Coupling between iron and phosphorus in sediments of shallow lakes in the middle and lower reaches of Yangtze River using diffusive gradients in thin films (DGT)

Abstract

It is universally accepted that the coupling relationship between phosphorus (P) and iron (Fe) is responsible for the migration of P, but there is little direct in situ evidence. In order to investigate the coupling relationship between P and Fe in sediments of shallow lakes, the concentrations of labile P and Fe in the sediments in Lakes Taihu, Chaohu, Poyang and Dongting were measured using ZrO-Chelex diffusive gradients in thin films (ZrO-Chelex DGT). The results showed that both labile Fe and P began to increase downward below the sediment-water surface followed by fluctuation up to the bottom of the sediment profiles. Their changes were consistent along the profiles, which were further supported by the positively linear correlations among them. Anaerobic incubation experiment further showed that the reductive dissolution of iron oxides led to the releases of ferrous Fe and P associated with iron oxides. The results proved that the remobilization of P in sediments was dominated by Fe redox.