Sediment Grain Size Distribution Research Articles

Particulate matter spatial–temporal distribution and associated surface sediment properties: Thermaikos Gulf and Sporades Basin, NW Aegean Sea

Particulate matter (PM) distribution was studied in the NW Aegean Sea (Eastern Mediterranean) over a series of four seasons. PM concentrations in the surface and bottom nepheloid layers exhibit persistent maxima close to the river mouths; the rivers are identified as the major sources of PM. In general, higher particulate matter concentration (PMC) values appear in the shelf of the Thermaikos Gulf, whereas the deep Sporades Basin represents the area of lowest PM concentration. PMC during winter is much higher than in summer. This strong seasonal feature is attributed to the variation of the fresh-water supply, which is maximised during winter and spring, and almost negligible during the dry seasons. PM is mainly transported southwards and preferentially along the western coastline of the study area, due to a well-defined and dominant cyclonic circulation. Lateral transport of the PM prevails, whereas vertical particle transport is relatively limited. BNL formation is mainly attributed to sediment resuspension forced by the near-bottom currents. Surface sediment grain-size distribution is characterised by the presence of relict sands in the central and eastern shelf, while fine-grained muddy sediments cover the western shelf and the Sporades Basin. Relict sands were deposited during the Holocene sea-level rise. The general water mass circulation and the distance from the PM sources seem to favour PM deposition close to the river mouths and along the western coastline, while PM hardly reaches the eastern part of the area. As a result, relict sands remain uncovered or partly mixed with modern fine sediments. The shelf traps most of the PM, while some portion escapes to the deep Basin, probably from the western side of the continental slope.

Carbonate Grain-Size Distribution in Hemipelagic Sediments from a Laser Particle Sizer

Laser grain-sizer instruments provide the opportunity to study the grain size distribution of sediments across a wide size range in a short time. Automatic measurements can therefore be made, on a routine basis, for a great number of samples. Oceanic studies have proved the utility of these methods in characterizing both climatic changes and changes in sediment provenances. In addition, carbonate content is estimated either directly by CaCO 3 measurement, by visual observations, or by proxies such as sediment color reflectance. Nevertheless, the grain size distribution of the carbonate fraction is still a matter of speculation, and only optical observations can distinguish the nature of each carbonate fraction. Here we present the improvements on a method to study rapidly, with a high resolution, the grain size distribution of the carbonate fraction by use of a laser grain-sizer. We describe the basic methodology and apply it to an example from the Pleistocene of the Northern Atlantic Ocean.

Sediment and rock strength controls on river incision into bedrock

Recent theoretical investigations suggest that the rate of river incision into bedrock depends nonlinearly on sediment supply, challenging the common assumption that incision rate is simply proportional to stream power. Our measurements from laboratory abrasion mills support the hypothesis that sediment promotes erosion at low supply rates by providing tools for abrasion, but inhibits erosion at high supply rates by burying underlying bedrock beneath transient deposits. Maximum erosion rates occur at a critical level of coarse-grained sediment supply where the bedrock is only partially exposed. Fine-grained sediments provide poor abrasive tools for lowering bedrock river beds because they tend to travel in suspension. Experiments also reveal that rock resistance to fluvial erosion scales with the square of rock tensile strength. Our results suggest that spatial and temporal variations in the extent of bedrock exposure provide incising rivers with a previously unrecognized degree of freedom in adjusting to changes in rock uplift rate and climate. Furthermore, we conclude that the grain size distribution of sediment supplied by hillslopes to the channel network is a fundamental control on bedrock channel gradients and topographic relief.

Carbonate Grain-Size Distribution in Hemipelagic Sediments from a Laser Particle Sizer: RESEARCH METHODS PAPERS

ABSTRACT Laser grain-sizer instruments provide the opportunity to study the grain size distribution of sediments across a wide size range in a short time. Automatic measurements can therefore be made, on a routine basis, for a great number of samples. Oceanic studies have proved the utility of these methods in characterizing both climatic changes and changes in sediment provenances. In addition, carbonate content is estimated either directly by CaCO3 measurement, by visual observations, or by proxies such as sediment color reflectance. Nevertheless, the grain size distribution of the carbonate fraction is still a matter of speculation, and only optical observations can distinguish the nature of each carbonate fraction. Here we present the improvements on a method to study rapidly, with a high resolution, the grain size distribution of the carbonate fraction by use of a laser grain-sizer. We describe the basic methodology and apply it to an example from the Pleistocene of the Northern Atlantic Ocean.

Annual Production of Burrowing Mayfly Nymphs ( Hexagenia spp.) in U.S. Waters of Lake St. Clair

Burrowing mayfly nymphs ( Hexagenia spp.) were sampled monthly, September through October 1995 and April through August 1996, with a standard Ponar grab (538 cm 2 jaw opening) at 16 stations in U.S. waters of Lake St. Clair. Annual production (production, P) was 0 to 477 mg dry weight/m 2 at three stations where pollution and sediment grain-size distribution limited the population, and was 738 to 5,255 mg dry weight/m 2 at the other 13 stations. The highest production value measured for Hexagenia in Lake St. Clair was about three times higher than the highest value reported for other areas in the northern United States and Canada (39° to 53° North latitude). The production-mean annual biomass (biomass, B) ratio (P/B) for Hexagenia in Lake St. Clair in 1995–96 was described by the straight line P = 2.4 B (R 2 = 0.94). Adding published P/B data for other North American populations changed the relation only slightly to P = 2.5B (R 2 = 0.96). A P/B ratio of 2.5 is consistent with the expected value for an aquatic insect with a 2-year life cycle and overlapping cohorts, and these data suggest this relation has general applicability for estimating production of Hexagenia in the northern United States and Canada. Size-class and seasonal partitioning of Hexagenia biomass and production were evident in the data. Both biomass and production were highest among nymphs 16.0 mm and larger, and biomass was highest in October and again in June, immediately before the annual emergence of subimagos. The large size of the mature nymphs and the concentration of biomass and production among the larger nymphs in the population is consistent with their importance in the diets of many fishes in the northern United States and Canada.

Basal-crevasse-fill origin of laminated debris bands at Matanuska Glacier, Alaska, U.S.A.

AbstractThe numerous debris bands in the terminus region of Matanuska Glacier, Alaska, U.S.A., were formed by injection of turbid meltwaters into basal crevasses. The debris bands are millimeter(s)-thick layers of silt-rich ice cross-cutting older, debris-poor englacial ice. The sediment grain-size distribution of the debris bands closely resembles the suspended load of basal waters, and of basal and proglacial ice grown from basal waters, but does not resemble supraglacial debris, till or the bedload of subglacial streams. Most debris bands contain anthropogenic tritium (3H) in concentrations similar to those of basal meltwater and ice formed from that meltwater, but cross-cut englacial ice lacking tritium. Stable-isotopic ratios (δ18O and δD) of debris-band ice are consistent with freezing from basal waters, but are distinct from those in englacial ice. Ice petrofabric data along one debris band lack evidence of active shearing. High basal water pressures and locally extensional ice flow associated with overdeepened subglacial basins favor basal crevasse formation.

Correlation of side-scan backscatter intensity with grain-size distribution of shelf sediments, New Jersey margin

The dependence of acoustic backscatter variations on sediment grain-size distribution is examined using a combined analysis of 95 kHz side-scan data and approx. 300 grab samples from the New Jersey margin. We show that, under well-controlled circumstances, an unprecedented degree of correlation can be obtained between backscatter intensity and mean grain size. However, backscatter is disproportionately affected by larger grain sizes. Addition of just a few extra weight percentage of the larger grain sizes (>4 mm), which in our study is typically represented by more abundant shell hash among the older sediments at greater water depths, can completely degrade this correlation.

Flow and Sediment Transport on a Tidal Salt Marsh Surface

The physical processes that control mineral sediment deposition on a mesotidal salt marsh surface on the Atlantic Coast of Virginia were characterized through a series of measurements of sediment concentration, flow velocity, turbulence, water surface elevation, marsh topography and particle size distributions of sediment deposited on the marsh surface. The comprehensive nature of the data set allowed assessment of the temporal and spatial variability in marsh surface deposition, the variability in depositional processes among tides of different amplitudes, as well as the specific processes that control deposition on this tidal marsh. Through three different types of measurements, it was found that sediment deposition occurred on the marsh surface during rising tides at tidal elevations ranging from those barely flooding the creek bank to high spring tides, and that sediment was not remobilized by tidal flows after initial deposition. Sediment deposition occurred on this marsh surface largely because fine sediment in suspension formed flocs. Analysis of inorganic grain size distributions of sediment deposited within 8m of the tidal creek indicated that 70–80% of this sediment was deposited in a flocculated form. The rest (particles larger than 20μm) were deposited as individual particles. In the marsh interior, 25m from the tidal creek, single grain settling predominated. Reduction of turbulence levels within the vegetation canopy on the marsh also promoted particle settling. The processes controlling sediment deposition did not vary among tides. However, suspended sediment concentrations near the creek bank increased with increasing tidal amplitude, consequently promoting higher rates of deposition on higher tides.

Characteristics of inhabitable environment of fiddler crabs (Genus Uca) in the Shikoku area

Fiddler crabs, Uca arcuata and Uca lactea lactea, are both listed as very rare species in the Red Data Book published by the Environmental Agency of Japan. We have been studying the influence of physical conditions, such as sediment properties and tidal flow, on the active individual densities of fiddler crabs, in particular, inhabiting the Sumiyoshi tidal flat in the mouth of Yoshino River. Furthermore, we carried out similar field observations of the habitat distribution of Genus Uca in the Shikoku area. In this paper, the influence of grain size distribution of tidal flat sediment and weather factors, such as precipitation, on the number of active individuals were examined by the neural network analysis method.

Evaluation of the simple settling theory for predicting sediment deposition by overland flow

Experiments were conducted in the laboratory to evaluate the influence of sediment concentration, sediment grain-size distribution, bed slope and flow discharge on sediment deposition rates and patterns associated with a reduction in bed slope. The experimental data clearly indicate that sediment deposition by overland flow is a very selective process: fine particles remain almost entirely in suspension and coarse particles are deposited quickly. Analysis of the data shows that up to a critical unit discharge a simple settling equation without a transport term, assuming continuous mixing of the sediment and water, gives a good prediction of the overall sediment delivery ratio and the grain-size distribution of the deposited and the exported sediment. However, there are some discrepancies for the clay, the coarse silt and the sand fractions. The assumption of continuous mixing is tested by investigating the sedimentation patterns of very narrow size classes. The observed decrease of sediment concentration versus distance from the inflow point for these individual sediment size classes closely agrees with the prediction assuming continuous mixing. When the critical unit discharge is exceeded, hydraulic properties of the overland flow do influence the sediment delivery outcomes. At discharges exceeding the threshold value the simple settling theory underpredicts the sediment delivery ratio. In these hydraulic conditions, a transport term needs to be incorporated into the simple settling theory. It is shown that the transport capacity and the re-entrainment model yield similar expressions for the description of sediment transport by overland flow over an area of net deposition. The experimental data indicate that the re-entrainment of previously deposited sediment is non-selective. Copyright © 1999 John Wiley & Sons, Ltd.

Sediment Grain Size Effect on Benthic Microalgal Biomass in Shallow Aquatic Ecosystems

Benthic microalgal biomass is an important fraction of the primary producer community in shallow water ecosystems, and the factors controlling benthic microalgal biomass are complex. One possible controlling factor is sediment grain-size distribution. Benthic microalgal biomass was sampled in sediments collected from two sets of North Carolina estuaries Massachusetts and Cape Cod bays, and Manukau Harbour in New Zealand. Comparisons of benthic microalgal biomass and sediment grain-size distributions in these coastal and estuarine ecosystems frequently showed a negative relationship between the proportion of fine-grained sediments and benthic microalgal biomass measured as chlorophylla. The highest sedimentary chlorophylla levels generally occurred in sediments with lower percentages of fine particles (diameter <125 mm). A negative relationship between the proportion of fine sediments and benthic microalgal biomass suggests anthropogenic loadings of fine sediment may reduce the biological productivity of shallow-water ecosystems.

Seasonal Variation of Suspended Particulate Matter in Two-layered İzmit Bay, Turkey

The spatial and temporal distribution of suspended particulate matter (SPM) concentration in İzmit Bay (Sea of Marmara) were studied in order to examine the prevailing transport mechanisms under varying seasonal hydrographical conditions. The prevailing current system of the Bay occurs in two opposite directions and changes seasonally, flowing into the Bay as a lower layer and flowing out to the Sea of Marmara as an upper layer in autumn and winter. SPM concentrations and distribution pattern of both upper and lower water layers display variations throughout the year, reflecting a seasonal cycle and variability of the circulation and stratification of two water layers seems to control the vertical and spatial distribution of SPM in İzmit Bay. The SPM concentration of the lower layer is higher than that of the upper layer with an increase in intensity of the pycnocline in summer. Homogeneous vertical distribution of SPM during February and March is supported by the weak stratification of the two layers. SPM transportation from İzmit Bay to the open sea occurs in winter, whereas it is carried to interior of the Bay from central to eastern basins in summer. Both the grain size distribution of the bottom sediments and the temporal-spatial variation of SPM content of the water column indicate that the transportation and depositional conditions are different in the three basins. Predominantly fine-grained-sized bottom sediments are deposited in the central and eastern basins due to the reduced current velocities in the lower layer. The western basin is subjected to deposition of sediments with various size, from both the central basin and the Sea of Marmara.

Characterisation of river bed and suspended sediments in the Rio Madeira drainage basin (Bolivian Amazonia)

The grain size distribution of river bed sediments in the Rio Madeira drainage basin shows rapid deposition of the coarser material (>10 mm) as the river flows out of the Andean range to enter the Amazon plain (Llanos). In the Andes, the suspended sediment grain size varies between 0.02 and 0.10 mm in diameter, while in the Llanos the suspended load is dominated by fine silts, between 7 and 13 μm in diameter. In the Llanos, neither the bed sediment nor the suspended sediment varied along a 800 km reach.

Temporal and spatial variability of the sediment grain-size distribution on the Eel shelf: the flood layer of 1995

Sediment grain-size characteristics observed on the Eel shelf have been analyzed using a wet-sieving technique that minimizes breakage of aggregates. At several sites on the 70-m isobath north of the river, where a 1995 flood layer attained a maximum thickness of about 9 cm, replicate box cores were collected on seven cruises during February 1995 to January 1997. These samples provide a unique opportunity to follow the evolution of a flood layer over a two-year period as it was modified and gradually buried. One month after the flood, a layer of tan-colored, high-porosity sediment with up to 96% of its particles in the size range of 0–20 μm had accumulated on the central part of the shelf, 7–30 km north of the river and principally between the 50-m and 90-m isobaths. Substantial coarsening of this layer occurred between February 1995 and May 1995, particularly along the southern and the landward edge of the deposit in water depths of <70 m. The early stage of coarsening was probably caused by physical reworking of the surface 0.5-cm of the deposit and by addition of new sediment from shallower regions of the shelf. Temporal changes in inventories of several grain-size fractions show that physical processes continued to add coarse sediment to the flood layer after May 1995, but the large increases in thickness of the surface mixed layer could only be attributed to bioturbation by a recovering, or seasonally fluctuating, benthic community. The 1995 flood layer has evolved from exhibiting limited variability and normal grading (i.e., upward fining) to a layer that (1) shows significant spatial variability on scales from centimeters to 10's of meters, (2) is substantially coarser owing to additions of sediment from the inner shelf, (3) is inversely graded (i.e., coarsens upward), and (4) is intensely bioturbated to depths of 4–5 cm.

Normalization of Sedimentary Lipid Biomarker Concentrations to Total Organic Carbon in Principal Component Analysis

The objective of this study is to demonstrate the importance of normalizing lipid biomarker concentrations in sediment to total organic carbon (TOC) for principal component analysis (PCA) by using n-alkanols and aliphatic hydrocarbons in marine sediments collected from the East China Sea shelf off northern Taiwan. In performing PCA, logarithmically transformed data and z-score function transformed data along with the raw data were compared with TOC normalized data. Results show that the positions of n-alkanol variables in the loading plot using TOC normalized data are in good agreement with the organic geochemical knowledge in terms of sources. For aliphatic hydrocarbons, the positions of samples in the score plot using TOC normalized data are different from those using the raw data and z-score function transformed data. It is suggested that normalization of lipid biomarker concentrations with TOC be taken into consideration in performing PCA when the grain size distributions of sediments in a study area vary in a wide range.

Sampling Heterogeneous Deposits in Gravel-Bed Streams

The methodology of combining subsamples into a single “composite” sample representative of an entire river reach is examined. Current methods of characterizing the overall grain-size distribution of a river reach are inadequate because they either require enormous amounts of material to be collected, are inherently biased, or fail to describe the local variations occurring within the sampled region. These problems can be overcome by employing the grid-by-number sampling technique. Criteria for obtaining an unbiased grid composite sample as well as its overall accuracy are provided. It is proposed that local variations in a river reach's grain-size distribution can be located by comparing the arithmetic means of adjacent subsamples through the use of statistical hypothesis testing. By systematically comparing the arithmetic means of adjacent subsamples throughout the area of interest and using a moving windows approach to locate sudden changes in a sediment's grain-size distribution more precisely, the local variability of the river reach can be described adequately.

Nutrient transfer between parafluvial interstitial water and river water: influence of gravel bar heterogeneity

1. Nutrient concentrations in interstitial water springs at the downstream ends of two gravel bars in the River Rhône were measured in order to estimate the importance of nutrient inputs [nitrate, dissolved organic carbon (DOC), biodegradable and refractory fractions of DOC] from the parafluvial zone (saturated sediments adjacent to the wetted channel, i.e. interstitial habitats of gravel bars) to the river as well as seasonal variations in these inputs.2. Compared with surface water, parafluvial water had lower concentrations of DOC (especially the refractory fraction) and generally higher concentrations of nitrate. These differences were at their lowest during winter.3. The influence of gravel bar geomorphological heterogeneity (grain size and spatial distribution of fine sediments) on parafluvial inputs was studied in terms of nutrient content and biofilm characteristics along transects across the gravel bars.4. A gravel bar located in a stable area of the river had low transversal heterogeneity and acted as a sink for DOC and as a source of nitrate. The low fine sediment content and the high oxygenation of interstitial water must have enabled aerobic processes such as mineralization of organic matter and nitrification to occur.5. In contrast, gravel bars located in a degradation zone of the river had a spatially variable structure, acting as a sink for DOC and nitrate because localized accumulation of fine sediment and ensuing hypoxic conditions induced anaerobic processes such as denitrification.6. This study highlights the important influence of geomorphological heterogeneity in gravel bars for nutrient transformations as well as nutrient exchanges between parafluvial interstitial systems and the adjacent river over a seasonal cycle.

Grain-size and SrNd isotopes as tracer of paleo-bottom current strength, Northeast Atlantic Ocean

A crucial question in modern paleoceanographic research is how vigourous was the bottom current in the glacial North Atlantic Ocean. Distribution of sediment grain size can provide such information, if the characteristics of the source functions are known. The interest of this paper is to use the SrNd isotopic composition of lithic particles as a tracer of origin, in order to determine possible changes in the source function, over the last 185 kyr. Grain-size distribution data are derived from a sediment core in the Icelandic basin (Gardar Drift). The distribution pattern reveals a well sorted silt size (modal size 20 μm) in the glacial deposits. Sr and Nd isotopic composition measured on separate size fractions indicates a more constant local origin (Iceland) for the silt fraction than for the fine fraction. These data suggest that the increase in the silt fraction during glacial periods is related primarily to an increase in the bottom current strength, rather than to changes in sediment supply (i.e. ice-rafting, turbidity current). The increase in vigour of the bottom current, recorded during the isotopic stages 6, 4 and the last post glacial periods, could have been initiated by a southward shift of the zone of deep water formation in the northern part of the Icelandic basin.

Sampling surficial fluvial gravels; the precision of size distribution percentile sediments

ABSTRACT Grid-by-number (Wolman) sampling is commonly used to characterize the texture of surficial fluvial sediments. Assessments of sampling precision have concentrated on the median grain size, but adequate representation of other grain size percentiles is paramount in a number of sedimentological contexts. The field effort required to construct percentile sampling distributions by replication is prohibitive, and the absence of any general size distribution for fluvial sediments precludes theoretical calculation of percentile standard errors. Bootstrapping is used in this paper to determine percentile standard errors for large samples from two gravel bar surfaces. The improvement of percentile precision with sample size follows the theoretical expectation, hence improvement in percentile recision is achieved only at the expense of much greater sampling effort once sample sizes reach about 400 stones. However, absolute percentile standard errors differ significantly from theoretically derived values. Of particular interest is the stability of coarser percentile estimates in coarse-skewed distributions; D95 estimates may be as precise as D50 estimates for a given sample size. The sensitivity of the precision of estimated percentiles to distribution shape is examined using synthetic skewed and bimodal grain size distributions. The absolute precision of percentile estimates is shown to vary with the grain size distribution of a particular sediment. Our field results provide a reference for further work.

Paleoenvironment and Period of The “Edoma” Formation in High Arctic Eastern Siberia

There exists large scale ground ice, which locally called “Edoma”, in plains along the Arctic coasts of eastern Siberia and the New Siberian Islands. The Edoma is mainly composed of massive ground ice with pillar-shaped frozen soil. The massive ice is considered as syngenetic ice-wedge origin, which develops alternative accumulations of ice-wedge and sedimentation on ground surface. The soil pillars are arranged in regular intervals of several meters in the massive ice, and contain a lot of ice lenses and several peat layers.A geological and geochemical survey was carried out in the Bykovsky Peninsula near the Lena Delta (Loc. 1), Bolshoi Lyakhovsky Island, the southern part of the New Siberian Islands (Loc. 2) and Oiyagosky Yar facing the Arctic Sea in middle of eastern Siberia (Loc. 3). Results of grain size analysis and determinations of radiocarbon datings of the Edoma in these surveyed sites were summarized as follows : 1) Sediments of the Edoma in Loc. 1 are composed of dark gray silt to fine sand with a lot of organic matters. Compositional ratio of grain size varies vertically, and is characterized by bimodality in the grain size distribution. This suggests that the sediments were formed under two different transportation agents. Sediments of the Edoma both at Loc. 2 and Loc. 3 characterized by dark gray to brown silt, and also contains abundant organic matter. Grain-size distribution of these sediments is similar to the finer population in Loc. 1. Judging from the characteristics of grain size distribution, these sediments are considered as aeolian deposits.2) Radiocarbon ages at Loc. 1 scatter within a range from about 30, 000 to 20, 000 yr BP in upper part and about 11, 000 yr BP in uppermost. The ages at Loc. 2 are resulted in about 30, 000 to 40, 000 yr BP in case of the most parts and about 7, 000 yr BP at uppermost part in permafrost just under the active layer. At Loc. 3, most of the ages of the Edoma are determined over 40, 000 yr BP and that of uppermost is determined as about 22, 000 yr BP.Based on the results of radiocarbon dating mentioned above, it is suggested that the Edoma in eastern Siberia might have formed during Karginkiy Interstadial to Sartan Stadial in the Last Glacial stage, and especially main parts of the Edoma developed during Karginkiy Interstadial, in which period climate was more unstable than Sartan Stadial. Grain size distribution of sediments also suggest that the Edoma have accumulated under the sedimental condition at water flood plain or marsh, which were favorable locations to growth of syngenetic ice wedge as well as loess accumulation. Supply of sediments in Loc. 1 may have been stable because the main transport of sediments have been performed by fluvial activities of the Lena River and the wind action. On the other hand, since the sediments in Loc. 2 and Loc. 3 is probably derived from aeolian loess, the amounts of supplied sediments might have been less than Loc. 1. Therefore, flux of sedimentation, forming the Edoma in Loc. 1 maintained longer than those at Loc. 2 and Loc. 3.