Response of internal phosphorus loading from dredged and inactivated sediment under repeated resuspension in a eutrophic shallow lake

Phosphorus release and distribution in sediment resuspension systems under disturbing conditions

The resuspension of phosphorus (P) in sediments has the most significant contribution to the overlying water. The PP release characterization during resuspension was investigated. The results indicated that the P in suspensions had more release risk compared to the sediments. The particulate P (PP) concentration (0.54 mg L-1) under high-intensity rotational speed (250 rad min-1) was about five times higher than others (0.11 mg L-1). The sorption parameters of zero equilibrium P concentration (EPC0F) and soluble reactive P (SRP) were significantly correlated with each other (p < 0.01, r = 0.73). Suspended solids expressed stronger P source than sediments. The values of EPC0F was highly significantly correlated with the sorption coefficient (KF) and native adsorbed P (NAP) (p < 0.01). The mean values of NAP were 0.0612 mg g-1 and 0.0604 mg g-1 in the Prophase and Metaphase, respectively, and 0.0586 mg g-1 at Anaphase. The values of P sorption index (PSI) ranged from 0.4359 to 0.6862 L g-1, with mean values of 0.5350 L g-1 (Prophase), 0.6061 L g-1 (Metaphase), and 0.4967 L g-1 (Anaphase). The degree of P saturation (DPS) decreased in the order of Anaphase (2.73%) > Prophase (2.53%) > Metaphase (2.12%). The release risk index of P (ERI) decreased in the order of Anaphase (5.47%) > Prophase (4.72%) > Metaphase (3.59%), with a range of 2.12%-8.56%. To fast and slow scale, the results of NaOH-P (V1<0, V2>0) contribution indicated that the persistent disturbance promoted the release of adsorbed dissolved PP from NaOH-P in suspended sediment to the overlying water. The contribution of HCl-P (V2 > 0) was positive in the Anaphase of the slow scale, and HCl-P was a PP source in the frequently disturbing conditions.

The effects of wind-wave disturbances on sediment resuspension and phosphate release in Lake Chao

As a typical shallow lake with a wind-generated flow, the resuspension state of sediment and phosphorus release under wind field disturbance plays an important role in controlling lake eutrophication in Lake Chao. In this study, we proposed a combination of experimental analysis of dynamic disturbances, wind-wave disturbance shear stress calculation, and model simulation (experimental-calculative-modeling) to quantitatively investigate the effects of wind-wave disturbances on the resuspension state of Lake Chao bottom sediment and phosphorus release and distribution. The results showed that the release rate of phosphorus from the Lake Chao bottom sediment was affected by the wind field and bottom sediment content, which varied significantly spatially and showed some difference between different seasons. Under the condition of sufficient water body disturbance, the substrate in the Western Lake area of Lake Chao mainly adsorbed phosphate from the water body, while the substrate in the Central Lake area and the Eastern Lake area adsorbed phosphate along with the release. The magnitude of the phosphorus release rate due to sediment resuspension was mainly affected by wind speed, and the distribution of phosphorus content was influenced by the circulation generated by different dominant wind directions. The wind-wave disturbances have a significant effect on the spatial and temporal distribution of phosphorus in Lake Chao, and the proposed experimental-calculative-modeling ensemble can provide relevant technical support for the study of water pollution control strategies and comprehensive remediation and management of Lake Chao.

Effect of capping mode on control of phosphorus release from sediment by lanthanum hydroxide

The use of in situ active capping to control phosphorus release from sediment has attracted more and more attentions in recent years. It is important to identify the effect of capping mode on the control of phosphorus release from sediment by the in situ active capping method. In this study, the impact of capping mode on the restraint of phosphorus migration from sediment into overlying water (OW) by lanthanum hydroxide (LH) was studied. Under no suspended particulate matter (SPM) deposition condition, LH capping effectively restrained the liberation of endogenous phosphorus into OW during anoxia, and the inactivation of diffusive gradient in thin film-unstable phosphorus (UP_DGT) and mobile phosphorus (P_Mobile) in the topmost sediment served as a significant role in the restraint of endogenous phosphorus migration into OW by LH capping. Under no SPM deposition, although the transformation of capping mode from the single high dose capping to the multiple smaller doses capping had a certain negative impact on the restraint efficiency of endogenous phosphorus liberation to OW by LH in the early period of application, it increased the stability of phosphorus in the static layer in the later period of application. Under SPM deposition condition, LH capping had the capability to mitigate the risk of endogenous phosphorus liberation into OW under anoxia conditions, and the inactivation of UP_DGT and P_Mobile in the topmost sediment was a significant mechanism for the control of sediment phosphorus liberation into OW by LH capping. Under SPM deposition condition, the change in the covering mode from the one-time high dose covering to the multiple smaller doses covering decreased the efficiency of LH to limit the endogenous phosphorus transport into OW in the early period of application, but it increased the performance of LH to restrain the sedimentary P liberation during the later period of application. The results of this work suggest that the multiple LH capping is a promising approach for controlling the internal phosphorus loading in freshwater bodies where SPM deposition often occurs in the long run.

Effect of common ions aging treatment on adsorption of phosphate onto and control of phosphorus release from sediment by lanthanum-modified bentonite

The objective of this work was to explore the influence of combined aging treatment using Na⁺, Ca²⁺, Cl^-, HCO₃^- and SO₄^2- on the adsorption of phosphate (H_iPO₄^i-3) onto and the restraint of internal phosphorus (P) migration into overlying water (OW) by lanthanum modified bentonite (LMB). To achieve this aim, the adsorption characteristics and mechanisms of H_iPO₄^i-3 onto the raw and aged LMBs (named as R-LMB and A-LMB, respectively) were comparatively studied, and the effects of R-LMB and A-LMB treatments (addition and capping) on the migration of P from sediment to OW were comparatively investigated. The results showed that the combined aging treatment of R-LMB with Na⁺, Ca²⁺, Cl^-, HCO₃^- and SO₄^2- inhibited the adsorption of H_iPO₄^i-3. Similar to R-LMB, the precipitation of H_iPO₄^i-3 with La³⁺ to form LaPO₄ and the ligand exchange between CO₃^2- and H_iPO₄^i-3 to form the inner-sphere lanthanum-phosphate complexes are the important mechanisms for the H_iPO₄^i-3 uptake by A-LMB. The R-LMB addition and capping can be effective in the suppression of endogenous P release to OW under hypoxia conditions. The inactivation of diffusive gradient in thin film-unstable P (DGT-UP) and potentially mobile P (PM-P) in sediment acted as a key role in the restraint of internal P release to OW by the R-LMB addition, and the immobilization of DGT-UP and PM-P in the topmost sediment played a key role in the interception of endogenous P migration into OW by the R-LMB capping. Although the Na⁺/Ca²⁺/Cl^-/HCO₃^-/SO₄^2- combined aging treatment had a certain negative effect on the efficiencies of LMB addition and capping to hinder the liberation of P from sediment into OW, the A-LMB addition and capping still can be effective in the control of sediment internal phosphorus pollution to a certain degree. The results of this work indicate that LMB has a high potential to be used as a capping/amendment material to control internal phosphorus pollution.