Evaluation of simulated dredging to control internal phosphorus release from sediments: Focused on phosphorus transfer and resupply across the sediment-water interface.
Sediment dredging is an effective restoration method to control the internal phosphorus (P) loading of eutrophic lakes. However, the core question is that the real mechanism of dredging responsible for sediment internal P release still remains unclear. In this study, we investigated the P exchange across the sediment-water interface (SWI) and the internal P resupply ability from the sediments after dredging. The study is based on a one-year field simulation study in Lake Taihu, China, using a Rhizon soil moisture sampler, high-resolution dialysis (HR-Peeper), ZrO-Chelex diffusive gradients in thin film (ZrO-Chelex DGT), and P fractionation and adsorption isotherm techniques. The results showed low concentration of labile P in the pore water with a low diffusion potential and a low resupply ability from the sediments after dredging. The calculated flux of P from the post-dredged sediments decreased by 58% compared with that of non-dredged sediments. Furthermore, the resupply in the upper 20mm of the post-dredged sediments was reduced significantly after dredging (P<0.001). Phosphorus fractionation analysis showed a reduction of 25% in the mobile P fractions in the post-dredged sediments. Further analysis demonstrated that the zero equilibrium P concentration (EPC0), partitioning coefficient (Kp), and adsorption capacity (Qmax) on the surface sediments increased after dredging. Therefore, dredging could effectively reduce the internal P resupply ability of the sediments. The reasons for this reduction are probably the lower contributions of mobile P fractions, higher retention ability, and the adsorption capacity of P for post-dredged sediments. Overall, this investigation indicated that dredging was capable of effectively controlling sediment internal P release, which could be ascribed to the removal of the surface sediments enriched with total phosphorus (TP) and/or organic matter (OM), coupled with the inactivation of P to iron (Fe) (hydr)oxides in the upper 20mm active layer.
State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Number 73 Beijing East Road, Nanjing 210008, People's Republic of China; CEER, Nanjing Hydraulic Research Institute, Nanjing 210029, People's Republic of China.
Juhua
J
Yu
State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Number 73 Beijing East Road, Nanjing 210008, People's Republic of China. Electronic address: smding@niglas.ac.cn.
Shiming
S
Ding
State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Number 73 Beijing East Road, Nanjing 210008, People's Republic of China. Electronic address: jczhong@niglas.ac.cn.
Jicheng
J
Zhong
State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Number 73 Beijing East Road, Nanjing 210008, People's Republic of China. Electronic address: cxfan@niglas.ac.cn.
Chengxin
C
Fan
CEER, Nanjing Hydraulic Research Institute, Nanjing 210029, People's Republic of China. Electronic address: qwchen@nhri.cn.
Qiuwen
Q
Chen
State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Number 73 Beijing East Road, Nanjing 210008, People's Republic of China. Electronic address: hbyin@niglas.ac.cn.
Hongbin
H
Yin
State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Number 73 Beijing East Road, Nanjing 210008, People's Republic of China. Electronic address: leizhang@niglas.ac.cn.
Lei
L
Zhang
Laboratory of Forestry Ecological Engineering of Jiangsu Province, Nanjing Forestry University, Nanjing 210037, People's Republic of China. Electronic address: ecoenvylz@163.com.
Yinlong
Y
Zhang
Lake Taihu; Phosphorus; Release flux; Sediment dredging; Sediment-water interface; ZrO-Chelex DGT