| Phosphorus (P) is a key factor for water eutrophication. South Region of Taihu Lake Basin in Zhejiang Province is increasingly threatened by water eutrophication, so understanding on ecological P movement among sediments-water interface of wetlands in this region is important to develop sound technologies for optimizing wetlands' ecological functions. Typical sampling sites with total number of 31 were chosen for field investigation in this region, and 3 sites located at Hangzhou West Lake, Deqing Xiazhuhu Wetland, and Changxing Baoyanghe River were selected for laboratory-scale rapid adsorption experiments, static column simulation experiments and steady-flow flume simulation experiments.According to the field investigation, total P (TP) and NaHCO2 extractable P (Olsen-P) in sampled sediments reached 0.169-1.200 g/kg and 7.08-67.08 mg/kg especially, and the corresponding maximal physical adsorption capacity (Qmax) varied from 269.5 to 824.5 mg/kg. NaOH+EDTA extractable P (NaOH+EDTA-P) constituted 52.0±11.6 % of TP, while Olsen-P was increased as NaOH+EDTA-P accumulating. Wetlands used for breeding were found to be of highest risk in releasing P. All 31 samples significantly fitted with Langmuir Isotherm and Freundlich Isotherm in P adsorption. TP in overlying water was found 0.036-0.944 mg/L, while dissolved reactive P (DRP) was relatively low. Total particle P (TPP) contributed 70.9±13.2 % of TP in water samples. It was found that the dominant forms of P in sampled sediments was NaOH-DP, followed by Res-P, BD-P, NaOH-OP, HCl-P and NH4Cl-P, according to the P fractionation followed by Psenner. There was no significant relationship between TP, DRP in overlying water and TP, NaOH+EDTA-P, Olsen-P in sediments, implying that P status in sediments was not the only factor restricting P in overlying water.Through analysis of the results from rapid adsorption simulation experiments, the P adsorption on sediments was found to have two phases, i.e. rapid adsorption and slow adsorption, and a modified Elovich model was found to fit well with the whole adsorbing process. The dissolved reactive P (DRP) attended a balance state after 24 hours of the experiment. All the 3 samples had the characteristics of Langmuir Isotherm and Freundlich Isotherm significantly, and the amount of adsorbed P had a significant positive linear relationship with DRP in overlying water. Equilibrium P concentrations (EPCo) of sediment sampled from Maojiabu, Xiazhuhu Wetland and Baoyanghe River calculated from the linear model were 0.050 mg/L, 0.010 mg/L and 0.023 mg/L respectively, which implies that the sediment collected from Xiazhuhu Wetland was not releasing P to overlying water.In the static column simulation experiments, DRP in overlying water decreased slowly at the beginning then the decreasing pace was found fast later on. Therefore, P retention by sediments can be divided into three phases, i.e. buffer phase, rapid adsorption phase and slow adsorption phase. A quasi U-pattern curve was found in the steady-flow flume simulation experiments, i.e. DRP in the overlying water decreased at first and then turned to be increasing, with a balance point where the wetland changes its P interception function existing on the dynamical curve. Probably due to microorganisms' function, there was no significant regression model for the laboratory-scale study.It was found in the simulation experiments that organic matter accelerated the rates of P adsorption on fresh sediments, but did not accelerate the rates of P adsorption on air-dried sediments. P was found to be retained mainly in forms of Fe-P and Al-P for samples from Maojiabu and Xiazhu Lake, while Al-P was the main form retained in sediments for sample from Baoyang River.It is reasonable to use wetlands as a water column restoration tool to intercept P universally. An integrated ecological restoration should contain source reduction, interception on the way and on-situ purification in target water column.
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