Understanding phosphorus fractions and influential factors on urban road deposited sediments

Phosphorus (P) is a primary pollutant that builds-up on urban road surfaces. Understanding the fraction and load characteristics of P, as well as their relationship with urban factors, is helpful for assessing the ecological risk of urban receiving water bodies. This study presents the characteristics of build-up loads of P fractions in road-deposited sediments (RDS) in Guangzhou, China, analyzes their correlation with three urban factors (road, traffic, and land-use area), and then estimates the exceedance probability of P in stormwater runoff over the past 10 years. The results showed that detrital apatite phosphorus (De-P) performed the highest build-up load on urban road surfaces, followed by apatite phosphorus (Ca-P), iron-bound phosphorus (Fe-P), exchangeable phosphorus (Ex-P), aluminum-bound phosphorus (Al-P), organophosphorus (POP), dissolved inorganic phosphorus (DIP), occluded phosphorus (Oc-P), and dissolved organic phosphorus (DOP). Depression depth, road materials, and land-use fractions affected the P fractions. The P in the RDS may have originated from three distinct sources: road background, domestic waste, and untreated wastewater discharge. In the most recent 10 years, the event mean concentrations of total P in the RDS have had a 30 % probability of exceeding 0.4 mg L-1, which indicates a serious threat of P to receiving water bodies. The outcomes of this study are expected to provide valuable guidance for elucidating the principal categories of urban non-point source P pollution and enhancing the ecological health of urban water environments.

Phosphorus distribution in the water and sediments of the Ganga and Yamuna Rivers, Uttar Pradesh, India: insights into pollution sources, bioavailability, and eutrophication implications

River nutrient enrichment is a significant issue, and researchers worldwide are concerned about phosphorus. The physicochemical characteristics and phosphorus (P) fractions of 36 sediment and water samples from the Ganga (Kanpur, Prayagraj, Varanasi) and Yamuna (Mathura, Agra, Prayagraj) rivers were examined. Among the physicochemical parameters, pH exceeded the permissible limit in Ganga and Yamuna River water and sediment samples. Electrical conductivity (EC) and alkalinity were within the permissible limits, whereas total nitrogen (TN) exceeded the limit in Yamuna water. The analysis of phosphorus fractions indicated the dominance of inorganic phosphorus (IP) (76% in Ganga and 96% in Yamuna) over organic phosphorus in both rivers, suggesting the mineralization and microbial degradation as major processes responsible for transforming OP to IP. The positive correlation of pH with IP, AP (apatite phosphorus), and NAIP (non-apatite inorganic phosphorus) explains the release of inorganic phosphorus under alkaline conditions. The correlation between total organic carbon (TOC), TN, and organic phosphorus (OP) indicated the organic load in the rivers from allochthonous and autochthonous sources. Phosphorus released from river sediments and the concentration of phosphate in overlying river water show a positive correlation, suggesting that river sediments may serve as phosphorus reservoirs. The average phosphorus pollution index (PPI) was above one in both rivers, with relatively higher PPI values observed in the Yamuna River, indicating the contamination of sediment with phosphorus, indicating the contamination of sediment with phosphorus. This study revealed variations in the P fractionation of the sediment in both rivers, primarily as a result of contributions from different P sources. This information will be useful for applying different mitigation techniques to lower the phosphorus load in both river systems.

Contrasting fertilization response of soil phosphorus forms and functional bacteria in two newly reclaimed vegetable soils

Fertilization is a pervasive approach to agricultural production enhancing vegetable nutrients such as phosphorus (P) absorption. However, unreasonable fertilization strategies result in high levels of residual P in vegetable planting systems. To better understand the mechanisms of soil phosphorus dynamics responding to inorganic/organic fertilization, we conducted a 3-year field experiment in two newly reclaimed vegetable fields in southern China. The results revealed that soil Olsen-P in CF (mineral fertilization) and OF (Combined application of organic and inorganic fertilizers) increased by approximately 210.6 % and 183.6 %, respectively, while stable P proportion decreased by approximately 9.2 % and 18.1 %, respectively, compared with CK. Combined application of organic and inorganic fertilizer increased the proportion of moderately labile P (NaOH-P) by 1-6 % in comparison with chemical fertilizer and facilitated the conversion from diester-P to monoester-P, indicating that applying pig manure enhanced the potential soil P bioavailability. Besides, organic-inorganic fertilization shaped a bacterial community with more connectivity and stability and changed keystone taxa related to the P transformation of the network. Phenylobacterium, Solirubrobacter, and Modestobacter were regarded as core genera for mobilizing soil phosphorus. However, residual P content in newly reclaimed soils under fertilization, especially for chemical fertilizer, remained non-negligible and may cause potential environmental risks. The partial least squares path modeling results demonstrated that fertilization management had both direct and indirect positive effects on P fraction through the improvement of soil nutrients e.g. total N and soil organic carbon, and bacterial community, while soil properties mainly determined the variation of soil P species. Our results provide comprehensive insights into the current status of legacy P forms and the vital role of fertilizer, key soil properties and bacteria in P dynamics in newly reclaimed vegetable field.

Spatial variation of soil phosphorus in the water level fluctuation zone of the Three Gorges Reservoir: Coupling effects of elevation and artificial restoration

The water level fluctuation zone (WLFZ) is a distinctive and important component of the reservoir ecosystem. Due to periodic inundation, the fraction, spatial distribution, and chemical reactivity of soil phosphorus (P) within the WLFZ can potentially impact the loading of P into reservoir waters. However, a detailed study of this subject is lacking. In this study, the soil P in the WLFZ of the Three Gorges Reservoir, China, was examined using a combination of chemical sequential extraction, 31P NMR, and adsorption experiments. The results of chemical sequential extraction showed that HCl-Pi constituted the largest P pool among all P forms, with a mean concentration of 338 mg/kg. The content of HCl-Pi decreased significantly toward the dam, while the content of Res-P decreased in the opposite direction. The highest contents of most P forms and total P were observed at an elevation of 160 m. 31P NMR measurements showed that NaOH-EDTA Pi detectable in WLFZ soils at 145 m, 160 m, and 175 m elevation consisted mainly of orthophosphate and pyrophosphate, while NaOH-EDTA Po contained phosphate monoesters and phosphate diesters, accounting for 1.4 % to 46.2 % of NaOH-EDTA TP. Adsorption experiments showed that soil P in the WLFZ was a potential P source for reservoir waters, with chemisorption being the dominant mechanism of P sequestration. The adsorption equilibrium concentration of WLFZ soil was lower at higher elevations (>170 m) compared to lower elevations (<150 m), exhibiting a decrease in the average maximum adsorption from 271 mg/kg to 192 mg/kg. Statistical analysis suggested that Ca and Fe content, particle size, elevation, and artificial restoration were key factors affecting the fraction and content of soil P in the WLFZ. Our findings contribute to an improved understanding of the behavior of soil P in the WLFZ of large reservoirs and its potential contribution to the reservoir waters.

Regulating method of microbial driving the phosphorus bioavailability in factory composting

Phosphorus bioavailability is essential for assessing compost quality. However, the effects of microbial and environmental factors on potentially active phosphorus (H2O-P + NaHCO3-Pi) in factory compost have not been investigated. The findings indicated that chicken manure had significantly higher available phosphorus (AP) and H2O-P + NaHCO3-Pi throughout the composting process than kitchen waste (P < 0.05). Chicken manure compost also exhibited higher α-microbial diversity. Novibacillus, Marinococcaceae and Bacillales were the core bacteria involved in bioavailable phosphorus conversion in both composts. The core bacteria in kitchen waste compost had a broader range of phosphorus metabolism functions. Moreover, moisture and pH were the key environmental factors that significantly influenced the bioavailable phosphorus (P < 0.05). These findings provide a scientific foundation for regulating the composting process and improving phosphorus utilization efficiency.

Metal oxide modified biochars for fertile soil management: Effects on soil phosphorus transformation, enzyme activity, microbe community, and plant growth

Metal oxide modified biochars are increasingly being used for intensive agricultural soil remediation, but there has been limited research on their effects on soil phosphorus transformation, soil enzyme activity, microbe community and plant growth. Two highly-performance metal oxides biochars (FeAl-biochar and MgAl-biochar) were investigated for their effects on soil phosphorus availability, fractions, enzyme activity, microbe community and plant growth in two typical intensive fertile agricultural soils. Adding raw biochar to acidic soil increased NH4Cl-P content, while metal oxide biochar reduced NH4Cl-P content by binding to phosphorus. Original biochar slightly reduced Al-P content in lateritic red soil, while metal oxide biochar increased it. LBC and FBC significantly reduced Ca2-P and Ca8-P properties while improving Al-P and Fe-P, respectively. Inorganic phosphorus-solubilizing bacteria increased in abundance with biochar amendment in both soil types, and biochar addition affected soil pH and phosphorus fractions, leading to changes in bacterial growth and community structure. Biochar's microporous structure allowed it to adsorb phosphorus and aluminum ions, making them more available for plants and reducing leaching. In calcareous soils, biochar additions may dominantly increase the Ca (hydro)oxides bounded P or soluble P instead of Fe-P or Al-P through biotic pathways, favoring plant growth. The recommendations for using metal oxides biochar for fertile soil management include using LBC biochar for optimal performance in both P leaching reduction and plant growth promotion, with the mechanisms differing depending on soil type. This research highlights the potential of metal oxide modified biochars for improving soil fertility and reducing phosphorus leaching, with specific recommendations for their use in different soil types.

Vertical distributions and risk assessment of phosphorus in core sediments from the Can Gio coastal district in southern Vietnam

In this study, total phosphorus (P) and P released forms were measured in core sediments from the areas affected by human settlement and shrimp farming activities and the core zone of the Can Gio Biosphere Reserve, a coastal district in south Vietnam. Furthermore, ecological risk assessment and parameters controlling P release from sediments were investigated, including pH, major elements (Al-Ca-Mg-Fe), and fine fraction. The average total amount of P in the sediments varied from 287 to 669 mg/kg, with significantly lower values being observed in the mangrove biosphere reserve area. According to the results of the correlation analysis, organic matter was the primary source of P in the sediments, but the majority of the P released was inorganic. Positive correlations were found between Fe and non-apatite inorganic P (NAIP) and apatite P (AP), as well as intercorrelations between P fractions (r = 0.40-0.79, p < 0.05), suggesting that Fe might be the controlling factor of P release in the investigated sediments. The rank orders of concentrations of P forms were significantly different between the areas. The range of P forms was AP (35-248 mg/kg) > NAIP (63-201 mg/kg) > LP (labile P) (4-25 mg/kg) in the human settlement and aquaculture areas and NAIP (84-99 mg/kg) > AP (20-38 mg/kg) > LP (7-12 mg/kg) in the mangrove biosphere reserve area. Risk assessment based on the total concentration of P and the availability of P from a single extraction suggested a relatively low risk of P from sediment as an internal load in the studied areas.

Unveiling the role of sediments in phosphorus removal in pilot-scale constructed wetlands for swine wastewater treatment

The accumulation rate, fractions, and sorption capacity of phosphorus in sediments determine the removal efficiency and service life of constructed wetlands (CWs). Nine pilot-scale three-stage surface flow CWs were constructed to treat three loading rates of lagoon-pretreated swine wastewater, and surface sediment samples at initial and one-year treatment were collected to analyze the phosphorus fractions and sorption capacity. After one-year treatment, concentration of total phosphorus (TP) in sediments increased for high loading rates of wastewater, but remained stable for low loading rates. The annual accumulation rate of TP in sediments (M_a) was -43-445 mg kg^-1 yr^-1 at surface loading rate (SLR) of 36-355 g P m^-2 yr^-1. Their association could be described well using a sigmoid model, i.e., M_a = -23 + 538/(1 + exp.(-(SLR-262)/48)) (R²_adj = 0.897, RMSE = 40.8, p < 0.01), indicating that the phosphorus accumulation rates in sediments were loading rate-dependent. The sum of inorganic phosphorus fractions contributed to 80-100% of the TP concentration, and accumulation of aluminum-bound phosphorus (AlP) and iron-bound phosphorus (FeP) was responsible for variability of TP concentration in sediments. Phosphorus sorption capacity of CW1 sediments increased by 1.3-1.8 times, attributed to increased pH, and concentrations of ammonium oxalate-extractable aluminum and iron in sediments due to the wastewater input. Selecting iron and aluminum-rich materials preferentially as substrates and regulating the ratio of metal ions to phosphorus in wastewater should be alternative enhancement strategies of CWs for phosphorus removal.

Dynamics of sediment phosphorus affected by mobile aeration: Pilot-scale simulation study in a hypereutrophic pond

Controlling the release of phosphorus (P) in sediments is important to prevent eutrophication and harmful algal blooms in water bodies. Here we explored the effect of mobile aerators on the control of P release from sediments in a eutrophic pond. The dissolved oxygen in the water body recovered significantly after six months of aeration, becoming 4.2-5.8 times higher than in the control. The pH and Eh values at the sediment-water interface considerably increased, while the concentration of soluble reactive phosphorus (SRP) in pore water significantly decreased, resulting in the alteration of SRP fluxes from 1.69 mg/m² d to -53.49 mg/m² d. Moreover, the inert P in sediments increased by 5.2% of the total P at the end of the study compared with the initial state, and the calcium-bound phosphorus (HCl-P) increased by 96.6%. However, although aeration reduced the concentration of SRP in the water column, the total P concentration was 2.45 times higher than that of the control, and the content of redox-sensitive P (BD-P) in the sediment also increased by 200%. Overall, although mobile aeration can maintain the microenvironment of the sediment interface and increase the inert P content in the sediment to reduce the P flux, it cannot reduce the risk of release of mobile P.

Alkaline phosphatase-harboring bacterial community and multiple enzyme activity contribute to phosphorus transformation during vegetable waste and chicken manure composting

The objective of this study was to evaluate changes in phosphorus fractions during vegetable waste and chicken manure composting. High throughput sequencing, quantitative PCR, and multiple analysis methods were applied to investigate interconnections among phosphorus fractions, enzyme activity, and phoD-harboring bacterial community composition. We found the highest composting temperature reached 61 °C and phosphorus fractions presented significant differences during a 60-day composting. The content of plant-absorbable phosphorus, including water soluble phosphorus, available phosphorus, and citric acid phosphorus increased by 121%, 87%, and 63%, respectively. Additionally, phoD gene abundance significantly correlated with the activities of nine enzymes. Our findings emphasize that microbial activity plays an important role in phosphorus transformation during composting, and the final composting product could be good biological phosphorus fertilizer. To our knowledge, this is the first report indicating that enzyme activity, community composition and abundance of phoD-harboring bacteria have direct and indirect effects on phosphorus transformation during composting.

Evaluating the effect of dam construction on the phosphorus fractions in sediments in a reservoir of drinking water source, China

It is widely acknowledged that dams affect sediment transport and water quality. To support water management of reservoirs, it is useful to explore how the fractions of phosphorus (P) in sediments were changed after the dam was built. The aim of this study was to assess the spatial and temporal trends of the P fractions in sediments from the Miyun Reservoir, a pivotal drinking water supply for Beijing City, the capital of China. Nine surface sediment samples, together with a sediment core, were collected. The concentrations of total P (TP) and their fractions were then determined by using a sequential extraction method. The results showed that the reservoir was classified into three areas spatially based on the TP concentrations, i.e., high (Baihe area), medium (transitional area), and low (Chaohe area) concentrations. The concentrations of iron-bound P (BD-P) and metal oxide-bound P (NaOH-P) were higher in the Baihe and Chaohe regions than those in the transitional area and tended to increase with water depth. Dam construction can lead to the concentrations of P increased in sediments and further increase the potential of internal P loadings. This study revealed the effect of dam construction on sedimentary P accumulation. The results will be helpful in better understanding the mobility and bioavailability of P in the aquatic ecosystem, which aim to achieve a more highly targeted environmental management for this important region.

Increased risk of phosphorus and metal leaching from paddy soils after excessive manure application: Insights from a mesocosm study

Livestock manure has gradually become an alternative fertilizer for maintaining soil fertility, whereas excessive application of manure leads to the release of phosphorus (P) and toxic metals that may cause complex environmental risks. To investigate the accumulation and migration of P within soil profiles, a mesocosm experiment was conducted to analyze the content and leaching of soil P, metals, and dissolved organic carbon after different fertilization treatments, including control (no fertilizer, CK), chemical fertilizer (CF), chemical fertilizer combined low (CF + LPM) and high (CF + HPM) rate of manure application. Results showed that a high rate of manure application significantly enhanced the accumulation of total soil P (by ~14%) and P availability (easily-available P, by ~24%; Olsen-P, by ~20%) in topsoil, and also increased the content of easily-available organic P (EA-Po) in both topsoil and subsoil compared to the CK treatment. The migration of dissolved inorganic and organic P (DIP and DOP) in leachate within soil profiles was strengthened by manure application. Moreover, significant positive correlations between P, metals, and dissolved organic carbon (DOC) in leachate indicated that downward co-migration occurred within the soil profiles, and also suggested that excessive manure application can intensify the risk of P loss by increasing the migration of manure-derived DOC. Overall, our findings provide insights into P accumulation and migration within soil profiles after excessive manure application, which is useful for predicting the potential risk of P and metal leaching from paddy soils.

Inoculation of fly ash amended vermicompost with phosphate solubilizing bacteria (Pseudomonas fluorescens) and its influence on vermi-degradation, nutrient release and biological activity

Due to the crucial role played by microbes during vermicomposting, deliberate inoculation of composts with specialized microbes as a way of further optimizing the vermicomposting process has been suggested. This study evaluated the potential of inoculating fly ash - cow dung - waste paper vermicompost with phosphate solubilizing bacteria (P. fluorescens) in improving vermi-degradation, nutrient mineralization and biological activity. Incorporation of E. fetida plus P. fluorescens accelerated the biodegradation process as indicated by the significant decrease in C/N ratio (P = 0.0012) resulting in a final C/N ratio of 11 compared to the control which had C/N ratio of 18. Inoculation with P. fluorescens resulted in improved availability of Olsen P which amounted to 48.3% more Olsen P relative to the control. The inoculation also caused a big decrease in alkaline phosphatase activity but yielded the highest FDA activity. Inclusion of E. fetida with or without P. fluorescens did not significantly influence microbial growth, however, these two treatments had relatively more colony counts compared to the control. It is concluded that the interaction of E. fetida earthworms with P. fluorescens can optimize vermi-degradation, nutrient release and biological activity during vermicomposting of fly ash- cow dung - waste paper substrate. It would be interesting to establish whether Pseudomonas species inoculated at different rates, or their combination with nitrogen fixing bacteria would have the same or better effects on the vermicomposting of fly ash- cow dung - waste paper substrates.

Lateral and longitudinal variation in phosphorus fractions in surface sediment and adjacent riparian soil in the Three Gorges Reservoir, China

Hydrological regimes have been significantly altered since the Three Gorges Dam (TGD) raised the water level of the reservoir to the maximum design level of 175 m in October 2010. This change might greatly influence the forms of phosphorus (P) in the sediment and the adjacent riparian soil. The purpose of this study was to reveal the lateral (sediment, water-level-fluctuation zone soil, and upland soil) and longitudinal (from the end of backwater area to the TGD) trends in P factions. Samples from 11 sites located along the main stem and ten sites located along eight tributaries were collected in June 2017. The P fractions were determined using the Standards, Measurements, and Testing (SMT) protocol. The results showed that the order of increase for average pH values was sediment (7.58 ± 0.62), WLFZ soil (7.44 ± 0.29), and adjacent upland soil (7.20 ± 0.68). The total organic carbon in the sediment was also highest with an average of 9.15 ± 2.97 mg·g^-1. The average concentrated HCl-extractable P (total P), organic P (OP), inorganic P (IP), HCl-extractable P (HCl-P), and NaOH-extractable P (NaOH-P) were 630.02 ± 212.24, 161.89 ± 90.77, 468.13 ± 194.92, 335.65 ± 159.88, and 51.40 ± 36.20 mg·kg^-1, respectively. The concentration of both total P and NaOH-P in the sediment of the main stem exhibited an increasing trend from the backwater area to the TGD. The average concentration of P species in the sediment was higher than those in the upland soil and the water-level-fluctuation zone (WLFZ) soil. For all the sediment and soil samples, the rank order of P species concentrations was HCl-P > OP > NaOH-P. Both IP and HCl-P were highly positively correlated with total P in the upland soil, the WLFZ soil and the sediment. However, only in the sediment, NaOH-P was positively correlated with total P and OP. All P species in the upland soil demonstrated greater spatial heterogeneity than those in the WLFZ soil and the sediment. Redundancy analysis revealed that the main variables explaining the variance in P species concentrations were Al in the upland soil and pH in the sediment.

The phosphorus fractions and adsorption-desorption characteristics in the Wuliangsuhai Lake, China

The phosphorus (P) fractions and adsorption-desorption characteristics in the Wuliangsuhai Lake were investigated through molybdenum blue/ascorbic acid method and indoor simulation experiments, respectively. The results showed that the highest total phosphorus concentration in overlying water (W-TP) was found in S1 which was in the hypereutrophic type. The mean concentration of particulate organic phosphorus (POP) was the most abundant P fraction (31.35% of the W-TP). The results of TP contents in sediments (S-TP) indicated that the most sampling sites were in the mild level of pollution. The contents of calcium-bound P (HCl-P) and residual P (Res-P) fractions together comprised 83.03-98.10% of the S-TP. Pseudo-second-order models fitted well with the adsorption-desorption kinetic of P fractions. The Langmuir and Freundlich models well described the adsorption isotherm of P fractions. The results of adsorption-desorption of P fractions indicated that the adsorption capacity was strong, the chemical adsorption was dominant, and the sediments was a source of P. Accordingly, we concluded that the Wuliangsuhai Lake was in the moderate pollution level, and the sediments as a source could desorb P in natural aquatic environment.

Distribution of phosphorus-solubilizing bacteria in relation to fractionation and sorption behaviors of phosphorus in sediment of the Three Gorges Reservoir

Phosphorus (P) fractionation and sorption behavior as well as the abundance and community composition of phosphorus-solubilizing bacteria (PSB) in sediments, including inorganic phosphate-solubilizing bacteria (IPB) and organic phosphate-mineralizing bacteria (OPB), were investigated in 27 sampling sites of five sections in the Three Gorges Reservoir (TGR) in December 2012. The calcium-bound phosphorus (CaCO₃∼P) accounted for the largest part for P fractions in the sediment of TGR, which was paralleled with IPB outnumbering OPB. Furthermore, some PSB isolates, such as Micromonospora sp., Aminobacter sp., and Arthrobacter sp., were shared by the IPB and OPB. Thus, some IPB species functioned as OPB and vise versa, which could be further reflected by a negative and significant relationship between PSB (IPB + OPB) number and content of CaCO₃∼P together with acid-soluble organic phosphorus (ASOP). Spatially, the highest ASOP content in the section Mudong and the highest CaCO₃∼P plus iron-bound phosphorus (Fe(OOH)∼P) as well as equilibrium phosphorus concentration (EPC₀) in the sections of Yunyang and Zigui due to sediment sequestration by the dam, as well as the positive relationship between EPC₀ and the ratios of different phosphorus species and phosphorus sorption maximum (Q _max), jointly indicated pathway diversification and potential risk of phosphorus release mediated by PSB in TGR.

Spatial-temporal variations of phosphorus fractions in surface water and suspended particles in the Daliao River Estuary, Northeast China

The transport and storage of phosphorus in estuary is a complex biogeochemical process as the result of the convergence of fresh and saline water. The objective of the current study is to investigate the spatial-temporal variations of phosphorus fractions in surface water and suspended particles of Daliao River Estuary, China. Samples were collected in August (wet season) and November (dry season), 2013. The results showed that total particulate phosphorus (TPP) in water accounted for more than 50 % of the total phosphorus (TP). Meanwhile, in suspended particles, more than 62 % of particulate phosphorus was in the form of bioavailable phosphorus, including exchangeable phosphorus (Exc-P), extractable organic phosphorus (Exo-P), and iron-bound phosphorus (Fe-P), which meant that the potential impacts of bioavailable phosphorus in suspended particles on estuarine water environment cannot be ignored. There were significantly seasonal variations of phosphorus fractions in the Daliao River Estuary. The concentrations of phosphorus fractions in water in wet season were much lower than that in dry season because of the dilution effect of larger rainfall in wet season. In addition, spatial distribution characteristics of phosphorus fractions were also obvious. Due to terrigenous phosphorus input from the upstream of tidal reach and seawater dilution effect in coastal estuary, total dissolved phosphorus (TDP) concentrations in water gradually decreased from tidal reach to coastal estuary. However, the concentrations of TPP and TP in water and Exo-P in suspended particles presented spatial fluctuation, and these were greatly attributed to sediment re-suspension in coastal estuary.