of the total environment