Managing Diffuse Phosphorus at the Source versus at the Sink

Integration of Eu-based metal-organic frameworks and carbon dots for multicolor visual intelligent detection of phosphate

Phosphate (Pi) has an important influence on the water environment and physiological processes. Therefore, developing fluorescent probe for quantitative detection of Pi is crucial for water environment monitoring and human health assessment. This work designed a dual-emission ratio nano-fluorescent probe GCDs/Eu-BDC based on europium-based metal-organic frameworks (Eu-MOFs) and blue carbon dots (GCDs) for multicolor fluorescence detection of Pi. The GCDs/Eu-BDC realized multicolor fluorescence detection of Pi based on the red-to-blue fluorescence change. The probe has high selectivity and a detection limit of 70 nM in the range of 0-45 μM. GCDs/Eu-BDC can be used to detect Pi in environmental water samples and serum samples, proving the feasibility of quantitative analysis of Pi in real samples. In addition, a portable paper-based sensor was prepared in this work. Combined with the chromaticity analysis App in smartphones, the intelligent real-time detection of Pi can be realized, which has certain practical application potential.

The phosphorus challenge: biotechnology approaches for a sustainable phosphorus system

Phosphorus (P) is essential for growing crops, but the supply of high-quality phosphate rock reserves used for fertilizer production is finite while losses of P from the food/waste system cause considerable environmental damage. A variety of emerging approaches in biotechnology are reviewed that hold promise for improving the sustainability of P use in the food/water systems. These include improved sensors, cell culture approaches to meat production, bio-based P adsorption and transformation strategies, advancements in understanding of polyphosphate-accumulating organisms, and new approaches involving biomineralization and anaerobic treatment. By advancing these technologies to scale, progress can be made in developing a circular phosphorus economy that improves food security while protecting drinking water and aquatic ecosystems.

Guidance on aqueous matrices for evaluating novel precipitants and adsorbents for phosphorus removal and recovery

Phosphorus (P) removal from water and recovery into useable forms is a critical component of creating a sustainable P cycle, although mature technologies for P removal and recovery are still lacking. The goal of this paper was to advance the testing of novel materials for P removal and recovery from water by providing guidance on the development of more realistic aqueous matrices used during materials development. Literature reports of "new" materials to remove P from water are often difficult to compare in terms of performance because authors use a myriad of water chemistries containing P concentrations, pH, and competing ions. Moreover, many tests are conducted in simplified matrices that do not reflect conditions in real systems. To address this critical gap, the research herein developed a systematic approach of identifying aqueous matrices relevant to P recovery, including key components in the aqueous matrices having the greatest influence on the mechanisms of P removal with emphasis on phosphate precipitation and phosphate adsorption, and providing guidelines on relevant "recipes" for aqueous solutions for testing novel materials. Key components in the aqueous matrices included hydrogen ion (i.e., pH), multivalent metal cations, and dissolved organic matter due to their influence on phosphate precipitation and adsorption mechanisms. Recipes for buffer solution and synthetic groundwater, surface water, anaerobic digestate, and stored urine are discussed in the context of P removal and recovery processes. Wherein the adoption of standard matrices in other fields have permitted direct comparison of processes or materials, it is anticipated that adoption of relevant aqueous matrix recipes for P removal and recovery will improve the ability to directly compare novel materials and processes.

Reducing phosphorus losses from agricultural land to surface water

Phosphorus (P) enrichment of water impairs its quality by stimulating algal growth and eutrophication, affecting an estimated 1.7 billion people. Remediation costs are substantial, estimated at $1 billion annually in Europe and $2.4 billion in the USA. Agricultural intensification over the past 50 years has increased P use brought into the system from mined fertiliser sources. This has enriched soil P concentrations and loss to surface waters via pathways such as surface runoff and subsurface flow, which are influenced by precipitation, slope, and farming practices. Effective mitigation of losses involves managing P sources, mobilisation, and transport/delivery mechanisms. The cost-effectiveness of mitigation actions can be improved if they are targeted to critical source areas (CSAs), which are small zones that disproportionately contribute to P loss. While targeting CSAs works well in areas with variable topography, flatter landscapes require managing legacy sources, such as enriched soil P to prevent P losses.

A regional examination of the footprint of agriculture and urban cover on stream water quality

Freshwater systems in cold regions, including the Laurentian Great Lakes, are threatened by both eutrophication and salinization, due to excess nitrogen (N), phosphorus (P) and chloride (Cl-) delivered in agricultural and urban runoff. However, identifying the relative contribution of urban vs. agricultural development to water quality impairment is challenging in watersheds with mixed land cover, which typify most developed regions. In this study, a self-organizing map (SOM) analysis was used to evaluate the contributions of various forms of land cover to water quality impairment in southern Ontario, a population-dense, yet highly agricultural region in the Laurentian Great Lakes basin where urban expansion and agricultural intensification have been associated with continued water quality impairment. Watersheds were classified into eight spatial clusters, representing four categories of agriculture, one urban, one natural, and two mixed land use clusters. All four agricultural clusters had high nitrate-N concentrations, but levels were especially high in watersheds with extensive corn and soybean cultivation, where exceedances of the 3 mg L-1 water quality objective dramatically increased above a threshold of ‍∼30 % watershed row crop cover. Maximum P concentrations also occurred in the most heavily tile-drained cash crop watersheds, but associations between P and land use were not as clear as for N. The most urbanized watersheds had the highest Cl- concentrations and expansions in urban area were mostly at the expense of surrounding agricultural land cover, which may drive intensification of remaining agricultural lands. Expansions in tile-drained corn and soybean area, often at the expense of mixed, lower intensity agriculture are not unique to this area and suggest that river nitrate-N levels will continue to increase in the future. The SOM approach provides a powerful means of simplifying heterogeneous land cover characteristics that can be associated with water quality patterns and identify problem areas to target management.

Unraveling spatial patterns and source attribution of nutrient transport: Towards optimal best management practices in complex river basin

A comprehensive understanding of nutrient transport patterns and clarification of pollutant sources' load contributions are critical prerequisites for developing scientific pollution control strategies in complex river basins. Here, we focused on the Minjiang River Basin (MRB) and employed the Soil and Water Assessment Tool (SWAT) model to systematically investigate the nitrogen (N) and phosphorus (P) loads from both point and non-point sources. Results revealed that the key source areas of N and P pollution in the MRB were predominantly located along the riverbanks, influenced by a combination of sediment, precipitation, agricultural activities such as fertilization. Our analysis indicated that soil nutrient loss, fertilization, and livestock farming were the major contributors to N and P inputs, accounting for over 70 % of the total input, followed by rural residential and urban point sources. Based on the identification of non-point source pollution as the primary load source, a multi-objective optimization was conducted using response surface methodology (RSM) coupled with the non-dominated sorting genetic algorithm-II (NSGA-II), resulting in the identification of optimal best management practices (BMPs) that achieve a reduction of 40.04 % in N load, 39.22 % in P load, and a net economic benefit of -1.13 billion yuan per year. Compared to the RSM and automated optimization results, the proposed management measures exhibited significant improvements in N and P load reduction and net benefits. Overall, the findings provide important insights for formulating agricultural management policies in the MRB and offering valuable implications for pollution management in other complex river basins.

Pollution source identification and abatement for water quality sections in Huangshui River basin, China

Accurately obtaining the pollution sources and their contribution rates is the basis for refining watershed management. Although many source analysis methods have been proposed, a systematic framework for watershed management is still lacking, including the complete process of pollution source identification to control. We proposed a framework for identification and abatement of pollutants and applied in the Huangshui River Basin. A newer contaminant flux variation method based on a one-dimensional river water quality model was used to calculate the contribution of pollutants. The contributions of various factors to the over-standard parameters of water quality sections at different spatial and temporal scales were calculated. Based on the calculation results, corresponding pollution abatement projects were developed, and the effectiveness of the projects was evaluated through scenario simulation. Our results showed that the large scale livestock and poultry farms and sewage treatment plants were the largest sources of total nitrogen (TP) in Xiaoxia bridge section, with contribution rates of 46.02% and 36.74%, respectively. Additionally, the largest contribution sources of ammonia nitrogen (NH3-N) were sewage treatment plants (36.17%) and industrial sewage (26.33%). Three towns that contributed the most to TP were Lejiawan Town (14.4%), Ganhetan Town (7.3%) and Handong Hui Nationality town (6.6%), while NH3-N mainly from the Lejiawan Town (15.9%), Xinghai Road Sub-district (12.4%) and Mafang Sub-district (9.5%). Further analysis found that point sources in these towns were the main contributor to TP and NH3-N. Accordingly, we developed abatement projects for point sources. Scenario simulation indicated that the TP and NH3-N could be significantly improved by closing down and upgrading relevant sewage treatment plants and building facilities for large scale livestock and poultry farms. The framework adopted in this study can accurately identify pollution sources and evaluate the effectiveness of pollution abatement projects, which is conducive to the refined water environment management.

Land-Water Transport and Sources of Nitrogen Pollution Affecting the Structure and Function of Riverine Microbial Communities

The characterization of variations in riverine microbiota that stem from contaminant sources and transport modes is important for understanding biogeochemical processes. However, the association between complex anthropogenic nitrogen pollution and bacteria has not been extensively investigated owing to the difficulties faced while determining the distribution of nitrogen contaminants in watersheds. Here, we employed the Soil and Water Assessment Tool alongside microbiological analysis to explore microbial characteristics and their responses to complex nitrogen pollution patterns. Significant variations in microbial communities were observed in sub-basins with distinct land-water pollution transport modes. Point source-dominated areas (PSDAs) exhibited reduced microbial diversity, high number of denitrification groups, and increased nitrogen cycling compared with others. The negative relative deviations (-3.38) between the measured and simulated nitrate concentrations in PSDAs indicated that nitrate removal was more effective in PSDAs. Pollution sources were also closely associated with microbiota. Effluents from concentrated animal feeding operations were the primary factors relating to the microbiota compositions in PSDAs and balanced areas. In nonpoint source-dominated areas, contaminants from septic tanks become the most relevant sources to microbial community structures. Overall, this study expands our knowledge regarding microbial biogeochemistry in catchments and beyond by linking specific nitrogen pollution scenarios to microorganisms.

Revealing the role of phosphorus supply on the phosphorus distribution and lipid production in Scenedesmus obliquus UTEX 393 during nitrogen starvation

Microalgal-based processes offer promise for addressing two sustainability challenges: recovering phosphorus (P) from wastewater and producing biofuel feedstock. This study investigated the role of phosphorus supply on microalgal growth, lipid yield, and P distribution for Scenedesmus during nitrogen starvation. Extracellular polymeric substances and intracellular polymeric substances were the most important pools for inorganic phosphorus (IP) and organic phosphorus (OP), respectively. The main P pool for microalgae with low phosphorus supply was EPS, which accounted for 57 % of the total biomass phosphorus; while under high P concentrations, 79 % of the phosphorus was stored in IPS. A high concentration of orthophosphate stimulated rapid P uptake as IP and promoted the transformation of IP to OP associating with biomass synthesis. The highest P content of microalgal biomass was 6.5 % of dry weight when the phosphorus concentration in medium was 113 mg/L, and the OP content was 4.9 % of dry weight. High phosphate-P enhanced the biomass's lipid content by 60 %, and the distribution of fatty acid methyl esters was not altered by P concentrations. Collectively, high phosphate-P availability could promote microalgal biomass synthesis, lipid production and P accumulation.

Growing for good: producing a healthy, low greenhouse gas and water quality footprint diet in Aotearoa, New Zealand

Food production plays a central role in the health of humanity and our environment. New Zealand produces a large amount of food, but it is unknown if it can produce enough of the right crops in the places to better the health of New Zealanders, profitably, while maintaining New Zealand's primary production exports and meeting ambitions to lower greenhouse gas (GHGs) emissions and nutrient losses to water. We tested two scenarios that aimed at delivering a healthy diet while maximising profit and minimising GHGs (climate-focused scenario) or losses of nitrogen (N) and phosphorus (P) to water (freshwater-focused scenario). Land use change was targeted to areas not currently meeting bottom lines for N or P loss but needed to spill over to other areas to meet dietary targets in both scenarios. The maximum cost of the required land use change was about 1% of the primary sector's export revenues, and orders of magnitude less than the estimated savings for the health system from an optimised diet. We conclude that shifting productive land uses can help meet environmental targets for GHGs, N and P while saving money and improving the health of its people.

Phosphorus removal and recovery: state of the science and challenges

Phosphorus is one of the main nutrients required for all life. Phosphorus as phosphate form plays an important role in different cellular processes. Entrance of phosphorus in the environment leads to serious ecological problems including water quality problems and soil pollution. Furthermore, it may cause eutrophication as well as harmful algae blooms (HABs) in aquatic environments. Several physical, chemical, and biological methods have been presented for phosphorus removal and recovery. In this review, there is an overview of phosphorus role in nature provided, available removal processes are discussed, and each of them is explained in detail. Chemical precipitation, ion exchange, membrane separation, and adsorption can be listed as the most used methods. Identifying advantages of these technologies will allow the performance of phosphorus removal systems to be updated, optimized, evaluate the treatment cost and benefits, and support select directions for further action. Two main applications of biochar and nanoscale materials are recommended.

Harmonizing science and management options to reduce risks of cyanobacteria

Management of cyanobacteria has become an increasingly complex venture. Cyanobacteria risks have amplified as society moves forward in an era of accelerated global changes. The cyanobacteria management "pendulum" has progressively shifted from prevention to mitigation, with management considerations often put forth after bloom formation. A universal system (i.e., one-size-fits-all management) fails to provide a management path forward due to the inherent complexities of each lake. A tailored management plan is needed: the right species at the right time in the right place (i.e., the three Rs). The three Rs represent a customizable management strategy that is flexible and informed by advances in scientific understanding to lower cyanobacteria-associated risks. Identifying thresholds in risk tolerance, where thresholds are defined by community collectives, is essential to frame cyanobacteria management targets and to decide on what management interventions are warranted.

Study on the Water Quality Characteristics of the Baoan Lake Basin in China under Different Land Use and Landscape Pattern Distributions

Land use and landscape pattern highly affect water quality. Their relationship can assist in land-use management and improve land-use efficiency. In this study, a water quality survey of rivers and lakes was performed in 2020 to analyze the effects of land use and the landscape pattern on the water quality of the rivers and lakes in the Baoan Lake basin and is expected to provide a reference for land use planning. The results demonstrated that the effects of land use on water quality were generally higher during the dry season than during the wet season; however, the opposite was demonstrated for the landscape pattern index. Cropland and urban land were closely correlated with deteriorating water quality, with contributions to total nitrogen, total phosphorous, and ammonia nitrogen in the basin. The impact of the landscape pattern of the basin on water quality was controlled by the original land-use type. In addition, the landscape configuration formed different land-use types to produce different effects on water quality. The basin scale better explained the changes in water quality, especially for construction land, followed by the 250 m and 500 m scales in the buffer zone.

Evaluation of phosphorus removal in floating treatment wetlands: New insights in non-reactive phosphorus

Excess phosphorus (P) in surface runoff has significant deleterious impacts on water quality through eutrophication. Commonly, P is transported via non-point pollution and the proportion of easily plant-available reactive P (RP) among other P forms may vary significantly. Non-reactive P (NRP) can potentially contribute to the eutrophication of waterbodies, however the cleavage into bio-available P forms and eventually their biological uptake remains uncertain. This holds also true for floating treatment wetlands (FTWs) which became established as nutrient mitigation measures for surface waters in recent years. However, little information is available about the conversion and removal of NRP in FTWs. In this study, the conversion and removal of different forms of P in FTWs were investigated. Experiments were operated in batch mode and treatments consisted of (1) two concentration levels: a high P concentration of 3.0 mg/L and a low P concentration of 1.0 mg/L, and (2) four mesocosm treatments: (a) artificial roots only, (b) substrates only, (c) plants only, (d) plants and substrates. The results showed that RP removal mainly depended on sedimentation, substrate sorption, and biological assimilation. The removal of NRP mainly depended on hydrolysis, microbial-mediated conversion, and biological absorption. The combination of plant and substrate provided stable and efficient phosphorus removal performance in high P conditions, while plants were important for P removal in low P conditions. Living plants were indispensable and greatly affected the performance of FTWs. The specific enrichment and culling of microorganisms by plants resulted in the formation of specific rhizosphere microbial communities and promoted the removal of NRP. Pseudomonas, Enterobacter, Acidovorax might be responsible for P mineralization in the FTWs. Comprehensive analysis indicated that the conversion and removal pathways of P in the FTWs were not mutually independent, and the plant-microbe-substrate interactions cannot be underestimated.

Use of iron-coated sand for removing soluble phosphorus from drainage water

Mitigation measures are needed for reducing chronic dissolved phosphorus (P) losses from agricultural soils with a legacy of excessive P inputs to surface waters. Since pipe drains are an important pathway for P transport from agricultural soils to surface waters in flat areas, removing P from drainage water can be an effective measure. During a 4.5 year-field experiment, we tested the performance of a pipe drain enveloped with Fe-coated sand for removing soluble P from drainage water. Iron-coated sand is a by-product of the drinking water industry and has a high ability to bind P. The P concentration in the effluent from the enveloped pipe drain remained at a very low level over the entire monitoring period, with a removal percentage amounting to 93% for total P. During the field experiment, the enveloped pipe drain was below the groundwater level for a prolonged time. Nevertheless, no reduction of Fe(III) in the Fe-coated sand occurred during the first two years, most likely due to preferential reduction of Mn oxides present in the coatings of the sand particles, as reflected in elevated effluent Mn concentrations. Thereafter, reductive dissolution of Fe oxides in the coatings caused a gradual increase in the Fe concentration in the enveloped pipe drain effluent over time. Concomitantly, the dissolved Mn concentration decreased, most probably due to the depletion in easily accessible Mn oxides in the Fe-coated sand. The Fe in the Fe-coated sand was identified as silicate-containing ferrihydrite (Fh). The submerged conditions of the enveloped pipe drain neither affected the stability of Fh in the Fe-coated sand nor the ability of this measure to capture P from drainage water. Enveloping pipe drains with Fe-coated sand is an effective method for reducing dissolved P inputs from agricultural soils to surface waters and holds great promise for implementation in practice.

Phosphate removal by a La(OH)3 loaded magnetic MAPTAC-based cationic hydrogel: Enhanced surface charge density and Donnan membrane effect

Cationic hydrogels have received great attention to control eutrophication and recycle phosphate. In this study, a type of La(OH)₃ loaded magnetic MAPTAC-based cationic hydrogel (La(OH)₃@MMCH) was developed as a potential adsorbent for enhanced phosphate removal from aqueous environment. La(OH)₃@MMCH exhibited high adsorption capacity of 105.72±5.99 mg P/g, and reached equilibrium within 2 hr. La(OH)₃@MMCH could perform effectively in a wide pH range from 3.0 to 9.0 and in the presence of coexisting ions (including SO₄^2-, Cl^-, NO₃^-, HCO₃^-, SiO₄^4- and HA). The adsorption-desorption experiment indicated that La(OH)₃@MMCH could be easily regenerated by using NaOH-NaCl as the desorption agent, and 73.3% adsorption capacity remained after five cycles. Moreover, La(OH)₃@MMCH was employed to treat surface water with phosphate concentration of 1.90  mg/L and showed great removal efficiency of 95.21%. Actually, MMCH showed high surface charge density of 34.38-59.38 meq/kg in the pH range from 3.0 to 11.0 and great swelling ratio of 3014.57% within 24 h, indicating that MMCH could produce the enhanced Donnan membrane effect to pre-permeate phosphate. Furthermore, the bifunctional structure of La(OH)₃@MMCH enabled it to capture phosphate through electrostatic attraction and ligand exchange. All the results prove that La(OH)₃@MMCH is a promising adsorbent for eutrophication control and phosphate recovery.

Ratiometric fluorescence sensor for sensitive detection of inorganic phosphate in environmental samples

Fast, simple, and low-cost on-site visualized detection of inorganic phosphate (Pi) is in great demand since phosphate is the major reason of eutrophication. In this work, a ratiometric fluorescent probe composed by green carbon dots (GCDs) and red carbon dots (RCDs) has been established for high-sensitivity and selective sensing of Pi. A trend of color change from red to green is observed for the detection of Pi under ultraviolet light and the detection limit is 0.09 μM in the range of 0 to 55 μM. Fluorescent test paper prepared from the probe solution was successfully applied to semi-quantitative visual detection of Pi in real-world water and soil samples, which shows great real-world application potentials.

Long-Term Mississippi River Trends Expose Shifts in the River Load Response to Watershed Nutrient Balances Between 1975 and 2017

Excess nutrients transported by the Mississippi River (MR) contribute to hypoxia in the Gulf of Mexico. Nutrient balances are key drivers to river nutrient loads and represent inputs (fertilizer, manure, deposition, wastewater, N-fixation, and weathering) minus outputs (nutrient uptake and removal in harvest, and N emissions). Here, we quantified annual changes in nitrogen (N) and phosphorus (P) river loads and nutrient balances at the MR Outlet and documented that the river load response to watershed nutrient balances shifted between 1975 and 2017. Annual nutrient balances and river loads were positively correlated between 1975 and 1985, but after, a disconnect between both the N and P balances and river loads emerged, and the subsequent river load patterns were different for N versus P. We evaluated the relative impacts of legacy nutrients and other latent factors, for which data were not available, on river nutrient load trends. Our analysis showed that in the case of N, latent factors were potentially just as important in explaining changes in river nutrient loads over time as N balances, and in the case of P, they were even more important. We hypothesized that these factors included implementation of best management practices, changes in watershed buffering capacity, the effects of tile drainage, or increased precipitation. Our analytical approach shows promise for the investigation of drivers of water quality trends that are not well-represented in typical national scale geospatial datasets.

What is the deal with the Green Deal: Will the new strategy help to improve European freshwater quality beyond the Water Framework Directive?

Agricultural land use covers almost half of the EU territory and reducing nutrient and pesticide losses to freshwaters is central to existing EU policy. However, the progress of improving freshwater quality and reducing eutrophication is slow and lags behind targets. The Green Deal is a key element of the EU plans to implement the United Nation's Sustainable Development Goals. Here, we discuss the opportunities that the Green Deal and associated strategies may provide for the achievement of the water quality goals of the Water Framework Directive in agricultural landscapes. We welcome Green Deal's aspirational stated goals. However, the reliance of mitigation of diffuse agricultural pollution on the reform of the Common Agricultural Policy represents grave risks for practical implementation and the achievement of the Green Deal objectives. We also argue that the new strategies should be targeted at tackling and understanding the sources of water quality problems along the full pollution continuum. To maximise the opportunities for tackling diffuse pollution from agricultural land use and achieving the delayed water quality targets, we stress that a range of targeted new instruments will be needed to close the gaps in the pollution continuum 'from source to impact'. These gaps include: (I) smart and standardised monitoring of the impacts of proposed eco-schemes and agri-environment-climate measures, (ii) active restoration of agricultural streams and ditches and their floodplains to reduce secondary pollution sources, (iii) options to draw down nutrient levels to or below the agronomic optimum that reduce legacy sources, (iv) integrating farm-scale and catchment-scale analysis of trade-offs in reducing different pollutants and their combined effects, and finally (v) accounting for emerging pressures to freshwater quality due to climate change. Incorporation of the pollution continuum framework into tackling diffuse agricultural pollution will ensure that the European water-related policy goals are achieved.

Conversion of soluble recalcitrant phosphorus to recoverable orthophosphate form using UV/H2O2

Soluble non-reactive phosphorus (sNRP), such as inorganic polyphosphates and organic P, is not effectively removed by conventional physicochemical processes. This can impede water resource reclamation facilities' ability to meet stringent total P regulations. This study investigated a UV/H₂O₂ advanced oxidation process (AOP) for converting sNRP to the more readily removable/recoverable soluble reactive P (sRP), or orthophosphate, form. Synthetic water spiked with four sNRP compounds (beta-glycerol phosphate, phytic acid, triphosphate, and hexa-meta phosphate) at varying H₂O₂ concentration, UV fluence, pH, and temperature was initially tested. These compounds represent simple, complex, organic, and inorganic forms of sNRP potentially found in wastewater. The efficiency of sNRP to sRP conversion depended on whether the sNRP compound was organic or inorganic and the complexity of its chemical structure. Using 1 mM H₂O₂ and 0.43 J/cm² (pH 7.5, 22 °C), conversion of the simple organic beta-glycerol phosphate to sRP was 38.1 ± 2.9%, which significantly exceeded the conversion of the other sNRP compounds. Although conversion was achieved, the electrical energy per order (E_EO) was very high at 5.2 × 10³ ± 5.2 × 10² kWh/m³. Actual municipal wastewater secondary effluent, with sNRP accounting for 15% of total P, was also treated using UV/H₂O₂. No wastewater sNRP to sRP conversion was observed, ostensibly due to interference from wastewater constituents. Wastewater utilities that have difficulty meeting stringent P levels might be able to target simple organic sNRP compounds, though alternative processes beyond UV/H₂O₂ need to be explored to overcome interference from wastewater constituents and target more complex organic and inorganic sNRP compounds.

Effects of nFe3O4 capping on phosphorus release from sediments in a eutrophic lake

This study applied the techniques of high-resolution dialysis (HR-Peeper) and diffusive gradients in thin films (DGT) to explore the effects and the behind mechanism for inhibition phosphorus (P) releasing from sediments by nFe₃O₄ capping. The highest decreasing rates of SRP and labile P (i.e., 49% and 47%, respectively) and the decreased flux of SRP showed that nFe₃O₄ capping can successfully control sediment internal P release. Adsorption by Fe(III) hydroxides with the oxidation of Fe(II) was one of the reasons for the decrease of P concentrations in nFe₃O₄ capping sediments. This was supported by the increase of Eh and significant negative correlation between Eh with Fe(II) (soluble and labile Fe(II)) and P (SRP and labile P) and significant positive correlation between Fe(II) and P in sediments by nFe₃O₄ capping. An outer-sphere complex between positively charged nFe₃O₄ surface groups and P formation was the other reason to decrease the concentrations of P in the nFe₃O₄ capping sediments. This was supported by the decrease of pH value in sediments by the capping of nFe₃O₄. This study shows that nFe₃O₄, when used as capping agent, can effectively control the sediment internal P release, which is expected to be used as a potential material for repairing lake eutrophication.

A data-driven framework for spatiotemporal characteristics, complexity dynamics, and environmental risk evaluation of river water quality

To evaluate the evolution of river water quality in a changing environment, measuring the objective water quality is critical for understanding the rules of river water pollution. Based on the sample entropy theory and a nonlinear statistical method, this study aims to identify the spatiotemporal dynamics of water quality and its complexity in the Yangtze River basin using time series data, to separate the contributions of human activity and climate change to water quality, and to establish a data-driven risk assessment framework for the spatial (potential risk) and temporal (direct risk) aspects of water pollution. The results demonstrate that the spatiotemporal dynamics of water quality and sample entropy in each monitoring section are closely related to the characteristics of the corresponding location. The water quality of the main stream is superior, and its complexity is less than that of the tributaries. Cascade reservoir operation and vegetation status, agricultural production, and rainfall patterns exert great influences in the upper, middle, and lower reaches, respectively. Dam construction, urban agglomeration development, and interactions between river and lake are also influencing factors. An attributional analysis found that climate change and human activities negatively contributed to the evolution of NH₃-N concentration in most of the monitored sections, and the average relative contribution rates of human activities to changes in water quality in the main and tributary streams were -55.46% and -48.49%, respectively. In addition, the construction of data-driven risk assessment framework can efficiently and accurately assess the potential and direct water pollution risks of rivers.

The Effectiveness of an Artificial Floating Wetland to Remove Nutrients in an Urban Stream: A Pilot-Study in the Chicago River, Chicago, IL USA

Ever expanding urbanized landscapes are increasingly impacting streams that run through them. Among other stressors, urban streams often are host to elevated concentrations of nutrients, salts, and heavy metals. The pollutants, coupled with high temperatures, are drivers of ecosystem degradation in urban streams. The installation of artificial floating wetlands (AFWs) has been successful in mitigating the effects of urbanization in lakes and wastewater treatment ponds, but rarely have they been tested in streams. This pilot-study examined the ability of an AFW to improve water quality in an urban stream. The small, 90 m2 AFW was installed to improve the aquatic habitat and aesthetics of a small section of the Chicago River, Chicago, IL USA. Water samples and in-situ measurements were collected from the surface and at 0.3 m depth of upstream and downstream of the AFW. Samples were analyzed for nitrate-as-nitrogen, phosphate, chloride, and heavy metals. Comparison of upstream and downstream waters showed that the AFW lowered the concentrations of nitrate-as-nitrogen and phosphate during the growing season by 6.9% and 6.0%, respectively. Nitrate was also removed during the dormant season; however, phosphate was not removed during that time. Plant or microbial uptake of the nutrients are believed to be the dominant mechanisms in the growing season with denitrification serving as the primary pathway in the dormant season. Despite not having a measurable effect on the water temperature, the AFW was an effective means to reduce concentrations of nitrate and phosphorus, decreasing the potential for eutrophication.

Residential catchments to coastal waters: Forms, fluxes, and mechanisms of phosphorus transport

Controlling phosphorus (P) loss from land to water bodies is of immense scientific and societal interest and scrutiny. We investigated P forms in a longitudinal gradient in three typical urban junctions: stormwater from a residential catchment, pond discharges from a stormwater retention pond, and 13 coastal waters (rivers and estuary). Concentrations of total P (TP) were 122.7 ± 99.1 μg/L in the stormwater, 89.7 ± 35.8 μg/L in the pond discharges, and 212.1 ± 51.2 μg/L in 13 coastal water sites. Lower P concentrations in pond discharges reflect P attenuation in the stormwater pond, and higher P concentrations in surface waters are likely attributed to the additional contributing P sources in the watershed. Dissolved reactive P (DRP) was 38% of TP load in stormwater and 46% of TP concentrations in surface water sites, whereas particulate unreactive P (PUP) was 52% of TP load in pond discharges. The first-flush strength of P forms in the stormwater indicated the dominance of particulate P over dissolved P. More particulate P was transported in the early stages of storms due to the runoff of P associated with sediment, plant materials, and built up on impervious surfaces. Whereas more dissolved P was transported in the later stages of storms likely due to the flushing of P, as exacerbated by greater runoff amounts, from the landscape sources, i.e., grass clippings, tree leaves, and soil. In the pond discharges, DRP was a minor form suggesting its utilization by bacteria and algae in the pond. The high concentration and proportion of DRP in surface waters suggest an abundance of bioavailable P in urban waters. These results imply that treatment designs in urban areas should consider ways to remove P in urban landscapes focusing on attenuating P before the initiation of runoff and discharge to surface waters to protect downstream water quality.

Phosphate recovery as vivianite using a flow-electrode capacitive desalination (FCDI) and fluidized bed crystallization (FBC) coupled system

It is critical to both effectively remove and recover phosphate (P) from wastewater given the wide-ranging environmental (i.e., preventing eutrophication and restoring water quality) and economic (i.e., overcoming P resource scarcity) benefits. More recently, considerable academic effort has been devoted towards harvesting P as vivianite, which can be used as a potential slow-release fertilizer and possible reagent for the manufacture of lithium iron phosphate (LiFePO₄), the precursor in fabricating Li-ion secondary batteries. In this study, we propose an innovative P recovery process, in which P is first preconcentrated via a flow-electrode capacitive deionization (FCDI) device followed by immobilization as vivianite crystals in a fluidized bed crystallization (FBC) column. The effects of different operational parameters on FCDI P preconcentration performance and energy consumption are investigated. Results show that 63% of P can be removed and concentrated in the flow-electrode chamber with a reasonable energy requirement under optimal operating conditions. The FBC system resulted in immobilization of ~80% of P as triangular or quadrangular pellets, which were verified to be high-purity vivianite crystals by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) and extended X-ray absorption fine structure (EXAFS) spectroscopy. This study provides a pathway for efficient recovery of P as a value-added product (i.e., vivianite) from P-rich wastewaters.

Trace metal dynamics in an industrialized Brazilian river: A combined application of Zn isotopes, geochemical partitioning, and multivariate statistics

The Paraiba do Sul (PSR) and Guandu Rivers (GR) water diversion system (120 km long) is located in the main industrial pole of Brazil and supplies drinking water for 9.4 million people in the metropolitan region of Rio de Janeiro. This study aims to discern the trace metals dynamics in this complex aquatic system. We used a combined approach of geochemical tools such as geochemical partitioning, Zn isotopes signatures, and multivariate statistics. Zinc and Pb concentrations in Suspended Particulate Matter (SPM) and sediments were considerably higher in some sites. The sediment partition of As, Cr, and Cu revealed the residual fraction (F4) as the main fraction for these elements, indicating low mobility. Zinc and Pb were mostly associated with the exchangeable/carbonate (F1) and the reducible (F2) fractions, respectively, implying a higher susceptibility of these elements to being released from sediments. Zinc isotopic compositions of sediments and SPM fell in a binary mixing source process between lithogenic (δ^66/64Zn_JMC ≈ + 0.30‰) and anthropogenic (δ^66/64Zn_JMC ≈ + 0.15‰) end members. The lighter δ^66/64Zn_JMC values accompanied by high Zn concentrations in exchangeable/carbonate fraction (ZnF1) enable the tracking of Zn anthropogenic sources in the studied rivers. Overall, the results indicated that Hg, Pb, and Zn had a dominant anthropogenic origin linked to the industrial activities, while As, Cr, and Cu were mainly associated with lithogenic sources. This work demonstrates how integrating geochemical tools is valuable for assessing geochemical processes and mixing source effects in anthropized river watersheds.

Sediment phosphorus buffering in streams at baseflow: A meta-analysis

Phosphorus (P) pollution of surface waters remains a challenge for protecting and improving water quality. Central to the challenge is understanding what regulates P concentrations in streams. This quantitative review synthesizes the literature on a major control of P concentrations in streams at baseflow-the sediment P buffer-to better understand streamwater-sediment P interactions. We conducted a global meta-analysis of sediment equilibrium phosphate concentrations at net zero sorption (EPC₀ ), which is the dissolved reactive P (DRP) concentration toward which sediments buffer solution DRP. Our analysis of 45 studies and >900 paired observations of DRP and EPC₀ showed that sediments often have potential to remove or release P to the streamwater (83% of observations), meaning that "equilibrium" between sediment and streamwater is rare. This potential for P exchange is moderated by sediment and stream characteristics, including sorption affinity, stream pH, exchangeable P concentration, and particle sizes. The potential for sediments to modify streamwater DRP concentrations is often not realized owing to other factors (e.g., hydrologic interactions). Sediment surface chemistry, hyporheic exchange, and biota can also influence the potential exchange of P between sediments and the streamwater. Methodological choices significantly influenced EPC₀ determination and thus the estimated potential for P exchange; we therefore discuss how to measure and report EPC₀ to best suit research objectives and aid in interstudy comparison. Our results enhance understanding of the sediment P buffer and inform how EPC₀ can be effectively applied to improve management of aquatic P pollution and eutrophication.

Evidence for the leaching of dissolved organic phosphorus to depth

Phosphorus (P) can leach from topsoil in inorganic and organic forms. While some evidence has shown inorganic P (orthophosphate) can leach to depth in some soils, less is known of dissolved organic P (DOP). This is not helped by a paucity DOP data for groundwater. We hypothesized that DOP species would leach in greater amounts to depth and at a faster rate through aquifer gravels than orthophosphate. We applied superphosphate with or without dung to a low P-sorption soil under pasture and irrigation. Between 0.7 (control) and 2.4 (dung +superphosphate) kg P ha^-1 was leached through 30 cm with a mean ratio of DRP to DOP of 1.5. At 50 cm, 0.7 and 1.3 kg P ha^-1 was leached with the DRP to DOP ratio decreasing to 1.1 due to greater DOP leaching (or DRP sorption). There was little difference in DRP losses measured at 50 and 150 cm depth. All DOP compounds except the monoester - inositol hexakisphosphate were leached at a faster rate than orthophosphate through aquifer gravels. These data suggest that where low P-sorption soils overlay similarly low P-sorption aquifers, DOP may reach groundwater at a faster rate than orthophosphate. Furthermore, as many DOP species are bioavailable to periphyton, our data suggest that DOP should be included in the assessment of the risk of P contamination of groundwater where connection to baseflow could be a long-term stimulant of periphyton growth.

Goethite dispersed corn straw-derived biochar for phosphate recovery from synthetic urine and its potential as a slow-release fertilizer

In this study, goethiete (α-FeOOH) -biochar (BC) composites were successfully developed from a co-precipitation reaction under alkaline conditions (pH = 11.93) and used as the adsorbent for phosphate recovery from urine. The morphology and crystallinity of α-FeOOH-BC composites were characterized by scanning electron microscopy and X-ray diffraction. α-FeOOH loaded BC was found to be amorphous. This may be caused by the Si residue in BC. The Elovich model and the Langmuir model fit better to the kinetic and isotherm results of α-FeOOH-600BC, respectively, indicating that phosphate adsorption is mainly a chemisorption and monolayer adsorption process. The α-FeOOH-600BC with amorphous structure showed higher adsorption capacity than crystalline α-FeOOH, and the maximum phosphate sorption capacity reached 57.39 mg g^-1. Additionally, the extractable phosphate of this material was approximately 967.5 mg P·kg^-1 suggesting the α-FeOOH-600BC after adsorption could be a promising alternative as a slow-phosphate-release fertilizer. Fourier-transform infrared and X-ray induced photoelectron spectroscopy results showed that the active sites of the adsorption of phosphate were the Fe-OH bonds that formed inner-sphere complexes (Fe-O-P).

A Dual Source of Phosphorus to Lake Sediments Indicated by Distribution, Content, and Speciation: Inle Lake (Southern Shan State, Myanmar)

In this study, grab and core sediments from Inle lake were collected and analysed for their water and organic matter (O.M.) contents. Total phosphorus (TPSMT) and P fractions, namely inorganic-P (IP), organic-P (OP), P bound to Al, Fe and Mn oxy-hydroxides (Fe-P), and calcium-bound P (Ca-P) were determined by a sequential extraction procedure. TPSMT varied considerably (152–1980 mg/kg), with minimum concentrations detected at sites away from the main inflow rivers and maximum concentrations in the floating gardens area. In core sediments, TPSMT concentrations tended to decrease with depth, reaching values of <100 mg/kg. Concerning P forms, the overall abundance sequence in grab sediments was IP >> OP and Ca-P ≥ OP > Fe-P, whereas in core sediments it showed marked differences with depth and between sites. The relative abundance of the inorganic species (Ca-P, Fe-P) was controlled by the mineralogy of the sediments. While the TPSMT distribution pointed to an increased anthropogenic input, the relative abundance of P species provided information on the P origin, incorporation processes, and evolution over time. This information, combined with chemical and mineralogical data, permitted to identify two different P sources: the agricultural input in the floating gardens area and the detrital input related to soil erosion.

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.

An experimental study about the effects of phosphorus loading in river sediment on the transport of lead and cadmium at sediment-water interface

Phosphorus (P) in the river sediment plays an important role in the fate and transport of heavy metals at sediment-water interface of the aquatic eutrophication environment. To explicate the effect of P loading, the sediments with different P contents were employed in this study to experimentally investigate the adsorption/desorption of Pb²⁺ and Cd²⁺ and the releasing behavior of P during the adsorption/desorption processes. Results illustrated a strong affinity between Pb²⁺ ions and the P-containing sediments in both single Pb and binary Pb + Cd systems. In single-metal systems, the Pb²⁺ adsorption capacities of all types of sediments (15.04-19.44 mg g^-1) were higher than those for Cd²⁺ (4.68-5.56 mg g^-1). While in binary-metal systems, the Pb²⁺ adsorption was slightly influenced by the coexisting Cd²⁺, but the Cd²⁺ adsorption capacities were decreased by over 5 times. Moreover, the adsorption amount and retention ability of Pb²⁺ on sediment were enhanced by increasing content of P in the sediment. Meanwhile, the releasing of P was also closely depended and significantly inhibited by the Pb²⁺ attached on the sediment. The P release amounts during the desorption processes of Pb- and Pb + Cd-loaded sediments were over 50 times lower than those from the raw sediments (sediments without heavy metals adsorbed), but the values decreased by a factor of two for the single Cd-loaded sediments. Furthermore, the results of X-ray photoelectron spectroscopy indicated the crucial role of P loading in Pb transport in the sediment and overlaying water. The findings in this study showed important implications for the transport of heavy metals and P at the sediment-water interface and offered new insights for further explicating the mechanisms of secondary pollution caused by heavy metals and P in aquatic eutrophication environment.

Hydroeconomic modeling of resource recovery from wastewater: Implications for water quality and quantity management

Emerging technologies and practices allow wastewater treatment facilities to recover valuable resources such as nutrients, energy, and recycled water during the wastewater treatment process. The ability to recover resources from wastewater introduces new tradeoffs in both water quality and quantity management. In particular, the fact that communities can obtain revenue from the sale of resources that are recovered from wastewater may help internalize the externalities of insufficient wastewater treatment. In this paper, we develop a theoretical model to characterize these tradeoffs within a hydroeconomic framework of optimal wastewater treatment with resource recovery, which is particularly well suited for applications in nutrient management. We use this model to derive analytical results that describe the economically optimal level of deployment, accounting for the fact that the technology or practice is costly and it generates benefits in the form of revenue from the recovered resource, as well as other societal benefits, such as improvements in human and ecosystem health. In addition, we present two examples using specific functional forms for treatment costs to demonstrate how the model can be applied to obtain general principles regarding societally optimal deployment. Our hydroeconomic framework can be used to explore the socioeconomic implications of strategies that target deployment of wastewater treatment with resource recovery, especially nutrients, at multiple scales.

Impact of P inputs on source-sink P dynamics of sediment along an agricultural ditch network

Phosphorus (P) loss from intensive dairy farms is a pressure on water quality in agricultural catchments. At farm scale, P sources can enter in-field drains and open ditches, resulting in transfer along ditch networks and delivery into nearby streams. Open ditches could be a potential location for P mitigation if the right location was identified, depending on P sources entering the ditch and the source-sink dynamics at the sediment-water interface. The objective of this study was to identify the right location along a ditch to mitigate P losses on an intensive dairy farm. High spatial resolution grab samples for water quality, along with sediment and bankside samples, were collected along an open ditch network to characterise the P dynamics within the ditch. Phosphorus inputs to the ditch adversely affected water quality, and a step change in P concentrations (increase in mean dissolved reactive phosphorus (DRP) from 0.054 to 0.228 mg L^-1) midway along the section of the ditch sampled, signalled the influence of a point source entering the ditch. Phosphorus inputs altered sediment P sorption properties as P accumulated along the length of the ditch. Accumulation of bankside and sediment labile extractable P, Mehlich 3 P (M3P) (from 13 to 97 mg kg^-1) resulted in a decrease in P binding energies (k) to < 1 L mg^-1 at downstream points and raised the equilibrium P concentrations (EPC₀) from 0.07 to 4.61 mg L^-1 along the ditch. The increase in EPC₀ was in line with increasing dissolved and total P in water, demonstrating the role of sediment downstream in this ditch as a secondary source of P to water. Implementation of intervention measures are needed to both mitigate P loss and remediate sediment to restore the sink properties. In-ditch measures need to account for a physicochemical lag time before improvements in water quality will be observed.

Using high-frequency phosphorus monitoring for water quality management: a case study of the upper River Itchen, UK

Increased concentrations of phosphorus (P) in riverine systems lead to eutrophication and can contribute to other environmental effects. Chalk rivers are known to be particularly sensitive to elevated P levels. We used high-frequency (daily) automatic water sampling at five distinct locations in the upper River Itchen (Hampshire, UK) between May 2016 and June 2017 to identify the main P species (including filterable reactive phosphorus, total filterable phosphorus, total phosphorus and total particulate phosphorus) present and how these varied temporally. Our filterable reactive phosphorus (considered the biologically available fraction) data were compared with the available Environment Agency total reactive phosphorus (TRP) values over the same sampling period. Over the trial, the profiles of the P fractions were complex; the major fraction was total particulate phosphorus with the mean percentage value ranging between 69 and 82% of the total P present. Sources were likely to be attributable to wash off from agricultural activities. At all sites, the FRP and Environment Agency TRP mean concentrations over the study were comparable. However, there were a number of extended time periods (1 to 2 weeks) where the mean FRP concentration (e.g. 0.62 mg L^-1) exceeded the existing regulatory values (giving a poor ecological status) for this type of river. Often, these exceedances were missed by the limited regulatory monitoring procedures undertaken by the Environment Agency. There is evidence that these spikes of elevated concentrations of P may have a biological impact on benthic invertebrate (e.g. blue-winged olive mayfly) communities that exist in these ecologically sensitive chalk streams. Further research is required to assess the ecological impact of P and how this might have implications for the development of future environmental regulations.

Fabrication and evaluation of a regenerable HFO-doped agricultural waste for enhanced adsorption affinity towards phosphate

Chemical modification of agricultural waste biomass has proved to be an economy and effective approach to capture phosphate ions, except for that under acidic conditions and highly competitive ion systems. According to this, a new nanocomposite (HFO@St+) was fabricated by incorporating nano-sized hydrous Fe(III) oxides (HFO) within aminated wheat straw in order to overcome the bottleneck. The optimal pH of phosphate uptake by HFO@St+ was greatly broadened and observed over a wide pH range between 2.0 and 7.0. The binary exchange reaction indicated that phosphate was strongly and preferably adsorbed by HFO@St+ with the separation factor K of phosphate over nitrate increasing from 0.23-1 or 0.20-0.26 to 2.5-38 or 2.5-15 for near neutral or acidic pHs, respectively. The sorption selectivity for HFO@St+ followed the order of phosphate > nitrate > chloride under experimental conditions. The presence of inorganic and organic ligands (SO₄ and HA) showed no significant effect on phosphate adsorption. XPS and FT-IR analyses were performed to explore the underlying mechanism of adsorption. The exhausted material could be regenerated with NaOH-NaCl solution for at least ten cycles, indicating that HFO@St+ can be used as a sustainable biomass product with excellent adsorption affinity for phosphate removal.

Electrochemical removal of phosphate in the presence of calcium at low current density: Precipitation or adsorption？

Phosphorus removal and recovery from waste streams are crucial to prevent eutrophication and sustain fertilizer production. As has been shown in our previous papers, electrochemical treatment has the potential to achieve this goal. However, the adoption of electrochemical approach is limited by its high energy consumption. Here, we investigate the possibility of electrochemical phosphorus removal at extremely low current density using graphite felt as the cathode. We found a current density as low as 0.04 A/m² can enhance the removal of phosphate in our electrochemical system. The removal of phosphate at extremely low current density resulted from electrochemical induced calcium phosphate precipitation and not by electrochemical adsorption. Electrochemical treatment of real domestic wastewater at 0.2 A/m² almost eliminates the precipitation of Mg(OH)₂ and limits the formation of CaCO₃. The recovered precipitates are dominated by calcium phosphate (59%), followed by 35% CaCO₃ and 6% Mg(OH)₂. The specific energy consumption of this newly electrochemical system is between 4.4 and 26.4 kW h/kg P, which is 2 orders of magnitude lower than our previous system (110-2238 kW h/kg P). Key factors for this improvement prove to be enlarged precipitation area and hydroxide flux retardation by graphite felt. Practically, our study offers a potential way to reduce the energy consumption in electrochemical removal of phosphate by using a graphite felt cathode and at a current density below 0.2 A/m². Fundamentally, our study contributes to the understanding of adsorption and precipitation in electrochemical removal of phosphate at an extremely low current density and with carbon-based electrodes.

Modeling phosphorus sources and transport in a headwater catchment with rapid agricultural expansion

Increasing riverine phosphorus (P) levels in headwaters due to expanded and intensified human activities are worldwide concerns, because P is a well-known limiting nutrient for freshwater eutrophication. Here we adopt the conceptual framework of the SPAtially Referenced Regressions On Watershed attributes (SPARROW) model to describe total phosphorus (TP) sources and transport in a headwater watershed undergoing rapid agricultural expansion in the upper Taihu Lake Basin, China. Our models, which include variables for land cover, river length, runoff depth, and pond density, explain 94% of the spatio-temporal variability in TP loads. Agricultural lands contribute the largest percentage (61%) of the TP loads delivered downstream, followed by forestland (21%) and urban land (18%). Future agricultural expansion to 15% of the total basin area is possible, which could lead to a 50% increase in TP loads. According to our analysis, an average of 24% of the total P export from the watershed landscape was intercepted in ponds. The exported amount was subsequently retained by tributaries and along the mainstem river, accounting for 14% and 43% of their inflowing loads, respectively. The remaining ∼6 tons yr^-1 of TP was eventually transported into Tianmu Lake, in Southeastern China. The model identified several sub-catchments as hotspots of TP loss and thus logical sites for targeted management. Our study underscores the significance of agricultural expansion as a factor that can exacerbate headwater TP pollution, highlighting the importance of landscapes to buffer TP losses from sensitive hilly catchments. This also points to a need for an integrated management strategy that considers the spatial-varying P sources and associated transport of TP in precious headwater resources.

An Integrative Framework to Control Nutrient Loss: Insights from Two Hilly Basins in China’s Yangtze River Delta

Rapid economic development and population growth in China’s Yangtze River Delta (YRD) are exerting significant environmental pressure on the region’s land and water, especially in hilly areas where many drinking water reservoirs have been constructed. These areas, which are characterized by steep slopes and thin soils, provide critical services, including flood control, water resource supply, food production, and recreational opportunities for nearby highly developed and heavily populated areas of the delta. We contrast two of these areas—the well-studied Tianmu Lake watershed and the much larger Qiandao Lake watershed. Both face similar challenges from nitrogen and phosphorus pollution due to rapid socio-economic development, but differences in watershed size and distinctions related to political boundaries influence the range of approaches available to maintain water quality. We review experiences of controlling nutrient pollution in these watersheds as case studies, and based on that information, propose an integrated framework to minimize nitrogen and phosphorus pollution in similarly challenged watersheds. The framework, which is designed to be generalizable rather than prescriptive, emphasizes source control, delivery interception, and fate management of nutrients.

Variable impacts of contemporary versus legacy agricultural phosphorus on US river water quality

Management of agricultural phosphorus (P) has been in effect for decades with limited improvements in downstream water quality. Accumulated legacy (historical) P sources can mobilize, serve as a continual nutrient source, and mask the effects of conservation efforts to improve water quality through reductions in contemporary agricultural inputs to surface waters. We used a proxy estimate of legacy sources and assessed if P lingering in soils long after application was a major contributor to river export. For most watersheds, contributions of legacy P to river export were small in comparison to contributions from contemporary surpluses (fertilizer + manure > crop uptake). Estimating the magnitude of contemporary versus legacy P sources provides critical information to support effective implementation of management plans.

Phosphorus (P) fertilizer has contributed to the eutrophication of freshwater ecosystems. Watershed-based conservation programs aiming to reduce external P loading to surface waters have not resulted in significant water-quality improvements. One factor that can help explain the lack of water-quality response is remobilization of accumulated legacy (historical) P within the terrestrial-aquatic continuum, which can obscure the beneficial impacts of current conservation efforts. We examined how contemporary river P trends (between 1992 and 2012) responded to estimated changes in contemporary agricultural P balances [(fertilizer + manure inputs)—crop uptake and harvest removal] for 143 watersheds in the conterminous United States, while also developing a proxy estimate of legacy P contribution, which refers to anthropogenic P inputs before 1992. We concluded that legacy sources contributed to river export in 49 watersheds because mean contemporary river P export exceeded mean contemporary agricultural P balances. For the other 94 watersheds, agricultural P balances exceeded river P export, and our proxy estimate of legacy P was inconclusive. If legacy contributions occurred in these locations, they were likely small and dwarfed by contemporary P sources. Our continental-scale P mass balance results indicated that improved incentives and strategies are needed to promote the adoption of nutrient-conserving practices and reduce widespread contemporary P surpluses. However, a P surplus reduction is only 1 component of an effective nutrient plan as we found agricultural balances decreased in 91 watersheds with no consistent water-quality improvements, and balances increased in 52 watersheds with no consistent water-quality degradation.

The problem of agricultural 'diffuse' pollution: Getting to the point

Despite introduction of legislation such as the EU Nitrates and Water Framework Directives (Directives 91/676/EEC and 2000/60/EC respectively), agricultural practices are often still regarded as a major factor in poor water quality across many EU member states. Elevated inputs of nutrients, organic matter and agro-chemicals to receiving waters from agricultural lands in particular are now widely recognised as potentially major causes of deteriorating water quality. Such inputs may emanate from diffuse sources such as agricultural fields, and small point- or intermediate-sources, including farmyards and farm trackways. However, while inputs from these latter intermediate sources may be substantial, their overall contribution to catchment-wide water quality at high temporal or spatial resolution is still largely unknown. In this study, we surveyed water chemistry throughout the multiple natural and artificial watercourses within a single drainage network at high spatial resolution in a predominantly dairy farming area in Southern Ireland. We found that most headwaters at the time of study were impacted by organic inputs via drainage ditches emanating from the vicinity of farmyards. These farmyard drains were found to have elevated concentrations of ammonium, phosphorus, potassium, suspended sediment and biochemical oxygen demand above background levels in the study catchment. Concomitant assessment of macro-invertebrate communities at study sites indicated that the ecological quality of headwaters was also impaired by these inputs. The individual and aggregate contributions of farmyard drains to water quality within a single catchment, when mapped at high spatial resolution, indicates that they constitute a major contribution to catchment scale 'diffuse' agricultural inputs. However, our data also suggest that engineering farmyard drains to maximise their retention and attenuation function may prove to be a cost-effective means of mitigating the effects of point source farmyard inputs.

Meta-analysis of non-reactive phosphorus in water, wastewater, and sludge, and strategies to convert it for enhanced phosphorus removal and recovery

Current and future trends indicate that mining of natural phosphorus (P) reserves is occurring faster than natural geologic replenishment. This mobilization has not only led to P supply concerns, but has also polluted many of the world's freshwater bodies and oceans. Recovery and reuse of this nuisance P offers a long-term solution simultaneously addressing mineral P accessibility and P-based pollution. Available physical, chemical, and biological P removal/recovery processes can achieve low total P (TP) concentrations (≤100 μg/L) and some processes can also recover P for direct reuse as fertilizers (e.g., struvite). However, as shown by our meta-analysis of over 20,000 data points on P quantity and P form, the P in water matrices is not always present in the reactive P (RP) form that is most amenable to recovery for direct reuse. Thus, strategies for removing and recovering other P fractions in water/wastewater are essential to provide environmental protection via P removal and also advance the circular P economy via P recovery. Specifically, conversion of non-reactive P (NRP) to the more readily removable/recoverable RP form may offer a feasible approach; however, extremely limited data on such applications currently exist. This review investigates the role of NRP in various water matrices; identifies NRP conversion mechanisms; and evaluates biological, physical, thermal, and chemical processes with potential to enhance P removal and recovery by converting the NRP to RP. This information provides critical insights into future research needs and technology advancements to enhance P removal and recovery.