Characterization of sedimentary phosphorus in Lake Erie and on-site quantification of internal phosphorus loading

Microplastics alter the microbiota-mediated phosphorus profiles at sediment-water interface: Distinct microbial effects between sediment and plastisphere

Microplastics (MPs) are ubiquitous in freshwater sediments, raising concern about their potential impacts on ecosystem services. However, the specific impacts of microbiota mediated by MPs in sediment and plastisphere compartments on P availability remain elusive. This investigation conducted a series of microcosm experiments utilizing eutrophic lake sediment amended with fuel-based polyethylene terephthalate (PET), bio-based polylactic acid (PLA) MPs, and a natural cobblestone substrate to unravel their effects. The findings highlighted that MPs induced alterations in bacterial communities in both sediment and plastisphere, consequently modifying P availabilities at the sediment-water interface (SWI). In comparison to non-biodegradable PET, biodegradable PLA MPs presented higher proportions of specific bacteria and functional genes associated with P profiles, such as Firmicutes, Ignavibacteriota, and P mineralizing genes in the sediment and plastisphere. This, in turn, elevated the levels of soluble reactive P in the porewater by 54.19 % (0-1 cm), 55.81 % (1-3 cm), and 18.24 % (3-5 cm), respectively. Additionally, PLA obviously altered P immobilization capacity and bioavailability, increasing the organic P fraction. Whereas, inert cobblestone exhibited negligible influence on P biogeochemical processes during the incubation. Moreover, the biofilm communities and those in the surrounding sediment specifically contributed to the changes in P profiles at the SWI. The functional genes associated with P profiles in the sediment mainly concentrate on P mineralization and P uptake/transport. In the plastisphere, P activation genes are obviously affected under MP exposure. This study fills the knowledge gap concerning the repercussions of MPs on ecosystem services.

Spatial dynamics and risk assessment of phosphorus in the river sediment continuum (Qinhuai River basin, China)

This study investigated the concentration and fractionation of phosphorus (P) using sequential P extraction and their influencing factors by introducing the PLS-SEM model (partial least squares structural equation model) along this continuum from the Qinhuai River. The results showed that the average concentrations of inorganic P (IP) occurred in the following order: urban sediment (1499.1 mg/kg) > suburban sediment (846.1-911.9 mg/kg) > rural sediment (661.1 mg/kg) > natural sediment (179.9 mg/kg), and makes up to 53.9-87.1% of total P (TP). The same as the pattern of IP, OP nearly increased dramatically with increasing the urbanization gradient. This spatial heterogenicity of P along a river was attributed mainly to land use patterns and environmental factors (relative contribution affecting the P fractions: sediment nutrients > metals > grain size). In addition, the highest values of TP (2876.5 mg/kg), BAP (biologically active P, avg, 675.7 mg/kg), and PPI (P pollution index, ≥ 2.0) were found in urban sediments among four regions, indicating a higher environmental risk of P release, which may increase the risk of eutrophication in overlying water bodies. Collectively, this work improves the understanding of the spatial dynamics of P in the natural-rural-urban river sediment continuum, highlights the need to control P pollution in urban sediments, and provides a scientific basis for the future usage and disposal of P in sediments.

Effects of switching redox conditions on sediment phosphorus immobilization by calcium/aluminum composite capping: Performance, ecological safety and mechanisms

There many materials were used in lake restoration to immobilize phosphorus (P) and reduce the effect of eutrophication. Among them, calcium/aluminum composite (CAC) showed a good capacity of P adsorption. However, a comprehensive of its performance, ecological safety, and the mechanism of P passivation in the aluminum-bound P (Al -P) dominated sediments under varying redox conditions remains incomplete. In the current study, both unwashed CAC (UCAC) and washed CAC (WCAC) showed good P adsorption properties, and the greatest maximum capacity for P adsorption (Qmax) reached 206.8 mg/g at pH 8.5 for UCAC. The SRP and TP in the overlying water of the uncapped sediments showed a decrease-increase-decrease trend in a sequence of transition from aerobic to anaerobic to re-aerobic stages. In contrast, the SRP and TP of the two CACs-capped sediments were maintained low. Phosphorus forms in the uncapped sediment also underwent significant changes during continuous variation of dissolved oxygen (DO) levels. In particular, the decrease in iron-bound P (Fe-P) and Al-P was significantly promoted in the anaerobic phase, and the released P was reabsorbed to form mainly Fe-P in the re-aerobic phase. The CACs-capping promoted the transformation of Fe-P to residual P (Res-P), forming a thick static layer in the surface sediment, thus significantly inhibiting sediment P release. Moreover, the CACs-capping did not induce the Al3+ leaching and significant changes of the microbial community in sediments, and their performances of P immobilization could keep stable to resist the redox variation, which promised to be a good choice for P passivation in eutrophic lake sediments dominated by Al/Fe-P. These findings also confirmed that the risk of P release from Al/Fe-P (mainly Al-P)-dominated sediments was strongly influenced by continuously changing redox conditions, and was probably enhanced by the formation of Fe-P from the resorption of the released P.

Legacy phosphorus delays the accomplishment of expected phosphorus management object

Legacy phosphorus (P) in watersheds continuously affects the water quality. The time lag between anthropogenic P input and algal bloom has made P dynamics prediction in aquatic ecosystems more challenging. Whether the legacy P in the Yangtze River Watershed (YRW) exceeds its storage threshold remains unknown, and the continuous impact of legacy P on the water quality has not been analyzed. This study aimed to evaluate variation trends (1970-2018) and influencing factors for accumulated P in the YRW under different economic development periods, quantitatively identify the watershed P storage threshold based on the two split line models and estimate the time required for the return of legacy P to the baseline level using an exponential decay process. The results showed that the P storage threshold of the YRW was surpassed due to intense anthropogenic activities, and the residual P still had an impact on aquatic ecosystems for a long time. The dissolved total P loadings may become the top priority to achieve better P management goals. The time lags for the legacy P restoration would require for about 1000 years to be exhausted. The legacy P in the YRW would continuously undermine the restoration efforts of the water quality. The combined effects of watershed P surplus reductions and depletion of residual P may become essential to better manage P in the future. We still need to strengthen our efforts to make soil legacy P more absorbed by crops and improve sewage treatment capacity to achieve sustainable development of YRW.

Seasonal sediment phosphorus release across sediment-water interface and its potential role in supporting algal blooms in a large shallow eutrophic Lake (Lake Taihu, China)

Seasonal sediment internal phosphorus (P) release is known to affect annual algal blooms in eutrophic lakes. In this study, a year-long field investigation and laboratory sediment core incubation were conducted to study the relationship between sediment internal P cycling and algal growth in Lake Taihu. The results indicated that the concentrations of water total phosphorus (TP) and chlorophyll-a (Chla) correlated with seasonal temperature and were assumed to be caused by internal P release. From cold winter to warm seasons, sediment internal P (porewater P concentration and P flux) exhibits dynamic changes. Sediment porewater soluble reactive phosphorus (SRP) and its flux in the summer were approximately five times and eight times those during winter, respectively. The release of sediment mobile P in the summer decreases its concentration and can supply SRP for algal blooms. Laboratory core incubation indicated that Chla and phycocyanin concentrations in the overlying water showed similar changes to sediment porewater P and P flux when cores were incubated from low to high temperature. The results of this study indicated that warmer conditions could increase the sediment porewater P concentration and sediment P flux into the bottom waters and consequently enhance sediment P availability to algae. This study provides new insights into the relationship between internal sediment P cycling and algal blooms in Lake Taihu.

Suspended phosphorus sustains algal blooms in a dissolved phosphorus-depleted lake

The expansion of algal bloom in surface waters is a global problem in the freshwater ecosystem. Differential reactivity of organic phosphorus (P_o) compounds from organic debris, suspended particulate matter (SPM), and sediment towards hydrolysis can dictate the extent of supply often limited inorganic P (P_i) for algal growth, thereby controlling the extent of bloom. Here, we combined solution P-31 nuclear magnetic resonance (³¹P NMR), sequential extraction, enzymatic hydrolysis, and 16S rRNA measurements to characterize speciation and biogeochemical cycling of P in Lake Erhai, China. Lower ratios of diester-P/monoester-P in SPM in January (mean 0.09) and July (0.14) than that in April (0.29) reflected the higher degree of diester-P remineralization in cold and warm months. Both H₂O-P_i and P_o were significantly higher in SPM (mean 1580 mg ·kg^-1 and 1618 mg ·kg^-1) than those in sediment (mean 8 mg ·kg^-1 and 387 mg ·kg^-1). In addition, results from enzymatic hydrolysis experiments demonstrated that 61% P_o in SPM and 58% in sediment in the H₂O, NaHCO₃, and NaOH extracts could be hydrolyzed. These results suggested that H₂O-P_i and P_o from SPM were the primarily bioavailable P sources for algae. Changes of P_i contents (particularly H₂O-P_i) in algae and alkaline phosphatase activity (APA) during the observation periods were likely to be controlled by the strategies of P uptake and utilization of algae. P remobilization/remineralization from SPM likely resulted from algae and bacteria (e.g., Pseudomonas). Collectively, these results provide important insights that SPM P could sustain the algal blooms even if the dissolved P was depleted in the water column.

Regulating phytoplankton-available suspended particulate phosphorus (P) to control internal P pollution in lake: Conclusion from a short review

The necessity on controlling internal P pollution has been widely reported for lake restoration; thus far, cutting the migrations of soluble P from sediment to overlying water, especially under anoxic condition, is the main target of the internal P pollution control to achieve favorable ecological responses in lake. Here, according to the types of P directly available by phytoplankton, phytoplankton-available suspended particulate P (SPP) pollution, which mainly occurs under aerobic condition and due to sediment resuspension and soluble P adsorption by suspended particle, is found to be the other kind of internal P pollution. The SPP has long been a key index for environmental quality assessment, which could be indirectly reflected by the developed various methods for phytoplankton-available P pool analysis; also, the P has been demonstrated to be a major cause of phytoplankton breeding, typically in shallow lakes. Importantly, compared to the soluble P, SPP pollution clearly has more complicated loading pathways and P activation mechanisms and involves in different fractions of P, even part of which are with relatively high stability in sediment and suspended particle, leading to the potential control measures for the pollution being more complex. Considering the potential differences of internal P pollution among various lakes, this study is therefore calling for more research to focus on regulating phytoplankton-available SPP pollution. Recommendations are also offered to bridge knowledge gap of the regulation to design proper measures for lake restoration.

Arrhenius equation construction and nitrate source identification of denitrification at the Lake Taihu sediment - water interface with 15 N isotope

Total nitrogen in Taihu Lake, China has gradually decreased since 2015 while the total phosphorus concentration has exhibited an increasing trend, indicating an asynchronous change. The dominant nitrogen removal process in freshwater ecosystems is denitrification which primarily occurs at the sediment-water interface. In this study, ¹⁵ N isotope incubation experiments were attempted to analyze the effect of water temperature on denitrification, to construct the regional denitrification Arrhenius equations considering water temperature, and to identify the nitrate source of denitrification in Lake Taihu sediments. The results indicated that the potential N₂ production rates and denitrification rates generally decreased in the west to east direction, which was significantly positively correlated with the nitrate concentration of overlying water by Pearson correlation coefficient analysis (P < 0.05). In addition, when the water temperature was lower than 30 °C, the rates of the potential N₂ production and denitrification were higher with an increase in water temperature, but when the water temperature was overhigh, denitrification was inhibited. The ratio of the total denitrification rate of nitrate from the water column in the sediment to the total denitrification rate during the incubation experiment was above 0.5 at each sampling site. This indicated that the denitrification in the Lake Taihu sediment primarily occurred at the expense of nitrate from the water column. The research results of Arrhenius equation construction and nitrate source identification of denitization can be applied to improve the accuracy of water quality model of Taihu Lake, which is of great significance to improve Taihu Lake water quality, and can act as a reference for the water environment treatment of other shallow eutrophic lakes in China and abroad.

Characterization of internal phosphorus loading in the sediment of a large eutrophic lake (Lake Taihu, China)

Lake Taihu suffers from severe algal blooms every year, which is attributed primarily to the release of sediment phosphorus (P), namely the internal P loading. However, the overall internal P loading and the P hotspots in sediment have not been fully studied. This paper presents several methods, including sequential P extraction, the use of diffusive gradient in thin film (DGT), and intact core incubation to give a detailed investigation of sediment internal P loading as well as its roles in algal dominated zones (ADZs) and grass dominated zones (GDZs) in Lake Taihu. Sediment microbial composition was also analyzed to investigate its relationship with P fractions. The results indicate that the total P and the mobile P fraction in the ADZ sediments are generally higher than those of the GDZ sediments. The percentage of sediment mobile P to TP is similar to the mobile P in their distributions. In contrast, calcium bound P accounts for most of the TP in GDZ, while mobile P contributes the most to TP in ADZ. Overall, sediment can release 256 tons of TP and 217 tons of soluble reactive phosphorus (SRP) over a period of six months in the warmer seasons. Similarly, a high concentration of DGT-measured P was observed in ADZs that are recognized as P hotspots in Lake Taihu. Sediments in ADZ and GDZ was dominated by the bacteria Firmicutes and Proteobacteria, respectively and which were closely related with mobile P and calcium bound P in sediment, respectively. GZD seems to be able to retain more P in sediments, thereby reducing its contribution to of internal P loading. These results indicate that the difference in sediment composition between ADZ and GDZ affects their roles in sediment internal P loading, therefore, different management strategies should be used to combat sediment internal P loads in the two zones.

Two-Phase Conceptual Framework of Phosphatase Activity and Phosphorus Bioavailability

The activity of extracellular phosphatases is a dynamic process controlled by both plant roots and microorganisms, which is responsible for the mineralization of soil phosphorus (P). Plants regulate the availability of soil P through the release of root mucilage and the exudation of low-molecular weight organic acids (LMWOAs). Mucilage increases soil hydraulic conductivity as well as pore connectivity, both of which are associated with increased phosphatase activity. The LMWOAs, in turn, stimulate the mineralization of soil P through their synergistic effects of acidification, chelation, and exchange reactions. This article reviews the catalytic properties of extracellular phosphatases and their interactions with the rhizosphere interfaces. We observed a biphasic effect of root metabolic products on extracellular phosphatases, which notably altered their catalytic mechanism. In accordance with the proposed conceptual framework, soil P is acquired by both plants and microorganisms in a coupled manner that is characterized by the exudation of their metabolic products. Due to inactive or reduced root exudation, plants recycle P through adsorption on the soil matrix, thereby reducing the rhizosphere phosphatase activity. The two-phase conceptual framework might assist in understanding P-acquisition (substrate turnover) and P-restoration (phosphatase adsorption by soil) in various terrestrial ecosystems.

Combined remediation mechanism of bentonite and submerged plants on lake sediments by DGT technique

The diffusive gradients in thin films (DGT) technique was applied to determine the mechanism by which bentonite improves the eutrophic lake sediment microenvironment and enhances submerged plant growth. The migration dynamics of N, P, S, and other nutrient elements were established for each sediment layer and the remediation effects of bentonite and submerged plants on sediments were evaluated. Submerged plant growth in the bentonite group was superior to that of the Control. At harvest time, the growth of Vallisneria spiralis and Hydrilla verticillata was optimal on a substrate consisting of five parts eutrophic lake sediment to one part modified bentonite (MB5/1). Bentonite addition to the sediment was conducive to rhizosphere microorganism proliferation. Microbial abundance was highest under the MB5/1 treatment whilst microbial diversity was highest under the RB1/1 (equal parts raw bentonite and eutrophic lake sediment) treatment. Bentonite addition to the sediment may facilitate the transformation of nutrients to bioavailable states. The TP content of the bentonite treatment was 22.47%-46.70% lower than that of the Control. Nevertheless, the bentonite treatment had higher bioavailable phosphorus (BIP) content than the control. The results of this study provide theoretical and empirical references for the use of a combination of modified bentonite and submerged plants to remediate eutrophic lake sediment microenvironments.

Synergistic Effects and Ecological Responses of Combined In Situ Passivation and Macrophytes toward the Water Quality of a Macrophytes-Dominated Eutrophic Lake

Combined use of in situ passivation and macrophytes is a valuable technology that exerts remarkable effects on aquatic systems. However, the effectiveness and ecological functions of this combined technology for macrophytes-dominated eutrophic (MDE) lakes with organophosphorus-controlled internal phosphorus (P) loading were poorly understood. In this study, aquatic simulation experiments were performed to study the combination of La-modified materials (LMM; La-modified bentonite (LMB), and La/Al co-modified attapulgite (LAA)) with macrophytes (Myriophyllum verticillatum L. (MVL), Hydrilla verticillata (Linn. f.) royle (HVR), and Ceratophyllum demersum L. (CDL)) for the control of P mobility in the water column, and to investigate the passivator effects on the physiological characteristics of macrophytes. The mineralization of organophosphates (BD−Po, HCl−Po, and Res−Po) is an important factor for maintaining high internal P loadings and overlying water P concentrations in the experiments. Compared with individual treatment groups, the reduction of internal P release flux and porewater SRP concentrations was more obvious in the combined treatments. Moreover, the redox-sensitive P forms transformation is more pronounced in the surface sediments. In the LAA+M group, internal P release flux was reduced by 55% and 55% compared with individual passivators and macrophytes retreatment groups, respectively. In contrast, the LMB+M group decreased by 16% and 46%, respectively. Simultaneously, LMM had less effect on macrophytes traits compared with individual macrophytes group and enhanced the absorption of phosphate by macrophytes. The phosphate content of macrophytes in the LAA+M and LMB+M groups increased by 24% and 11%, respectively, in comparison with the individual macrophytes group. Results concluded that the combination of passivator and macrophytes enhanced the effect of ecological restoration and exerts a synergistic effect on internal P pollution with macrophytes.

Drinking water treatment residue recycled to synchronously control the pollution of polycyclic aromatic hydrocarbons and phosphorus in sediment from aquatic ecosystems

Great efforts have long been made to control sediment pollution from persistent organic pollutants and phosphorus for aquatic ecosystem restoration. This study proposed a novel recycling of drinking water treatment residue (DWTR) to synchronously control sediment polycyclic aromatic hydrocarbons (PAHs) and phosphorus pollution based on a 350-day incubation test. The results suggested that DWTR addition reduced approximately 88%- 96% of potential bioavailable PAHs and 76% of mobile phosphorus in sediment. The dominant mechanisms for both reductions by DWTR were immobilization, mainly through increasing sediment amorphous aluminum and iron. The tendency of enhanced PAHs degradation by DWTR was also observed, especially for high molecular weight PAHs (e.g., chrysene, indeno(1, 2, 3-cd)pyrene, and benzo(g, hi)perylene), which decreased by approximately 21.1%- 22.0% of the total. Additionally, accompanying a clear increase in the connections of microbial cooccurrence networks, the variations in bioavailable PAHs, amorphous aluminum and iron, and other properties (e.g., pH, nitrogen, and organic matter) significantly (p < 0.01) enhanced Flavobacterium enrichment, although the enrichment of many other microbes potentially related to PAHs degradation (e.g., C1-B045) decreased after DWTR addition. Therefore, DWTR could promote the construction of a "PAHs immobilization with microbial augmentation" system while immobilizing phosphorus in sediment, indicating the high feasibility of controlling multiple sediment pollution.

Quantifying the contribution of direct runoff and baseflow to nitrogen loading in the Western Lake Erie Basins

Soluble nitrogen is highly mobile in soil and susceptible to leaching. It is important to identify nitrogen transport pathways so that the sources can be efficiently targeted in environment management. This study quantified the contribution of direct runoff and baseflow to nitrate + nitrite loading by separating flow and nitrate + nitrite concentration measurements into two periods depending on whether only baseflow was present or not using baseflow separation methods. When both direct runoff and baseflow were present in streamflow, their nitrate + nitrite concentrations were assumed based on the hydrological reasoning that baseflow does not change rapidly, and streamflow mostly consists of direct runoff within a rainfall event. For this study, we obtained and investigated daily flow and nitrate + nitrite concentration observations made at the outlets of 22 watersheds located in the Western Lake Erie area. Results showed that baseflow was responsible for 26 to 77% of the nitrate + nitrite loads. The relative nitrate + nitrite load contributions of direct runoff and baseflow substantially varied with the sizes of drainage areas and agricultural land uses. Increases in drainage areas tend to prolong the travel time of surface runoff and thus help its reinfiltration into soil, which then could increase the baseflow contribution. In addition, the artificial drainage networks common in the agricultural fields of the study areas would promote the drainage of nutrient-laden excess water from soils. Such findings suggest the need for environmental management customized considering nitrogen transport pathways.

Variability in Soil Parent Materials at Different Development Stages Controlled Phosphorus Fractions and Its Uptake by Maize Crop

An adequate phosphorus (P) supply in the rhizosphere is essential for proper P uptake through plant roots. Distributions of P varies depending on the soil structure, formation, and the parent material from which it originates. More research is needed to determine whether soil depth and parent materials have an impact on P distribution. It was hypothesized that the type of soil formed by different parent materials is related to P uptake and soil P fractions. Soil samples were taken from different profiles at various stages of development in loess, alluvium, shale, and sandstone parent materials. The samples were analyzed for P fractions using the Jiang and Gu fractionation scheme. In the present study, the P fractions were controlled according to the quantity and the components, such as organic matter, clay minerals, carbonates, iron, and aluminum oxides. Studying the phosphatase enzyme activity related to P fractions, the soil parent material, and their development was highly beneficial in defining which P pools are more accessible to plants, as well as the effect of phosphatase in limiting P availability. Among all the tested parent materials, the total P in soils derived from the loess parent material was higher (792 mg kg−1) than in soils derived from alluvium, shale, and sandstone, respectively. The amount of apatite P in alluvium parent material was higher, accounting for 51–56% of total P. Other P forms varied significantly in parent materials in the following order loess > alluvium > shale >> sandstone. Phosphatase enzyme was found to be an indicator of P availability by limiting its uptake by plants.

Particle size-related vertical redistribution of phosphorus (P)-inactivating materials induced by resuspension shaped P immobilization in lake sediment profile

Lake geoengineering with phosphorus (P)-inactivating materials to reduce sediment P loading is often used for eutrophication control. The redistribution of materials in sediment, especially those induced by resuspension, is reportedly a common phenomenon during practical applications, which may interfere with the pollution control. Notably, a recent study by the authors initially found that the heterogeneous properties of materials and sediments varied the P immobilization in different sized sediments which exhibited diverse movement characteristics. Therefore, this study hypothesizes a particle size-related vertical redistribution of materials in the sediment profile induced by resuspension, which shapes sediment P immobilization at different depths. Based on two differently sized materials, lanthanum (La)-modified bentonite clay (Phoslock) and drinking water treatment residue (DWTR), this study found a weakened reduction of mobile P and bioavailable P pool by both DWTR and Phoslock in surface sediment after resuspension. As the depth decreased from >12 to surface 0-1 cm, the remaining mobile P increased from 7.11%-10.8% to 11.0%-17.8% of the total P in the sediment with Phoslock and from 1.66%-4.73% to 9.70%-20.7% of the total P in the sediment with DWTR; meanwhile, bioavailable P pool reduction proportions decreased from 48.6%-72.3% to 3.23%-45.1% for Phoslock and from 51.5%-71.4% to 4.94%-25.2% for DWTR. Further analysis verified the hypothesis of this study; importantly, the redistributions of the potential target P (including mobile and bioavailable P) for immobilization were regulated by relatively small sediments (e.g., <8 μm fraction), which tended to become enriched in surface sediment after resuspension, while relatively large materials (e.g., >63 μm fraction) regulated their redistributions and were more likely to be buried at the bottom of the sediments. Accordingly, to design appropriate strategies for lake geoengineering, relatively small materials (e.g., <8 μm) targeting to immobilize both mobile and bioavailable P are typically recommended to be developed for restoration of lakes with frequent sediment resuspension.

A critical review on operation and performance of source water control strategies for cyanobacterial blooms: Part II-mechanical and biological control methods

This review summarizes current knowledge on mechanical (artificial mixing, hypolimnetic aeration, dredging, and sonication) and biological (biomanipulation, macrophytes, and straws) methods for the management of cyanobacterial blooms in drinking water sources. Emphasis has been given to (i) the mechanism of cyanobacterial control, (ii) successful and unsuccessful case studies, and (iii) factors influencing successful implementation. Most mechanical and biological control strategies offer long-term control. However, their application can be cost-prohibitive and treatment efficacy is influenced by source water geometry and continual nutrient inputs from external sources. When artificial mixing and hypolimnetic oxygenation units are optimized based on source water characteristics, observed water quality benefits included increased dissolved oxygen contents, reduced internal loading of nutrients, and lower concentrations of reduced ions . Treatment efficacy during oxygenation and aeration was derailed by excessive sedimentation of organic matter and sediment characteristics such as low Fe/P ratios. Dredging is beneficial for contaminated sediment removal, but it is too costly to be a practical bloom control strategy for most systems. Sonication control methods have contradictory findings requiring further research to evaluate the efficacy and applicability for field-scale control of cyanobacteria. Biological control methods such as biomanipulation offer long-term treatment benefits; however, investigations on the mechanisms of field-scale cyanobacterial control are still limited, particularly with the use of macrophytes and straws. Each control method has site-specific strengths, limitations, and ecological impacts. Reduction of external nutrient inputs should still be a significant focus of restoration efforts as treatment benefits from mechanical and biological control were commonly offset by continued nutrient inputs.

Species, fractions, and characterization of phosphorus in sewage sludge: A critical review from the perspective of recovery

Phosphorus recovery from municipal sewage sludge is a promising way to alleviate the shortage of phosphorus resources. However, the recovery efficiency and cost depend greatly on phosphorus species and fractions in different sewage sludges, i.e., waste activated sludge and chemically enhanced primary sludge. In this review, the phosphorous (sub-)species and fractions in waste activated sludge and chemically enhanced primary sludge are systematically overviewed and compared. The factors affecting phosphorus fractions, including wastewater treatment process, as well as sludge treatment methods and conditions are summarized and discussed; it is found that phosphorus removal method and sludge treatment process are the dominant factors. The characterization methods of phosphorus species and fractions in sewage sludge are reviewed; non-destructive extraction of poly-P and microscopic IP characterization need more attention. Anaerobic fermentation is the preferable solution to achieve advanced phosphorus release both from waste activated sludge and chemically enhanced primary sludge, because it can make phosphorus species and fractions more suitable for recovery. A post low strength acid extraction after anaerobic fermentation is recommended to facilitate phosphorous release and improve the total recovery rate.