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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.

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

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.].

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.

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.

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.

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.

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.

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.

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.

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.

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.

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

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.

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.

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.

Adsorption of natural organic matter (NOM) to mineral surfaces is an important process determining the environmental fate and biogeochemical cycling of many elements. Natural organic matter consists of a heterogeneous mixture of soft and flexible organic molecules. Upon adsorption, size fractionation may occur, as well as changes in molecular conformation. Although very important, these phenomena have been omitted in existing adsorption models. Filling this gap, a novel framework for NOM adsorption to metal (hydr)oxides is presented. Humic acid (HA) was used as an analog for studying experimentally the NOM adsorption to goethite and its size fractionation as a function of pH, ionic strength, and surface loading. Size fractionation was evaluated for adsorption isotherms collected at pH 4 and 6, showing HA molecules of low molar mass were preferentially adsorbed. This phenomenon was incorporated into the new model. Consistent description of the HA adsorption data over the entire range of pH (3–11), ionic strength (2–100 mM), and surface loading (0.1–3 mg m−2) indicated that the spatial distribution of HA molecules adsorbed in the interface is a trade-off between maximizing the interaction of the HA ligands with the oxide surface and minimizing the electrostatic repulsion between HA particles as a result of interfacial crowding. Our advanced consistent framework is able to quantify changes in molar mass and molecular conformation, thereby significantly contributing to an improved understanding of the competitive power of HA for interacting on oxides with other adsorbed small organic acids as well as environmentally important oxyanions, such as phosphate, arsenate, and others.

International audience; A number of negative emission technologies (NETs) have been proposed to actively remove CO2 from the atmosphere, with enhanced silicate weathering (ESW) as a relatively new NET with considerable climate change mitigation potential. Models calibrated to ESW rates in lab experiments estimate the global potential for inorganic carbon sequestration by ESW at about 0.5–5 Gt CO2 year−1, suggesting ESW could be an important component of the future NETs mix. In real soils, however, weathering rates may differ strongly from lab conditions. Research on natural weathering has shown that biota such as plants, microbes, and macro-invertebrates can strongly affect weathering rates, but biotic effects were excluded from most ESW lab assessments. Moreover, ESW may alter soil organic carbon sequestration and greenhouse gas emissions by influencing physicochemical and biological processes, which holds the potential to perpetuate even larger negative emissions. Here, we argue that it is likely that the climate change mitigation effect of ESW will be governed by biological processes, emphasizing the need to put these processes on the agenda of this emerging research field.

Since ancient times, irrigation has been fundamental for achieving large agricultural yields, especially in the more arid areas of the world. An example of this practice is represented by the vast water infrastructures found near Udhruḥ (southern Jordan). These engineering works were constructed, maintained and restored from the Nabataean to early Islamic periods (first century BCE to eighth century CE). It still remains unknown why the ancient agricultural landscape of the region shifted towards an unproductive desert. In this study, we analysed the soil chemical and physical properties of an ancient irrigated field to assess whether ancient agricultural practices have altered soil properties that are still noticeable today, and might have contributed to the abandonment of the area. Soil samples were taken randomly from within an ancient qanat-irrigated agricultural field and from adjacent surfaces believed never to have been irrigated. Our results indicate that the effects of irrigation are still detectable today; electrical conductivity and total Na, B, Li and Sr in the soil of the ancient fields were significantly lower than those in the undisturbed control soils, which suggests leaching of soluble elements due to irrigation. Our results provide evidence of the mastery of ancient civilizations in their agricultural practices. Engineers and farmers apparently managed to conduct irrigation in the area of Udhruḥ for long periods of time without causing soil degradation.

Purpose The tropical phosphorus cycle and its relation to soil phosphorus (P) availability are a major uncertainty in projections of forest productivity. In highly weathered soils with low P concentrations, plant and microbial communities depend on abiotic and biotic processes to acquire P. We explored the seasonality and relative importance of drivers controlling the fluctuation of common P pools via processes such as litter production and decomposition, and soil phosphatase activity. Methods We analyzed intra-annual variation of tropical soil phosphorus pools using a modified Hedley sequential fractionation scheme. In addition, we measured litterfall, the mobilization of P from litter and soil extracellular phosphatase enzyme activity and tested their relation to fluctuations in P- fractions. Results Our results showed clear patterns of seasonal variability of soil P fractions during the year. We found that modeled P released during litter decomposition was positively related to change in organic P fractions, while net change in organic P fractions was negatively related to phosphatase activities in the top 5 cm. Conclusion We conclude that input of P by litter decomposition and potential soil extracellular phosphatase activity are the two main factors related to seasonal soil P fluctuations, and therefore the P economy in P impoverished soils. Organic soil P followed a clear seasonal pattern, indicating tight cycling of the nutrient, while reinforcing the importance of studying soil P as an integrated dynamic system in a tropical forest context.

Seawater absorption of anthropogenic atmospheric carbon dioxide (CO2) has led to a range of changes in carbonate chemistry, collectively referred to as ocean acidification. Stoichiometric dissociation constants used to convert measured carbonate system variables (pH, pCO2, dissolved inorganic carbon, total alkalinity) into globally comparable parameters are crucial for accurately quantifying these changes. The temperature and salinity coefficients of these constants have generally been experimentally derived under controlled laboratory conditions. Here, we use field measurements of carbonate system variables taken from the Global Ocean Data Analysis Project version 2 and the Surface Ocean CO2 Atlas data products to evaluate the temperature dependence of the carbonic acid stoichiometric dissociation constants. By applying a novel iterative procedure to a large dataset of 948 surface-water, quality-controlled samples where four carbonate system variables were independently measured, we show that the set of equations published by Lueker et al. (2000), currently preferred by the ocean acidification community, overestimates the stoichiometric dissociation constants at temperatures below about 8 ∘C. We apply these newly derived temperature coefficients to high-latitude Argo float and cruise data to quantify the effects on surface-water pCO2 and calcite saturation states. These findings highlight the critical implications of uncertainty in stoichiometric dissociation constants for future projections of ocean acidification in polar regions and the need to improve knowledge of what causes the CO2 system inconsistencies in cold waters.

One way of avoiding societal rejection of crop protection practices is to design them in line with stakeholders’ priorities and preferences. This report describes the involvement in crop protection and the opinions regarding the use of plant protection products (PPPs) for the following stakeholder groups: (1) the stakeholders who primarily look at crop protection from a consumption perspective (i.e. consumers, retailers and the food industry), (2) the stakeholders who look at crop protection from a production perspective (i.e. farmers and growers), (3) the stakeholders who look at crop protection from a supply chain perspective (i.e. crop protection industry, plant breeders and other suppliers), and (4) the stakeholders who look at crop protection from a societal perspective (i.e. citizens and NGOs). Four explorative scenarios were developed that look at ways in which existing and emerging crop protection practices might be combined to ensure plant pests and diseases are effectively controlled. These scenarios were discussed in a brainstorming meeting with relevant stakeholders. For each scenario, the potential implications of the crop protection practices for different stakeholder groups (farmers, consumers, industry, NGOs) as well as the identification of their hopes and fears (i.e. potential positive as well as negative knock-on effects) were identified.

Crop protection in prevailing agricultural systems in the EU is highly dependent on plant protection products (PPPs) to protect plants against harmful weeds, pests and diseases. The use of PPPs is a cause of health, environmental and public concerns, and a key question is whether their use can be reduced while maintaining adequate yields. This study provides an overview and description of current and new crop protection practices, including mechanical techniques, plant breeding, biocontrol, induced resistance, applying ecological principles, precision agriculture (PA), and emerging plant protection products. The potential and impact of the new crop protection practices is assessed. It may be feasible to design resilient systems that are economically viable, have limited environmental impact and help improve biodiversity. Diverse cropping systems would have a natural resilience to weeds, pests, and diseases, and potentially reduce the dependency on PPPs, enabled by PA technologies. The main challenge is to integrate new varieties, mechanisation, and biocontrol tools in these systems. Continuous development of all crop protection practices is needed to ensure sufficient control of pests, weeds and diseases. The drivers and enablers for implementing alternative crop protection practices are identified, and an analysis of key legislation to support their use is presented.

The authors would like to apologize for missing the correction provided below: To calculate the tea bag decomposition, the final weight of the tea bag instead of the % mass loss (i.e. 1-final weight/initial weight) was taken. Hence, the negative partial correlation originally found should be positive. The corrections have been made in the online version of the manuscript. Table 4. Partial correlation coefficients (ρ) between the labile organic carbon fractions expressed in mg kg−1 soil (Hy-DOC, DOC, POXC, HWEC and POMC) and % (TOC) and various soil chemical, physical and biological indicators used as dependent variable, corrected for the long term field experiments (LTEs). The number of samples used in the analyses was 167, but 101 for earthworm number, and earthworms biomass. In the table also the average correlation coefficients for each indicator group (chemical, physical and biological indicators) is reported, in addition to the overall average correlation coefficient (calculated across all the indicators). [Table presented] Hy-DOC hydrophilic dissolved organic carbon, DOC dissolved organic carbon, POXC permanganate oxidizable carbon, HWEC hot water extractable carbon, POMC particulate organic matter carbon, TOC total organic carbon, TON total nitrogen, CEC cation exchange capacity, WSA water stable aggregates, BD bulk density, MBC microbial biomass carbon, MBN microbial biomass nitrogen, SR soil respiration, qCO2 metabolic quotient, qMIC microbial quotient. *p ≤ 0.01, **p ≤ 0.001, ***p ≤ 0.0001.

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 tropical soils from Sub-Saharan Africa (SSA). Blanket fertilizer recommendations including only macronutrients are most common practice in SSA. Alternatively, science-based approaches have been developed for formulating site-specific fertilizer recommendations. Such science-based approaches could be extended to account for micronutrients, based on the knowledge about the processes that affect their availability for plant uptake.Micronutrient bioavailability depends partly on the soil micronutrient status, and in particular on the labile, reactive or potentially available pool that is distributed over the solid and solution phase, through sorption/desorption and precipitation/dissolution. A fraction of this labile pool is present in the soil solution and is therefore directly available for plant uptake. Together, the soluble and potential available pool represent the soil micronutrient environmental availability.The aim of this thesis was to gain insight in the soil chemical processes that control the solid-solution partitioning of Zn, Cu, and B in tropical soils from SSA, and to use this knowledge to develop accessible tools for predicting the soluble concentrations of these micronutrients. This was done using geochemical multi-surface models and partition relations.Geochemical multi-surface models require input data about the amount of reactive surfaces and their corresponding reactivity for ion adsorption. The metal (hydr)oxides and soil organic matter have been previously identified as the most important reactive surfaces for micronutrient adsorption in soils. The first objective of this thesis was therefore to better understand the reactivity of metal (hydr)oxides and soil organic matter in tropical soils from SSA. Soils from the humid tropics are often intensively weathered, resulting in a high abundance of metal (hydr)oxides. These metal (hydr)oxides are mainly present as well-crystallized metal (hydr)oxides while the contribution of oxide nanoparticles (i.e. ferrihydrite-like materials) may be relatively small on a mass basis. Nevertheless, we have shown in this thesis that irrespective of weathering stage, ferrihydrite is a good model oxide to describe the surface reactivity of the natural metal (hydr)oxides in soils. With regard to the soil organic matter content, our results showed that in soils, the mean particle size of the natural oxide fraction explains the organic carbon content found in soils, irrespective of origin, land use and soil depth. According to these results, soil organic carbon is predominantly stored in primary organo-oxide aggregates that are additionally organized by association with larger mineral particles.In addition to the amount and reactivity of the adsorption surfaces, geochemical multi-surface models also require well-parameterized models to describe the ion adsorption processes to these surfaces. Since ferrihydrite was identified as the best proxy for the natural metal (hydr)oxides in tropical soils, the second objective of this thesis was to use a consistent modeling approach for describing the adsorption of Zn, Cu and B to ferrihydrite with the Charge Distribution model in combination with a Multi Site Ion Complexation model.The third objective of this thesis was to apply a multi-surface model for calculating the solid-solution partitioning of Zn, Cu, and B in tropical soils, and to translate these results in easily accessible prediction tools in the form of partition relations.First, the chemical speciation of B in soils was studied with a geochemical multi-surface model that included B adsorption to dissolved and solid organic matter, ferrihydrite, and clay mineral edges. This was done for five temperate and five tropical. In addition, the performance of previously proposed extraction methods for measuring reactive B were evaluated, since this information is needed as input variable for multi-surface modeling calculations. Based on modeling calculations, the reactive B in soils corresponded best to the B measured in a 0.05 M KH2PO4 (pH 4.5) extraction. In general, the multi-surface modeling showed that 68% or more of reactive boron was present in the solution phase for the soils in this study and that the adsorption was dominated by oxides in the tropical soils, while organic matter was the main adsorbent in the temperate soils. When changing the soil pH, B concentration was found to decrease with increasing pH, and both experimental data and modelling suggested that this effect is mainly due to increased binding of B to organic matter.Next, the solid-solution partitioning of Zn, Cu and B was studied for 172 soils from Burundi, Rwanda and Kenya, using extensive soil characterization in combination with multi-surface modelling and two types of Freundlich-like partition relations. The results showed 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 observed and modeled solid-solution partitioning of Cu and B was found to be rather constant among soils, and the soluble concentration was consistently mainly controlled by the reactive concentration. The solid-solution partitioning of Zn was strongly related to the soil pH. The partition relations in which the soluble concentration was optimized, resulted in an average overestimation for the lowest observed concentrations, and an underestimation for highest concentrations of all three elements. Partition relations in which the Zn solid-solution partitioning was optimized, resulted in more robust predictions since the prediction error was not related to the actual measured concentration.Overall, this thesis delivered valuable information on the micronutrient soil status in SSA, and knowledge on the processes that control soil micronutrient availability. Based on this knowledge, a low-cost and reliable method was developed for predicting soluble micronutrient concentrations, based on partition and transfer relations. This method can be used for testing soils for Zn, Cu and B availability and for making regional and national soil maps showing micronutrient availability. The soil micronutrient information obtained by these methods, can be used in future work for establishing micronutrient fertilizer recommendation systems.&nbsp

Humic substances are increasingly used as biostimulants in agriculture because of their supposed effects on nutrient uptake and crop yield. The objective of this study was to assess the effect of fulvic acid (FA) and humic acid (HA) addition with and without fertilization (N, P, K, S, and Ca) on (i) grass yield (Poa trivialis) and nutrient uptake and (ii) composition of soil porewater and 0.01 M CaCl2 soil extracts. Therefore, a pot experiment was performed using a loamy soil and a non-calcareous sandy soil. Fertilization increased N and P uptake and grass yield but there was no effect of FA or HA application (200 mg C kg���1 soil) regardless of whether N or P was the growth limiting nutrient. Nutrient availability was assessed in soil pore water samples extracted by centrifugating moist soil and by 0.01 M CaCl2 extracts of oven-dried soil. HA and FA had no effect on the availability of NO3 or ortho-P, neither in soil porewater nor in 0.01 M CaCl2 soil extracts. Fertilization led to an increase in 0.01 M CaCl2-extractable ortho-P but, remarkably, to a decrease in ortho-P and Dissolved Organic Carbon (DOC) concentrations in soil pore water samples. This discrepancy was explained by the higher ionic strength of pore water in the fertilized soils, which caused the pH to drop by 0.2 to 0.4 units and thereby stimulated adsorption of ortho-P and DOC to reactive soil minerals. Such salt-induced effects do not occur in 0.01 M CaCl2 soil extracts where the ionic strength is nearly constant.

The aim of this study was to develop an analytical method to determine free concentrations of Europium (Eu(III)) in natural waters. Europium(III) in solution was detected using cathodic stripping voltammetry after complexation with N-nitroso-N-phenylhydroxylamine (cupferron). Optimization of analytical parameters allowed us to detect nanomolar levels of Eu(III) in solution. Free Eu(III) in solution was measured using the Donnan membrane technique in which a natural solution (the “donor”, containing various ligands) is separated from a ligand-free solution (the “acceptor”) by a cation-exchange membrane. This membrane allows only non-colloidal cationic species to pass through it, and after an adequate time equilibrium is reached between both compartments. Total Eu(III) concentration can then be quantified in the acceptor solution and related to free Eu(III) in the natural sample. Due to its high valency, free Eu(III) tends to adsorb strongly to the cation-exchange membrane. In order to determine the physicochemical conditions minimizing this adsorption, we analyzed solutions of different Eu(III) and Ca(II) (as background ion) concentrations. Results showed that 100 mM of Ca(II) were necessary to make adsorption of Eu(III) onto the membrane negligible. The optimized setup was then used to quantify Eu(III) complexation in a Eu(III)-dissolved organic matter solution.

Crop protection in prevailing agricultural systems in the EU is highly dependent on plant protection products (PPPs) to protect plants against harmful weeds, pests and diseases. The use of PPPs is a cause of health, environmental and public concerns, and a key question is whether their use can be reduced while maintaining adequate yields. This study provides an overview and description of current and new crop protection practices, including mechanical techniques, plant breeding, biocontrol, induced resistance, applying ecological principles, precision agriculture (PA), and emerging plant protection products. The potential and impact of the new crop protection practices is assessed. It may be feasible to design resilient systems that are economically viable, have limited environmental impact and help improve biodiversity. Diverse cropping systems would have a natural resilience to weeds, pests, and diseases, and potentially reduce the dependency on PPPs, enabled by PA technologies. The main challenge is to integrate new varieties, mechanisation, and biocontrol tools in these systems. Continuous development of all crop protection practices is needed to ensure sufficient control of pests, weeds and diseases. The drivers and enablers for implementing alternative crop protection practices are identified, and an analysis of key legislation to support their use is presented.

Analysis of dissolved organic carbon (DOC) is widely used to quantify the sum of organic carbon species in water. Analyzers based on wet chemical oxidation (WCO) usually have a relatively low detection limit (±1 μg of C/L) and are, therefore, well suited for analyses of DOC in environmental samples (e.g., surface water, groundwater, or seawater). However, these matrices might contain relatively high concentrations of chloride that can affect the DOC oxidation efficiency. We validated the DOC analysis using a combined persulfate and ultraviolet oxidation method in various prepared samples (humic and fulvic acids and selected organic acids) with different background concentrations of chloride. The results show that chloride is an effective radical scavenger (at concentrations of >355 mg of Cl–/L) that reduces the oxidation efficiency of DOC analyses based on WCO. The oxidation efficiency correlates well with the proton dissociation constant of the selected organic acids. Our findings imply that the DOC analyses by WCO methods should include an assessment of the chloride concentrations in the samples to check for potential interference. The results are relevant for DOC analysis in samples containing high background levels of chloride (e.g., brackish water) and for samples from DOC fractionation methods to quantify humic substances.

Source identification of heavy metals in agricultural soils using small sample sizes, simple experimental procedures, and convenient analysis is urgently required. This study employed a simple source identification model using a visual comparison via radar plots, cluster analysis, principal component analysis, and a multiple linear regression model to determine the source of heavy metal pollution in soil samples from the Chang-Zhu-Tan urban agglomeration area of China. The elemental compositions of major pollution sources (atmospheric deposition, organic fertilizer, irrigation water, and tailings) were compared with soil samples from 11 study locations and the model was used to determine the relative contribution of different pollution sources at each sample site. The results showed that the model successfully calculated the contribution of different pollution sources at each site based on the pollution characteristics and contaminant transport rules of the region. The proposed method overcomes the requirement for extensive data and complex experimental procedures. Furthermore, the model can determine the source of heavy metal contamination in single or small plots, which is important for the prevention and control of heavy metal soil pollution and remediation at the plot scale.

Arsenic (As) and cadmium (Cd) are nonessential toxic metal(loids) that are carcinogenic to humans. Hence, reducing the bioavailability of these metal(loids) in soils and decreasing their accumulation in rice grains is essential for agroecology, food safety, and human health. Iron (Fe)-enriched corncob biochar (FCB), Fe-enriched charred eggshell (FEB), and Fe-enriched corncob-eggshell biochar (FCEB) were prepared for soil amelioration. The amendment materials were applied at 1% and 2% application rates to observe their alleviation effects on As and Cd loads in rice paddy tissues and yield improvements using pot trials. The FCEB treatment increased paddy yields compared to those of FCB (9-12%) and FEB (3-36%); this could be because it contains more plant essential nutrients than FCB and a lower calcite content than that of FEB. In addition, FCEB significantly reduced brown rice As (AsBR, 29-60%) and Cd (CdBR, 57-81%) contents compared to those of the untreated control (CON). At a 2% application rate, FCEB reduced the average mobility of As (56%) and Cd (62%) in rhizosphere porewater and enhanced root Fe-plaque formation (76%) compared to those of CON. Moreover, the enhanced Fe-plaque sequestered a substantial amount of As (171.4%) and Cd (90.8%) in the 2% FCEB amendment compared to that of CON. Pearson correlation coefficients and regression analysis indicated that two key mechanisms likely control AsBR and CdBR accumulations. First, rhizosphere soil pH and Eh controlled As and Cd availabilities in porewaters and their speciation in the soil. Second, greater Fe-plaque formation in paddy roots grown in the amended soils provided a barrier for plant uptake of the metal(loids). These observations demonstrate that soil amendment with Fe-enriched corncob-eggshell biochar (e.g., 2% FCEB) is a prospective approach for the remediation of metal accumulation from the soil to grain system while simultaneously increasing paddy yield.

One way of avoiding societal rejection of crop protection practices is to design them in line with stakeholders’ priorities and preferences. This report describes the involvement in crop protection and the opinions regarding the use of plant protection products (PPPs) for the following stakeholder groups: (1) the stakeholders who primarily look at crop protection from a consumption perspective (i.e. consumers, retailers and the food industry), (2) the stakeholders who look at crop protection from a production perspective (i.e. farmers and growers), (3) the stakeholders who look at crop protection from a supply chain perspective (i.e. crop protection industry, plant breeders and other suppliers), and (4) the stakeholders who look at crop protection from a societal perspective (i.e. citizens and NGOs). Four explorative scenarios were developed that look at ways in which existing and emerging crop protection practices might be combined to ensure plant pests and diseases are effectively controlled. These scenarios were discussed in a brainstorming meeting with relevant stakeholders. For each scenario, the potential implications of the crop protection practices for different stakeholder groups (farmers, consumers, industry, NGOs) as well as the identification of their hopes and fears (i.e. potential positive as well as negative knock-on effects) were identified.

Cadmium is an extremely toxic substance known to cause serious health problems. The uptake of Cd in plants is critically affected by dissolved Cd in soil porewater, controlled by soil physicochemical properties. Rhizo-availability of Cd is assumed, as the Cd fraction is found on the plasma membrane of surface root cells. Based on the theory of Cd transformation in soil–crop systems, we established a novel combined mechanistic model related to soil, soil solutions, and crops. The combined model comprises a multisurface model (MSMs; solid adsorbent and porewater) and the Gouy–Chapman–Stern model (GCS; porewater and root surface). The results suggested that in mildly contaminated soil samples, optimum prediction was achieved when DTPA-extractable Cd was used as input variable (R2 = 0.723). Our approach was superior to single-step model calculation (MSMs: R2 = 0.613; GCS: R2 = 0.629) and prediction based on extractable soil Cd (R2 = 0.281). Introducing DTPA extraction expanded the range of model applications at different soil pHs. Our proposed mechanism model was based on soil physicochemical properties for Cd migration from soil to cabbage. Our model showed promise in predicting Cd bioavailability in soil with a wide pH range and evaluating soil risk near the standard Cd safety level.

Currently it is normal practice to landfill biomass ash. As an alternative, biomass ash has been proposed as a substitute for raw clinker materials, a secondary cementitious material, or as a soil amendment. This alternative use of biomass ash avoids landfilling, saves traditional resources for cement production, and hence lowers the carbon footprint of cement products.This thesis has shown that biomass ash can be successfully used as raw material for clinker production and substitute a large part of the raw feed minerals. The direct use of biomass ash as secondary cementitious material was also found to be feasible for specific biomass ash types. The inclusion of biomass ash at 20 and 40% by weight of Portland cement reduced the compressive strength after 28 days but a functional strength was still obtained.Results also showed that an assessment and regulatory criteria based on the leaching rather than total content of elements may widen the application of biomass ash as soil amendment. When biomass ash was mixed in cement, the cement matrix dominated the release of elements in leaching tests.Results from the life cycle assessment established that biomass ash use in cement is always a more sustainable solution than landfilling. The environmental performance of biomass ash blended with cement was equal to that of traditional cement during all the considered life stages of materials

International audience; A comprehensive study of the toxicity of lanthanides (LN) in relation to the media composition will enhance the prediction of their potential adverse effects for living organisms. Here we examined the effect of different media on the V. faba root elongation and on the cytotoxic (mitotic index) and the genotoxic (micronucleated cell number) effects from toxicity tests with Ce, Gd and Lu (100, 800 and 6400 μg L −1). Three different exposure media were selected: the standard Hoagland media (SH); an alternative SH, without phosphates (SH-P); and distilled water (DW). In the SH no cyto-genotoxic effects were observed and even, for low LN content, potential root elongation stimulation was reported. The absence of toxic effects was explained by a drastic decrease of the total dissolved LN concentration due to the presence of phosphates causing LN precipitation. In SH-P, LN remained largely soluble and inhibition of root elongation was observed mainly for the highest treatments. While in the tests done in DW, toxic effects were obtained for all treatments. Our results showed that in absence of phosphorous, LN appear mainly as free form and complexed in carbonates and sulphates, and can cause toxic effects, whereas toxicity is not expected when phosphorous is available in aquatic media. The highest LN root contents were observed for the tests using distilled water, possibly due to the absence of competition by Ca 2+ for uptake. The present work demonstrated that media composition has a great impact in assessing the ecotoxicology of lanthanides.

Purpose: This study evaluates the potential of biomass ash as raw clinker material and the influence of biomass feedstock and thermal conversion technology on biomass ash properties. Methods: A set of criteria for biomass feedstock and ash properties (i.e. CaO/SiO2 ratio and burnability) are established. A large dataset was collected and the best combination of biomass feedstock and conversion technology regarding the desired ash quality was identified. Results: Wood biomass has the highest potential to provide the right CaO/SiO2 ratio which is needed to form clinker minerals. Bark content and exogenous Si inclusion in wood biomass have a large influence on the CaO/SiO2 ratio. Paper sludge is composed of Ca, Si and Al and can potentially serve as a source of cement elements. Wood fly ash from pulverized fuel combustion can substitute a considerable amount of raw clinker materials due to its similar burnability. The replacement ratio is determined by the content of adverse elements in the ash (i.e. MgO2 and P2O5). Conclusion: Using biomass ash to lower the CO2 emission from clinker production depends on the joint effort of bioenergy producers, by providing higher quality biomass ash, and cement makers, by adapting the kiln operation to enable a high level of raw material replacement by biomass ash.The presented evaluation of the ash production chain, from biomass selection through combustion technology and ash management, provides new insights and recommendations for both stakeholders to facilitate this sustainable development. Graphic Abstract

Phthalates (PAEs) often exist simultaneously in contaminated soil and wastewater systems, and their adsorption to biochar might impact their behavior in the environment. So far, the competitive adsorption of PAEs to biochar has not been reported. In this study, the competitive adsorption of Dibutyl phthalate (DBP) and Di(2-ethylhexyl) phthalate (DEHP) on corncob biochar (fresh and oxidized) was investigated, and experiments of kinetics, isotherms, and thermodynamics were conducted. Langmuir and Freundlich models, pseudo-first-order and second-order kinetic models were used to simulate the experimental data. In the mono PAEs component systems, the biochar showed significantly greater adsorption capacity for DEHP (11.8–16.16 mg g−1) than for DBP (9.86–13.2 mg g−1). The oxidized biochar has higher adsorption capacities than the fresh one. Moreover, a fast adsorption rate for DBP was observed, which can be attributed to the smaller size and shorter carbon chains in the DBP molecule, resulting in faster diffusion into the biochar pores. In the binary PAEs component systems, competition between DEHP and DBP in their adsorption to the biochars was observed, and DEHP (11.7–15.0 mg g−1) was preferred over DBP (3.4–7.9 mg g−1). The stronger adsorption of DEHP can be explained by stronger hydrophobic interaction with biochar. Compared to DBP, DEHP has a high octanol-water partition coefficient (logKow) and low water solubility. The positive entropy ( Δ S 0 ) and enthalpy ( Δ H 0 ) values for the adsorption of both DEHP and DBP further indicated that hydrophobic interaction played an important role, even though H-bonds and π-π interactions could also be involved.

The authors would like to apologize for missing the correction provided below: To calculate the tea bag decomposition, the final weight of the tea bag instead of the % mass loss (i.e. 1-final weight/initial weight) was taken. Hence, the negative partial correlation originally found should be positive. The corrections have been made in the online version of the manuscript. Table 4. Partial correlation coefficients (ρ) between the labile organic carbon fractions expressed in mg kg−1 soil (Hy-DOC, DOC, POXC, HWEC and POMC) and % (TOC) and various soil chemical, physical and biological indicators used as dependent variable, corrected for the long term field experiments (LTEs). The number of samples used in the analyses was 167, but 101 for earthworm number, and earthworms biomass. In the table also the average correlation coefficients for each indicator group (chemical, physical and biological indicators) is reported, in addition to the overall average correlation coefficient (calculated across all the indicators). [Table presented] Hy-DOC hydrophilic dissolved organic carbon, DOC dissolved organic carbon, POXC permanganate oxidizable carbon, HWEC hot water extractable carbon, POMC particulate organic matter carbon, TOC total organic carbon, TON total nitrogen, CEC cation exchange capacity, WSA water stable aggregates, BD bulk density, MBC microbial biomass carbon, MBN microbial biomass nitrogen, SR soil respiration, qCO2 metabolic quotient, qMIC microbial quotient. *p ≤ 0.01, **p ≤ 0.001, ***p ≤ 0.0001.