Light Organic Matter Research Articles

SOIL CARBON STOCKS AND LABILE FRACTIONS OF ORGANIC MATTER UNDER DIFFERENTS VEGETATIONS COVERAGES IN GURUPI – TO

Soils represent a large reservoir of carbon (C), and changes in use and management can impact C balance and global climate control. The study aimed to determine the effect of changes in vegetation cover on soil C stocks and labile fractions in the Cerrado biome in the southern region of Tocantins. The work was developed in areas of Eucalyptus sp., pasture, agriculture and cerrado sensu stricto at the experimental farm in Federal University of Tocantins. The soil samples were collected in trenches of 70 x 70 cm at depths 0-10, 10-20, 20-30, 30-40 and 40-50 cm, with six replications. Statistical analysis was performed using the normality test, analysis of variance and comparison of means by the Tukey test at 5% significance. On Eucalyptus stands, the soil's carbon was higher than native forest vegetation, pasture and agriculture. The contents of labile carbon (C-labile) and light organic matter (LOM) were 26.80 and 41.58% higher for the Eucalyptus sp. compared to native forest, 25.75 and 35.76% for pasture, and 48.39 and 9.50% for agriculture, respectively. Among the different areas evaluated, it was found that Eucalyptus sp. it has great potential to increase the carbon storage in the soil, C-labile and light organic matter.

Combinations of Plant Species for Rotation With Onion Crops: Effects on the Light Fraction, Carbon, and Nitrogen Contents in Granulometric Fractions of the Soil Organic Matter

The conversion of conventional tillage system (CTS) into no-tillage system (NTS) for onion crops with use of soil cover crops increases carbon and nitrogen contents in the soil aggregates. The objective of this work was to evaluate the effects of combinations of different plant species and soil management systems using rotation with soil cover crops for onion crops on the light organic matter (LOM), carbon (C), and nitrogen (N) contents in the organic matter granulometric fractions in soil macroaggregates and bulk soil. A nine-year experiment (2007-2016) was conducted using the treatments (T): maize-onion in NTS (T1); soil cover crops (winter)-onion in NTS(T2); maize-winter grasses-onion in NTS (T3); velvet bean-onion in NTS (T4); millet-soil cover crops (winter)-onion in NTS (T5); velvet bean-rye-onion in NTS (T6); maize-onion in CTS (T7); intercropped soil cover crops (summer)-onion in NTS (T8). C and N contents in the LOM, particulate organic C and N (POC and PON), and mineral- associated C and N (MOC and MON) were evaluated in soil macroaggregates (8.0 to 2.0 mm) and bulk soil (<2.0 mm) from the 0–5 cm, 5–10 cm, and 10–20 cm layers. High diversity and combinations of plant species in T2-T6, and T8 resulted in higher POC and MON contents in aggregates, and higher MOC and PON contents in bulk soil, when compared to T1 and T7. T2 was a better option to increase LOM and POC contents in aggregates (0-5 cm). The evaluation of POC (0–5 cm), PON, and MON (0-10 cm) contents in soil aggregates showed more significant differences between the treatments than the contents found in bulk soil. The onion crops under NTS combined with use of rotations with soil cover crops were more efficient to improve the evaluated soil attributes than those under CTS.

Land-use perturbations in ley grassland decouple the degradation of ancient soil organic matter from the storage of newly derived carbon inputs

Abstract. In a context of global change, soil has been identified as a potential carbon (C) sink, depending on land-use strategies. To detect the trends in carbon stocks after the implementation of new agricultural practices, early indicators, which can highlight changes in short timescales, are required. This study proposes the combined use of stable isotope probing and chemometrics applied to solid-state 13C nuclear magnetic resonance (NMR) spectra to unveil the dynamics of the storage and mineralization of soil carbon (C) pools. We focused on light organic matter fractions isolated by density fractionation of soil water stable aggregates because they respond faster to changes in land use than the total soil organic matter (SOM). Samples were collected from an agricultural field experiment with grassland, continuous maize cropping, and ley grassland under temperate climate conditions. Our results indicated contrasting aggregate dynamics depending on land-use systems. Under our experimental conditions, grassland returns larger amounts of C as belowground inputs than maize cropping, evidencing a different distribution of light C fractions between aggregate classes. Coarse aboveground inputs from maize contributed mostly to larger macroaggregates. Land-use changes with the introduction of ley grassland provoked a decoupling of the storage and/or degradation processes after the grassland phase. The newly derived maize inputs were barely degraded during the first 3 years of maize cropping, whereas grassland-derived material was depleted. As a whole, results suggest large microbial proliferation as shown by 13C NMR under permanent grassland, then reduced within the first years after the land-use conversion, and finally restored. The study highlighted a fractal structure of the soil, determining a scattered spatial distribution of the cycles of storage and degradation of soil organic matter related to detritusphere dynamics. As a consequence, vegetal inputs from a new land use are creating new detritusphere microenvironments that may be disconnected from the dynamics of C cycle of the previous land use. The formation of those different and unconnected microenvironments may explain the observed legacy effect of the previous land use, since each microenvironment type contributes separately to the overall soil C cycle. The effects of the new land use on the soil C cycle are delayed until the different detritusphere microenvironments remain unconnected, and the ones from the previous land use represent the predominant microenvironment type. Increasing knowledge of the soil C dynamics at a fine scale will be helpful in refining the prediction models and land-use policies.

The yield values of densimetric fractions from typical chernozems of different land use types

One of the most justified and applied approaches to isolating pools of soil organic matter is fractionation in heavy liquids. The main problem with this approach is rather large losses in the separation of fractions at the stage of washing fractions from heavy liquids. The paper presents a densimetric fractionation protocol that can significantly reduce these losses. It is suggested to use 0.001 M HCl for washing. This approach, in comparison with distilled water, allows reducing losses of weight from 15 to 5% and of carbon from 7.5 to 2.5%. The paper provides a detailed protocol, used by the Laboratory of Soil Biochemistry of V.V. Dokuchaev Soil Science Institute, to isolate four densimetric fractions using sodium polytungstate solutions: free and occluded SOM with a density of <1.6 g/cm3, occluded SOM – of 1.6–2.0 g/cm3, and a mineral residue with a density >2.0 g/cm3. In the work we used samples of typical chernozems of different land use types. It was shown that the processes of soil restoration and degradation significantly affect the content of light occluded soil organic matter.

Influence of management on maintenance and dynamics of carbon in the soil

This work aimed to analyze the dynamics of soil carbon in agricultural areas under different soil management systems and natural ecosystems with Cerrado vegetation. The study was carried out in a grain production area equivalent to soybeans and corn located in the Western region of Bahia State with the adoption of conventional and no-tillage + Brachiaria and vegetable production in the southernmost tip of Piauí State under organic cultivation and vegetable cultivation + no-tillage, besides the native area of ​​the Cerrado. Total organic C content, light organic matter, and soil organic matter were evaluated. Furthermore, the C stock and light organic matter were assessed at four depths (0.0-0.05, 0.05-0.10, 0.10-0, 20, and 0.20-0.40 m). The systems under vegetable cultivation and native area presented the highest levels of C, organic matter, and soil carbon stocks in the superficial layers. However, the NTS + B2 showed higher levels in depth, except for light organic matter. Thus, the content, dynamics, and maintenance of C into the soil are nearly influenced by the management system adopted, both for the lighter fractions of organic matter and the more mineralized forms such as TOC, OSM, and StkC.

Seabed Resuspension in the Chesapeake Bay: Implications for Biogeochemical Cycling and Hypoxia

Sediment processes, including resuspension and transport, affect water quality in estuaries by altering light attenuation, primary productivity, and organic matter remineralization, which then influence oxygen and nitrogen dynamics. The relative importance of these processes on oxygen and nitrogen dynamics varies in space and time due to multiple factors and is difficult to measure, however, motivating a modeling approach to quantify how sediment resuspension and transport affect estuarine biogeochemistry. Results from a coupled hydrodynamic–sediment transport–biogeochemical model of the Chesapeake Bay for the summers of 2002 and 2003 showed that resuspension increased light attenuation, especially in the northernmost portion of the Bay, shifting primary production downstream. Resuspension also increased remineralization in the central Bay, which experienced larger organic matter concentrations due to the downstream shift in primary productivity and estuarine circulation. As a result, oxygen decreased and ammonium increased throughout the Bay in the bottom portion of the water column, due to reduced photosynthesis in the northernmost portion of the Bay and increased remineralization in the central Bay. Averaged over the channel, resuspension decreased oxygen by ~ 25% and increased ammonium by ~ 50% for the bottom water column. Changes due to resuspension were of the same order of magnitude as, and generally exceeded, short-term variations within individual summers, as well as interannual variability between 2002 and 2003, which were wet and dry years, respectively. Our results quantify the degree to which sediment resuspension and transport affect biogeochemistry, and provide insight into how coastal systems may respond to management efforts and environmental changes.

A novel method to evaluate cleaning quality of oil in shale using pyrolysis pyrogram

AbstractComplete and thorough core cleaning is a critical prerequisite for the precise measurements of most rock's petrophysical parameters. In shale, the oil cleaning process, aimed to remove the volatile hydrocarbons, is often complicated by the requirement for intact solid organic. Evaluation of shale's cleaning methods needs to take structural integrity of organic matrix into account but neglected in the existing researches. Here, we develop a novel evaluation method using a modified ESH (extended slow heating) pyrolysis cycle, which starts at a lower initial temperature of 150°C for 10 minutes and then slowly increases to 650°C by 10°C/min. Hydrocarbons on the ESH pyrogram were divided into light free hydrocarbon (SA), FHR (fluid‐like hydrocarbon, SB), and solid organic matter (SC). We propose a set of quantitative evaluation criterions comparing the results of pyrograms, for different types of the hydrocarbons, at different cleaning conditions. We showed that a modified pyrogram achieves complete cleaning with SA and SB removed while SC remains almost intact. The modified pyrogram achieves complete removal of FHR in the second stage of pyrogram, while earlier researches often report residual FHR. The introduced method improves the accuracy in the identification of production potential in kerogen‐rich shale reservoirs up to about 3% of the total pore volume. Further, the new approach allows a quantitative assessment for the cleaning quality without altering the sample's organic matrix. Future studies on the petrophysical properties of the hydrocarbon‐bearing reservoir rocks may benefit from the thorough hydrocarbon removal achieved through the modified pyrogram methods proposed in this study.

Microwave pyrolysis of food waste for high-quality syngas production: Positive effects of a CO2 reaction atmosphere and insights into the intrinsic reaction mechanisms

CO2 steam reformation technology for the conventional pyrolysis of food waste has been proven to effectively improve the bio-gas yield. However, the syngas proportion is low. This work systematically investigated the effects of a CO2 reaction atmosphere on the improvement of the syngas yield and the intrinsic reaction mechanisms during the microwave pyrolysis of food waste. The results show that an increased microwave power promoted the generation of bio-gas by rapidly increasing the pyrolysis temperature of the food waste. When the microwave power was 1400 W, the bio-gas yield in the CO2 reaction atmosphere reached 67.90 wt%, and the yield of the syngas in the bio-gas was 44.13% higher than that in the N2 atmosphere (46.73 L/kg food waste). The concentrations of H2, CH4, and CO in the bio-gas increased rapidly at temperatures between 200 °C and 600 °C. However, the concentrations of H2 and CH4 gradually decreased as the pyrolysis temperature increased from 600 °C to 900 °C, which was caused by H2 and CH4 reacting with CO2 to form CO. In addition, the reaction of the light organic matter (e.g., aliphatic hydrocarbons and oxygen-containing compounds) in the bio-oil with CO2 was the critical process that improved the syngas yield. The content of polycyclic aromatic hydrocarbons decreased by 6.13% due to the inhibition of the aromatization reaction of the organic matter. Compared to the N2 atmosphere, the CO2 atmosphere not only promoted the generation of CO from bio-char gasification but also significantly improved the specific surface area of the bio-char (from 143.66 m2/g to 205.71 m2/g), which provided the possibility for subsequent resource utilization.

Colloidal biliquid aphron demulsification using polyaluminum chloride and density modification of DNAPLs: optimal conditions and common ion effect.

Dense non-aqueous phase liquids (DNAPLs) entrapped and pooled in aquifers serve as a long term source of groundwater contamination because of their low solubility and high density. Density modification displacement (DMD) with colloidal biliquid aphrons (CBLAs) is a promising approach to prevent DNAPL downward migration during surfactant-based remediation processes. CBLA demulsification and quick release of internal light organic matter is the key to density modification of DNAPLs. In this work, it is reported for the first time that polyaluminum chloride (PAC) could destabilize CBLAs efficiently. The optimum conditions for demulsification of CBLAs by PAC were obtained; the effects of several specific ions in groundwater on demulsification of CBLAs by PAC were investigated. The results indicated that the CBLA was completely demulsified by PAC within 10 minutes and released light organic matter. It recorded the highest demulsification efficiency when the addition ratio (VPAC/VCBLA) was 2 : 1, concentration of PAC was 0.7 g L-1 and the PVR of CBLAs was 8. Most cations (sodium, magnesium and calcium ions) had inhibitory effects on demulsification of CBLAs by PAC with increasing ion concentration, but iron ions had no effect on it. Sulfate anions showed a stronger inhibitory effect on demulsification of CBLAs by PAC compared to chloride ions. With PAC as the demulsifier, CBLAs could be demulsified efficiently, irreversibly modifying the density of trichloroethylene in 5 minutes.

The Influence of the Rotation Length of Eucalypt Plantations on Soil Organic Matter Dynamics in Southern Brazil

The rotation length of forest plantations can influence soil organic matter (SOM) pools. However, this is not well documented in eucalypt systems in Brazil. Therefore, we assessed the total organic carbon (TOC), total nitrogen (TN), and SOM fractions with different turnover rates (i.e., light organic matter [LOM], alkali extractable [AE], and nonextractable [ANE]) in the top 1 m of soil of 10‐, 13‐, and 22‐yr eucalypt rotations, and compared them with those of a native grassland in southern Brazil. The 22‐yr rotation yielded greater TOC stocks in the 0‐ to 60‐cm soil depth (107.2 Mg ha−1) than the grassland (86.7 Mg ha−1). Total N stocks were lower in the upper soil layers (0‐ to 40‐cm depth interval) in the eucalypts than in the grassland, except for the 10‐yr rotation. The changes in TOC and TN resulted in wider soil C/N ratios in the soil (0‐ to 100‐cm depth interval) in longer rotations (13 and 22 yr). The LOM‐C and LOM‐N fractions were similar between the grassland and longer rotations but were reduced in the 10‐yr stand. Overall, afforestation increased AE‐C stocks; the 10‐ and 13‐yr stands yielded the greatest AE‐C stocks at the 0‐ to 60‐cm and 0‐ to 100‐cm soil depths, respectively. For ANE‐C, the 22‐yr stand yielded the greatest stock at the 0‐ to 100‐cm depth (88.8 Mg ha−1). Our study showed that longer eucalypt rotations promoted soil C accrual compared with the grassland and shorter rotations; however, TN stocks were less affected, resulting in wider soil C/N ratio as rotation length increased.

Evaluation of degradation of a novel sulfone bactericide in soils: identification of degradation product and kinetics study

Fubianezuofeng is a novel bactericide that shows good inhibitory activity on rice bacterial leaf streak and leaf blight. In this study, the probable influencing factors such as light, soil moisture, soil types, temperature, soil sterilization, and soil organic matter on this bactericide degradation were investigated. The results showed that the degradation experiments of Fubianezuofeng follow the first-order kinetics equation. The rate of degradation was remarkably affected by the types of soil with the degradation half-life t1/2 3.89, 5.21, 4.56, 7.22, 213.05, and 137.29 h for Tianjin, Hefei, Guiyang, Nanning, Harbin, and Changsha soils, respectively. The high moisture and increased temperature can accelerate its degradation rate in soil. Moreover, the degradation rate was faster under non-sterilized condition (t1/2 9.24 days) than under sterilized condition (t1/2 31.51 days) and removed organic matter from soil (t1/2 57.76 days). And the degradation under ultraviolet light (t1/2 0.47 days) was the fastest followed by xenon light (t1/2 5.42 days) and dark condition (t1/2 9.24 days). Finally, the major degradation product, named 2-(4-fluorobenzyl)-5-methoxy-1,3,4-oxadiazole, was identified by ultra-high-performance liquid chromatography equipped with high-resolution mass spectrometry, and the probable mechanism and degradation pathway of FBEZF under the present experimental conditions were proposed in soil. This research can be helpful for the security evaluation of FBEZF and provide some useful data for further investigations and developments on sulfone pesticides in the agricultural and environmental field.

THE IMPACT OF AGRICULTURAL SYSTEMS IN THE SOIL ORGANIC MATTER CONTENT IN BRAZILIAN CERRADO

Were quantified the plant residues on the soil, total soil organic carbon (TOC) and nitrogen (TN) contents and the different soil organic matte (SOM) fractions and to determine 13C and 15N isotopic soil composition and plant residues in the crop–livestock integration system (CLIS), pasture and Cerrado areas, in Goias, Brazil. TOC and TN, C and N light organic matter content (C-LOM/N-LOM); C and N of particulate organic matter (C-POM/N-POM); and mineral organic matter (C-MOM/N-MOM) were evaluated. δ13C and δ15N of soil and LOM, POM, and MOM fractions, as well as the δ13C of plant residues, were also determined. Plant residues from pasture were more enriched with nutrients and C, and CLIS which are richer in N. δ13C of pasture and CLIS soils indicated that the C from the Cerrado vegetation (typically C3) was replaced by vegetation with C4 photosynthetic mechanisms. CLIS accumulated more TOC than the pasture, and provided higher C-MOM and N-MOM values than pasture, and higher N-LOM levels than pasture and Cerrado. δ13C of LOM is associated with more recent origins of carbon. δ15N of POM and soil of the CLIS and pasture indicate greater mineralization of SOM.

Chemostratigraphy of the Mesoproterozoic Shennongjia Group, Yangtze Craton (South China): Implications for oxidized shallow seawaters

The relatively low Mesoproterozoic oxygen concentrations in atmospheric and marine environments remained controversial because the marine chemical evolution has not been sufficiently researched. To provide a better understanding of the secular redox conditions of shallow-water sedimentary environments and to perform global isotopic comparisons, we present new data of rare earth elements and yttrium (REE + Y), redox-sensitive elements (RSEs), and carbonate carbon-oxygen isotopes from Mesoproterozoic marine succession in the Shennongjia Group of the Yangtze Shennongjia area. Seawater-like REE + Y distribution patterns with significantly negative Ce anomalies, which had previously been screened to avoid detrital effects in the leached carbonates, illustrate the oxidation of shallow seawaters during the deposition of this group. Although the Ce/Ce* and (Pr/Yb)SN values remain relatively low in carbonate samples throughout the Mesoproterozoic, these values are higher than those of the modern oxygenated ocean, indicating less intense oxygenation. This conclusion is supported by the high enrichment factors of the RSEs in screened samples resulting from a considerable marine reservoir for dissolved RSEs in a constantly oxidized environment. Under these circumstances, the δ13Ccarb chemostratigraphy is moderately varied, with values near +3.5‰ and lower than +5‰, and more dynamic variability is observed over time, which is related to progressively smaller marine dissolved inorganic carbon (DIC) reservoirs. In addition, the significant negative excursion of δ13Ccarb near to or less than 0‰ in this lower subgroup is globally matched in different blocks and may correspond to the oxidation of isotopically light organic matter in oceans. A worldwide comparison indicates that the δ13Ccarb chemostratigraphies combined with limited geochronological data may constrain this extended negative excursion to ca. 1.3–1.2 Ga and the Shennongjia Group to ca. 1.3–1.1 Ga.

Non-chromatographic method for separation and determination of Fe, Ni and V porphyrins in crude oil

A method combining ultracentrifugation and cloud point extraction is proposed for the separation and determination of Fe, Ni and V porphyrins in crude oil. An emulsion containing about 200 mg of crude oil, 6% (w v−1) of Triton X-100™, 1.6% (v v−1) of chloroform and 0.1 mol L−1 of HCl was prepared. An aliquot (1.5 mL) of this emulsion was ultracentrifuged to separate the crude oil heavy fraction (asphaltene and particulate matter) and inorganic species, organometallic compounds and porphyrins of Fe, Ni and V remained in the supernatant. Another aliquot (1.5 mL) was heated up to 90 °C for 5 min to separate the porphyrins, both heavy and light organics compounds, light organic and particulate matter by cloud point extraction, only the inorganic and ionic organometallic compounds species remained in the aqueous phase. The supernatant and aqueous phase were analysed by simultaneous graphite furnace atomic absorption spectrometry. The concentration determined in the supernatant was subtracted from that determined in the aqueous phase, providing the quantification of Fe, Ni and V porphyrin in the crude sample. The accuracy of the proposed method was checked using SARA reference method. The elemental determinations in the fractions obtained using the proposed method and the comparison by SARA showed an absence of Fe in the aromatics and resins fractions. The results showed that about 40% of Ni and 70% of V in the crude oil sample are bounded to porphyrins.

A blessing in disguise? Natural organic matter reduces the UV light-induced toxicity of nanoparticulate titanium dioxide

Besides their economic value, engineered inorganic nanoparticles (EINPs) may pose a risk for the integrity of ecosystems. Among EINPs, titanium dioxide (nTiO2) is frequently used and released into surface waters in the μg range. There, nTiO2 interacts with environmental factors, influencing its potential to cause adverse effects on aquatic life. Although factors like ultra violet (UV) light and natural organic matter (NOM) are considered as ubiquitous, their joint impact on nTiO2-induced toxicity is poorly understood. This study addressed the acute toxicity of nTiO2 (P25; 0.00–64.00 mg/L; ~60 nm) at ambient UV light (0.00–5.20 W UVA/m2) and NOM levels (seaweed extract; 0.00–4.00 mg TOC/L), using the immobility of Daphnia magna as response variable. Confirming previous studies, effects caused by nTiO2 were elevated with increasing UV radiation (up to ~280 fold) and mitigated by higher NOM levels (up to ~12 fold), possibly due to reduced reactive oxygen species (ROS; measured as •OH radicals) formation at lower UV intensities. However, contradicting to former studies, nTiO2-mediated ROS formation was not proportional to increasing NOM levels: lower concentrations (0.04–0.40 mg TOC/L) slightly diminished, whereas a higher concentration (4.00 mg TOC/L) promoted the ROS quantity, irrespective of UV intensity. Measured ROS levels do not fully explain the observed nTiO2-induced toxicity, whereas increasing acetylcholinesterase and glutathione-S-transferase activities in daphnids (in presence of 8.00 mg/L nTiO2 and elevated UV intensity) point towards neurotoxic and oxidative stress as a driver for the observed effects. Hence, despite higher •OH levels in the treatments where 4.00 mg TOC/L were present, NOM was still capable of reducing nTiO2-induced stress and ultimately adverse effects in aquatic life.

Soil Organic Matter Fractions Under Eucalypt Plantation in Reform Management

ABSTRACT Harvesting and reform in eucalyptus can lead to changes in soil organic matter (SOM). The objective of this work was to evaluate the changes in total organic C (TOC) and N (NT), C and N in humic acid (HA), fulvic acid (FH), light organic matter (LOM) and microbial biomass (MB), in Ultisol of eucalypt stands over one, two and four years of renovated areas in Rio Grande do Sul state. After the first year of eucalyptus reform, there were 78% of increases in TOC (0.0-1.0-m soil layer). After two years, there was an increase in TN and an average reduction of 52% in LOM-C (0.0-0.1-m soil layer). FA-C, HA-C, and HU-C presented mean reductions of 43 Mg ha–1 (0.0-1.0-m soil layer) after four years of reform. The litter contribution of previous crop and the crop residues from the harvest resulted in increments of the SOM fractions. However, there is a negative effect in later years.

Gas production from dredged sediment

The anaerobic degradation of sediment organic matter leads to considerable gas production in constructions made from sediments and in landfills where contaminated sediments are disposed of, inducing problems with the mechanical stability of constructions or necessitating extraction and treatment of gas. However, little is known about the magnitude of gas generation from dredged sediment, hence validated input parameters for gas production modelling are missing. On the occasion of drillings performed for the installation of inclinometers on a mono-landfill for contaminated dredged sediment, eleven waste layers of known were sampled. Samples were analysed for gas generation in a long-term laboratory incubation experiment carried out for 757 days. It was found that the residual gas potential of the deposited dredged material ranged between 2 and 12 m3 MgDW−1, relating to 3–11% of the organic matter being degraded. Correlation analyses with material properties suggest a strong role of nitrogen, either directly or as indicative parameter, with the gas potential increasing with total nitrogen content and the share of degradable carbon decreasing with increasing TOC/TN ratio. The by far greatest share of organic matter was bound in the heavy density fraction >1.4 g cm−3, suggesting that the readily available light organic matter pool had already been depleted during pre-treatment of the dredged sediment in dewatering fields and the subsequent years of landfilling. Consequently, the correlation of the remaining gas potential with heavy fraction nitrogen was even stronger than for bulk nitrogen. The gas potential as revealed from the long-term test correlated well with short-term values, but outreached the commonly applied potential measured for 21 days by the factor of four. The data improve the state of knowledge on gas production from the large mineral waste stream of dredged material and serve to improve gas production modelling for these types of wastes. The strong correlation of gas potential to TN suggests that TN may serve as a proxy to estimate total gas potential.

Changes in the stocks of C and N in organic matter fractions in soil cropped with coffee and fertilized with sunn hemp and ammonium sulfate

Despite the potential to provide N to crops, the rapid incorporation of green manure nutrients into stable fractions of organic matter in the soil (SOM) may reduce the efficiency of green manuring. Thus, the objective of this work was to characterize the changes of C and N stocks in fractions of SOM cultivated with coffee (Coffea arabica L.) and fertilized with sunn hemp (Crotalaria juncea) and ammonium sulfate. To study the changes in organic C (OC) and total N (TN) in soil and fractions of SOM over time, soil samples were collected in the 0–5 and 5–10 cm layers, with the initial sampling done prior to the application of sunn hemp residues and ammonium sulfate. Five samples were collected every 2 months after the application of the legume and ammonium sulfate. The soil samples were submitted to densimetric and granulometric fractionation, obtaining the free light organic matter (F-LOM), particulate organic matter (POM), and organic matter associated with minerals (MAM). OC and TN stocks were then determined in soil and the SOM fractions. The changes in the stocks of OC (?StcC) in the soil in relation to time zero were positive in the evaluations carried out in the two layers. The fractions of SOM showed positive ?StcC at almost all of the evaluated times. The N supplied to the soil in the form of mineral and organic fertilizer promoted an increase of 0.24 Mg ha-1 of N in the 0–5 cm layer until after 60 days. Of this total, 0.03 Mg ha-1 was associated with F-LOM, 0.07 Mg ha-1 with POM, and the remainder was associated with MAM. Nearly 60% of the N that was supplied to the soil was drawn to the stable fractions of the SOM, indicating a rapid stabilization of this nutrient in the most recalcitrant organic compartments. Despite that, the variations in N stocks of MAM became smaller over time, and eventually became negative, in relation to time zero. This indicates the mineralization of N of this compartment. In the 5–10 cm layer, no effect of time was observed in the soil TN, N-POM, or N-MAM stocks. Additionally, under the conditions of this experiment, the majority of the N supplied to the soil was rapidly incorporated into the most stable fraction of SOM, and this might can reduced the efficiency of the green manuring.

Structure and composition of rhodoliths from the Amazon River mouth, Brazil

Rhodolith beds are one of the main habitats of the Brazilian Equatorial Margin continental shelf due to their wide extent and provision of ecosystem services. Northern, Central and Southern zones of the Amazon River mouth were sampled between water-depths of 23 and 120 m, covering a continental shelf area of 9500 km2, to characterize the structure and composition of rhodoliths along depth gradients and related river plume influence. The deepest rhodoliths consist of a thin algal/bryozoan/encrusting foraminifer cover around relatively large nuclei that determine the nodule size and shape. At 120-m depth in the Northern zone the nuclei are made of fragments of invertebrate boundstone or oolite rudstone, whereas at 100-m depth in the Central zone the nuclei consist of sandstone clasts. In both cases, the nuclei are fragments of sedimentary rocks that accumulated on the outer shelf during significantly lower sea level. Low-light levels prevent substantial growth of the algal cover around the nuclei. Reduced illumination an d high nutrient levels led to the composition of rhodoliths at 95-m depth in the Northern zone, predominantly built by bryozoans with subordinate coralline algae around small bioclastic nuclei. In the Central zone at 50–55 m depths, coralline algae are the main components of mostly sub-spheroidal rhodoliths. They have relatively recent ages of hundreds of years or show two phases of growth with the older phase beginning 1300 years ago and then being interrupted from about 1000 years BP to 600 years BP. All this suggests relatively high burial rates due to sediment flux, changing in time to favor exhumation after burial in some instances. The rhodoliths from 23 m in the Southern zone are growing under a low influence of the river plume and have the highest diversity of coralline algae and other builders. The rhodolith structure in the different sampling zones and depths reflects plume influence on light penetration, nutrient and organic matter levels, and sedimentation on the shelf, determining residence times of rhodoliths on the seafloor before burial.

Assessment of Soil Aggradation through Soil Aggregation and Particulate Organic Matter by Riparian Switchgrass Buffers

The restoration of riparian zones has been an important issue in many regions for the recovery of ecosystem functions. The objective of this study was to assess soil aggradation in a 7-year established riparian switchgrass buffer (SGB) and in a non-buffered riparian zone with an annual row crop (ARC). We measured the aggregate size distribution and stability of macroaggregates, aggregate-associated soil organic carbon, soil organic matter fractions and the chemical composition of light particulate organic matter to monitor soil aggregation in a riparian soil following the conversion of agricultural row crops to switchgrass filters. Aggregate size fractions were separated by wet sieving using the aggregate size-stability protocol. The proportion of soil and total organic C was quantified for each aggregate size class. Soil organic matter fractions were isolated by size and density into light particulate organic matter and heavy particulate organic matter and mineral fraction organic matter. The categorization of aggregates by size and water stability (slaking resistance) showed a significantly larger (p < 0.001) proportion of water-unstable large macroaggregates (>2000 µm) under SGB (34%) compared to that under ARC (29%), while the proportion of water-unstable small macroaggregates (250–2000 µm) was significantly higher under ARC (14%) than under SGB (10%). Our results showed that the amounts of light and heavy particulate organic matter did not change in the short-term (7 years) after SGB establishment. It appears that the lower soil stabilization and soil organic C storage under SGB is related to (i) the large number of coarse roots; (ii) lower inputs of light and heavy particulate organic matter; (iii) no changes in the alkyl-C/O-alkyl-C ratio over time; and (iv) light particulate organic matter with a high C/N ratio.