Showing papers on "Silt published in 1995"
TL;DR: In this paper, the authors measured the size distribution of the removed component by repeated size measurement with intermediate steps of removal of components by dissolution, allowing inference of the size distributions of removed component as well as the residue.
Abstract: Fine sediment size (< 63 Ixm) is best measured by a sedimentation technique which records the whole size distribution. Repeated size measurement with intermediate steps of removal of components by dissolution, allows inference of the size distribution of the removed component as well as the residue. In this way, the size of the biogenic and lithogenic (noncarbonate) fractions can be determined. Observations of many size distributions suggest a minimum in grain size frequency curves at 8 to 10 Ixm. The dynamics of sediment erosion, deposition, and aggregate breakup suggest that fine sediment behavior is dominantly cohesive below 10-1xm grain size, .and noncohesive above that size. Thus silt coarser than 10 Ixm displays size sorting in response to hydrodynamlc processes and its properties may be used to infer current speed. Silt that is f'mer than 10 Ixm behaves in the same way as clay (< 2 !xm). Useful parameters of the distribution are the 10-63 Ixm mean size and the percentage 10-63 Ixm in the fine fraction. We cannot use size distributions to distinguish the nature of the currents. Therefore, to infer water mass advection speeds (i.e., the mean kinetic energy of the flow, Ku), regions of high eddy kinetic energy (KE) must be avoided. At the present, such abyssal regions lie under the high surface K E of major current systems: Gulf Stream, Kuroshio, Agulhas, Antarctic Circmpolar Current, and Brazil/Falldand currents in the Argenthe Basin. This is probably a satisfactory guide for the Pleistocene. With regard to the carbonate subfraction of the size spectrum, size modes due to both cocco!iths and foramlnlferal fragments can be recognized and analyzed, with the boundary between them again at about 10 lm. The flux of less than 10 lm carbonate, at pelagic sites above the lysocline, is another candidate for a productivity indicator.
593 citations
TL;DR: The average silt and clay flux (rate of deposition) in southern Nevada and southeastern California ranges from 4.3 to 15.7 g/m2/yr as discussed by the authors.
Abstract: Dust samples collected annually for 5 years from 55 sites in southern Nevada and California provide the first regional source of information on modern rates of dust deposition, grain size, and mineralogical and chemical composition relative to climate and to type and lithology of dust source. The average silt and clay flux (rate of deposition) in southern Nevada and southeastern California ranges from 4.3 to 15.7 g/m2/yr, but in southwestern California the average silt and clay flux is as high as 30 g/m2/yr. The climatic factors that affect dust flux interact with each other and with the factors of source type (playas versus alluvium), source lithology, geographic area, and human disturbance. Average dust flux increases with mean annual temperature but is not correlated to decreases in mean annual precipitation because the regional winds bring dust to relatively wet areas. In contrast, annual dust flux mostly reflects changes in annual precipitation (relative drought) rather than temperature. Although playa and alluvial sources produce about the same amount of dust per unit area, the total volume of dust from the more extensive alluvial sources is much larger. In addition, playa and alluvial sources respond differently to annual changes in precipitation. Most playas produce dust that is richer in soluble salts and carbonate than that from alluvial sources (except carbonate-rich alluvium). Gypsum dust may be produced by the interaction of carbonate dust and anthropogenic or marine sulfates. The dust flux in an arid urbanizing area may be as much as twice that before disturbance but decreases when construction stops. The mineralogic and major-oxide composition of the dust samples indicates that sand and some silt is locally derived and deposited, whereas clay and some silt from different sources can be far-traveled. Dust deposited in the Transverse Ranges of California by the Santa Ana winds appears to be mainly derived from sources to the north and east.
310 citations
TL;DR: In this article, the physicochemical properties of the cryptogamic crust of sand dunes in the Negev Desert were studied. And the authors presented quantitative measurements of the physical properties of this crust which are important to the water regime in desert dunal areas, including granulometry, porosity and water retention capacity.
233 citations
TL;DR: In this article, NMR spectroscopy was used to compare SOM composition across size separates and between land-use regimes and showed that the intensity of signals assigned to carbohydrates and lignin (phenolic and methoxyl C) declined with decreasing particle size.
Abstract: Soils from A horizons of Eutrochrepts under spruce forest (Sf), mixed deciduous forest (Df), permanent grassland (Gp), and arable rotation (Ar) were fractionated into clay- (< 2 μm), silt (2-20 μm) and sand- (20-2000 μm) sized separates. 13 C NMR spectroscopy was used to compare SOM composition across size separates and between land-use regimes. CPMAS 13 C NMR spectroscopy showed that the intensity of signals assigned to carbohydrates (representing most O-alkyl C) and lignin (phenolic and methoxyl C) declined with decreasing particle size. Concurrently, alkyl C and C-substitution of aromatic C increased in the order sand, silt, clay. The amount of alkyl C correlated well with microbial resynthesis of carbohydrates. Solution 13 C NMR spectra suggested that humic acids (HA) extracted from the size separates were richer in carboxyl C and aromatic C than the bulk size separates. Also HA reflected increasing percentage of alkyl C with decreasing particle size. O-alkyl C were lower in silt HA than in clay HA whereas aromatic C tended to peak in silt HA. These results suggested that sand-sized separates were enriched in plant residues (primary resources) whereas clay-sized separates were dominated by products of microbial resynresis (secondary resources). Silt was rich in selectively preserved and microbially transformed primary resources. 13 3C NMR spectroscopy showed only small differences in SOM composition between land-use regimes, except that silt and silt HA from Ar were richer in aromatic C than rose from the other plots. But enrichment factors (E = content in fraction/content in whole soil) revealed differences in the distribution of C species across the size separates. Relatively high E aromatic (0.9) and E O-alkyl (1.0) for sand from Gp indicated high amounts of plant residues, probably due to intense rhizodeposition and to occlusion of plant debris within aggregates. Low E aromatic (O.3) and E O-alkyl (0.3) for sand from Ar suggested depletion of primary resources, which could be attributed to disintegration of soil aggregates upon cultivation. A pronounced enrichment of alkyl C in Ar claysized separates (E alkyl = 3.1) suggested large amounts of microbial carbon. Microbial products attached to clay surfaces by a variety of physico-chemical bondings appeared more stable against mineralization induced by cultivation than plant residues sequestered in aggregates
200 citations
TL;DR: In this article, it was shown that there is a belt of soil D3 which could include considerable loess deposits; it stretches from the Matmata ‘loess’ in Tunisia, across northern Libya to the western part of the Egyptian coastal region.
158 citations
TL;DR: In this paper, the authors examined the effects of the conversion of tropical forest to pasture on soil organic matter origin and quality along a chronosequence of sites, including a primary forest and six pastures.
Abstract: We examined the effects of the conversion of tropical forest to pasture on soil organic matter (SOM) origin and quality along a chronosequence of sites, including a primary forest and six pastures. Bulk soil samples received a physical size-fractionation treatment to assess the contribution of each compartment to total SOM pool. Besides a general increase in total C and N stocks along the chronosequence, we observed a reduction of the relative contribution of the coarser fractions to total soil C content, and an increased concentration in the finer fractions. The origin of the C in each size fraction was established from measurements of13C abundance. After 80 years about 93% of the C in the least humified fraction of the top 10 cm of soil was of pasture origin, while in the most humified it was 82%. Chemical analyses indicated that the fine silt and coarse clay fractions contained the most refractory carbon.
149 citations
TL;DR: Five layers of sediment taken from research ponds are proposed to be referred to as F (flocculent layer), S (stirred or mixed sediment), M (mature, bulk, un-mixed sediment), T (transitional layer), and P ( original, undisturbed pond bottom) horizons, respectively, to delineate horizons in pond soil profiles.
Abstract: Soil cores were taken from each of three, 2-, 23-, and 52-yr-old research ponds (650–1,010 m2 area) at Auburn, Alabama. Many physical and chemical variables changed in intensity with increasing depth in cores. Compared to original compacted pond soil, sediment contained more moisture; had lower bulk density (<1.4 g/cm3); possessed higher percentages of silt and clay; had greater porosity, specific surface area, and cation exchange capacity; and contained greater concentrations of organic matter and nutrients. Sediment organic matter was highly decomposed as evidenced by low proportions (5–15%) of carbon and nitrogen associated with the light fraction (soil retained on a 53-μm sieve). Sediment depth at 100-cm water depth increased with pond age (11.7 cm, 28.3 cm, and 48.3 cm in 2-, 23-, and 52-yr-old ponds, respectively), but sediment composition did not change greatly over time. Successive layers in cores were as follows: 1) water near the soil-water interface with a high concentration of solids; 2) high moisture content sediment with dry bulk density <0.3 g/cm3; 3) lower moisture content sediment with bulk density between 0.3 and 0.5–0.7 g/cm3; 4) rapid transition of bulk density from 0.5–0.7 g/cm3 to 1.4 g/cm3; 5) original compacted soil with bulk density of 1.4–1.7 g/cm3. We propose that these five layers be referred to as F (flocculent layer), S (stirred or mixed sediment), M (mature, bulk, un-mixed sediment), T (transitional layer), and P (original, undisturbed pond bottom) horizons, respectively. Superficial, oxidized sediment is termed an So horizon, and the reduced part of the S horizon is termed an Sr horizon. The upper part of the T horizon is an MT horizon when it is similar to the M horizon, or a FT horizon when it resembles the P horizon. A system for delineating horizons in pond soil profiles will be valuable in future attempts to classify pond soils.
125 citations
TL;DR: A series of soil column studies were conducted to evaluate the effects of high rates of fly ash on soil hydraulic properties and elemental leaching of trace metals and boron as mentioned in this paper. But this work focused on coal fly ash, which has the potential to permanently change soil texture and increase moisture holding capacity.
Abstract: A major limitation to crop yields in the Atlantic Coastal Plain is drought stress caused by the low moisture-holding capacities of the coarse-textured soils common to the area. Because coal fly ash is comprised primarily of silt and clay-sized particles, it has the potential, if applied at high enough rates, to permanently change soil texture and increase moisture holding capacity. A series of soil column studies were conducted to evaluate the effects of high rates of fly ash on soil hydraulic properties and elemental leaching of trace metals and boron. Fly ash from two Delaware power plants (EM=Edgemoor and IR=Indian River) was incorporated in a Hammonton loamy sand (fine-loamy, siliceous, mesic, Typic Hapludults) at six rates (0, 5, 10, 20, 30, and 40%, by weight). The effect of fly ash on soil moisture holding capacity, hydraulic conductivity, and wetting front velocity was determined. Leachates from columns amended with 30% fly ash were analyzed for B, Cd, Ni, Pb, Cu, and Zn. Soil moisture holding capacity was increased from 12% in the soil alone to 25% in the soil amended with 30% fly ash. Boron and soluble salts leached rapidly from ash amended soils while only trace quantities of Cd, Ni, Pb, Cu, and Zn were detected in column leachates.
105 citations
TL;DR: In this article, the influence of acid sulfate soils on stream water geochemistry was studied in thirteen catchment basins in western Finland, and the median concentrations of several elements, including Al, Co, Li, Mn and Ni, are much higher than those in headwater streams of Finland and in Fennoscandian rivers.
103 citations
TL;DR: In this article, sediment cores from underconsolidated mudflats 300 km downdrift of the Amazon river mouth record an ephemeral surface layer of fine-grained sediment up to 1.5 m thick.
101 citations
Journal Article•
TL;DR: The Fly River sediment is mostly fine silt with a mean particle size of 8 µm; the clay fraction makes up less than 20% of the suspended sediment by volume.
Abstract: The suspended sediment of the Fly River is mostly fine silt with a mean particle size of 8 µm; the clay fraction makes up less than 20% of the suspended sediment by volume. On reaching brackish water in the estuary, the sediment flocculates. The flocs are small (typical mean size of 30 µm) and are a mixture of fine silt and clay particles, with silt particles dominating. Because of the dominance of silt particles incorporated in the flocs, the flocs are structurally weak and are destroyed by tidal turbulence at spring tides. The clay particles are selectively trapped in the turbidity maximum zone of the estuary.
TL;DR: In this paper, it was shown that polysaccharide gels gradually fill additional 1-3 µm wide pores within the portions of the silt/clay matrix.
Abstract: Samples taken from the two textural phases of the surface soil of an irrigated natrixeralf and its clay subsoil were dried at wilting point and in air. Water retention increased linearly with C content, with values extrapolated to zero C content proportional to clay content. Emerson et al. (1994) (Aust. J. Soil Res., 32, 939-51) had already shown that water held by the surface samples at 10 kPa suction increased approximately linearly with C content, independently of clay content. Similar linear relations were deduced for other soils using values of field capacity and wilting point reported in the literature. A constant amount of water is considered to be held by portions of the silt/clay matrix. As the C content of the soil is increased, polysaccharide gels gradually fill additional 1-3 µm wide pores within the portions. It was calculated that, after a long period in grass, gel present increases available water on a weight basis, by 34% and 125% in loamy sand and sandy clay A horizons respectively. Where farmyard manure (FYM) was incorporated, gel only formed from the added C. Nevertheless the large increase in field capacity of a sandy loam produced by rotavation was temporarily preserved by prior addition of FYM. It is suggested that the gel here was mainly on microbial filaments.
TL;DR: In this article, residual shear strength, density, and penetration resistance of very loose, water-deposited silty sands and sandy silts capable of liquefying and developing large s...
Abstract: Laboratory and field evidence on residual shear strength, density, and penetration resistance of very loose, water-deposited silty sands and sandy silts capable of liquefying and developing large s...
TL;DR: In this article, the authors reported that the observed signals come from the more labile pools of soil organic matter (SOM), on the presumption that these pools are less closely associated with soil minerals and iron oxides and are likely to be less protected from microbial or enzymic decomposition.
Abstract: Summary
l3C–nuclear magnetic resonance (NMR) spectra taken using magic–angle spinning (MAS), cross polarization (CP) and with total suppression of side bands (TOSS) are reported for soils from two long–term field experiments. One set of soils was from the Broadbalk Experiment at Rothamsted, UK (monoculture of winter wheat since 1843) and the other was from the Lermarken site of the Askov Long–Term Experiment on Animal Manure and Mineral Fertilizers (arable rotation since 1894). At both sites soil samples were taken from three fertilizer treatments: nil, inorganic fertilizers, animal manure. Spectra were obtained from whole soil samples and from the size fractions clay (<2 μrn), silt (2–20 μm) and, in some cases, sand (20–2000 μm).
Comparison of the total strengths of the 13C–NMR signal for each size separate in relation to its total organic C content shows that clay, particularly, contains large percentages of C not detected by NMR because of the large magnetic susceptibilities of the soil minerals. It is proposed that the observed signals come from the more labile pools of soil organic matter (SOM), on the presumption that these pools are less closely associated with soil minerals and iron oxides and are likely to be less protected from microbial or enzymic decomposition.
For both Rothamsted and Askov, functional groups in the 45–110 ppm region (N– and O–alkyls) dominate in the spectra for whole soils, with aromatics (110–160 ppm) and alkyls (0–45 ppm) signals being the next prominent. In the Askov whole soil samples 13C–NMR revealed no differences between nil, inorganic fertilizer and animal manure treatments but in the Rothamsted whole soil there were some small differences.
Clay and silt fractions from Askov contain more alkyls and less aromatics than those from Rothamsted. For both sites clay in enriched in alkyls and depleted in aromatics relative to silt. Clay from Askov, but not Rothamsted, contains more N–alkyls (45–65 ppm) and less acetals (90–110 ppm) than silt. O–alkyls (65–90 ppm) account for more than 20% of the total signal in clay and silt from both sites. Fertilization regimes have not significantly affected the chemical composition of SOM associated with clay– and silt–sized fractions in the soils at either site. We conclude that the chemical composition of SOM is determined primarily by the interaction between the organisms responsible for decomposition and the mineral soil matrix rather than the nature of substrate input.
TL;DR: In this paper, the effect of fine content on the pore pressure generation in sand was investigated using laboratory cyclic triaxial tests with a cyclic shear strain range of 0·015-1·5%.
07 May 1995
TL;DR: The nature of a substantial part of the soil microbiota, including soil microorganisms such as bacteria, fungi and protozoans, is essentially unknown due to their unculturability.
Abstract: Soil represents a highly heterogeneous environment consisting of solid, liquid and gaseous phases. The dominating soil solid phase is composed of inorganic (sand, silt and clay) and organic (humic matter) materials, which are to varying degrees complexed with one another. The soil biota, including soil microorganisms such as bacteria, fungi and protozoans, are known to inhabit different sites in the soil pore matrix. Organisms associate in particular with soil solids, e.g. clay/organic matter complexes, in soil pores conducive to their survival. Although a wealth of information is available about many microorganisms isolated from soil by culturing techniques, the nature of a substantial part of the soil microbiota is essentially unknown due to their unculturability.
TL;DR: In this paper, an approach identical to the one utilized in particle size analysis with an estimation of the recoveries from aliquots ("aliquot" method) of the 0-2 and 0-20 μm fractions and no entire isolation of clay and silt was proposed.
Abstract: Particle size fractionation is becoming commonly used for studying soil organic matter (OM). However, isolation of clay and silt represents a long and thus tedious step in the fractionation procedure. We propose an approach identical to the one utilized in particle size analysis with an estimation of the recoveries from aliquots ("aliquot”; method) of the 0–2 and 0–20 μm fractions and no entire isolation ("decanting”; method) of clay and silt. In comparison with the “decanting”; method, the fraction and carbon (C) recoveries obtained by the “aliquot”; method were satisfactory, but those of nitrogen (N) being hardly interpretable because of an insufficient accuracy of the determination method. The recommended method saves time and laboratory space and could be used as a routine particle size fractionation of soil OM. Finally, this paper lists various methodological aspects of considerable significance but rarely reported in published studies.
TL;DR: Results suggest that solid-phase sediment bioassays using bioluminescence bacteria may be useful for testing the toxicities of single contaminants in formulated artificial sediments of known particle-size composition, and for repeated samples collected from the same site.
Abstract: Clean and spiked sediment formulations of various silt:sand and clay:sand ratios were tested for toxicity using a bioassay that utilizes bioluminescent bacteria. Measured toxicities of clean and copper sulfate-spiked sediments were negatively but nonlinearly related with percent silt and percent clay, but no significant relationship existed between measured toxicity and sediment composition for methyl parathion-spiked formulations. Results suggest that solid-phase sediment bioassays using bioluminescence bacteria may be useful for testing the toxicities of single contaminants in formulated artificial sediments of known particle-size composition, and for repeated samples collected from the same site. However, extreme caution must be taken when testing sediments of varying composition or which may be differentially contaminated or contain a suite of contaminants.
TL;DR: In this article, the authors used core samples and hydrographic data from 50° to 60°N and 15° to 25°W in the Northeast Atlantic Ocean to study changes in current activity from the last glacial to present and established a new method to distinguish between the effects of changing bottom current speed and varying size input by drawing upon sediment flux data and detailed grain size analysis.
Abstract: Core samples and hydrographic data from 50° to 60°N and 15° to 25°W in the Northeast Atlantic Ocean are used to study changes in current activity from the last glacial to present. We establish a new method to distinguish between the effects of changing bottom current speed and varying size input by drawing upon sediment flux data and detailed grain size analysis. Changes in current speed are recorded by the mean size of the sortable (coarse) noncarbonate silt component, which increases with current vigor by winnowing away of fines. Our method involves the definition of an ideal sortable silt “input function”, recorded at a site accumulating unmodified pelagic flux only. The ideal profile is then compared with records from other sites to determine the history of current speed at a range of water depths. The upper surface of Southern Source Water (SSW) probably shoaled during the glacial, as indicated by the covariation of sortable silt records from sites presently covered by SSW and Lower North Atlantic Deep Water (LNADW). The data suggest that production of LNADW was suppressed during the glacial, increased following the last glacial maximum, and declined at the start of Termination 1A. A second pulse of production occurred immediately before the Younger Dryas event. Intermediate waters were generally faster-flowing during the glacial and may have expanded their depth domain, such that a single glacial intermediate water mass covered depths from 1100 to more than 2000 m.
TL;DR: In this paper, changes in tensile strength with clay type, clay particle size, and amounts of spontaneously and mechanically dispersible clays were assessed for dry, remoulded samples of eight Australian Vertisols and Alfisols varying in clay mineralogy.
TL;DR: In this paper, the authors use sediment deposition on the sea floor, on lake bottoms, as well as on land as accumulations of windblown silt (loess) and as ancient soils (paleosols) formed in the loess to record past changes in climate.
Abstract: Sediments deposited on the sea floor, on lake bottoms, as well as on land as accumulations of windblown silt (loess) and as ancient soils (paleosols) formed in the loess possess many different properties that record past changes in climate. Geologically recoverable information on paleoclimate includes changes in global temperature as it may affect global ice volume and thus temperature of sea water, net precipitation, storm intensity (wind speed) and frequency, as well as wind direction. Such information further contributes to interpretations about changes in oceanic and atmospheric circulation patterns. As such, the understanding of past climatic changes can provide baselines of natural climatic fluctuations as related to those that may be induced or influenced by human activities.
01 Jan 1995
TL;DR: In this article, the authors presented general conclusions derived from a two dimensional unsaturated flow analysis coupled with a slope stability evaluation using limit equilibrium analysis, where the change in strength is taken into account by means of a linear increment of apparent cohesion with suction.
Abstract: The paper presents general conclusions derived from a two dimensional unsaturated flow analysis coupled with a slope stability evaluation using limit equilibrium analysis. The change in strength is taken into account by means of a linear increment of apparent cohesion with suction. The evolution of safety factor in a typical clay, silt and silty-sand slope is obtained for various rainfall histories. A sensitivity analysis has been carried out in order to obtain the influence of rain duration and intensity, shape of the water retention relationship and water permeability. Finally the method developed for slope stability analysis in partially saturated soils is applied to study a natural, non homogeneous slope located in Ancona (Italy). (A) For the covering abstract see IRRD 881647.
TL;DR: In this article, the authors measured the rates of N mineralization in 27 forest soils encompassing a wide range of forest types and management treatments in south-east Australia and found that only 0.1% of the total N present at 0-30 cm in depth was mineralized during the incubation, and both the amount and the percentage of total N mineralized decreased with increasing soil depth.
Abstract: Rates of N mineralization were measured in 27 forest soils encompassing a wide range of forest types and management treatments in south-east Australia. Undisturbed soil columns were incubated at 20°C for 68 days at near field-capacity water content, and N mineralization was measured in 5-cm depth increments to 30 cm. The soils represented three primary profile forms: gradational, uniform and duplex. They were sampled beneath mature native Eucalyptus sp. forest and from plantations of Pinus radiata of varying age (<1 to 37 years). Several sites had been fertilized, irrigated, or intercropped with lupins. The soils ranged greatly in total soil N concentrations, C:N ratios, total P, and sand, silt, and clay contents. Net N mineralization for individual soil profiles (0–30 cm depth) varied from 2.0 to 66.6 kg ha-1 over 68 days, with soils from individual depths mineralizing from <0 (immobilization) to 19.3 kg ha-1 per 5 cm soil depth. Only 0.1–3.1% of the total N present at 0–30 cm in depth was mineralized during the incubation, and both the amount and the percentage of total N mineralized decreased with increasing soil depth. N fertilization, addition of slash residues, or intercropping with lupins in the years prior to sampling increased N mineralization. Several years of irrigation of a sandy soil reduced levels of total N and C, and lowered rates of N mineralization. Considuring all soil depths, the simple linear correlations between soil parameters (C, N, P, C:N, C:P, N:P, coarse sand, fine sand, silt, clay) and N mineralization rates were generally low (r<0.53), but these improved for total N (r=0.82) and organic C (r=0.79) when the soils were grouped into primary profile forms. Prediction of field N-mineralization rates was complicated by the poor correlations between soil properties and N mineralization, and temporal changes in the pools of labile organic-N substrates in the field.
TL;DR: In this article, the authors tested the hypothesis that earthworms stimulate the formation of the sandy surface soils by producing clay-rich worm casts that are susceptible to erosion, in an undisturbed forested watershed in southwestern Ivory Coast.
TL;DR: In this paper, the results of the equilibrium tensile strength and the mellowing ratio of the compacted soils in relation to the properties of the clay fractions were measured before and after a number of wetting and drying cycles, wet at either fast or slow rates.
01 Jan 1995
TL;DR: In this article, aeolian silt accumulation making up the Loess Plateau of North China reaches more than 250m in thickness in the Lanzhou region and there is a clear gradient in collapsibility from the dry north-west to the moist south-east of the Plateau.
Abstract: The aeolian silt accumulation making up the Loess Plateau of North China reaches more than 250m in thickness in the Lanzhou region. Regional studies have shown that there is a clear gradient in collapsibility from the dry north-west to the moist south-east of the Plateau. On the western margins, collapsibility is significantly greater in the young (Malan) loess: as the surface drape, it is also very vulnerable to human disturbance. High collapsibility is a factor in the extensive pipe-and-sinkhole morphology known as ‘loess karst’. Population pressure has led to abuse by mechanical disruption of thick loess. Also, unwise extension of irrigation waters enhances the natural effect of severe summer rainstorms, resulting in subsidence and landslides.
TL;DR: In this paper, the results of a simulation study designed to examine abrasion and size reduction of quartz grains under "grinding" conditions analogous to those experienced in a subglacial environment were presented.
TL;DR: In this paper, a transect of Pinery Provincial Park in southwestern Ontario has been studied using pedogenic properties to evaluate the rates and pathways of soil genesis in the late Holocene dune chronosequence.
Abstract: Soils on a late Holocene dune chronosequence were studied along Lake Huron at Pinery Provincial Park, in southwestern Ontario. Progressive exposure of new materials, associated with declining lake levels, has allowed the development of soils in a sequential manner from the shoreline (approximately time zero) to about 2.3 km inland. Six soil pits were excavated and sampled in narrow depth increments along a transect ranging in estimated age from 100 to 4700 yr B.P. Chronofunctions were formulated based on pedogenic properties in order to evaluate the rates and pathways of soil genesis in southern Ontario. The soils graded from an Orthic Regosol near the shore to an Eluviated Dystric Brunisol to 2.3 km inland. The increasing thickness of the solum and darker chroma in the B horizons were the most obvious morphological indications of a progression in soil weathering. Linear chronofunctions of increasing total silt and clay contents with soil age suggest that physical breakdown of sand particles to silt and c...
TL;DR: In low-food situations, if mussels are pumping large volumes of water, contaminant uptake rates could be enhanced, whereas abundant food would result in lower pumping rates and lower uptake rates.
Abstract: The effect of exposure to different concentrations of food and suspended silt on filtration, respiration and condition were studied in the freshwater mussel Hyridella menziesi. Using a milk solids-based food and kaolin to simulate silt, mussels were maintained at different combinations of food and silt concentrations for 3 weeks. Between treatments mean filtration rates ranged from 0.97–1.66 l g−1 h−1, and respiration from 0.50–1.35 mg O2 g−1 h−1. Silt (non-volatile suspended solids up to 35 mg l−1) failed to have a significant effect on filtration rate or condition, but with increasing food levels (volatile suspended solids up to 35 mg l−1) filtration rate was reduced, and condition was reduced at the lowest food concentration (<5 mg l−1). Respiration showed a food × silt interaction between treatment blocks. When food was low respiration increased with increasing silt concentrations, and when silt was low (<5 mg l−1) respiration increased with increasing food concentrations. The observed effects of food and silt on filtration, respiration and condition are discussed in terms of their potential for affecting contaminant bioaccumulation. In low-food situations (i.e., <5 mg l−1), if mussels are pumping large volumes of water, contaminant uptake rates could be enhanced, whereas abundant food would result in lower pumping rates and lower uptake rates. Changes in metabolism with food concentration have implications for contaminant elimination, and changes in biochemical composition associated with changing condition could affect the tissue distribution and retention of contaminants.
TL;DR: In this article, the physical and chemical properties of the two common termite mounds in southeastern Nigeria, Macrotermes (MM) and Cubitermes (CM) mounds, were compared and their relationships with the surrounding top and subsoils investigated.
Abstract: Some physical and chemical properties of the two common termite mounds in southeastern Nigeria, Macrotermes (MM) and Cubitermes (CM) mounds, were compared and their relationships with the surrounding top and subsoils investigated. Percentage sand, silt, pH, calcium, magnesium, potassium, sodium, iron, and organic carbon were higher and clay and penetrometer resistance lower in the CM than the MM. Sand, silt, organic carbon, and calcium decreased and clay increased from the forest to the derived savanna in the CM, but no clear trend was shown with the other properties in both the CM and the MM. Most of the nutrients were higher in the CM than in the adjacent top or subsoil but the reverse was the case with the MM. More nutrients are associated with the inorganic fractions of the soil than with the organic carbon in the mounds and the soils surrounding them. The Ca:Mg ratio in the mounds and the top and subsoils adjacent to them was low for most crops but the K:Mg ratio was mostly adequate. Because of these differences in properties and sizes of the mounds, different management strategies are recommended for them and the soils around them.