Human Perturbation of the Global Phosphorus Cycle: Changes and Consequences

Precipitation patterns of nitrogen and phosphorus in reservoirs: A study in typical sand-source area of Inner Mongolia using PMF-HYSPLIT model

Analyzing the sources of nitrogen and phosphorus pollution in atmospheric deposition is crucial for protecting the surface water environment in vulnerable areas. This study focused on the Dahekou Reservoir, Shayuan District, Xilin Gol League, Inner Mongolia, China. It established 12 monitoring sites, conducted one-year monitoring, and collected 144 samples. The concentrations of nitrogen, phosphorus, and water-soluble ions in atmospheric wet sedimentation were measured. This study identified atmospheric precipitation types, revealed seasonal variations in nitrogen and phosphorus concentrations, assessed the contribution of atmospheric wet sedimentation to reservoir water quality. Utilizing the air mass backward trajectory (HYSPLIT) model and PMF model, the main pollution sources were analyzed. The results were as follows. 1) During the observation period, the atmospheric precipitation types were nitric acid rain in spring, sulfuric acid rain in winter, and mixed acid rain in summer and autumn. 2) The monthly concentrations of nitrogen and phosphorus of various forms varied significantly, with NH4+-N peaking in spring, NO3--N and DOP in autumn, and DIP and DON in summer. Annual pollution loads of atmospheric nitrogen and phosphorus precipitation into the reservoir were 35.77 and 4.17 t/a, respectively, severely impacting reservoir water quality. 3) Precipitation was negatively correlated with TN concentration, particularly with the NO3--N/TN ratio, and positively correlated with TP and DIP concentrations. 4) The analysis of pollution sources indicated that the sources of atmospheric nitrogen and phosphorus wet deposition pollution in the study area included agricultural, anthropogenic, dust, and coal sources, with contribution rates of 32.4 %, 25.6 %, 21.0 %, and 21.0 %, respectively.

Local nutrient addition drives plant diversity losses but not biotic homogenization in global grasslands

Nutrient enrichment typically causes local plant diversity declines. A common but untested expectation is that nutrient enrichment also reduces variation in nutrient conditions among localities and selects for a smaller pool of species, causing greater diversity declines at larger than local scales and thus biotic homogenization. Here we apply a framework that links changes in species richness across scales to changes in the numbers of spatially restricted and widespread species for a standardized nutrient addition experiment across 72 grasslands on six continents. Overall, we find proportionally similar species loss at local and larger scales, suggesting similar declines of spatially restricted and widespread species, and no biotic homogenization after 4 years and up to 14 years of treatment. These patterns of diversity changes are generally consistent across species groups. Thus, nutrient enrichment poses threats to plant diversity, including for widespread species that are often critical for ecosystem functions.

Advancements in phosphorus species profiling and bioavailability assessment with implications for phosphorus sustainability

Phosphorus (P) is an essential nutrient that governs ecosystem productivity, drives global biogeochemical cycles, and plays a central role in water-energy-food nexus. The increasing scarcity of P reserves and their environmental losses necessitate precise detection to monitor P in all contexts for effective and sustainable resource management. This review highlights recent advances in analytical techniques for P speciation and bioavailability across environmental matrices, including both bulk and single-cell methods. Furthermore, recent emerging insights into microbial P cycling were discussed, particularly the role of polyphosphate and polyphosphate-accumulating organisms in dynamic P transformations. By emphasizing the sustainability implications of P, we stress the importance of precise and quantitative detection methods to inform sustainable P management and mitigate the global P crisis.

One-Step Esterification of Phosphoric, Phosphonic and Phosphinic Acids with Organosilicates: Phosphorus Chemical Recycling of Sewage Waste

Global concerns regarding the depletion and strategic importance of phosphorus resources have increased demand for the recovery and recycling. However, waste-derived phosphorus compounds, primarily as chemically inert phosphoric acid or its salts, present a challenge to their direct conversion into high-value chemicals. We aimed to develop an innovative technology that utilizes the large quantities of sewage waste, bypasses the use of white phosphorus, and enables esterification of phosphoric acid to produce widely applicable phosphate triesters. Tetraalkyl orthosilicates emerged as highly effective reagents for the direct triple esterification of 85 % phosphoric acid, as well as the esterification of organophosphinic and phosphonic acids. Furthermore, we achieved esterification of recovered phosphoric acid with tetraalkyl orthosilicate, thus pioneering a recycling pathway from sewage waste to valuable phosphorus chemicals. Experimental and theoretical investigations revealed a novel mechanism, wherein tetraalkyl orthosilicates facilitate multimolecular aggregation to achieve alkyl transfer from tetraalkylorthosilicate to phosphoric acid via multiple proton shuttling.

Acclimation of functional traits leads to biomass increases in leafy green species grown in aquaponics

As human population size continues to increase and climate change effects worsen, future food security has become a primary concern for agricultural industries worldwide. Yields of traditional agricultural methods are commonly limited by water and nutrient availability and many crop yields are predicted to decline. Alternative farming practices like aquaponics, which can alleviate these negative yield pressures, may become critical to reaching food production targets. Aquaponics approaches involve the cyclic joint production of fish and hydroponic plants where the fish efflux provides nutrients to plants that then purify the water to be recycled to the fish tanks. In this study, we investigated the acclimation of physiology and functional traits of plants grown in aquaponics versus soil for three leafy green species. We compared gas exchange, stomatal anatomy, water-use efficiency, and foliar chemistry on newly formed leaves across weekly measurements. Increased photosynthetic rate, driven by higher stomatal conductance and increases in tissue nitrogen, led to higher biomass production in aquaponics for all species. Aquaponics plants adjusted stomatal behavior and to a lesser degree stomatal anatomy to become less water-use efficient than plants grown in soil. Collectively, our findings demonstrate the ability of plants to acclimate quickly to aquaponics growing systems that largely remove water and nutrient limitations to plant growth. The increased biomass production of broccoli, pak choi, and salanova by 185%, 116%, and 362% in aquaponics compared to soil-grown plants demonstrates the potential of small-scale aquaponics systems as an efficient and sustainable alternative farming practice.

The role of wetland restoration in mediating phosphorus ecosystem services in agricultural landscapes

Phosphorus (P) is an essential plant nutrient that often limits agricultural productivity. Human activities, especially fertiliser use, have significantly altered the P cycle, causing eutrophication of aquatic systems. Restoring wetlands to agricultural landscapes can retain P, improving water quality and other ecosystem services. The effectiveness of P retention in restored wetlands varies with hydrology, soil properties, vegetation, and other factors. Challenges such as wetland P saturation, legacy P release, and plant invasions can limit P retention capacity. Furthermore, climate-related changes in temperature and hydrology have the potential to undermine long-term P retention. New methods such as Integrated Constructed Wetlands and new technologies that provide high-resolution temporal and spatial data enable managers to optimise multifunctionality in agricultural landscapes.

Drivers analysis and future scenario-based predictions of nutrient loads in key lakes and reservoirs of the Yangtze River Catchment

The excessive nutrient loading in lakes and reservoirs poses significant threats to water quality and ecological health, especially under the influence of global climate change and intensified human activities. This study focuses on the long-term trends in nutrient content and ratios, as well as their driving factors in six major lakes and reservoirs (Chaohu Lake, Danjiangkou Reservoir, Dianchi Lake, Dongtinghu Lake, Poyanghu Lake, and Taihu Lake) within the Yangtze River Catchment from 2002 to 2021. Utilizing Redundancy Analysis, Random Forest and Generalized Additive Model, we identify the shifts in natural and socio-economic factors influencing nutrient concentrations and predict future trends under various scenarios. The main driving factors of nutrient content and their ratios have undergone significant changes at different historical stages, with livestock poultry breeding (LPB) and hydraulic retention time (Res_time) being consistently influential. Our findings highlight the dominant role of livestock and poultry breeding and hydraulic retention time in shaping TN content, whereas TP levels are significantly affected by both natural factors (Temperature and Rainfall) and socio-economic activities. Scenario analyses reveal that despite improvements in water management, nutrient loads remain high, posing ongoing risks of eutrophication. Future lakes nutrient content can meet existing water quality standards under socio-economic development scenarios that significantly reduce hydraulic retention time and the contributions of livestock poultry breeding and other socio-economic drivers.

Unlocking the phosphorus circularity potential of corn belt watersheds with biorefinery phosphorus recovery incentives

As global phosphorus (P) stores rapidly decline, P fed algal blooms continue to threaten critical freshwater resources across the globe. In the Midwestern United States (US), particularly the Corn Belt, biorefineries could play a key role in addressing this issue. By recovering P from the byproducts of ethanol production these facilities could reduce the P content of distillers grain feed, thereby reducing P excreted in manures. This process could potentially divert P away from concentrated animal feeding operations (CAFOs) and toward renewable P (rP) fertilizer production utilizing the recovered P. To foster the inclusion of P recovery incentives in state nutrient reduction strategies, this study elucidates the cascading benefits of rP recovery from corn biorefineries in watersheds across six Upper Midwestern states. Incentivizing P recovery in watersheds that contain both biorefineries and CAFOs could foster the production of 107,500 metric tons (MT) rP fertilizer while diverting 26,800 MT P from CAFO wastes each year, nearly double the estimated P reduction potential for municipal wastewater in the analysis region. These estimates can inform nutrient reduction analysts and policymakers in determining P load reduction potential. To further guide incentive strategies, four priority watersheds are highlighted to illustrate P reduction and circularity typologies across the region.

Transcriptomic Response of White Lupin Roots to Short-Term Sucrose Treatment

White lupin (Lupinus albus) has become a model plant for understanding plant adaptations to phosphorus (P) and iron (Fe) deficiency, two major limiting factors for plant productivity. In response to both nutrient deficiencies, white lupin forms cluster roots, bottle-brush-like root structures that aid in P and Fe acquisition from soil. While the cluster root function is well-studied, not much is known about the signaling pathways involved in sensing and responding to a P and Fe deficiency. Sucrose has been identified as a long-distance signal sent in increased concentrations from shoot to root in response to both a P and Fe deficiency. Thus, sucrose plays a dual role both as a signal and as a major source of energy for the root. To unravel the responses to sucrose as a signal, we performed an Illumina paired-end cDNA sequencing of white lupin roots treated with sucrose for 20, 40 or 80 min, compared to untreated controls (0 min). We identified 634 up-regulated and 956 down-regulated genes in response to sucrose. Twenty minutes of sucrose treatment showed the most responses, with the ethylene-activated signaling pathway as the most enriched Gene Ontology (GO) category. The number of up-regulated genes decreased at 40 min and 80 min, and protein dephosphorylation became the most enriched category. Taken together, our findings indicate active responses to sucrose as a signal at 20 min after a sucrose addition, but fewer responses and a potential resetting of signal transduction pathways by the dephosphorylation of proteins at 40 and 80 min.

Diffuse soil pollution from agriculture: Impacts and remediation

Agricultural activities are essential for sustaining the global population, yet they exert considerable pressure on the environment. A major challenge we face today is agricultural pollution, much of which is diffuse in nature, lacking a clear point of origin for chemical discharge. Modern agricultural practices, which often depend on substantial applications of fertilizers, pesticides, and irrigation water, are key contributors to this form of pollution. These activities lead to downstream contamination through mechanisms such as surface runoff, leaching, soil erosion, wind dispersal, and sedimentation. The environmental and human health consequences of diffuse pollution are profound and cannot be ignored. Accurate assessment of the risks posed by agricultural pollutants is crucial for ensuring the production of safe, high-quality food while safeguarding the environment. This requires systematic monitoring and evaluation of agricultural practices, including soil testing and nutrient management. Furthermore, the development and implementation of best management practices (BMPs) are critical in reducing the levels of agricultural pollution. Such measures are essential for mitigating the negative impacts on ecosystems and public health. Therefore, the adoption of preventive strategies aimed at minimizing pollution and its associated risks is highly recommended to ensure long-term environmental sustainability and human well-being.

The Pb capture mechanism of soil prophylactic agents prepared from phosphorus tailings and the influence of phosphorus speciation on its slow-release mechanism

This research activated phosphorus tailings to prepare a high‑phosphorus core (HPC) for multi-species composite slow-release heavy metal soil prophylactic agents (MCP), aiming to extend the slow-release period of MCP and enhance the efficiency of Pb stabilization. During the preparation of HPC, the proportion of non-apatitic inorganic phosphorus (NAIP) and apatite phosphorus (AP) continuously decreased with increasing polymerization temperature. At 400 °C, polyphosphates (PP) began to form, reaching 74.26 % at 600 °C. Initially, the rapidly soluble NAIP remained the major component of HPC, but the proportion of AP increased with higher polymerization temperatures, reaching 40.8 % at 600 °C. After 120 days of cultivation with four MCPs (MCP 300-21, MCP 400-12, MCP 500-14, MCP 600-14), the total soil phosphorus (TSP), soil organic matter (SOM), and Pb stabilization capacity of the cultivated soil showed significant improvements, reaching maximum values of 2.39 mg/g, 38.16 mg/g, and 45.4 mg/g, respectively, which are 9.9, 4.4, and 5.9 times higher than those of the CK soil. KEGG (Kyoto Encyclopedia of Genes and Genomes) functional prediction analysis indicated that MCPs contribute directly or indirectly to the forms and chemical stability of Pb by stimulating soil physiological and biochemical processes. This research proposes a novel approach for using phosphates in soil heavy metal management strategies and provides new insights into the mechanisms of heavy metal stabilization in soil using environmental functional materials.

Machine learning prediction and exploration of phosphorus migration and transformation during hydrothermal treatment of biomass waste

Hydrothermal treatment (HTT) held promise for phosphorus (P) recovery from high-moisture biomass. However, traditional experimental studies of P hydrothermal conversion were time-consuming and labor-intensive. Thus, based on biomass characteristics and HTT parameters, Random Forest (RF) and Gradient Boosting Regression machine learning (ML) models were constructed to predict HTT P migration between total P in hydrochar (TP_HC) and process water (TP_PW) and hydrochar P transformation among inorganic P (IP_HC), organic P (OP_HC), non-apatite inorganic P (NAIP_HC), and apatite P (AP_HC). Results demonstrated that the RF models (test R2 > 0.86) exhibited excellent performance in both single-target and multi-target predictions. Feature importance analysis identified TP_feed, O, C, and N as critical features influencing P distribution in hydrothermal products. TP_feed, NAIP_feed, temperature, and IP_feed were crucial factors affecting P form transformation in HC. This study provided valuable insights into understanding the migration and transformation of P and further guided experimental research.

Towards planetary boundary sustainability of food processing wastewater, by resource recovery & emission reduction: A process system engineering perspective

Meeting the needs of a growing population calls for a change from linear production systems that exacerbate the depletion of finite natural resources and the emission of environmental pollutants. These linear production systems have resulted in the human-driven perturbation of the Earth's natural biogeochemical cycles and the transgression of environmentally safe operating limits. One solution that can help alleviate the environmental issues associated both with resource stress and harmful emissions is resource recovery from waste. In this review, we address the recovery of resources from food and beverage processing wastewater (FPWW), which offers a synergistic solution to some of the environmental issues with traditional food production. Research on resource recovery from FPWW typically focuses on technologies to recover specific resources without considering integrative process systems to recover multiple resources while simultaneously satisfying regulations on final effluent quality. Process Systems Engineering (PSE) offers methodologies able to address this holistic process design problem, including modelling the trade-offs between competing objectives. Optimisation of FPWW treatment and resource recovery has significant scope to reduce the environmental impacts of food production systems. There is significant potential to recover carbon, nitrogen, and phosphorus resources while respecting effluent quality limits, even when the significant uncertainties inherent to wastewater systems are considered. This review article gives an overview of the environmental challenges we face, discussed within the framework of the planetary boundary, and highlights the impacts caused by the agri-food sector. This paper also presents a comprehensive review of the characteristics of FPWW and available technologies to recover carbon and nutrient resources from wastewater streams with a particular focus on bioprocesses. PSE research and modelling advances are discussed in this review. Based on this discussion, we conclude the article with future research directions.

Increasing phosphorus loss despite widespread concentration decline in US rivers

The loss of phosphorous (P) from the land to aquatic systems has polluted waters and threatened food production worldwide. Systematic trend analysis of P, a nonrenewable resource, has been challenging, primarily due to sparse and inconsistent historical data. Here, we leveraged intensive hydrometeorological data and the recent renaissance of deep learning approaches to fill data gaps and reconstruct temporal trends. We trained a multitask long short-term memory model for total P (TP) using data from 430 rivers across the contiguous United States (CONUS). Trend analysis of reconstructed daily records (1980-2019) shows widespread decline in concentrations, with declining, increasing, and insignificantly changing trends in 60%, 28%, and 12% of the rivers, respectively. Concentrations in urban rivers have declined the most despite rising urban population in the past decades; concentrations in agricultural rivers however have mostly increased, suggesting not-as-effective controls of nonpoint sources in agriculture lands compared to point sources in cities. TP loss, calculated as fluxes by multiplying concentration and discharge, however exhibited an overall increasing rate of 6.5% per decade at the CONUS scale over the past 40 y, largely due to increasing river discharge. Results highlight the challenge of reducing TP loss that is complicated by changing river discharge in a warming climate.

Tracing phosphorus sources in the river-lake system using the oxygen isotope of phosphate

The biogeochemical cycling of phosphorus (P) in river-lake systems presents significant challenges in tracing P sources, highlighting the importance of effective traceability approaches for formulating targeted management measures to mitigate lake eutrophication. In this study, we used the oxygen isotope of phosphate (δ18Op) as a tracer in the river-lake systems, establishing a tracing pathway from potential end-members, through inflow rivers, and eventually to the lake. Taking Dianshan Lake and its main inflow rivers as the study area, we measured δ18Op values of potential end-members, including domestic sewage treatment plant effluents, industrial effluents from phosphorus-related enterprises (printing and dyeing, electroplating, plastics, etc.), and farmland soils. Notably, the industrial effluent signatures ranged from 13.1 ‰ to 21.0 ‰ with an average of 16.8 ‰ ± 3.2 ‰, enriching the δ18Op threshold database. Using the MixSIAR model, it was found that phosphorus in the Jishuigang River primarily originated from agricultural non-point sources and domestic sewage in the dry season, while the Qiandengpu River, with a higher proportion of urban area, had a greater influence from domestic sewage and industrial effluents. Moreover, significant differences were observed between δ18Op values at the lake entrances of the inflow rivers (13.7 ‰ ± 1.0 ‰) and in acid-soluble phosphate of the lake sediments (9.9 ‰ ± 1.0 ‰). Isotopic tracing revealed that phosphorus in the lake originated from both external inputs (80.6 %) and internal release (19.4 %) in the dry season. Alongside pollutant flux calculations based on the hydrological conditions and water quality of the inflow rivers, our findings indicated that phosphorus in Dianshan Lake was mainly attributed to agricultural non-point sources, domestic sewage and sediment release in the dry season. This study provided novel insights into the identification of pollution sources in the river-lake systems, with broad implications for pollution control and environmental protection.

Trapped Urban Phosphorus: An Overlooked and Inaccessible Stock in the Anthropogenic Phosphorus Cycle

Urban landscapes are high phosphorus (P) consumption areas and consequently generate substantial P-containing urban solid waste (domestic kitchen wastes, animal bones, and municipal sludge), due to large population. However, urbanization can also trap P through cultivated land loss and urban solid waste disposal. Trapped urban P is an overlooked and inaccessible P stock. Here, we studied how urbanization contributes to trapped urban P and how it affects the P cycle. We take China as a case study. Our results showed that China generated a total of 13 (±0.9) Tg urban trapped P between 1992-2019. This amounts to 6 (±0.5) % of the total consumed P and 9 (±0.6) % of the chemical fertilizer P used in China over that period. The loss of cultivated land accounted for 15% of the trapped urban P, and half of this was concentrated in three provinces: Shandong, Henan, and Hebei. This is primarily since nearly one-third of the newly expanded urban areas are located within these provinces. The remaining 85% of trapped urban P was associated with urban solid waste disposal. Our findings call for more actions to preserve fertile cultivated land and promote P recovery from urban solid waste through sound waste classification and recycling systems to minimize P trapped in urban areas.

Identifying leverage points using material flow analysis to circularise resources from urban wastewater and organic waste

Anthropogenic systems are synonymous with linear economies that cause widespread resource waste and environmental degradation. Urban areas are hotspots for this behaviour due to their high population density and resource consumption. Changing this situation is limited by the lack of a holistic but sufficiently detailed understanding of system units where resource waste occurs. The objectives of this study were: (1) to develop and apply a model of the material and substance (nitrogen, phosphorus, and carbon) flows of organic waste and wastewater systems at a local scale, taking Christchurch, New Zealand, as a study case, and (2) to identify leverage points within the system to achieve resource circularisation. Results show that groundwater, infiltrated water, and industrial wastewater are the predominant material flows into the system. Nitrogen and phosphorus inputs predominantly come from food products, detergents, green waste, and industrial wastewater. The Christchurch wastewater system is a prime example of a linear economy, where ∼66 % of the nitrogen and ∼63 % of the phosphorus entering the wastewater system is discharged to the ocean. Leakage from the water supply system reduces water resource efficiency, while water infiltration into the wastewater network inflates the quantity of wastewater treated at the centralised treatment plant, limiting nutrient recovery. In the compost facility, 86 % of the waste is composted, with 33% of the nitrogen and all the phosphorus exiting as compost, while ∼66 % of the nitrogen treated exits through volatilisation. The remaining 14 % of the organic waste entering the treatment plant is deemed unsuitable for composting and is landfilled. The material and substance flow analysis allowed the identification of flows with leverage points in the system where there are opportunities to reduce, reuse, or recover materials and substances to encourage circularisation. These flows include food products, detergents, unsuitable materials for composting, domestic water supply leakages, wastewater network infiltration, and wastewater treatment plant's nutrient recovery.

Unraveling spatial heterogeneity of soil legacy phosphorus in subtropical grasslands

Humans have profoundly altered phosphorus (P) cycling across scales. Agriculturally driven changes (e.g., excessive P-fertilization and manure addition), in particular, have resulted in pronounced P accumulations in soils, often known as "soil legacy P." These legacy P reserves serve as persistent and long-term nonpoint sources, inducing downstream eutrophication and ecosystem services degradation. While there is considerable scientific and policy interest in legacy P, its fine-scale spatial heterogeneity, underlying drivers, and scales of variance remain unclear. Here we present an extensive field sampling (150-m interval grid) and analysis of 1438 surface soils (0-15 cm) in 2020 for two typical subtropical grassland types managed for livestock production: Intensively managed (IM) and Semi-natural (SN) pastures. We ask the following questions: (1) What is the spatial variability, and are there hotspots of soil legacy P? (2) Does soil legacy P vary primarily within pastures, among pastures, or between pasture types? (3) How does soil legacy P relate to pasture management intensity, soil and geographic characteristics? and (4) What is the relationship between soil legacy P and aboveground plant tissue P concentration? Our results showed that three measurements of soil legacy P (total P, Mehlich-1, and Mehlich-3 extractable P representing labile P pools) varied substantially across the landscape. Spatial autoregressive models revealed that soil organic matter, pH, available Fe and Al, elevation, and pasture management intensity were crucial predictors for spatial patterns of soil P, although models were more reliable for predicting total P (68.9%) than labile P. Our analysis further demonstrated that total variance in soil legacy P was greater in IM than SN pastures, and intensified pasture management rescaled spatial patterns of soil legacy P. In particular, after controlling for sample size, soil P was extremely variable at small scales, with variance diminished as spatial scale increased. Our results suggest that broad pasture- or farm-level best management practices may be limited and less efficient, especially for more IM pastures. Rather, management to curtail soil legacy P and mitigate P loading and losses should be implemented at fine scales designed to target spatially distinct P hotspots across the landscape.

Climate change impacts on eutrophication in the Po River (Italy): Temperature-mediated reduction in nitrogen export but no effect on phosphorus

Rivers worldwide are under stress from eutrophication and nitrate pollution, but the ecological consequences overlap with climate change, and the resulting interactions may be unexpected and still unexplored. The Po River basin (northern Italy) is one of the most agriculturally productive and densely populated areas in Europe. It remains unclear whether the climate change impacts on the thermal and hydrological regimes are already affecting nutrient dynamics and transport to coastal areas. The present work addresses the long-term trends (1992-2020) of nitrogen and phosphorus export by investigating both the annual magnitude and the seasonal patterns and their relationship with water temperature and discharge trajectories. Despite the constant diffuse and point sources in the basin, a marked decrease (-20%) in nitrogen export, mostly as nitrate, was recorded in the last decade compared to the 1990s, while no significant downward trend was observed for phosphorus. The water temperature of the Po River has warmed, with the most pronounced signals in summer (+0.13°C/year) and autumn (+0.16°C/year), together with the strongest increase in the number of warm days (+70%-80%). An extended seasonal window of warm temperatures and the persistence of low flow periods are likely to create favorable conditions for permanent nitrate removal via denitrification, resulting in a lower delivery of reactive nitrogen to the sea. The present results show that climate change-driven warming may enhance nitrogen processing by increasing respiratory river metabolism, thereby reducing export from spring to early autumn, when the risk of eutrophication in coastal zones is higher.

Atmospheric wet and dry phosphorus deposition in Lake Erhai, China

Lake Erhai is a potentially phosphorus (P)-limited lake and its water quality may have been affected by atmospheric P deposition. However, there have been few studies on atmospheric P deposition in this lake. In this study, we established five wet deposition monitoring sites and two dry deposition monitoring sites around Lake Erhai to quantify the wet and dry deposition of total phosphorus (TP), including dissolved inorganic phosphorus (DIP), dissolved organic phosphorus (DOP) and particulate phosphorus (PP) from July 2022 to June 2023. Wet deposition fluxes of P species were collected by automatic rainfall collection instrument, and dry deposition fluxes were estimated using airborne concentration measurements and inferential models. The results reveal that among the different P components, DOP had the highest contribution (50%) to wet TP deposition (average all sites 12.7 ± 0.7 mg P m2/yr), followed by PP (40%) and DIP (10%). Similarly, DOP (51%) was the major contributor to dry TP deposition (average two sites 2.4 ± 0.9 mg P m2/yr), followed by DIP (35%) and PP (14%). Wet deposition dominated the annual total TP deposition (wet plus dry), accounting for approximately 83%. The key seasons for dry deposition were spring and autumn, which accounted for 64% of the annual total dry TP deposition. In comparison, wet deposition was significantly higher in the summer, accounting for 73% of the annual total wet TP deposition. The results of the potential source contribution function and concentration-weighted trajectories analysis indicate that local source emission and long-range transport from surrounding cities jointly exerted a substantial influence on aerosol P concentrations, particularly in the eastern and northwestern regions of the lake. These findings provide a comprehensive understanding of the different P components in atmospheric deposition, which is beneficial for developing effective strategies to manage the P cycle in Lake Erhai.

Molecular mechanism of a coastal cyanobacterium Synechococcus sp. PCC 7002 adapting to changing phosphate concentrations

Phosphorus concentration on the surface of seawater varies greatly with different environments, especially in coastal. The molecular mechanism by which cyanobacteria adapt to fluctuating phosphorus bioavailability is still unclear. In this study, transcriptomes and gene knockouts were used to investigate the adaptive molecular mechanism of a model coastal cyanobacterium Synechococcus sp. PCC 7002 during periods of phosphorus starvation and phosphorus recovery (adding sufficient phosphorus after phosphorus starvation). The findings indicated that phosphorus deficiency affected the photosynthesis, ribosome synthesis, and bacterial motility pathways, which recommenced after phosphorus was resupplied. Even more, most of the metabolic pathways of cyanobacteria were enhanced after phosphorus recovery compared to the control which was kept in continuous phosphorus replete conditions. Based on transcriptome, 54 genes potentially related to phosphorus-deficiency adaptation were selected and knocked out individually or in combination. It was found that five mutants showed weak growth phenotype under phosphorus deficiency, indicating the importance of the genes (A0076, A0549-50, A1094, A1320, A1895) in the adaptation of phosphorus deficiency. Three mutants were found to grow better than the wild type under phosphorus deficiency, suggesting that the products of these genes (A0079, A0340, A2284-86) might influence the adaptation to phosphorus deficiency. Bioinformatics analysis revealed that cyanobacteria exposed to highly fluctuating phosphorus concentrations have more sophisticated phosphorus acquisition strategies. These results elucidated that Synechococcus sp. PCC 7002 have variable phosphorus response mechanisms to adapt to fluctuating phosphorus concentration, providing a novel perspective of how cyanobacteria may respond to the complex and dynamic environments.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42995-024-00244-y.

Multidirectional Fate Path Model to Connect Phosphorus Emissions with Freshwater Eutrophication Potential

Excessive anthropogenic phosphorus (P) emissions put constant pressure on aquatic ecosystems. This pressure can be quantified as the freshwater eutrophication potential (FEP) by linking P emissions, P fate in environmental compartments, and the potentially disappeared fraction of species due to increase of P concentrations in freshwater. However, previous fate modeling on global and regional scales is mainly based on the eight-direction algorithm without distinguishing pollution sources. The algorithm fails to characterize the fate paths of point-source emissions via subsurface pipelines and wastewater treatment infrastructure, and exhibits suboptimal performance in accounting for multidirectional paths caused by river bifurcations, especially in flat terrains. Here we aim to improve the fate modeling by incorporating various fate paths and addressing multidirectional scenarios. We also update the P estimates by complementing potential untreated point-source emissions (PSu). The improved method is examined in a rapidly urbanizing area in Taihu Lake Basin, China in 2017 at a spatial resolution of 100 m × 100 m. Results show that the contribution of PSu on FEP (62.6%) is greater than that on P emissions (58.5%). The FEP is more spatially widely distributed with the improved fate modeling, facilitating targeted regulatory strategies tailored to local conditions.

Missing phosphorus legacy of the Anthropocene: Quantifying residual phosphorus in the biosphere

A defining feature of the Anthropocene is the distortion of the biosphere phosphorus (P) cycle. A relatively sudden acceleration of input fluxes without a concomitant increase in output fluxes has led to net accumulation of P in the terrestrial-aquatic continuum. Over the past century, P has been mined from geological deposits to produce crop fertilizers. When P inputs are not fully removed with harvest of crop biomass, the remaining P accumulates in soils. This residual P is a uniquely anthropogenic pool of P, and its management is critical for agronomic and environmental sustainability. Managing residual P first requires its quantification-but measuring residual P is challenging. In this review, we synthesize approaches to quantifying residual P, with emphasis on advantages, disadvantages, and complementarity. Common approaches to estimate residual P are mass balances, long-term experiments, soil test P trends and chronosequences, with varying suitability or even limitations to distinct spatiotemporal scales. We demonstrate that individual quantification approaches are (i) constrained, (ii) often complementary, and (iii) may be feasible at only certain time-space scales. While some of these challenges are inherent to the quantification approach, in many cases there are surmountable challenges that can be addressed by unifying existing P pool and flux datasets, standardizing and synchronizing data collection on pools and fluxes, and quantifying uncertainty. Though defined as a magnitude, the distribution and speciation of residual P is relatively less understood but shapes its utilization and environmental impacts. The form of residual P will vary by agroecosystem context due to edaphoclimatic-specific transformation of the accumulated P, which has implications for management (e.g., crop usage) and future policies (e.g., lag times in P loading from non-point sources). Quantifying the uncertainty in measuring residual P holds value beyond scientific understanding, as it supports prioritization of monitoring and management resources and inform policy.

Smoothing the Phosphorus Resource Stress under the Socioeconomic Development in China

Phosphorus (P) is the key in maintaining food security and ecosystem functions. Population growth and economic development have increased the demand for phosphate rocks. China has gradually developed from zero phosphate mining to the world's leading P miner, fertilizer, and agricultural producer since 1949. China released policies, such as designating phosphate rock as a strategic resource, promoting eco-agricultural policies, and encouraging the use of solid wastes produced in mining and the phosphorus chemical industry as construction materials. However, methodological and data gaps remain in the mapping of the long-term effects of policies on P resource efficiency. Here, P resource efficiency can be represented by the potential of the P cycle to concentrate or dilute P as assessed by substance flow analysis (SFA) complemented by statistical entropy analysis (SEA). P-flow quantification over the past 70 years in China revealed that both resource utilization and waste generation peaked around 2015, with 20 and 11 Mt of mined and wasted P, respectively. Additionally, rapidly increasing aquaculture wastewater has exacerbated pollution. The resource efficiency of the Chinese P cycle showed a U-shaped change with an overall improvement of 22.7%, except for a temporary trough in 1975. The driving force behind the efficiency decline was the roaring phosphate fertilizer industry, as confirmed by the sharp increase in P flows for both resource utilization and waste generation from the mid-1960s to 1975. The positive driving forces behind the 30.7% efficiency increase from 1975 to 2018 were the implementation of the resource conservation policy, downstream pollution control, and, especially, the circular agro-food system strategy. However, not all current management practices improve the P resource efficiency. Mixing P industry waste with construction materials and the development of aquaculture to complement offshore fisheries erode P resource efficiency by 2.12% and 9.19%, respectively. With the promotion of a zero-waste society in China, effective P-cycle management is expected.

Nutrient-induced acidification modulates soil biodiversity-function relationships

Nutrient enrichment is a major global change component that often disrupts the relationship between aboveground biodiversity and ecosystem functions by promoting species dominance, altering trophic interactions, and reducing ecosystem stability. Emerging evidence indicates that nutrient enrichment also reduces soil biodiversity and weakens the relationship between belowground biodiversity and ecosystem functions, but the underlying mechanisms remain largely unclear. Here, we explore the effects of nutrient enrichment on soil properties, soil biodiversity, and multiple ecosystem functions through a 13-year field experiment. We show that soil acidification induced by nutrient enrichment, rather than changes in mineral nutrient and carbon (C) availability, is the primary factor negatively affecting the relationship between soil diversity and ecosystem multifunctionality. Nitrogen and phosphorus additions significantly reduce soil pH, diversity of bacteria, fungi and nematodes, as well as an array of ecosystem functions related to C and nutrient cycling. Effects of nutrient enrichment on microbial diversity also have negative consequences at higher trophic levels on the diversity of microbivorous nematodes. These results indicate that nutrient-induced acidification can cascade up its impacts along the soil food webs and influence ecosystem functioning, providing novel insight into the mechanisms through which nutrient enrichment influences soil community and ecosystem properties.

Losses of low-germinating, slow-growing species prevent grassland composition recovery from nutrient amendment

Nutrient enrichment often alters the biomass and species composition of plant communities, but the extent to which these changes are reversible after the cessation of nutrient addition is not well-understood. Our 22-year experiment (15 years for nutrient addition and 7 years for recovery), conducted in an alpine meadow, showed that soil nitrogen concentration and pH recovered rapidly after cessation of nutrient addition. However, this was not accompanied by a full recovery of plant community composition. An incomplete recovery in plant diversity and a directional shift in species composition from grass dominance to forb dominance were observed 7 years after the nutrient addition ended. Strikingy, the historically dominant sedges with low germination rate and slow growth rate and nitrogen-fixing legumes with low germination rate were unable to re-establish after nutrient addition ceased. By contrast, rapid recovery of aboveground biomass was observed after nutrient cessation as the increase in forb biomass only partially compensated for the decline in grass biomass. These results indicate that anthropogenic nutrient input can have long-lasting effects on the structure, but not the soil chemistry and plant biomass, of grassland communities, and that the recovery of soil chemical properties and plant biomass does not necessarily guarantee the restoration of plant community structure. These findings have important implications for the management and recovery of grassland communities, many of which are experiencing alterations in resource input.

Occurrences and implications of pathogenic and antibiotic-resistant bacteria in different stages of drinking water treatment plants and distribution systems

Different stages of drinking water treatment plants (DWTPs) play specific roles in diverse contaminants' removal present in natural water sources. Although the stages are recorded to promote adequate treatment of water, the occurrence of pathogenic bacteria (PB) and antibiotic-resistant bacteria (ARB) in the treated water and the changes in their diversity and abundance as it passed down to the end users through the drinking water distribution systems (DWDSs), is a great concern, especially to human health. This could imply that the different stages and the distribution system provide a good microenvironment for their growth. Hence, it becomes pertinent to constantly monitor and document the diversity of PB and ARB present at each stage of the treatment and distribution system. This review aimed at documenting the occurrence of PB and ARB at different stages of treatment and distribution systems as well as the implication of their occurrence globally. An exhaustive literature search from Web of Science, Science-Direct database, Google Scholar, Academic Research Databases like the National Center for Biotechnology Information, Scopus, and SpringerLink was done. The obtained information showed that the different treatment stages and distribution systems influence the PB and ARB that proliferate. To minimize the human health risks associated with the occurrence of these PB, the present review, suggests the development of advanced technologies that can promote quick monitoring of PB/ARB at each treatment stage and distribution system as well as reduction of the cost of environomics analysis to promote better microbial analysis.

Integrating impacts of climate change on aquatic environments in inter-basin water regulation: Establishing a critical threshold for best management practices

Inter-basin water diversion (IBWD) is a viable strategy to tackle water scarcity and quality degradation due to climate change and increasing water demand in headwaters regions. Nevertheless, the capacity of IBWD to mitigate the impacts of climate change on water quality has rarely been quantified, and the underlying processes are not well understood. Therefore, this study aims to elucidate how the IBWD manipulated total phosphorus (TP) loading dilution and conveying patterns under climate change and determine a critical threshold for the quantity of water entering downstream reservoirs (WIN) for operational scheduling. To resolve this issue, climate-driven hydrologic variability over a 60-year period was derived utilizing the least square fitting approach. Subsequently, six scenarios evaluating the response of in-lake TP concentrations (TPL) to increased temperatures and IBWDs of 50 %, 100 %, and 150 % from the baseline water volume in 2030 and 2050 were studied by employing a calibrated hydrological-water quality model (SWAT-YRWQM). In the next stage, three datasets derived from mathematical statistics based on the observed data, the Vollenweider formula, and modeled projections were integrated to formulate best management practices. The results revealed that elevated air temperatures would lead to reduced annual catchment runoff but increased IBWD. Additionally, our study quantified the IBWD potential for mitigating water quality degradation, indicating the adverse effects of climate change on TPL would be weakened by 4.2-14.4 %. A critical threshold for WIN was also quantified at 617 million m3, maintaining WIN at or near 617 million m3 through optimized operational scheduling of IBWD could effectively restrict external inflow TP loading to lower levels. This study clearly illustrates the intricate interactive effects of climate change and IBWD on aquatic environments. The methodology elucidated in this study for determining the critical threshold of WIN could be applied in water management for analogous watershed-receiving waterbody systems.

Coastal degradation regulates the availability and diffusion kinetics of phosphorus at the sediment-water interface: Mechanisms and environmental implications

Coastal wetlands have experienced considerable loss and degradation globally. However, how coastal degradation regulates sediment phosphorus (P) transformation and its underlying mechanisms remain largely unknown in subtropical coastal ecosystems. This study conducted seasonal field measurements using high-resolution diffusive gradient in thin films (DGT) and dialysis (Peeper) techniques, as well as a DGT-induced fluxes in sediments (DIFS) model, to evaluate the mobilization and diffusion of P along a degradation gradient ranging from pristine wetlands to moderately and severely degraded sites. We observed that sediment P is diminished by coastal degradation, and severely degraded sites exhibit a decline in the concentration of available P, despite the presence of distinct seasonal patterns. High-resolution data based on DGT/Peeper analysis revealed that labile P and soluble reactive P (SRP) concentrations varied from 0.0006 mg L-1 to 0.084 mg L-1 (mean 0.0147 mg L-1) and from 0.0128 mg L-1 to 0.1677 mg L-1 (mean 0.0536 mg L-1), respectively. Coastal degradation had a substantial impact on increasing SRP and labile P concentrations, particularly at severely degraded sites. Although severely degraded wetlands appeared to be P sinks (negative P flux at these sites), we did also observe positive diffusive flux in October, indicating that coastal degradation may accelerate the diffusion and remobilization of sediment P into overlying water. The simulations of the DIFS model provided compelling proof of the high resupply capacity of sediment P at severely degraded sites, as supported by the increased R and k-1 values but decreased Tc values. Taken together, these results suggest coastal degradation reduces the sediment P pool, primarily attributed to the strong remobilization of P from the sediment to porewater and overlying water by enhancing the resupply capability and diffusion kinetics. This acceleration induces nutrient loss which adversely impacts the water quality of the surrounding ecosystem. To reduce the adverse effects of coastal degradation, it is essential to adopt a combination of conservation, restoration, and management efforts designed to mitigate the risk of internal P loading and release, and ultimately maintain a regional nutrient balance.

Global scale identification of catchments phosphorus source shifts with urbanization: A phosphate oxygen isotope and Bayesian mixing model approach

Different scenarios of urban expansion can influence the dynamic characteristics of catchments in terms of phosphorus (P). It is important to identify the changes in P sources that occur during the process of urbanization to develop targeted policies for managing P in catchments. However, there is a knowledge gap in quantifying the variations of potential P sources associated with urbanization. By combining phosphate oxygen isotopes from global catchments with a Bayesian model and the urbanization process, we demonstrate that the characteristics of potential P sources (such as fertilizers, urban wastewater, faeces, and bedrock) change as urban areas expand. Our results indicate that using phosphate oxygen isotopes in conjunction with a Bayesian model provides direct evidence of the proportions of potential P sources. We classify catchment P loadings into three stages based on shifts in potential P sources during urban expansion. During the initial stage of urbanization (urban areas < 1.5 %), urban domestic and industrial wastewater are the main contributors to P loadings in catchments. In the mid-term acceleration stage (1.5 % ≤ urban areas < 3.5 %), efforts to improve wastewater treatment significantly reduce wastewater P input, but the increase in fertilizer P input offsets this reduction in sewage-derived P. In the high-level urbanization stage (urban areas ≥ 3.5 %), the proportions of the four potential P sources tend to stabilize. Remote areas bear the burden of excessive P loadings to meet the growing food demand and improved diets resulting from the increasing urban population. Our findings support the development of strategies for water quality management that better consider the driving forces of urbanization on catchment P loadings.

Attributing Atmospheric Phosphorus in the Himalayas: Biomass Burning vs Mineral Dust

Atmospheric phosphorus is a vital nutrient for ecosystems whose sources and fate are still debated in the fragile Himalayan region, hindering our comprehension of its local ecological impact. This study provides novel insights into atmospheric phosphorus based on the study of total suspended particulate matter at the Qomolangma station. Contrary to the prevailing assumptions, we show that biomass burning (BB), not mineral dust, dominates total dissolved phosphorus (TDP, bioavailable) deposition in this arid region, especially during spring. While total phosphorus is mainly derived from dust (77% annually), TDP is largely affected by the transport of regional biomass-burning plumes from South Asia. During BB pollution episodes, TDP causing springtime TDP fluxes alone accounts for 43% of the annual budget. This suggests that BB outweighs dust in supplying bioavailable phosphorus, a critical nutrient, required to sustain Himalayas' ecological functions. Overall, this first-hand field evidence refines the regional and global phosphorus budget by demonstrating that BB emission, while still unrecognized, is a significant source of P, even in the remote mountains of the Himalayas. It also reveals the heterogeneity of atmospheric phosphorus deposition in that region, which will help predict changes in the impacted ecosystems as the deposition patterns vary.

Managing mineral phosphorus application with soil residual phosphorus reuse in Canada

With limited phosphorus (P) supplies, increasing P demand, and issues with P runoff and pollution, developing an ability to reuse the large amounts of residual P stored in agricultural soils is increasingly important. In this study, we investigated the potential for residual soil P to maintain crop yields while reducing P applications and losses in Canada. Using a P cycling model coupled with a soil P dynamics model, we analyzed soil P dynamics over 110 years across Canada's provinces. We found that using soil residual P may reduce mineral P demand as large as 132 Gg P year-1 (29%) in Canada, with the highest potential for reducing P applications in the Atlantic provinces, Quebec, Ontario, and British Columbia. Using residual soil P would result in a 21% increase in Canada's cropland P use efficiency. We expected that the Atlantic provinces and Quebec would have the greatest runoff P loss reduction with use of residual soil P, with the average P loss rate decreasing from 4.24 and 1.69 kg ha-1 to 3.45 and 1.38 kg ha-1 , respectively. Ontario, Manitoba, and British Columbia would experience relatively lower reductions in P loss through use of residual soil P, with the average runoff P loss rate decreasing from 0.44, 0.36, and 4.33 kg ha-1 to 0.19, 0.26, and 4.14 kg ha-1 , respectively. Our study highlights the importance of considering residual soil P as a valuable resource and its potential for reducing P pollution.

Revealing the hidden burden for lake management: the sediment phosphorus storage pools in Eastern Plain Lake Zone, China

As one of the essential components in ecosystems, lakes play a major role in the global phosphorus (P) cycle. It is helpful for further understanding of the inside lake P geochemical cycle to research P pollution and storage in lakes, which is of positive significance for lake eutrophication restoration. In this study, we investigated the total phosphorus concentrations (TPC) of water and sediments from 37 lakes in the Eastern Plain Lake Zone (EPL) of China, evaluated the P pollution degree of lakes, and estimated P storage in lake sediments with quantitative data of lake area and number. The results indicate that the total phosphorus concentrations of water (TPCW) and total phosphorus concentrations of the surface sediments (0-1 cm, TPCSS) in EPL were high, the mean values were 0.11 mg·L-1 and 869.85 mg·kg-1 respectively, with obvious differences between urban and rural areas, as well as between different river basins. Over half (56.76% and 70.27% respectively) of the lakes reached severe pollution levels in water and surface sediments. There were 16224 lakes (> 0.01 km2) with a total area of 21662.37 km2 in the EPL, and the P storage in the lake sediments (0-30 cm) was about 4.87 ± 2.08 Tg (1 Tg = 1 × 1012 g), accounting for about 2.74% of the basin soil. TPCW and TPCSS of lakes in the EPL were significantly positively correlated, may suggest a close nutrient cycling relationship between the lake water and the sediment. During periods of high winds and waves, the stored P in the top sediments in the EPL may continue to participate in the internal P geochemical cycle and migrate to the overlying water, posing a potential pollution hazard. Therefore, it is crucial to take into account the sediment P pools when formulating effective lake phosphorus management strategies.

Biogeochemical Processes and Microbial Dynamics Governing Phosphorus Retention and Release in Sediments: A Case Study in Lower Great Lakes Headwaters

The ability of headwater bed and suspended sediments to mitigate non-point agricultural phosphorus (P) loads to the lower Great Lakes is recognized, but the specific biogeochemical processes promoting sediment P retention or internal P release remain poorly understood. To elucidate these mechanisms, three headwater segments located within priority watersheds of Southern Ontario, Canada, were sampled through the growing season of 2018-2020. The study employed equilibrium P assays along with novel assessments of legacy watershed nutrients, nitrogen (N) concentrations, sediment redox, and microbial community composition. 20-year data revealed elevated total P (TP) and total Nitrogen (TN) at an inorganic fertilizer and manure fertilizer-impacted site, respectively. Overall, sampled sites acted as P sinks; however, agricultural sediments exhibited significantly lower buffering capacity compared to a reference forested watershed. Collection of fine suspended sediment (<63 µm) through time-integrated sampling showed the suspended load at the inorganic-fertilized site was saturated with P, indicating a greater potential for P release into surface waters compared to bed sediments. Through vertical microsensor profiling and DNA sequencing of the sediment microbial community, site-specific factors associated with a distinct P-source event were identified. These included rapid depletion of dissolved oxygen (DO) across the sediment water interface (SWI), as well as the presence of nitrate-reducing bacterial and ammonia-oxidizing archaeal (AOA) genera. This research provides valuable insights into the dynamics of P in headwaters, shedding light on P retention and release. Understanding these processes is crucial for effective management strategies aimed at mitigating P pollution to the lower Great Lakes.

Characteristics and mechanism of phosphate removal by lanthanum modified bentonite in the presence of dissolved organic matter

Lanthanum modified bentonite (LMB) is a widely used adsorbent for removing inorganic phosphorus from polluted water to prevent eutrophication. However, its efficiency can be affected by various environmental factors, including dissolved organic matter (DOM), which is still unclear. In this study, we systematically explored the influence of model DOMs, including HA, bovine serum albumin (BSA), and sodium alginate (SA), on phosphate adsorption by LMB, as well as to elucidate the underlying adsorption mechanisms. Our results showed that only HA had a significant effect on phosphate adsorption by LMB, causing inhibition. When three DOMs were mixed with phosphate in different proportions and DOM was mainly HA, the performance of phosphate adsorption on LMB became worse, while BSA can slightly offset this impact. The kinetics of HA and phosphate adsorption on LMB followed the pseudo-second-order kinetic model, and isotherms fitted the Langmuir model, with a maximum adsorption capacity of 5.7 mg g-1 for P and 12 mg g-1 for HA. However, when HA and phosphate were mixed based on their Qm, a C/P molar ratio of 5.35, LMB preferentially adsorbed phosphate. HA invasion was also disadvantageous for phosphate removal by LMB, in which P adsorption was less efficient at low-concentrations. However, during co-adsorption the adsorption capacity for HA was higher. With a secondary addition of higher levels of P, both pollutants were adsorbed more effectively. In the natural water experiment, phosphate concentration decreased with increasing shaking time, while the UV254 value showed a downward trend, indicating that LMB also adsorbed HA. Characterization results showed that La and phosphate formed LaPO4 precipitation, forming La-O-P inner-sphere complexes as the main mechanism of phosphate removal by LMB. La and HA formed La-HA complexes, with O-CO bonds from HA competing for lanthanum with phosphate. Despite HA obstructing pores from adsorbent, LMB still maintained a good binding ability with phosphate. It may form La-P-HA ternary complexes during adsorption to keep HA adsorption amount.

Elemental sulfur redox bioconversion for selective recovery of phosphorus from Fe/Al-bound phosphate-rich anaerobically digested sludge: Sulfur oxidation or sulfur reduction?

The biological oxidation of elemental sulfur (S0) to sulfate and the reduction of S0 to sulfide provide a potential route for extracting and reclaiming phosphorus (P) from anaerobically digested sludge (ADS). However, the treatment performance, stability, and cost-effectiveness of the two opposing bioprocesses based on S° for selective P recovery from ADS remain unclear. This study aimed to compare the roles of S0-oxidizing bacteria (S0OB) and S0-reducing bacteria (S0RB) in liberating insoluble P from ADS through single-batch and consecutive multibatch experiments. Changes in P speciation in the sludge during the biological extraction processes were analyzed by using complementary sequential extraction and P X-ray absorption near-edge spectroscopy. Results showed that S0OB treatment extracted more phosphate from the sludge compared with S0RB treatment, but it also released a considerable amount of metal cations (e.g., heavy metals, Mg2+, Al3+, Ca2+) and negatively affected sludge dewaterability due to intense sludge acidification and cell lysis. At pH 1.2, the S0OB treatment released 92.9% of P from the sludge, with the dissolution of HAP, Fe-PO4, Mg3(PO4)2, and P-fehrrihy contributing 26.8%, 22.1%, 12.8%, and 10.5%, respectively. The S0RB treatment released 63.6% of P from the sludge at pH 7.0, with negligible dissolution of metal cations, thereby avoiding costly purification of the extract and alkali neutralization for pH adjustment. This treatment involved the replacement of phosphates bounded with Fe-PO4 (FePO4 and P-fehrrihy) and Al-PO4 (P-Alumina and AlPO4) with biogenic sulfides, with contributions of 72.7%, and 20.9%, respectively. Consecutive bioprocesses for P extraction were achieved by recirculating the treated sludge. Both S0OB and S0RB treatments did not affect the extent of sludge dewatering but considerably weakened the dewatering rate. The S0OB-treated sludge exhibited prolonged filtration time (from 3010 s to 9150 s) and expressing time (from 795 s to 4690 s) during compression dewatering. After removing metal cations using cation exchange resin (CER) and neutralizing using NaOH, a vivianite product Fe3(PO4)2·8H2O (purity: 84%) was harvested from the S0OB-treated extract through precipitation with FeSO4·7H2O. By contrast, a vivianite product Fe3(PO4)2·8H2O (purity: 81%) was directly obtained from the S0RB-treated extract through precipitation with FeSO4·7H2O. Ultimately, 79.8 and 57.9wt% of P were recovered from ADS through S0OB extraction-CER purification-alkali neutralization-vivianite crystallization, and S0RB extraction-vivianite crystallization, respectively. Collectively, biological S0 reduction is more applicable than biological S0 oxidation for selectively reclaiming P from Fe/Al-associated phosphate-rich ADS due to better cost-effectiveness and process simplicity. These findings are of significance for developing sludge management strategies to improve P reclamation with minimal process inputs.

Source partitioning using phosphate oxygen isotopes and multiple models in a large catchment

Excessive phosphorus (P) loadings cause major pollution concerns in large catchments. Quantifying the point and nonpoint P sources of large catchments is essential for catchment P management. Although phosphate oxygen isotopes (δ18O(PO4)) can reveal P sources and P cycling in catchments, quantifying multiple P sources in a whole catchment should be a research focus. Therefore, this study aimed to quantitatively identify the proportions of multiple potential end members in a typical large catchment (the Yangtze River Catchment) by combining the phosphate oxygen isotopes, land use type, mixed end-element model, and a Bayesian model. The δ18O(PO4) values of river water varied spatially from 4.9‰ to18.3‰ in the wet season and 6.0‰ to 20.9‰ in the dry season. Minor seasonal differences but obvious spatial changes in δ18O(PO4) values could illustrate how human activity changed the functioning of the system. The results of isotopic mass balance and the Bayesian model confirmed that controlling agricultural P from fertilizers was the key to achieving P emission reduction goals by reducing P inputs. Additionally, the effective rural domestic sewage treatment, development of composting technology, and resource utilization of phosphogypsum waste could also contribute to catchment P control. P sources in catchment ecosystems can be assessed by coupling an isotope approach and multiple-models.

Isolation of phosphorus-hyperaccumulating microalgae from revolving algal biofilm (RAB) wastewater treatment systems

Excess phosphorus (P) in wastewater effluent poses a serious threat to aquatic ecosystems and can spur harmful algal blooms. Revolving algal biofilm (RAB) systems are an emerging technology to recover P from wastewater before discharge into aquatic ecosystems. In RAB systems, a community of microalgae take up and store wastewater P as polyphosphate as they grow in a partially submerged revolving biofilm, which may then be harvested and dried for use as fertilizer in lieu of mined phosphate rock. In this work, we isolated and characterized a total of 101 microalgae strains from active RAB systems across the US Midwest, including 82 green algae, 9 diatoms, and 10 cyanobacteria. Strains were identified by microscopy and 16S/18S ribosomal DNA sequencing, cryopreserved, and screened for elevated P content (as polyphosphate). Seven isolated strains possessed at least 50% more polyphosphate by cell dry weight than a microalgae consortium from a RAB system, with the top strain accumulating nearly threefold more polyphosphate. These top P-hyperaccumulating strains include the green alga Chlamydomonas pulvinata TCF-48 g and the diatoms Eolimna minima TCF-3d and Craticula molestiformis TCF-8d, possessing 11.4, 12.7, and 14.0% polyphosphate by cell dry weight, respectively. As a preliminary test of strain application for recovering P, Chlamydomonas pulvinata TCF-48 g was reinoculated into a bench-scale RAB system containing Bold basal medium. The strain successfully recolonized the system and recovered twofold more P from the medium than a microalgae consortium from a RAB system treating municipal wastewater. These isolated P-hyperaccumulating microalgae may have broad applications in resource recovery from various waste streams, including improving P removal from wastewater.

Role of phosphite in the environmental phosphorus cycle

In modern geochemistry, phosphorus (P) is considered synonymous with phosphate (Pi) because Pi controls the growth of organisms as a limiting nutrient in many ecosystems. The researchers therefore realised that a complete P cycle is essential. Limited by thermodynamic barriers, P was long believed to be incapable of redox reactions, and the role of the redox cycle of reduced P in the global P cycling system was thus not ascertained. Nevertheless, the phosphite (Phi) form of P is widely present in various environments and participates in the global P redox cycle. Herein, global quantitative evidences of Phi are enumerated and the early origin and modern biotic/abiotic sources of Phi are elaborated. Further, the Phi-based redox pathway for P reduction is analysed and global multienvironmental Phi redox cycle processes are proposed on the basis of this pathway. The possible role of Phi in controlling algae in eutrophic lakes and its ecological benefits to plants are proposed. In this manner, the important role of Phi in the P redox cycle and global P cycle is systematically and comprehensively identified and confirmed. This work will provide scientific guidance for the future production and use of Phi products and arouse attention and interest on clarifying the role of Phi in the environmental phosphorus cycle.

The impact of anthropogenic pollutants on the distribution of a marine top predator within a coastal estuarine system

Due to anthropogenic pressures, estuarine systems are among the most broadly impacted areas for marine top predator species. Given this, it is crucial to study the interaction between the vulnerable marine species that inhabit these regions with environmental and anthropogenic variables. This study aims to determine whether nutrient pollution is related to the presence of bottlenose dolphins in a coastal environment. Using a multi-year dataset and GAMs, we studied the relationship between marine pollutants and the presence of bottlenose dolphins in this highly impacted coastal marine environment. We observed that urban fertilizers were linked to the spatial distribution of bottlenose dolphins. There was a higher presence of bottlenose dolphins in areas with high levels of phosphoric acid. In contrast, at higher concentrations of nitrate, the presence of bottlenose dolphins decreased.

Scenario analysis of phosphorus flow in food production and consumption system in the Mwanza region, Tanzania

Since the mineral, phosphorus (P), has dual properties of being limited resources for use, and being a pollutant for studying sustainable management of anthropogenic P flows in wetlands and soils, currently P receives the highest interests among researchers around the world. This study has successfully mapped P flows for a reference year (2017) and a future year (2030) using different scenarios of food production and consumption system (hereafter 'system') in the Mwanza region (Tanzania). The results showed that the total P input and output for 2017 alone were 9770 t and 7989 t, respectively. However, as high as 1781 tP accumulated in the system and the potentially recyclable P found, is yet to be recovered due to economic reasons and the lack of market. The main anthropogenic P input to the system occurred via imported feed, fertilizer, and crop food, accounting for about 99.72 % of the total input flow. The output was comprised of animal products exported with 3428 tP, and various P-contained wastes which were lost to water bodies with 4561tP. Analysis of the 2030 scenario showed that setting P management objectives from different perspectives such as the total P budget balance, potential recyclable P, and P emission, can help develop differentially preferred management strategies and measures in the Mwanza region. The combination of diet change, precision feeding, and integrated waste management practices presents the best prospects for decreasing P budget and losses, and the amount of P that can be potentially recovered from the system. We propose a package of integrated P management measures for the Mwanza region. Given the similarity of regional socio-economic development background around the Lake Victoria basin, the model can be used to guide the study of anthropogenic P flow analysis in other areas along the shore of Lake Victoria (Africa).

Changes in plant phosphorus demand and supply relationships in response to different grazing intensities affect the soil organic carbon stock of a temperate steppe

Ongoing climate change and long-term overgrazing are the main causes of grassland degradation worldwide. Phosphorus (P) is typically a limiting nutrient in degraded grassland soils, and its dynamics may play a crucial role in the responses of carbon (C) feedback to grazing. Yet how multiple P processes respond to a multi-level of grazing and its impact on soil organic carbon (SOC), which is critical for sustainable grassland development in the face of climate change, remains inadequately understood. Here, we investigated P dynamics at the ecosystem level in a 7-year-long multi-level grazing field experiment and analyzed their relation to SOC stock. The results showed that, due to the greater P demand for compensatory plant growth, grazing by sheep increased the aboveground plants' P supply (by 70 % at most) while decreasing their relative P limitation. The increase in P in aboveground tissue was associated with changes in plant root-shoot P allocation and P resorption, and the mobilization of moderately labile organic P in soil. Affected by the altered P supply under grazing, corresponding changes to root C stock and soil total P were two major factors impacting SOC. Compensatory growth-induced P demand and P supply processes responded differently to grazing intensity, resulting in differential effects on SOC. Unlike the light and heavy grazing levels, which reduced the SOC stock, moderate grazing was capable of maintaining maximal vegetation biomass, total plant biomass P, and SOC stock, mainly by promoting biologically- and geochemically-driven plant-soil P turnover. Our findings have important implications for addressing future soil C losses and mitigating higher atmospheric CO₂ threats, as well as maintaining high productivity in temperate grasslands.

Who does better for in-situ eutrophic remediation in anoxic environment improvement and nutrient removal: MgO2 versus CaO2

The long-term insufficient dissolved oxygen (DO), excessive nitrogen (N) and phosphorus (P) have become the main causes of the troublesome eutrophication. Herein, a 20-day sediment core incubation experiment was conducted to comprehensively evaluate the effects of two metal-based peroxides (MgO₂ and CaO₂) on eutrophic remediation. Results indicated that CaO₂ addition could increase DO and ORP of the overlying water more effectively and improve the anoxic environment of the aquatic ecosystems. However, the addition of MgO₂ had a less impact on pH of the water body. Furthermore, the addition of MgO₂ and CaO₂ removed 90.31% and 93.87% of continuous external P in the overlying water respectively, while the removal of NH₄⁺ was 64.86% and 45.89%, and the removal of TN was 43.08% and 19.16%. The reason why the capacity on NH₄⁺ removal of MgO₂ was higher than that of CaO₂ is mainly that PO₄^3- and NH₄⁺ can be removed as struvite by MgO₂. Compared with MgO₂, mobile P of the sediment in CaO₂ addition group was reduced obviously and converted to more stable P. Notably, the microbial community structure of sediments was optimized by MgO₂ and CaO₂, which showed that the relative abundance of anaerobic bacteria decreased and that of aerobic bacteria increased significantly, especially some functional bacteria involved in the nutrient cycle. Taken together, MgO₂ and CaO₂ have a promising application prospect in the field of in-situ eutrophication management.

Optimized multilateral crop trade patterns can effectively mitigate phosphorus imbalance among the involved countries

Phosphorus imbalance for cropland can greatly influence environmental quality and productivity of agricultural systems. Resolving cropland phosphorus imbalance may be possible with more efficient multilateral crop trade within the involved trading countries; however, the driving mechanisms are unclear. This study calculates phosphorus budgets in China and five central Asian countries and proposes two optimal multilateral crop trade models to mitigate the phosphorus imbalance. Results show that the current trading pattern between China and Central Asia is causing a phosphorus imbalance intensification. Phosphorus surpluses in China and Uzbekistan are 41.7 and 8.9 kg/ha, while Kazakhstan, Kyrgyzstan, Tajikistan, and Turkmenistan exhibit phosphorus deficits with the negative value of -0.7, -1.2, -0.8, and -0.8 kg/ha, respectively. However, under the optimal multilateral crop trade patterns, phosphorus budget of China and Central Asia will become balanced. Phosphorus imbalance intensification for China is reduced to -2525 and -2472 kt under the single- and bilevel-objective-based crop trades. In Kyrgyzstan, it will drop 61.5 % and 50.0 % and change to 321 and 417 kt under the two optimal crop trades. Moreover, changes of phosphorus imbalance mitigations for other central Asian countries range from 11.9 % to 28.2 %. This provides a scientific basis when establishing policies for strengthening optimal multilateral crop trading across the world to promote global phosphorus management.

Uncovering the spatio-temporal dynamics of crop-specific nutrient budgets in China

Nitrogen (N) and phosphorus (P) are two critical nutrients for agroecosystems. In meeting food demands, human use of both nutrients has crossed planetary boundaries for sustainability. Further, there has been a dramatic shift in their relative inputs and outputs, which may generate strong N:P imbalances. Despite enormous efforts on agronomic N and P budgets, the spatio-temporal characteristics of different crop types in using nutrients are unknown as are patterns in the stoichiometric coupling of these nutrients. Thus, we analyzed the annual crop-specific N and P budgets and their stoichiometric relations for producing ten major crops at the provincial level of China during 2004-2018. Results show that, China has generally witnessed excessive N and P input over the past 15 years, with the N balance remaining stable while the P balance increasing by more than 170%, thus resulting in a decline in the N:P mass ratios from 10.9 in 2004 to 3.8 in 2018. Crop-aggregated nutrient use efficiency (NUE) of N has increased by 10% in these years while most crops have shown a decreasing trend of this indicator for P, which reduced NUE of P from 75% to 61% during this period. At the provincial level, the nutrient fluxes of Beijing and Shanghai have obviously declined, while the nutrient fluxes of provinces such as Xinjiang and Inner Mongolia have increased significantly. Although N management has made progress, P management should be further explored in the future due to eutrophication concerns. More importantly, N and P management strategies for sustainable agriculture in China should take account of not only the absolute nutrient use, but also their stoichiometric balance for different crops in different locations.

Long-term cattle manure addition enhances soil-available phosphorus fractions in subtropical open-field rotated vegetable systems

INTRODUCTION

Evaluation of the changes in phosphorus (P) fractions (various P forms) and their availability at different soil layers is critical for enhancing P resource use efficiency, mitigating subsequent environmental pollution, and establishing a suitable manure application strategy. However, changes in P fractions at different soil layers in response to cattle manure (M), as well as a combined cattle manure and chemical fertilizer application (M+F), remain unclear in open-field vegetable systems. If the amount of annual P input remains the same, identifying which treatment would cause a higher phosphate fertilizer use efficiency (PUE) and vegetable yield while simultaneously reducing the P surplus is especially warranted.

METHODS

Based on a long-term manure experiment that started in 2008, we used a modified P fractionation scheme to analyze P fractions at two soil layers for three treatments (M, M+F, and control without fertilizer application) in an open-field cabbage (Brassica oleracea) and lettuce (Lactuca sativa) system, and assessed the PUE and accumulated P surplus.

RESULTS

The concentrations of the soil P fractions were higher in the 0-20-cm soil layer compared to the 20-40-cm layer, except for organic P (Po) and residual-P. M application significantly increased the inorganic P (Pi) (by 8.92%-72.26%) and the Po content (by 5.01%-61.23%) at the two soil layers. Compared with the control and M+F treatments, M significantly increased residual-P, Resin-P, and NaHCO3-Pi at both soil layers (by 31.9%-32.95%, 68.40%-72.60%, and 48.22%-61.04%), whereas NaOH-Pi and HCl-Pi at 0-20 cm were positively correlated with available P. Soil moderately labile-P was the predominant P component in the two soil layers (accounting for 59%-70%). With the same annual P input amount, M+CF created the highest vegetable yield (117.86 t ha-1), and PUE (37.88%) and M created the highest accumulated P surplus (128.80 kg ha^-1yr^-1).

DISCUSSION

Collectively, a combined manure-chemical fertilizer application has great potential to yield a long-term positive outcome both in terms of vegetable productivity and environmental health in open-field vegetable systems. This highlights the methods' benefits as a sustainable practice in subtropical vegetable systems. Specific attention should be given to a P balance to avoid excessive P input if a rational strategy for manure application is to be attained. This is especially the case for stem vegetables that require manure application and decreases the environmental risk of P loss in vegetable systems.

Improvement of fungal extraction of phosphorus from sewage sludge ash by Aspergillus niger using sludge filtrate as nutrient substrate

Fungal extraction is a promising approach for reclaiming phosphorus (P) from sewage sludge ash (SSA). However, this approach faces notable technical and economic challenges, including an unknown P speciation evolution and the addition of expensive chemical organic carbon. In this study, the use of an organic-rich effluent produced in sludge dewatering as nutrient source is proposed to initiate the fungal extraction of SSA-borne P with Aspergillus niger. The changes in P speciation in the ash during fungal treatment was analyzed by combined sequential extraction, solid-state ³¹P nuclear magnetic resonance, and P X-ray absorption near edge spectroscopy. Results showed that after 5 days of fungal treatment using sludge-derived organics, 85 % of P was leached from SSA. Dominantly, this considerable release of P resulted from the dissolution of Ca₃(PO₄)₂, AlPO₄, FePO₄, and Mg₃(PO₄)₂ in the ash, and their individual contribution rates to P released accounted for 28.0 %, 24.3 %, 20.6 %, and 18.8 %, respectively. After removal of metal cations (e.g., Mg²⁺, Al³⁺, Fe³⁺, and heavy metals) by cation exchange resin (CER), a hydroxyapatite (HAP) product with a purity of > 85 % was harvested from the extract by precipitation with CaCl₂. By contrast, without CER purification, a crude product of Ca/Mg-carbonates and phosphates mixture were obtained from this extract. A total of 73.2 wt% of P was ultimately recovered from SSA through integrated fungal extraction, CER purification, and HAP crystallization. These findings provide a mechanistic basis for the development of waste management strategies for improved P reclamation with minimal chemical organics consumption.

Substantial increase in P release following conversion of coastal wetlands to aquaculture ponds from altered kinetic exchange and resupply capacity

The reclamation of wetlands and its subsequent conversion to aquaculture may alter regional nutrient (im)mobilization and cycling, although direct assessments of phosphorus (P) cycling and its budget balance following wetland conversion are currently scarce. Here, parallel field experiments were conducted to investigate and compare the availability and mobilization mechanisms of P from natural coastal wetlands and the adjacent converted aquaculture ponds based on high-resolution diffusive gradient in thin films (DGT) and dialysis (HR-Peeper) techniques and the DGT-induced fluxes in sediments (DIFS) model. The study found that the conversion of wetland to pond strongly reduced the sediment P pool by changing its forms and distribution. High-resolution data showed that concentrations of labile P and soluble reactive P across the sediment-water profiles were markedly enhanced by the converted aquaculture pond, although they exhibited large spatiotemporal heterogeneity. Moreover, the synchronous distribution of labile P, iron (Fe) and sulfur (S) across profiles in coastal wetlands indicated that the dissolution of Fe (III) oxyhydroxide-phosphate complexes coupled with sulfate reduction were the main mechanisms regulating sediment P mobilization in coastal areas. However, the converted aquaculture pond weakened or even reversed this dependence by decoupling the Fe-S-P reactions by changing the sediment structure and nutrient balance. Substantial increases in labile P, Fe and S fluxes in the pond suggested the conversion of wetland to aquaculture facilitated the internal release of P, Fe and S from sediment into water. The high resupply parameter (R) and desorption rate (k_-1) combined with low response time (T_c) in the pond, as fitted by DIFS model, indicated the strong resupply capacity and fast kinetic exchange of sediment P across the sediment-water interface, which is consistent with the high P diffusion fluxes recorded in the pond. It was concluded that converted aquaculture ponds act as an important source of P release in coastal areas, potentially exacerbating water quality degradation and eutrophication. Specific initiatives and actions are therefore urgently needed to alleviate the internal P-loading during aquaculture.

Iron-enhanced sand filters: Multi-year urban runoff (stormwater) quality performance

Untreated urban runoff (stormwater) is a major pathway for contaminants, e.g., nutrients and metals, to receiving waters. Where eutrophication occurs, dissolved phosphorus (DP) treatment is often necessary to protect receiving waters, yet few practical methods exist. Iron-enhanced sand filters (IESFs) have successfully treated DP in laboratory and limited field studies. Yet, multi-year-IESF studies to understand reportedly variable performance are unavailable. Herein, nine IESFs were sampled from 2015 to 2018 (528 samples; 70 rainfall-runoff events). Analysis focused on influent/effluent concentrations and removal efficiencies alongside design and catchment parameters. Overall, IESFs significantly removed most total and dissolved metal analytes. Generally, phosphorus removal efficiencies correlated positively with influent concentrations and IESF:catchment area ratios, demonstrating the importance of proper sizing and siting. For all paired influent-effluent samples, respective median total phosphorus, orthophosphate, and DP removal efficiencies were 33 %, 41 %, and 13 %, and respective median effluent concentrations were 120, 25, and 75 (μg/L); with two malfunctioning sites omitted, these respective concentrations were 92, 11, and 47, which better matched relevant goals and (indirectly applicable) standards. Nonetheless, phosphorus removal efficiency and effluent concentrations varied significantly across IESFs and events. Seasonality appeared influential, yet variable influent concentrations confounded spatiotemporal removal efficiency comparisons. Thus, compared to removal efficiencies, effluent concentrations may be better indicators of receiving water risk/benefit and of equal importance for water quality crediting. Although 122 influent-effluent pairs were analyzed, a greater sample size would allow multivariate hypothesis tests with additional predictors. Overall, in this multi-site-year study, most IESFs performed at (n = 5) or near (n = 2) phosphorus effluent concentration and less-so, removal efficiency benchmarks. This research provides new quantitative knowledge on long-term IESF performance for real-world conditions and goals. Research recommendations include multivariate dimension reduction studies and comprehensive, effective information transfer to improve IESF understanding and performance and address practitioner needs, e.g., for refined design, operation, and assessment guidance.

Development of water quality index as a tool for urban water resources management

Urban stream monitoring programs rarely consider the daily cycle of water quality. Furthermore, water quality indexes (WQIs) often rely on an excessive number of correlated parameters. To the best of our knowledge, no previous study used both the principal component analysis (PCA) and the daily cycle of the water quality of urban streams to create better WQIs. In this context, the present study aimed to develop a novel urban WQI (WQIurban) considering these two factors. Moreover, the main WQI in Brazil for water quality assessment for public supply (WQIcetesb) was used as a starting point (parameters: total solids (TS), temperature, turbidity, biochemical oxygen demand, pH, dissolved oxygen (DO), total nitrogen, total phosphorus, and thermotolerant coliforms (Escherichia coli)). The selected parameters to integrate the WQIurban received weights according to their importance for the conformation of water quality and a quality value was assigned to each parameter as a function of its concentration or measure. The developed WQIurban (parameters: pH, TS, E. coli, and DO) was able to maintain the seasonal and daily patterns of the urban stream water quality compared to the WQIcetesb. Nevertheless, the spatial relationship among the sampling sites was somewhat lacking. Our findings can help environmental managers, policy planners, and local researchers to improve their urban stream monitoring programs, saving money, time, and resources. Moreover, the WQIurban can be helpful during exceptional circumstances in which the water quality of urban streams must be quickly assessed.