BG1.5 | Interdisciplinary session on the global phosphorus cycle

BG1.5

Interdisciplinary session on the global phosphorus cycle

Phosphorus (P) is an essential element for life on Earth and is tightly cycled within the biosphere. Throughout geological history, P availability has regulated biological productivity with impacts on the global carbon cycle. Today, human activities are significantly changing the natural cycling of P. Phosphate mining has depleted geological P reserves, while increased inputs of P to terrestrial ecosystems have enhanced fluxes of P to lakes and the oceans.

Direct anthropogenic perturbations of the P cycle, coupled with other human-induced stresses, have impacted numerous environments. Forest ecosystems may be losing their ability to recycle P efficiently, due to excessive N input, extensive biomass removal, and climatic stress. Soils, which serve as the biogeochemical fulcrum of the terrestrial P cycle, have been greatly altered by fertilizer use in recent decades. Changes in the P cycle on land impact on the magnitude and timing of P fluxes into aquatic ecosystems, influencing their trophic state. Burial in sediments returns P to the geological sink, eventually forming economically viable P deposits. Throughout the P cycle, redox conditions play a key role in transformations and mobility of P.

This interdisciplinary session invites contributions to the study of P from across the geosciences, and aims to foster links between researchers working on different aspects of the P cycle. We target a balanced session giving equal weight across the continuum of environments in the P cycle, from forests, soils and groundwater, through lakes, rivers and estuaries, to oceans, marine sediments and geological P deposits. We welcome studies of both past and present P cycling, with a focus on novel techniques and approaches.

Share:

Co-organized by OS3/SSS9

Convener: Tom Jilbert | Co-conveners: Sonya Dyhrman, Federica Tamburini, Phil Haygarth, Melanie Münch

Orals

| Tue, 25 Apr, 10:45–12:30 (CEST)

Room 1.15/16

Posters on site

| Attendance Wed, 26 Apr, 08:30–10:15 (CEST)

Hall A

Posters virtual

| Attendance Wed, 26 Apr, 08:30–10:15 (CEST)

vHall BG

Orals: Tue, 25 Apr | Room 1.15/16

The oral presentations are given in a hybrid format supported by a Zoom meeting featuring on-site and virtual presentations. The button to access the Zoom meeting appears just before the time block starts.

Chairpersons: Tom Jilbert, Melanie Münch, Federica Tamburini

10:45–10:50

5-minute convener introduction

10:50–11:10

EGU23-7734

solicited

Highlight

On-site presentation

Land plant evolution and volcanism led to the Late Devonian mass extinction

Gabriel Filippelli, Matthew Smart, William Gilhooly, Kazumu Ozaki, Christopher Reinhard, Jessica Whiteside, and John Marshall

The evolution of land plants in terrestrial environments brought about one of the most dramatic shifts in the history of the Earth system — the birth of modern soils — and likely stimulated massive changes in marine biogeochemistry and climate. In particular, multiple marine mass extinctions characterized by widespread anoxia, including the Late Devonian mass extinction around 375 million years ago (Ma), may have been linked to terrestrial nutrient release driven by newly-rooted landscapes. Here, we use recently generated constraints from Earth’s lacustrine rock record as variable inputs in an Earth system model of the coupled C-N-P-O₂-S biogeochemical cycles in order to evaluate whether recorded changes to phosphorus fluxes would be adequate to sustain Devonian marine biogeochemical perturbations and extinction dynamics. Results show that globally scaled riverine phosphorus export during the Late Devonian mass extinction generates widespread marine anoxia and produces carbon isotope, temperature, oxygen, and carbon dioxide perturbations generally consistent with the geologic record. Similar results for a competing extinction mechanism, large scale volcanism, suggest the Late Devonian mass extinction was likely multifaceted with both land plants and volcanism as contributing factors.

How to cite: Filippelli, G., Smart, M., Gilhooly, W., Ozaki, K., Reinhard, C., Whiteside, J., and Marshall, J.: Land plant evolution and volcanism led to the Late Devonian mass extinction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7734, https://doi.org/10.5194/egusphere-egu23-7734, 2023.

11:10–11:20

EGU23-2919

ECS

On-site presentation

Mycorrhizal fungi alleviate acidification-induced phosphorus limitation: Evidence from a decade-long field experiment of simulated acid deposition in a tropical forest in south China

Yuanliu Hu, Ji Chen, and Qi Deng

Tropical forests in southern China have been suffering high level of acid rain in recent decades, which may alter soil phosphorus (P) supply capacity and thus affect ecosystem productivity. We conducted a 10-yr field experiment of simulated acid rain (SAR) to examine how acidification impacts seasonal changes of soil P fractions in a tropical forest with highly-acidic soils in south China. The results showed that SAR significantly reduced soil P bioavailability, with increased occluded P pool but reduced the other more labile P pools in the dry season. The decreased soil P bioavailability was primarily related to the repressed P desorption capacity and enhanced P sorption during soil acidification, which regulated by acid-activated soil iron/aluminum minerals and soil organic matter. However, in the wet season, SAR did not change microbial P, soluble P and labile organic P pools. Different from the decline of microbial abundance in the dry season, SAR increased ectomycorrhizal fungi and its ratio to arbuscular mycorrhiza fungi in the wet season, which significantly stimulated phosphomonoesterase activities and likely promoted the dissolution of occluded P. Our results suggest that, even in already highly-acidic soils, the acidification-induced P limitation could be alleviated by stimulating ectomycorrhizal fungi and phosphomonoesterase activities. The differential responses and microbial controls of seasonal soil P transformation revealed here should be implemented into ecosystem biogeochemical model for predicting plant productivity under future acid deposition scenarios.

How to cite: Hu, Y., Chen, J., and Deng, Q.: Mycorrhizal fungi alleviate acidification-induced phosphorus limitation: Evidence from a decade-long field experiment of simulated acid deposition in a tropical forest in south China, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2919, https://doi.org/10.5194/egusphere-egu23-2919, 2023.

11:20–11:30

EGU23-15528

ECS

On-site presentation

Nitrogen and Phosphorus co-limitation impact on temperate forests productivity

(withdrawn)

Andre (Mahdi) Nakhavali, Lina M. Mercado, Iain P. Hartley, and Stephen Sitch

11:30–11:40

EGU23-3112

ECS

On-site presentation

Can we account for the “missing” phosphorus in simulated low phosphorus agricultural systems?

Jennifer Davies, Victoria Janes-Bassett, Martin Blackwell, Andrew Burgess, Jessica Davies, and Philip Haygarth

Long term total phosphorus (P) concentration, inorganic P and / or organic P concentration in agricultural soils is not commonly measured. As a consequence, computer-based models, that have been developed to predict P responses to changing management practices, are typically tested against soil “agronomically available” P data (as measured by tests such as; Olsen-P, Morgan’s-P, Mehlich-3, etc.) and those that do test against total P are limited to a few agricultural experimental sites across the world. While there is some correlation with total soil P, the term “available P” is arguably a functional concept, influenced by a large number of biotic and abiotic factors, rather than a direct soil measurement. This highlights a developmental gap in P modelling which could help to further unlock our understanding of P biogeochemical cycling when used in conjunction with contemporary empirical P research.

Investigating P cycling in agricultural systems using the computer-based model N14CP has demonstrated that the model can predict carbon and nitrogen cycling and crop yields well for systems receiving abundant fertiliser. However, in systems where there is no P applied, predicted yield responses are greatly underestimated, with “missing” P input concentrations equivalent to annual fertiliser application rates. To date, the testing of N14CP has not included the P pools due to a lack of soil total P and/or soil organic P data from long-term field trials. Using recent total, organic and inorganic phosphate concentrations in the topsoil and yield data from two contrasting long-term field trial sites in the UK and the USA, this research will test P outputs and modelled yields from N14CP. It is hypothesised that the model will underestimate soil P concentrations, and crop yield, in the absence of P fertiliser inputs. This study will then apply changes to the mode model inputs, outputs and control processes to investigate whether these are sufficient to supply the crops and soil with the “missing” P.

Understanding this source of “missing” P in N14CP will not only be useful for developing our understanding of P processes in computer-based models but could also further understanding of P processes linked to P draw-down in agricultural systems that have a history of high legacy P concentrations.

How to cite: Davies, J., Janes-Bassett, V., Blackwell, M., Burgess, A., Davies, J., and Haygarth, P.: Can we account for the “missing” phosphorus in simulated low phosphorus agricultural systems?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3112, https://doi.org/10.5194/egusphere-egu23-3112, 2023.

11:40–11:50

EGU23-16011

On-site presentation

Speciation of soil organic phosphorus: Steps from NMR spectra to bioavailability

Jürgen Schleucher, Lenny Haddad, Marina Paneque, David Wardle, Andrea Vincent, and Reiner Giesler

Phosphorus (P) is an essential element for all life on Earth. Understanding P cycling is in the context of global change crucial both for modelling of global biogeochemical cycles and for agricultural productivity. Recently, concerns about the future of P fertilizer supply have prompted much research on soil P and method development. ³¹P Nuclear Magnetic Resonance (NMR) Spectroscopy has been used to analyse speciation of inorganic and of organic P species (Po), using in alkaline soil extracts¹. The region containing signals from phosphomonoesters is particularly important because these compounds are considered biologically active, but there are still significant problems to be resolved particularly for this region of P NMR spectra, including: 1. Poor signal resolution often makes quantification of Po species in this region very challenging. 2. It is unclear if observed signals are due to free P species, or originate from P compounds bound to high-molecular weight soil matter. 3. The question needs to be addressed how signals observed in alkaline extracts relate to P species that were originally present in the soil. Here we present two approaches to address these problems:

In a study of a 5000-year soil chronosequence in Northern Sweden², we found that humus P composition barely changed, although time since fire varied up to 5000 years. We will present a new method to back-calculate original Po speciation from the observed composition. Results of this method indicate absence of “recalcitrant” Po species, and instead indicate that most Po was originally present as biologically active P metabolites, probably present in live soil organisms. We will discuss implication of these findings for P biogeochemistry.

Second, we studied a diverse group of soils to address how the poorly resolved phosphomonoester region should best be analysed. Deconvolution techniques are required to handle the overlap, but a better understanding of the nature of the signals is required for reliable quantification. Based on combined analysis of 1D ³¹P NMR, 2D ¹H-³¹P NMR and ³¹P linewidth measurements, we present a strategy for quantification of phosphomonoester species, as next step in linking observed Po speciation to P bioavailability.

(1) Cade-Menun BJ, Preston CM (1996) A comparison of soil extraction procedures for 31P NMR spectroscopy. Soil Sci 161:770–785

(2) Andrea G. Vincent, Jürgen Schleucher, Reiner Giesler, David A. Wardle (2022) Soil phosphorus forms show only minor changes across a 5000‑year‑old boreal wildfire chronosequence. Biogeochemistry (2022) 159:15–32 https://doi.org/10.1007/s10533-022-00910-2

(3) Vestergren J, Vincent AG, Jansson M et al (2012) High-resolution characterization of organic phosphorus in soil extracts using 2D 1H–31P NMR correlation spectroscopy. Environ Sci Technol 46:3950–3956. https:// doi. org/ 10. 1021/ es204016h

How to cite: Schleucher, J., Haddad, L., Paneque, M., Wardle, D., Vincent, A., and Giesler, R.: Speciation of soil organic phosphorus: Steps from NMR spectra to bioavailability, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16011, https://doi.org/10.5194/egusphere-egu23-16011, 2023.

11:50–12:00

EGU23-17064

ECS

On-site presentation

Formation and aging of Fe(III) and Ca precipitates in exfiltrating anoxic groundwater and effects on phosphate retention

Ville Nenonen, Ralf Kaegi, Stephan J. Hug, Stefan Mangold, Jörg Göttlicher, Lenny H.E. Winkel, and Andreas Voegelin

The oxidation of dissolved Fe(II) upon exfiltration of anoxic groundwaters into oxic surface waters leads to precipitation of poorly crystalline Fe(III)-solids that strongly bind phosphate (PO₄) and thereby can attenuate eutrophication. Fresh Fe(III)-precipitates may transform into more crystalline phases over time, which may lead to the release of initially co-precipitated PO₄. The formation and transformation of Fe(III)-precipitates in natural waters is strongly affected by other solutes (Ca, Mg, PO₄, silicic acid (SiO₄)) that interfere with Fe(III) precipitation and transformation, and thereby also affect PO₄ binding. Furthermore, in Ca-containing waters, the repartitioning of PO₄ released from Fe(III)-precipitates into Ca-carbonates or –phosphates, could limit PO₄ release.

For better understanding the fate of PO₄ in aquatic environments, there is a need for a mechanistic understanding of coupled Fe(III)- and Ca-precipitate formation and transformation processes induced by groundwater exfiltration, and their effects on PO₄ sequestration. In this laboratory study, we examined the effects of Ca, Mg, and SiO₄ on the formation and transformation of Fe(III)- and Ca-precipitates in bicarbonate-buffered aqueous solutions upon Fe(III)-precipitate formation by Fe (II) oxidation in the presence of PO₄, over aging periods up to 100 d. Changes in precipitate structures were probed with spectroscopic and microscopic techniques and linked to changes in the retention or release of PO₄ over time.

The results show that especially Ca and SiO₄ contribute to effective PO₄ retention via multiple interdependent processes, and thereby strongly attenuate PO₄ release over extended periods of time.

REFERENCES

Senn, A.-C.; Kaegi, R.; Hug, S. J.; Hering, J. G.; Mangold, S.; Voegelin, A., Composition and structure of Fe(III)-precipitates formed by Fe(II) oxidation in near-neutral water: Interdependent effects of phosphate, silicate and Ca. Geochim. Cosmochim. Acta 2015, 162, 220–246.

Senn, A.-C.; Kaegi, R.; Hug, S. J.; Hering, J. G.; Mangold, S.; Voegelin, A., Effect of aging on the structure and phosphate retention of Fe(III)-precipitates formed by Fe(II) oxidation in water. Geochim. Cosmochim. Acta 2017, 202, 341–360.

How to cite: Nenonen, V., Kaegi, R., Hug, S. J., Mangold, S., Göttlicher, J., Winkel, L. H. E., and Voegelin, A.: Formation and aging of Fe(III) and Ca precipitates in exfiltrating anoxic groundwater and effects on phosphate retention, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17064, https://doi.org/10.5194/egusphere-egu23-17064, 2023.

12:00–12:10

EGU23-12467

ECS

On-site presentation

Human-caused increases in phosphorus burials in global lake sediments during the Holocene

Luyao Tu, Madeleine Moyle, John Boyle, Paul Zander, Tao Huang, Lize Meng, Changchun Huang, Martin Grosjean, and Xin Zhou

12:10–12:30

Discussion

Posters on site: Wed, 26 Apr, 08:30–10:15 | Hall A

The posters scheduled for on-site presentation are only visible in the poster hall in Vienna. If authors uploaded their presentation files, these files are linked from the abstracts below, but only on the day of the poster session.

Chairpersons: Melanie Münch, Phil Haygarth, Tom Jilbert

Tour of the posters

A.219

EGU23-16254

ECS

On-site presentation

Phosphate pools and oxygen signature in the hyper-arid Atacama Desert

Xiaolei Sun, Wulf Amelung, Federica Tamburini, Erwin Klumpp, Ramona Morchen, and Roland Bol

The Atacama Desert is a temperate desert restricted by the Pacific Ocean and the Andeans, which is an ideal place to study the biogeochemical phosphate-water dynamics in the conditions with extreme limited water and biomass. We hypothesized that phosphate pools and oxygen signature change along with the increasing distance to the coast and thus aridity. The surface soils (0-10 cm) were sampled along the transect with distance to coast in Paposo region (~25°S) which is located in the Coastal Cordillera nearby the Pacific Ocean from 2.3 to 22.9 km, including 9 altitude sites (600 m, 900 m, 880 m, 920 m, 1000 m, 1200 m, 1450 m, 1700 m, 2110 m). Each site involved 3 samples surrounding the plant with a distance of 0-10 cm and other 3 samples far from the plant with 1 m. The Ca-bound P (HCl-extracted P followed the Hedley sequential P fractionation) accumulated along the increasing distance to coast within 37.9 km and could be described by a mono-exponential regression mode. However, an initial declining trend was detected for phosphate ¹⁸O of HCl-P_i and it reached a steady-state condition beyond 10 km from the coastline, which was the maximum distance that advective fog could penetrate inland. Only the nearest site at 2.3 km (600 m.a.s.l) to coast showed an isotope value within the range of full isotopic equilibrium with biologically cycled phosphate. Furthermore, the effects of the present plant distribution on surface soil Hedley P stocks and phosphate ¹⁸O signatures were very limited. We concluded that both P stocks and phosphate ¹⁸O signatures followed primarily the aridity gradient but phosphate ¹⁸O signatures could work as a tracer for long-term climate conditions.

How to cite: Sun, X., Amelung, W., Tamburini, F., Klumpp, E., Morchen, R., and Bol, R.: Phosphate pools and oxygen signature in the hyper-arid Atacama Desert, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16254, https://doi.org/10.5194/egusphere-egu23-16254, 2023.

A.220

EGU23-12271

ECS

On-site presentation

The impact of changing freeze-thaw dynamics under recent climatic changes on nutrient leaching in a Swedish agricultural field

Anna Lackner, Tobias Klöffel, and Jennie Barron

Agriculture can be a significant contributor of nutrients, such as phosphorus (P) and nitrogen (N) to surface water, increasing the risk of eutrophication. Soil frost and freeze-thaw (FT) cycles impact both the transport of nutrients through changes in the hydrologic regime of the field and the mobility/availability of nutrients through changes in the biogeochemistry of the field. With a changing climate, changes in the frequency and duration of FT cycles are expected in regions of higher latitudes and altitudes. However, there is a knowledge gap related to the response of nutrient leaching with changing FT patterns in a changing climate.

The aim of this study was to investigate the impact of soil freezing and thawing on nutrient leaching (N, P) from an agricultural field in northern Sweden for the period 1989-2021. The FT dynamics were modelled in terms of a soil temperature profile using an explicit soil moisture and energy-based process model – the COUP, at an hourly time step. Long term environmental monitoring data of surface and drainage runoff, combined with soil temperature and soil moisture data were used for model calibration and validation. Finally, the modelled FT dynamics and measured nutrient concentrations and runoff were statistically related to each other.

Our preliminary findings confirm the importance of soil frost occurrence for the separation of surface runoff and drainage. However, no clear relationship between soil FT dynamics and nutrient loads (or concentrations) in surface or drainage water could be observed. This suggests that changes in the hydrological regime through freezing and thawing are most important for the amount and export pathways of nitrogen and phosphorous as compared to alternative mechanisms of nutrient mobilisation.

How to cite: Lackner, A., Klöffel, T., and Barron, J.: The impact of changing freeze-thaw dynamics under recent climatic changes on nutrient leaching in a Swedish agricultural field, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12271, https://doi.org/10.5194/egusphere-egu23-12271, 2023.

A.221

EGU23-17071

ECS

On-site presentation

Impact of agricultural land use and management on available soil phosphorus content in agricultural catchments of Ireland

Ognjen Zurovec, Daniel Hawtree, Simon Leach, and Bridget Lynch

The build-up of soil phosphorus (P) in agricultural soils exceeding crop requirements can lead to diffuse P losses that could impair surface water quality. Therefore, adequate spatial information is required to develop viable tools and recommendations for sustainable P management at the local scale. Here, we present a database of nearly 8.000 samples, collected over a 12-year period in four meso-scale (~10 km²) agricultural catchments in Ireland. The agricultural area of each catchment is divided into sampling units (up to 2 ha) and soil samples are repeatedly taken from each sampling unit every 4 years. Four soil sampling campaigns were carried out to date. The results were analysed in the context of soil test P values (Morgan’s P) and classified according to the P index system as defined in the Ireland’s Nitrates Action Programme.

Overall, levels of soil test P did not show substantial changes, with the exception of the most recent sampling campaign. However, when the collected data are considered in a spatial context and accompanied with soil data and land use information, they reveal a more complex story. Notable differences in soil P trends are observed at the individual catchments scale and impacted by land use, agricultural management intensity and some soil properties across and within the catchments. Similarly to the overall soil test P trends, the total area under P index 4 soils (above optimal) decreased in the period preceding the most recent sampling campaign. The most notable decreases in P index 4 soils are found in tillage and drystock fields, but also in the catchment dominated by highly stocked dairy farms availing of a nitrate derogation.

Recent increases in soil test P and consequently areas under P index 4 may not be linked to increased organic or mineral P inputs, but rather come as a result of an overall increase in soil pH from increased lime application observed over the most recent period, which had an impact on the extractable Morgan’s P content. On-farm redistribution of fertilizer P inputs to soils with lower P index status has the potential to increase P use efficiency and decrease P loss risk to surface water.

How to cite: Zurovec, O., Hawtree, D., Leach, S., and Lynch, B.: Impact of agricultural land use and management on available soil phosphorus content in agricultural catchments of Ireland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17071, https://doi.org/10.5194/egusphere-egu23-17071, 2023.

A.222

EGU23-7187

On-site presentation

Phosphorus Bioavailability and Speciation dynamics within fluvial suspended sediments

David O'Connell, Qingzin Zhang, Diogo Ferreira, Sara Sandstrom, Robbie Goodhue, Laurence Gill, and Yongfeng Hu

Eutrophication of agricultural catchment streams remains a global problem despite increasingly stringent regulations. Long term, sustained release of bioavailable phosphorus (P) from legacy P stored in fluvial sediments may impact downstream water quality, hence greater understanding is required regarding P speciation dynamics and potential release mechanisms from fluvial sediments to the water column.

This study examined the dynamic P fractions, speciation and bioavailability of suspended fluvial sediments from two geologically contrasting agricultural catchment streams (Ballyboughal (BB) and Tintern Abbey (TTA)) using a combination of complimentary techniques including sequential chemical fractionations (SCF), Dual Culture Diffusion Apparatus mesocosm experiments (DCDA), X-ray fluorescence spectroscopy (XRF) and X-ray Absorption Near-edge Structure (XANES) spectroscopy. Results from the SCF of fluvial suspended sediments pre- and post DCDA microcosm experiment’s revealed that loosely bound P (P_H2O), exchangeable P against OH^–ions (P_NaOH), and organic P (P_Org) are the major P fraction contributors to the bioavailable P fraction which would promote algal growth. Other P fractions including acid-soluble P principally associated with calcium phosphate compounds (P_HCl) and ferric bound P (P_CBD) showed relatively lower mineralisation to bioavailable P. Significantly, P K-edge XANES spectra enabled identification of seasonal and spatial P speciation dynamics and the existence of major P fractions including Fe-P and Ca-P associated mineral phases along with organic P compounds. Additionally, SCF, XRF and Ca K-edge XANES show contrasting Ca associated phases between both catchments, with calcite dominant in the BB sediments and Ca humic-complexes predominant in the TTA sediments. Contrasting Ca-P fraction transformation mechanisms of the two catchments are indicated by P redistributions in SCF and the reduction of elemental Ca amounts from XRF analysis. Calcium (Ca) K-edge XANES shows the BB catchment has a large amount of calcite while TTA was shown to contain organic Ca compounds, likely in the form of Ca-humic-complexes. This study provides a conjunctive method for future studies and validation of P speciation and bioavailability assessment associated with fluvial suspended sediments from agricultural catchments streams. The results contribute to future catchment scale sedimentary fluvial P modelling and enhanced catchment management strategies to improved water quality.

How to cite: O'Connell, D., Zhang, Q., Ferreira, D., Sandstrom, S., Goodhue, R., Gill, L., and Hu, Y.: Phosphorus Bioavailability and Speciation dynamics within fluvial suspended sediments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7187, https://doi.org/10.5194/egusphere-egu23-7187, 2023.

A.223

EGU23-13516

On-site presentation

P-TRAP – Reducing diffuse phosphorus input to surface waters

Thilo Behrends and Sylvia Walter

A.224

EGU23-13631

On-site presentation

Fe solid phase chemistry and its effect on P retention in the sediment of a eutrophic peat lake 10 years after Fe amendment

Melanie Münch, Rianne van Kaam, Karel As, Stefan Peiffer, Gerard ter Heerdt, and Andreas Voegelin

Globally, surface water quality and ecosystem functioning are challenged by anthropogenic P inputs. While sterner legislation has led to lower external P loading, internal loading fed by legacy P accumulated in the sediment has become the controlling factor of surface water P concentrations in many European freshwater systems. Fe amendment is a treatment method to control internal P loading, but is not always successful on the long term. In Lake Terra Nova, a polymictic shallow peat lake in the Netherlands, treatment with FeCl₃ only led to a temporary decrease in sedimentary P release. Two years after treatment seasonal peaks in surface water P concentrations started to appear and have been increasing in intensity for the past 8 years. Depth-resolved solid phase analysis by sequential Fe and P extractions was combined with bulk X-ray absorption spectroscopy (XAS) at the Fe K-edge and high-resolution micro-X-ray fluorescence spectrometry (µ-XRF) and µ-XAS. At spots with distinctively high Fe contents, pyrite and silicate-bound Fe are identified by microscopic and spectroscopic analyses. The spectroscopic data, however, also point to a finely dispersed Fe species in the sediment matrix which most likely corresponds to Fe complexed by OM in the surface sediment. The correlation of the distribution of P and Fe suggests that P is bound to these Fe-OM complexes. This interpretation is supported by the sequential extraction results which showed that the Fe treatment induced a shift in the dominant P pool from Ca-bound P to Fe- and OM-bound P. Overall, the results indicate that FeCl₃ application caused a change in sediment P dynamics towards a highly redox sensitive system in which P bound to Fe-OM is released to the surface water during seasonally low bottom water oxygen concentrations. The results of this study therefore indicate that FeCl₃ may not be the ideal additive for the remediation of internal P loading in peaty water bodies due to the high affinity of Fe to OM.

How to cite: Münch, M., van Kaam, R., As, K., Peiffer, S., ter Heerdt, G., and Voegelin, A.: Fe solid phase chemistry and its effect on P retention in the sediment of a eutrophic peat lake 10 years after Fe amendment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13631, https://doi.org/10.5194/egusphere-egu23-13631, 2023.

A.225

EGU23-17209

On-site presentation

Effect of increased sulfate reduction on the stability of authigenic vivianite in lake sediment

Harm van Kuppevelt and Michael Hupfer

The presence of high levels of phosphorus (P) in surface waters can negatively impact the functioning of ecosystems and water quality. Despite efforts to decrease P concentrations, the accumulation of P reservoirs in sediment from past high external inputs still poses a problem. This legacy P can contribute to internal P loading, which has been shown to extent eutrophication in many freshwater systems. To effectively restore these systems, it is important to understand the geochemical processes that control the fixation and release of P in the sediment. While it is known that under anoxic conditions, P can be stored in the form of the mineral vivianite, it is not well understood if the vivianite reservoir can also act as a source of P. In a field study, mixed sediment from Lake Arendsee, Germany that naturally contained vivianite was placed in the sediment floor of the same lake, in both sulfate reduction depths and below (0-45cm). After three months, the sediment was retrieved and analyzed to investigate the effect of sulfide production on the vivianite pool. Sequential extraction and XRD analysis of the sediment solid phase showed that at shallower depths where sulfide concentrations were higher, there was a significant reduction of the vivianite reservoir and a decrease of P bound to Fe relative to S bound Fe forms. This suggests that P bound in vivianite can act as a P source in sulfidic sediment. Further research is needed to determine the extent of this phenomenon in lakes with increased sulfide production.

How to cite: van Kuppevelt, H. and Hupfer, M.: Effect of increased sulfate reduction on the stability of authigenic vivianite in lake sediment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17209, https://doi.org/10.5194/egusphere-egu23-17209, 2023.

A.226

EGU23-17179

On-site presentation

The paradox of internal phosphorus loading from oxic areas of iron-rich eutrophic boreal lakes: insights from porewater geochemistry

Tom Jilbert, Siqi Zhao, and Martijn Hermans

Internal phosphorus (P) loading from sediments is an important component of total P supply to the water column of many eutrophic lakes. A long-standing paradigm states that the magnitude of internal loading through diffusion of P is limited in the presence of iron (Fe) oxides at the sediment-water-interface, due to efficient sorption and co-precipitation of P with oxide minerals. Iron-rich sediments underlying oxic water columns in shallow lake areas are thus expected to retain, rather than release P. However, recent statistical investigations have suggested that oxic epilimnetic areas of stratifying lakes may be responsible for a significant fraction of the internal P loading in these systems [1], implying a "leaky" seal of Fe oxides even under oxic conditions. Here we study the mechanisms of internal P loading in two Fe-rich eutrophic lakes in southern Finland through geochemical analysis of porewaters, over one annual cycle at five study sites per lake. Diffusive flux calculations using Fick's Law, and upscaling to whole-lake areal estimates, confirm that shallow (approx. <10 m) areas dominate internal P loading even during stratified conditions in summer. Furthermore, the highest instantaneous fluxes of the study were observed in shallow sites in late summer. The results suggest in shallow eutrophic settings with a high organic matter flux to sediments and elevated summer temperatures, remineralization reactions at the sediment-water interface regenerate P efficiently enough to escape capture by Fe oxides, even under sediment molar Fe/P ratios >20.

[1] Tammeorg, O., Möls, T., Niemistö, J., Holmroos, H., & Horppila, J. (2017). The actual role of oxygen deficit in the linkage of the water quality and benthic phosphorus release: potential implications for lake restoration. Science of the Total Environment, 599, 732-738.

How to cite: Jilbert, T., Zhao, S., and Hermans, M.: The paradox of internal phosphorus loading from oxic areas of iron-rich eutrophic boreal lakes: insights from porewater geochemistry, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17179, https://doi.org/10.5194/egusphere-egu23-17179, 2023.

Posters virtual: Wed, 26 Apr, 08:30–10:15 | vHall BG

The posters scheduled for virtual presentation are visible in Gather.Town. Attendees are asked to meet the authors during the scheduled attendance time for live video chats. If authors uploaded their presentation files, these files are also linked from the abstracts below, but only on the day of the poster session. The button to access Gather.Town appears just before the time block starts.

Chairpersons: Melanie Münch, Phil Haygarth, Tom Jilbert

vBG.1

EGU23-17121

ECS

Virtual presentation

Strategies for optimizing the scalable microbial synthesis of vivianite

Lordina Eshun, Victoria Coker, Sam Shaw, and Jonathan Lloyd

Vivianite (Fe₃(PO₄)₂·8H₂O) has been reported to form as a secondary mineralization product during the microbial reduction of phosphate-containing Fe(III) minerals [1 – 3]. The phosphate-rich nature of vivianite makes it a suitable sink for phosphorus, which is a scarce and irreplaceable resource, and a major contributor to eutrophication in surface water bodies. There is, therefore, interest in synthesizing vivianite by Fe(III) reducing bacteria such as Geobacter sulfurreducens and Shewanella putrefaciens, to treat phosphate-rich waters, recovering the phosphate for re-use in agriculture. In this study, factors including the presence and absence of phosphate and electron shuttle, the buffer system, pH, microbial load, and the type of Fe(III)-reducing bacteria that influence the formation of vivianite under laboratory batch systems have been investigated. The rate of Fe(II) production, and its interaction with the residual Fe(III) and other oxyanions (e.g., PO₄^3-, CO₃^2-) was found to be the main driving factor for secondary mineral formation. Magnetite was formed in treatments with zero phosphates whereas vivianite and green rust were formed in treatments containing phosphate. The rate and extent of Fe(III) bioreduction were higher in Shewanella putrefaciens than in Geobacter sulfurreducens. Vivianite and green rust were both identified as the dominant endpoints in treatments with Geobacter sulfurreducens and Shewanella putrefaciens.

[1] Fredrickson, Zachara, Kennedy, Dong, Onstott, Hinman, & Li (1998). Geochimica et Cosmochimica Acta 62, 3239-3257.

[2] O’Loughlin, Boyanov, Gorski, Scherer, & Kemner (2021). Minerals 11, 149

[3] Zachara, Kukkadapu, Fredrickson, Gorby, & Smith (2002). Geomicrobiology Journal 19, 179–207.

How to cite: Eshun, L., Coker, V., Shaw, S., and Lloyd, J.: Strategies for optimizing the scalable microbial synthesis of vivianite, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17121, https://doi.org/10.5194/egusphere-egu23-17121, 2023.