Human Perturbation of the Global Phosphorus Cycle: Changes and Consequences

How anthropogenic factors influence the dissolved oxygen in surface water over three decades in eastern China?

The aquatic environment, linked to the sustainable development of human existence and ecological environment, is influenced comprehensively by anthropogenic and natural activities. In light of the continuously low concentration of dissolved oxygen (DO) in surface water in plain river networks and the phenomenon of delay in the improvement of surface water quality, this research aims to introduce a method that may be utilized in identifying the critical driving forces of DO in surface water and their lagging characteristics, which will contribute to the assessment and adjustment of water quality drivers and/or policies. The research analyzes a typical small watershed in a river network region of the Yangtze River Delta plain as the study area, collecting 35-year (1986-2020) data on several water quality parameters, decades of anthropogenic activities, and two natural factors. The time series methods of vector autoregressive model, Granger causality tests, forecast error variance decompositions, and impulse response functions (hereinafter referred to as VAR+), which are rarely applied in related research, were employed in this study and proved helpful for screening out pivotal drivers and capturing the lagging responses of DO level to driving forces at each lagged time. Results show that there exists a fluctuating drop in DO level in surface water from 1986 to 2008 and a steady climb from 2008 to 2020, with the lowest DO level being present in 2008. The impulsive perturbations of phosphate fertilizer consumption (PFC), motor vessel number, and precipitation minimally increase DO concentration, while the impulsive perturbation of gross domestic product (GDP) causes the sharpest drop in DO level. With these perturbations, the driving force of PFC persists for approximately seven years, and the driving forces of water temperature, permanent population, and GDP persist for only five years. Future research could be conducted with spatial hysteresis, selection of lag order and variable quantity within the model, as well as intermediate variables between drivers and DO level for exploring driving pathways and mechanisms.

Coastal wetland conversion to aquaculture pond reduced soil P availability by altering P fractions, phosphatase activity, and associated microbial properties

Reclamation and conversion of wetlands strongly affect nutrient cycling and ecosystem functions, while little attention has been paid to the effects of converting coastal wetland to aquaculture on the cycling and balance of soil phosphorus (P). Herein, we investigated soil P fractions, alkaline phosphatase (ALP) activity, and associated microbial properties following coastal wetland conversion in subtropical China. Soil P availability (especially resin-P) concentration and ALP activity in wetland were significantly higher than those in pond. The conversion of coastal wetlands to aquaculture significantly reduced the abundance and diversity of bacterial phoD genes and altered their community structure. The lower phosphatase activity and associated microbial properties after wetland conversion suggested a weaker capacity of microbes to transform organic P (Po) to inorganic P (Pi), consistent with the low P availability but the high Po:Pi ratio in pond. Structural equation modeling indicated that the conversion of the wetland to the pond decreased ALP activity and P availability by affecting soil variables such as bulk density, pH, the carbon: nitrogen ratio, and/or moisture. It was concluded that wetland conversion to pond reduced soil P availability and phosphatase activity, altered the abundance, diversity and community composition of the phoD gene, and ultimately affected coastal P cycles and balances. Moreover, an extended corollary is that the smaller amounts of variation in soil total P and lower labile P concentrations in pond than in wetland suggest that large amounts of P (introduced in feed and not harvested in shrimp) are "lost" from the system. Thus, aquaculture ponds might serve as a source of P for the surrounding environment. More investigations focusing on the P biogeochemical cycle and its potential impacts on adjacent ocean environments at regional and global scales is urgently needed, which could contribute to better management of coastal land uses.

A review of adsorption techniques for removal of phosphates from wastewater

Phosphate is considered the main cause of eutrophication and has received considerable attention recently. Several methods have been used for removal of phosphates in water and these include biological treatment, membrane filtration processes, chemical precipitation, and adsorption. Adsorption technology is highly effective in the removal of phosphate from wastewater even at low phosphate concentrations. Nanomaterials/nanoparticles, carbon-based materials (activated carbon and biochar), and their composites have been widely employed for the adsorptive removal and recovery of phosphate from wastewater due to their exceptional properties such as high surface area and high phosphate adsorption properties. This article is a review of the recently reported literature in the field of nanotechnology and activated carbon for the adsorption of phosphate from wastewater. Highlights of the adsorption mechanisms, adsorption behaviour, experimental parameters, effects of co-existing ions, and adsorbent modifications are also discussed.

Biochar addition regulates soil phosphorus fractions and improves release of available phosphorus under freezing-thawing cycles

Currently, the shortage of phosphorus resources is becoming more and more serious. In general, phosphorus fertilizer is poorly utilized in soil and tends to gradually accumulate. Freezing-thawing cycles (FT) are seasonal phenomenon occurring in high latitudes and altitudes regions, which have obvious influence on the form of phosphorus in soil. This study investigates the effect of biochar on soil physicochemical properties, phosphorus form and availability under FT and thermostatic incubation (TH) condition. Compared with treatment without biochar, 4 % biochar addition increased the soil pH value, electrical conductivity, organic matter and Olsen-P of soil by a maximum of 0.76, 285.55 μS/cm, 28.60 g/kg and 139.27 mg/kg, respectively. Moreover, according to Hedley-P classification results, under FT condition, the content of labile phosphorus pool is always higher than those under TH. FT may promote the conversion of phosphorus from other fractions to labile phosphorus pool. Redundancy analysis results show that biochar addition and FT can not only directly change the soil phosphorus pool, but also alter the soil physicochemical properties and microbial community, which further affect the adsorption and mineralization of phosphorus in soil. The results of this study will be devoted to understanding the changes in soil phosphorus fractions under the effects of biochar addition and FT, providing references for agricultural production in areas where FT occur.

Removal of nutrients and other emerging inorganic contaminants from water and wastewater by electrocoagulation process

The continual discharge of emerging inorganic pollutants into natural aquatic systems and their negative effects on the environment have motivated the researchers to explore and develop clean and efficient water treatment strategies. Electrocoagulation (EC) is a rapid and promising pollutant removal approach that does not require any chemical additives or complicated process management. Therefore, inorganic pollutant treatment via the EC process is considered one of the most feasible processes. The potential developments of EC process may make the process a wise choice for water treatment in the future. Thus, the present study mainly focuses on the use of EC technology to remove nutrients and other emerging inorganic pollutants from water medium. The operating factors that influence EC process efficiency are explained. The major advancement of the EC technique as well as field-implemented units are also discussed. Overall, this study mainly focuses on emerging issues, present advancements, and techno-economic considerations in EC process.

Removal and recovery of phosphorus from secondary effluent using layered double hydroxide-biochar composites

Removal of phosphorus (P) from wastewater and its recovery as a fertilizer are solutions to both P pollution control and resource recycling for agriculture. In this study, various layered double hydroxide biochar composites (LDH/BCs), namely, Zn-Al-LDH/BC, Mg-Al-LDH/BC, and Mg-Fe-LDH/BC, were synthesized to remove P from secondary effluents and then applied as fertilizers. Batch experiments showed that LDH/BCs could adsorb P in fast kinetics, with adsorption capacities ranging 35.19-55.76 mg P/g. A dynamic experiment was performed under different column heights and flow rates, and the results fitted well with Thomas model (R² > 0.90). These LDH/BCs effectively removed P in the continuous mode, even when treating secondary effluents. Furthermore, when the used LDH/BCs applied as fertilizers, the adsorbed Mg-Al-LDH/BC and Mg-Fe-LDH/BC stimulated crop growth; however, Zn-Al-LDH/BC did not. These differences were attributed to not only the availability of P, but also the stimulation or inhibition of photosynthetic pigment synthesis in crops by adsorbents. Overall, we synthesized LDH/BCs, which effectively removed and recovered P from secondary effluents, and investigated the factors influencing the effects of LDH/BCs on crops. We suggest that both P availability and physiological influences of adsorbents on crops should be considered when using adsorbents as fertilizers.

Ecological footprint analysis of the phosphorus industry in China

Mitigating the effects of environmental deterioration requires a focus on not just CO₂ emissions from energy consumption, but also environmental pollution from industry sectors. To reach this goal, recent studies have extended ecological footprint (EF) analysis to identify the ecological drivers of various key industry sectors. The role of the phosphorus (P) industry on the EF within the environmental Kuznets curve (EKC) framework for China is the emphasis of this study. Autoregressive distributive lag (ARDL) as well as the impulse response function and robustness analysis were used to consider a time from 1985 to 2018. The study verifies the EKC hypothesis for China in both the long and the short run, and indispensable determinants are proposed to be included to assure the model's fitness and robustness when conducting EF analysis of industry sectors. Energy consumption-based carbon emissions have been verified as the dominant contributor to EF, but P use and urbanization have a significant lagged positive influence on EF in the short run. P exports, in particular, have been highlighted as a critical driver of the EF of China's P industry. The conducted frequency domain causality test reinforced the above findings and demonstrated bidirectional causality at different frequencies. This work suggests that formulating plausible P export policies to alleviate the conflict between the output of China's P industry and the environmental sustainability of this industry are necessary. In this context, "multidisciplinary, multidimensional, and practical solutions" are most desirable for sustainable P management.

Arable land and water footprints for food consumption in China: From the perspective of urban and rural dietary change

Since the adoption of the open-door policy, the Chinese dietary pattern has changed greatly. Based on the dietary changes, this study analyzed the arable land and water footprints (WFs) for the food consumption of urban and rural residents in China. The results showed that the arable land demand and WFs for meat, vegetable oil, soybeans and liquor exceeded those for other foods, and the per capita arable land and WFs for food consumption of urban residents were higher than those of rural residents. The total arable land and WFs for the food consumption of residents increased by 16.9 million ha (from 91.1 to 108 million ha) and 214.5 billion m³ (from 457.9 to 672.4 billion m³), respectively, from 1983 to 2017. Specifically, the total arable land and WFs for the food consumption of urban residents increased by 45.9 million hm² (from 22.6 to 68.5 million hm²) and 318.3 billion m³ (from 113.2 to 431.5 billion m³), respectively. Additionally, those of rural residents decreased by 29.7 million hm² (from 69.2 to 39.5 million hm²) and 103.9 billion m³ (344.8 to 240.9 billion m³), respectively, mainly due to the migration of the rural population to cities and the reductions in per capita arable land and WFs due to increased crop yields. The arable land and blue WFs required for food consumption will reach 127.7 million hm² and 221.1 billion m³, respectively, in 2030. However, these values will be reduced by approximately 23% and 20%, respectively, to 98.9 million hm² and 177.8 billion m³ under a balanced dietary pattern. Measures such as improving the investment in agricultural research and development, advocating a balanced diet, and increasing the import of resource-intensive foods could alleviate the pressure on land and water resources.

The Effect of Rainfall on Aquatic Nitrogen and Phosphorus in a Semi-Humid Area Catchment, Northern China

The impact of rainfall on water quality may be more important in semi-arid regions, where rainfall is concentrated over a couple of months. To explore the impact of rainfall changes on water quality, e.g., nitrogen (TN) and phosphorous (TP), the diversion from Luan River to Tianjin Watershed in the northern semi-humid area was selected as the study area. TN and TP concentrations in rivers and the Yuqiao Reservoir during the three-year high-flow season (2019-2021) were analyzed. The response relationship and influencing factors among the watershed's biogeochemical process, rainfall, and water quality were clarified. The results showed that rainfall in the high flow season mainly controlled the river flow. The concentration of TN and TP in the inflow rivers is regulated by rainfall/flow, while the concentration of TN and TP in the water diversion river has different variation characteristics in the water diversion period and other periods. The lowest annual concentrations of TN and TP were observed in the normal year, while the highest annual concentration was observed in the wet year, indicating that the hydrological process drove the nutrient transport in the watershed. For the tributaries, the Li River catchment contributed a large amount of N and P to the aquatic environment. For the reservoir, the extreme TN concentrations were the same as the tributaries, while the extremes of TP concentrations decreased from the dry year to wet year, which was in contrast to the tributaries. The spatial variation of TN and TP concentrations in the reservoir showed that the concentration decreased following the flow direction from the river estuary to the reservoir outlet. Considering climate change, with the increase of rainfall in North China in the future, the TN and TP transport fluxes in the watershed may continue to increase, leading to the nitrogen and phosphorus load of the downstream reservoir. To ensure the impact of the increase of potential N and P output fluxes in the watershed on the water quality of the reservoir area, it is necessary to strengthen the effective prevention and control of non-point source pollution in the watershed.

The sixth R: Revitalizing the natural phosphorus pump

Phosphorus (P) is essential for all life on Earth and sustains food production. Yet, the easily accessible deposits of phosphate-rich rock, which underpin the green revolution are becoming rarer. Here we propose a mechanism to help alleviate the problem of "peak phosphorus". In the past, wild animals played a large role in returning P from ocean depths back to the continental interiors. In doing so, they collectively retained and redistributed P within the biosphere, supporting a more fertile planet. However, species extinctions and population reductions have reduced animal-mediated P transport >90% over the past 12,000 years. Recently a 5R strategy was developed to Realign P inputs, Reduce P losses, Recycle P in bio-resources, Recover P in wastes, and Redefine P in food systems. Here, we suggest a sixth R, to Revitalize the Natural Phosphorus Pump (RNPP). Countries are starting to mandate P recycling and we propose a P-trading scheme based on REDD+, where a country could partially achieve its recycling goals by restoring past animal-mediated P pathways. Accrued money from this scheme could be used to restore or conserve wild animal populations, while increasing natural P recycling.

Cognizing and characterizing the organic phosphorus in lake sediments: Advances and challenges

Organic phosphorus (OP) is one of the main forms of phosphorus in lake ecosystems. Mounting evidence has shown that sediment OP has become a major but underestimated issue in addressing lake eutrophication and algal bloom. However, a holistic view of sediment OP remains missing. This review aims to provide an overview of progress on the studies of OP in lake sediments, focusing on the contribution of OP to internal P loading, its potential role in algal bloom, and the migration and transformation. In addition, this work systematically summarized current methods for characterizing OP content, chemical fraction, composition, bioavailability, and assessment of OP release in sediment, with the pros and cons of each method being discussed. In the end, this work pointed out following efforts needed to deepen the understanding of sediment OP, namely: (1) In-depth literature review from a global perspective regarding the contribution of sediment OP to internal P loading with further summary about its pattern of distribution, accumulation and historical changes; (2) better mathematical models for describing drivers and the linkages between the biological pump of algal bloom and the replenishment of sediment OP; (3) fully accounting the composition and molecular size of OP for better understanding its transformation process and mechanism; ; (4) developing direct, high-sensitivity and combined techniques to improve the precision for identifying OP in sediments; (5) establishing the response of OP molecular properties and chemical reactivity to OP biodegradability and designing a comprehensive and accurate composite index to deepen the understanding for the bioavailability of OP; and (6) integrating fundamental processes of OP in current models to better describe the release and exchange of P in sediment-water interface (SWI). This work is expected to provide critical information about OP properties and deliver perspectives of novel characterization methods.

International trade reduces global phosphorus demand but intensifies the imbalance in local consumption

International trade has led to increasing levels of economic development; however, its role in altering the global phosphorus (P) demand and local P footprint (PF) is unclear. Here, through a multi-regional input-output (MRIO) analysis, we quantified the PF associated with the global consumption of agricultural products for 159 countries and 169 crops over the period of 1995-2015. The results suggested that the international network of P flows was highly connected and the flow distribution was overridingly driven by developed economies (e.g., USA and Germany) and large emerging economies (e.g., China and India). A decoupling between the PF and economic growth was observed in most countries. The high PF per capita in developed economies was mainly driven by imports from developing countries rather than domestic P applications. Our results also highlighted that international trade had two impacts on global P management. Firstly, it reduced the total global P demand from agricultural production by 16%; secondly, it intensified the imbalance of local P consumption. Therefore, the future sustainable management of P requires consideration of the original suppliers and final consumers along the global supply chains and the associated consequences on P management from both local and global perspectives.

Tracing phosphorus cycle in global watershed using phosphate oxygen isotopes

The Phosphorus (P) cycle is a crucial biochemical process in the earth system. However, an extensive increase of P input into watersheds destroyed the ecosystem. To explore the effects of internal P loading and external P input in global watersheds, we reviewed the research progress and synthesized the isotope data of experimental results from literatures. An integrated result of the observational and experimental studies revealed that both internal P and external P largely contribute to watershed P loadings in watersheds. Internal P can be released to the overlying water during sediment resuspension process and change of redox conditions near the sediment-water interface. Growing fertilizer application on farmlands to meet food demand with population rise and diet improvement contributed to an huge increase of external P input to watersheds. Therefore, water quality cannot be improved by only reducing internal P or external P loadings. In addition, we found that phosphate oxygen isotope technology is an effectively way to trace the P biogeochemical cycle in watersheds. To better predict the dynamic of P in watersheds, future research integrating oxygen isotope fractionation mechanisms and phosphate oxygen isotope technology would be more effective.

Grazing by wild red deer can mitigate nutrient enrichment in protected semi-natural open habitats

Eutrophication through atmospheric nutrient deposition is threatening the biodiversity of semi-natural habitats characterized by low nutrient availability. Accordingly, local management measures aiming at open habitat conservation need to maintain habitat-specific nutrient conditions despite atmospheric inputs. Grazing by wild herbivores, such as red deer (Cervus elaphus), has been proposed as an alternative to mechanical or livestock-based measures for preserving open habitats. The role of red deer for nutrient dynamics in protected open habitat types, however, is yet unclear. Therefore, we collected data on vegetation productivity, forage removal, quantity of red deer dung and nutrient concentrations in vegetation and dung from permanent plots in heathlands and grasslands (eight plots à 225 m² per habitat type) on a military training area inhabited by a large population of free-ranging red deer over one year. The annual nutrient export of nitrogen (N) and phosphorus (P) by red deer grazing was higher than the nutrient import through red deer excreta, resulting in an average net nutrient removal of 14 and 30 kg N ha⁻¹ a⁻¹ and 1.1 and 3.3 kg P ha⁻¹ a⁻¹ in heathlands and grasslands, respectively. Even when considering approximate local atmospheric deposition values, net nutrient depletion due to red deer grazing seemed very likely, notably in grasslands. Demonstrating that grazing by wild red deer can mitigate the effects of atmospheric nutrient deposition in semi-natural open habitats similarly to extensive livestock grazing, our results support the idea that red deer are suitable grazing animals for open habitat conservation.

Towards Balanced Fertilizer Management in South China: Enhancing Wax Gourd (Benincasa hispida) Yield and Produce Quality

Balanced fertilizer management promotes plant growth, enhances produce quality, minimizes inputs, and reduces negative environmental impacts. Wax gourd (Benincasa hispida) is an important vegetable crop species in China and in South Asia. Two crop nutrition options, NPK and the natural mineral polyhalite, were tested, separately and combined, with the aim of enhancing wax gourd yield and quality and simultaneously to increase nutrient use efficiency and reducing inputs. The experiments tested the optimization of NPK by reducing the proportion of phosphorus (P), and the effect of enriching the soil with essential macronutrients by the use of the supplementary mineral fertilizer polyhalite containing magnesium (Mg), calcium (Ca) and sulfur (S). Two experiments were carried out in Foshan County, Guangdong, China, in 2018 and 2019. Experiments included four treatments: (1) Conventional NPK (15:15:15); (2) Optimized NPK (16:8:18); (3) Conventional NPK + polyhalite; (4) Optimized NPK + polyhalite. Fertilizers were applied prior to planting. While optimized NPK alone had no effects on fruit yield and quality, supplementary polyhalite resulted in a 10–17% increase in yield and significantly improved produce quality due to increased nutrient uptake from polyhalite, resulting in better foliar biomass. We conclude that the combined crop nutrition options improved yield and quality, enhanced nutrient use efficiency, and reduced risks of nutrient pollution. Inclusion of polyhalite in balanced fertilization practices as a supplementary source of secondary macronutrients seems promising. Nevertheless, plenty of space remains open for further adjustments of NPK application management, focusing on reduced rates, optimized ratio, and accurate timing of application for each nutrient.

Effect of salinity on the determination of dissolved non-reactive phosphorus and total dissolved phosphorus in coastal waters

The salinity may affect the phosphorus (P) determination accuracy in coastal waters, especially for the dissolved non-reactive P (DNRP) and total dissolved P (TDP). In this work, the competition mechanism between NaCl and DNRP for oxidants (K₂ S₂ O₈ , the most commonly used and recognized oxidant) was identified in different DNRP determinations. Furthermore, salinity influences on determinations of tetrasodium pyrophosphate decahydrate, glyphosate, phytic acid sodium salt hydrate, adenosine-5'-nomophosphate disodium, and TDP were investigated. The results indicated that approximately 10% IHP6 and AMP would be transferred to dissolved reactive P (DRP) during digestion without K₂ S₂ O₈ . When NaCl increased from 0% to 3.5% with fresh water method, the determination of Gly + K₂ HPO₄ and IHP6 + K₂ HPO₄ decreased by 8.0% ± 0.00% and 24% ± 0.01%, respectively. In addition, the determinations of DNRPs and TDP with different salinities in natural coastal waters by fresh water method and seawater method were performed. It showed that when the salinity >5.0 PSU, the DNRPs and TDP determination results presented deviations. At a salinity of 35.0 PSU, the TDP (KH₂ PO₄  + Gly + IHP6 + AMP) reduction measured by two methods was more than 12.3% ± 0.46%. Furthermore, oxidants with higher digestion efficiency than K₂ S₂ O₈ should be developed. PRACTITIONER POINTS: ~10% IHP6 and AMP could be transferred to DRP during digestion without K₂ S₂ O₈ addition. Salinity affects the DNRPs determination results mainly due to competition for oxidants and complexation with metal ions. More than 12.3% TDP in coastal waters could not be measured when the salinity was 35.0 PSU.

Conditioning of Feed Material Prior to Feeding: Approaches for a Sustainable Phosphorus Utilization

A circular phosphorus (P) bioeconomy is not only worthwhile for conserving limited mineral P reservoirs, but also for minimizing negative environmental impacts caused by human-made alterations. Although P is an essential nutrient, most of the P in concentrates based on cereals, legumes and oilseed byproducts is organically bound to phytate. The latter cannot be efficiently utilized by monogastric animals and is therefore diluted into the environment through the manure pathway. This review examines various strategies for improved P utilization in animals and reflects the respective limitations. The strategies considered include feeding of debranned feedstuffs, pre-germinated feed, co-feeding of phytase and feeding material with high native phytase activity. All these approaches contribute to an improved P bioavailability. However, about half of the organic P content continues to be excreted and therefore remains unused by the animals. Nevertheless, technologies for an efficient utilization of P from cereal-based feed already exist; however, these are not industrially established. Conditioning feed material prior to feeding fosters P-reduced feed; meanwhile, P bound to phytate can be recovered. Based on known techniques for P separation and solubilisation from cereal products and phytate conversion, potential designs for feed material conditioning processes are proposed and evaluated.

Using knowledge-based management for sustainable phosphorus use in China

Sustainable phosphorus (P) management presents challenges in crop production and environmental protection; the current understanding of chemical P-fertilizer manufacturing, rock phosphate (RP) mining, P loss within supply chains, and strategies to mitigate loss is incomplete because of a fragmented understanding of P in the crop production supply chain. Therefore, we develop a knowledge-based management theoretical framework to analyze P supply chains to explore ways to mitigate China's P crisis. This framework connects upstream P industries and crop production, addressing knowledge gaps and stakeholder involvement. We demonstrate the potential to improve P use efficiency in the supply chain, thereby mitigating the P crisis using optimized P management. Our results showed that P footprint and grain production demand for RP can be reduced without yield penalty using a crop-demand-oriented P supply chain management that integrates P use in crop production, P-fertilizer manufacturing, and RP mining. Food security and P-related environment sustainability can be achieved by sharing responsibility and knowledge among stakeholders.

Impact of river dams on phosphorus migration: a case of the Pubugou Reservoir on the Dadu River in China

Reservoirs in agricultural catchments retain large proportions of inflowing phosphorus (P). However, the effects of reservoirs on the P cycle and related biogeochemical processes remain unclear. Therefore, this study investigated the degree to which a typical river-transition-reservoir in Southwest China retains both inflowing particulate phosphorus (PP) and dissolved total phosphorus (DTP) and various forms of P in sediments over different water seasons [normal-water season (NWS), low-water season (LWS), and high-water season (HWS)]. The proportions of inflowing PP and DTP retained were 37% and 27%, respectively. This result could be attributed to the absorption of DTP by the large load of intercepted sediment in the dam and the interception of PP itself. The rank of water seasons in terms of the proportion and load of inflowing TP retained was LWS (79%, 336 t P yr^-1) > NWS (21%, 43 t P yr^-1) > HWS (4%, 27 t P yr^-1), which might be due to the high P concentration 0.78 mg L^-1 and long hydraulic retention time (HRT) 780 d during the LWS. In the long-term, there was a high rate of retention of bioavailable phosphorus (BAP) in sediments (63%). This result could be attributed to the combined effect of fine sediment particles and organic matter (OM). In addition, HRT (R² = 0.89, p < 0.05) affected the retention of P more significantly than P concentration (R² = 0.56, p < 0.05). Dam interception during the LWS resulted in high BAP contents (280 mg kg^-1) in sediments, high P concentrations (0.78 mg L^-1), and weak hydrodynamics (HRT: 780 d) in overlying water. Therefore, further regulatory measures are urgently demanded during the LWS to prevent reservoir algal blooms.

The wheat secreted root proteome: Implications for phosphorus mobilisation and biotic interactions

Root secreted acid phosphatases and organic anions are widely perceived as major players of plant phosphorus (P) mobilisation from the rhizosphere under P limiting growth conditions. Previous research indicated that other mechanisms play a role, especially in species with fine roots, such as wheat. In this study we characterised the plant-derived extracellular proteome of wheat roots by profiling root tip mucilage, soluble root secreted and root tip proteomes. Extracellular acid phosphatases and enzymes of the central carbon metabolism were targeted using selected reaction monitoring. More than 140 proteins with extracellular localisation prediction were identified in mucilage. P starvation induced proteins predicted to be localised to the apoplast which are related to cell wall modification and defence in both, root tip and soluble root-secreted proteomes. Glycolytic enzymes were strongly increased in abundance by P limitation in root tips, as were PEPC and plastidial MDH. Soluble acid phosphatases were not identified in extracellular protein samples. Our results indicate that root tip mucilage contains proteins with the functional potential to actively shape their immediate environment by modification of plant structural components and biotic interactions. Wheat acid phosphatases appear to play a minor role in P mobilisation beyond the immediate root surface. SIGNIFICANCE: Phosphorus (P) is a plant growth limiting nutrient in many agricultural situations and the development of phosphorus efficient crops is of paramount importance for future agricultural management practices. As P is relatively immobile in soils, processes occurring at the root-soil interface, the rhizosphere, are suspected to play a key role in plant-induced P mobilisation. According to the current view, the secretion of extracellular acid phosphatases and organic anions enhances P mobilisation within several millimetres beyond the root surface, either directly or indirectly through the selection and appropriate soil microbes. However, the mechanisms of P mobilisation in species with fine roots, such as wheat, and the role of other secreted root proteins are poorly understood. Here, we carried out the profiling of wheat root tip mucilage, soluble root secreted and root tip proteomes. We analysed proteome changes in response to P starvation. We found that proteins with a predicted localisation to the apoplast made up a major proportion of stress-responsive proteins. Acid phosphatases were not identified within extracellular protein samples, which were enriched in proteins with predicted extracellular localisation. The absence of extracellular APases was further validated by multiple reaction monitoring. Our data indicates that wheat acid phosphatases play a minor role in P mobilisation beyond the immediate root surface and provides a resource for breeding strategies and further investigations of the functional roles of root tip-released proteins in the rhizosphere under P limitation.

Bulk phosphorous deposition at four typical land use sites in Southwest China

Whilst ongoing increases in the deposition of atmospheric nitrogen (N) in China have attracted a lot of attention, to date there has been little research on phosphorus (P) deposition. In this study, we quantified inorganic P (PO₄^3-), dissolved organic P (DOP) and total P (TP) in bulk deposition at four sites in the Sichuan Basin, Southwest China. Chengdu (CD), Shifang (SF), Yanting (YT), and Gongga (GG). They represent the land use categories urban, suburban, agricultural and forest, respectively, during 2008-2018 at CD and YT, 2015-2018 at SF, and 2007-2014 at GG. Annual average TP concentrations (deposition rates) were 0.07 (0.61), 0.49 (3.22), 0.17 (1.07) and 0.01 (0.20) mg L^-1 (kg ha^-1 yr^-1), at CD, SF, YT and GG, respectively. The TP concentrations at YT and GG showed significant increasing trends over the years, with very little change at CD and a decline at SF because of the implementation of environmental control measures. Average PO₄^3- to DOP ratios were 0.65, 0.95, 0.82 and 0.81 at CD, SF, YT and GG, respectively, indicating that DOP accounts for a higher proportion at the urban site, and dominated by combustion sources. Bulk P deposition showed higher deposition rates in summer and lower in winter. These results highlight the importance of long term monitoring in detecting spatial and temporal changing trends of the chemical composition, so as to implement effective policies to eliminate air pollution, especially for Southwest China, where there is limited research on atmospheric P deposition.

Excessive phosphorus inputs dominate soil legacy phosphorus accumulation and its potential loss under intensive greenhouse vegetable production system

Phosphorus (P) is an essential element for crop growth and it plays a critical role in agricultural production. Excessive P applications has become a serious concern in Chinese greenhouse vegetable production (GVP) systems. Nevertheless, P accumulation (legacy P) in GVP profile soils and its potential loss remain poorly documented. Hence, this study aimed to response this issue via paired collection of 136 soil samples (0-30, 30-60 and 60-90 cm depth) and 41 vegetable samples from both plastic greenhouses (PG) and solar greenhouses (SG) in Shouguang, Shandong province. Results showed that the annual input of P ranged from 772 to 2458 kg ha^-1 for different vegetables through the whole growing season versus little vegetable P uptake (ranging from 47.8 to 155 kg ha^-1). Results also revealed significant P accumulation in both SG and PG profile soils. Compared to arable soils (background soils), legacy P to the depth of 90 cm in PG and SG soils were 3.28 and 11.16 Mg P ha^-1, respectively. The content of total P in PG and SG soils significantly increased with cultivation duration. The maximum environmental capacity of P in SG soils was 187 Mg ha^-1, and the maximum number of years for safe planting was 38 yrs. After four years of cultivation, P loss would occur in these soils and the loss rate of P increased with cultivation duration. Opposite to PG soils, a potentially higher risk of P losses took place in SG soils. Our results also demonstrated that excessive P inputs driven by intensive agricultural practices dominated legacy P accumulation within the profile soils and its losses in GVP systems. Site-specific P managements, including improving P use efficiency, reducing further P surplus and reusing legacy P in soils, are urgently needed to minimize P loss. At the same time, the potential loss of subsoil P could not be neglected.

Electrochemically mediated precipitation of phosphate minerals for phosphorus removal and recovery: Progress and perspective

Phosphorus (P) is an essential element for the growth and reproduction of organisms. Unfortunately, the natural P cycle has been broken by the overexploitation of P ores and the associated discharge of P into water bodies, which may trigger the eutrophication of water bodies in the short term and possible P shortage soon. Consequently, technologies emerged to recover P from wastewater to mitigate pollution and exploit secondary P resources. Electrochemically induced phosphate precipitation has the merit of achieving P recovery without dosing additional chemicals via creating a localized high pH environment near the cathode. We critically reviewed the development of electrochemically induced precipitation systems toward P removal and recovery over the past ten years. We summarized and discussed the effects of pH, current density, electrode configuration, and water matrix on the performance of electrochemical systems. Next to ortho P, we identified the potential and illustrated the mechanism of electrochemical P removal and recovery from non-ortho P compounds by combined anodic or anode-mediated oxidation and cathodic reduction (precipitation). Furthermore, we assessed the economic feasibility of electrochemical methods and concluded that they are more suitable for treating acidic P-rich waste streams. Despite promising potentials and significant progress in recent years, the application of electrochemical systems toward P recovery at a larger scale requires further research and development. Future work should focus on evaluating the system's performance under long-term operation, developing an automatic process for harvesting P deposits, and performing a detailed economic and life-cycle assessment.

Current and future threats to human health in the Anthropocene

It has been widely recognised that the threats to human health from global environmental changes (GECs) are increasing in the Anthropocene epoch, and urgent actions are required to tackle these pressing challenges. A scoping review was conducted to provide an overview of the nine planetary boundaries and the threats to population health posed by human activities that are exceeding these boundaries in the Anthropocene. The research progress and key knowledge gaps were identified in this emerging field. Over the past three decades, there has been a great deal of research progress on health risks from climate change, land-use change and urbanisation, biodiversity loss and other GECs. However, several significant challenges remain, including the misperception of the relationship between human and nature; assessment of the compounding risks of GECs; strategies to reduce and prevent the potential health impacts of GECs; and uncertainties in fulfilling the commitments to the Paris Agreement. Confronting these challenges will require rigorous scientific research that is well-coordinated across different disciplines and various sectors. It is imperative for the international community to work together to develop informed policies to avert crises and ensure a safe and sustainable planet for the present and future generations.

Improved utilization of active sites for phosphorus adsorption in FeOOH/anion exchanger nanocomposites via a glycol-solvothermal synthesis strategy

Metal oxide/hydroxide-based nanocomposite adsorbents with porous supporting matrices have been recognized as efficient adsorbents for phosphorus recovery. Aiming at satisfying increasingly restrictive environmental requirements involving improving metal site utilization and lowering metal leakage risk, a glycol-solvothermal confined-space synthesis strategy was proposed for the fabrication of FeOOH/anion exchanger nanocomposites (Fe/900s) with enhanced metal site utilization and reduced metal leakage risk. Compared to composites prepared using alkaline precipitation methods, Fe/900s performed comparably, with a high adsorption capacity of 19.05 mg-P/g with an initial concentration of 10 mg-P/L, a high adsorption selectivity of 8.2 mg-P/g in the presence of 500 mg-SO₄^2-/L, and high long-term resilience (with a capacity loss of ~14% after five cycles), along with substantially lower Fe loading amount (4.11 wt.%) and Fe leakage percentage. Mechanistic investigation demonstrated that contribution of the specific FeOOH sites to phosphate adsorption increased substantially (up to 50.97% under the optimal conditions), in which Fe(III)-OH was the dominant efficient species. The side effects of an excessively long reaction time, which included quaternary ammonium decomposition, FeOOH aggregation, and Fe(III) reduction, were discussed as guidance for optimizing the synthesis strategy. The glycol-solvothermal strategy provides a facile solution to environmental problems through nanocrystal growth engineering in a confined space.

Excessive application of chemical fertilizer and organophosphorus pesticides induced total phosphorus loss from planting causing surface water eutrophication

Total phosphorus (TP) loss from planting was one of the resources causing agricultural non-point source pollution. It is significant to clarify the factors influencing TP loss, as well as explore the relationship between TP loss from planting and surface water eutrophication for making recommendations on the reduction of environmental pollution. In this study, the minimum and maximum of average TP loss was appeared in Qinghai and Shandong province with the TP loss of 7.7 × 10² t and 7.5 × 10³ t from 2012 to 2014, respectively. The results of structural equation model (SEM) indicating that the effect of anthropogenic drivers on TP loss was more important than natural conditions due to the higher path coefficient of anthropogenic drivers (0.814) than that of natural conditions (0.130). For anthropogenic drivers, the path coefficients of usage of fertilizer and pesticides, which was often excessively applied in China, were 0.921 and 0.909, respectively causing they the two dominant factors affecting TP loss. Annual precipitation and relative humidity, which were belongs to natural conditions, increased TP loss by enhancing leaching and surface runoff. However, light duration could reduce TP loss by promoting crop growth and increasing TP absorption of crops, with a path coefficient of - 0.920. TP loss of each province in per unit area from planting was significantly correlated with TP concentration of its surface water (p < 0.05), suggesting that TP loss from planting was the main factor causing surface water eutrophication. This study targeted presented three proposals to reduce the TP loss from planting, including promotion of scientific fertilization technologies, restriction of organophosphorus pesticides, and popularization of water saving irrigation technologies. These findings as well as suggestions herein would provide direction for the reduction of TP loss from planting.

Evidence of a rapid phosphorus-induced regime shift in a large deep reservoir

Ecological regime shift studies in freshwater systems are mainly limited to shallow lakes and reservoirs, while abrupt changes in deeper lakes are often attributed to climate change. Here, we demonstrate the application of regime shift theory to one of California's newest and deepest reservoirs, Diamond Valley Lake (DVL), which in recent years showed an unexpected rapid departure from its water quality conditions of the previous decade. The reservoir shifted from a well oxygenated condition with low phytoplankton growth to a hypoxic, phytoplankton-dominated turbid system. We statistically identified the critical stressor (phosphorus (P)), switch points, and its load threshold and characterized its transition to an alternative stable state and the stabilizing mechanisms contributing to hysteresis. We analyzed long-term environmental, chemical and flow data, conducted a hydrographic survey, and developed a hydrodynamic model to characterize the factors that contributed to regime shift and to evaluate different management strategies that might reverse this shift. Our findings indicate that large deep systems exhibit different transition dynamics in the presence of an acute stressor compared to regime shifts in shallow systems. A cumulative external TP load threshold of 4.6 mg m^-2 d^-1 added to the reservoir over nearly 11 months was identified as the critical stressor. For large deep systems, inherent morphometric features such as large relative depth combine with external stressors to drive regime shifts. Light winds, morphometric conditions impeding deep mixing, and a stable stratification that lasts up to 9 months makes DVL more susceptible to hypolimnetic hypoxia, an intrinsic factor accelerating regime shift. Results also suggest regime shift occurred in 2013, when new limnological processes were established to reinforce the new alternative stable state and existing ecosystem services were impaired. Interactions between hypoxia, internal P loading (~2.1 mg m^-2 d^-1), and seasonal cyanobacterial blooms were identified as mechanisms perpetuating the new alternative state.

Natural and artificial humic substances to manage minerals, ions, water, and soil microorganisms

The chemistry of humic substances (HSs) occurs hidden from our sight, but is of key importance to agriculture and the environment, and nowadays even to medicine and technology. HSs are nowadays not only natural, but extracted and engineered, and in the past 20 years such products have been widely used in soil improvement and environment governance. In this review, we collate and summarize the applications and working principles of such HSs in agriculture and environmental ecology, mainly to elaborate the multiple roles of this functional polymer along with physical chemical quantification. Then several of the latest synthesis technologies, including hydrothermal humification technology (HTH), hydrothermal carbonization technology (HTC) and hydrogen peroxide oxidation technology (HOT) are presented, which were introduced to prepare artificial humic substances (A-HSs). The availability of reproducible and tunable synthetic A-HSs is a new chemical tool, and effects such as solubilization of insoluble phosphorus minerals, recovery of phosphorus, improvement of soil fertility for crop growth and reduction of toxicity of typical pollutants, can now be analyzed in detail and quantified. As a result, we can provide an effective chemical technology for utilizing biomass side products ("biowaste") to generate A-HSs of different types, thus realizing improvement in agricultural production and control of environmental pollution by the macro-synthesis of A-HSs-.

The need to integrate legacy nitrogen storage dynamics and time lags into policy and practice

Increased fluxes of reactive nitrogen (N_r), often associated with N fertilizer use in agriculture, have resulted in negative environmental consequences, including eutrophication, which cost billions of dollars per year globally. To address this, best management practices (BMPs) to reduce N_r loading to the environment have been introduced in many locations. However, improvements in water quality associated with BMP implementation have not always been realised over expected timescales. There is a now a significant body of scientific evidence showing that the dynamics of legacy N_r storage and associated time lags invalidate the assumptions of many models used by policymakers for decision making regarding N_r BMPs. Building on this evidence, we believe that the concepts of legacy N_r storage dynamics and time lags need to be included in these models. We believe the biogeochemical research community could play a more proactive role in advocating for this change through both awareness raising and direct collaboration with policymakers to develop improved datasets and models. We anticipate that this will result in more realistic expectations of timescales for water quality improvements associated with BMPs. Given the need for multi-nutrient policy responses to tackle challenges such as eutrophication, integration of N stores will have the further benefit of aligning both researchers and policymakers in the N community with the phosphorus and carbon communities, where estimation of stores is more widespread. Ultimately, we anticipate that integrating legacy N_r storage dynamics and time lags into policy frameworks will better meet the needs of human and environmental health.

Quantify phosphorus transport distinction of different reaches to estuary under long-term anthropogenic perturbation

Typical diffuse pollutants such as phosphorus (P) have long been a hot topic in the surface-water research field. As the fifth-largest river in the world, the Yellow River Basin (YRB) suffers from significant soil erosion and relatively high intensity of agricultural activities, which bring large amounts of P loads. However, owing to the large drainage area, few studies have investigated the transport and attenuation dynamic processes or provided a precise calculation of the total phosphorus (TP) load for the entire YRB. In this study, the SPAtially Referenced Regressions on Watershed Attributes (SPARROW) model was used to simulate and investigate the spatial variation and transport mechanism of P in the YRB. The YRB was divided into 60 sub-basins, and the data of drainage area, spatial attribute, streamflow, and monitored flux were integrated into the model correspondingly. Calculated R² values confirm that 84% of the spatial variability in annual TP loads can represent regional processes. The estimated YRB TP load was 41,760 tons per year, contributed by farmland (64%), construction land (27%), grassland (5%), and forest (4%). In addition, the P transport dynamic process, contribution, and sensitivity of different P flux sources in different reaches were represented and identified. Our study highlights the significance of farmland as the most significant factor exacerbating TP pollution. As the study conducted the first attempt to develop a SPARROW model, integrated management strategies that consider the spatially varying P sources and associated TP transport were proposed. Additionally, to improve the ecological health of basin, it is critical to further increase P utilization efficiency and enhance cross-regional cooperation throughout the basin.

Responses of Chlamydomonas reinhardtii during the transition from P-deficient to P-sufficient growth (the P-overplus response): The roles of the vacuolar transport chaperones and polyphosphate synthesis

Phosphorus (P) assimilation and polyphosphate (polyP) synthesis were investigated in Chlamydomonas reinhardtii by supplying phosphate (PO₄^3- ; 10 mg P·L^-1 ) to P-depleted cultures of wildtypes, mutants with defects in genes involved in the vacuolar transporter chaperone (VTC) complex, and VTC-complemented strains. Wildtype C. reinhardtii assimilated PO₄^3- and stored polyP within minutes of adding PO₄^3- to cultures that were P-deprived, demonstrating that these cells were metabolically primed to assimilate and store PO₄^3- . In contrast, vtc1 and vtc4 mutant lines assayed under the same conditions never accumulated polyP, and PO₄^3- assimilation was considerably decreased in comparison with the wildtypes. In addition, to confirm the bioinformatics inferences and previous experimental work that the VTC complex of C. reinhardtii has a polyP polymerase function, these results evidence the influence of polyP synthesis on PO₄^3- assimilation in C. reinhardtii. RNA-sequencing was carried out on C. reinhardtii cells that were either P-depleted (control) or supplied with PO₄^3- following P depletion (treatment) in order to identify changes in the levels of mRNAs correlated with the P status of the cells. This analysis showed that the levels of VTC1 and VTC4 transcripts were strongly reduced at 5 and 24 h after the addition of PO₄^3- to the cells, although polyP granules were continuously synthesized during this 24 h period. These results suggest that the VTC complex remains active for at least 24 h after supplying the cells with PO₄^3- . Further bioassays and sequence analyses suggest that inositol phosphates may control polyP synthesis via binding to the VTC SPX domain.

Waste to phosphorus: A transdisciplinary solution to P recovery from wastewater based on the TRIZ approach

Phosphorus (P) is a limited yet essential resource. P cannot be replaced, but it can be recovered from waste. We proposed the TRIZ approach (Teoria reszenija izobretatielskich zadacz - Rus., Theory of Inventive Problem Solving - Eng.) to identify a feasible solution. We aimed at minimizing the environmental impact and, by eliminating contradictions, proposed viable technical solutions. P recovery can be more sustainable based on circular economy and 4Rs (reduction, recovery, reuse, and recycling). The TRIZ approach identified sewage sludge (SS) as waste with a large potential for P recovery (up to 90%). Successful selection and application of SS management and P recovery require a transdisciplinary approach to overcome the various socio-economic, environmental, technical, and legal aspects. The review provides an understanding of principles that must be taken to improve understanding of the whole process of P recovery from wastewater while building on the last two decades of research.

Source identification of particulate phosphorus in the atmosphere in Beijing

We tracked atmospheric phosphorus (P) in suspended particulate matter (PM) from a site in Beijing, China over a three-year period and found a new relationship between plants and atmospheric P. Concentrations of total phosphorus (TP) in the atmosphere during plant growing seasons were 2.5 times those observed in other months and levels of organic phosphorus (OP) were 3.9 times as high. TP and OP increases during growing seasons were much more significant in PM with diameters of over 2.5 μm (PM_>2.5). PM collected during growing seasons included high levels of P but less nitrogen than that in primary biogenic aerosol particles (PBAPs) and differed from other emission sources such as combustion emissions and dust. A time series of OP concentrations in the atmosphere shows a time lag relative to Normalized Difference Vegetation Index (NDVI) data with high levels found during early growing periods and much lower levels found during flourishing periods. Thus, we find that plants contribute to atmospheric P and especially to OP rather than to PBAP levels.

Roles of Phosphate Solubilizing Microorganisms from Managing Soil Phosphorus Deficiency to Mediating Biogeochemical P Cycle

Phosphorus (P) is a vital element in biological molecules, and one of the main limiting elements for biomass production as plant-available P represents only a small fraction of total soil P. Increasing global food demand and modern agricultural consumption of P fertilizers could lead to excessive inputs of inorganic P in intensively managed croplands, consequently rising P losses and ongoing eutrophication of surface waters. Despite phosphate solubilizing microorganisms (PSMs) are widely accepted as eco-friendly P fertilizers for increasing agricultural productivity, a comprehensive and deeper understanding of the role of PSMs in P geochemical processes for managing P deficiency has received inadequate attention. In this review, we summarize the basic P forms and their geochemical and biological cycles in soil systems, how PSMs mediate soil P biogeochemical cycles, and the metabolic and enzymatic mechanisms behind these processes. We also highlight the important roles of PSMs in the biogeochemical P cycle and provide perspectives on several environmental issues to prioritize in future PSM applications.

Human-driven spatiotemporal distribution of phosphorus flux in the environment of a mega river basin

Large river basins transport considerable nutrients to the ocean every year. However, phosphorus (P) generated by human activities not only threatens aquatic ecosystem health in the river basin, but also has a negative effect on the estuary water environment. To better understand the environmental effects of anthropogenic P in a mega basin, we examined its inputs and distribution characteristics, and analyzed the factors driving it in the Yangtze River Basin (YRB) and sub-catchments. Anthropogenic P flux in the sub-catchments gradually increased from upper to lower reaches, and hotspots were primarily concentrated in traditional agricultural areas such as the Sichuan Basin and the Middle-Lower Yangtze plains. Agricultural sources were the main anthropogenic P inputs, of which fertilizer P was the leading contributor and driver of P changes, but livestock manure also accounted for a high proportion. Presently, anthropogenic P inputs in the YRB are considerably higher than in other parts of the world. Although long-distance transportation allows some P from the entire basin to be deposited in freshwater, a large amount of P still reaches the estuary and has a negative effect on water quality, outweighing the influence of local coastal inputs. To maintain the ecological health of the river basin and estuary, it will be necessary to further improve P utilization efficiency and encourage greater cooperation between different regions in the river basin.

Phosphate and Ammonium Removal from Water through Electrochemical and Chemical Precipitation of Struvite

Batch electrocoagulation (BEC), continuous electrocoagulation (CEC), and chemical precipitation (CP) were compared in struvite (MgNH4PO4·6H2O) precipitation from synthetic and authentic water. In synthetic water treatment (SWT), struvite yield was in BEC 1.72, CEC 0.61, and CP 1.54 kg/m3. Corresponding values in authentic water treatment (AWT) were 2.55, 3.04, and 2.47 kg/m3. In SWT, 1 kg struvite costs in BEC, CEC, and CP were 0.55, 0.55, and 0.11 €, respectively, for AWT 0.35, 0.22 and 0.07 €. Phosphate removal in SWT was 93.6, 74.5, and 71.6% in BEC, CEC, and CP, respectively, the corresponding rates in AWT were 89.7, 77.8, and 74.4%. Ammonium removal for SWT in BEC, CEC, and CP were 79.4, 51.5, and 62.5%, respectively, rates in AWT 56.1, 64.1, and 60.9%. Efficiency in CEC and BEC are equal in nutrient recovery in SWT, although energy efficiency was better in CEC. CP is cheaper than BEC and CEC.

How long-term excessive manure application affects soil phosphorous species and risk of phosphorous loss in fluvo-aquic soil

The excessive application of manure has caused a high load of phosphorus (P) in the North China Plain. Having an understanding of how manure application affects soil P changes and its transport between different soil layers is crucial to reasonably apply manure P and reduce the associated loss. Based on our 28-year field experiments, the compositions and changes of P species and the risk of P loss under excessive manure treatments were investigated, i.e., no fertilizer (CK), mineral fertilizer NPK (NPK), NPK plus 22.5 t ha^-1 yr^-1 swine manure (LMNPK), and NPK plus 33.75 t ha^-1 yr^-1 swine manure (HMNPK). Manure application increased the content of orthophosphate and myo-inositol hexaphosphate (myo-IHP), especially the orthophosphate content exceeded 95%. The amount of orthophosphate in manure and the conversion of organic P to inorganic P in soil were the main reasons for the increased soil orthophosphate. Compared with NPK treatment, soil microbial biomass phosphorus and alkaline phosphatase activity in LMNPK and HMNPK treatments significantly increased. Compared with NPK treatment, a high manure application rate under HMNPK treatment could increase the abundance of organic P-mineralization gene phoD by 60.0% and decrease the abundance of inorganic P-solubilization gene pqqC by 45.9%. Due to the continuous additional manure application, soil P stocks significantly increased under LMNPK and HMNPK treatments. Furthermore, part of the P has been leached to the 60-80 cm soil layer. Segmented regression analysis indicated that CaCl₂-P increased sharply when Olsen-P was higher than 25.1 mg kg^-1, however the content of Olsen-P did not exceed this value until 10 years after consecutive excessive manure application. In order to improve soil P availability and decrease the risk of P loss, the manure application rate should vary over time based on soil physicochemical conditions, plants requirements, and P stocks from previous years.

Short-chain fatty acids recovery from sewage sludge via acidogenic fermentation as a carbon source for denitrification: A review

Wastewater treatment plants face the problem of a shortage of carbon source for denitrification. Acidogenic fermentation is an effective method for recovering short-chain fatty acids (SCFAs) as a carbon source from sewage sludge. Herein, the most recent advances in SCFAs production from primary sludge and waste activated sludge are systematically summarised and discussed. New technologies and problems pertaining to the improvement in SCFAs availability in fermentation liquids, including removal of ammoniacal nitrogen and phosphate and extraction of SCFAs from fermentation liquids, are analysed and evaluated. Furthermore, studies on the use of recovered SCFAs as a carbon source for denitrification are reviewed. Based on the above summarisation and discussion, some conclusions as well as perspectives on future studies and practical applications are presented. In particular, the recovery of carbon source/bioenergy from sewage sludge must be optimised considering nutrient removal/recovery simultaneously.

Network resilience of phosphorus cycling in China has shifted by natural flows, fertilizer use and dietary transitions between 1600 and 2012

The resilience of the phosphorus (P) cycling network is critical to ecosystem functioning and human activities. Although P cycling pathways have been previously mapped, a knowledge gap remains in evaluating the P network's ability to withstand shocks or disturbances. Applying principles of mass balance and ecological network analysis, we examine the network resilience of P cycling in China from 1600 to 2012. The results show that changes in network resilience have shifted from being driven by natural P flows for food production to being driven by industrial P flows for chemical fertilizer production. Urbanization has intensified the one-way journey of P, further deteriorating network resilience. Over 2000-2012, the network resilience of P cycling has decreased by 11% owing to dietary changes towards more animal-based foods. A trade-off between network resilience improvement and increasing food trade is also observed. These findings can support policy decisions for enhanced P cycling network resilience in China.

Long-term (1980-2015) changes in net anthropogenic phosphorus inputs and riverine phosphorus export in the Yangtze River basin

Quantitative information on long-term net anthropogenic phosphorus inputs (NAPI) and its relationship with riverine phosphorus (P) export are critical for developing sustainable and efficient watershed P management strategies. This is the first study to address long-term (1980-2015) NAPI and riverine P flux dynamics for the Yangtze River basin (YRB), the largest watershed in China. Over the 36-year study period, estimated NAPI to the YRB progressively increased by ∼1.4 times, with NAPI_A (chemical fertilizer input + atmospheric deposition + seed input) and NAPI_B (net food/feed imports + non-food input) contributing 65% and 35%, respectively. Higher population, livestock density and agricultural land area were the main drivers of increasing NAPI. Riverine total phosphorus (TP), particulate phosphorus (PP) and suspended sediment (SS) export at Datong hydrological station (downstream station) decreased by 52%, 75% and 75% during 1980-2015, respectively. In contrast, dissolved phosphorus (DP) showed an increase in both concentration (∼7-fold) and its contribution to TP flux (∼16-fold). Different trends in riverine P forms were mainly due to increasing dam/reservoir construction and changes in vegetation/land use and NAPI components. Multiple regression models incorporating NAPI_A, NAPI_B, dam/reservoir storage capacity and water discharge explained 84% and 92% of the temporal variability in riverine DP and PP fluxes, respectively. Riverine TP flux estimated as the sum of DP and PP fluxes showed high agreement with measured values (R² = 0.87, NSE = 0.84), indicating strong efficacy for the developed models. The model forecasted an increase of 50% and 7% and a decrease of 15% and 22% in riverine DP flux from 2015 to 2045 under developing, dam building, NAPI_A and NAPI_B reduction scenarios, respectively. This study highlights the importance of including enhanced P transformation from particulate to bioavailable forms due to river regulation and changes in land-use, input sources and legacy P pools in development of P pollution control strategies.

Response of Eutrophication Development to Variations in Nutrients and Hydrological Regime: A Case Study in the Changjiang River (Yangtze) Basin

Data and literature related to water quality as well as nutrient loads were used to evaluate the Changjiang River (also Yangtze or Yangzi) Basin with respect to its hydrological regime, sediment transport, and eutrophication status. Waterbodies exhibited different eutrophic degrees following the ranking order of river < reservoir < lake. Most of the eutrophic lakes and reservoirs distributed in the upstream Sichuan Basin and Jianghan Plain are located in the middle main stream reaches. During the past decade, the water surface area proportion of moderately eutrophic lakes to total evaluated lakes continually increased from 31.3% in 2009 to 42.7% in 2018, and the trophic level of reservoirs rapidly developed from mesotrophic to slightly eutrophic. Construction and operation of numerous gates and dams changed the natural transportation rhythm of runoff, suspended solids (SS), and nutrients, and reduced flow velocity, resulting in decreased discharge runoff, slow water exchange, and decreased connectivity between rivers and lakes as well as accumulated nutrient and SS, which are the main driving forces of eutrophication. To mitigate eutrophication, jointly controlling and monitoring nutrient concentrations and flux at key sections, strengthening water quality management for irrigation backwater and aquaculture wastewater, and balancing transportation among runoff, SS, and nutrients is recommended.

Historic Trends and Future Prospects of Waste Generation and Recycling in China's Phosphorus Cycle

Intensified human activities have generated a large amount of phosphorus-containing waste (P waste). Unrecycled P waste is lost to the environment and causes eutrophication, while the increasing phosphate consumption risks the depletion of phosphorus resources. The management of P waste is critical to solving these problems. In this study, we quantified the historic trends of P waste generation and recycling in China. From 1900 to 2015, the annual generation of P waste increased from 1 Mt P to 12 Mt P. Crop farming was the largest P waste source in most years, while P waste from phosphate mining and phosphorus chemical production increased the fastest. The total recycled P waste increased 5-fold, but phosphorus loss increased 26-fold. In 2015, 28% of the P waste was lost on cultivated land, and 21% was lost on nonarable land. The largest phosphorus contributor to inland water changed from crop farming to aquaculture. The full recycling of P waste would have reduced phosphate consumption by more than one-third in 2015. The results of a scenario analysis showed that a healthier diet would greatly increase the generation and loss of P waste, but balanced fertilization could reduce the generation of P waste by 17% and promoting waste recycling could reduce the phosphorus loss by 35%.

Resource recovery from wastewaters using microalgae-based approaches: A circular bioeconomy perspective

The basic concepts of circular bioeconomy are reduce, reuse and recycle. Recovery of recyclable nutrients from secondary sources could play a key role in meeting the increased demands of the growing population. Wastewaters of different origin are rich in energy and nutrients sources that can be recovered and reused in a circular bioeconomy perspective. Microalgae can effectively utilize wastewater nutrients for growth and biomass production. Integration of wastewater treatment and microalgal cultivation improves the environmental impacts of the currently used wastewater treatment methods. This review provides comprehensive information on the potential of using microalgae for the recovery of carbon, nitrogen, phosphorus and other micronutrients from wastewaters. Major factors influencing large scale microalgal wastewater treatment are discussed and future research perspectives are proposed to foster the future development in this area.

Anthropogenic global shifts in biospheric N and P concentrations and ratios and their impacts on biodiversity, ecosystem productivity, food security, and human health

The availability of carbon (C) from high levels of atmospheric carbon dioxide (CO2 ) and anthropogenic release of nitrogen (N) is increasing, but these increases are not paralleled by increases in levels of phosphorus (P). The current unstoppable changes in the stoichiometries of C and N relative to P have no historical precedent. We describe changes in P and N fluxes over the last five decades that have led to asymmetrical increases in P and N inputs to the biosphere. We identified widespread and rapid changes in N:P ratios in air, soil, water, and organisms and important consequences to the structure, function, and biodiversity of ecosystems. A mass-balance approach found that the combined limited availability of P and N was likely to reduce C storage by natural ecosystems during the remainder of the 21st Century, and projected crop yields of the Millennium Ecosystem Assessment indicated an increase in nutrient deficiency in developing regions if access to P fertilizer is limited. Imbalances of the N:P ratio would likely negatively affect human health, food security, and global economic and geopolitical stability, with feedbacks and synergistic effects on drivers of global environmental change, such as increasing levels of CO2 , climatic warming, and increasing pollution. We summarize potential solutions for avoiding the negative impacts of global imbalances of N:P ratios on the environment, biodiversity, climate change, food security, and human health.