Ferrihydrite–humic associations: magnetic hyperfine interactions

7 pages, 6 figures, 1 table, 18 references.Humic–iron oxide associations are believed to exist in various surface environments, such as soils and surface waters, and may add substantially to the stability of organic matter under oxidizing surface conditions. However, a nondestructive, solid-state characterization of such associations is still lacking. In this paper synthetic coprecipitates between humic material (dissolved organic matter; DOM) obtained from a Podzol and synthetic ferrihydrite are examined using X-ray diffraction (XRD) patterns and Fe-specific Mössbauer spectra at temperatures between 4.2 K and room temperature. Lepidocrocite formed in the absence of DOM. However, DOM induced the formation of a four (XRD)-line ferrihydrite that contained 96 mg C/kg. In contrast to a pure four-line ferrihydrite, which was completely magnetically ordered at 4.2 K, the synthesized DOM–ferrihydrite was not fully ordered at 4.2 K and had a magnetic hyperfine field 1 to 2 T lower than the pure ferrihydrite. Such an effect was not observed when DOM was only surface-adsorbed. We conclude that organic components of the DOM coprecipitated with the ferrihydrite. Their interaction with the Fe atoms of the oxide prevents complete spin freezing at 4.2 K. Solid-state 13C nuclear magnetic resonance (NMR) spectra suggested that O-alkyl C of the DOM was mainly responsible for the interaction with the Fe in the oxide.Deutsche Forschungsgemeinschaft financial support.Peer reviewe

Chemical and spectroscopic characterization of marine dissolved organic matter isolated using coupled reverse osmosis-electrodialysis

The coupled reverse osmosis-electrodialysis (RO/ED) method was used to isolate dissolved organic matter (DOM) from 16 seawater samples. The average yield of organic carbon was 75 ± 12%, which is consistently greater than the yields of organic carbon that have been commonly achieved using XAD resins, C18 adsorbents, and cross-flow ultrafiltration. UV-visible absorbance spectra and molar C/N ratios of isolated samples were consistent with the corresponding properties of DOM in the original seawater samples, indicating that DOM samples can be isolated using the coupled RO/ED method without any bias for/against these two properties. Five of the samples were desalted sufficiently that reliable measurements of their 13C and 1HNMR spectra and their Fourier transform ion cyclotron resonance (FTICR) mass spectra could be obtained. The 13C and 1HNMR spectra of RO/ED samples differed distinctly from those of samples that have been isolated in much lower yields by other methods. In particular, RO/ED samples contained a relatively lower proportion of carbohydrate carbon and a relatively greater proportion of alkyl carbon than samples that have been isolated using cross-flow ultrafiltration. From the FTICR mass spectra of RO/ED samples, samples from the open ocean contained a much lower proportion of unsaturated compounds and a much higher proportion of fatty acids than coastal samples.This material is based upon work supported by the National Science Foundation (NSF) under Grants No. 0425624 and 0425603.Peer Reviewe

Improving structural characterization of soil organic matter BY-2 dimenstional heteronucleus corelation solid state 13C NMR (HETCOR) spectroscopy

Póster presentado en la sesión S07.02: Innovation and soil science - Application of advanced NMR and MRI techniques for improving our understanding of soil organic matter formation and its interaction with the mineral phase.-- Congreso celebrado del 2-6 de julio 2012, en Fiera del Levante, Bari, Italia.One emphasis of NMR spectroscopy is to determine, via chemical shift assignments, the gross chemical structure of a material, and to quantitatively correlate between the different signal intensities and the chemical composition.Peer reviewe

Relaxometry properties of water saturated lignin chars

Comunicación presentada en la Sesión S07.02: Innovation and soil science - Application of advanced NMR and MRI techniques for improving our understanding of soil organic matter formation and its interaction with the mineral phase.-- Congreso celebrado del 2-6 de julio 2012, en Fiera del Levante, Bari, Italia.Char is a very important organic system due to its role in affecting physical and chemical soil properties.Peer reviewe

Caracterización del endocarpio de Acrocomia aculeata como sustrato de cultivos

5 páginas.-- 3 figuras.-- 2 tablas.-- 12 referenciasSe ha estudiado el residuo de Acrocomia aculeata (coco paraguayo) para su uso potencial como sustrato y en enmiendas de suelos; se ha realizado la caracterización fisicoquímica de este residuo al natural y en forma pirolizada (Biochar) a tres temperaturas, 200º, 325º y 450ºC. El estudio se ha realizado con muestras molidas siendo el tamaño de partícula menor de 1 mm. El contenido de nitrógeno aumenta en los biochars respecto a la muestra cruda y entre los biochars aumenta al aumentar la temperatura, igual que ocurre con el P asimilable. Este aumento puede ser debido al incremento de compuestos heterociclos. Mediante el estudio de resonancia magnética nuclear en estado sólido se ha podido confirmar la presencia de lignina y celulosa en la muestra cruda. También se comprueba que después de una pirolisis a 200ºC o no hay cambios de composición o si los hay son tan sutiles que no se detectan. Los espectros de las muestras pirolizadas a 325 y 450ºC muestran cambios químicos significativos, las señales en los espectros indican degradación de la lignina y la celulosa. Con el análisis de las muestras mediante la técnica de microscopía electrónica de barrido se han observado diferencias significativas en la morfología y tamaño de poros de la muestra cruda respecto a las pirolizadas. Las isotermas de adsorción obtenidas muestran el aumento del área superficial en las muestras pirolizadas.Ministerio de Economía y Competitividad (España) CGL2015-64811-P y CITIUS- UNIVERSIDAD DE SEVILLAPeer reviewe

Charcoal input increases C sequestration potential of subsoils in umbric Ferralsols

2 pages.-- Póster P5 presentado en European Science Foundation-Exploratory Workshop, celebrado del 5-7 de noviembre 2013, en Sevilla, España.Climatic conditions of subtropical and tropical regions support fast carbon (C) mineralization, and thus an accelerated degradation of soil organic matter (SOM) if compared to temperate region. However, even in those regions, there are still soils that show notable C accumulation even in the deeper horizons. Examples for the latter are umbric horizons in typical tropical soils, such as Ferralsols.Peer reviewe

Cold-season soil respiration in response to grazing and warming in High-Arctic Svalbard

The influence of goose grazing intensity and open-topped chambers (OTCs) on near-surface quantities and qualities of soil organic carbon (SOC) was evaluated in wet and mesic ecosystems in Svalbard. This study followed up a field experiment carried out in 2003-05 (part of the project Fragility of Arctic Goose Habitat: Impacts of Land Use, Conservation and Elevated Temperatures). New measurements of soil CO(2) effluxes, temperatures and water contents were regularly made from July to November 2007. SOC stocks were quantified, and the reactivity and composition measured by basal soil respiration (BSR) and solid-state 13C nuclear magnetic resonance (NMR) spectroscopy. Results reveal variations in soil carbon cycling, with significant seasonal trends controlled by temperature, water content and snow. Experimental warming (OTCs) increased near-surface temperatures in the growing season, resulting in significantly higher CO(2) effluxes. Different grazing intensities had no significant effects on observed soil respiration, but BSR rates at the mesic site (13-23 mu g CO(2) g soil-C-1 h-1) were highest with moderate grazing and lowest in the absence of grazing. A limited effect of grazing on microbial respiration is consistent with a lack of significant differences in SOC quantity and quality. NMR data show that the composition of A-horizon SOC is dominated by O-N-alkyl C and alkyl C groups, and less by carboxyl C and aromatic C groups: but again no marked variation in response to grazing was evident. It can be concluded that two years after a goose grazing experiment, SOC cycling was less than the natural variation within contrasting vegetation types.This study was funded by: the University Centre in Svalbard, Longyearbyen, Norway; Oticon Fonden; Loeffler; Stennsbys Travel Fond; and the Danish Natural Science Research Council.Peer Reviewe

Charcoal as important factor in soil organic matter formation in Brazilian ecosystem

2 pages, 4 references.-- Póster presentado al citado congreso en la Sesión II: Soil (S) Nº 485.-- Book of Abstracts of the Communications presented to the 26th International Meeting on Organic Geochemistry (IMOG), held in Costa Adeje, Tenerife – Spain, September 15 – 20, 2013.Ferralsols cover almost 40% of Brazil and can be found under a wide variety of vegetation and in many different landscapes. Some of them exhibit a high content of organic carbon (umbric epipedon) and thus represent a important sink of stable C. Also, many of them contain charcoal fragments suggesting that frequent (natural) fires affected their organic matter (OM) composition. However, in spite of many effort, the composition of its OM and the mechanisms involved in its stabilization are still to explore (Marques et al., 2011).Peer reviewe

Organic matter in low weathered soils from Pantanal region, Brazil

Congreso celebrado del 16-19, julio, 2007, en Poitiers, Francia.The organic matter (SOM) from five representative soil profiles from Pantanal region, Brazil, was investigated aiming to evaluate the relationship between SOM composition with the soil class and the environmental conditions. The observed low C soil contents are probably related to the flood pulse and some aspects of climate (high temperatures in dry season), soils (predominance of light textures in the upper horizons) and spontaneous and frequent fire in this region. The N content was comparatively high, resulting low C/N ratios. In comparison to other tropical soils, the proportion of aromatic structures is high and the Oalkyl tends to be low. Considering that the vegetation shows little influence on the SOM composition, these results are most probably related to the annual fires. The increase of both aromatic C and carboxylic C with depth may indicate that aromatic organic acids are migrating along the profile as result of the flood pulse. The input of vegetation residues with high contents of C-O alkyl, on the upper horizons may dilute the recalcitrant groups.Peer reviewe