[Phosphorus Enrichment Efficiency of CaO2@FA Composites and the Effect of Its Recovered Material on Soil Improvement].

To explore the resource utilization of phosphorus (P) in wastewater and industrial waste fly ash, we used an efficient composite material (CaO2@FA) for phosphorus removal by loading nano-CaO2 on the surface of fly ash as well as in the pores using the surface precipitation method. The results showed that the material had a larger specific surface area and porosity after loading CaO2 on the fly ash surface. The specific surface area increased to 4.641 m2·g-1, and the total pore volume was up to 0.025 cm3·g-1. The adsorption process of CaO2@FA on P could be described using the Langmuir isothermal adsorption model, and its maximum adsorption capacity was 185.776 mg·g-1(20℃). The adsorption mechanism was attributed to chemical precipitation, mainly the formation of calcium hydroxyphosphate. The enrichment efficiency of CaO2@FA composites on P was significantly higher than that of fly ash, and the efficiency was increasing with the increase in the dosage added. HCO3- and CO32- in the coexisting ions had a negative effect on P adsorption by the composites. The enrichment rate of P in domestic wastewater was up to 93% when the dosage of CaO2@FA composites was 2.0 g·L-1. The content of biological P in the recovered precipitates reached 1.658 mg·g-1. The soil improvement test showed that the biological P content in soil increased by 102.9% when the recovered precipitates were added into the soil. This indicated that the operating cost of recovering 100 mg of P by this composite was as low as 0.76 yuan.

Study on community structure and metabolic mechanism of dominant polyphosphate-accumulating organisms (PAOs) and glycogen-accumulating organisms (GAOs) in suspended biofilm based on phosphate recovery.

Biofilm sequencing batch reactor (BSBR) can achieve efficient phosphate (P) removal and enrichment, but its process performance and metabolic mechanisms for P removal and enrichment of municipal wastewater remain largely unclear. In the present study, we assessed the P removal and enrichment of municipal wastewater at influent P concentrations of 2.5 mg/L and 10 mg/L. The efficiency of P removal and enzyme activity in polyphosphate-accumulating organisms (PAOs) and glycogen-accumulating organisms (GAOs) were compared, and the growth and metabolic characteristics of dominant PAOs and GAOs at different influent P concentrations were studied with the macro-sequencing technology. The results showed that the P recovery efficiencies were 70.03% and 76.19% when the influent P concentration was 2.5 mg/L and 10 mg/L in BSBR, respectively, and the maximum P concentration of recovery liquid was 81.29 mg/L and 173.12 mg/L, respectively. There were no phosphate kinase (PPK) and phosphate hydrolase (PPX) in extracellular polymeric substances (EPS). The dominant PAOs were Candidatus_Contendobacter, Dechloromonas, and Flavobacterium, and the dominant GAO was Candidatus_Competibacter. The abundance of Candidatus_Contendobacter was the highest with the most potential contribution to P removal. PAOs had competitive advantages in carbon (C) source uptake, glycogen metabolism, P metabolism, and adenosine triphosphate (ATP) metabolism. HMP was unique to PAOs, EMP had the highest abundance in glycogen metabolism, and ED was contained in PAOs of BSBR. These results indicated that BSBR provided sufficient reducing power and ATP for PAOs through different glycogen decomposition pathways to promote P uptake and obtained competitive advantages in P metabolism, C source uptake, and ATP utilization to achieve efficient P removal and enrichment. Collectively, our current findings provided valuable insights into the P removal and enrichment mechanism of BSBR in municipal sewage.

Enhanced phosphorus storage in suspended biofilm by increasing dissolved oxygen.

The phosphorus recovery efficiency in PAOs-biofilm system is so far limited to stimulating phosphorus release by adding concentrated organic carbon solution during the anaerobic stage. In present study, a PAOs-biofilm sequence batch reactor (BSBR) were operated to investigate whether increase of the phosphorus storage content via DO control can stimulate the release in the biofilm. During the operation of BSBR for 160 days, the phosphorus content in biofilm (Pbiofilm) was doubled via increasing dissolved oxygen (DO) from 4 to 6 mg/L. With the COD of 200 mg/L in the anaerobic phase, the phosphorus release was enhaced, resulting in an significant increase of phosphorus concentration from 94.85 to 179.5 mg/L in recirculated solution. Batch tests further clarified explicitly the increase of Pbiofilm stimulated a phosphorus release rate but this must be balanced since high Pbiofilm reduced the phosphorus removal capacity of the biofilm. With analysis of P31-NMR, Ortho-P and Poly-P were the main phosphorus species stored in biofilm. The microbial cell played a more important role than EPS in phosphorus storage. The dominant phylum in the master reactor was Proteobacteria with an abundance of 64.4%, in which the Rhodocyclaceae was the dominant PAOs with an abundance of 10.1%. The outcome of this study elucidated that increase of phosphorus storage via DO control which facilitated more efficient phosphorus release with much lower organic carbon source consumption during the enrichment of phosphorus. Meanwhile, we provided a new perspective for the recovery of phosphorus in future wastewater treatment plants.

[Environmental Significance of Phosphorus Fractions of Phytoplankton-and Macrophyte-Dominated Zones in Taihu Lake].

It is of great importance to study the environmental significance of phosphorus fractions in overlying water and sediments of typical phytoplankton-and macrophyte-dominated zones. It will help to clarify the process of phosphorus migration and transformation in the sediment-water interface, and has practical significance for understanding the eutrophication process and its treatment in different regions of Taihu Lake. The investigation was conducted within typical phytoplankton-and macrophyte-dominated zones of Taihu Lake over four seasons to analyze the spatial and temporal differences between phosphorus fractions in water and sediments, and reveal their environmental significance. The results showed that:① Total phosphorus (TP), total soluble phosphorus (DTP), dissolved inorganic phosphorus (DIP), and particulate phosphorus (PP) in the overlying water of phytoplankton-dominated zones were much higher than those in macrophyte-dominated zones. Most of them showed seasonal characteristics, which were higher in summer and autumn than in winter and spring. PP is the main component of TP, accounting for 71.8% to 89.6%. A similar distribution character was found in the content of chlorophyll (Chl-a) compared with phosphorus concentration in overlying water. ② The concentration of TP in the surface sediments of phytoplankton-dominated zones was 372.38-529.64 mg·kg-1, and that in macrophyte-dominated zones was 304.29-454.27 mg·kg-1. In surface sediments, concentrations of TP in phytoplankton-dominated zones were significantly higher than in phytoplankton-dominated zones. The highest TP concentrations appeared in winter, and the lowest in summer. These were owing to the input of exogenous pollution, and the migration and transformation of internal phosphorus between sediments and overlying water under different environmental conditions. ③ The order of the mass fraction of phosphorus in sediments was:NH4Cl-P < Fe-P < Org-P < Res-P < Al-P < Ca-P. Mobile-P=NH4Cl-P+Fe-P+Org-P, accounting for 9.10%-16.93% of TP in phytoplankton-dominated zones, and slightly higher in macrophyte-dominated zones, where it was 8.11%-13.50%. Res-P accounted for 10.06%-14.97% of TP in phytoplankton-dominated zones, and 11.02%-20.28% in macrophyte-dominated zones. The risk of internal phosphorus release in phytoplankton-dominated zones is high, which is not conducive to the fixation and burial of phosphorus. The eutrophication degree of different regions in Taihu Lake is obviously different, and different characteristics of phosphorus release and burial are showed. The phytoplankton-dominated zones deserve special attention because of their high internal phosphorus load and release potential.

[Effect of Different Adding Means of Ignited Water Purification Sludge on Phosphorus Adsorption and Forms].

The adsorption of external phosphorus (P) and the distribution of dissolved inorganic P (DIP) in the sediment interstitial water and sedimentary P forms were researched under the ignited water purification sludge (IWPS) addition (mixing and capping). The results showed that the adsorption ability of the IWPS increased obviously, compared with the water purification sludge (WPS). It indicated that the Smax increased by 43.7%, the EPC0 decreased by 69.1% and the DPS decreased by 54.4%. The contribution of P disappearance in the overlying water had almost no difference between the mixing and capping with IWPS, but it was obviously higher than the control in both cases. Under the mixing condition, the adsorption of external P by unit IWPS was 2.3 times of that under the capping condition, if the contacting probability between the IWPS and the overlying water was considered. Under the capping condition, the DIP in the sediment interstitial water (1-2 cm) was 33.17 times (average) of that under the mixing condition. It was attributed to the decrease of the dissolved oxygen penetration due to capping. Under the mixing condition, the external P tended to form Ca-P, while the percentages of NH4Cl-P and Fe/Al-P to Tot-P were bigger under the capping condition. It was suggested that the improvement of the sedimentary microenvironment by mixing with the IWPS was favorable for the adsorption of the external P and the immobilization of the internal P.

[External Phosphorus Adsorption and Immobility with the Addition of Ignited Water Purification Sludge].

The cumulative adsorption of external phosphorus (P) by water purification sludge after ignition under different addition methods (mix and cover) was investigated along with the adsorption isotherm and the release of internal P after external P adsorption. The cumulative adsorption of external P was 11.496 mg (mix) and 11.042 mg (cover) and these values were higher than those in the control (7.219 mg). The maximum sorption capacity (Smax) increased under the mix and cover and the former (7.795 mg·g-1) was higher than the latter (6.807 mg·g-1). However, the zero equilibrium P concentration (EPC0) in the mix was 0.83 mg·L-1, higher that in the cover (0.64 mg·L-1). The result suggests that the internal P was easily released in the mix method, compared to the cover method. Under anaerobic conditions, the release of the internal P was 0.93 mg in the mix, lower than that in the cover (1.49 mg) and in the control (7.76 mg). In addition, the specific release rate in the cover method was 0.00614 (mean), higher than that (0.00396) in the mix method. Noticeably, these data were lower than those in the control, indicating that the retention of P under the mix method was higher, compared to the cover and the control and it is challenging to evaluate the P retention with EPC0.

[Distribution of Phosphorus Forms in the Overlying Water Under Disturbance with the Addition of Algae].

Distribution of different phosphorus (P) forms in the overlying water and the contribution of different algae to the P disappearance were investigated under disturbance with the addition of algae (Microcystis aeruginosa and Selenastrum capricornutum, respectively). The sediments and overlying water were taken from Meiliang Bay in Taihu Lake. The results showed that the concentrations of total P (TP), dissolved total P (DTP), dissolved inorganic P (DIP) and biavailable P (BAP) decreased with and without disturbance. The uptake of DTP and DIP by Microcystis aeruginosa was better than that of Selenastrum capricornutum under the disturbance, but it was the opposite without the disturbance. The disappearance of P in the overlying water was attributed completely to the physico-chemical adsorption of the suspended solids and the uptake of algae. But the contribution of suspended solids and algae depended on the disturbance. The contribution of Microcystis aeruginosa and Selenastrum capricornutum to DTP and DIP absorption was about 60% without disturbance. However, the value was reduced to 40% (Microcystis aeruginosa) and 25% ( Selenastrum capricornutum) under the disturbance. Under the disturbance and the action of algae, the distribution of sedimentary P forms changed. NH4 Cl-P and Ca-P release and Fe/Al-P increase were observed with and without disturbance. The decrease of NH4 Cl-P and Ca-P and the increase of Fe/Al-P were more obvious with disturbance than without disturbance. Selenastrum capricornutum was favor of the release of Ca-P and the formation of Fe/Al-P.

[Impacts of Sediment Disturbance on the Distribution of Suspended Particle Size and Phosphorus].

To clarify the influence of the sediments disturbance on the particle size distribution of suspended solids, and the influence of particle distribution on the forms of dissolved phosphorous in the overlaying water, the sediments and overlying water from Meiliang Bay, Taihu Lake, were used to conduct the indoor simulation experiments to investigate the particle size of suspended solids according to the Ubbelobde particle size criteria and the distribution of phosphorus compounds in the overlying water under the disturbance circumstances. The results indicated that the average proportions of small (0-10 microm), middle (10-20 microm) and large (> or = 20 microm) diameter particles presented different trends of increasing, decreasing and staying stable, respectively. It indicated the possible transformation of particle size of suspended solids from small-middle diameter to large diameter. In addition, the data of DTP/TP and DIP/TP showed a periodical variation with the corresponding periodical variety of particle diameter in suspended solids, while ns obvious variety of DTP and DIP was observed. It suggested that disturbance enhanced the ability of phosphorus immobilization by suspended solids. On the other band, the percentages of DTP in TP and DIP in TP were 19% and 13% under the disturbance, respectively, and they were obviously lower than those (DTP/TP, 80% and DIP/TP, 69% ) in the control. It indicated that tbs transformation of particle size of suspended solids from small-middle diameter to large diameter due to disturbance was in favor of tbe adsorption and sedimentation of dissolved phosphorus. Accordingly, the formation of particle phosphorus was enhanced. Therefore, it delayed the development of eutrophication in the water body.

[Impacts of Multiple Disturbance on Migration and Transformation of Endogenous Phosphorus in Lake].

This work aimed to clarify the influence of multiple disturbance factors on the migration and transformation of endogenous phosphorus. In this experiment, the sediment of Meiliang Bay in Taihu Lake was studied as the major research object. With the help of Rhizon sampling technique, Unisense microelectrode system and so on, this experiment studied the change regularities of dissolved oxygen between sediment and water interface, different forms of phosphorus and iron ions under disturbance. The results indicated that the dissolved oxygen content in sediment decreased in the presence of Corbicula fluminea as compared with the control experiment. Disturbance made the peak area of DIP in interstitial water to migrate from 3-4 cm to 4-5 cm, which suggested that the "active region" of DIP regeneration went deeply into sediment with the appearance of Chironomus plumosus and Corbicula fluminea. Meanwhile, the existence of Corbicula fluminea and algae further reduced DIP in the interstitial water. That was because the released NH4Cl-P was transferred to phosphorus in overlying water and Fe/Al-P. With the increase of disturbance factors, the transformation ratio from NH4Cl-P to Fe/Al-P also increased gradually (from 44% to 59%).

Identification of schisandrin as a vascular endothelium protective component in YiQiFuMai Powder Injection using HUVECs binding and HPLC-DAD-Q-TOF-MS/MS analysis.

YiQiFuMai Powder Injection (YQFM) is a re-developed preparation based on the well-known traditional Chinese medicine formula Sheng-mai-san. It has been widely used for the treatment of cardiovascular disease with definite clinical efficacy in China, but its bioactive molecules remain obscure. In this study, an effective method has been employed as a tool for screening active components in YQFM, using human umbilical vein endothelial cells (HUVECs) extraction and liquid chromatography coupled with electrospray ionization quadrupole time-of-flight tandem mass spectrometry (Q-TOF MS/MS). Nine compounds, which could interact with HUVECs, were identified as ginsenosides Rb1, Rc, Rb2, Rd, 20(S)-Rg3, 20(R)-Rg3, Rk1/Rg5 and schisandrin by comparing with reference substances or literature. In vitro assays showed that schisandrin at concentrations of 10-100 µM protected HUVECs from hypoxia/reoxygenation (H/R) injury, increased cell viability, nitric oxide (NO) content and decreased lactate dehydrogenase (LDH) leakage, malonaldehyde (MDA) content and ROS generation. Moreover, schisandrin pretreatment inhibited cell apoptosis, as evidenced by inhibiting activation of caspase-3 and increasing the Bcl-2/Bax ratio. These data indicate that HUVECs biospecific extraction coupled with HPLC-ESI-Q-TOF-MS/MS analysis is a reliable method for screening potential bioactive components from traditional Chinese medicines. Meanwhile, the vascular endothelium protective property of schisandrin might be beneficial for the treatment of cardiovascular disease.

[Synergistic effect of physical and Chironomus plumosus combined disturbance on regeneration and transformation of internal phosphorus].

To explain the synergistic effect of physical and Chironomus plumosus combined disturbance on the regeneration and transformation of internal phosphorus, laboratory static incubation experiments were carried out with the sediments and overlying water from a eutrophic river in Suzhou. Rhizon samplers were used to acquire the pore water. In the experiment, we compared the variation of different phosphorus forms in the overlying water, the pore water and sediments under the Chironomus plumosus disturbance and the combined disturbance. The results indicated that the amount of different forms of phosphorus (TP, PP, DTP, DIP) in the overlying water under combined disturbance was higher than that under Chironomus plumosus combination disturbance. It was attributed to the significant increase of the microbial activity in the sediments. Compared with Chironomus plumosus disturbance, the amount of DIP and ferrous decreased with the greater magnitude and range. It was attributed to the superposition effect of the physical and benthos disturbance on the penetration depth of the dissolved oxygen. In addition, the amount of NH4C1-P decreased remarkably in the 0-2 cm sediment while Fe/Al-P increased obviously. Furthermore, the variation magnitude of NH4Cl-P and Fe/Al-P was higher under combined disturbance than that under Chironomus plumosus disturbance, which suggested the superposition effect of the physical and benthos disturbance on the regeneration and migration of phosphorus.

[Annual variation of different phosphorus forms and response of algae growth in Meiliang bay of Taihu Lake].

Based on the monthly investigations of different forms of phosphorus(P) and algae growth from January to December 2013 in Meiliang bay of Taihu Lake, the transformation of different P forms and the relationship between different P forms and algae growth was investigated under the dual conditions of disturbance due to wind and wave and algae growth. Results of the total P(TP), particulate P (PP), dissolved total P(DTP), dissolved inorganic P(DIP) and bioavailable P(BAP) showed that the monthly concentrations reached the maximum in summer and autumn while the minimum in winter and spring. In addition, the algae growth showed the same trends as above. However, no variation was found in the dissolved organic P(DOP) and bioavailable particulate P(BAPP). The bioavailability of PP was only 12.75% from June to October, which was obviously lower than the annual mean (37.14%). It was attributed to the acceleration on the transformation of PP to DTP due to the immobilization of sedimentary P under sediment disturbance and algae adsorption. The percentage of DTP in BAP was up to 69.33% (average), which was obviously higher than the percentage of bioavailable PP (30.66%, average) and the annual mean (56.63%) of DTP during the interval. In addition, the algae bloom appeared in the interval.

[Sedimentary Phosphorus Forms Under Disturbances and Algae in Taihu Lake].

Sedimentary phosphorus forms were investigated to clarify the release of sedimentary phosphorus forms under the repeated disturbance with the addition of algae at different initial concentrations. The sediments and overlying water were taken from the Meiliang Bay in Taihu Lake. The results showed that the concentrations of NH4 Cl-P and Res-P decreased, while the content of Fe/Al-P and Ca-P increased without disturbance. In addition, the Ca-P increased with the increase of the initial concentration of algae and the net increase of Ca-P increased by 48% (30 µg · L⁻¹), 66% (60 µg · L⁻¹), 74% (120 µg · L⁻¹), respectively. However, under the disturbance, the NH4Cl-P and Res-P were significantly reduced, the Fe/Al-P increased significantly. The percentage of Fe/Al-P to Tot-P was up to 66. 2% (average of the 3 experiments with the addition of algae of 30 µg · L⁻¹, 60 µg · L⁻¹ and 120 µg L-¹), it was higher than the value (53.%, average of the 3 experiments) without the disturbance. Moreover, under the disturbance, the percentage of Ca-P to Tot-P was 24.1% (average of the 3 experiments with the addition of algae of 30 µg · L⁻¹, 60 µg⁻¹ and 120 µg · L⁻¹) and it was slightly lower than that (33.0%, average of the 3 experiments) without the disturbance. It is suggested that the coexistence of disturbance and algae facilitated the formation of Fe/Al-P, but the algae accelerated the formation of Ca-P without disturbance.

[Development of Sediment Micro-Interface Under Physical and Chironomus plumosus Combination Disturbance].

Synergistic effect of physical and Chironomus plumosus combination disturbance on the characteristics of the micro-environment and micro-interface was investigated by the Rhizon samplers and Unisense micro sensor system. The results showed that the oxygen penetration depth (OPD), total oxygen exchange (TOE), water content and total microbial activity increased under the combination disturbance and bioturbation and were kept at the higher level, compared with the control. These parameters increased with the physical intensity under combination disturbance. However, the content of Fe2+ decreased under the combination disturbance and bioturbation and the decrease was more obvious than that in the control. The changes of the Fe2+, the water content and the total microbial activity were large at 0-4 cm depth in the sediments. Therefore, the area might be the active area for the transformation of internal sedimentary phosphorus forms. The curve fitting was used for the OPD, TOE, the content of Fe2+, the water content and the total microbial activity with the physical intensity under combination disturbance. It was observed that the second-order polynomial equation was suitable for the curve fitting. In addition, jump type synergistic effect was presented in the above mentioned parameters under combination disturbance when the physical intensity was higher than 34 r x min(-1). The remodeling on the sediment micro-interface and micro-environment might be the main inducing mechanism for the transformation of internal phosphorus.

[Bioavailable phosphorus on suspended solids of lake under short-term and repeated sediment disturbance].

Variation of bioavailable phosphorus forms on suspended solids under short-term and repeated sediment disturbance was investigated, using sediments and overlying water from Meiliang Bay and Yueliang Bay. The results showed that the average percentage of algae available phosphorus (AAP) in the dissolved total phosphorus (DTP) decreased with the increase of disturbance number. The NH4Cl-P and bioavailable particulate phosphorus (BAPP) on the suspended solids increased by 3.5%, 37.3% (Meiliang Bay) and 2.0%, 50.7% (Yueliang Bay), respectively. In addition, the AAP and its percentage of AAP in Tot-P on the suspended solids in Meiliang Bay increased with the increase of disturbance number. However, the case was the opposite for Yueliang Bay. During the disturbance, the BAPP was higher than the sum of NH4Cl-P and AAP, indicating that the sum of NH4Cl-P and AAP constituted 80% of BAPP. It also suggested that estimating the BAPP on the suspended solids using the sum of NH4Cl-P and AAP is problematic.

[Influence of different disturbance intensity on the phosphorus adsorption and immobilization by the sediments from an inner city heavily polluted canal].

The mechanism of phosphorus (P) adsorption and immobilization under different disturbance intensities was investigated in laboratory. The sediments and water used were taken from an inner-city heavily polluted canal. Addition of KH2PO4 into the experimental units were made similar to the external P input into the canal and carried out periodically. The results show that sediment disturbance could increase the P adsorption amount by suspended solids. The higher disturbance intensity is, the greater P adsorption amount is obtained. Dissolved inorganic P (DIP) is the main form of additional KH2PO4, but sediment disturbance enhances the transformation of P from DIP to PP (particulate P), indicating that sediment disturbance decreases the bioavailable P in the overlying water. Sequential fractionation indicated that the NH4Cl-P decreased, but the Fe/Al-P, HCl-P and Res-P increased. More than 80% (the average value under three disturbance intensities) of the incorporated P accounts for Fe/Al-P in the sediments. The incorporated Fe/Al-P accounts for 37.49% (100 r x min(-1)), 42.32% (200 r x min(-1)) and 54.24% (300 r x min(-1)) of non-occluded Fe/Al-P in the sediments respectively, indicating that the percentage of incorporated P to occluded Fe/Al-P decreases with the increase of disturbance intensity. The variation of HCl-P under the same disturbance intensity is the same as the occluded Fe/Al-P. It suggests that the continuous addition of external P is mainly incorporated into the mobile P forms under short-term and high-intensity disturbance, which means the adsorption of P by sediments is the short-term immobility.

[Regeneration and transformation of BAPP in suspended solids under short term sediment disturbance].

The change of phosphorus forms in suspended solids under short-term sediment disturbance of different modes and its influence on BAPP in suspended solids were investigated, using sediments and overlying water from Meiliang Bay. The results showed that the concentrations of DIP in the overlying water decreased under disturbance. The concentrations of DIP under continuous disturbance were lower than those under intermittent disturbance. The NH4Cl-P, Ca-P and Res-P concentrations increased by 2.97%, 12.23%, 4.09% under continuous disturbance and 3.53%, 10.35%, 2.07% under intermittent disturbance and the non-occluded Fe/Al-P decreased by 5.55% under continuous disturbance and 1.78% under intermittent in suspended solids during the experiment, indicating that sediment disturbance could promote the transformation of sedimentary phosphorus from mobile forms to refractory forms. According to the speculation, the content of BAPP should decrease. However, it increased from 20.68% (initial state) to 49.27% (average, under continuous disturbance) and 57.92% (average, under intermittent disturbance). This result indicated that it is problematic to estimate the BAPP using solely the mobile phosphorus forms, such as NH4 Cl-P and non-occluded Fe/Al-P.

[Phosphorus exchange between suspended solids sediments overlying water under repeated disturbance].

The variation of phosphorus (P) exchange between suspended solids, sediments and overlying water under repeated disturbance was investigated, with the sediments from Meiliang Bay (MLB) and Moon Bay (MB) as materials. The results showed that the concentrations of total P (TP) and particulate P (PP) decreased under repeated disturbance. Dissolved total P (DTP) reached equilibrium at 8 d, and was kept at 0.019 mg x L(-1) (MLB) and 0.039 mg x L(-1) (MB). On the contrary, dissolved inorganic P (DIP) increased in the overlying water, due to the highest concentration of NH4Cl-P in the sediments, and then decreased. It reached equilibrium at 8 d, and was kept at 0.013 mg x L(-1) (MLB) and 0.028 mg x L(-1) (MB). It was coincided with the variation of DO. In addition, the concentrations of DTP and DIP in MLB were higher than those of MB under repeated disturbance. The distribution of P forms (NH4Cl-P, Fe/Al-P, HCl-P) changed due to repeated disturbance. During the repeated disturbance, the concentrations of NH4Cl-P, Fe/Al-P and HCl-P decreased gradually. At the same time, the concentrations of TP, PP, DTP and DIP decreased in the overlying water, but the NH4Cl-P, Fe/Al-P, HCl-P increased in the sediments gradually. The trend in MB was not obvious, but the trend was the same as MLB. The results suggested that suspended solids were the medium in the phosphorus exchange between sediments and overlying water under repeated disturbance.

[Effect of disturbance intensity on phosphorus release and its transformation in the sediment from Taihu Lake].

Lab-scale experiments were conducted to investigate the effect of sediment disturbance under different intensity conditions on phosphorus (P) release and sedimentary P transformation. The sediments came from Taihu Lake. The results show that the concentrations of total P (TP), particulate P (PP) and dissolved total P (DTP) in the overlying water under high intensity conditions (equal to the force of 12 m x s(-1) wave velocity on the bottom sediment in Taihu Lake) were higher than those under low intensity conditions (equal to the force of 8 m x s(-1)). The concentrations of TP and PP were up to 0.950 mg x L(-1), 0.384 mg x L(-1) and 0.882 mg x L(-1), 0.328 mg x L(-1) for both intensities after 1 h and then the levels kept unchanged almost till the end of the experiments. However, the DTP decreased gradually. It is attributed to the adsorption by suspended sediments and quick uptake by microorganisms. Under both intensities conditions, the Tot-P of the suspended particulate matter (SPM) due to disturbance increased by 10 mg x kg(-1) (mean during 0-12 h) and 60 mg x kg(-1) (mean during 0-12 h). The changes of Fe/Al-P during the experiment (0-12 h) verified the transformation trend between sedimentary P forms in the SPM under high intensity. Because the net increase (85.7 mg x kg(-1), mean during 0-12 h) was higher than the measured value (10 mg x kg(-1), mean during 0-12 h) and the theoretically calculated value (27 mg x kg(-1), mean during 0-12 h). It suggests that other sedimentary P forms were transformed into Fe/Al-P. Correspondingly, the decrease of NH4Cl-P and HCl-P can verify this. It suggested that sediment disturbance might induce the indirect transformation between sedimentary P forms by the assistance of overlying water.

[Impacts of sediment disturbance time on the distribution of phosphorus forms in suspended solids].

To examine the impact of sediment disturbance time (disturbance 10 min and 9h, respectively) on the transformation of phosphorus forms in suspended solids, the microcosm experiment was carried out with sediment and lake water from Yueliang estuary in Taihu Lake. The transformation of phosphorus forms in suspended solids was analyzed. The longer disturbance time, the greater of dissolved total phosphorus (DTP) in the overlying water was observed. However, in the control experiment, the concentration of DTP was higher than that in the disturbance experiment. Sequential fractionations indicted that mass fraction of Fe/Al-P to Tot-P in the suspended solids decreased gradually under disturbance conditions (10 min, 9 h) with increasing the experiment time, and then, the values decreased to 42.5% (10 min) and 38.1% (9 h) at 10 d, respectively. At the end, they increased slightly, compared with the values at 10d. However, mass fraction of HCl-P to Tot-P in the suspended solids increased gradually with time, and then went up to the highest (48.9%, 10 min and 53.7%, 9 h) value at 10 d. It suggested that sediment disturbance promoted the transformation of phosphorus forms in the suspended solids, especially from mobile phosphorus forms to refractory forms.