Silt Size Fractions Research Articles

The silicon isotopic composition of fine-grained river sediments and its relation to climate and lithology

The δ30Si stable isotopic composition of silicon in soils and fine-grained sediments can provide insights into weathering processes on continents, with important implications on the Si budget of modern and past oceans. To further constrain the factors controlling the distribution of Si isotopes in sediments, we have analysed a large number (n = 50) of separate size-fractions of sediments and suspended particulate materials collected near the mouth of rivers worldwide. This includes some of the world’s largest rivers (e.g. Amazon, Congo, Mackenzie, Mississippi, Murray-Darling, Nile, Yangtze) and rivers from the case study areas of the Congo River Basin and Northern Ireland. Silt-size fractions exhibit a mean Si isotopic composition (δ30Si = −0.21 ± 0.19‰; 2 s.d.) similar to that previously inferred for the upper continental crust. In contrast, clay-size fractions display a much larger range of δ30Si values from −0.11‰ to −2.16‰, which yield a global δ30Siclay of −0.57 ± 0.60‰ (2 s.d.) representative of the mean composition of the average weathered continental crust. Overall, these new data show that the Si isotopic signature transported by river clays is controlled by the degree of chemical weathering, as inferred from strong relationships with Al/Si ratios. At a global scale, the clay-bound Si isotopic composition of the world’s largest river systems demonstrates a link with climate, defining a general correlation with mean annual temperature (MAT) in corresponding drainage basins. While the distribution of Si isotopes in river sediments also appears to be influenced by the tectonic setting, lithological effects and sediment recycling from former sedimentary cycles, our results pave the way for their use as paleo-weathering and paleo-climate proxies in the sedimentary record.

Remediation of heavy hydrocarbon impacted soil using biopolymer and polystyrene foam beads

A green chemistry solution is presented for the remediation of heavy hydrocarbon impacted soils. The two-phase recovery system relies on a plant-based biopolymer, which releases hydrocarbons from soil, and polystyrene foam beads, which recover them from solids and water. The efficiency of the process was demonstrated by comparisons with control experiments, where water, biopolymer, or beads alone yielded total petroleum hydrocarbon (TPH) reductions of 25%, 52%, and 58%, respectively, compared to 94% when 1.25 mL of 1% biopolymer and 15 mg beads per gram of soil were agitated for 30 min. Reductions in TPH content were substantial regardless of soil fraction, with removals of 97%, 91%, and 75% from sand, silt, and clay size fractions, respectively. Additionally, treatment efficiency was independent of carbon number, C13 to C43, as demonstrated by reductions in both diesel fuel (C13–C28) and residual-range organics (C25–C43) of ∼90%. Compared to other published polymer- and surfactant-based treatment methods, this system requires less mobilizing agent, sorbent, and mixing time. The remediation process is both efficient and sustainable because the biopolymer is re-useable and sourced from renewable crops and polystyrene beads are obtained from recycled materials.

Functional soil organic matter fractions in response to long-term fertilization in upland and paddy systems in South China

Soil organic matter (SOM) and its fractions play key roles in optimizing crop yield and improving soil quality. However, how functional SOM fractions responded to long-term fertilization and their relative importance for C sequestration were less addressed. In this study, we determined the effects of long-term fertilization on six functional SOM fractions (unprotected, physically protected, physico-biochemically protected, physico-chemically protected, chemically protected, and biochemically protected) based on two long-term fertilization experiments carried out in South China. The unprotected coarse particulate organic matter (cPOM), the biochemically and chemically protected silt-sized fractions (NH-dSilt and H-dSilt) were the primary C storage fractions under long-term fertilization, accounting for 23.6–46.2%, 15.7–19.4%, and 14.4–17.4% of the total soil organic carbon (SOC) content in upland soil and 19.5–29.3%, 9.9–15.5%, and 14.2–17.2% of the total SOC content in paddy soil, respectively. Compared with the control treatment (CK) in upland soil, the application of manure combined with mineral NPK (NPKM) resulted in an increase in the SOC content in the cPOM, pure physically protected fraction (iPOM), the physico-chemically protected (H-μSilt), and the chemically protected (H-dSilt) fraction by 233%, 166%, 124%, and 58%, respectively. Besides, the SOC increase in upland soil expressed as SOC content per unit of total SOC for iPOM, H-μSilt, cPOM and H-dSilt were the highest and as large as 283%, 248%, 194%, and 105% respectively. In paddy soil, the highest increase per unit of total SOC was H-dSilt (190%), followed by H-dClay (156%) and H-μSilt (155%). These results suggested that the upland soil could stabilize more C through the pure physical, whereas the chemical protection mechanism played a more important role in paddy soil. Chemical protection mechanism within the microaggregates played important roles in sequestrating C in both upland and paddy soils. Overall, the different responses of functional SOM fractions to long-term fertilization indicate different mechanisms for SOM cycling in terms of C sequestration under upland and paddy systems.

Are fixed grain size ratios useful proxies for loess sedimentation dynamics? Experiences from Remizovka, Kazakhstan

Loess-paleosol sequences (LPS) are sensitive terrestrial archives of past aeolian dynamics and paleoclimatic changes within the Quaternary. Grain size (GS) analysis is commonly used to interpret aeolian dynamics and climate influences on LPS, based on granulometric parameters such as specific GS classes, ratios of GS classes and statistical manipulation of GS data. However, the GS distribution of a loess sample is not solely a function of aeolian dynamics; rather complex polygenetic depositional and post-depositional processes must be taken into account. This study assesses the reliability of fixed GS ratios as proxies for past sedimentation dynamics using the case study of Remizovka in southeast Kazakhstan. Continuous sampling of the upper 8 m of the profile, which shows extremely weak pedogenic alteration and is therefore dominated by primary aeolian activity, indicates that fixed GS ratios do not adequately serve as proxies for loess sedimentation dynamics. We find through the calculation of single value parameters, that “true” variations within sensitive GS classes are masked by relative changes of the more frequent classes. Heatmap signatures provide the visualization of GS variability within LPS without significant data loss within the measured classes of a sample, or across all measured samples. We also examine the effect of two different commonly used laser diffraction devices on GS ratio calculation by duplicate measurements, the Beckman Coulter (LS13320) and a Malvern Mastersizer Hydro (MM2000), as well as the applicability and significance of the so-called “twin peak ratio” previously developed on samples from the same section. The LS13320 provides higher resolution results than the MM2000, nevertheless the GS ratios related to variations in the silt-sized fraction were comparable. However, we could not detect a twin peak within the coarse silt as detected in the original study using the same device. Our GS measurements differ from previous works at Remizovka in several instances, calling into question the interpretation of paleoclimatic implications using GS data alone.

Grain size dependent magnetic discrimination of Iceland and South Greenland terrestrial sediments in the northern North Atlantic sediment record

We use isothermal and temperature dependent in-field and magnetic remanence methods together with electron microscopy to characterize different sieved size fractions from terrestrial sediments collected in Iceland and southern Greenland. The magnetic fraction of Greenland silts (3–63 μm) and sands (>63 μm) is primarily composed of near-stoichiometric magnetite that may be oxidized in the finer clay (<3 μm) fractions. In contrast, all Icelandic fractions dominantly contain titanomagnetite of a range of compositions. Ferrimagnetic minerals preferentially reside in the silt-size fraction and exist as fine single-domain (SD) and pseudo-single-domain (PSD) size inclusions in Iceland samples, in contrast to coarser PSD and multi-domain (MD) discrete magnetites from southern Greenland. We demonstrate the potential of using magnetic properties of the silt fraction for source unmixing by creating known endmember mixtures and by using naturally mixed marine sediments from the Eirik Ridge south of Greenland. We develop a novel approach to ferrimagnetic source unmixing by using low temperature magnetic susceptibility curves that are sensitive to the different crystallinity and cation substitution characteristics of the different source regions. Covariation of these properties with hysteresis parameters suggests sediment source changes have driven the magnetic mineral variations observed in Eirik Ridge sediments since the last glacial maximum. These observations assist the development of a routine method and interpretative framework to quantitatively determine provenance in a geologically realistic and meaningful way and assess how different processes combine to drive magnetic variation in the North Atlantic sediment record.

Geochemical and mineralogical characterization of tailings of the Dexing copper mine, Jiangxi Province, China

The Dexing copper mine is the largest open pit copper mines in Asia, with mining and beneficiation history stretching back more than half a century; consequently it has large amounts of ore tailings. The mineralogy, chemical composition and distribution of elements in the impounded tailings are of great significance to the future utilization and reclamation of the tailings ponds. In total, 1400 tailing samples from 35 drill cores were collected from the 1 tailings pond at the Dexing copper mine. All samples were analyzed to determine their chemical composition. The particle size, XRD, pH and sequential extraction fractions of selected samples were determined. The silt-size fraction dominates the grain-size distribution. Quartz and sericite are the most abundant gangue minerals in the tailings, with medians of 54.3 and 23.7%, respectively. 3D modeling of the tailings pond suggests that the distribution of particle size, minerals and elements is mainly controlled by the gravitational separation during tailings discharge. Silica, Cu, Mo and Ti are enriched in the dam area of the tailings pond, whereas Al 2 O 3 and K 2 O are enriched in the impoundment area. The potential Cu, Ti and sericite reserves in the tailings pond were estimated at 38 149 tons, 142 175 tons and 8.15 million tons, respectively. The tailings are not significantly oxidized and so their environmental risk is low under the present circumstances. Their weak alkalinity and presence of carbonate minerals provide the tailings buffering capacity to weak acids. Sequential extraction data suggest that the mobility of elements in the tailings pond is low; however, about 6040 tons of Cu, 428 tons of Zn, 252 tons of Mo, 145 tons of As and 66 tons of Pb, may be released if the physicochemical conditions change and the tailings become acidic.

Early- to mid-Holocene paleohydrology in northeast Mediterranean: The detrital record of Aliakmon River in Loudias Lake, Greece

One of the prominent features of northeast Mediterranean (NEM) Holocene climate are recurrent phases of cold and aridity; their impacts on the hydrological cycle remain at large unknown, as few existing paleohydrological records are either restricted to lake-level fluctuations or focus near the ‘8.2 kyr BP’ event. Here, we present the detrital record of Aliakmon River in Lake Loudias between 9500 and 3000 cal. BP. Magnetic susceptibility (MS) exhibits high correlation with mean grain size ( r = 0.7) of silt-sized fractions and is used as a proxy of the distal clastic input of Aliakmon River, whereas organic matter (OM), carbonate content (CaCO3), water content (WC), and clay concentrations decipher sedimentological and biological processes in Lake Loudias. Periods of high hydrological activity were interrupted by short intervals of low river discharge at c. 9400, 8600, 8200, 7500, 7000, 6200, 5300, and 4500 cal. BP and during a multi-century event centered at 3500 cal. BP, in agreement with marine and terrestrial paleoclimatic reconstructions from NEM. With exception of the wet period between c. 8.6 and 7.9 cal. BP, periods of increased hydrological activity are synchronous to contraction of Pinus forests and increased sea surface temperatures and silt transport in the Aegean Sea. The long-term (~580 years) variability of MS is in-phase with southeast Europe pollen-inferred annual temperature variations and with North Atlantic Ice Rafted Debris (IRD) events.

Response of soil organic matter fractions and composition of microbial community to long-term organic and mineral fertilization

The effects of organic and mineral fertilization on four soil organic matter (SOM) fractions (non-protected, physically protected, chemically protected, and biochemically protected) and microbial community composition were investigated by sampling soil of a 35-year-long fertilization experiment. The SOM fractions were investigated by combined physical and chemical approaches, while microbial community composition was determined by phospholipid fatty acid analysis (PLFA). Organic C (SOC) was primarily distributed within the microaggregate-protected particulate organic matter (iPOM) and the hydrolysable and non-hydrolysable silt-sized (H-Silt, NH-Silt) fractions, which accounted for 11.6–16.9, 23.4–28.9, and 25.4–30.6% of the total SOC content, respectively. The contributions of these “slow” fractions (iPOM, H-Silt, NH-Silt) to the increased SOC were 178–293, 118–209, and 85–109% higher after long-term sole manure or manure in combination with inorganic N fertilization compared with unfertilized soil (control). The combination of manure and mineral fertilizers increased the coarse and fine non-protected C (cPOM and fPOM) contents much more (34.1–60.7%) than did manure alone. PLFAs, bacteria, G (+) bacteria, and actinomycete abundances were the highest in soil with manure, followed by soil treated with manure combined with mineral N. The addition of inorganic and organic fertilization both altered the microbial community composition compared with the control. All SOM fractions contributed to 81.1% of the variance of the PLFAs-related microbial community composition by direct and indirect effects. The change in coarse unprotected particulate organic matter (cPOM) was the major factor affecting soil microbial community composition (p < 0.001). Our study indicates that physical, chemical, and biochemical protection mechanisms are important in maintaining high SOC level after the addition of manure. A close linkage between soil microbial community composition and cPOM suggests that C availability is an important factor for influencing microbial composition after long-term inorganic and organic fertilization.

Evaluation of the particle sizes of four clay minerals

The particle size distributions (PSD) of four clay minerals from the US Clay Minerals Society, kaolinite, illite, Ca2+-montmorillonite, and Na+-montmorillonite, were analyzed using different dispersion techniques to evaluate their PSD variability and intrinsic particle sizes. Both dry dispersion in pressurized air and wet dispersion in water and ethyl alcohol with and without an interlayer expanding agent, glycerol, were employed, along with mechanical ultrasound disaggregation and chemical dispersion. Results show that all four clay minerals exhibit multimodal PSD consisting of superimposed subordinate lognormal distributions from submicron and 1–2μm primary particles, 10–20μm flocculi (and trace impurities). Microflocs of 50–500μm occur only in the dry dispersion mode. Owing to the presence of relatively strong flocculi that are not prone to breakdown to smaller primary particles, the intrinsic PSD of these clay minerals cannot be readily obtained by the adopted dispersion methods. The two swelling clay minerals, Na+-montmorillonite and Ca2+-montmorillonite, are more sensitive than the non-swelling ones, kaolinite and illite, to different dispersion solvents. The variability of these clay minerals' PSD is further discussed in terms of the complex interactions among clay mineral particles, polar or less polar solvent, and dispersant, such as swelling, cation exchange, exfoliation, and electrical double layer repulsion. A significant practical implication is that most existing dispersion methods for PSD analysis tend to overestimate the silt-sized fraction but underestimate the clay-sized fraction, which may yield misleading classification for clay mineral-rich soils. For expansive clay minerals, appropriate dispersants should be selected to avoid cation exchange between the sample and dispersants, which can change their intrinsic PSD.

Characterization of Clay‐ and Silt‐Sized Fractions and Corresponding Humic Acids Along a Terra Rossa Soil Profile

This study focuses on the relationship between soil mineralogy and soil organic matter stabilization along a Terra Rossa soil profile in Southern Italy. This soil profile is characterized by three horizons: Namely Ap, 2AB, and 2Bt, where the clay, silt, and sand size fractions were isolated and their mineralogical composition, and the different forms of iron, silicon, and aluminum were determined. Humic acids (HAs) were isolated from clay‐size (C‐HA) and silt‐size (S‐HA) fractions, and characterized by chemical and physico‐chemical techniques. The clay fraction had the largest amount of amorphous and crystalline oxides, kaolinite, and chlorite. In all fractions, the 2AB horizon differed from the other two horizons showing a very high content of iron and aluminum bound to organic matter (Fep and Alp). Chemical and spectroscopic analyses of humic acids indicated the presence of macromolecules with larger size and polycondensation degree in S‐HAs, apparently less susceptible to degradation than simpler hydrophilic compounds occurring in the clay‐size HAs. A good correlation was found between Fep and Alp contents and HA organic carbon. These properties are expected to slow down organic matter dynamics in Terra Rossa Mediterranean soils even in the presence of a fast turnover of aggregates.

Type and quantity of organic amendments determine the amount of carbon stabilized in particle-size fractions of a semiarid degraded soil

ABSTRACTA 9-month lab experiment was carried out with three different amendments (vine pruning wastes, PW; composted vine pruning wastes, cPW; and sewage sludge, SS) added at three different rates (90, 180, and 240 t ha−1, dry weight) in order to test whether the type or the quantity of the amendments applied to a semiarid, degraded soil determined the Corg accumulation in its particle-size fractions (coarse sand, 200–2,000 µm; fine sand, 63–200 µm; silt, 2–63 µm; and clay, 0.1–2 µm). All amendments, independently of their C/N ratios, resulted in similar Corg content and accumulation in coarse sand and silt-sized fractions after 9 months. In the clay-sized fraction, enrichment in Corg produced the incorporation of particles from this particle-size fraction into the silt-sized fraction. Likewise, increasing the application rates of the amendments led to larger Corg contents into the particle-size fractions of all amended soils except for the clay-sized fraction. The application of SS resulted in lower basal respiration-to-Corg ratios in the clay-sized fraction than the application of PW and cPW, suggesting a higher protection of the Corg in the SS treatment. These results indicate that organic amendments from woody plants with C/N ratios higher than 30, such as PW, favor Corg accumulation in the fine sand-sized fractions. Furthermore, our findings suggest that the application rate of such amendments, rather than the C/N ratios and amendment origin (from sludge or woody plants), is the key factor for promoting Corg accumulation in the silt-sized fractions of semiarid degraded soils.

How do changes in bulk soil organic carbon content affect carbon concentrations in individual soil particle fractions?

We test the common assumption that organic carbon (OC) storage occurs on sand-sized soil particles only after the OC storage capacity on silt- and clay-sized particles is saturated. Soil samples from a Brookston clay loam in Southwestern Ontario were analysed for the OC concentrations in bulk soil, and on the clay (<2 μm), silt (2–53 μm) and sand (53–2000 μm) particle size fractions. The OC concentrations in bulk soil ranged from 4.7 to 70.8 g C kg−1 soil. The OC concentrations on all three particle size fractions were significantly related to the OC concentration of bulk soil. However, OC concentration increased slowly toward an apparent maximum on silt and clay, but this maximum was far greater than the maximum predicted by established C sequestration models. In addition, significant increases in OC associated with sand occurred when the bulk soil OC concentration exceeded 30 g C kg−1, but this increase occurred when the OC concentration on silt + clay was still far below the predicted storage capacity for silt and clay fractions. Since the OC concentrations in all fractions of Brookston clay loam soil continued to increase with increasing C (bulk soil OC content) input, we concluded that the concept of OC storage capacity requires further investigation.

Assessment of heavy metal enrichment in the offshore fine-grained sediments of the Caspian Sea.

Sampling of the offshore seabed sediments of southwestern part of the Caspian Sea was carried out by gravity corer in order to study heavy metal concentration and the physicochemical factors controlling their distribution in the fine-grained fraction. The grain size distribution, amount, and type of clay minerals, total organic carbon (TOC) content, and Eh-pH of the sediments were determined. The average concentrations of the heavy metals in ppm are Mn (563), Cu (207.5), Sr (187), Zn (94), Pb (26.3), Ni (14.5), Co (11.5), Cd (2.56), and Ag (1.04) in their order of abundances. Co and Zn mostly indicate increase in silt-size fraction of the sediments suggesting their probable detrital provenance but the Mn, Ni, Cu, Sr, Pb, Cd, and Ag concentrations show a similar trend to distribution of the clay-size fraction. The concentrations of Mn, Co, and Cd increase with increase in the TOC content but the Cu, Pb, Ni, Ag, and Sr concentrations decrease with increase of the TOC content. The amounts of Zn, Cu, Sr, Pb, Cd, and Ag increase with increase in the CaCO3 content. The calculated enrichment factor indicates that the sediments are very strong to extremely enriched in Ag, significantly enriched in Cu and Cd, and depleted to mineral for Pb, Sr, Co, Ni, and Zn. Variations of the Cu, Sr, Cd, Ag, and Pb concentrations are similar to the clay and CaCO3 distributions.

Can mima-like mounds be Vertisol relics (Far North Region of Cameroon, Chad Basin)?

Non-anthropogenic earth mounds, defined as mima-like mounds in this study, have recently been observed in non-carbonate watersheds along the Sudano-Sahelian belt in the Chad Basin. In the Diamare piedmont (northern Cameroon) they are particularly well developed within stream networks. In less eroded areas, they occur as whaleback, flattened morphologies, or even as buried features. All these shapes are composed of clay-rich sediment associated with high proportions of secondary carbonate nodules and FeMn micro-nodules. Their soil structure is prismatic to massive and vertical cracks are observed locally. Grain-size distributions emphasize the clay-rich nature of the sediment, with average clay contents of 32%±12.8% (n=186), which is significantly higher than the clay content in the adjacent sediments in the landscape (mean=10%±4%, n=21). Moreover, high proportions of smectite characterize the soil, with average contents of 34±7% (n=25). At the micro-scale, the groundmass has a cross-striated b-fabric, with embedded smooth subangular quartz and feldspar grains of the silt-size fraction. All the characteristics point to altered vertic properties in the clay-rich sediment composing the mima-like mounds. Mima-like mounds are thus interpreted as degraded Vertisols. Compared to present-day Vertisols occurring in the piedmont, mima-like mounds are located upstream. It is thus proposed that the Vertisol areas were more extensive during a former and wetter period than the present-day. Subsequent changing climatic conditions increased erosion, revealing the gilgai micro-relief by preferential erosion in micro-lows rather than in micro-highs. Mima-like mounds of the Chad Basin might thus result from pedogenesis combined with later erosion. These local processes can be inherited from regional climatic variations during the Late Pleistocene-Holocene and likely be related to the African Humid Period.

Collapse Behaviour of Compacted Coal Ashes

Coal ash is a by-product produced from the thermal power plants. It is characterized with low unit weight, high shear strength and low compressibility and finds a major application as an alternate material in the geotechnical engineering applications. However, some coal ash fills are susceptible to wetting-induced collapse due to the loss of capillary suction which stabilizes the inter-granular bonds. The present study examines the influence of placement conditions, vertical stress and pore fluid concentration on the collapse behaviour of compacted fly ash specimens. The experimental results showed that the maximum collapse potential for the coal ash specimens compacted to relative compaction of 80 % and water content of 15 % was in the range of 8.6–13 % at vertical stress of 100 kPa, which indicates that the apparent preconsolidation stress for the coal ash specimens is equal to 100 kPa. Among the coal ashes, the compacted fly ash specimens are more susceptible to wetting-induced collapse in comparison to bottom ash and pond ash specimens which is attributed to the higher silt size fraction in the fly ash. This study also presents the collapse behaviour of lime stabilized compacted coal ash.

Environmental Hf–Nd isotopic decoupling in World river clays

The hafnium and neodymium radiogenic isotope systems behave differently during Earth surface processes, causing a wide dispersion of Hf and Nd isotopic compositions in sediments and other sedimentary rocks. The decoupling between Hf and Nd isotopes in sediments is generally attributed to a combination of preferential sorting of zircon during sediment transport and incongruent weathering processes on continents. In this study, we analysed size-fractions of sediment samples collected near the mouth of 53 rivers worldwide to better understand the factors controlling the distribution of Hf and Nd isotopes in sediments. Our results for rivers draining old cratonic areas and volcanic provinces demonstrate that both granite and basalt weathering can lead to significant grain-size dependent Hf isotopic variability. While silt-size fractions mainly plot along the Terrestrial Array, World river clays are systematically shifted towards more radiogenic Hf isotopic compositions, defining together with published data a new Clay Array (εHf=0.78×εNd+5.23). The Hf–Nd isotope decoupling observed in volcanogenic sediments is best explained by selective alteration of Lu-rich mineral phases (e.g. olivine) and preferential enrichment of resistant unradiogenic minerals, such as spinel and ilmenite, in silt fractions. We also show that the extent to which World river clays deviate from the Clay Array (ΔεHf clay) is not linked to the presence of zircons. Instead, it correlates positively with weathering indices and climatic parameters (temperature, rainfall) of the corresponding drainage basins. Overall, these findings demonstrate that the distribution of Hf–Nd isotopes in clay-size sediments is related to a large extent to weathering conditions on continents, although the precise mechanisms controlling this relationship remain unclear. We finally propose that the Hf–Nd isotope pair proxy could be used in palaeoenvironmental studies to provide semi-quantitative information on past climates.

Carbon storage in soil size-density fractions after 20 years of compost fertilization

Fractionation by particle size provides a rough differentiation between young active, and older intermediate and passive soil organic matter. Soil samples from three treatments of a 20 years` fertilization experiment, C2 which had been fertilized with 10 t ha -1 (wet wt.) compost per year on average, N2 with mineral N fertilizer at 32 kg N ha -1 year -1 , and the unfertilized control (O) were subjected to particle size fractionation and to density fractionation. After low-energy sonication the samples were separated into the size fractions coarse sand (200-200 µm), fine sand (200-63 µm) silt (63-2 µm) and clay (2-0,1 µm). Density fractionation using Na-polytungstate with 1.8 g cm -3 density was applied to separate particulate organic matter (POM) from the sand-sized fraction. Compost fertilization resulted in an increase in C org in all size and density fractions. In total, the C org content was 10 % higher with compost fertilization than in the unfertilized control. Approximately 40 % of the additional soil carbon was located in the POM, 56 % in the silt-sized fraction and 3 % in the clay-sized fraction. With mineral N fertilization the sum of C org contents of all fractions was about the same as without fertilization, with an increase of POM-C org and a decrease of C org in the silt and clay-sized fraction. Keywords: fractionation, particulate organic matter, POM, soil organic matter

Levels and sources of potassium, calcium, sulfur, iron and manganese in major paddy soils of the Philippines

Nutrient levels in rice areas can be translated to the soils’ capacity to supply the essential elements for rice, while information about nutrient sources can be used to formulate management options to areas deficient or toxic in nutrients. This study was then conducted to assess the potassium (K), calcium (Ca), sulfur (S), iron (Fe) and manganese (Mn) levels in the Philippines’ major rice areas. The study also determined the contributions of soil properties, land uses, irrigation water, and farm practices to the nutrient levels. Strategic collection of soil and plant samples, laboratory analyses of samples, and farmer interviews were done. Potassium concentrations of rice plants in La Paz (Tarlac) and Sta. Rosa City (Laguna) exceeded the toxic concentration of 3%. These K concentrations can be due to the increase of the nutrient’s availability owing to the neutral soil pH levels in the two sites. The highest total Ca levels were found in the Polangui (Albay), La Paz, and Villasis (Pangasinan) soils. These Ca levels can be ascribed to the occurrence of Ca in sand and silt-sized soil fractions. Total Fe and Mn concentrations were very high in the Sta. Cruz (Zambales) soil due to the input of mine wastes. The San Leonardo (Nueva Ecija) soil’s high total Fe concentration is probably due to the occurrence of Fe in clay-sized soil fractions. Iron and Mn levels of rice in most Central Luzon sites exceeded the toxic concentrations of 1000 mg kg-1 for Fe and 300 mg kg-1 for Mn. These concentrations can be due to the high total soil Fe and Mn levels, and their increased plant uptake due to periodic soil submergence and increased soil acidity from continuous cropping. The study implies that K, Ca, Fe and Mn are enriched in rice areas due to soil properties and farm practices. Keywords—potassium, calcium, sulfur, iron, manganese, paddy soils

Clay mineralogy of the ocean sediments from the Wilkes Land margin, east Antarctica: implications on the paleoclimate, provenance and sediment dispersal pattern

Core U1359 collected from the continental rise off Wilkes Land, east Antarctica, is analyzed for the clay mineralogy and carbon content. The temporal variation of the clay mineralogical data shows a dominance of illite with chlorite, smectite and kaolinite in decreasing concentration. Clay mineral illite is negatively correlated with smectite which shows enrichment during 6.2–6.8, 5.5–5.8, 4.5 and 2.5 Ma. The mineralogical analyses on the silt size fraction (2–53 μm) of some selected samples were also carried out. The combined result of both the size fractions shows the presence of chlorite and illite in both size fractions, smectite and kaolinite only in clay size fraction (<2 μm) and similarity in the crystallinity and chemistry of illite in both fractions. Similar nature of illite in both fractions suggests negligible role of sorting probably due to the deposition from the waxing ice sheet. During times of ice growth, nearby cratonic east Antarctica shield provided biotite-rich sediments to the depositional site. On the other hand, the presence of smectite, only in the clay size fraction, suggests the effective role of sorting probably due to the deposition from distal source in ice retreat condition. During times of ice retreat, smectite-rich sediment derived from Ross Orogen is transported to the core site through surface or bottom water currents. Poor crystallinity of illite due to degradation further corroborates the ice retreat condition. The ice sheet proximal sediments of U1359 show that in the eastern part of Wilkes Land, the ‘warming’ was initiated during late Miocene.

Size distribution studies of 137Cs in river water in the Abukuma Riverine system following the Fukushima Dai-ichi Nuclear Power Plant accident

The occurrence of 137Cs in size fractionated samples in river water from the Abukuma River system, (the Kuchibuto and Abukuma Rivers, five sampling events for three sites) was studied from June 2011 – approximately some three months after the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident until December 2012. The total concentration of 137Cs (mBq/L) in river water was generally high at the upper stream site in the Yamakiya District within the evacuation/off-limits zone. The 137Cs concentration was about 1Bq/L for the first sampling campaign (June 2011) at all sites, but then decreased substantially to about one-tenth of that by the time of a second sampling campaign (November or December 2011). The 137Cs in the <0.45μm fraction was present exclusively as a dissolved species rather than as a species adsorbed on suspended solids or complexed with organic materials. The contribution of the dissolved fraction ranged from 1.2 to 48.9% (averaged 20%) of the total concentration of 137Cs throughout the observation period. The maximum contribution of 137Cs was found in the silt size fraction (3–63μm), which can be explained by the relatively large Kd values and the suspended solids (SS) concentration of this size fraction. Although the concentration (Bq/g) of 137Cs ineach size fraction did not show any significant trends and/or variations for any of the sampling campaign, Kd values for each site increased with time. Furthermore, it was found that the Kd values decreased with distance from the headstream in the off-limits zone. Thus, the data acquired in this study give an overview of the radiological situation for Fukushima including temporal and spatial variation of radiocaesium in a natural riverine system, within a few years after the accident.