Effects of sediment dredging on internal phosphorus: A comparative field study focused on iron and phosphorus forms in sediments

摘要

Sediment dredging is a controversial technology for eutrophication control. Its effects on phosphorus (P) cycling are still unclear. In this study, a long term 3 year field investigation was conducted at Dongqian Lake, China, following a sediment dredging project. The amount of iron (Fe) and P forms presented in the sediment from a dredged region (Y region) and a nearby un-dredged region (N region) were monitored and compared. The results showed that soon after the sediment dredging, there were no significant differences in NH4Cl extractable P (NH4Cl-P), NaHCO3/Na2S2O4 extractable P (BD-P) and residual P (Res-P) levels between the Y and N region. However, NaOH extractable reactive P (NaOH-rP) and non-reactive P (NaOH-nrP) were higher, and HCl extractable P (HCl-P) was lower, in the N region than in the Y region. Three years after dredging, considerable reduction in Fe (P < 0.01) was observed in the surface sediment from the N region, contrarily the amount of Fe (P < 0.05) accreted in the newly formed surface sediment from the Y region. Compared with the first year after the sediment dredging, TP increased by 35.2 and 42.3 mg/kg in the sediment of Y and N regions in the third year, respectively. The increased amount of TP in sediments may result from external loadings and existed primarily in two bioavailable forms (BD-P and NaOH-rP) in both the Y region and the N region. This result indicated that it is better to conduct dredging after external P loading has been blocked. In addition, more BD-P and NaOH-rP accumulated in the N region than the Y region. The observed increase in BD-P and NaOH-rP in the N region may result from Fe- and aluminum-adsorbed P from the water column. Our study suggests that Fe cycling in lakes following sediment dredging is an important factor for understanding the environmental effects of sediment dredging. (C) 2015 Elsevier B.V. All rights reserved.