Endogenous Phosphorus Research Articles

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 (UPDGT) and mobile phosphorus (PMobile) 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 UPDGT and PMobile 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.

Comparative study of sediment phosphorus immobilization via the addition of lanthanum-modified and thermal-modified drinking water treatment sludge.

Lanthanum-modified drinking water treatment sludge (DTSLa) and thermal-modified drinking water treatment sludge (TDTS) were prepared from drinking water treatment sludge(DTS). The adsorption properties of DTSLa and TDTS on phosphate in water and the effects on the controlled release and morphology of phosphorus in sediment at different dosages (0%, 2.5%, 5%) were discussed. Combining with SEM, BET, XRD, FTIR, and XPS characterization methods, the immobilization mechanism of DTSLa and TDTS on phosphorus in sediment was explored. The addition of TDTS can transform NH4Cl-P (loosely sorbed P), BD-P (bicarbonate-dithionite extractable P), and Org-P (organic P) into stable NaOH-rP (metal oxide-bound P) in sediment, and the conversion amount will increase with the increase of TDTS supplemental amount. DTSLa converted NH4Cl-P, BD-P, Org-P, and NaOH-rP to more stable HCl-P (calcium-bound P). At the same time, the content of WSP (water-soluble phosphorus) and olsen-P (NaHCO3 extractable P) in sediment can be reduced by the addition of DTSLa and TDTS, reducing the risk of the release of phosphorus from the sediment to the overlying water. In addition, phosphorus can be directly removed from the interstitial water by DTSLa and TDTS, so as to reduce the phosphorus concentration gradient between the overlying water and the interstitial water, thus inhibiting the release of phosphorus from interstitial water to overlying water. The results showed that DTSLa is better than TDTS in terms of its adsorption capacity and adsorption effect on endogenous phosphorus in water, so DTSLa is more suitable to be used as a sediment conditioner to control the phosphorus content in water and sediment.

Terrestrial sources regulate the endogenous phosphorus load in Taihu Lake, China after exogenous controls: Evidence from a representative lake watershed

Identifying phosphorus (P) sources and contributions from terrestrial sources is important for clean water and eutrophication management in lake watersheds. However, this remains challenging owing to the high complexity of P transport processes. The concentrations of different P fractions in the soils and sediments from Taihu Lake, a representative freshwater lake watershed, were obtained using sequential extraction procedure. The dissolved phosphate (PO4–P) and alkaline phosphatase activity (APA) in the lake's water were also surveyed. The results showed that different P pools in the soil and sediments displayed different ranges. Higher concentrations of P fractions were measured in the solid soils and sediments from the northern and western regions of the lake watershed, indicating a larger input of P from exogenous sources, including agriculture runoff and industrial effluent from the river. Generally, higher Fe–P and Ca–P concentrations of up to 399.5 and 481.4 mg/kg were detected in soils and lake sediments, respectively. Similarly, the lake's water had higher concentrations of PO4–P and APA in the northern region. A significant positive correlation was found between Fe–P in the soil and PO4–P concentrations in the water. Statistical analysis indicated that appropriately 68.75% P was retained in the sediment from terrigenous sources, and 31.25% P experienced dissolution and shifted to the solution phase in the water-sediment ecosystems. The dissolution and release in Fe–P in the soils were responsible for the increase of Ca–P in the sediment after the afflux of soils into the lake. These findings suggest that soil runoff predominantly controls P occurrence in lake sediments as an exogenous source. Generally, the strategy of reducing terrestrial inputs from agricultural soil discharge is still an important step in P management at the catchment scale of lakes.

Comparison of magnetite, hematite and goethite amendment and capping in control of phosphorus release from sediment.

The characteristics and mechanism of phosphate adsorption onto magnetite, hematite and goethite were comparatively studied, and the effects of magnetite, hematite and goethite amendment and capping on endogenous phosphorus (P) liberation from sediment into overlying water (OW) were comparatively investigated. The adsorption of phosphate onto magnetite, hematite and goethite mainly obeyed the inner-sphere complexation mechanism, and the phosphate adsorption capacity decreased in the order of magnetite > goethite > hematite. The magnetite, hematite and goethite amendment all can decrease the risk of endogenous Prelease into OW under anoxic conditions, and the inactivation of diffusion gradients in thin films-labile P in sediment made a great contribution to the restraint of endogenous P release into OW by the magnetite, hematite and goethite amendment. The efficiency of endogenous P release restraint by the iron oxide addition decreased in the order of magnetite > goethite > hematite. The magnetite, hematite and goethite capping all can be effective for the suppression of endogenous P release from sediment into OW under anoxic conditions, and most of P immobilized by the magnetite, hematite and goethite capping layers is relatively or very stable. The results obtained from this work suggest that magnetite is more suitably used a capping/amendment material to prevent P release from sediment than hematite and goethite, and magnetite capping is a promising approach for hindering sedimentary P release into OW.

Physicochemical Properties and Environmental Effects of Suspended Sediment Particles in the Largest Freshwater Lake, China

Suspended sediment particles (SSPs) act as a potential source of and sink for aquatic pollution. This study sampled six sites in Poyang Lake in August and November 2019. Changes in the physicochemical properties of SSPs were analyzed using scanning electron microscope energy-dispersive spectrometry (SEM-EDS). The results showed that SSPs consisted mainly of clay and chalk, with an average content of 39.71% and 57.52%, respectively. The average particle size distribution of SSPs in the study area ranged from 5.54 to 15.97 μm and the spatial distribution pattern showed the north lake area (I) > west lake area (II) > east lake area (III). The angle (K) of morphological indicators varied widely, with coefficients of variation between 0.25 and 1.23. Water-flow velocity was negatively correlated with SSP size, while suspended-solid concentration was positively correlated with SSP surface roughness. Morphological parameters, chemical composition, and correlation between each SSP form were analyzed to identify morphological distribution characteristics. Linear regression equations estimated endogenous phosphorus load in zones I, II, and III as 1027.202 mg/kg, 1265.343 mg/kg, and 1013.111 mg/kg respectively. Therefore, we conclude that the morphological differences in particulate matter, the interaction between chemical fractions, and the aqueous environment affecting the distribution of phosphorus fugitive forms, may contribute to endogenous lake pollution. These results are essential for revealing the intrinsic relationship between SSP physicochemical properties and lake eutrophication and studying other water–sediment interface processes of lake pollutants.

Combined amendment and capping of sediment with ferrihydrite and magnetite to control internal phosphorus release

This study developed novel active capping systems with recycling convenience using ferrihydrite (Fh) combined with magnetite (Mag), and investigated the effectiveness and mechanism for the restriction of endogenous phosphorus movement from sediment into overlying water (OW) by the combined use of Fh and Mag. The Fh/Mag combined amendment effectively hindered endogenous phosphorus release from sediment to OW in dissolved oxygen (DO)-deficit environment, and the immobilization of diffusion gradient in thin film-labile phosphorus (LPDGT) and mobile phosphorus in the sediment played a key role in the control of endogenous phosphorus liberation by the Fh/Mag combined amendment. Combined capping sediment with Fh and Mag effectively hindered endogenous phosphorus release from sediment to OW in anoxic environment, and the inactivation of LPDGT in the upper sediment played a key part in the control of sediment phosphorus release by the Fh/Mag mixture capping. The stability of phosphorus immobilized by the Fh/Mag combined covering layer was related to its construction way, and the majority (around 90%) of P immobilized to the Fh/Mag mixture covering layer had low risk of release in common pH (5–9) and DO-deficit environments. The Fh/Mag mixture amendment or capping did not increase the risk of sediment iron release, and it also did not produce a large impact on the diversity and richness of bacterial community in the sediment. The combined utilization of Fh and Mag as a composite amendment or capping material to prevent the internal phosphorus from being moved to OW can make full use of their respective advantages. The Fh/Mag mixture capping wrapped by permeable fabric has high potential to reduce the risk of endogenous phosphorus from sediment into OW due to its advantages of high internal phosphorus release suppression efficiency, environmental friendliness, application convenience and sustainability.

Effects of forage phosphorous content on faecal phosphorous excretion and possible markers of low phosphorous intake in foals fed forage-only diets.

Knowledge of endogenous nutrient losses is important when estimating the nutrient requirements of animals. It has been suggested that faecal endogenous phosphorus (P) losses differ between growing and adult horses, but studies on foals are scarce. In addition, studies on foals on forage-only diets with different P contents are lacking. Thus this study: (1) assessed faecal endogenous P losses in foals fed a grass haylage-only diet close to or below estimated P requirements; (2) evaluated use of serum cross-linked carboxyterminal telopeptides of type-I collagen (CTx) as a marker of bone resorption secondary to low-P intake; and (3) examined whether analysis of faecal P concentration on a dry matter (DM) basis could be used as an indicator of P intake. Six foals were fed three grass haylages (fertilised to contain different amounts of P: 1.9, 2.1, 3.0 g/kg DM) for 17-day periods in a Latin square design. Total collection of feaces was performed by the end of each period. Faecal endogenous P losses were estimated using linear regression analysis. There was no difference in the concentration of CTx in plasma between diets in samples collected on the last day of each period. A correlation was found (y = 0.64x - 1.51; r2 = 0.75, p < 0.0001) between P intake and faecal P content, but regression analysis indicated that underestimation as well as overestimation of intake is likely if faecal P content is used to assess intake. It was concluded that faecal endogenous P losses in foals are low, probably no higher than in adult horses. It was also concluded that plasma CTx cannot be used to assess short-term low-P intake in foals and that faecal P content cannot be used to assess differences in P intake, at least not when P intake is close to or below estimated P requirements.

Effect of increasing dietary fermentable fiber on diet nutrient digestibility and estimation of endogenous phosphorus losses in growing pigs.

Fermentable fiber may increase endogenous losses of phosphorus (EPL) and amino acids (AA), thereby reducing apparent nutrient digestibility. Acacia gum with medium-to-high fermentability and low viscosity was increasingly included in diets to investigate its effect on apparent ileal digestibility (AID) and apparent total tract digestibility (ATTD) of nutrients, gross energy (GE), and standardized total tract digestibility (STTD) of P in growing pigs. A control diet (49% cornstarch; 18% bovine plasma protein) was formulated to measure basal EPL. Three additional diets were formulated to include 2.5%, 5.0%, or 7.5% acacia gum at the expense of cornstarch. Diets contained 16.1% to 17.4% CP and 0.31% to 0.33% total P (DM-basis). The four diets were fed to eight ileal-cannulated barrows (initial BW, 54.6 kg) for four 9 d periods in a double 4 × 4 Latin square. Apparent hindgut fermentation (AHF) was calculated as ATTD minus AID. Feeding increasing acacia gum quadratically affected (P < 0.05) AID of DM, GE, linearly decreased (P < 0.05) ATTD of DM, crude protein (CP), GE, digestible (DE) and predicted net energy (NE) value of diets, and linearly increased (P < 0.001) AHF of DM and GE. Increasing acacia gum did not affect AID and standardized ileal digestibility (SID) of CP and AA. Basal EPL was 377 mg/kg DM intake (DMI) and increasing acacia gum linearly increased (P < 0.05) total tract EPL. Increasing acacia gum linearly decreased (P < 0.05) diet ATTD of P, and STTD of P based on either the calculated EPL or NRC (2012) recommended value (190 mg P/kg DMI). Increasing acacia gum did not affect AID and ATTD of Ca of diets. In conclusion, feeding increasing dietary fermentable, low-viscous acacia gum decreased diet AID and ATTD of DM and GE, but did not affect AID or SID of CP and AA. Increasing acacia gum decreased ATTD of P, which might have been due to increased specific endogenous losses of P in the total tract of growing pigs.

Distribution characteristics and controlling factors of reduced inorganic sulfur forms in Three Gorges Reservoir sediment and its influence on the release of endogenous phosphorus

还原性无机硫(RIS)包括硫酸盐还原产物和活性铁(Fe_HR)形成的酸可挥发性硫(AVS)、硫的中间产物元素硫(S⁰)及沉积物中硫铁元素的最终积累物质黄铁矿硫(S_py),RIS不仅可以影响沉积物重金属的生物有效性,还控制铁还原及内源磷的释放等生源要素的地球化学行为。为了研究三峡库区沉积物中RIS分布特征及其环境意义,于2017年7-8月和12月采集三峡库区云阳至秭归段17个点的表层沉积物样品并测定其RIS含量。结果表明: 与其他湖泊、河流相比,三峡库区表层沉积物RIS含量较低,其中,AVS的含量为0.06~0.65 μmol/g,S⁰为0.50~1.66 μmol/g,S_py为0.96~17.54 μmol/g. AVS和S⁰含量夏季高于冬季,云阳至秭归段RIS变化趋势大致为先降低后增加再降低,有较明显的季节和地域差异。相关性分析、主成分分析和聚类分析表明,研究区沉积物生物可利用磷(BAP)、Fe_HR及上覆水体SO^2-₄含量为沉积物RIS的主要限制因子。库区冬季RIS与有机磷(Org-P)和可交换态磷(Ex-P)呈显著相关性,当硫化物含量增加时,会促进Org-P的矿化分解和Ex-P向上覆水体迁移,增加释磷风险。同时,本研究从硫驱动富营养化的角度评估了三峡库区存在污染风险的水域。除库区内已发生过典型水华的重点支流外,长滩河和九畹溪也存在富营养化问题。;Reduced inorganic sulfur (RIS) includes acid volatile sulfur (AVS) formed from sulfate reduction products and reactive iron (Fe_HR), elemental sulfur (S⁰), an intermediate product of sulfur, and pyrite sulfur (S_py), the ultimate accumulation material of elemental sulfur and iron in sediments. RIS can affect not only the biological effectiveness of sediment heavy metals, but also control the geochemistry of biogenic elements such as iron reduction and release of endogenous phosphorus behavior. In order to study the distribution characteristics of RIS in the sediments of the Three Gorges Reservoir area and its environmental significance, surface sediment samples were collected from 17 points in the section from Yunyang to Zigui in the Three Gorges Reservoir area in July-August and December 2017, and the RIS content was measured. The results showed that, compared with other lakes and rivers, the RIS content of surface sediments in the Three Gorges Reservoir area was lower, with AVS content ranging from 0.06 to 0.65 μmol/g, S⁰ from 0.50 to 1.66 μmol/g, and S_py from 0.96 to 17.54 μmol/g. The AVS and S⁰ contents are higher in summer than in winter, and the trend of RIS in the section from Yunyang to Zigui is roughly decreasing, then increasing and then decreasing, with obvious seasonal and regional difference. Correlation analysis, principal component analysis and cluster analysis showed that bioavailable phosphorus (BAP), Fe_HR and SO^2-₄ content in the overlying water were the main limiting factors of sediment RIS in the study area. The winter RIS in the reservoir area was significantly correlated with organic phosphorus (Org-P) and exchangeable phosphorus (Ex-P), and when the sulfide content increased, it promoted the mineralized decomposition of Org-P and the migration of Ex-P to the overlying water column, increasing the risk of phosphorus release. Meanwhile, this study assessed the waters at risk of pollution in the Three Gorges Reservoir area from the perspective of sulfur-driven eutrophication. In addition to the key tributaries in the reservoir area where typical water blooms have occurred, the Changtan River and Jiuwan River also have eutrophication problems.

Microbial pathways in the coupling of iron, sulfur, and phosphorus cycles at the sediment–water interface of a river system: An in situ study involving the DGT technique

It is imperative to solve the problem of endogenous phosphorus (P) release from sediments in the governance of natural water bodies. Deciphering P migration and transformation patterns that are coupled to iron (Fe) and sulfur (S) cycling at the sediment–water interface (SWI) is the key to understanding the mechanisms underlying endogenous P release. In the present study, we deployed diffusive gradients in thin films (DGT) probes in situ at the SWI in Fuyang River, Hebei Province, China. When the probes were retrieved, the surrounding sediments were synchronously sampled. We analyzed the longitudinal spatiotemporal distribution of Fe, S, and P at the SWI. We also explored how functional bacterial community diversity was associated with the coupling reactions of Fe, S, and P as well as endogenous P release from sediments at the functional gene level. The results showed that labile Fe, S, and P occurred at low concentrations in sediments 0–2 cm below the SWI, while they were enriched in sediments at depths of 4–8 cm. The longitudinal distribution of different labile elements exhibited greater differences between October and February than regional differences, with higher concentrations at downstream locations than upstream locations. In February, Fe/Al-bound P and sulfide (S2−) concentrations increased in sediments compared with those in October owing to an increase in the relative abundances of dominant genera among P-mineralizing bacteria and sulfate-reducing bacteria. As a result, Fe in Fe-bound P precipitated as FeS2, which induced P remobilization and release into the overlying water. The spatiotemporal distribution patterns of functional genes related to P (phoD and ppk) and S (aprA) transformation were consistent with those of labile P and S, which strongly suggests that microorganisms played a role in driving and regulating the coupled cycling of P and S at the SWI.

Nutrient Accumulation During Vegetative and Reproductive Growth Affected by Endogenous and Exogenous Phosphorus Applications in Maize Crop

ABSTRACT Although maize (Zea mays L.) crop has high production potential for forage and grain, however it requires efficient managerial practices for optimum yield. Adequate nutrients for optimum growth led to good vegetative and reproductive growth. Field studies were conducted to evaluate the effects of two endogenous seed phosphorus (P); i.e. SLP: seed with low endogenous phosphorus (1.5 mg kg −1 seed dry weight), and SHP: seed with high endogenous phosphorus (3.2 mg kg −1 seed dry weight). Pre-categorized seeds were tested against five rates of exogenous soil P, namely, (1) control: no P (0 kg P ha −1); (2) 50 kg P ha −1; (3) 100 kg P ha −1; (4) 150 kg P ha −1; and (5) 200 kg P ha −1. Seeds having different P contents depicted non-prominent effects on accumulation patterns with few exceptions of P (at physiological maturity (R6) and of potassium (K) (at grain filling (R4) and R6); exogenous P expressed significant effects. Nitrogen (N), P, K, zinc (Zn), and boron (B) exhibited differential accumulation behavior during maize growth. Nitrogen expressed accumulation from tasseling (VT) to R4; however, P, K, Zn, and B depicted remobilization from VT to R6. Maximum accumulation efficiency of P (50.7%), Zn (46.9%), and B (51.4%) was observed from VT to R4 growth, whereas maximum response of K (60.3%) and N (21.8%) was witnessed from R4 to R6, representing variant source-sink capacities. Boron depicted greater remobilization under low exogenous P applications. Results suggest that exogenous P application severely affects nutrient accumulation during pre- and post-grain filling growth.

Rapidly increasing sulfate concentration: a hidden promoter of eutrophication in shallow lakes

Abstract. Except for excessive nutrient input and climate warming, the rapidly rising SO42- concentration is considered as a crucial contributor to the eutrophication in shallow lakes; however, the driving process and mechanism are still far from clear. In this study, we constructed a series of microcosms with initial SO42- concentrations of 0, 30, 60, 90, 120, and 150 mg L−1 to simulate the rapid SO42- increase in Lake Taihu, China, subjected to cyanobacteria blooms. Results showed that the sulfate reduction rate was stimulated by the increase in initial SO42- concentrations and cyanobacteria-derived organic matter, with the maximal sulfate reduction rate of 39.68 mg (L d)−1 in the treatment of 150 mg L−1 SO42- concentration. During the sulfate reduction, the produced maximal ∑S2− concentration in the overlying water and acid volatile sulfate (AVS) in the sediments were 3.15 mg L−1 and 11.11 mg kg−1, respectively, and both of them were positively correlated with initial SO42- concentrations (R2=0.97; R2=0.92). The increasing abundance of sulfate reduction bacteria (SRB) was also linearly correlated with initial SO42- concentrations (R2=0.96), ranging from 6.65×107 to 1.97×108 copies g−1. However, the Fe2+ concentrations displayed a negative correlation with initial SO42- concentrations, and the final Fe2+ concentrations were 9.68, 7.07, 6.5, 5.57, 4.42, and 3.46 mg L−1, respectively. As a result, the released total phosphorus (TP) in the overlying water, to promote the eutrophication, was up to 1.4 mg L−1 in the treatment of 150 mg L−1 SO42- concentration. Therefore, it is necessary to consider the effect of rapidly increasing SO42- concentrations on the release of endogenous phosphorus and the eutrophication in lakes.

Effect of Fiber Fermentation and Protein Digestion Kinetics on Mineral Digestion in Pigs.

Simple SummaryThere is increasing interest in improving nutrient utilization in pigs and poultry and thereby reduce nutrient excretion into the environment. The present review aims to provide an overview on interactions between fermentable substrates (e.g., starch, fiber, and protein) and selected minerals on nutrient digestion and absorption to determine nutritional solutions to maximize animal performance, principally in the grower–finisher phase. Using in vitro models, the site and rate (kinetics) of nutrient digestion or fermentation of a feed ingredient or diet can be estimated. However, for minerals, no standardized methodology to assess in vitro mineral digestion exists. In vivo, the diet total tract digestibility of phosphorus might be underestimated in diets with fermentable ingredients because of increased diet-specific endogenous phosphorus losses and requires further clarification to better calculate the true total tract digestibility of phosphorus in pigs. The quantification of fiber type, composition of fiber fractions within individual raw materials, their influence on digestion kinetics, and effects on digesta pH and nutrient solubility related to fermentation should be considered. In conclusion, applications of nutrient kinetic data should be considered as part of an integrated approach to support nutrient digestion and absorption in the gastrointestinal tract of pigs, thereby helping to reduce nutrient excretion.Nutrient kinetic data and the timing of nutrient release along the gastrointestinal tract (GIT), are not yet widely used in current feed formulations for pigs and poultry. The present review focuses on interactions between fermentable substrates (e.g., starch, fiber, and protein) and selected minerals on nutrient digestion and absorption to determine nutritional solutions to maximize animal performance, principally in the grower–finisher phase, with the aim of minimizing environmental pollution. For phosphorus (P), myo-inositol 1,2,3,4,5,6-hexakis (dihydrogen phosphate) (InsP6), copper (Cu), and zinc (Zn), no standardized methodologies to assess in vitro mineral digestion exist. The stepwise degradation of InsP6 to lower inositol phosphate (InsP) forms in the GIT is rare, and inositol phosphate4 (InsP4) might be the limiting isomer of InsP degradation in diets with exogenous phytase. Furthermore, dietary coefficients of standardized total tract digestibility (CSTTD) of P might be underestimated in diets with fermentable ingredients because of increased diet-specific endogenous P losses (EPL), and further clarification is required to better calculate the coefficients of true total tract digestibility (CTTTD) of P. The quantification of fiber type, composition of fiber fractions, their influence on digestion kinetics, effects on digesta pH, and nutrient solubility related to fermentation should be considered for formulating diets. In conclusion, applications of nutrient kinetic data should be considered to help enhance nutrient digestion and absorption in the GIT, thereby reducing nutrient excretion.

Characterization of phosphorus sorption and microbial community in lake sediments during overwinter and recruitment periods of cyanobacteria.

The release of endogenous phosphorus from lacustrine sediment is a key element of freshwater eutrophication. The microbes in sediments may affect phosphorus migration and transformation during the growth of cyanobacteria, which may lead to the release of phosphorus from sediments and contribute to water eutrophication. To study phosphorus sorption and the microbial community structure in the overlying water and the vertical depth of sediments, samples in Meiliang Bay were collected during the dormancy and resuscitation phases of cyanobacteria. The results showed that there were high total phosphorus (TP) concentrations in the overlying water and sediment, with maximum values reached 0.24 mg L−1 and 1059 mg kg−1, respectively. Fitting by modified Langmuir model indicated that the partitioning coefficients (KP) was, from greatest to least: bottom sediment (maximum of 0.923 L g−1) > middle sediment (0.571 L g−1) > surface sediment (0.262 L g−1). During the cyanobacteria resuscitation stage, the relative abundance of Proteobacteria (18.37%–33.56%), Chloroflexi (9.57%–17.76%), Cyanobacteria (0.38%–2.62%), and the Nitrospirota phylum Thermodesulfovibrionia (4.61%–10.14%) were higher than the dormant period of cyanobacteria, and bacteria with phosphorus-solubilizing (27.27%–52.01%) accounted for the majority. The redundancy analysis (RDA) found that the structure of the microbial communities in sediments was significant correlation with organic phosphorus (OP) (P = 0.002) during recruitment period of cyanobacteria, which would accelerate the conversion of OP into soluble inorganic phosphorus and then gets released from sediment to water. The most predominant phylum among phosphorus-solubilizing bacteria (PSB) is Proteobacteria, followed by Actinobacteriota, which were positively correlated with equilibrium phosphorus concentration (EPC0) (P < 0.05) during the cyanobacterial resuscitation phase. The sediments from the cyanobacteria resuscitation phase had phosphorus release risk and highlighted the significant role of the bacterial community.

Control of Endogenous Phosphorus Release at the Sediment–Water Interface by Lanthanum-Modified Fly Ash

This study optimizes the modification and granulation of fly ash to make it more stable at the sediment–water interface. Through laboratory simulations, the modified fly ash pellets were optimally granulated to cover the sediment–water interface, and its control effect and mechanism were evaluated. The results showed that the phosphorus adsorption effect of lanthanum-modified fly ash was 34% and 40% higher compared with those of acid-modified and alkali-modified fly ash, respectively, with the phosphorus adsorption effect reaching 85%. The best dosing ratio was about 0.3 g/L. Adsorption was affected by pH and was more effective under weak alkalinity, close to the Langmuir adsorption model, which was consistent with the unimolecular layer adsorption characteristics and the presence of chemisorption and physical adsorption. The saturation adsorption amount of phosphate by lanthanum-modified fly ash was 8.89 mg/g. The optimized granulation conditions for lanthanum-modified fly ash pellets were a fly ash/montmorillonite ratio of 7:3, a roasting temperature of 900 °C, a roasting time of 4 h, and a particle size of 3 mm. After 20 days, the orthophosphate removal rate was more than 60% higher than that of the control group, with a total phosphorus removal rate of 43%. After covering for 60 days, active phosphorus in the surface layer of the sediment was gradually transformed into a stable phosphorus form, with calcium phosphorus accounting for 70% of the total inorganic phosphorus. The ability of the sediment to release phosphorus to the overlying water body was also significantly weakened. Meanwhile, the total phosphorus removal rate in the overlying water at the sediment–water interface reached more than 40%, and orthophosphate removal reached more than 60%, indicating an obvious phosphorus control effect. Transmission electron microscopy analysis showed that lanthanum was present at locations enriched with elemental phosphorus and was adsorbed onto the material surface. Therefore, lanthanum-modified fly ash pellets are a promising in situ phosphorus control agent with good endogenous phosphorus pollution control abilities in eutrophic water bodies.

Phosphorus Adsorption Characteristics and Loss Risk in Sediments of Lake Bay During the Overwinter Period of Cyanobacteria

The overwinter period is the pre-stage of the algal bloom, and the endogenous phosphorus (P) in sediments is one of the main P sources of algal blooms during this period. Based on the investigation of the water quality and sediment pollutants during the overwinter period of cyanobacteria (recruitment period and dormancy period), this study analyzed the P release characteristics of sediments in the horizontal and vertical directions and clarified the P release risk of sediments and the change in microbial community structures. The results showed that the lake bay was moderately eutrophic in the two periods of the study area, and the water quality and sediment nitrogen and P pollution were more serious, and the chlorophyll a content (Chl-a) was still at a high level in the overwinter period. The pseudo-second order model and the modified Langmuir model could respectively describe the P kinetics and sorption isotherm behavior in the sediment. The theoretical maximum P sorption capacities (Qmax) of sediments were bottom layer>middle layer>surface layer, and the highest value was 1.648 mg·g-1 with the highest P sorption rate constant of the pseudo second-order kinetic model of 6.292 g·(mg·min)-1. Additionally, the P adsorption parameters (Qmax, NAP, and EPC0) were mainly affected by the physical and chemical properties of the sediment itself and the nutritional level of the lake bay. The surface sediments from the dormancy period mainly played the role of P sinks, and the part of sediments from the recruitment period played the role of P sources, in which existed the risk of endogenous P release. The analysis of the microbial community structure in sediments indicated that the microbial diversity in the sediments during the dormancy period was higher than that during the recruitment period, and some microbial categories with phosphate-solubilizing function of relative abundance was high.

High-resolution characteristics and mechanisms of endogenous phosphorus migration and transformation impacted by algal blooms decomposition

Extremely high phosphorus (P) concentrations can be found in eutrophic freshwater sediments during algal blooms (ABs). However, few investigations have revealed the mechanism of labile P production in anoxic sediments following ABs decomposition. This limits our understanding of P cycling and mitigation of ABs in aquatic ecosystems. To identify such a mechanism, we conducted a microcosm experiment to identify how ABs decomposition enhances endogenous P release, using the combined techniques of diffusive gradients in thin films, high-resolution dialysis, and 16S rRNA amplicon sequencing. We show the concentrations of labile iron, manganese, sulfide, and P can be well predicted by quality and quantity of algal biomass. The relative abundance of iron reduction bacteria positively correlated with the decrease of pH induced by ABs decomposition, suggesting that this decomposition facilitates microbial iron and manganese reduction. In addition, the reductive dissolution of iron and manganese oxides leads to the labile P release, resulting in higher concentrations of labile P in those sediments affected by ABs compared with those not affected. The P fluxes in the algae-dominated regions exhibited higher values in the algae group than in the control group, with gains of 14.07–100.04%. Furthermore, endogenous P release is strongly controlled by Mn when the Fe(II):Mn(II) ratio is low (below 0.47), and by both Fe and Mn when the Fe(II):Mn(II) ratio is high (above 0.63). Our results quantify the endogenous P diffusion fluxes across the sediment–water interface can be attributed to ABs decomposition, and are therefore useful for further understanding of P cycling in freshwater.

Advances in researches on phosphorous inactivation materials in lake sediment

通常认为，磷是湖泊富营养化的主要限制因子，因此控制湖泊磷浓度和水平被认为是湖泊治理的关键.在外源磷输入得到有效控制之后，湖泊富营养化仍可持续几十年，这主要归咎于内源磷的释放.底泥原位化学钝化控磷技术因其操作性强、控磷效果明显，而被广泛作为湖泊内源磷的控制技术之一，而钝化材料的研发和应用是本项技术的核心.在世界范围内，研发了众多的用于底泥磷控制的钝化修复材料.本文主要梳理了国际上常用钝化材料的基本特性与研究近况，点明不同材料之间钝化效果的差异，并讨论了不同类型钝化材料的改性方法、钝化机制，分析不同环境因子对钝化材料稳定性的影响.论文最后探讨了原位化学钝化控磷技术与其他修复技术联用的污染控制效果及其可行性，并根据国际上钝化控磷技术的主要研究进展，提出钝化材料现阶段存在的不足，并对未来研究方向与应用前景进行展望.;It is generally believed that phosphorus is the main limiting factor of eutrophication, so controlling the concentration of phosphorus is considered to be the key to lake management. Lake eutrophication could continue for decades after the effective control of exogenous phosphorus input, due to the release of endogenous phosphorus from lake sediment. The technology of in-situ chemical inactivation of sediment is widely used as one of the control technologies of endogenous phosphorus in lakes because of its strong operability and obvious effect of inactivating phosphorus. The development and application of inactivation materials are the cores of this technology. Many phosphorous inactivation materials have been developed around the world. This paper reviews the research on phosphorus inactivation materials in lake sediment, including the following aspect:(1) The basic characteristics and research status of inactivation materials commonly used; (2) The differences of inactivation effect between different materials; (3) The modification methods and inactivation mechanisms of different types of inactivation materials; (4) The effects of different environmental factors on the stability of inactivation materials; (5) The effect of pollution control and feasibility of the technology of in-situ chemical inactivation combined with other remediation technologies. According to the main research progress of the technology of phosphorus inactivation, the shortcomings of inactivation materials at present are put forward, and the future research direction and application prospect are expected.

Preparation and application of an innovative integrated agent product for phosphorus control and oxygen release

Abstract In this study, an oxygen-releasing and phosphorus-controlling agent (ORPC) consisting of calcium peroxide (CaO2), bentonite, cement, stearic acid (SA), citric acid (CA) and fine sand was synthesized successfully and used to purify phosphorus-rich river water. The removal of phosphorus using ORPC was studied in actual river water and the results found that over 75.0% phosphorus was removed by adding ORPC at 30 mL h−1 flow rate in initial phosphorus concentrations of 0.76 mg L−1. The ORPC was further used to evaluate the changes of aluminum phosphate (Al-P), ferric phosphate (Fe-P) and calcium phosphate (Ca-P) in sediment. Fe-P, Al-P, and Ca-P in the sediment increased from 0.14, 0.196, and 1.63 mg g−1 to 0.159, 0.372, and 2.74 mg g−1 respectively within 28 days, indicating that the total dissolved phosphorus in the overlying water could be adsorbed by ORPC and further transformed into Al-P, Ca-P, and Fe-P in the sediment, thus inhibiting the release of endogenous phosphorus in sediment to the water. In addition, the performance of ORPC with various contents of SA and CaO2 was investigated. In summary, ORPC can be employed to adsorb phosphorus in water and prevent phosphorus release from sediment, therefore achieving the purpose of controlling phosphorus and maintaining DO at a reasonable level.

Effects of Sediment Microenvironment on Sedimentary Phosphorus Release Under Capping

The sediment microenvironment has an important effect on the release of endogenous phosphorus. In this study, the influence of two different in-situ covering materials on the sediment microenvironment were compared, and the controlling effect of endogenous phosphorus release were studied. The sediment microenvironment was represented by the concentration of NH4+-N, Fe2+ in interstitial water, and microbial activity. The results showed that the concentrations of NH4+-N and Fe2+ were lower under ACPM coverage than those of the Phoslock® group, and the microbial activity was higher, indicating that the redox potential of ACPM coverage was higher than that of Phoslock®. Furthermore, the bottom sediment microenvironment was in an aerobic state. Compared with the Phoslock® group, the DIP concentrations in both the overcover water and porewater in the ACPM group were higher, indicating that Phoslock® was superior to ACPM with respect to the phosphate adsorption capacity, suggesting that the sediment microenvironment was not the only criterion for phosphorus adsorption. In the fixation process of endogenous phosphorus, both of the covering materials were conducive to the fixation of inter phosphorus, and Ca-P increased significantly. On the other hand, oxidizing ACPM led to an increase in NH4Cl-P and a significant decrease in Fe/Al-P. This promotes the release of active phosphorus, which is conducive to the cleaning of the sediment and phosphorus release.