Phosphorus (P) is essential to life, and as a key limiting nutrient, regulates productivity in terrestrial and aquatic systems. Strong geochemical interactions between P and other elements control the mobility and bioavailability of P in the environment, necessitating a coupled understanding of element cycles influencing P. At the same time P provides perhaps the most topical example of a critical resource element whose use is currently inefficiently managed. Leakage of mined P into the environment through a variety of processes (e.g. excess chemical fertiliser usage, or effluent discharges) is responsible for eutrophication and the acceleration of natural P cycling in terrestrial and aquatic systems. This puts P at the forefront of environmental and societal concerns and demands that our biogeochemical knowledge of P cycling ought to be developed through interdisciplinary research. This session aims to explore biogeochemical P cycling in the context of benefitting ‘systems understanding’ spanning terrestrial and aquatic compartments.
Topics included will explore:
Links between P and wider element cycles, for example with other macro- and micro- nutrients and controls of P availability through geochemical parameters such as Fe;
P cycling studies that bring into focus the interplay of biotic and abiotic controls within, and between, environmental compartments;
Drivers of change (climate, management, societal) acting on the coupling of P with other element cycles.
Processes, modelling and management against a background of the key issues for: P release from soil to plants; P release from soil to water; long term P supplies and the global P cycle.
Sustainable use of P, recovering of P from natural and waste water, managing P fluxes in agricultural areas.
vPICO presentations: Fri, 30 Apr
Present day phosphorus (P) enrichment and accelerated P cycling are changes superimposed on a dynamic Holocene history of landscape recovery from glaciation, changes in climate, and long-term low-intensity human activity. Knowledge of the changing role of human activity in driving long-term P dynamics is essential for understanding landscape P export and managing both terrestrial and aquatic environments.
Here we apply a simple process model to published lake sediment geochemical P records from 24 sites distributed across the Northern Hemisphere, producing Holocene records of landscape P yield and reconstructions of lake water TP concentrations. These records are a first attempt to produce values for average P export for the Northern Hemisphere over the Holocene, which can be used for constraining long-term landscape P cycling models.
Individual site trajectories of reconstructed Holocene landscape P yield and lake water TP varied systematically, with differences attributable to landscape development history, in turn driven by climate, human impact and other local factors. Three distinct traits are apparent across the records. Mountain sites with minimal direct human impact show falling Holocene P supply, and conform to conceptual models of natural soil development (Trait 1). Lowland sites where substantial (pre-)historic agriculture was present show progressively increasing Holocene P supply (Trait 2). Lowland sites may also show a rapid acceleration in P supply over the last few centuries, where high intensity land use, including settlements and farming, are present (Trait 3).
This long-term perspective is pivotal to understanding drivers of change in coupled terrestrial and aquatic P cycling. Our reconstructions of long-term lake water TP are particularly useful for target-driven management of aquatic systems.
How to cite: Moyle, M., Boyle, J., and Chiverrell, R.: Towards a history of Holocene P dynamics for the Northern Hemisphere using lake sediment geochemical records, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14897, https://doi.org/10.5194/egusphere-egu21-14897, 2021.
Lake sediment records offer the opportunity to quantify past changes in catchment P exports, information essential if we are to understand the long-term drivers that control P cycling. However, the interpretation of such records generally depends on the assumption that sediment P concentration profiles remain intact after burial. This assumption appears to be in conflict with the phenomenon of internal P loading, whereby P is exported from sediment to the water column. Here we apply a simple long-term mass balance model to published sediment record data from Søbygaard, a site that has an exceptionally high internal P loading, and an exceptionally well-studied sediment P record (Søndergaard and Jeppesen, 2019). Repeat cores collected from 1985 to 2004 constrain the temporal evolution of a sediment P peak arising from past sewage inflows, providing a critical test of our modelling approach. We find that useful sediment inference of long-term mean lake water TP is preserved in the sediment record, and predict also useful inference of long-term mean external P loading. Limitation on temporal resolution of the records is examined.
How to cite: Boyle, J. and Moyle, M.: Using lake sediment P records to estimate internal and external P loading and historic long-term lake water mean TP: a case study using published records from Søbygaard Sø, Denmark., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13278, https://doi.org/10.5194/egusphere-egu21-13278, 2021.
Phosphorus (P), an essential element for living organisms, is often considered as the limiting factor of eutrophication in aquatic environments, especially in reservoirs. In order to limit their environmental degradation and to meet the requirements of good ecological quality imposed by the European Water Framework Directive (WFD), actions have been implemented in the past decades to reduce the exogenous P influx to reservoirs. However, despite the decrease in external P inputs to the water from agriculture and domestic wastewater, eutrophication keeps expanding due to sedimentary P flux to the water column. Assessing the quality of sediments in reservoirs and the risk of of sedimentary P transfer to the water column is therefore a major issue. The POMOSED project aims to investigate the relevance of the WFD regulatory parameters, monitored since 2005, in the evaluation of sediment quality with respect to P. This work presents an inventory of sedimentary P contents in French reservoirs and identifies the factors contributing to the observed P variability from the physico-chemical sedimentary composition and the reservoirs and watersheds characteristics.
Statistical analyses were conducted on sedimentary composition data (total phosphorus (TP), iron (Fe), manganese (Mn), aluminium (Al), Kjeldahl nitrogen (NTK) and organic carbon (OC)) from 219 French reservoirs. The characteristics of their watersheds (geology, altitude, agricultural and artificial surfaces, …) and their morphology (e.g. depth, surface area, …) were also included in the statistical analyses.
The sediments showed large variability in the TP concentration varying from 172 to 4350 mg.kg-1 with mean and median values of 1310 and 1060 mg.kg-1 respectively. The variability of sedimentary TP was observed both spatially and temporally. We highlighted significant correlations of PT content with Fe, Al, NTK and OC. We pointed out that the geological substratum, the level of anthropization of the watershed and the depth of the reservoirs are driving factors for TP concentration in sediments. Therefore, the WFD monitoring allows to distinguish several typologies of sediment with respect to TP. The typologies inducing an enrichment in TP of the sediments are crystalline substrate sediments rich in Fe and OC, deep reservoirs inducing anoxia development and an anthropized watershed. However, an enrichment in TP of the sediments does not necessarily indicate an anthropic pressure as shown by the influence of geology and the composition of sediments. These results might be included into multiple linear models linking PT concentrations to the other elements concentrations (CO and Fe) and the different factors (geology > anthropization > reservoir depth).
How to cite: Lix, C., Rabiet, M., Grybos, M., Danis, P.-A., Blondeau, A., Louvet, F., and Deluchat, V.: Statistical study of sedimentary phosphorus content in French reservoirs and identification of P variability driving factors , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13066, https://doi.org/10.5194/egusphere-egu21-13066, 2021.
Phosphorus (P) is essential to life but a limiting nutrient in many ecosystems. Understanding the role of microorganisms in P cycling, especially the processes of P uptake and storage, is a major environmental issue. Only few models with a high capability to sequester P are known, mostly in marine environments. We thus need to improve our knowledge about other model of sequestration and especially in freshwater environments.
Freshwater magnetotactic bacteria (MTB) affiliated to the Magnetococcaceae family have been identified within the water column of Lake Pavin in France . Similarly, to the marine sulfoxidizers Thiomargarita and Beggiatoa [1, 2], they accumulate intracellular polyphosphates (PolyP) to a uniquely high extent, up to 90% of their cell volume. However, the MTB cocci inhabiting the water column of Lake Pavin harbor the specific capability to store P as PolyP below the oxygen detection limit (pO2 < 0.1%). Preliminary results tend to indicate that these MTB cocci represent the major population of MTB located right under the oxic-anoxic interface, in a zone of strong chemical and redox gradients. These gradients allow the study of the impacts of varying chemical conditions on the structuration of MTB populations and on the PolyP sequestration capability of MTB cocci.
We combined a variety of methods to identify the different MTB populations as a function of the water column depth and characterize their potential biogeochemical niches.
We used a new sampling system, an online pumping system, that allowed us to reach a better spatial (vertical) resolution , down to 20 cm. This sampling system was coupled to the measure of the physicochemical parameters of the water column (e.g. pO2, pH, redox, conductivity, FDOM, turbidity). We were therefore able to better estimate the impact of the chemical parameters on the MTB. We then sampled the water to measure the geochemical parameters using ICP-OES and to characterize MTB via optical and electron microscopy. Optical microscopy permitted the identification of the main populations of MTB and their concentrations, while electron microscopy allowed the characterization of the different magnetosome organisation and PolyP accumulation capability. We evidenced the stratification of the two main populations of MTB sequestrating two distinct sets of elements (PolyP and counterions, or amorphous calcium carbonates, respectively) and inhabiting different niches whose specific geochemical parameters were identifies using multivariate statistics.
Different environmental conditions, such as the concentration of dissolved sulfate, are correlated to the MTB cocci abundance. Moreover, the proportion of MTB cocci accumulating PolyP is negatively correlated to the concentration of dissolved sulfur. These results bring into light the potential link between the sulfur metabolism of these bacteria and their capability to sequestrate P as PolyP. Moreover, our reccurent observations of intracellular sulfur granules suggest that this new bacterial model for P sequestration below the oxygen detection limit are sulfoxidizers,
Genomic analyses will be done in the future to allow further comprehension on molecular mecanisms and PolyP formation.
 Brock J, Schulz-Vogt HN. (2011) ISME Journal 5, 497-506.  Mubmann M et al. (2007) PLoS Biology 5(9), e230.  Rivas-Lamelo S et al. (2017) Geochem. Persp. Let. 5, 35–41.  Busigny et al., 2021 Env. Microbiol. 1462-2920 .
How to cite: Bidaud, C., Monteil, C. L., Menguy, N., Busigny, V., Jézéquel, D., Viollier, E., Travert, C., Skouri-Panet, F., Benzerara, K., Lefevre, C. T., and Duprat, E.: Population structure of magnetotactic bacteria forming intracellular polyphosphates in the water column of Lake Pavin, a freshwater ferruginous environment, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11061, https://doi.org/10.5194/egusphere-egu21-11061, 2021.
Phosphorus (P) is the key and limiting nutrient in the eutrophication of freshwater resources. Modeling P retention in lakes using steady-state mass balance models (i.e. Vollenweider-type models) provides insights into the lake P management and a simple method for large-scale assessments of P in lakes. One of the basic problems in the mass balance modeling of P in lakes is the removal of P from the lake water column by settling. A fraction of the incoming P into the lake from the watershed is associated with fast-settling particles (e.g. sediment particles) that result in the removal of that fraction of P quickly at the lake entrance. However, existing models considering a constant fraction of fast-settling TP for all lakes are shown to result in overestimation of the retention of P in lakes with short hydraulic residence time. In this study, we combine a hypothesis of the fast- and slow-settling P fractions into the steady-state mass balance models of P retention in lakes. We use a large database of lakes to calibrate the model and evaluate the hypothesis. The results of this work can be used for the improvement of the prediction power of P retention models in lakes and help to better understand the processes of P cycling in lakes.
How to cite: Khorasani, H. and Zhu, Z.: Investigating Fast- and Slow-settling Phosphorus Fractions in Lakes using Steady-state Modeling, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13910, https://doi.org/10.5194/egusphere-egu21-13910, 2021.
The dynamics of sediment phosphorus (P) remobilization and recycling in many polymictic systems due to distinct external and internal loading conditions are poorly understood. Here we used a multifaceted approach of quantifying sediment P binding forms and corresponding metal contents in sediment cores down to 30 cm from 8 different locations at Lake of Woods (LOW) in different seasons. We also measured pH, redox potential and dissolved oxygen uptake across the sediment-water interface and the concentration of nutrient and metals in pore water at different depths. Additionally, we applied a reaction-transport diagenetic model to construct the spatial and temporal trend of internal P loading in response to environmental variations. The summer diffusive fluxes of P ranged between 3 and 83 µmol m-2 d-1 whereas the winter fluxes were lower ranged from 0.1 to 0.35 µmol m-2 d-1. P recycling efficiency were 13% to 77%. P bound to redox sensitive iron (Fe)-P binding forms in sediments were the major source of P release in all stations, while P immobilization is controlled by redox-insensitive calcium (Ca)-P phases. The modeling results supported the notion that P release was mostly driven by the diagenetic recycling of redox sensitive and organic bound P.
How to cite: Alam, M. S., Zastepa, A., and Dittrich, M.: Phosphorus recycling and retention in Lake of the Woods: Reactive-transport diagenetic modeling across spatial and temporal Scales, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14068, https://doi.org/10.5194/egusphere-egu21-14068, 2021.
Phosphate (P) as an essential resource for food production is becoming scarce. Its uncontrolled loss from agricultural areas is in conflict with the principles of a circular economy. Enhanced loading of surface waters with P is the main cause for eutrophication and presents a key challenge in meeting the objectives of the EU Water Framework Directive. Understanding and controlling environmental P fluxes therefore is key to target both problems, to develop new methods and approaches to manage environmental P fluxes, and to improve surface water quality.
In March 2019 the EU Marie Sklodowska-Curie Innovative Training Network P-TRAP has been launched. P-TRAP establishes a framework of partners from multiple science and engineering disciplines. Integration of non-academic partners from various stakeholder groups into the P-TRAP consortium paves the way for direct implementation of the acquired knowledge. The project is targeting the diffuse flux of phosphate (P) into surface waters, i.e. the problems of understanding and controlling environmental P fluxes. P-TRAP aims to develop new methods and approaches to trap P in drained agricultural areas and in the sediments of eutrophic lakes. Trapping of P involves the application of iron(Fe)-containing by-products from drinking water treatment. P-TRAP aspires the ideas of a circular economy and aims at recovering the retained P in agricultural systems. Novel microbial technologies will be developed to convert P-loaded Fe-minerals into marketable fertilizers whose suitability will be evaluated. The P-TRAP technologies have in common that they rely on the naturally strong connection between P and Fe and the innovative P-TRAP strategies will be underpinned by process-orientated investigations on the behaviour of P during the transformation of Fe minerals. The latter are key in trapping and recycling of P in agricultural systems and lakes. Here we will present the structure and the planned research of the project, including a first overview of achievements of the first two years.
How to cite: Behrends, T. and Walter, S.: P-TRAP – Reducing diffuse phosphorus input to surface waters, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3317, https://doi.org/10.5194/egusphere-egu21-3317, 2021.
Sulfidation of Fe(III) (hydr)oxides plays an important role in the phosphate(P) cycle in oceans and lakes. P has a strong affinity to Fe(III) (hydr)oxides and can either become incorporated via coprecipitation or adsorb onto the solid’s surface. Consequently, P enters aquatic sediments often associated with Fe(III) (hydr)oxides. In the sediments, when sulfidic conditions are prevalent, the reaction of Fe(III) (hydr)oxides with sulfide can lead to the formation of Fe(II) sulfides and P release. The released P can, in turn, diffuse upwards into the overlying water and thus aggravate eutrophication in water bodies. Although it is generally expected that P is released during the sulfidation of P containing Fe(III) (hydr)oxides, questions remain whether part of the P could be re-adsorbed onto the products of the sulfidation reaction, or trigger the formation of vivianite  (Fe3(PO4)2 · 8H2O). Furthermore, it is still unclear how the rates of P release are related to the progress of the sulfidation reaction.
In order to study the P dynamics during sulfidation, we performed experiments in flow-through reactors with P-bearing lepidocrocite (γ-FeOOH). The inflow solution contained sulfide and we monitored P, dissolved S(-II) and Fe(II) in the outflow to follow the progress of sulfide consumption and P release. Sulfide concentrations in the outflow of reactors containing lepidocrocite with adsorbed P tended to be lower than in the outflow of reactors with lepidocrocite but no P. Consequently, the preliminary results indicate that consumption rates of sulfide by the reaction with lepidocrocite were lower when P was present, implying that adsorbed P reduced the rates of sulfidation. At the beginning of the experiment, P concentrations in the outflow remained low, then started to increase and reached a steady state after passing several reactor volumes. This indicates that P was not instantaneously released upon sulfide adsorption but only as lepidocrocite sulfidation progressed. At the end of the experiment, the fraction of P released from the reactor was significantly lower than the fraction of lepidocrocite that had reacted with sulfide(calculated from cumulative sulfide consumption and solid phase characterization). This implies that part of the P has been retained in the solid phase despite the reductive transformation of lepidocrocite. The underlying mechanisms of P retention and the complex relationship between the rates of sulfide consumption and P release will be discussed.
 Jilbert and Slomp, 2013. Geochimica et Cosmochimica Acta 107, 155-169.
How to cite: Ma, M., Voegelin, A., and Behrends, T.: Kinetics and mechanism of phosphate release upon sulfidation of phosphate-containing lepidocrocite, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13645, https://doi.org/10.5194/egusphere-egu21-13645, 2021.
The decline of surface water quality due to excess phosphorus (P) input is a global problem of increasing urgency. Finding sustainable measures to restore the surface water quality of eutrophic lakes with respect to P, other than by decreasing P inputs, remains a challenge. The addition of iron (Fe) salts has been shown to be effective in removing dissolved phosphate from the water column of eutrophic lakes. However, the resulting changes in biogeochemical processes in sediments as well as the long-term effects of Fe additions on P dynamics in both sediments and the water column are not well understood.
In this study, we assess the impact of past Fe additions on the sediment P biogeochemistry of Lake Terra Nova, a well-mixed shallow peat lake in the Netherlands. The Fe-treatment in 2010 efficiently reduced P release from the sediments to the surface waters for 6 years. Since then, the internal sediment P source in the lake has been increasing again with a growing trend over the years.
In 2020, we sampled sediments at three locations in Terra Nova, of which one received two times more Fe during treatment than the other two. Sediment cores from all sites were sectioned under oxygen-free conditions. Both the porewaters and sediments were analysed for their chemical composition, with sequential extractions providing insight into the sediment forms of P and Fe. Additional sediment cores were incubated under oxic and anoxic conditions and the respective fluxes of P and Fe across the sediment water interface were measured.
The results suggest that Fe and P dynamics in the lake sediments are strongly coupled. We also find that the P dynamics are sensitive to the amount of Fe supplied, even though enhanced burial of P in the sediment was not detected. The results of the sequential extraction procedure for P, which distinguishes P associated with humic acids and Fe oxides, as well as reduced flux of Fe(II) across the sediment water interface in the anoxic incubations, suggest a major role of organic matter in the interaction of Fe and P in these sediments.
Further research will include investigations of the role of organic matter and sulphur in determining the success of Fe-treatment in sequestering P in lake sediments. Based on these data in combination with reactive transport modelling we aim to constrain conditions for successful lake restoration through Fe addition.
How to cite: Münch, M., van Kaam, R., As, K., Peiffer, S., ter Heerdt, G., Slomp, C. P., and Behrends, T.: Effects of Fe addition on sediment P dynamics in a eutrophic lake, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4941, https://doi.org/10.5194/egusphere-egu21-4941, 2021.
As global reserves of phosphorus (P) become scarce, recycling of P will be key to sustainable food production in future. The hypolimnetic withdrawal and purification circuit (HWPC) is a novel method that aims to remove and capture P accumulated in the near-bottom water of eutrophic lakes. Similar to the basic principle of wastewater treatment, the lake water is treated for the precipitation of P and other elements, and the formed particles are collected in a filtering unit while the purified water flows back into the lake. The method has been tested in a pilot project at Lake Kymijärvi, southern Finland.
In the current study, we observed the efficiency of three different water treatments in the HWPC in terms of P precipitation: 1) water aeration; 2) aeration + Ca(OH)2 addition; 3) aeration + tannin-based biopolymer addition. Moreover, we studied the chemical composition of the precipitate formed in each treatment to understand its potential for P recycling. The aim of the study was to provide a better understanding to further develop and apply techniques to recover and recycle P from eutrophic lakes.
How to cite: Silvonen, S., Niemistö, J., Myyryläinen, J., Huotari, S., Nurminen, L., Horppila, J., and Jilbert, T.: Investigating methods of phosphorus recovery from eutrophic lakes through hypolimnetic withdrawal and purification, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6188, https://doi.org/10.5194/egusphere-egu21-6188, 2021.
The cycling of phosphorus in terrestrial and aquatic systems is tightly coupled to the redox-cycling of iron (Fe). The oxidation of dissolved Fe(II) in natural waters leads to the precipitation of amorphous to poorly crystalline Fe(III)-solids that can bind phosphate (P) and other nutrients as well as toxic compounds. The EU project P-TRAP is aimed at developing methods to reduce diffuse P inputs into surface waters to mitigate eutrophication, by using Fe-rich byproducts from water treatment (https://h2020-p-trap.eu/). Within this project, we study mechanistic aspects of the formation and transformation of P-containing Fe(III)-precipitates and their implications for P retention in soils and water filters.
Freshly formed Fe(III)-precipitates are metastable and can transform into more stable phases over time. This may lead to the release of co-precipitated P. In laboratory experiments, we assessed how Ca, Mg, silicate (Si) and P impact on the formation and transformation of Fe oxidation products (at 0.5 mM Fe) and their P retention in synthetic bicarbonate-buffered groundwater. The time-resolved experiments were performed in electrolyte solutions containing Na, Ca, or Mg as electrolyte cation, without or with Si (at molar Si/Fe of 1), and P (P/Fe of 0.3 and 0.05). Changes in dissolved element concentrations over time were linked to changes in the structure and composition of the Fe(III)-solids; with Fe coordination probed by X-ray absorption spectroscopy, mineralogy by X-ray diffraction, and nano-scale morphology and composition heterogeneity by transmission electron microscopy with energy-dispersive X-ray detection.
The freshly-formed Fe(III)-precipitates were mixtures of amorphous Fe(III)-phosphate with either poorly-crystalline lepidocrocite (without Si) or Si-containing ferrihydrite (with Si). Increases in dissolved P during aging were largest in Na electrolytes without Ca, Mg or Si, and were linked to the transformation of amorphous Fe(III)-phosphate into lepidocrocite with a lower P retention capacity than Fe(III)-phosphate. In Ca- and to a lesser extent Mg-containing electrolytes, the Ca or Mg stabilized the amorphous Fe(III)-phosphate and thereby reduced P release over time. The presence of Si increased initial P uptake and inhibited P release during aging by causing the formation of Si-ferrihydrite with higher P sorption capacity than lepidocrocite formed in the absence of Si. In conclusion, the extents to which P is trapped by fresh Fe(III)-precipitates and released during aging can be attributed to the individual and coupled impacts of Ca, Mg and Si on Fe(III)-precipitate structure, stability and transformation.
In continuing work, we aim to expand our work to study how organic compounds impact on the formation and colloidal stability of Fe(III)-precipitates and P retention.
How to cite: Nenonen, V., Kaegi, R., Hug, S. J., Mangold, S., Göttlicher, J., Winkel, L., and Voegelin, A.: Effects of aging and transformation of Fe(III)-precipitates on the retention of co-precipitated phosphate, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13281, https://doi.org/10.5194/egusphere-egu21-13281, 2021.
The recovery of PO4 from wastewaters by using biochar proves not to be completely satisfactory. The surface of the biochar is typically negatively charged, which prevents the adsorption of PO4. For this reason, mixtures of biochar and natural carbonate materials have been tested as a novel sorbent material for PO4 recovery from both synthetic-and waste- water. The goal of the research is to obtain a PO4 based complex starting from natural second-generation materials such as food industry byproducts, plants and other residues to prepare fertilisers compliant to the component material category CMC 6 defined in the Regulation (EU) 2019/1009/EU It has to be noted that natural carbonate materials are not pure CaCO3, but present small impurities that contribute to modify their properties. Therefore, the use of carbonate materials obtained from different sources can lead to different performances when it comes to PO4 removal from wastewaters.
In this work we present results of PO4 removal obtained from a mixture of biomass and different carbonate materials. The mixture has been treated through a specific thermal protocol to obtain two different calcium-oxide rich charcoals here named composites C1 and C2. Initially, each composite was added to synthetic waters with different PO4 concentration, with a composite:water ratio of 1:1000. The initial concentrations of PO4 were 10, 100 and 1000 mg/l. After treatment with the composite, regardless of whether C1 or C2 was used, the PO4 concentration in the waters with initial concentration of 10 and 100 mg/L was nearly zero, with pH values at equilibrium around 11.9. The treatment of the water with initial PO4 concentration of 1000 mg/l shows a reduction of 20% and 40% with C1 and C2, respectively, with final pH values around 7.8.
After addition of the composites to the water, the solutions present very high pH values except for the water with the highest concentration. Although this is an optimal situation for the removal of PO4, it leads to two problems. First, the filtered water is not suitable for direct disposition in sewers, since the pH is higher than the limit established by the wastewater legislation (9.5). Second, a pH value larger than 9 determines the precipitation of PO4 regardless of the presence of the composite, which suggests that the PO4 is not adsorbed by the composites, thus not leading to the desired complex
In order to quantify the exact amount of PO4 adsorbed by the composite, the experiments have been repeated under controlled pH, keeping it around a value of 7 by the use of a mild acid. In this condition, after 1h treatment, 50% of phosphate was removed and bound to the composite
The work intends to present the results at laboratory scale and next steps at higher TRL.
How to cite: Carlini, C., Primante, A., Greggio, N., Balugani, E., Contin, A., and Marazza, D.: PO4 recovery using mixtures of biochar and carbonate materials, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2716, https://doi.org/10.5194/egusphere-egu21-2716, 2021.
The vital element phosphorus (P) invokes two extremes in the environment; (i) scarcity, as a non-renewable resource and as a poorly bioavailable limiting nutrient for plants, and (ii) excess, as cause of eutrophication in surface waters. To tackle both these problems, the inter-relationship between the P and the iron (Fe) cycle is widely discussed with a special interest in the ferrous iron-phosphate mineral vivianite (Fe(II)3(PO4)2*8H2O). Vivianite forms naturally in sub-/anoxic environments with high Fe(II) and PO4 concentrations, and is a sink to the dissolved P concentration. On the other hand, vivianite has been proposed as a P source through application as a slow-release Fe-P fertilizer prepared from recycled P. However, vivianite is a metastable mineral under oxic conditions; it readily oxidizes, notably changing color from white to dark blue/purple. This transformation changes the properties of the mineral (surface), and thus its suitability as a fertilizer.
We investigated the oxidation and dissolution of vivianite under different environmental conditions with the aim of developing a mechanistic and kinetic model that relates the oxidation process with dissolution rates. Moreover, the effect of secondary mineral precipitation on the ‘net’ availability of P and Fe for soil organisms was also studied. Quantifying dissolution rates and secondary mineral formation under environmentally relevant conditions provides the fundamental knowledge needed to assess the suitability of vivianite as Fe and P fertilizer. This information is also paramount to the idea of a circular economy concept: starting with the reduction of P loads of (waste) waters and using the byproduct vivianite as P source for fertilization.
How to cite: Metz, R., Kumar, N., Schenkeveld, W., and Kraemer, S.: Biogeochemical mechanisms influencing the bioavailability of P and Fe from vivianite, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12798, https://doi.org/10.5194/egusphere-egu21-12798, 2021.
Contradictory data exists on the impact of biosolids incorporation on ortho-phosphate (IP) binding to arid and semi-arid Mediterranean soils. We used two mature organic amendments (OA) with low IP solubility to study the effect of OAs addition on the IP adsorption parameters of Mediterranean soils. Seven soils, encompassing a wide range of mechanical, chemical and mineralogical properties, were mixed with a biosolids compost (DSC) at 9:1 ratio (w/w dry weight basis). The soils and mixtures were either incubated for seven years under constant temperature (30℃) and moisture content (80% of 30 kPa tension) or were unincubated. IP adsorption parameters were also measured in not-incubated soil DSC mixtures at 97:3 ratio. In all the soils, DSC addition significantly increased the IP adsorption capacities (by Langmuir's model) from 126 to 397 mg IP kg-1 in the soils to 254 through 669 mg IP kg-1 in the soil-DSC-mixtures. The increased capacities were accompanied by a significant decrease in the adsorption affinities, from values of 0.12 to 1.02 L kg-1 in the soils to 0.05 and 0.25 L kg-1 in the mixtures. Biosolids addition at 97:3 ratio had a similar effect on the IP adsorption parameters as the 9:1 ratio. These two IP adsorption parameters continued to change along the incubation. The other OA tested was a municipal solid waste compost (MSWC), which was mixed with two montmorillonitic soils at 97:3 ratio (soil:OA), one with high lime and low Al/Fe-oxides contents and the other with low lime and high Al/Fe-oxides content. OA addition increased the IP adsorption capacity in the lime-rich soil, while it did not affect the other. Overall, our results show that the solid matrix of the two OA's used by us embodied IP adsorption sites, most likely through metal bridging with Ca2+, which increases the total adsorption capacity of the soil-OA mixture. Concomitantly, DOM from the OAs competes with IP on adsorption sites reducing the soil's adsorption capacity. The magnitude of each one of these two processes depends on the soil and the added OA characteristic and will determine the overall change in the soil's capability to retain IP after biosolids incorporation.
How to cite: Freiberg, Y., Fine, P., Borisover, M., and Baram, S.: Biosolids Incorporation in Mediterranean Soils Increase Phosphate Adsorption, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16486, https://doi.org/10.5194/egusphere-egu21-16486, 2021.
Understanding how the solubility of forms of inorganic and organically-complexed phosphorus (P) in agricultural soil is affected by inputs of organic matter (OM) could inform decisions on sustainable future farming practices. Different forms of OM provide organic P, carbon (C) and other nutrients to the system at different rates, depending upon their recalcitrance to decomposition, and the stoichiometric balance of elements between soil, OM amendment and microbial requirements.
We describe an 18-month pot experiment that tested the hypothesis that additions of organic matter will affect the solubility of P forms in soil. Mesocosms (~30 kg soil) of two agricultural top-soils, of moderate and low P availability, were amended with a commercial humic soil amendment (lignite) or crop residue (barley straw) at two addition levels. Treatments with/without chemical P fertilizer were superimposed on OM treatments. The system was planted with Lolium perenne (perennial rye grass) and exposed to a natural rain and temperature regime. Leachate was collected and analyzed for soluble P, nitrogen and dissolved organic C (DOC) at 6 weekly intervals in order to investigate solubility over time. Destructive sampling at the end of the experiment yielded plant and soil samples for comparison of C, N and P stoichiometry between the treatments.
Initial results showed increases in leachate DOC relating to crop residue OM treatments and a positive effect of P fertilizer on plant biomass in the low P soil. Concentrations of dissolved P in leachate were higher in the moderately P-sorbing soil compared to the highly P-sorbing soil. Ongoing analysis includes measures of biological activity including soil microbial biomass C, N and P by fumigation-extraction and soil phosphatase activity. Chemical measures include total C, N and P, soil carbon forms using Fourier-transform infrared spectroscopy (FTIR), total organic P and water and acid ammonium oxalate extractions. Interpretation of the final results will consider how the release of C and nutrients from OM and their subsequent impact on the system, are controlled by microbial activity and macronutrient stoichiometry. These results should help to inform future research into improving P utilization in agriculture through balancing nutrient ratios to regulate nutrient cycling. Such research seeks to improve agronomic P efficiencies alongside wider benefits associated with the drive to increase soil C.
How to cite: Tweedie, A., Haygarth, P. M., and Stutter, M.: Is the solubility of inorganic and organically complexed phosphorus in agricultural soils affected by chemical fertilizer and organic carbon additions?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7075, https://doi.org/10.5194/egusphere-egu21-7075, 2021.
Phosphorus solubilisation with varying drying and rewetting stresses under four contrasting soils from different regions of China
Nyamdavaa Mongol1, Jianbo Shen2, Philip M. Haygarth1
1Lancaster Environment Centre, Lancaster University, Lancaster, LA1 4YW, United Kingdom.
2Department of Plant Nutrition, China Agriculture University, Key Laboratory of Plant-Soil Interactions, Beijing 100193, PR China
We tested the hypothesis that agricultural soils with a recent history of drying and rewetting (DRW) can trigger phosphorus (P) solubilisation in the rhizosphere, with a subsequent growth response of maize (Zea mays). Specifically, it aimed at investigating a possible delayed effect of DRW stresses on the soils by studying the relationship between P solubilisation in the rhizosphere, plant P acquisition and performance, and root growth under different types of agricultural soils with the previous history of a series of DRW events. The soils were collected from four different agricultural regions of China, Shandong, Chongqing, Heilongjiang and Beijing (sieved <2 mm), and then treated with four varying cycles of DRW events prior to the experiment to raise levels of soil biotic and abiotic activities. A controlled pot experiment was conducted in order to establish the Olsen’s P concentration in the soil, maize shoot P concentrations, root morphology and other rhizosphere parameters, for a duration of 43 days after planting. The results show a positive relationship between plant biomass, plant P concentration and Olsen`s P. The effect was most clearly demonstrated by the level of plant growth and their biological performance in the rhizosphere, as the plants responded better in the soil with a DRW background than to a soil that did not have a history of DRW in the past. Notably, the most positive results were obtained from the Haplic Phaeozems soil of Heilongjiang, leading to an acceptance of the hypothesis. However, the soluble P concentration and plant growth response varied depending on P application rates and soil types.
How to cite: Mongol, N.: Phosphorus solubilisation with varying drying and rewetting stresses under four contrasting soils from different regions of China , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13596, https://doi.org/10.5194/egusphere-egu21-13596, 2021.
Phosphorus (P) is critical to our food production systems with many crop systems dependent on continual inputs to meet yield demands. However, a consequence of the widespread application of P to agricultural soils in the past 60 years has led to concerns about the long-term sustainability of P fertiliser supply and to P being transferred from soil systems to watercourses, causing diffuse pollution. This highlights the multi-scaled and interdisciplinary nature of the past, present and future of P management.
The aim of this research is to define a starting framework to consider the best ways to develop a model that addresses the contemporary understanding of P processes, integrating the needs of the crop, with biogeochemical and hydrological modelling considerations, going beyond P transfer to the role of P in both food and water challenges.
So, this review explores some of the current P models and the future opportunities for expanding their representation of P processes in agricultural systems. This goes beyond nesting existing models and reshapes approaches to posing research and modelling questions to achieve P models that cross disciplinary boundaries and have meaning and usability in practice. As part of this contribution, we welcome modellers and P scientists to come forward and help drive this complex issue of P in agriculture.
How to cite: Davies, J. M., Janes-Bassett, V., Blackwell, M., Burgess, A., Davies, J., and Haygarth, P. M.: Time to re-think agricultural phosphorus modelling for the 2020s , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15873, https://doi.org/10.5194/egusphere-egu21-15873, 2021.
Phosphorus is closely linked to other nutrient cycles, notably carbon and nitrogen, therefore, to understand potential risks to food production models are required that simulate integrated nutrient cycling over long timescales. The soil-plant system model N14CP meets these requirements and simulates both semi-natural and agricultural environments. N14CP has been validated both spatially and temporally across a range of long-term agricultural experimental sites comparing soil C, N and P, and crop yields, and in most instances performs well. However, under experimental conditions where N is applied in the absence of P, the model indicates exhaustion of P reserves and a decline in yields that is not observed at these sites, highlighting a gap in the model process representation. Potential sources of this ‘missing P’ such as enhanced atmospheric deposition, weathering and flexible plant stoichiometries were explored yet cannot account for this deficit. We hypothesise that access of organic P through other mechanisms not fully represented within the model, such as phosphatase enzymes, could be part of this explanation.
In order to test this, we conducted a meta-analysis of phosphatase enzyme activity in agricultural settings, comparing response to P sufficient and deficient conditions. Results suggest phosphatase enzyme activity is higher in P deficient conditions compared to inorganic P addition, yet lower compared to organic P addition. Meta-regression analysis indicates magnitude of P addition and pH of substrate are significant factors influencing enzyme response. However, due to numerous additional processes and adaption strategies in response to P deficiency and the difficulty isolating the role of phosphatase enzymes it is not possible to determine the degree to which this mechanism alone accounts for the missing P. We discuss the continuing need for additional empirical evidence to understand the cycling of organic P, and the development of models to include these processes to inform sustainable land management and ensure long-term food security.
How to cite: Janes-Bassett, V., Haygarth, P., Blackwell, M., Mezeli, M., Stewart, G., Blair, G., and Davies, J.: Integrated carbon-nitrogen-phosphorus cycling for sustainable agriculture – a knowledge gap and investigation of the role of phosphatase enzymes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3037, https://doi.org/10.5194/egusphere-egu21-3037, 2021.
Phosphorus (P) limitation is prevalent around the world,primarily because most soil P have low bioavailability. In P poor ecosystems, deposition of P-rich desert dust is recognized as a major component of the P cycle. The acknowledged paradigm is that plants acquire P deposited in soil primarily via their roots. We tested whether, and to what extent, plants acquire P directly from dust deposited on their leaves and what are the underlining uptake mechanisms of insoluble P. P-rich dust was applied to P sufficient and P deficient chickpea, maize and wheat plants and was compared to plants which received inert silica powder. Foliar application of dust doubled the growth of P stressed chickpea and wheat, two crops originating near the Syrian Desert. P deficiency enhanced the acquisition of insoluble P through series of leaf modifications that increased foliar dust capture, acidified the leaf surface and, in chickpea, enhanced exudation of P-solubilizing organic acids. In in-situ trials, we demonstrated that the modifications of leaf pH and exudation of oxalic and malic acids substantially promoted P solubilisation from dust. Foliar responses did not occur in maize and in P sufficient plants which displayed only a marginal response to dust. Our results demonstrate that foliar uptake of P from dust can be an alternative P acquisition pathway in P-deficient plants. Interestingly, the abovementioned foliar responses are comparable to known P uptake root responses. Given that P limitation is almost universal, foliar P uptake pathway will have significant ecological and agricultural implications.
How to cite: Erel, R., Tiwari, S., Shtein, I., and Gross, A.: Phosphorus in Aeolian desert dust deposits can be captured, dissolved, and absorbed by plant leaves, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3071, https://doi.org/10.5194/egusphere-egu21-3071, 2021.
Tropical rainforests play an important role in sequestering carbon (C) and mitigating climate warming. Many terrestrial biosphere models (TBMs) estimate productivity increase in tropical rainforests due to the CO2 fertilization effect. However, most TBMs neglect phosphorus (P) limitation on tropical rainforest productivity. Here, we used a process-based Dynamic Land Ecosystem Model with coupled C-N-P dynamics (DLEM-CNP) with varied Vcmax25 to examine how P limitation has affected C fluxes of tropical rainforests to environmental and anthropogenic factors, including N deposition, land-use changes, climate variability, and atmospheric CO2, during 1860-2018. The model results showed that consideration of the P cycle reduced the response of tropical rainforests gross primary production (GPP) by 25% and 39%, net primary production (NPP) by 25% and 43%, and net ecosystem production (NEP) by 21% and 41% to the CO2 fertilization effect relative to CN-only and C-only models. The DLEM-CNP estimated that the tropical rainforests had a GPP of 41.1 + 0.5 Pg C year-1, NPP of 19.7 + 0.3 Pg C year-1 and NEP of 0.44 + 0.34 Pg C year-1 under 1860-2018 environmental conditions. Factorial experiments with DLEM-CNP suggested that deforestation has stronger impacts on GPP and NPP reduction compared to the enhanced GPP and NPP benefiting from the CO2 fertilization effect. Additionally, tropical rainforests NEP showed a continuously increasing trend owing to the CO2 fertilization effect. Our study highlights the importance of P limitation on the C cycle and the weakened CO2 fertilization effect due to nutrients limitation in the tropical rainforests.
How to cite: Wang, Z., Tian, H., Pan, S., Shi, H., Yang, J., Kalin, L., Anderson, C., and Liang, N.: Phosphorus limit to the CO2 fertilization effect in tropical rainforests as informed from a coupled biogeochemical model, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10508, https://doi.org/10.5194/egusphere-egu21-10508, 2021.
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