It has been advocated that nitrogen (N) availability plays an essential role in mediating plant and microbial growth in cold environment, and could thus regulate the direction and magnitude of permafrost carbon (C)-climate feedback. However, compared to widely concerned N, little is known about soil phosphorous (P) availability and its biological acquisition strategies in permafrost environment. Here we explored soil microbial P acquisition strategies using shotgun metagenomics across the Tibetan permafrost area, encompassing a large scale survey spanning 1,000 km. In contrast to the traditional opinion that microorganisms in cold area usually obtain P mainly through mineralization process, our results revealed that the P cycling genes responsible for solubilization, mineralization and transportation were widespread, illustrating multiple microbial strategies for acquiring P in permafrost regions. Moreover, the higher gene abundance related to solubilization and mineralization as well as an increased ration of MAGs carrying these genes were detected in the active layer, while the greater abundance of low affinity transporter gene (pit) and proportions of MAGs harbouring pit gene were observed in permafrost deposits, reflecting a stronger potential for P activation in active layer but an enhanced P transportation potential in permafrost deposits. Taken together, these results highlight that besides microbial P mineralization, multiple P-related acquisition strategies and their differences among various soil layers should be considered simultaneously to improve model prediction for the responses of biogeochemical cycles in permafrost ecosystems to climate change.

How to cite: Wang, L. and Yang, Y.: Divergent microbial phosphorous acquisition strategies between active layer and permafrost deposits, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2973, https://doi.org/10.5194/egusphere-egu24-2973, 2024.

[Background] Phosphorus (P) availability in soils and sediments is a critical parameter influencing primary production in terrestrial and aquatic ecosystems, controlled by both P chemical fractions in solid phase and solution composition. A recent study using Arctic soils reported that the addition of Si to the soil released P bound to Fe(II) compounds, but reports on other soils and sediments are limited. In our previous study, we detected higher P concentrations in stream water and iron-bound P content in river sediments in the marine sedimentary rock catchments of the Akita coastal area compared to catchments in the adjacent igneous rock area. Furthermore, high-P stream waters were NaCl water type with relatively lower Ca²⁺ and higher SiO₂ concentrations. In this study, we evaluated the effects of different solution compositions and amorphous Si addition on P solubilization in sediments using river sediments from marine sedimentary and igneous rock regions. [Method] We tested each five river sediments (<2 mm) in the headwaters of western Akita Prefecture, Japan, where the surface geology is composed of marine sedimentary rocks and igneous rocks. Available Si (easily water-soluble Si) was measured by a long-term flooded incubation in distilled water at 30°C for 30 days. In the P dissolution incubation, four types of treatment solutions (distilled water, 1 mM NaCl and NaHCO₃ solutions, and 0.5 mM CaCl₂ solution) were added to 0.5 g sediment and in the Si addition treatment, amorphous Si (hydrophilic fumed silica, AEROSIL300) was also added. SRP, DOC and pH in the solution were measured after shaking for 48 hours. A statistical analysis was performed using a linear mixed model (LMM) with SRP, DOC and pH in the liquid phase as objective variables. The surface geology, four types of solutions, and the Si addition as explanatory variables. Additionally, each five sediment was treated as a random effect. [Results and discussion] Easily water-soluble Si content in sediments was significantly higher in marine sedimentary rock areas (p < 0.001), indicating that the easily soluble Si causes higher SiO₂ concentration in stream water. The incubation results showed Si addition significantly increased P concentration in the liquid phase (p < 0.001), and combined Si addition with NaHCO₃ treatment further increased P concentration. Conversely, CaCl₂ treatment significantly decreased the liquid-phase P concentration. The influence of surface geology on extracted P concentration was not significant. Si addition did not affect pH (p = 0.58) and DOC (p = 0.90), while the effects of solution composition on pH and DOC were also significant; NaHCO₃ solution increased pH and DOC while CaCl₂ solution decreased pH and DOC. In conclusion, in marine sedimentary rock areas in coastal Akita with NaCl water type where Ca²⁺ concentration is relatively low and sediments have higher easily soluble Si, P release from sediments easily occurs and a high P concentration keeps in the liquid phase.

How to cite: Hayakawa, A., Kuroe, Y., Kawata, A., Nishina, K., Ishikawa, Y., and Takahashi, T.: Silicone availability and NaCl water type enhances the phosphorus release from sediments in coastal forest catchments in Akita, Japan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4491, https://doi.org/10.5194/egusphere-egu24-4491, 2024.

Baltic Sea is a geologically young semi-enclosed brakish-water body which water exchange with the ocean has been gradually declining. Approximately 85 million people live in the Baltic Sea's catchment area, resulting in significant human impact on the basin's ecosystem. Eutrophication due to anthropogenic discharge of nutrients is considered to be the most serious environmental problem which leads to a greater growth of phytoplankton and algae, deterioration of water quality, and lack of oxygen in near-bottom water masses. As a result of recent large-scale input of nutrients, phosphorus has accumulated in the seabed sediments from where it can be remobilized and released into the water column under favorable conditions (hypoxic or anoxic). Marine sediments contain phosphorus in various components i.e. fractions, but not all of them are affected by remobilization. Therefore, knowing how phosphorus fractions are distributed in seabed sediments is important.

One part of the Baltic Sea that has received little attention, but will significantly affect the entire Baltic Sea in the future, is the Gulf of Riga. The Gulf of Riga accounts for less than 5% of the total area of the Baltic Sea and less than 2% of the total water volume. Due to its shallowness and limited connection with the open Baltic Sea, the Gulf of Riga is strongly influenced by riverine input. Intense agriculture, rapid development of industry, and urbanization have resulted in high loads of nutrients into the Gulf of Riga already since the 1960s.

Phosphorus fractions and their vertical distribution were studied from the sea-bottom sediments from the Gulf of Riga and other coastal areas of western Estonia. The amount of potentially mobile phosphorus stored in the surface sediments of the Gulf of Riga is several times higher than in other accumulation areas of the Baltic Sea, with concentrations as high as 980 mg/kg(dw). A strong correlation between Mn and mobile phosphorus concentration suggests that Fe-Mn concretions control the amount of phosphorus in the sediments of the Gulf of Riga. Although the bottom waters of the Gulf of Riga are currently predominantly oxic, a decreasing trend of deep-layer oxygen concentrations and more frequent hypoxia in the Gulf of Riga during previous decades have been documented. Considering the large amount of potentially mobile phosphorus in the sediments of the Gulf of Riga, surpassing the annual total phosphorus input to the Baltic Sea, a substantial release of phosphorus could be inevitable, possibly impacting the entire Baltic Sea ecosystem.

How to cite: Ausmeel, M., Liira, M., Paiste, P., Lepland, A., and Suuroja, S.: Phosphorous in the seabed sediments of the Gulf of Riga, Baltic Sea: Fe-Mn concretions as main carriers of mobile phosphorous , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6352, https://doi.org/10.5194/egusphere-egu24-6352, 2024.

Phosphorus (P), as an indispensable nutrient element in Earth’s biological system, exerts a pivotal role on the burial of organic carbon over million-year time scales. By producing oxygen and consuming carbon dioxide, organic carbon burial may have paved the path for multicellular organisms by reforming the anoxic atmosphere to an oxic one. Organic carbon burial, on long time scales, is ultimately limited by continental P influx released by chemical weathering of P-bearing minerals. As crystalline rocks characterized by prominent discrepancy in P-bearing mineral composition undergoing various dominant weathering forces on surficial environment, P availability for organic carbon burial could be controlled by lithology. To decipher the conundrum of P releasement, a catchment scale case study was conducted, encompassing a series of lithologies following the crystalline rock order. Preliminary data suggests that the P release efficiency is lithology-constrained, indicating an enhanced P releasement in felsic catchment. The result gives us a hint that felsic crust would export more P to the ocean and promote the organic carbon burial, the lithology-constrained P releasement also enlightens us a new perspective to understand the coevolution among crust, atmosphere and life.

How to cite: Ouyang, S.: Lithology-constrained phosphorus (P) releasement, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9578, https://doi.org/10.5194/egusphere-egu24-9578, 2024.

Phosphorus (P) is a key nutrient controlling primary production in aquatic systems. In coastal systems, the P cycle involves dynamic interactions between terrestrial, aquatic and sedimentary compartments. Over the last century, human activities such as deforestation, intensive agricultural practices and the disposal of municipal and industrial wastes have increased P inputs to coastal ecosystems. As a result, this increase in P inputs has led to an increase in the occurrence of algal blooms and higher oxygen demand in estuaries. In the Loire estuary, dissolved oxygen deficits have been a recurrent and worrying issue for several decades despite the improvement of water quality over the last 30 years due to reduced wastewater discharge and better effluent treatment. In this context, the burial of bioavailable P may influence the recovery of waters from eutrophication. The major P burial phases are apatite, organic P and iron-bound P. The results of sequential chemical extraction and pore water analysis carried out over a 5m-long sediment core from the intertidal Brillantes mudflat in the Loire estuary indicated a greater abundance of the iron-bound P compared to other phases. Iron-bound P occurs in two different forms: phosphorus bound to iron oxides and in the iron phosphate mineral known as vivianite. Vivianite is a ferrous iron phosphate mineral formed under reducing and low sulphate conditions in sediments where organic matter serve as electron donor for ferric iron reduction. Results of sequential chemical extraction of freeze-dried sediment samples combined with pore water data and scanning electron microscope–energy dispersive x-ray spectroscopy (SEM-EDXS) on resin-embedded sediment samples indicated that vivianite-type minerals may act as an important sink for P at the studied site. Authigenic vivianite crystals were found below the shallow sulphate/methane transition zone (SMTZ) at 94 cm depth and contain significant amounts of manganese, as observed in freshwater sediments. We therefore hypothesise that anthropogenic over-fertilization of coastal regions in the last century may have increased the importance of vivianite authigenesis in surface sediments. Consequently, vivianite is likely to be an important sink for P in estuarine systems worldwide.

This study is part of a PhD financed by the European Project Life REVERS’EAU.

How to cite: Barhdadi, M., Mouret, A., Barras, C., Morin, G., Maillet, G., Durand, M., Mojtahid, M., Bénéteau, E., Dubosq, N., and Metzger, E.: Vivianite as a phosphorus sink in estuarine systems: The case study of the Brillantes mudflat, Loire, France, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17700, https://doi.org/10.5194/egusphere-egu24-17700, 2024.

Many eutrophic lakes suffer from long term accumulation of legacy phosphorus (P) in sediments. Repeated cycling of P between sediments and water column leads to delayed recovery from eutrophication even after abatement of external loading. Moreover, in complex multi-basin lake systems, legacy P can be internally redistributed over time, leading to spatial heterogeneity in regeneration and burial of P and consequent impacts on water quality. Few studies have attempted to map such internal variability in individual lakes in the context of understanding long term recovery from eutrophication. Here we use a combination of sediment trap deployments through one full stratification cycle (May-October 2021), sediment core biogeochemical analyses, and mass balance calculations, to quantify P cycling in Lake Hiidenvesi, a dimictic lake with 5 sub-basins in southern Finland. We show that exchange of P between sediments and water column is more intense in shallow (approximately 0-10 m depth) non-stratified sub-basins, due to both sediment resuspension and diffusive fluxes across the sediment-water interface. In contrast, deeper stratified sub-basins serve as P sinks by promoting sedimentation in relatively quiescent conditions. Due to lateral exchange of water and suspended materials between sub-basins, P is shuttled towards long term burial in deeper, downstream sub-basins. Budget calculations show that net sediment P burial exceeds external loading on the whole-lake scale, indicating a long-term trend towards recovery from eutrophication. However, temporary retention and repeated recycling of legacy P in the shallower upstream sub-basins continues to impact negatively on water quality, despite external loading reductions. The results have implications for understanding the timescales of recovery and for targeting restoration actions aimed at modifying internal P cycling to improve water quality.

How to cite: Jilbert, T., Zhao, S., Vesterinen, J., and Niemistö, J.: A spatial perspective on internal phosphorus cycling in morphologically complex eutrophic lakes: the importance of stratification, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20517, https://doi.org/10.5194/egusphere-egu24-20517, 2024.

          Utilisation of dissolved organic phosphorus (DOP) by marine microbes as an alternative phosphorus (P) source when phosphate is scarce can help sustain non-Redfieldian carbon:nitrogen:phosphorus ratios and efficient ocean carbon export. Alkaline phosphatase (AP) is an important enzyme group that facilitates the remineralisation of DOP to phosphate and thus its activity is a promising proxy for DOP-utilisation, particularly in P-stressed regions. In order tounderstand the global spatial patterns and rates of microbial DOP utilization and their environmental controls, we compiled a Global Alkaline Phosphatase Activity Dataset (GAPAD) with 4083 measurements collected from 79 published manuscripts and one database， and further investigated the possible mechanisms controlling global ocean APA. We find that DOP concentration, salinity, excess phosphate (P*), and chlorophyll a concentrations are critical factors in predicting global patterns of APA, which together explain as much as 39% of the variance in the observed APA dataset. Among all environmental factors, DOP concentration explains the most variance in the observed APA data and is negatively correlated with APA. P* is negatively correlated with APA，while chlorophyll a concentration is positively correlated.  Moreover, wind speed, dust iron deposition rate, and zinc concentration are also possible important environmental factors controlling APA. Using structural equation modeling, DOP and P* concentrations have a total negative effect on APA of -0.36. and -0.2 respectively, while chlorophyll a concentration and salinity have a total positive effect of 0.16 and 0.24. Via a set of numerical competition experiments between an AP-producing phytoplankton and a non AP-producing competitor, AP-producing phytoplankton are found to have an advantage in regions with low P*, but only alongside sufficiently high DOP and DIN concentrations. This trend arises due to the trade-off between P acquisition and N allocation to AP synthesis and is not affected by varying the model assumptions regarding nutrient supplies, N-demand, and key physiological traits.  Extending our results to the global ocean using DIN, DIP, and DOP datasets enables us to pinpoint key regions where optimal conditions for DOP-utilisation are prevalent. These findings align closely with the patterns illuminated by our APA dataset. Our results show that on a global scale, when phosphate limitation is severe, plankton utilize DOP through producing AP, and this will help understand the biogeographical shift of different microbial groups in response to future climate change. Further work is needed to include the parallel role of the trace metal co-factors iron and zinc in driving AP synthesis and its spatial distribution in our modelling experiments.

How to cite: Su, B., Song, X., Duhamel, S., Mahaffey, C., Davis, C., Ivančić, I., Zhou, S., and Liu, J.: Controls on global patterns of dissolved organic phosphorus utilisation in the surface ocean, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20917, https://doi.org/10.5194/egusphere-egu24-20917, 2024.

Phosphorus (P) is essential for cellular metabolism. Many metabolic pathways and processes depend on it, including energy production through ATP, DNA and RNA synthesis, and protein phosphorylation during post-translational signaling adaptation.

In marine sediments and oceanic water, the stoichiometric ratio between carbon and phosphorus has been found to vary with latitude, but in algae and phytoplankton, which are responsible for primary production and CO₂ uptake from the atmosphere, this ratio is relatively constant. This constant ratio is known as the Redfield ratio and  it is often used as a constraint in modeling.

In soils, where microorganisms control nutrient cycling and consequent carbon sequestration, the C:P is more variable both in soil and microbial biomass. First, microorganisms exhibit a wide range of metabolic adaptations to environmental pressure, and the physical and mineralogical properties of the soil play a significant role in nutrient control, e.g. through sorption/desorption reactions. Due to these complexities, using nutrient ratios for modeling soil organic carbon dynamics and predicting the impact of anthropogenic influences on global changes is challenging. Is it possible to find a connection between carbon and phosphate that encompasses the "Redfield" ratio and reflects their tight link in cellular metabolism?

By examining the oxygen isotope composition in inorganic phosphate (δ¹⁸O-Pi), we can determine the extent of oxygen exchange between water and phosphate, which is controlled by biological processes. Intracellularly, this exchange occurs through phosphoryl transfer, a fundamental process in cellular phosphate cycling. 

During the last 10 years, we conducted a series of incubation experiments where we measured CO₂ respiration and δ¹⁸O in resin and microbial cytosolic phosphate in soils from different environments. These incubations were performed with waters of varying ¹⁸O isotopic composition. By analyzing δ¹⁸O in microbial cytosolic phosphate at the beginning and end of the incubation, we could measure the level of oxygen exchange between water and phosphate.

Comparing the results from these incubations, we observed a significant correlation between the percentage of oxygen exchange and the cumulative CO₂ respired during the incubation. This correlation was consistent  through different soil ages, mineralogy, phosphate levels, and incubation length. When normalizing the percentage of oxygen exchange to moles of oxygen exchanged per moles of carbon respired, it appears that for every mole of oxygen exchanged due to phosphoryl transfer, there is a nearly fixed amount of carbon respired. This suggests that the moles of oxygen exchanged through phosphoryl transfer recorded in soil microbial phosphate can provide information about metabolic carbon expenditure.

This finding would provide new insights on the link between P and C in soil microbial biomass. The controlled nature of the incubation experiments may not fully reflect the biological activity in soil environments, so it would be necessary to perform field-based incubation experiments to confirm the link between carbon respiration and phosphorus microbial cycle. This information could potentially improve our understanding of carbon dynamics and be used for further modeling purposes.

How to cite: Tamburini, F., Siegenthaler, M., and Pistocchi, C.: Beyond “Redfield ratio”: Oxygen exchange between water and phosphate can provide insights into carbon dynamics in soils, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21673, https://doi.org/10.5194/egusphere-egu24-21673, 2024.

For a comprehensive understanding of the phosphorus (P) storage and cycling in temperate soils, it is necessary to explore further the bonding pathways of organic P (Po) and inorganic P (Pi) to mineral surfaces and soil organic matter (SOM), and their interconnections with organic carbon (OC) at a micro-scale other than conventional bulk analysis. In the past decade, nanoscale secondary ion mass spectrometry (NanoSIMS) has been increasingly recognized as a promising imaging technique to understand soil biogeochemical processes, particularly in exploring organo-mineral associations in soils at the microscale (Mueller et al., 2023). However, its application in studying P, and the identification and distinction of Po and Pi remains challenging, hindering a comprehensive understanding of the P cycling in soils.

In our study, four temperate soil types, including Cambisol, Luvisol, Phaeozem and Fluvisol, were taken from Bavarian Forest in South-East Germany. The pH of these soils ranges from 5.4 to 6.3, with poor to medium P stocks but distinct Po stocks in fine fractions (<20 μm). Previous bulk studies have hinted at different pathways in P bonding to mineral surfaces and SOM. NanoSIMS was employed to further explore and visualize these bonding pathways. Recent advancements in NanoSIMS technology, particularly improved O^- sources for cation detection and the capability for ³¹P^- and ³¹P¹⁶O^2- detection enable us to identify and distinguish Po and Pi at a microscale by ³¹P¹⁶O^2-/³¹P^- ratio, in which a lower ratio in specific areas corresponds to a more dominant presence of Po, and vice versa.

From NanoSIMS images, preliminary results reveal that a proportion of Po associates with either clay minerals or Fe (hydr)oxdies without assimilating into SOM. This Po fraction is suspected to originate from highly decomposed SOM, where N has either been assimilated by microorganisms or leached away, and Po is stabilized to mineral surfaces due to strong bonding strength. In contrast, the Po assimilated into SOM is associated with various cations, including Ca, Al and Fe, which may suggest the origin from particulate organic matter. Interestingly, the fine plant residue is depleted in Po in the fine fraction.

In conclusion, our study provides valuable insights into distinguishing different bonding pathways of these P forms within clay minerals, Fe (hydro)oxides, and SOM by using advanced NanoSIMS data, and emphasizes the interconnection with OC and Po and Pi in the fine fraction.

Reference: Mueller, C. W., Hoeschen, C., Koegel-Knabner, I., 2023. Understanding of soil processes at the microscale—Use of NanoSIMS in soil science. Encyclopedia of Soils in the Environment (Second Edition). Elsevier. 10.1016/B978-0-12-822974-3.00045-8

How to cite: Lei, K., Bucka, F. B., Höschen, C., Hu, Y., and Kögel-Knabner, I.: Exploring spatial distribution and characterization of inorganic and organic phosphorus in temperate soils using NanoSIMS , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21972, https://doi.org/10.5194/egusphere-egu24-21972, 2024.