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The transport of ferrihydrite colloid (FHC) through porous media is influenced by anions (e.g., PO43-) and cations (e.g., Ca2+) in the aqueous environment. This study investigated the cotransport of FHC with P and P/Ca in saturated sand columns. The results showed that P adsorption enhanced FHC transport, whereas Ca loaded onto P-FHC retarded FHC transport. Phosphate adsorption provided a negative potential on the FHC, while Ca added to P-FHC led to electrostatic screening, compression of the electric double layer, and formation of Ca5(PO4)3OH followed by heteroaggregation at pH ≥ 6.0. The monodentate and bidentate P surface complexes coexisted, and Ca mainly formed a ternary complex with bidentate P (≡(FeO)2PO2Ca). The unprotonation bidentate P at the Stern 1-plane had a considerable negative potential at the Van der Waals molecular surface. Extending the potential effect to the outer layer of FHC, the potential at the Stern 2-plane and zeta potential exhibited a corresponding change, resulting in a change in FHC mobility, which was validated by comparison of experimental results, DFT calculations, and CD-MUSIC models. Our results highlighted the influence of P and Ca on FHC transport and elucidated their interaction mechanisms based on quantum chemistry and colloidal chemical interface reactions.

The association of poorly crystalline iron (hydr)oxides with organic matter (OM), such as extracellular polymeric substances (EPS), exerts a profound effect on Fe and C cycles in soils and sediments, and their behaviors under sulfate-reducing conditions involve complicated mineralogical transformations. However, how different loadings and types of EPS and water chemistry conditions affect the sulfidation still lacks quantitative and systematic investigation. We here synthesized a set of ferrihydrite-organic matter (Fh-OM) coprecipitates with various model compounds for plant and microbial exopolysaccharides (polygalacturonic acids, alginic acid, and xanthan gum) and bacteriogenic EPS (extracted from Bacillus subtilis). Combining wet chemical analysis, X-ray diffraction, and X-ray absorption spectroscopic techniques, we systematically studied the impacts of C and S loadings by tracing the temporal evolution of Fe mineralogy and speciation in aqueous and solid phases. Our results showed that the effect of added OM on sulfidation of Fh-OM coprecipitates is interrelated with the amount of loaded sulfide. Under low sulfide loadings (S(-II)/Fe < 0.5), transformation to goethite and lepidocrocite was the main pathway of ferrihydrite sulfidation, which occurs more strongly at pH 6 compared to that at pH 7.5, and it was promoted and inhibited at low and high C/Fe ratios, respectively. While under high sulfide loadings (S(-II)/Fe > 0.5), the formation of secondary Fe-S minerals such as mackinawite and pyrite dominated ferrihydrite sulfidation, and it was inhibited with increasing C/Fe ratios. Furthermore, all three synthetic EPS proxies unanimously inhibited mineral transformation, while the microbiogenic EPS has a more potent inhibitory effect than synthetic EPS proxies compared at equivalent C/Fe loadings. Collectively, our results suggest that the quantity and chemical characteristics of the associated OM have a strong and nonlinear influence on the extent and pathways of mineralogical transformations of Fh-OM sulfidation.

Sedimentary interfaces between contrasting hydrogeological facies in alluvial aquifers drive the development of biogeochemical interfaces that influence subsurface and surface water quality. Here, we calibrate a reactive transport model on a series of dual-domain column experiments, where centimeter-scale, low-permeability, organic-rich anoxic lenses are embedded in coarser-grained aquifer material. Simulations explicitly account for C, Fe, and S cycling at the interface between the lenses and the aquifer in water-saturated conditions. Our results highlight the role of fine-grained, organic-rich inclusions not only as sources or sinks for redox-sensitive species, but also as exporters of nutrients that stimulate downgradient biogeochemical cycling. By releasing large amounts of organic carbon into the surrounding aquifer, such lenses drive the development of proximal secondary reduction zones (“halos”), characterized by high microbial activity (e.g., sulfate reduction) and accumulation of reduced reaction products (e.g., iron sulfide). If similar secondary reduction zones develop within the hydraulically conductive domain of an aquifer, they would be highly susceptible to changes in hydrologic conditions, for instance oxygen pulses associated with seasonal snowmelt. Our results also emphasize the limitations of relying solely on aqueous species measurements to inform reactivity in systems where fast redox cycling and/or sizeable particulate transport may limit the signature of reactivity in the dissolved phase.

Microbial reduction of soluble hexavalent uranium (U(VI)) to sparingly soluble tetravalent uranium (U(IV)) has been explored as an in situ strategy to immobilize U. Organic ligands might pose a potential hindrance to the success of such remediation efforts. In the current study, a set of structurally diverse organicligands were shown to enhance the dissolution of crystalline uraninite (UO2) for a wide range of ligand concentrations under anoxic conditions at pH 7.0. Comparisons were made to ligandinduced U mobilization from noncrystalline U(IV). For both U phases, aqueous U concentrations remained low in the absence of organic ligands (500 times more U mobilization). This work shows the potential of numerous organic ligands present in the environment to mobilize both recalcitrant and labile U forms under anoxic conditions to hazardous levels and, in doing so, undermine the stability of immobilized U(IV) sources.

Nanoplastics (NPs) and natural organic matter (NOM) are ubiquitous and usually present simultaneously in the environment. Both NPs and NOM can be adsorbed to minerals such as iron-(hydr)oxides, with such interactions being important for controlling their fate in the environment. However, the quantification of NPs and NOM in mixtures remains challenging even under controlled conditions in laboratory studies. In this research, a UV–Vis method was established to quantify concentrations of NOM, such as humic acid (HA) and fulvic acid (FA), and polystyrene NPs (PSNPs) in mixtures. In addition, both original NOM samples and those recovered following adsorptive fractionation using an iron oxide (goethite, α-FeOOH) were mixed separately with PSNPs and their concentrations were further calculated via the developed UV–Vis method. The UV–Vis method performed well (recovery of 100 ± 16 %) with original NOM and PSNPs system at detection limits of 20.8 and 7.4 mgC L−1, respectively. Particularly, for original FA and PSNPs systems with carboxylic groups (PSNPs-COOH, 200 nm), a similar recovery rate could be obtained at detection limits of only 2.5 and 1.9 mgC L−1, respectively. For fractionated NOM and PSNPs systems, detection limits (31.2 mgC L−1 and 27.5 mgC L−1, respectively) are increased to reach the same accuracy. Furthermore, the UV–Vis method can be used to estimate the proportion of HA that is adsorbed to PSNPs. The relative errors are < 13.7 % when the mass ratios of PSNPs and HA was between 1.6:1 and 8:1 and HA concentration was higher than 4.6 mgC L-1. This method developed can be applied to future laboratory research to investigate the interaction between NOM, NPs, and minerals.

The sustainability of tree harvest is questioned since harvest results in increased nutrient losses which may reduce nutrient stocks in forest soils, particularly in forests on acidified and poor soils with low base saturation. We used a new forest experiment to quantify nutrient stocks and nutrient uptake rates in mature forest stands, and to assess the forest nutrient balance in relation to different forest management scenarios: clearcutting, shelterwood and thinning; and whole-tree harvest (WTH), stem-only harvest (SOH) and wood only harvest (WOH, with on-site bark stripping). Forests were dominated by trees of Fagus sylvatica, Pseudotsuga Menziesii or Pinus sylvestris, all situated on poor, acidified soils. We measured forest biomass and nutrient stocks based on destructive sampling of fifteen mature trees per species and by using new, calibrated allometric relationships. Aboveground stocks of N, P, S, K, Ca, Mg, Mn, Cu, Fe and Zn were calculated for foliage, branches, stem bark and stem wood. Annual forest growth and nutrient uptake were determined using tree ring measures and allometric relationships. Organic layer nutrient stocks and available nutrients in the mineral soil were determined following intensive soil sampling. Stands of beech, Douglas fir and Scots pine differed in aboveground biomass and nutrient stocks, with highest biomass stocks in Douglas fir. However, beech stands had the highest aboveground nutrient stocks, nutrient uptake rates and nutrient losses following harvest, followed by Scots pine. Organic layer nutrient stocks generally exceeded aboveground nutrient stocks, except for the base cations and Mn. Compared to SOH, WTH increased nutrient export between 66% (Douglas fir) up to 100% (Scots pine), while WOH decreased the nutrient export between 23% (beech) up to 41% (Douglas fir). High aboveground base cation and Mn stocks indicate potential long-term threats to forest nutrition if trees are harvested. However, in Douglas fir stands, nutrient losses through SOH may fully recover when using rotation periods of 80 years. Contrary, negative Ca balances are predicted when applying SOH in beech and Scots pine, since Ca stocks are potentially depleted within 2 final fellings. WTH poses, regardless of the species, potential threats for sustainable biomass harvest as nutrients cannot be recovered using common rotation periods. WOH conserves nutrients within the forest posing opportunities for sustainable biomass harvest. For similar temperate forest on acidified, sandy soils, we therefore recommend to limit tree harvest depending on the tree species, and to avoid WTH and consider WOH to better conserve critical nutrients required for long-term forest recovery.

This study demonstrates two sustainable processes to produce electroactive biochars and their application in electroactive constructed wetlands (CWs) for providing a circular route for biomass utilization and technology up-gradation for wastewater treatment along with electricity generation. With the use of Canna indica biomass generated in CWs operation, the current study produced two different biochars that differ in their physico-(electro)chemical properties related to the preparation method used. This study used plasma based processing to produce ultrafast biochar (PB) within a few minutes resulting in more crystalline biochar with high electrical conductivity compared to the amorphous biochar material produced by using the drum kiln processed biochar (KB) method. These biochars were used in developing electroactive constructed wetlands coupled with microbial fuel cells (CW-MFC) and were operated in batch mode together with commercial granular graphite (GG) substrate-based CW-MFC as control. PB was developed from high-temperature plasma processing in 6.0 min, whereas KB was prepared in bulk amount from semi-controlled combustion process in kiln method and took 3–4 days before final biochar preparation. Electrical conductivity (EC) of the biochar and GG material were found to be in the order of PB > GG > KB, indicating PB as a highly conductive material that assisted in microbial electron transfer. Accordingly, the highest current and power densities of 628 mA m-3 and 126 mW m-3, respectively, were also achieved with PB. The COD removal of 72.42 ± 2.61 %,72.32 ± 2.98 % and 59.91 ± 3.21 % was found in CW-MFC-GG, CW-MFC-KB and CW-MFC-PB microcosms, respectively.

The contamination of greenhouse vegetable soils with antibiotics and antibiotic resistance genes (ARGs), caused by the application of livestock and poultry manure, is a prominent environmental problem. In this study, the effects of two ecological earthworms (endogeic Metaphire guillelmi and epigeic Eisenia fetida) on the accumulation and transfer of chlortetracycline (CTC) and ARGs in a soil–lettuce system were studied via pot experiments. The results revealed that earthworm application accelerated the removal of the CTC from the soil and lettuce roots and leaves, with the CTC content reducing by 11.7–22.8 %, 15.7–36.1 %, and 8.93–19.6 % compared with that of the control, respectively. Both earthworms significantly reduced the CTC uptake by lettuce roots from the soil (P < 0.05) but did not change the CTC transfer efficiency from the roots to leaves. The high-throughput quantitative PCR results showed that the relative abundance of ARGs in the soil and lettuce roots and leaves decreased by 22.4–27.0 %, 25.1–44.1 %, and 24.4–25.4 %, respectively, with the application of earthworms. Earthworm addition decreased the interspecific bacterial interactions and the relative abundance of mobile genetic elements (MGEs), which helped reduce the dissemination of ARGs. Furthermore, some indigenous soil antibiotic degraders (Pseudomonas, Flavobacterium, Sphingobium, and Microbacterium) were stimulated by the earthworms. The results of redundancy analysis indicated that the bacterial community composition, CTC residues, and MGEs were the main parameters affecting the distribution of ARGs, accounting for 91.1 % of the total distribution. In addition, the bacterial function prediction results showed that the addition of earthworms reduced the abundance of some pathogenic bacteria in the system. Overall, our findings imply that earthworm application can substantially reduce the accumulation and transmission risk of antibiotics and ARGs in soil–lettuce systems, providing a cost-effective soil bioremediation practice for addressing antibiotic and ARGs contamination to guarantee the safety of vegetables and human health.

Excessive application of fertilizers has caused a high load of phosphorus (P) in the North China Plain. The fate of P and its effects on aquatic ecosystems depend on its chemical speciation in soils. However, few studies systematically investigated the transport and retardation of different P species in the fluvo-aquic soil. In this study, the transport of inorganic P (orthophosphate, PO4), organic P (phytic acid, PA) and particulate P (hydroxyapatite nanoparticles, nHAP) in the fluvo-aquic soil were investigated by column experiments, and their retardation from major soil components such as kaolin, CaCO3, Al2O3, and goethite (GT) was also investigated by monitoring breakthrough curves and fitting transport models. The transport of P species in fluvo-aquic soil followed the order of PO4 > PA > nHAP. A high fraction of increased clay and mineral particle-associated P (P-E) was observed for PO4 and PA; while significant Ca-associated P (P-Ca) for nHAP. Under the experimental conditions, both CaCO3 and GT were the most influential factors for PO4, PA, and nHAP retention. Goethite strongly inhibited PO4 transport due to its high PO4 adsorption capacity, while CaCO3 strongly inhibited PA transport due to its strong association with PA under alkaline conditions. Both CaCO3 and GT can severely inhibit nHAP transport due to the favorable electrostatic conditions as well as the Ca2+ bridging effect. These results indicated that CaCO3 played a key role in regulating the retention of organic P and particulate P in the calcareous soil, and also suggested the important role of Fe (hydr)oxides in controlling the transport of inorganic P, which could out-compete that of CaCO3.

To explore the responses of soil microbial communities to concentration gradients of antibiotic residues in soil, 32 soil samples were collected from a typical greenhouse vegetable production base in Northern China in 2019. The total concentrations of 26 antibiotic residues in these soil samples was 83.24–4237.93 μg·kg−1, of which metabolites of tetracyclines were 23.34–1798.80 μg·kg−1. The total concentrations in 32 samples were clustered into three levels (L: 300 μg·kg−1) to elucidate the impacts of antibiotic residues on the diversity, structure, composition, function and antibiotic resistome of soil microbial community. Results showed that higher concentration of antibiotic residues in soil was prone to decrease the diversity and shift the structure and composition of soil microbial community. Antibiotic resistome occurred in soils with antibiotic residues exceeding 300 μg·kg−1. Interactions among soil bacteria followed the order of H > L > M, consistent with the relative abundances of mobile genetic elements. Bacteroidetes and Firmicutes were the top attributors impacting the profile of antibiotics in soil. According to weighted comprehensive pollution index of risk quotient, in 28.1 % of soil samples the residual antibiotics presented high ecological risk, whereas in the rest of soil samples the ecological risk is medium. The results will enrich the database and provide references for antibiotic contamination control in soils of the region and alike.

In this work, comparative study of paddy and upland soils were carried out to unravel mechanisms of enhanced soil organic carbon (SOC) sequestration in paddy soils using fractionation methods, 13C NMR and Nano-SIMS analysis, as well as organic layer thickness calculations (Core-Shell model). The results showed that although there is a strong increase in particulate SOC in paddy soils compared to that in the upland soils, the increase in mineral-associated SOC is more important, explaining 60–75% of SOC increase in the paddy soils. In the wet and dry alternate cycles of paddy soil, iron (hydr)oxides adsorb relatively small and soluble organic molecules (fulvic acid-like), promote catalytic oxidation and polymerization, thus accelerating formation of larger organic molecules. Upon reductive iron dissolution, these molecules are released and incorporated into existing less soluble organic compounds (humic acid or humin-like), which are coagulated and associated with clay minerals, becoming part of the mineral-associated SOC. The functioning of this “iron wheel” process stimulates accumulation of relatively young SOC into mineral-associated organic carbon pool, and reduces the difference in chemical structure between oxides-bound and clay-bound SOC. Further, the faster turnover of oxides and soil aggregates in paddy soil also facilities interaction between SOC and minerals. The formation of mineral-associated SOC may delay degradation of organic matter during both wet and dry period in the paddy field, therefore enhancing carbon sequestration in paddy soils.

Phosphate is one of the most frequently used fertilizers to promote the crop growth, whereas the impact of phosphate on the adsorption behaviors of cadmium (Cd) is complex. The objectives of this study were to reveal effects of pH, phosphate, and organic molecules on Cd adsorption onto soil (hydr)oxides, and to validate the reliability of the NOM-CD model in depicting effect of pH and phosphate on Cd solubility in soil systems. Materials and methods: In this study, effects of phosphate on Cd adsorption onto goethite and a paddy soil at pH 3–8 were studied by combing batch adsorption experiments with an advanced surface complexation model, i.e., natural organic matter-charge distribution (NOM-CD) model. In the NOM-CD model, the adsorption of ions onto oxides in the absence of NOM is calculated with the charge distribution and multi-site complexation (CD-MUSIC) model. Results and discussion: Adsorption of Cd onto goethite is dramatically increased with the addition of phosphate at pH 5–8, whereas effects of citric acid on Cd adsorption are weaker. The synergic co-adsorption of Cd and phosphate onto goethite, according to CD-MUSIC model, is mainly due to electrostatic attractions of these two ions instead of formation ternary surface complex. The NOM-CD model can basically predict variations of Cd solubility in the soil system, and it is observed only a slight increase of Cd solubility with phosphate addition under acidic conditions. It might be caused by competitive adsorption between NOM and phosphate to soil (hydr)oxides, which leads to a higher amount of Cd binding by dissolved organic matters in soil solution, thus inhibiting Cd adsorption. Conclusions: Electrostatic attraction dominates the co-adsorption of Cd and phosphate onto goethite, whereas the interactions between Cd-P-oxide-NOM result in negligible effects of phosphate on Cd solubility in the soil. Overall, this study revealed that the NOM-CD model could make predictions on the distribution of Cd at soil–water interface, and the outcome of this study can provide a more in-depth understanding of the factors controlling Cd solubility and mobility in contaminated soil and sediment environment. Graphical Abstract: [Figure not available: see fulltext.].

Enhanced weathering is a negative emission technology that involves the spread of crushed silicate minerals and rocks on land and water. When applied to agricultural soils, the resulting increase in soil pH and release of nutrients may co-benefit plant productivity. Silicate minerals and rocks differ in their enhanced weathering potential, i.e., their potential for both carbon dioxide (CO2) sequestration and soil quality improvements. However, studies comparing silicate minerals and rocks for this dual potential are lacking. Therefore, we compared the enhanced weathering potential of olivine (Mg2SiO4), basalt, wollastonite (CaSiO3), and two minerals that are novel in this context, anorthite (CaAl2Si2O8) and albite (NaAlSi3O8). A down-flow soil column experiment was designed allowing for measurements on soils and leachate, and calculations of organic and inorganic carbon budgets. Our results showed comparatively high CO2 capture by enhanced wollastonite and olivine weathering. Furthermore, CO2 capture per m2 specific surface area indicated potential for enhanced anorthite and albite weathering. Calculated carbon budgets showed that most treatments produced net CO2 emissions from soils, likely related to the short duration of this experiment. All silicates generally improved soil quality, with soil nickel contents remaining below contamination limits. However, nickel concentrations in leachates from olivine-amended soils exceeded the groundwater threshold value, stressing the importance of monitoring nickel leaching. We found a relatively high enhanced weathering potential for wollastonite, while the potential for olivine may be constrained by nickel leaching. The promising results for anorthite and albite indicate the need to further quantify their enhanced weathering potential.

Nanotechnology may be used to design more performant copper agrochemicals. Assessing the benefits and risks of the novel nano-products requires a good understanding of their fate in soil relative to other forms of copper. This study compares nine forms of Cu including nano and conventional Cu-based formulations, as well as their salt or bulk equivalents. Readily available Cu was extracted with 0.01 M CaCl2 over a period of 29 days in three soils with contrasting properties. For eight out of nine formulations, available Cu decreased over time indicating that complexation of Cu with soil phases was the process determining the availability of Cu. Freshly suspended CuO nanoparticles were the only form where available Cu increased over time, indicating that dissolution was limiting availability. The complexation/dissolution kinetics were mainly determined by the soil pH, whereas both soil pH and OC% determined the equilibrium concentration of Cu in the soil solution, in line with results from equilibrium modelling. Overall, the fraction of readily available Cu was very low in all cases, reaching

The transport of nanoplastics (NPs) through porous media is influenced by dissolved organic matter (DOM) released from agricultural organic inputs. Here, cotransport of NPs with three types of DOM (biocharDOM (BCDOM), wheat strawDOM (WSDOM), and swine manureDOM (SMDOM)) was investigated in saturated goethite (GT)-coated sand columns. The results showed that codeposition of 50 nm NPs (50NPs) with DOM occurred due to the formation of a GT-DOM-50NPs complex, while DOM loaded on GT-coated sand and 400 nm NPs (400NPs) aided 400NPs transport due to electrostatic repulsion. According to the quantum chemical calculation, humic acid and cellulose played a significant role in 50NPs retardation. Owing to its high concentration, moderate humification index (HIX), and cellulose content, SMDOM exhibited the highest retardation of 50NPs transport and promoting effect on 400NPs transport. Owing to a high HIX, the effect of BCDOM on the mobility of 400NPs was higher than that of WSDOM. However, high cellulose content in WSDOM caused it to exhibit a 50NPs retardation ability that was similar to that of BCDOM. Our results highlight the particle size selectivity and significant influence of DOM type on the transport of NPs and elucidate their quantum and colloidal chemical-interface mechanisms in a typical agricultural environment.

Aerobic methane oxidation (MOx) depends critically on the availability of copper (Cu) as a crucial component of the metal centre of particulate methane monooxygenase, one of the main enzymes involved in MOx. Some methanotrophs have developed Cu acquisition strategies, in which they exude Cu-binding ligands termed chalkophores under conditions of low Cu availability. A well-characterised chalkophore is methanobactin (mb), exuded by the microaerophilic methanotroph Methylosinus trichosporium OB3b. Aerobic methanotrophs generally reside close to environmental oxic-anoxic interfaces, where the formation of Cu sulphide phases can aggravate the limitation of bioavailable Cu due to their low solubility. The reactivity of chalkophores towards such Cu sulphide mineral phases has not yet been investigated. In this study, a combination of dissolution experiments and equilibrium modelling was used to examine the dissolution and solubility of bulk and nanoparticulate Cu sulphide minerals in the presence of mb as influenced by pH, oxygen and natural organic matter. In general, we show that mb is effective at increasing the dissolved Cu concentrations in the presence of a variety of Cu sulphide phases that may potentially limit Cu bioavailability. More Cu was mobilised per mole of mb from Cu sulphide nanoparticles compared with well-crystalline bulk covellite (CuS). In general, the efficacy of mb at mobilising Cu from Cu sulphides is pH-dependent. At lower pH, e.g. pH 5, mb was ineffective at solubilizing Cu. The presence of mb increased dissolved Cu concentrations between pH 7 and 8.5, where the solubility of all Cu sulphides is generally low, both in the presence and absence of oxygen. These results suggest that chalkophore-promoted Cu mobilisation from sulphide phases is an effective extracellular mechanism for increasing dissolved Cu concentrations at oxic-anoxic interfaces, particularly in the neutral to slightly alkaline pH range. This suggests that aerobic methanotrophs may be able to fulfil their Cu requirements via the exudation of mb in natural environments where the bioavailability of Cu is constrained by very stable Cu sulphide phases., Geobiology, 20 (5), ISSN:1472-4677, ISSN:1472-4669

Atmospheric deposition is an essential cadmium (Cd) pollution source in agricultural ecosystems, entering crops via roots and leaves. In this study, atmospherically deposited Cd was simulated using cadmium sulfide nanoparticles (CdSN), and chili (Capsicum frutescens L.) was used to conduct a comparative foliar and root experiment. Root and foliar uptake significantly increased the Cd content of chili tissues as well as the subcellular Cd content. Scanning electron microscopy and high-resolution secondary ion mass spectrometry showed that Cd that entered the leaves via stomata was fixed in leaf cells, and the rest was mainly through phloem transport to the other organs. In leaf, stem, and root cell walls, Cd signal intensities were 47.4%, 72.2%, and 90.0%, respectively. Foliar Cd uptake significantly downregulated purine metabolism in leaves, whereas root Cd uptake inhibited stilbenoid, diarylheptanoid, and gingerol biosynthesis in roots. Root uptake contributed 90.4% Cd in fruits under simultaneous root and foliar uptake conditions attributed to xylem and phloem involvement in Cd translocation. Moreover, root uptake had a more significant effect on fruit metabolic pathways than foliar uptake. These findings are critical for choosing pollution control technologies and ensuring food security.

The combination of biochar (BC) and iron minerals improves their pollutant adsorption capacity. However, little is known about the reactivity of BC-iron mineral composites regarding their interaction and change in the pore structure. In this study, the mechanism of cadmium (Cd) adsorption by BC-iron oxide composites, such as BC combined with ferrihydrite (FH) or goethite (GT), was explored. The synergistic effect of the BC-FH composite significantly improved its Cd adsorption capacity. The adsorption efficiencies of BC-FH and BC-GT increased by 15.0% and 10.8%, respectively, compared with that of uncombined BC, FH, and GT. The strong Cd adsorption by BC-FH was attributed to stable interactions and stereoscopic pore filling between BC and FH. The scanning electron microscopy results showed that FH particles entered the BC pores, whereas GT particles were loaded onto the BC surface. FTIR spectroscopy showed that GT covered a larger area of the BC surface than FH. After loading FH and GT, BC porosities decreased by 9.3% and 4.1%, respectively. Quantum chemical calculations and independent gradient mode analysis showed that van der Waals interactions, H-bonds, and covalent-like interactions maintained stability between iron minerals and BC. Additionally, humic acid increased the agglomeration of iron oxides and formed larger particles, causing additional aggregates to load onto the BC surface instead of entering the BC pores. Our results provide theoretical support to reveal the interfacial behavior of BC-iron mineral composites in soil and provide a reference for field applications of these materials for pollution control and environmental remediation.

We steered the soil microbiome via applications of organic residues (mix of cover crop residues, sewage sludge + compost, and digestate + compost) to enhance multiple ecosystem services in line with climate-smart agriculture. Our result highlights the potential to reduce greenhouse gases (GHG) emissions from agricultural soils by the application of specific organic amendments (especially digestate + compost). Unexpectedly, also the addition of mineral fertilizer in our mesocosms led to similar combined GHG emissions than one of the specific organic amendments. However, the application of organic amendments has the potential to increase soil C, which is not the case when using mineral fertilizer. While GHG emissions from cover crop residues were significantly higher compared to mineral fertilizer and the other organic amendments, crop growth was promoted. Furthermore, all organic amendments induced a shift in the diversity and abundances of key microbial groups. We show that organic amendments have the potential to not only lower GHG emissions by modifying the microbial community abundance and composition, but also favour crop growth-promoting microorganisms. This modulation of the microbial community by organic amendments bears the potential to turn soils into more climate-smart soils in comparison to the more conventional use of mineral fertilizers.

Adsorption and transport of levofloxacin (LEV) and ofloxacin (OFL) enantiomers in a matrix containing goethite and natural organic matter (NOM) were investigated using batch and column experiments. In batch studies, competition and enantioselectivity were observed in the adsorption of LEV and OFL. Enantioselectivity upon adsorption was investigated by comparing changes in the enantiomer fraction (EF) (the ratio of LEV to the sum of LEV and OFL remaining in the solution) after and before adsorption. At pH < 7, there was hardly any selectivity in adsorption of OFL and LEV to goethite. At pH > 7, OFL showed a stronger adsorption than LEV to goethite, and this preference remained when NOM samples of Leonardite humic acid (LHA) and Elliott Soil fulvic acid (ESFA) were added. However, when Suwannee River NOM (SRNOM) was added, the preference was reversed, and LEV was adsorbed more strongly. In single systems, the presence of different types of NOM increased adsorption of LEV and OFL, especially LEV. In column studies, preloaded NOM decreased the transport of LEV and OFL through goethite-coated sand. The EF values in the effluent increased with retention time and reached the largest values (0.59–0.72) at around 1.5 pore volume (PV), and then decreased again, reaching a stable value at 5.0–30.0 PV. Both batch and column experiments showed that, fractionation of LEV and OFL occurred during adsorption and transport in the presence of NOM-goethite complexes, which would eventually affect their environmental fate

Knowledge of how arsenic (As) partitions among various phases in Fe-rich sulfidic environments is critical for understanding the fate and mobility of As in such environments. We studied the reaction of arsenite and arsenate sorbed on ferrihydrite nanoparticle surfaces with dissolved sulfide at varying S/Fe ratios (0.1–2.0) to understand the fate and transformation mechanism of As during sulfidation of ferrihydrite. By using aqueous As speciation analysis by IC-ICP-MS and solid-phase As speciation analysis by synchrotron-based X-ray absorption spectroscopy (XAS), we were able to discern the mechanism and pathways of As partitioning and thio-arsenic species formation. Our results provide a mechanistic understanding of the fate and transformation of arsenic during the codiagenesis of As, Fe, and S in reducing environments. Our aqueous-phase As speciation data, combined with solid-phase speciation data, indicate that sulfidation of As-sorbed ferrihydrite nanoparticles results in their transformation to trithioarsenate and arsenite, independent of the initial arsenic species used. The nature and extent of transformation and the thioarsenate species formed were controlled by S/Fe ratios in our experiments. However, arsenate was reduced to arsenite before transformation to trithioarsenate.

Phosphorus (P) is essential for plant growth, but most of the P in soils is not available for plant uptake as it binds strongly to mineral soil constituents. Additionally, the use of P in agriculture is challenged by both the current increase of the world population as well as a changing human diet towards more consumption of animal products. This results in a growing demand for food and P. Furthermore, the reserves of phosphate rock as source of mineral P fertiliser are declining, while areas that have historically received excessive P additions face environmental risks that are related to chronic dissolved P losses from legacy P soils to ground- and surface waters. These challenges associated with agricultural P use enforce us to increase productivity while using mineral P fertiliser in a more sustainable manner. Sustainable agricultural intensification will require adequate P fertiliser inputs, overcoming global P imbalances and finding ways to improve the utilisation of P already present in soil. This last strategy requires finding new ways to access soil P pools that are less available to plants. Exploring the role of earthworms in sustaining optimal P acquisition for plants can therefore contribute to solving the P challenges we are currently facing. In this thesis, I explored the role of earthworm-enhanced P-availability for improving soil P utilisation. My research primarily focussed on the effect of earthworms in grassland systems from the Netherlands, as grasslands are important to global food production, and can sustain large earthworm populations.The main objective of my thesis was to elucidate the effect of earthworms on plant-available P in soil and P uptake by grass, and to explore its potential to increase the sustainability of P nutrition of grass. The specific research objectives were (1) to assess the effect of different earthworm species on plant-available P and relate this to a) physico-chemical soil properties and b) earthworm ecology; (2) to determine the controlling mechanisms of earthworm-enhanced P-availability and quantify the relative importance of all contributing mechanisms; (3) to assess the effect of earthworm diversity on plant-available P; and (4) to evaluate if the effect of earthworms on plant-available P results in an increased grass P uptake and biomass production under realistic field conditions.My results showed that while all investigated earthworm species increased the total pool of reversibly adsorbed P, a large variation exists in the ability of earthworm species to alter the extent to which P is present in readily plant-available forms. This variation was not related to classical earthworm ecological classification, and species from the same functional group showed large variation in cast properties like pH and dissolved organic carbon as measured in water extracts. In turn, this variation could be linked to the existing variation in ortho-P solubility measured in the same extracts. It was therefore concluded that multiple pathways contributed to earthworm-enhanced P-availability.These multiple pathways were quantified further, and their relative importance was assessed. The probe-ion method, which derives the reactive surface area (RSA) of a soil, in combination with surface complexation modelling revealed a so far unconsidered mechanism: the decrease of the RSA of metal-(hydr)oxides in casts by particle growth, resulting in a decrease of the surface area that is available for P adsorption. The contribution of the controlling mechanisms of earthworm-enhanced P-availability in earthworm casts consists of: a) a relatively small effect of the increase of pH in casts; b) a major contribution of P addition through stimulated mineralisation inside the earthworm gut; c) a potentially major effect of a decrease in the RSA of casts by particle growth which is catalysed by the formation of Fe2+ during the reducing conditions caused by mineralisation; and d) a decrease in the competition between natural organic matter and P for binding sites on metal-(hydr)oxides in casts compared to the bulk soil. The reduction of the RSA was only observed for Fe-(hydr)oxide-dominated soils, whereas it was absent or minor in Al-(hydr)oxide-dominated soils. This demonstrated that soil mineralogy influences earthworm-enhanced P-availability and suggests that earthworms have the largest potential to improve the sustainability of P use in Fe-(hydr)oxide-dominated soils.All controlling mechanisms of earthworm-enhanced P-availability are directly or indirectly related to the capacity of an earthworm to mineralise the organic material it ingests. The potential activity of phosphatase enzymes that catalyse the mineralisation process of monoester P compounds was considerably increased by earthworms in the order casts>burrows>bulk soil. Phosphatase activity varied among earthworm species, and correlated with the P content of grass shoots, suggesting a direct earthworm-induced effect on grass P uptake through mineralisation of organic P.My mesocosm field experiment to the effect of earthworm diversity on grass biomass production and P uptake did not show an effect of a larger number of earthworm species on P uptake at the end of the experiment. However, using a multiple linear regression model on established communities, A. longa and L. terrestris were identified as keystone species to increase grass P uptake and biomass production. Furthermore, this study showed that the effect of earthworms on grass P uptake was not only present under controlled greenhouse conditions but can also be observed at the larger scale of more realistic field conditions.This research concludes that earthworm-enhanced P-availability has potential to contribute to a more sustainable P nutrition for agricultural grasslands in (the future of) the Netherlands. However, the challenges associated with agricultural P use are likely too large to be solved by a single approach. A combination of several approaches is needed by agriculture to provide an adequate P nutrition to grass on low agronomic P-status soils. My research shows that stimulating earthworm populations to increase the utilisation of P in soil could be one of those approaches. Future research should focus on assessing the effect of earthworm-enhanced P-availability on a global scale and its contribution to the utilisation of soil P over longer periods of time. Furthermore, future research should particularly focus on combining earthworms with other approaches that aim to increase P uptake from soils with a low P-status.&nbsp

Hematite is ubiquitous in nature and holds great promise for a wide variety of applications in many frontiers of environmental issues such as heavy metal remediation in environment. Over the past decades, numerous efforts have been made to control and tailor the crystal structures of hematite to improve its adsorption performance for heavy metal ions (HMIs). It is now well established that the adsorption behavior of hematite nanocrystals is strongly affected by their particle sizes, crystal facet contributions, and defective structures. This review examined the size- and facet-dependent hematite, as well as the defective hematite according to their fabrication methods and growth mechanisms. Furthermore, the adsorption performance of various hematite particles for HMIs were introduced and compared to clarify the structure-active relationships of hematite. We also overviewed the advances in charge distribution (CD)-multisite complexation (MUSIC) modeling studies about the HMIs adsorption at the hematite-water interface and the binding parameters. The Present review systematically describes how the formation conditions impact the structural and surface properties of hematite particles, thereby providing new strategies for enhancing the performance of hematite for environmental remediation.

In nature, zinc (Zn) ions interact with natural organic matter and soil metal (hydr)oxides. The resulting solid-solution partitioning is of major importance for the geochemical cycling and environmental risks of toxicity and deficiency. Ferrihydrite (Fh) is an important proxy for the natural metal (hydr)oxide fraction in soils. At its surfaces, Zn2+ ions have multi-component interactions, for instance with phosphate (PO43−). In nature, the latter is particularly relevant in topsoils since PO4 is omnipresent and has a high affinity for Fh. Zinc and phosphate ions may bind cooperatively by electrostatic forces and/or by ternary complex formation. This was studied presently with batch adsorption experiments using freshly prepared and well-characterized Fh nanoparticles. The data have been interpreted using the charge distribution (CD) model combined with a surface structural model for Fh that includes site heterogeneity. The CD coefficients have been derived independently by optimization of the surface geometries with molecular orbital calculations applying density functional theory (MO/DFT/B3LYP/6-31+G**). These computations confirm that upon adsorption Zn can change spontaneously its coordination number from 6 to 4. In agreement with literature results from X-ray absorption spectroscopy (XAS), Zn is bound at low loading as a double-corner bidentate complex. At higher loading, the number of ions in the second shell of Zn decreases according to published XAS results. Our model with the formation of surface complexes with single corner-sharing can quantitatively predict this decrease. Zn polymerization only occurs at a very high molar Zn/Fe ratio (>0.1), which can be described using a neutral, hydrolyzed Zn-dimer species. The presence of PO4 enhances the Zn adsorption, especially in the pH range 5–6. At the Zn and PO4 levels studied, no ternary Zn-P surface complexes can be revealed. For comparison, we re-interpreted copper (Cu)-PO4-Fh adsorption literature data with similar metal and PO4 loadings. In line with the results for Zn, no ternary Cu-P surface complexes were found. We conclude that electrostatic interactions explain metal adsorption at background levels in multi-component systems, and that ternary complexes may form only at rather extreme metal or PO4 loading conditions.

The method for the dynamical calculation of leaching and run-off of heavy metals from agricultural and natural soils has been improved on the basis of the most recent measurements and knowledge. The number of metals has been expanded to 14 and now includes next to the metal included previously (Cd, Cu, Ni, Pb, Zn) also models for As, Ba, Co, Cr, Mo, Sb, Se, V, and U. To this purpose Freundlich partition relations have been derived for these 14 metals. The vertical distribution of the reactive metals content in soil used to calculate the solution concentration has been revised using recently acquired data and auxiliary variables include the P content in the soil and the amount of Fe and Al oxides. Finally also the regional schematization of concentrations in the upper groundwater has been revised and extended with information on the 9 new metals. In the context of the national and international obligation to report the emissions and pollution of surface water, the diffuse source leaching and run-off of heavy metals from the soil to the surface water has been calculated using the revised model. For consistency, the data used for and results from the National Water Quality Model for nutrients have been used

Assessing the surface reactivity of metal (hydr)oxides in soils is essential for quantifying ion adsorption phenomena that control the availability of nutrients and pollutants. Despite the high natural abundance of Fe and Al (hydr)oxides in intensively weathered environments, the surface reactivity of these pedogenic materials has not been consistently characterized for weathered tropical soils. Here, we used a novel probe-ion methodology combined with state-of-the-art surface complexation modelling (SCM) to derive the reactive surface area (RSA) of the soils, as well as the amount of phosphate (PO4) that can be potentially desorbed (R-PO4) from the natural fraction of metal (hydr)oxides and thereby controlling the solid-solution partitioning of PO4. We applied this methodology to a series of weathered topsoils from the sub-Saharan region. The results showed that nanocrystalline ferrihydrite (Fh) is a better proxy than well-crystallized goethite for describing with SCM the reactivity of the natural metal (hydr)oxides, even though well-crystallized materials dominate the mass fraction of metal (hydr)oxides of these weathered tropical soils. Using Fh as a proxy in the SCM, the RSA ranged from ∼2 to 40 m2 g−1 soil. Nanoparticles with a mean diameter of ∼1.5–5.0 nm dominate the reactive fraction of metal (hydr)oxides in these tropical topsoils. Our SCM in conjunction with soil extractions indicates that only a fraction of the total PO4 associated with the metal (hydr)oxides is reversibly adsorbed, whereas the majority of the total PO4 pool, on average ∼64%, is occluded in the crystalline Fe and Al (hydr)oxide fraction. Only this smaller reversibly adsorbed fraction is thus available for participating in sorption reactions that determine the solid-solution partitioning of PO4. Overall, this research provides new insights into the reactivity of the metal (hydr)oxide fraction in weathered tropical soils and highlights the relevance of these pedogenic materials in determining the speciation and availability of PO4.

Eén van de maatregelen die in het klimaatakkoord is voorgesteld om de klimaatdoelen van 2030 te gaan halen is het vastleggen van koolstof in minerale landbodems. Een maatregel die niet leidt tot emissiebeperking, maar zorgt voor CO2 vastlegging. Het ministerie van Landbouw, Natuur en Voedselkwaliteit heeft in het kader van het onderzoek hoe de klimaatdoelen voor landbouw en landgebruik kunnen worden gehaald, gevraagd de belangrijkste vragen en antwoorden rondom koolstofvastlegging in minerale landbouwbodems op een toegankelijke manier te beschrijven. Deze publicatie geeft in 30 vragen en antwoorden de stand van het onderzoek op dit moment weer.

Forensic methods to independently trace timber origin are essential to combat illegal timber trade. Tracing product origin by analysing their multi-element composition has been successfully applied in several commodities, but its potential for timber is not yet known. To evaluate this potential the drivers of wood multi-elemental composition need to be studied. Here we report on the first study relating wood multi-elemental composition of forest trees to soil chemical and physical properties. We studied the reactive soil element pools and the multi-elemental composition in sapwood and heartwood for 37 Azobé (Lophira alata) trees at two forest sites in Cameroon. A total of 46 elements were measured using ICP-MS. We also measured three potential drivers of soil and wood elemental composition: clay content, soil organic matter and pH. We tested associations between soil and wood using multiple regressions and multivariate analyses (Mantel test, db-RDA). Finally, we performed a Random Forest analysis of heartwood elemental composition to check site assignment accuracy. We found elemental compositions of soil, sapwood and heartwood to be significantly associated. Soil clay content and organic matter positively influenced individual element concentrations (for 13 and 9 elements out of 46 respectively) as well as the multi-elemental composition in wood. However, associations between wood and topsoil elemental concentrations were only significant for one element. We found close associations between element concentrations and composition in sapwood and heartwood. Lastly, the Random Forest assignment success was 97.3 %. Our findings indicate that wood elemental composition is associated with that in the topsoil and its variation is related to soil clay and organic matter content. These associations suggests that the multi-elemental composition of wood can yield chemical fingerprints obtained from sites that differ in soil properties. This finding in addition to the high assignment accuracy shows potential of multi-element analysis for tracing wood origin.

We steered the soil microbiome via applications of organic residues (mix of cover crop residues, sewage sludge + compost, and digestate + compost) to enhance multiple ecosystem services in line with climate-smart agriculture. Our result highlights the potential to reduce greenhouse gases (GHG) emissions from agricultural soils by the application of specific organic amendments (especially digestate + compost). Unexpectedly, also the addition of mineral fertilizer in our mesocosms led to similar combined GHG emissions than one of the specific organic amendments. However, the application of organic amendments has the potential to increase soil C, which is not the case when using mineral fertilizer. While GHG emissions from cover crop residues were significantly higher compared to mineral fertilizer and the other organic amendments, crop growth was promoted. Furthermore, all organic amendments induced a shift in the diversity and abundances of key microbial groups. We show that organic amendments have the potential to not only lower GHG emissions by modifying the microbial community abundance and composition, but also favour crop growth-promoting microorganisms. This modulation of the microbial community by organic amendments bears the potential to turn soils into more climate-smart soils in comparison to the more conventional use of mineral fertilizers.

It is generally assumed that the dependence of conventional agriculture on artificial fertilizers and pesticides strongly impacts the environment, while organic agriculture relying more on microbial functioning may mitigate these impacts. However, it is not well known how microbial diversity and community composition change in conventionally managed farmers' fields that are converted to organic management. Here, we sequenced bacterial and fungal communities of 34 organic fields on sand and marine clay soils in a time series (chronosequence) covering 25 years of conversion. Nearby conventional fields were used as references. We found that community composition of bacteria and fungi differed between organic and conventionally managed fields. In the organic fields, fungal diversity increased with time since conversion. However, this effect disappeared when the conventional paired fields were included. There was a relationship between pH and soil organic matter content and the diversity and community composition of bacteria and fungi. In marine clay soils, when time since organic management increased, fungal communities in organic fields became more dissimilar to those in conventional fields. We conclude that conversion to organic management in these Dutch farmers' fields did not increase microbial community diversity. Instead, we observed that in organic fields in marine clay when time since conversion increased soil fungal community composition became progressively dissimilar from that in conventional fields. Our results also showed that the paired sampling approach of organic and conventional fields was essential in order to control for environmental variation that was otherwise unaccounted for.

Multi-surface modelling (MSM) is an important tool to predict heavy metal partitioning and speciation in soils. However, calcareous clay soils contaminated by smelting activities and mine waste have so far received little attention in MSM studies. In this work, 6 paired soil samples taken nearby former Zn smelters and at further distance were used for quantifying the essential input parameters for MSM including the size of the geochemically reactive pool of heavy metals and the reactivity of soil organic matter (SOM) for metal binding. The reactive heavy metal pool (Cd, Cu, Ni, Pb, and Zn) in these samples was determined by extracting soil with 0.43 M HNO3 and 0.005 M DTPA. For both extraction methods, the contribution of all heavy metals to their total contents was larger in most of the soil samples taken nearby former Zn smelters than in the paired samples from further distance. Furthermore, the amounts of heavy metals extracted with 0.43 M HNO3 were consistently larger than those extracted with 0.005 M DTPA. The sum of the humic acid (HA), fulvic acid (FA) + hydrophobic organic neutral (HON) fraction varied between 6.2 and 43% of total SOM with an average of 24%, which is at the lower end of what is commonly reported in literature. The lower SOM reactivity might be attributed to a lower humification rate of fresh soil organic matter due to heavy metal contamination. The accuracy of the MSM-predicted predictions of solubility of the heavy metals, especially for Ni and Zn, was higher when the results of the DTPA extraction method were used as model input, than when using the results of the HNO3 extraction method, especially when the soil carbonate content was > 4%. Hence, the measurement of the geochemical reactivity of heavy metals by the 0.005 M DTPA extraction method and the reactivity of SOM enable adequate MSM predictions of the solubility of heavy metals in smelter slag-contaminated calcareous clay soils.

The method for the dynamical calculation of leaching and run-off of heavy metals from agricultural and natural soils has been improved on the basis of the most recent measurements and knowledge. The number of metals has been expanded to 14 and now includes next to the metal included previously (Cd, Cu, Ni, Pb, Zn) also models for As, Ba, Co, Cr, Mo, Sb, Se, V, and U. To this purpose Freundlich partition relations have been derived for these 14 metals. The vertical distribution of the reactive metals content in soil used to calculate the solution concentration has been revised using recently acquired data and auxiliary variables include the P content in the soil and the amount of Fe and Al oxides. Finally also the regional schematization of concentrations in the upper groundwater has been revised and extended with information on the 9 new metals. In the context of the national and international obligation to report the emissions and pollution of surface water, the diffuse source leaching and run-off of heavy metals from the soil to the surface water has been calculated using the revised model. For consistency, the data used for and results from the National Water Quality Model for nutrients have been used De methode voor het dynamisch berekenen van de uit- en afspoeling van zware metalen uit landbouw- en natuurbodems is verbeterd op basis van de meest recente metingen en kennis. Daarbij is het aantal metalen uitgebreid van 5 (Cd, Cu, Ni, Pb, Zn) naar in totaal 14 (As, Ba, Co, Cr, Mo, Sb, Se, V, U). Voor deze 14 metalen zijn opnieuw Freundlich-partitierelaties afgeleid waarbij deels een aangepast Freundlich model wordt gebruikt. De schematisering voor de verdeling van de reactieve gehalten aan metalen in de bodem is herzien op basis van data in boven- en ondergrond en hulpvariabelen waaronder fosfaat en het gehalte aan oxiden. Tot slot is ook de schematisering van concentraties in het bovenste grondwater verbeterd, o.a. met een uitbreiding met data voor de 9 nieuwe metalen. In het kader van de nationale en internationale verplichting om de emissies en belasting van oppervlaktewater te rapporteren, is met het herziene model de diffuse bron uit- en afspoeling van zware metalen vanuit de bodem naar het oppervlaktewater berekend. Voor de consistentie is aangesloten op de data gebruikt voor en resultaten afkomstig uit het Landelijk Waterkwaliteitsmodel voor nutriënten.

We screened different organic amendments as single application or in combination to observe their influence on their GWP as well as on plant yield in a mesocosm experiment with two agricultural soils. Additionally, we screened changes occurring in microorganisms through the application of organic amendments.

A thorough understanding of the complex redox coupling among manganese, arsenic, sulfur and oxygen in subsurface environments is still obscured by their metastable intermediate valances and speciation. Arsenic sulfide minerals may be disturbed by natural or anthropogenic activities, and encounter oxidants such as oxygen and reactive trivalent Mn species, and how these abiotic interactions impact the mineral dissolution and transformation of arsenic and sulfur species, remains unknown. In this study, we investigated the effects of dissolved Mn(III) and manganite (γ-MnIIIOOH) on the dissolution behaviors of orpiment (As2S3) and realgar (AsS) under anoxic and oxic conditions. Complementary control experiments were also performed with dissolved arsenite without reduced sulfur. Oxygen, dissolved Mn(III) or manganite did not induce the oxidation of dissolved arsenite within several weeks. Orpiment's initial dissolution is a non-redox process releasing of arsenite and sulfide, and the three above oxidants promoted the dissolution of orpiment by rapid oxidation of dissolved sulfide. However, only when both dissolved Mn(III) and dissolved oxygen were present, substantial accumulation of arsenate and sulfate were observed. These results suggested the critical role of sulfur species in abiotic arsenic transformation and a synergetic effect of Mn and oxygen on sulfur oxidation. In contrast to orpiment, the dissolution of realgar was a redox reaction that involved the oxidation of As(II) to As(III) and the direct releasing of sulfide, which could be promoted by both dissolved oxygen and manganite. The effect of dissolved Mn(III) and oxygen on the formation of arsenate and sulfate was also clearly observed during the dissolution of realgar. Despite of the slow abiotic oxidation of dissolved arsenite to arsenate in the presence dissolved Mn(III) and oxygen, the coexistence of sulfide could enable rapid accumulation of arsenate, accompanied by substantial transformation to sulfate. The evidence of thioarsenic species in these experiments provided a plausible explanation as an alternative pathway for the oxidation of the two elements by dissolved Mn(III). These results provide new insights for the Mn-As-S cycling in redox transition environments.

De grondwaterkwaliteit staat onder druk door klimaatverandering en maatschappelijke en technologische ontwikkelingen. In de bodem en ondergrond beschermen drie van nature aanwezige ‘barrières’ het grondwater tegen verontreinigingen. Afsluitende lagen zorgen voor een fysieke barrière; reactieve bestanddelen in de ondergrond vormen door afbraak, omzettingen en binding een geochemische barrière; en afbraak door micro-organismen in de bovengrond fungeert als een biologische barrière. In het project Kennisimpuls grondwaterkwaliteit is de beschermende werking van deze barrières in beeld gebracht en zijn risico’s voor aantasting van de barrières geanalyseerd.

In this study, the nano-scale spatial distribution of natural organic matter (NOM) on the surface of iron (hydr)oxides and its relevance to oxyanion (PO43−) and metal cation (Cd2+ and Cu2+) adsorption to the assemblage of oxide (goethite) and NOM (humic acids (HA) or fulvic acids (FA)) was investigated with experiments and advanced surface complexation modeling. Both the linear additive Multi-Surface model (MSM) and the more sophisticated Natural Organic Matter-Charge Distribution (NOM-CD) model were used. The MSM model ignores the effects of NOM-mineral interaction on ion adsorption, whereas the NOM-CD model considers this effect. The results showed that with the increase of NOM loading on oxides, deviation between the MSM and NOM-CD model became bigger for PO43−, but smaller for Cd2+ and Cu2+. Oxyanions bind mainly to oxides and therefore the competitive effect of NOM cannot be neglected, which explains the large difference between these two models for PO43−. On the contrary, at a relatively high NOM loading, a large fraction of NOM extends further away from the surface of oxides. Thus for metal cations that bind mainly to NOM, the influence of NOM-mineral interaction on their adsorption is small and the results of the MSM and NOM-CD model are similar. In top soils, the NOM loading on oxides is often high, therefore the linear additive MSM is applicable for metal cation speciation calculations as reported in many literatures. An approach based on the NOM-CD model was proposed, which can not only calculate the macroscopic solid-solution distribution of both cations and anions, but can also provide information regarding their microscopic surface speciation.

Biochars can remove potentially toxic elements, such as inorganic mercury [Hg(II)] from contaminated waters. However, their performance in complex water matrices is rarely investigated, and the combined roles of natural organic matter (NOM) and ionic composition in the removal of Hg(II) by biochar remain unclear. Here, we investigate the influence of NOM and major ions such as chloride (Cl-), nitrate (NO3-), calcium (Ca2+), and sodium (Na+) on Hg(II) removal by a wood-based biochar (SWP700). Multiple sorption sites containing sulfur (S) were located within the porous SWP700. In the absence of NOM, Hg(II) removal was driven by these sites. Ca2+bridging was important in enhancing removal of negatively charged Hg(II)-chloro complexes. In the presence of NOM, formation of soluble Hg-NOM complexes (as seen from speciation calculations), which have limited access to biochar pores, suppressed Hg(II) removal, but Cl-and Ca2+could still facilitate it. The ability of Ca2+to aggregate NOM, including Hg-NOM complexes, promoted Hg(II) removal from the dissolved fraction (

This article is composed of a commentary about the state of Integrated, Coordinated, Open, and Networked (ICON) principles (Goldman etal., 2021, https://doi.org/10.1029/2021ea002099) in Volcanology, Geochemistry, and Petrology (VGP), and discussion on the opportunities and challenges of adopting them. VGP encompasses a broad field that addresses volcanic, magmatic, hydrothermal, geomicrobial systems; process investigations that span the physical, geochemical and biological realms, including planetary geology; and one that is extensively supported by state-of-the-art research facilities. We suggest that an open, inclusive, collaborative and evolving model of an international coordinated network is critical to answering the most pressing challenges in VGP. In this commentary piece, we begin to discuss the elements of, challenges to, and path forward in developing such a model. For this team, ICON means collaboration, equitable access to data for the entire scientific community, and forging of partnerships that potentially contribute to more innovative ways of coordinating and sharing research. It also means bringing more equity to science, by implementing effective measures which consider access to funding, analytical equipment, resources, and mentors. More importantly, ICON to us means having important conversations around what we value in the advancement of science, perhaps exploring outside the idea of meritocracy and evaluating what individual traits can contribute to science outside what has traditionally been considered the norm.

Biochar nanoparticles (BCNPs) and iron mineral nanoparticles (IMNPs), such as ferrihydrite nanoparticles (FHNPs), magnetite nanoparticles (MTNPs), and goethite nanoparticles (GTNPs), are often combined and used in soil remediation. However, the stability and interaction of nanoparticles under various environmental conditions have not been investigated previously. In this study, settling experiments, a semi-empirical model, the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory, scanning electron microscopy (SEM) observations, and quantum chemical calculations were used to study the interaction and heteroaggregation of BCNPs and IMNPs. Settling of BCNPs-FHNPs and BCNPs-GTNPs was stable at neutral and alkaline pH (relative concentration of unsettled nanoparticles Cres’ = 0.679–0.824), whereas fast settling of BCNPs-IMNPs was observed at acidic pH (Cres’ = 0.104–0.628). By contrast, BCNPs-MTNPs consistently showed moderate settling regardless of the mass of magnetite at all pH (Cres’ = 0.423–0.673). Both humic acid (HA, 10 mg L−1) and ionic strength (IS, 10 and 100 mM) facilitated the settling of BCNPs-FHNPs and BCNPs-MTNPs systems, whereas the settling of BCNPs-GTNPs was sensitive only to IS. Fulvic acid (10 mg L−1) had a general stabilizing effect on the BCNPs-IMNPs systems. The results of SEM and quantum chemical calculations suggested that the interaction between BCNPs and FHNPs (-2755.58 kJ mol−1) was stronger than that between BCNPs and GTNPs (−1706.23 kJ mol−1) or MTNPs (−1676.73 kJ mol−1). The enhancement of heteroaggregation between BCNPs and IMNPs under unfavorable conditions (acidic pH, HA, and IS) was regulated by the strength of the interaction. Therefore, the enhancement of heteroaggregation of BCNPs-FHNPs was greater than that of BCNPs-MTNPs. In the BCNPs-GTNPs system, the high concentration and elongated structure of GTNPs may contribute greatly to heteroaggregation and settling with small interactions. Our results highlight the influence of pH, IS, and HA on the interaction between BCNPs and IMNPs. These results will be helpful in the application of BCNPs and IMNPs for soil remediation. Graphical Abstract

Eén van de maatregelen die in het klimaatakkoord is voorgesteld om de klimaatdoelen van 2030 te gaan halen is het vastleggen van koolstof in minerale landbodems. Een maatregel die niet leidt tot emissiebeperking, maar zorgt voor CO2 vastlegging. Het ministerie van Landbouw, Natuur en Voedselkwaliteit heeft in het kader van het onderzoek hoe de klimaatdoelen voor landbouw en landgebruik kunnen worden gehaald, gevraagd de belangrijkste vragen en antwoorden rondom koolstofvastlegging in minerale landbouwbodems op een toegankelijke manier te beschrijven. Deze publicatie geeft in 30 vragen en antwoorden de stand van het onderzoek op dit moment weer.

The production and degradation of plastic remains can result in nanoplastics (NPs) formation. However, insufficient information regarding the environmental behaviors of NPs impedes comprehensive assessment of their significant threats. In this study, the transport behavior of unmodified NPs (PSNPs), carboxyl-modified NPs (PSNPs−COOH), and amino-modified NPs (PSNPs−NH2) was investigated using column experiments in the presence and absence of goethite (GT) and diethylhexyl phthalate (DEHP). Quantum chemical computation was performed to reveal the transport mechanisms. The results showed that GT decreased the transport of NPs and the presence of DEHP decreased it further. Van der Waals forces and small electrostatic interactions coexisted between the PSNPs and GT and caused deposition. Ligand exchange caused greater deposition of PSNPs−COOH on GT-coated sand than that of PSNPs. Although hydrogen bonding existed between the DEHP and NPs with functional groups, an increase in the positive charge and chemical heterogeneity of the collector was the main reason for DEHP promoting the deposition of NPs. Because of low absolute negative zeta potential values, PSNPs−NH2 was sensitive to chemical heterogeneity, and thus fully deposited (over 96.9%) in GT and GT-DEHP-coated columns. Generally, the deposition of NPs due to chemical heterogeneity was more significant than that due to the formation of chemical bonds and van der Waals, electrostatic, and hydrogen interactions. Our results highlight that the surface charge and functional groups significantly influence the transport behaviors of NPs and elucidate the fate of NPs in the terrestrial environment.

Multi-element soil extractions such as Mehlich 3 (M3) have gained popularity in recent years, but comparing outcomes to other soil testing methods is not always straightforward. In this study, extraction mechanisms of M3, Olsen and neutral 1 M ammonium acetate (AA) soil tests were explored and transfer functions were derived between P-Olsen and P-M3 as well as between K-AA and K-M3. Soils from tropical and temperate areas were used to derive these P and K transfer functions and were evaluated separately. The application of these transfer functions for tropical soils was evaluated by using them as input for the Quantitative Evaluation of the Fertility of Tropical Soils (QUEFTS). AA and M3 generally extracted similar amounts of K, but relations between K-AA and K-M3 were different for tropical and temperate soils. For tropical soils, the transfer function did not require additional parameters besides K-M3 to predict K-AA, but for temperate soils inclusion of clay content and pH was needed. This difference between tropical and temperate soils was explained by clay mineralogy. The relation between P-Olsen and P-M3 in tropical soils was found to be dependent on pH, Al-M3, Fe-M3 and Ca-M3. P-Olsen and K-AA values, calculated with their respective transfer functions, were used as input for QUEFTS. The yields predicted with measured P-Olsen and Exch. K were used as benchmark. For 63 out of 81 soil samples, predicted maize yields with transfer functions deviated less than 10% from the benchmark. The largest deviations from the benchmark were found for low P-Olsen and K-AA values, which corresponds to QUEFTS maize yield predictions up to 3000 kg ha−1. We conclude that a M3 extraction results and soil pH can reliably be transferred to, and thus replace P-Olsen and K-AA determinations with the functions developed for tropical soils. The transfer functions can be used to generate input for the QUEFTS model with minor effects on yield predictions, thus expanding its applicability in cases where only M3 extraction results are available.

The key nutrient phosphorus (P) binds strongly to reactive soil particles, which makes it poorly available for plant uptake. In the search for sustainable ways to overcome a resulting P shortage, it has been shown that earthworms can increase the pool of plant available P and enhance plant P uptake under controlled (greenhouse) conditions. To validate these findings under field conditions and to study the effect of earthworm community composition, we conducted a mesocosm-field experiment on grassland. Mesocosms containing a sandy soil with a low P-status and communities of five earthworm species common to the Netherlands (Lumbricus rubellus, Aporrectodea caliginosa, Allolobophora chlorotica, Lumbricus terrestris and Aporrectodea longa; monocultures, three- or five-species mixtures and controls without earthworms) were installed in a field. Aboveground biomass production and P uptake of Lolium perenne were monitored for over two years. Earthworm community composition varied between the start and the end of the experiment, but multiple linear regression on the final earthworm communities yielded strong indications that earthworms increased both biomass production (R2adj = 0.52, p < 0.001, n = 76) and P uptake (R2adj = 0.48, p < 0.001, n = 76). The species A. longa and L. terrestris were most influential for this earthworm effect. We did not observe any general relations between the number of earthworm species in a community and a P effect. Our results suggest that earthworms can indeed increase grass biomass production and P uptake on a low P soil in the field, and can thereby contribute to making the P nutrition of our agricultural systems more sustainable.

It is generally assumed that the dependence of conventional agriculture on artificial fertilizers and pesticides strongly impacts the environment, while organic agriculture relying more on microbial functioning may mitigate these impacts. However, it is not well known how microbial diversity and community composition change in conventionally managed farmers’ fields that are converted to organic management. Here, we sequenced bacterial and fungal communities of 34 organic fields on sand and marine clay soils in a time series (chronosequence) covering 25 years of conversion. Nearby conventional fields were used as references. We found that community composition of bacteria and fungi differed between organic and conventionally managed fields. In the organic fields, fungal diversity increased with time since conversion. However, this effect disappeared when the conventional paired fields were included. There was a relationship between pH and soil organic matter content and the diversity and community composition of bacteria and fungi. In marine clay soils, when time since organic management increased, fungal communities in organic fields became more dissimilar to those in conventional fields. We conclude that conversion to organic management in these Dutch farmers’ fields did not increase microbial community diversity. Instead, we observed that in organic fields in marine clay when time since conversion increased soil fungal community composition became progressively dissimilar from that in conventional fields. Our results also showed that the paired sampling approach of organic and conventional fields was essential in order to control for environmental variation that was otherwise unaccounted for.

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

Data belonging to methodological comparison of organic carbon methods to quantify organic carbon in particulate (POM) and mineral-associated (MAOM) fractions in calcaerous soils.

Trace elements such as zinc (Zn), copper (Cu) and boron (B) are important micronutrients for crop production. Their bioavailability is essential to crops yield quantity and quality in many tropical soils. Nutrient bioavailability depends partly on the soil nutrient status, and in particular on the reactive and soluble fractions. Adsorption/desorption and precipitation/dissolution processes control the partitioning of the reactive pool over the solid and solution phase. However, so far the solid-solution partitioning of trace elements has mostly been studied in temperate and often contaminated soils. We studied, therefore, the solid-solution partitioning of Zn, Cu and B for 172 soils from Burundi, Rwanda and Kenya, using extensive soil characterization in combination with multi-surface modelling and two types of empirical Freundlich type partition relations. Our aim was to enhance the understanding of the soil chemical processes that control the solid-solution partitioning of the three micronutrients in these soils from the tropics with a multi-surface model, and to use this knowledge as benchmark to develop partition relations that require less input data and are more convenient tools for predicting the concentration in solution based on existing soil data. We show that the generic multi-surface model applied to these tropical soils performs similarly for Zn and Cu as in previous studies on temperate and contaminated soils. The Zn and Cu speciation was dominated by adsorption to soil organic matter, with an increased importance of metal (hydr)oxides with increasing pH. Given its generally low concentrations in these soils, dissolved organic matter was found to be important only for the solution speciation of Cu. The adsorption of B was mainly to metal (hydr)oxides at low pH, and with increasing pH soil organic matter became more important. The multi-surface model overestimated the dissolved B concentration for most soil samples, which we attributed to an inaccurate estimation of reactive B. Interestingly, the variation in observed and modeled solid-solution partitioning expressed as Kd of Cu and B among the soils was relatively small (∼1 log L kg−1), and the concentration in solution was consistently mainly controlled by the reactive concentration. Generally, the optimized partition relations resulted in a smaller prediction error compared to the multi-surface models. The partition relations in which the concentration in solution was optimized, resulted generally in an overestimation for the lowest observed concentrations, and an underestimation for highest concentrations of all three elements. Partition relations with optimized Freundlich parameters Kf and n resulted in more robust predictions since the prediction error was not related to the actual measured concentration. The partition relations from this study are easy-to-use tools for predicting the dissolved concentrations of Zn, Cu and B in soils from the tropics with low contents of these micronutrients and can therefore enhance the use of current existing soil information data for Sub-Saharan Africa.

De grondwaterkwaliteit staat onder druk door klimaatverandering en maatschappelijke en technologische ontwikkelingen. In de bodem en ondergrond beschermen drie van nature aanwezige ‘barrières’ het grondwater tegen verontreinigingen. Afsluitende lagen zorgen voor een fysieke barrière; reactieve bestanddelen in de ondergrond vormen door afbraak, omzettingen en binding een geochemische barrière; en afbraak door micro-organismen in de bovengrond fungeert als een biologische barrière. In het project Kennisimpuls grondwaterkwaliteit is de beschermende werking van deze barrières in beeld gebracht en zijn risico’s voor aantasting van de barrières geanalyseerd.