Organic Matter In Particle Size Fractions Research Articles

Effect of particulate organic matter fractions on the distribution of heavy metals with aided phytostabilization at a zinc smelting waste slag site

Particulate organic matter (POM) significantly affects the distribution of heavy metals in contaminated soil. However, the effect of POM on the fate of heavy metals during in situ-aided phytostabilization of waste slag is unclear. The objective of this study was to investigate the distributions of heavy metals such as Cu, Pb, Zn, and Cd in the POM fractions at a zinc smelting waste slag site under in situ-aided phytostabilization after five years. The results showed that the litters and residues of four plants―Arundo donax, Broussonetia papyrifera, Cryptomeria fortunei, and Robinia pseudoacacia―decomposed to form different POM size fractions. The percentage of the 0.05–0.25 mm POM size fraction was the highest, followed by the >1 mm and 0.5–1 mm POM size fractions, and that of the 0.25–0.5 mm POM size fraction was the lowest. The masses of POM derived from the four plants were in the following order: C. fortunei > B. papyrifera > A. donax > R. pseudoacacia. The contents, enrichment coefficients, and mass loads of heavy metals such as Cu, Pb, Zn, and Cd in the POM increased with decreasing POM size, and those in the 0.05–0.25 mm POM size fraction were the highest. The mass load of heavy metals in the POM occurred in the following order: Cu > Cd > Zn > Pb. The surfaces of the POM with coarser and smaller size fractions were smoother and rougher, respectively, and the smaller POM size fractions had larger specific surface areas. The main functional groups in the different POM size fractions were –COOH, –OH, CO, CC, C–H, Si–O, and –CH3. The POM fractions played a significant role in determining the distribution of heavy metals in the revegetated waste slag. These findings have important implications for aided phytostabilization, which significantly influences the fate and speciation of heavy metals at the phytoremediation site.

Effects of organic matter fraction and compositional changes on distribution of cadmium and zinc in long-term polluted paddy soils

Soil particulate organic matter (POM) has rapid turnover and metal enrichment, but the interactions between organic matter (OM) and metals have not been well studied. The present study aimed to investigate changes in the OM concentration and composition of the POM fraction and their corresponding effects on metal distribution and extractability in long-term polluted paddy soils. Soil 2000–53 μm POM size fractions had higher contents of C–H and C=O bonds, C–H/C=O ratios and concentrations of fulvic acid (FA), humic acid (HA), cadmium (Cd) and zinc (Zn) than the bulk soils. Cadmium and Zn stocks in soil POM fractions were 24.5–27.9% and 7.12–16.7%, respectively, and were more readily EDTA-extractable. Compared with the control soil, the 2000–250 μm POM size fractions had higher organic carbon concentrations and C/N ratios in the polluted soils. However, there were no significant differences in the contents in C–H and C=O bonds or C–H/C=O ratios of POM fractions among the control, slightly and highly polluted soils. In accordance with the lower contents of C=O bonds and FA and HA concentrations, the Cd and Zn concentrations in 250–53 μm POM size fractions were lower than those in 2000–250 μm POM size fractions. Enrichment of Cd in POM fractions increased with increasing soil pollution level. These results support the view that changes in the OM concentration and the size and composition of POM fractions play a key role in determining the distribution of Cd and Zn in paddy soils.

Quantifying spatial and temporal variations in phytoplankton and kelp isotopic signatures to estimate the distribution of kelp‐derived detritus off the west coast of Vancouver Island, Canada

AbstractWe used stable isotopes to determine spatial and temporal patterns of suspended kelp‐derived detritus (KDD) along a Macrocystis kelp abundance gradient driven by recovering sea otter (Enhydra lutris) populations along the west coast of Vancouver Island. Three dominant kelp species (order Laminariales) and surface marine size‐fractionated particulate organic matter (POM) were sampled along offshore transects (0–30 km) within three regions during summer and winter. Nearshore phytoplankton isotope values were identified in regions with high chlorophyll a concentrations. Summer blooming phytoplankton δ13C values were enriched by 2.4‰ and 0.8‰ and δ15N was enriched by 1.2‰ and 0.3‰ for 20–63 μm and 0.7–20 μm POM, respectively. Macrophyte stable isotope values varied significantly within and among regions, as well as between seasons. Primary producer values were used in a Bayesian isotope mixing model (MixSIR) to estimate the KDD contribution to POM. In general, the kelp abundant region had a greater contribution of KDD to POM further away (from 4 km to 30 km) from the kelp forest (range of medians 7–58%) compared to the kelp sparse region (4–30%). Seasonally, the KDD contribution to 20–63 μm POM size fractions was greater during summer (33% average) compared to winter (16% average). These results indicated that kelp abundance is not the only driver of KDD dispersal spatially and temporally. Factors such as local oceanography, large variation in kelp isotope values, and similarity between kelp and shelf phytoplankton isotope values affect these patterns and lead to high uncertainty in modeled KDD contributions.

Structural composition of organic matter in particle-size fractions of soils along a climo-biosequence in the main range of Peninsular Malaysia

AbstractInformation on structural composition of organic matter (OM) in particle-size fractions of soils along a climo-biosequence is sparse. The objective of this study was to examine structural composition and morphological characteristics of OM in particle-size fractions of soils along a climo-biosequence in order to better understand the factors and processes affecting structural composition of soil organic matter. To explore changes in structural composition of OM in soils with different pedogenesis, the A-horizon was considered for further analyses including particle-size fractionation, solid-state13C nuclear magnetic resonance (NMR) spectroscopy and scanning electron microscopy (SEM). Due to the increase in the thickness of organic layer with increasing elevation, the A-horizon was situated at greater depth in soils of higher elevation. The relationship between relative abundances of carbon (C) structures and particle-size fractions was examined using principal component analysis (PCA). It was found that alkyl C (20.1-73.4%) and O-alkyl C (16.8-67.7%) dominated particle-size fractions. The proportion of alkyl C increased with increasing elevation, while O-alkyl C showed an opposite trend. Results of PCA confirmed this finding and showed the relative enrichment of alkyl C in soils of higher elevation. Increase in the proportion of alkyl C in 250-2000 μm fraction is linked to selective preservation of aliphatic compounds derived from root litter. SEM results showed an increase in root contribution to the 250-2000 μm fraction with increasing elevation. For the <53 μm fraction, pedogenic process of podzolization is responsible for the relative enrichment of alkyl C. This study demonstrates that changes in structural composition of OM in particle-size fractions of soils along the studied climo-biosequence are attributed to site-specific differences in pedogenesis as a function of climate and vegetation.

Organic amendments as strategy to increase organic matter in particle-size fractions of a semi-arid soil

The distribution of organic matter (OM) in soil particle-size fractions is a key process in the dynamic and persistence of soil organic carbon. In order to study the distribution of organic amendments among the different soil particle-size fractions in a semi-arid, degraded soil (a sandy loam Haplic Regosol), a 9-month-incubation experiment was carried out after the application of composted organic amendments (90Mgha−1) differing in nature (farmyard manure, cFYM; vine pruning wastes, cPW, and sewage sludge, cSS). A physical fractionation based on the separation of soil according to particle size was carried out and chemical and microbiological parameters were measured both in the whole soil and in the particle-size fractions. After amendment, all the particle-size fractions in the amended soils showed higher organic carbon (Corg) and N concentration than the control soil. At the end of the experiment, the amount of Corg in the silt-sized (2–63μm) and clay-sized (0.1–2μm) fractions did not show significant differences among amended soils, indicating that the accumulation and protection of the OM in the fine fractions of this semi-arid soil are not affected by the nature of the composted amendment. Furthermore, the fine fractions (silt and clay) of the amended soils showed intermediate C/N ratios, suggesting that the organic compounds of these fractions are derived from both microorganisms and organic amendments. At the end of the experiment, the soils amended with cPW showed the highest Corg content in the whole soil and in the coarse sand fraction (200–2000μm). In contrast, soils amended with cSS showed the highest Corg loss among treated soils and showed in general the highest microbial and enzymatic activities in the coarse sand fraction. These results highlight the importance of the recalcitrance of the amendment (high C/N ratio) to avoid fast degradation of non-protected OM in the coarse sand fraction. In conclusion, the type of the composted organic amendment did not influence the OM accumulation in fine fractions of the studied semi-arid soil, but was determinant for the degradation of OM in the coarse sand fractions.

Longitudinal and seasonal changes in the origin and quality of transported particulate organic matter along a gravel-bed river

Particulate organic matter (POM) plays an important role in nutrient dynamics in river ecosystems, but little is known about changes in the origin and quality of POM in relation to physical and seasonal changes along rivers. Using stable isotope and stoichiometric analyses, we investigated the changes in origin and quality of POM of three different size fractions (fine [FPOM], 1.2–100 μm; medium [MPOM], 100–250 μm; and coarse [CPOM], 250–1,000 μm) at 14 sites along a gravel-bed river over four seasons. FPOM and MPOM accounted for 90% of all POM at all study sites. At each site, the δ13C level was lower for FPOM (range: −29.0 to −21.1‰) than for MPOM (−26.9 to −17.2‰) and CPOM (−27.5 to −16.3‰). The C:N ratio was lower for FPOM (6.9–15.6) than for MPOM (6.3–17.4) and CPOM (5.7–27.1). The contribution of periphyton to POM of all size fractions had a tendency to increase downstream, though the trend was less clear and varied seasonally for MPOM and CPOM between sites in middle and downstream reaches. Contrastively, the C:N ratio in all size fractions of POM consistently decreased downstream. The downstream decrease in the C:N ratio of POM can be partly explained by the increase in the contribution of periphyton, which seems to be associated with increased discharge and enhanced periphyton dislodgement, especially in winter. In addition, an increase in bacterial biomass associated with the greater nutrient availability in pool areas is another possible reason for the decrease in the C:N ratio of POM downstream.

Buffer capacity and Cu affinity of soil particulate organic matter (POM) size fractions

SummaryParticulate organic matter fractions (POM), defined as sand‐sized organic separates in soils, are known to be labile organic components with a rapid turnover. Recently, POM fractions were identified to be metal‐enriched in both metal‐contaminated and uncontaminated soils. However, mechanisms for such metal‐enrichment are poorly understood, because of the paucity of information on the chemical properties of POM. The aim of this study was to quantify the reactivity of POM towards Cu and to show a POM‐size effect on this reactivity. POM was isolated from soils with different organic amendment managements: straw (S), conifer compost (CC), and non‐amended (NA). Two POM size fractions were isolated by density‐fractionation in water: 50–200 μm and 200–2000 μm. These fractions were studied for their metal contents, acid‐base properties and affinity toward Cu. The buffer capacity and Cu affinity were modeled by FITEQL 4.0 software and compared between the two POM size fractions. Each POM size fraction provided a buffer capacity due to the presence of reactive sites, the greatest being for the 50–200 μm POM fractions. A signature of organic inputs as seen by the buffer capacities was observed for the 50–200 μm but not for the 200–2000 μm POM fractions. But Cu affinity was comparable between the coarse and fine POM fractions and no significant differences were found between NA, S and CC samples. We checked the hypothesis that decreasing POM size due to degradation processes generates more reactive surface sites. Results confirmed that soil POM plays a key role as a metal sink, due to its chemical properties.

Fate of metal-associated POM in a soil under arable land use contaminated by metallurgical fallout in northern France

Organic matter is a major metal-retaining constituent in soils. Among the diversity of organic components in soils, particulate organic matter (POM) accumulates large amounts of metals, but the fate of such metal-associated POM is unknown. We studied different POM size fractions and their corresponding mineral size-fractions isolated from the surface horizon of a soil affected by metallurgical fallout. Analyses of total and EDTA extractible metal contents performed on all size fractions demonstrated that with decreasing POM size, larger metal concentrations were observed but they were less extractable. Micromorphological study revealed the occurrence of opaque parts in decaying POM fragments and their individualization as fine, irregularly shaped opaque fragments in the soil matrix. This work suggested a mutual sequestration of metal pollutants and organic carbon as micro-meter sized, metal-enriched organic particles derived from POM, representing an original pathway for natural attenuation of risk related to metal contaminated soils.

Distinguishing trophic variation from seasonal and size-based isotopic (δ15N) variation of zooplankton

We measured the δ15N of particulate organic matter (POM), Daphnia pulex (D), Holopedium gibberum (H), Leptodiaptomus tyrelli (LT), Epischura nevadensis (E), and Chaoborus trivittatus (C) over an annual cycle in Council Lake, a pristine, oligotrophic, fishless lake. Annual averages of the δ15N of plankton (C, LT, E > D, H > POM) matched expected differences in trophic position, but seasonal patterns differed among species. During midsummer, the δ15N of D, H, and LT increased above the δ15N of E and C, despite little temporal or spatial variation in the δ15N of POM (<41 µm). Larger size fractions of POM (41–200 µm) helped explain some of the temporal variability of zooplankton δ15N. Body size of zooplankton was correlated with δ15N for D, C, and E, which could indicate size-based, trophic-level variation; selective feeding; or physiological differences in 15N enrichment. We propose that detailed time series of δ15N for multiple zooplankton species can help determine the seasonal variability of trophic structure in zooplankton assemblages.

Impact of brown coal dust on the organic matter in particle-size fractions of a Mollisol

The influence of brown coal emissions from a briquette factory on the organic matter of a Mollisol has been investigated. Non-contaminated, heavily contaminated soils and airborne particles are compared by using chemical and spectroscopic methods ( 13C CPMAS-NMR, Py-GC-MS, 14C dating). Bulk soils as well as their particle-size fractions are investigated. Organic carbon content of the bulk contaminated soil (138.6 g C/kg) is higher by a factor of six than the non-contaminated soil. For particle-size fractions, the highest content of organic carbon is found in the fine sand fraction (347.2 g C/kg). Furthermore, organic matter of the contaminated site shows a trend for relatively higher abundance of aliphatic compounds in the fraction ranging from 6 to 2000 μm, whereas for particles < 6 μm no trend was observed. The A horizon of the contaminated soil is much older (15,750 yr BP0 than the non-contaminated soil, which indicates input of anthropogenic material. Py-GC-MS analyses show for the non-contaminated site a homologous series of mainly alkanes, low amounts of prist-1-ene and a high abundance of lignin- and carbohydrate-derived structures. In contrast, composition of the samples from the contaminated site are similar to a sample of brown coal analyzed and show a homologous series of n-alkane, alkene, α, ω-alkadiene triplets and a high relative abundance of prist-1-ene with few lignin derived compounds, except for the clay fraction. Reflected light microscopy shows large amounts of brown coal dust particles with typical maceral groups, huminite, liptinite, and inertinite, in the fine sand fraction from the contaminated soil. Additionally, minor amounts of thermally altered brown coal-derived particles, i.e. coke particles, are observed.

Characterization of organic matter in particle-size fractions of Vertisols

The nature of organic matter (OM) of five Vertisols was investigated by means of Diffuse Reflectance Fourier Transform Infrared Spectroscopy (DRIFT) on whole soil samples and on stable aggregates of different size, separated by water dispersion. This method allows the IR spectra of soil OM to be obtained in its original state, unaltered by chemical treatments and with part of the functional groups bound to the mineral components. Further information on the nature of OM was obtained by electrofocusing (EF) analyses of the 0.1 M Na 4P 20 7-NaOH extracts of soils and of water stable soil aggregates. The relationship of OM with soil fabric was investigated by determining the organic carbon distribution in the different waterstable fractions. Our results show that OM is concentrated in the silt size aggregates and its nature appears rather uniform in the five Vertisols. In particular, DRIFT analyses reveal the existence of very strong hydrogen bonds between the OM and the soil mineral fraction and the presence, in the natural soils, of compounds, such as cyclic anhydrides. Moreover, aromatic substances appear concentrated in the water-stable, silt-size aggregates, while relatively simple aliphatic compounds seem to prevail in clay fractions. In the “apparent”silt fraction EF analyses show the presence of considerable amounts of organo-metal complexes, probably responsible for the aggregation of fine clay particles.

Differential thermal analysis, thermogravimetry and pyrolysis-field ionisation mass spectrometry of soil organic matter in particle-size fractions and bulk soil samples

Differential thermal analysis (DTA), thermogravimetry (TG) and pyrolysis-field ionisation mass spectrometry (Py-FIMS) were compared in investigations of soil organic matter in particle-size fractions and bulk soil samples of two treatments (untreated and farmyard manure) of a 108 year old long-term agricultural experiment. The shapes of the DTA curves and Py-FIMS thermograms showed differences insofar as the latter were less resolved into distinct peaks and reached their maximum values at higher temperatures. The losses of weight obtained by the two methods were found to be strongly correlated. An adaption of the heating rates improved the conformity of the DTA, TG and Py-FIMS results. It is demonstrated that Py-FIMS yields additional information on the molecular chemical composition of soil organic matter by calculating the proportions of different compound classes based on relative abundances of characteristic FI signals. These results are essentially unaffected by different heating rates. Py-FIMS spectra were integrated for temperature ranges where DTA curves show marked reactions. Their evaluation improves the basis for the interpretation of the more common DTA and TG analyses of soil organic matter.