Organic matter in small mesopores in sediments and soils

Abstract. The spatial distribution and accessibility of organic matter (OM) to soil microbes in aggregatesdetermined by the fine-scale, 3-D distribution of OM, pores and mineral phases -may be an important control on the magnitude of soil heterotrophic respiration (SHR). Attempts to model SHR on fine scales requires data on the transition probabilities between adjacent pore space and soil OM, a measure of microbial accessibility to the latter. We used a combination of osmium staining and synchrotron X-ray computed tomography (CT) to determine the 3-D (voxel) distribution of these three phases (scale 6.6 µm) throughout nine aggregates taken from a single soil core (range of organic carbon (OC) concentrations: 4.2-7.7 %). Prior to the synchrotron analyses we had measured the magnitude of SHR for each aggregate over 24 h under controlled conditions (moisture content and temperature). We test the hypothesis that larger magnitudes of SHR will be observed in aggregates with (i) shorter length scales of OM variation (more aerobic microsites) and (ii) larger transition probabilities between OM and pore voxels.After scaling to their OC concentrations, there was a 6-fold variation in the magnitude of SHR for the nine aggregates. The distribution of pore diameters and tortuosity index values for pore branches was similar for each of the nine aggregates. The Pearson correlation between aggregate surface area (normalized by aggregate volume) and normalized headspace C gas concentration was both positive and reasonably large (r = 0.44), suggesting that the former may be a factor that influences SHR. The overall transition probabilities between OM and pore voxels were between 0.07 and 0.17, smaller than those used in previous simulation studies. We computed the length scales over which OM, pore and mineral phases vary within each aggregate using 3-D indicator variograms. The median range of models fitted to variograms of OM varied between 38 and 175 µm and was generally larger than the other two phases within each aggregate, but in general variogram models had ranges < 250 µm. There was no evidence to support the hypotheses concerning scales of variation in OM and magnitude of SHR; the linear correlation was 0.01. There was weak evidence to suggest a statistical relationship between voxel-based OM-pore transition probabilities and the magnitudes of aggregate SHR (r = 0.12). We discuss how our analyses could be extended and suggest improvements to the approach we used.

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“…We assume an OM density of 1.4 g cm −3 (Mayer et al, 2004). We computed the volume of OM (cm −3 ) by dividing the mass of OM by its density.…”

Section: Segmentation Of Solid and Pore Phasesmentioning

confidence: 99%

Three-dimensional soil organic matter distribution, accessibility and microbial respiration in macroaggregates using osmium staining and synchrotron X-ray computed tomography

Rawlins

Wragg

Reinhard

et al. 2016

SOIL

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“…The second, more resistant pool of HPH-crenarchaeol likely stems from the water column where IPL-GDGTs are found in >0.7 lm size SPM ( Schouten et al, 2012), where they are probably being protected from degradation by adsorption to particles and into mesopores (Mayer, 1994;Hedges and Keil, 1995;Mayer et al, 2004). The rapid decrease of the HPH-crenarchaeol below the surface sediment production peak at stations P1300 and P3000 and the relatively low amounts of HPH crenarchaeol at station P900, are in accordance with the rapid degradation kinetics for phosphoester-lipids found by Harvey et al (1986).…”

Section: Sedimentary Production and Preservation Of Gdgtsmentioning

confidence: 99%

Intact polar and core glycerol dibiphytanyl glycerol tetraether lipids in the Arabian Sea oxygen minimum zone. Part II: Selective preservation and degradation in sediments and consequences for the TEX86

Lengger

Hopmans

Reichart

et al. 2012

Geochimica et Cosmochimica Acta

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The TEX 86 is a proxy based on a ratio of pelagic archaeal glycerol dibiphytanyl glycerol tetraether lipids (GDGTs), and used for estimating past sea water temperatures. Concerns exist that in situ production of GDGTs lipids by sedimentary Archaea may affect its validity. In this study, we investigated the influence of benthic GDGT production on the TEX 86 by analyzing the concentrations and distributions of GDGTs present as intact polar lipids (IPLs) and as core lipids (CLs) in three sediment cores deposited under contrasting redox conditions across a depth range from 900 to 3000 m below sea level in and below the Arabian Sea oxygen minimum zone (OMZ). Direct analysis of IPLs with crenarchaeol as CL via HPLC/ESI-MS 2 revealed that surface sediments in the OMZ were relatively depleted in the phospholipid hexose, phosphohexose (HPH)-crenarchaeol compared to suspended particulate matter from the water column, suggesting preferential and rapid degradation of this IPL. In sediment cores recovered from deeper, more oxic environments, concentrations of HPH-crenarchaeol peaked at the surface, probably due to in situ production by ammonia-oxidizing Archaea, followed by a rapid decrease with increasing depth. No surface maximum was observed in the sediment core from within the OMZ. In contrast, the glycolipids, monohexose-crenarchaeol and dihexose-crenarchaeol, did not change in concentration with depth in the sediment, indicating that they were relatively well preserved and likely mostly derived from fossil pelagic GDGTs. These results suggest that phospholipids are more sensitive to degradation, while glycolipids might be preserved over longer time scales, in line with previous incubation and modeling studies. Furthermore, in situ produced IPL-GDGTs did not accumulate as IPLs, and did not influence the CL-TEX 86 . This suggests that in-situ produced GDGT lipids were more susceptible to degradation than fossil CL and IPL and did not accumulate as CL. In agreement, no significant changes of TEX 86 with sediment depth in the core lipids were observed. However, consistent differences between IPL-derived TEX 86 and CL-TEX 86 were found. These could be explained by a different composition of CL-GDGT of the glyco-and phospholipids, in combination with dissimilar degradation rates of phospholipids vs. glycolipids. We also observed consistent differences in both IPL-derived and CL-TEX 86 between the different cores, equivalent to 3°C when converted to temperature, despite the proximity of the core locations. These differences may potentially be due to a larger addition of GDGTs produced in deeper, colder waters to the (sub)surface-derived GDGTs for the deeper core sites.

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“…A similar high clay content (41 %) was found at 30 cm in sample MS1. Previous studies have established a relationship between soil texture and particulate SOM: adsorption of the latter onto the clay fraction of soil is a significant form of its preservation (Mayer and Xing, 2001, Mayer et al 2004, Bruun et al 2010, Clemente et al 2011. In muddy source rocks too, most DOM concentrates in the clay fraction, but the link between DOM and clay fraction is not well understood at present (CaiJ et al 2009, CaiJ et al 2010, Ding et al 2011.…”

Section: D Fluorescence Of Dom In the Soil Profilesmentioning

confidence: 99%

Characterization of Dissolved Organic Matter in an Agricultural Wastewater-Irrigated Soil, in Semi Arid Mexico

Fuentes-Rivas

León²,

Ramos-Leal

et al. 2017

Rev. Int. Contam. Ambie.

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Most agricultural soils in semi-arid regions present a deficiency of organic matter (SOM). In order to improve this soil, wastewater is used due to its high organic carbon content. The objective of the present work was to characterize the dissolved organic matter in five residual water samples and ten soil samples from the agricultural area of the municipality of San Luis Potosí by 3D fluorescence spectroscopy. The changes in some physical and chemical properties of the soil were also analyzed. The soil samples were collected at different depths to observe the anthropogenic organic matter presence, their retention in the soil profile, their fluorescence intensity changes and their migration into the aquifer. Temperature, electrical conductivity, dissolved oxygen, oxidation-reduction potential and total dissolved solids were determined in situ. The major anions and cations: Na3-, SO4 2-, NO 3-, NO2 -, were analysed in laboratory. The results show the great contribution of organic matter (>2020 mg/L) in the residual water used for irrigation, as well as, the low content of SOM. The physical and chemical results indicate that the high electrical conductivity of the water, represents a risk of salinization for soils, but not of short term sodicity. The 3D fluorescence spectra of the soil profile, shows the presence of humic and fulvic acids, aromatic proteins and products of microbial degradation. The latter observed in that depth where there is a greater percentage of clay.Palabras clave: fluorescencia 3D, proteínas aromáticas, ácidos húmicos, ácidos fúlvicos, contaminación de suelo RESUMEN La mayoría de los suelos agrícolas en regiones semiáridas presentan una deficiencia de materia orgánica (MOS) y para compensarla se recurre al uso de agua residual por R.M. Fuentes Rivas et al. 576 su alto contenido de carbono orgánico. El objetivo del presente trabajo fue caracterizar la materia orgánica disuelta con espectroscopía de fluorescencia 3D, en cinco muestras de agua residual y 10 de suelo de la zona agrícola del municipio de San Luis Potosí. Se analizaron los cambios de algunas propiedades físicas y químicas del suelo y del agua. Las muestras se colectaron a diferentes profundidades para observar la presencia de materia orgánica, su retención a lo largo del perfil de suelo y su migración hacia el acuífero. La temperatura, la conductividad eléctrica, el oxígeno disuelto, el potencial de oxido-reducción y los sólidos totales disueltos se determinaron in situ. En laboratorio fueron analizados los aniones y cationes mayoritarios: Na . Los resultados muestran el gran aporte de materia orgánica del agua residual empleada para el riego, así como, el bajo contenido de MOS. Los resultados físicos y químicos indican que la alta conductividad eléctrica del agua representa un riesgo de salinización para los suelos, pero no de sodicidad a corto plazo. Los espectros de fluorescencia 3D del perfil del suelo evidencian la presencia de ácidos húmicos, acidos fúlvicos, proteínas aromáticas y productos de degradación microbian...

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Organic matter in small mesopores in sediments and soils

Cited by 225 publications

References 47 publications

Three-dimensional soil organic matter distribution, accessibility and microbial respiration in macroaggregates using osmium staining and synchrotron X-ray computed tomography

Three-dimensional soil organic matter distribution, accessibility and microbial respiration in macroaggregates using osmium staining and synchrotron X-ray computed tomography

Intact polar and core glycerol dibiphytanyl glycerol tetraether lipids in the Arabian Sea oxygen minimum zone. Part II: Selective preservation and degradation in sediments and consequences for the TEX86

Characterization of Dissolved Organic Matter in an Agricultural Wastewater-Irrigated Soil, in Semi Arid Mexico

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