Loss of subsurface particulate and truly dissolved phosphorus during various flow conditions along a tile drain-ditch-brook continuum.

Subsurface losses of colloidal and truly dissolved phosphorus (P) from arable land can cause ecological damage to surface water. To gain deeper knowledge about subsurface particulate P transport from inland sources to brooks, we studied an artificially drained lowland catchment (1550 ha) in north-eastern Germany. We took daily samples during the winter discharge period 2019/2020 at different locations, i.e., a drain outlet, ditch, and brook, and analyzed them for total P (TPunfiltered), particulate P >750 nm (TP>750 nm), colloidal P (TPcolloids), and truly dissolved P (truly DP) during baseflow conditions and high flow events. The majority of TPunfiltered in the tile drain, ditch, and brook was formed by TP>750 nm (54 to 59 %), followed by truly DP (34 to 38 %) and a small contribution of TPcolloids (5 to 6 %). During flow events, 63 to 66 % of TPunfiltered was present as particulate P (TP>750 nm + TPcolloids), whereas during baseflow the figure was 97 to 99 %; thus, truly DP was almost negligible (1 to 3 % of TPunfiltered) during baseflow. We also found that colloids transported in the water samples have their origin in the water-extractable nanocolloids (0.66 to 20 nm) within the C horizon, which are mainly composed of clay minerals. Along the flow path there is an agglomeration of P-bearing nanocolloids from the soil, with an increasing importance of iron(III) (hydr)oxides over clay particles. Event flow facilitated the transport of greater amounts of larger particles (>750 nm) through the soil matrix. However, the discharge did not exhaust colloid mobilization and colloidal P was exported through the tile-drainage system during the complete runoff period, even under baseflow conditions. Therefore, it is essential that the impact of rainfall intensity and pattern on particulate P discharge be considered more closely so that drainage management can be adjusted to achieve a reduced P export from agricultural land.

Implications of Free and Occluded Fine Colloids for Organic Matter Preservation in Arable Soils.

Colloidal organo-mineral associations contribute to soil organic matter (OM) preservation and mainly occur in two forms: (i) as water-dispersible colloids that are potentially mobile (free colloids) and (ii) as building units of soil microaggregates that are occluded inside them (occluded colloids). However, the way in which these two colloidal forms differ in terms of textural characteristics and chemical composition, together with the nature of their associated OM, remains unknown. To fill these knowledge gaps, free and occluded fine colloids <220 nm were isolated from arable soils with comparable organic carbon (Corg) but different clay contents. Free colloids were dispersed in water suspensions during wet-sieving, while occluded colloids were released from water-stable aggregates by sonication. The asymmetric flow field-flow fractionation analysis on the free and occluded colloids suggested that most of the 0.6-220 nm fine colloidal Corg was present in size fractions that showed high abundances of Si, Al, and Fe. The pyrolysis-field ionization mass spectrometry revealed that the free colloids were relatively rich in less decomposed plant-derived OM (i.e., lipids, suberin, and free fatty acids), whereas the occluded colloids generally contained more decomposed and microbial-derived OM (i.e., carbohydrates and amides). In addition, a higher thermal stability of OM in occluded colloids pointed to a higher resistance to further degradation and mineralization of OM in occluded colloids than that in free colloids. This study provides new insights into the characteristics of subsized fractions of fine colloidal organo-mineral associations in soils and explores the impacts of free versus occluded colloidal forms on the composition and stability of colloid-associated OM.

Fate of weathered multi-walled carbon nanotubes in an aquatic sediment system.

The widespread application of carbon nanotubes (CNT) in various consumer products leads to their inevitable release into aquatic systems. But only little is known about their distribution among aquatic compartments. In this study, we investigated the partitioning of radiolabeled, weathered multi-walled CNT (14C-wMWCNT) in an aquatic sediment system over a period of 180 days (d). The applied nanomaterial concentration in water phase was 100 µg L-1. Over time, the wMWCNT disappeared exponentially from the water phase and simultaneously accumulated in the sediment phase. After 2 h incubation just 77%, after seven days 30% and after 180 d only 0.03% of applied radioactivity (AR) remained in the water phase. The respective values for the disappearance times DT50 and DT90 were 3.2 d and 10.7 d. Further, minor mineralization of 14C-wMWCNT to 14CO2 was observed with values below 0.06% of AR. In addition, a study was carried out to estimate the deposition of wMWCNT in the water phase with and without sediment in the test system for 28 d. We found no influence of a sediment phase on the sedimentation behavior of wMWCNT in the water phase: After 6.5 d and 7.3 d 50% of the applied wMWCNT subsided in the presence and absence of sediment, respectively. The slow removal of wMWCNT from the water body by deposition into sediment implies that in addition to sediment-dwelling organisms, pelagic organisms are also at risk of exposure to nanomaterials and prone for their take-up.

A trophic transfer study: accumulation of multi-walled carbon nanotubes associated to green algae in water flea Daphnia magna.

Carbon nanotubes (CNT) are promising nanomaterials in modern nanotechnology and their use in many different applications leads to an inevitable release into the aquatic environment. In this study, we quantified trophic transfer of weathered multi-walled carbon nanotubes (wMWCNT) from green algae to primary consumer Daphnia magna in a concentration of 100 µg L-1 using radioactive labeling of the carbon backbone (14C-wMWCNT). Trophic transfer of wMWCNT was compared to the uptake by daphnids exposed to nanomaterials in the water phase without algae. Due to the rather long observed CNT sedimentation times (DT) from the water phase (DT50: 3.9 days (d), DT90: 12.8 d) wMWCNT interact with aquatic organisms and associated to the green algae Chlamydomonas reinhardtii and Raphidocelis subcapitata. After the exposition of algae, the nanotubes accumulated to a maximum of 1.6 ± 0.4 µg 14C-wMWCNT mg-1 dry weight-1 (dw-1) and 0.7 ± 0.3 µg 14C-wMWCNT mg-1 dw-1 after 24 h and 48 h, respectively. To study trophic transfer, R. subcapitata was loaded with 14C-wMWCNT and subsequently fed to D. magna. A maximum body burden of 0.07 ± 0.01 µg 14C-wMWCNT mg-1 dw-1 and 7.1 ± 1.5 µg 14C-wMWCNT mg-1 dw-1 for D. magna after trophic transfer and waterborne exposure was measured, respectively, indicating no CNT accumulation after short-term exposure via trophic transfer. Additionally, the animals eliminated nanomaterials from their guts, while feeding algae facilitated their excretion. Further, accumulation of 14C-wMWCNT in a growing population of D. magna revealed a maximum uptake of 0.7 ± 0.2 µg mg-1 dw-1. Therefore, the calculated bioaccumulation factor (BAF) after 28 d of 6700 ± 2900 L kg-1 is above the limit that indicates a chemical is bioaccumulative in the European Union Regulation REACH. Although wMWCNT did not bioaccumulate in neonate D. magna after trophic transfer, wMWCNT enriched in a 28 d growing D. magna population regardless of daily feeding, which increases the risk of CNT accumulation along the aquatic food chain.

Effects of nasal high flow on nocturnal hypercapnia, sleep, and sympathovagal balance in patients with neuromuscular disorders.

PURPOSE: In neuromuscular disorders (NMD), inspiratory muscle weakness may cause sleep-related hypoventilation requiring non-invasive ventilation (NIV). Alternatively, nasal high flow therapy (NHF) may ameliorate mild nocturnal hypercapnia (NH) through washout of anatomical dead space and generation of positive airway pressure. Ventilatory support by NIV or NHF might have favourable short-term effects on sympathovagal balance (SVB). This study comparatively investigated the effects of NHF and NIV on sleep-related breathing and SVB in NMD patients with evolving NH. METHODS: Transcutaneous CO2 (ptcCO2), peripheral oxygen saturation (SpO2), sleep outcomes and SVB (spectral analysis of heart rate, diastolic blood pressure variability) along with haemodynamic measures (cardiac index, total peripheral resistance index) were evaluated overnight in 17 patients. Polysomnographies (PSG) were randomly split into equal parts with no treatment, NIV and NHF at different flow rates (20 l/min vs. 50 l/min). In-depth analysis of SVB and haemodynamics was performed on 10-min segments of stable N2 sleep taken from each intervention. RESULTS: Compared with no treatment, NHF20 and NHF50 did not significantly change ptcCO2, SpO2 or the apnea hypopnea index (AHI). NHF50 was poorly tolerated. In contrast, NIV significantly improved both gas exchange and AHI without adversely affecting sleep. During daytime, NHF20 and NHF50 had neutral effects on ventilation and oxygenation whereas NIV improved ptcCO2 and SpO2. Effects of NIV and NHF on SVB and haemodynamics were neutral during both night and daytime. CONCLUSIONS: NHF does not correct sleep-disordered breathing in NMD patients with NH. Both NHF and NIV exert no immediate effects on SVB.

Short-term impacts of forest clear-cut on soil structure and consequences for organic matter composition and nutrient speciation: A case study.

Clear-cuts of forests severely affect soil structure and thus soil organic matter (SOM) and nutrient cycling dynamics therein, though with yet unknown consequences for SOM composition as well as phosphorus (P) and sulfur (S) chemical form within the soil microaggregate size fraction. To determine the effects of conventional clear-cutting on soil chemistry in a Cambisol of the Wüstebach Forest (northwestern Germany), we sampled the mineral A- and B-horizons prior to clear-cut as well as 10 and 24 month thereafter. We measured the SOM composition of soil microaggregates using pyrolysis field ionization mass spectrometry (Py-FIMS), as well as P and S chemical form and speciation using wet-chemical extractions and X-ray absorption near edge structure (XANES) spectroscopy. We found that clear-cut led to an increase of the microaggregate size fraction up to 6% due to break-down of macroaggregates and initially significantly increased total elemental concentrations (C, N, P, S) due to the introduction of slash-residues. The SOM of slash-residues consisted to a substantial amount of sterols and was generally found to be of low thermal stability and probably did not contribute to aggregate stability. Deterioration of the aggregate structure probably led to an exposure of originally inaccessible sites within aggregates to the attack by soil microorganisms and thus to an increased P and S turnover as reflected in a significantly reduction of available P proportions (4 to 7%) and a reduction of the most reduced S forms (5%). A probable increased microbial activity and contribution to SOM after clear-cut is also reflected in the significantly increasing hexose:pentose ratio by 0.25 between 10 and 24 month after clear-cut, significantly increasing the general thermal stability of SOM in the microaggregate size fraction and believed to contribute to aggregate stability. This indicated that a first deterioration of the aggregate structure after clear-cut might in the long-term be remediated with time.

Quantitative imaging of 33P in plant materials using 14C polymer references.

Phosphorus (P) research still lacks techniques for rapid imaging of P use and allocation in different soil, sediment, and biological systems in a quantitative manner. In this study, we describe a time-saving and cost-efficient digital autoradiographic method for in situ quantitative imaging of 33P radioisotopes in plant materials. Our method combines autoradiography of the radiotracer applications with additions of commercially available 14C polymer references to obtain 33P activities in a quantitative manner up to 2000 Bq cm-2. Our data show that linear standard regressions for both radioisotopes are obtained, allowing the establishment of photostimulated luminescence equivalence between both radioisotopes with a factor of 9.73. Validating experiments revealed a good agreement between the calculated and applied 33P activity (R2 = 0.96). This finding was also valid for the co-exposure of 14C polymer references and 33P radioisotope specific activities in excised plant leaves for both maize (R2 = 0.99) and wheat (R2 = 0.99). The outlined autoradiographic quantification procedure retrieved 100% ± 12% of the 33P activity in the plant leaves, irrespective of plant tissue density. The simplicity of this methodology opens up new perspectives for fast quantitative imaging of 33P in biological systems and likely, thus, also for other environmental compartments.

Bone char vs. S-enriched bone char: Multi-method characterization of bone chars and their transformation in soil.

To decrease environmental impacts from usage of mineral P fertilizers based on rock phosphate, alternative P fertilizers are urgently necessary but have to be critically evaluated for their characteristics and behaviour or effects in soil. For this reason, bone char (BC) and S-enriched BC (BCplus), original and after one vegetation period in soil, were analysed by wet chemical analyses and XANES spectroscopy. According to X-ray absorption near edge structure (XANES) spectroscopy, both chars were dominated by P bound in hydroxyapatite, which was well reflected by wet chemical P fractionation, where Ca-P was the dominant fraction. Sulfur fractionation of both chars confirmed low percentages of sulfate-S according to XANES analysis but failed to detect elemental S in BCplus. Because S concentrations in BCplus were comparable to that of activated carbon used for biogas desulfurization and sorbed S was dominantly elemental S, BC seems to be well suited for biogas desulfurization. After one year in soil the disappearance of more easily soluble Ca(H2PO4)·2H2O and strongly reduced proportions of sulfates and sulfonates in soil-BCplus compared to BCplus pointed to considerable advantages of BCplus over BC. Taking into consideration the acidic pH of BCplus, the high Ca, P, and S concentrations and the expected microbial induced "in situ digestion" of BC by oxidation of elemental S, it can be concluded that a cascade usage of BC as biogas adsorber and following subsequent usage of BCplus as S/P/Ca/Mg (multi-element) fertilizer could be an alternative to mineral fertilizers based on rock phosphate. The agronomic efficiency and detailed application guidelines must be derived from established and currently running longer-term plot and field experiments.

Role of rain intensity and soil colloids in the retention of surfactant-stabilized silver nanoparticles in soil.

Undisturbed outdoor lysimeters containing arable loamy sand soil were used to examine the influence of either heavy rain events (high frequency of high rain intensity), steady rain (continuous rainfall of low rain intensity), and natural rainfall on the transport and retention of surfactant-stabilized silver nanoparticles (AgNP). In addition, the AgNP-soil associations within the Ap horizon were analyzed by means of particle-size fractionation, asymmetrical flow field-flow fractionation coupled with UV/Vis-detection and inductively coupled plasma mass spectrometer (AF4-UV/Vis-ICP-MS), and transmission electron microscopy coupled to an energy-dispersive X-ray (TEM-EDX) analyzer. The results showed that AgNP breakthrough for all rain events was less than 0.1% of the total AgNP mass applied, highlighting that nearly all AgNP were retained in the soil. Heavy rain treatment and natural rainfall revealed enhanced AgNP transport within the Ap horizon, which was attributed to the high pore water flow velocities and to the mobilization of AgNP-soil colloid associations. Particle-size fractionation of the soil revealed that AgNP were present in each size fraction and therefore indicated strong associations between AgNP and soil. In particular, water-dispersible colloids (WDC) in the size range of 0.45-0.1 µm were found to exhibit high potential for AgNP attachment. The AF4-UV/Vis-ICP-MS and TEM-EDX analyses of the WDC fraction confirmed that AgNP were persistent in soil and associated to soil colloids (mainly composed of Al, Fe, Si, and organic matter). These results confirm the particularly important role of soil colloids in the retention and remobilization of AgNP in soil. Furthermore, AF4-UV/Vis-ICP-MS results indicated the presence of single, homo-aggregated, and small AgNP probably due to dissolution.

Recycled Products from Municipal Wastewater: Composition and Effects on Phosphorus Mobility in a Sandy Soil.

Recycled products from wastewater may contain high concentrations of phosphorus (P) and are thus promising alternative fertilizers. However, to better predict their P fertilizer efficiency and potential for P leaching, investigations on P forms and P mobility in soil are essential. In this study, different recycled products-an untreated sewage sludge ash (SSA), an HSO-digested SSA, four thermochemically treated SSAs (two Mg-SSAs and two Ca-SSAs), and struvite-were investigated using a combination of wet chemical methods and P K-edge X-ray absorption near-edge structure (XANES) spectroscopy concerning their composition and their effects on P sorption in a sandy soil in comparison to triple superphosphate. Most of the P in the SSAs was associated with Ca in stable P fractions. The lowest P values in labile fractions (HO-P, NaHCO-P) were found for the untreated SSA and struvite. However, the addition of struvite resulted in an immediate increase in the bioavailable P fractions and the degree of P saturation in soil after only 1 d of incubation. This suggests a high P fertilizer potential for struvite but also a risk of P losses. Among the SSAs, the two Mg-SSAs increased the bioavailable P fractions in soil the most, whereas the lowest values were measured after application of the untreated SSA. Our results demonstrate that chemical analyses of recycled P products may involve the risk of misjudging the fertilizer quality when performed alone, without considering the behavior of these products in soil.

Phosphorus Containing Water Dispersible Nanoparticles in Arable Soil.

Due to the limited solubility of phosphorus (P) in soil, understanding its binding in fine colloids is vital to better forecast P dynamics and losses in agricultural systems. We hypothesized that water-dispersible P is present as nanoparticles and that iron (Fe) plays a crucial role for P binding to these nanoparticles. To test this, we isolated water-dispersible fine colloids (WDFC) from an arable topsoil (Haplic Luvisol, Germany) and assessed colloidal P forms after asymmetric flow field-flow fractionation coupled with ultraviolet and an inductively coupled plasma mass spectrometer, with and without removal of amorphous and crystalline Fe oxides using oxalate and dithionite, respectively. We found that fine colloidal P was present in two dominant sizes: (i) in associations of organic matter and amorphous Fe (Al) oxides in nanoparticles <20 nm, and (ii) in aggregates of fine clay, organic matter and Fe oxides (more crystalline Fe oxides) with a mean diameter of 170 to 225 nm. Solution P-nuclear magnetic resonance spectra indicated that the organically bound P predominantly comprised orthophosphate-monoesters. Approximately 65% of P in the WDFC was liberated after the removal of Fe oxides (especially amorphous Fe oxides). The remaining P was bound to larger-sized WDFC particles and Fe bearing phyllosilicate minerals. Intriguingly, the removal of Fe by dithionite resulted in a disaggregation of the nanoparticles, evident in higher portions of organically bound P in the <20 nm nanoparticle fraction, and a widening of size distribution pattern in larger-sized WDFC fraction. We conclude that the crystalline Fe oxides contributed to soil P sequestration by (i) acting as cementing agents contributing to soil fine colloid aggregation, and (ii) binding not only inorganic but also organic P in larger soil WDFC particles.

Innovative methods in soil phosphorus research: A review.

Phosphorus (P) is an indispensable element for all life on Earth and, during the past decade, concerns about the future of its global supply have stimulated much research on soil P and method development. This review provides an overview of advanced state-of-the-art methods currently used in soil P research. These involve bulk and spatially resolved spectroscopic and spectrometric P speciation methods (1 and 2D NMR, IR, Raman, Q-TOF MS/MS, high resolution-MS, NanoSIMS, XRF, XPS, (µ)XAS) as well as methods for assessing soil P reactions (sorption isotherms, quantum-chemical modeling, microbial biomass P, enzymes activity, DGT, 33P isotopic exchange, 18O isotope ratios). Required experimental set-ups and the potentials and limitations of individual methods present a guide for the selection of most suitable methods or combinations.

Origin and alteration of organic matter in termite mounds from different feeding guilds of the Amazon rainforests.

The impact of termites on nutrient cycling and tropical soil formation depends on their feeding habits and related material transformation. The identification of food sources, however, is difficult, because they are variable and changed by termite activity and nest construction. Here, we related the sources and alteration of organic matter in nests from seven different termite genera and feeding habits in the Terra Firme rainforests to the properties of potential food sources soil, wood, and microepiphytes. Chemical analyses comprised isotopic composition of C and N, cellulosic (CPS), non-cellulosic (NCPS), and N-containing saccharides, and molecular composition screening using pyrolysis-field ionization mass spectrometry (Py-FIMS). The isotopic analysis revealed higher soil δ13C (-27.4‰) and δ15N (6.6‰) values in nests of wood feeding Nasutitermes and Cornitermes than in wood samples (δ13C = -29.1‰, δ15N = 3.4‰), reflecting stable-isotope enrichment with organic matter alterations during or after nest construction. This result was confirmed by elevated NCPS:CPS ratios, indicating a preferential cellulose decomposition in the nests. High portions of muramic acid (MurAc) pointed to the participation of bacteria in the transformation processes. Non-metric multidimensional scaling (MDS) revealed increasing geophagy in the sequence Termes < Embiratermes < Anoplotermes and increasing xylophagy for Cornitermes < Nasutitermes., and that the nest material of Constrictotermes was similar to the microepiphytes sample, confirming the report that Constrictotermes belongs to the microepiphyte-feeders. We therewith document that nest chemistry of rainforest termites shows variations and evidence of modification by microbial processes, but nevertheless it primarily reflects the trophic niches of the constructors.

Bone char: a clean and renewable phosphorus fertilizer with cadmium immobilization capability.

Soil contamination with Cd from P fertilizer and other anthropogenic and geogenic sources is a serious problem. In situ immobilization by P application to soil is known as an applicable remediation technique leading to reduced Cd uptake by plants, and use of a Cd-free P fertilizer from renewable sources would be most favorable. Bone char (BC) (15% P, 28% Ca, 0.7% Mg) may be used as such a quality P fertilizer, but it is unknown if its dissolution in soil provides sufficient P and immobilizes Cd in moderately contaminated soils. We incubated BC and triple superphosphate (TSP) in 11 soils that contained between 0.3 to 19.6 mg Cd kg and determined the kinetics of P dissolution during a time period of 145 d. The concomitant Cd immobilization was determined by extracting the mobile Cd with 1 mol L NHNO solution. For most soils, BC increased the concentration of labile P immediately after application, reaching a maximum after 34 d, although the solubility was below that of TSP (2.9-19.3 vs. 4.1-24.0%). Among five kinetic models, the Langmuir-type equation provided the best description of P dissolution from BC and TSP. The Cd immobilization resulting from BC dissolution exceeded that of TSP by a factor of 1.4 to 2.7. The P dissolution from BC was negatively correlated with pH and positively with P sorption capacity, whereas Cd immobilization was positively correlated with soil pH. These causal relationships were expressed in multiple equations that enable predictions of P dissolution and Cd immobilization and thus may help to introduce BC as sustainable P fertilizer and useful soil amendment.

Solid-phase cadmium speciation in soil using L3-edge XANES spectroscopy with partial least-squares regression.

Cadmium (Cd) has a high toxicity and resolving its speciation in soil is challenging but essential for estimating the environmental risk. In this study partial least-square (PLS) regression was tested for its capability to deconvolute Cd L(3)-edge X-ray absorption near-edge structure (XANES) spectra of multi-compound mixtures. For this, a library of Cd reference compound spectra and a spectrum of a soil sample were acquired. A good coefficient of determination (R(2)) of Cd compounds in mixtures was obtained for the PLS model using binary and ternary mixtures of various Cd reference compounds proving the validity of this approach. In order to describe complex systems like soil, multi-compound mixtures of a variety of Cd compounds must be included in the PLS model. The obtained PLS regression model was then applied to a highly Cd-contaminated soil revealing Cd(3)(PO(4))(2) (36.1%), Cd(NO(3))(2)·4H(2)O (24.5%), Cd(OH)(2) (21.7%), CdCO(3) (17.1%) and CdCl(2) (0.4%). These preliminary results proved that PLS regression is a promising approach for a direct determination of Cd speciation in the solid phase of a soil sample.