Showing papers on "Silt published in 1992"

Hierarchical Levels of Heterogeneity in a Mississippi River Meander Belt and Application to Reservoir Systems: Geologic Note (1)

Abstract: Six hierarchical levels of sand heterogeneity that would be present in analogous reservoirs are recognized in a Mississippi River meander-belt system in southeastern Missouri: (1) meander belt, (2) meander scroll, (3) channel, point bar, and splay, (4) lobe sheet, (5) bedding unit, and (6) laminae Heterogeneity level 1 is similar in size to an oil field and consists of (1) 9 million ac-ft (111 billion m{3}) of high-permeability channel sands in numerous meander scrolls and (2) 4 million ac-ft (49 billion m{3}) of low-permeability clay plugs (in numerous abandoned channels) that separate a field into isolated pools and reservoirs Overbank flood-plain muds capping the meander-belt system are barriers to vertical migration of fluids Heterogeneity level 2 is the size of pools within a field and has 12 million ac-ft (15 billion m{3}) of highly permeable, laterally accreted channel and point-bar sands, partly or wholly isolated from other sand bodies by low-permeability, abandoned-channel clay plugs Abandoned mud-filled chutes impede lateral migration of fluids in the upper pa ts of the meander scroll The third level of heterogeneity is composed of about 70,000 ac-ft (863 million m{3}) of individual, permeable channel, point-bar, and crevasse-splay sand bodies, with numerous thin sheets and lenses of low-permeability muds and silts (derived from chute fill and mud drapes) that impede vertical migration of fluids Heterogeneity level 4 is the lobe sheet unit (reservoir pay zone about 450 ac-ft or 555,000 m{3} in volume) comprising channel, point-bar, and splay sand bodies The fifth level of heterogeneity is the single bedding unit (about 10 ac-ft or 12,000 m{3}) at the scale of a reservoir flow unit or perforated interval Permeable, cross-bedded sand bundles are separated by low-permeability, inclined and horizontal mud-silt layers and lenses present along bed-set boundaries Heterogeneity level 6 is individual sand laminae (grain-flow lenses or grain-fall sheets) separated by textural variations (and hence permeability-porosity variations) and isolated mud-silt laminae Permeabilities range from 90-160 d in sand; several millidarcys to 50 d in muddy sand, silt, and sandy silt beds from the levee, crevasse, and abandoned-channel fill; and less than 10 md in muddy silts and muds from abandoned-channel and chute-fill mud sheets and laminae At all levels within a fluvial meander-belt system, these permeability heterogeneities are the principal controls on productivity throughout the life of a reservoir

Control of C,N,P distribution in soils of riparian forests

Abstract: It is now well accepted that riparian forests have an important role in regulating upstream/downstream flow of matter and energy in river ecosystems. Since geomorphic processes determine the structure of channels and floodplains, we have investigated whether different geomorphic features of riparian forests had any effects on the ability of their soils to retain nutrients and organic carbon. Willow riparian forests were chosen within the annual floodplain of the Garonne River, southwest France, to represent two different geomorphic types. Erosional types of riparian forests (E-type) were characterized by sand deposition on their soils because of high current velocity which hampered fine particle deposition. Depositional types of riparian forests (D-type) were characterized by slower overflow velocity; consequently silt and clay were dominant in their soils. Soil samples were taken at the end of the vegetation growth period, coinciding with low water levels prior to annual floods. Erosion and sedimentation processes affected the distribution of total C,N, and P contents in riparian forest soils, since they were significantly correlated with soil grain size. D-type riparian forest soils act as a sink for upstream/downstream nutrients and carbon flows during floods through accumulation of total C,N and P from year to year. In contrast, E-type riparian forests act as potential nutrient sources during high water periods, since they may release from their soils large amounts of easily available C, N and P into the river. These results demonstrate that nutrients and carbon retention ability of riparian forests soils should be analyzed through their geomorphic features rather than by their vegetation composition. Even if they belong to the same vegetation succession, riparian forests should not be considered as a homogeneous buffering system for upstream/downstream flows of nutrients and organic carbon.

Dry‐Soil Aggregate Stability as Influenced by Selected Soil Properties

Abstract: Dry aggregate stability is an important soil physical property for evaluating tillage and wind-erosion research. Research in this study was aimed at developing a model for predicting soil aggregate stability as influenced by intrinsic soil properties, with particular application to wind erosion. Aggregates from 10 Kansas soils with a wide textural range were tested periodically for stability during a 3-yr period. The logarithm of aggregate stability was regressed against the intrinsic soil properties (geometric mean diameter of primary particles, specific surface area, water content at -1500 J/kg matric potential, and clay content). Clay content and water content at —1500 J/kg were both good predictors of mean aggregate stability. A resulting empirical model estimates mean aggregate stability from either clay or water content with coefficients of determination of 0.97 and 0.96, respectively. Further testing is planned by running the model with several independent data sets to estimate the probability of aggregate stability within specified limits for particular soils. W RESEARCH SCIENTISTS have been charged with developing improved wind-erosion prediction technology as a possible replacement for the wind-erosion equation (Hagen, 1991a). Improved wind-erosion prediction technology requires that we improve our ability to measure and predict, in time and space, the susceptibility of soil to wind erosion. The main properties of dry soil aggregates affecting E.L. Skidmore, USDA-ARS and Kansas State Univ., and J.B. Layton, Agronomy Dep., Kansas State Univ., Manhattan, KS 66506-4006. Joint contribution of the USDA-ARS and Kansas Agric. Exp. Stn. Contribution no. 91-201-J. Received 8 Feb. 1991. * Corresponding author. Published in Soil Sci. Soc. Am. J. 56:557-561 (1992). their susceptibility to wind erosion are stability and size distribution. Soil aggregate stability and size distribution vary widely in time and space. Aggregate density affects soil credibility to a lesser extent but is much less variable than stability and size distribution. Chepil (1950), using a wind tunnel, determined relative credibility of soil as a function of the proportions of dry soil aggregates in various sizes. Chepil (1960) later converted relative credibility to actual field soil loss for specified conditions, which was the basis for soil -credibility factor of the wind-erosion equation (Woodruff and Siddoway, 1965). Their data show nonaggregated sandy soils with only 1% of the sand having diameters >0.85 mm are 100 times more erodible than aggregated soils with 77% of their aggregates >0.85 mm (Woodruff and Siddoway, 1965). Similarly, dry AS may differ a hundredfold between soils. Aggregates with low stability fracture easily and break into small sizes. Hagen (1991b) found that AS was the dominant predictor of soil erosion from surface abrasion. He concluded that major improvements in predicting the abrasion coefficient of the abrasive flux equation can come only from improved predictions of the stability of aggregates and crusts. The aggregate status of a soil at any instant in time is the result of many aggregate-forming and -degrading processes. Those processes comprise a complex interrelationship of physical, chemical, and biological Abbreviations: AS, aggregate stability; SD, standard deviation; CDN, calendar-day number; CDMAX, calendar-day number when aggregate stability is at maximum; GMD, geometric mean diameter; GSD, geometric standard deviation; CV, coefficient of variation; PWP, water content at 1500 J/kg. 558 SOIL SCI. SOC. AM. J., VOL. 56, MARCH-APRIL 1992 reactions. Aggregates may form by the breakdown of consolidated soil mass into smaller sizes or by the coalescing of finer materials. Chepil (1955) observed a definite relationship between amounts of erosion in a wind tunnel and the percentage of clay contained in the soil. Soils containing 20 to 35% clay were least credible. Coarsetextured soils apparently lack sufficient amounts of silt and clay to bind individual sand particles together, or they may form weakly cemented clods that are readily broken down and eroded. On medium-textured soils, the proportions of silt and clay appear to be sufficient to bind the sand grains together, yet not so high as to cause excessive cleavage by weathering and consequent granulation. This research was aimed at developing a model for predicting soil AS as influenced by intrinsic soil properties, with particular application to wind erosion. 1965). In our application of the error function, Z, = (InAS, mAS)/(V2 SD) [4] where InAS, is the natural logarithm of AS corresponding to a probability, P,, for a soil with a mean log stability of InAS and SD. Because Eq. [3] is for only one-half of the area integral, it follows that P, = 0.5 + erf(Z,)/2 [5] where P, is the cumulative probability that AS will not exceed the value specified in Eq. [4] for the soil with the given mean and SD. Combining Eq. [4] and [5] gives P( = 0.5 + erf[(lnAS, mAS)/(V2 SD)]/2. [6]

An examination of podzolization near Lake Michigan using chronofunctions

Abstract: A chronosequence of sandy soils was investigated on four terraces near Lake Michigan to assess rates of podzolization and changes in soil properties with age. The terraces ranged in age from 3000 to 10 000 BP. Each surface was systematically sampled to determine the modal profile, which was then described and sampled. Quantities of OC, Fe, and Al in the B horizons of modal soils increased with soil age. Silt content of surface horizons also increased with age, possibly due to eolian input or physical weathering. For weighted profile and B horizon Al and Fe averages and a variety of soil development indices, a single logarithmic model generally gave the highest statistical significance of the three chronofunction models used. All pedons sampled failed to classify as Podzols, but the oldest two met the criteria for the Spodosol order. Thus, more than 4000, but less than 10 000, years are required for the development of a spodic horizon in Michigan. Key words: Soil chronosequence, Podzol development, soil ge...

Size characteristics of sediment from agricultural soils

Abstract: Size characteristics of sediment eroded from 22 intensively cropped Mid-South and Midwest soils during intense simulated rainstorms were analyzed before and after dispersion. The undispersed sediment often was much coarser than the primary soil particles because of aggregation. When this sediment was dispersed, the size distributions of the primary sediment particles usually were similar to those of the dispersed soil. Soils high in silt generally had the finest undispersed sediment. High-sand soils were coarser, and high-clay soils had the coarsest sediment. Much of the sediment from soils with medium to high clay contents consisted of sand-sized aggregates. These coarse aggregates contained much of the eroding clay. Therefore, control practices that trap coarse sediment have major potential to reduce losses of nutrients and pollutants associated with clay particles.

The mass balance of soil evolution on late Quaternary marine terraces, northern California

Abstract: Mass-balance interpretation of a soil chronosequence provides a means of quantifying elemental addition, removal, and transformation that occur in soils from a flight of marine terraces in northern California. Six soil profiles that range in age from several to 240,000 yr are developed in unconsolidated, sandy-marine, and eolian parent material deposited on bedrock marine platforms. Soil evolution is dominated by (1) open-system depletion of Si, Ca, Mg, K, and Na; (2) open-system enrichment of P in surface soil horizons; (3) relative immobility of Fe and Al; and (4) transformation of Fe, Si, and Al in the parent material to secondary clay minerals and sesquioxides. Net mass losses of bases and Si are generally uniform with depth and substantial, in some cases approaching 100 percent; however, the rate of loss of each element differs markedly, causing the ranking of each by relative abundance to shift with time. Loss of Si from the sand fraction by dissolution and particle-size diminution, from about 100 percent to less than 35 percent over 240 ky, mirrors a similar gain in the silt and clay size fractions. The Fe originally present in the sand fraction decreases from greater than 80 percent to less than 10 percent, whereas the amount of Fe present in the clay and crystalline oxyhydroxide fractions increases to 25 percent and 70 percent, respectively.

Upper Pleistocene turbidite sand beds and chaotic silt beds in the channelized, distal, outer-fan lobes of the Mississippi fan

Abstract: Cores from a Mississippi outer-fan depositional lobe demonstrate that sublobes at the distal edge contain a complex local network of channelized-turbidite beds of graded sand and debris-flow beds of chaotic silt. Off-lobe basin plains lack siliciclastic coarse-grained beds. The basin-plain mud facies exhibit low acoustic backscatter on SeaMARC IA sidescan sonar images, whereas high acoustic backscatter characteristic of the lobe sand and silt facies. The depth of the first sand-silt layer correlates with relative backscatter intensity and stratigraphic age of the distal sublobes (i.e., shallowest sand = highest backscatter and youngest sublobe). The high proportion (>50%) of chaotic silt compared to graded sand in the distal, outer-fan sublobes may be related to the unstable, muddy, canyon-wall source areas of the extensive Mississippi delta-fed basin slope. A predominace of chaotic silt in cores or outcrops from outer-fan lobes thus may predict similar settings for ancient fans.

239,240 Pu and 137 Cs in the East China and the Yellow Seas

Abstract: The distribution and inventory of artificial radionuclides,239,240Pu and137Cs were determined in the East China and the Yellow Seas in 1987. Almost all of239,240Pu and 50 to 80% of137Cs in the continental shelf area are retained in the sediment column.239,240Pu sediment inventory in the sea area is larger than the fallout input and tends to increase southwardly. This excess239,240Pu and the lateral distribution are attributable to the supply of239,240Pu by the Yangtze River discharge. On the contrary,137Cs sediment inventory shows a decrease to the south, and the fact can be accounted for by the southward dispersion of fine silt particles discharged from the Yellow River. Total137Cs inventory is smaller than the estimated fallout input, and the fact seems to indicate dispersion of137Cs out of the shelf region. Vertical profiles of239,240Pu and137Cs contents in sediments differ from that of natural210Pb, implying the effect of varied accumulation rates of the artificial radionuclides over the sediment particle mixing by benthic organisms. Apparent maximum sediment particle mixing coefficient (D B ) calculated from the excess210Pb profiles in stations located between the inner and outer shelves ranged from 1.4 to 8.3 cm2y−1. ThisD B value is higher than that in the Okinawa Trough (1.0 cm2y−1), but lower than previously estimatedD B value (≈26 cm2y−1) in the outer shelf mud.

The influence of different fertilization practices on concentrations of organic carbon and total nitrogen in particle-size fractions during 34 years of a soil formation experiment in loamy marl

Abstract: The concentrations of organic C and total N in five different particle-size fractions were studied under different mineral and organic fertilizer regimens by examining soil samples from the 34-year-old soil-formation pot experiment Hu 3 in Rostock. The C and N concentrations were generally highest in the clay fraction and decreased in the order medium silt >fine silt >coarse silt and sand. For nearly all years and size fractions the following order was obtained for C and N concentrations under the various fertilizer regimens: Compost >farmyard manure >straw + mineral fertilizer >mineral fertilizer. The various particle-size fractions and fertilizer regimens differed in the development of soil organic matter levels. Consequently, characteristic redistributions were found in the proportions of C and N in the various particle-size fractions, particularly after organic fertilizer was no longer applied (years 20–34). This experimental phase was characterized by decreased organic C and increased total N concentrations, and increased proportions of C and N in the clay-size at the expense of the sand fractions.

Changes in chemistry and mineralogy of forest soils by acid rain

Abstract: The goal of the present study was a qualitative and quantitative determination of chemical and mineralogical changes in forest soils due to acid atmospheric depositions. In the NE/SE Vienna Woods soil samples were taken at 4 depths (0 to 5 cm, 5 to 10 cm, 10 to 20 cm, 20 to 30 cm) in the contaminated infiltration zone of stemflow (S) of 8 beech trees (Fagus sylvatica), strongly influenced by acid atmospheric depositions (soil-pH 2.8 to 3.0) and in their non contaminated reference areas (R) between trees, where acid imput is much smaller (soil-pH 5.0 to 6.0). The results show that intensive weathering processes took place in the contaminated soil areas, which show higher clay and silt contents and smaller aggregates, as well as clay illuviation. Moreover, in the top of the contaminated soil areas higher contents of Ct and St and of the heavy metals Pb, Zn and Cu could be observed, accompanied by extreme low base saturation (expecially of Ca and Mg) and high Al-saturation (50 to 80% of the CEC). These data were confirmed by analysis of the water saturation extract. Moreover, in the contaminated top soils high amounts of Fe-oxides were found, whereas no “secondary” Al-chlorite (due to its instability at pH-values <4.0) could be traced. The desilification process which took place at the same time could be shown through total element analysis. In the clay-fraction strong weathering led to a loss of layer charge and to the genesis of highly expandable three-layer-silicates which could be determined by X-ray diffraction using n-alkylammonium-chloride technics and other chemical treatments.

Cesium‐137 in soil texture fractions and its impact on cesium‐137 soil‐to‐plant transfer

Abstract: Field studies at two sites contaminated by the Chernobyl fallout showed 137Cesium (Cs) soil‐to‐plant transfer factors in wheat, rye and potato. Transfer values ranged from 0.0017 (potato tuber) to 0.07 (wheat straw). Generally transfer coefficients in cereal grains and potato tubers were significantly below the values of the shoots. A comparison of the two sites led to the conclusion that for all plants investigated 137Cs ‐ transfer factors were higher in Lower Austria (Calcic Chernozem) than in Upper Austria (Eutric Cambisol). The specific activities of the texture fractions of the two soil types increased from sand to silt and clay. In the Calcic Chernozem the ratio of the 137Cs‐activity in the silt fraction to the total activity in the soil was considerably higher than in the Eutric Cambisol. At the same time extractability of 137Cs from the silt fraction of the latter soil was clearly lower. Both results mainly were attributed to the differences between the soils according to the organic matt...

Aspects of modelling sediment transport and light conditions in Lake Marken

Abstract: In lake Marken (Markermeer), a shallow lake in the Netherlands, sediment transport and suspended solids concentration are dominated by wind induced resuspension of sediment. The suspended solids concentration in the lake determines the attenuation of light. A 2-dimensional sediment transport model, STRESS-2d, was used to estimate the spacial distribution of the silt content for periods with different wind conditions. The model was calibrated using measured values of the fall velocity distributions of sediment, freshly deposited material and suspended solids. The specific light attenuation coefficient of the various sediment classes was also measured and used in the light attenuation model, CLEAR, together with simulation results from the STRESS-2d model, to simulate the light attenuation variations in time and space. By comparison of the simulation results for different scenarios, the influence of regional planning features on the sediment balance and the light attenuation can quantified. A provisional example of this method is presented.

Hydrologic and sedimentologic data collected during three cruises at low water on the Mississippi River and some of its tributaries, July 1987-June 1988

Abstract: Water, suspended-sediment, and bed-sediment samples were collected for physical (particle size and mineralogy) and chemical analysis (radioactive elements, trace metals, nutrients, petrochemical hydrocarbons, organic volatiles, pesticides, detergents, organic carbon, and humic substances) from 21 sites on the Mississippi River and its main tributaries. Three cruises were made at low water during a 1-year period from July 18, 1987, to June 7, 1988. The maximum measured discharge was about 10,400 cubic meters per second on December 15, 1987, at Vicksburg, Mississippi, and the maximum measured suspended-sediment discharge was 354,000 metric tons per day in the Missouri River at Hermann, Missouri, on July 20, 1987. The equal-width-increment (equal-transit-rate), depth-integration method was used at 10-40 verticals across the river to collect between 70 and 137 liters of river water with an isokinetic sampler (made of Teflon to prevent chemical contamination). This report contains the following hydrologic data associated with the suspended-sediment samples: cross-sectional area of the river; mean depth; mean velocity; water discharge; particle sizes; concentrations of the suspended sand, silt, and colloid fractions; and surface temperature and conductivity at 10-40 locations across the river. These data provide the framework for subsequent interpretive chemical analyses of the samples collected during the three cruises.

Dust transport and palaeoclimate during the Oldest Dryas in Central Europe―implications from varves (Lake Constance)

Abstract: This paper evaluates evidence for seasonal loess deposits in peri-Alpine Lake Constance at the end of the last Glacial (Oldest Dryas chronozone). The usefulness of such lacustrine deposits for palaeoclimatic interpretations is discussed. The sedimentology of laminated couplets comprising yellow and grey silts has been investigated to test the hypothesis that the couplets are varves (i.e. annual rhythmites) comprising alternations of loess and glacial silt and clay. The laminae are mostly less than 1 mm thick and include from bottom to top: (1) a matrix of well-sorted, non-graded fine yellow silt with sand-size intraclasts, (2) coarsening-upward grey silt with a cap of fining-upward silt to clay. The latter is typical for varves in modern proglacial lakes and reflects summer and winter deposits (silt and clay, respectively). We propose that the lack of grading and the matrix supported fabric is indicative of aeolian transport and therefore interpret the yellow laminae as loess deposits. Volcanic glass intraclasts in the loess layers are probably derived from volcanic terrain to the west of the lake, indicating an easterly palaeowind direction. Deposition of loess in the lake occurred regularly at the beginning of each annual cycle, suggesting that the palaeowinds were associated with winter and/or spring conditions. Two transport scenarios are suggested to explain the sand grains scattered in this deep-water lacustrine record. 1. The grains may have been transported as bedload over the annual winter ice-cover of the lake under moderate wind strengths, frozen into the ice, and released for deposition during spring melt. 2. The sand grains were blown directly out onto the lake water by very strong winds during spring. The first scenario is contrary to the general view that loess was transported during summer, and that loess deposits thus reflect summer conditions only. Loess input to the lake shows a transitional decrease after ca. 14.3 kyr BP and cessation at ca. 14 kyr BP, probably as a result of a change of wind behaviour, increased humidity and/or vegetational changes during the Oldest Dryas in central Europe.

Forms of Potassium in Some Soils of Assam in Relation to Soil Properties

Abstract: Forms of potassium and their relationship with soil physico chemical properties were investigated on sixteen representative surface samples of alluvial (Inceptisols) and lateritic (Alfisols) soils of Assam. Alluvial soils contained relatively higher amount of total, non-exchangeable and lattic K as well as higher K-fixation capacity vis-a-vis lateritic soils. Available K as measured by water soluble and exchangeble forms were higher in lateritic soils. Different forms of potassium and K-fixation capacity showed a positive relationship with clay, silt, organic carbon, CEC and base saturation and negative relationship with sand. In respect of pH, water soluble, exchangeable, non-exchangeable K and K-fixation capacity showed positive relationship whereas total and lattice K showed negative relationship.

Distribution of micronutrients in arid zone soils of Punjab and their relation with soil properties

Abstract: Profile distribution was investigated for total and DTPA‐extractable Zn, Cu, Mn, and Fe in soils developed on three physiographic zones (alluvial terraces, interdunal areas, and sand dunes) in the arid zone of Punjab in northwest India. Total and DTPA‐extractable micronutrient cations were highest in soils of alluvial terraces followed by soils of interdunal areas and sand dunes. Irrespective of physiographic zone the soils did not show any pattern of depth distribution of DTPA‐extractable micronutrients. Total Zn and Mn showed accumulation in the B horizons, whereas Cu and Fe did not exhibit any specific pattern. Differences in organic carbon content and size fractions that were associated with changes in physiography had a strong influence on the micronutrient status of the soil. Based on linear coefficients of correlation, DTPA‐extractable micronutrients increased with an increase in organic carbon, cation exchange capacity, silt, and clay, and decreased with an increase in sand content, where...

Estimating Interrill Erodibility of Forest Soils

Abstract: A method to develop erodibility prediction equations was developed and tested using published data. Published sediment yield data for 21 California forest soils developed using laboratory plots subjected to simulated rainfall were used to develop an equation that explains 90% of the variation in sediment yield from the plots. The predicted sediment yield values can be considered an index of relative interill erodibility because only soil type varied among the plots. Sediment yield was a function primarily of soil texture for soils with less than 50% Si+Cl content. Beyond 50% Si+Cl content, the erodibility of the soil related more to the type of clay: kaolin or smectite. The hypothesis proposed to explain the shape of the curve is based on aggregate strength under rainfall. A second hypothesis that increased silt and clay increases the degree of aggregation of the soil as a whole is rejected. Soils with a relatively high smectite clay content had reduced aggregate strength and higher sediment yield when exposed to rainfall than soils with a relatively high kaolin clay content. The relationship of texture and clay mineral content to erodibility should be general and applicable to other soils.

Aluminum mobility along a geochemical catena in an alpine watershed, Front Range, Colorado

Abstract: Summary Soils and soil solutions were studied in order to assess the mobility of Al in an alpine watershed, Front Range, Colorado. The concept of a geochemical catena was invoked to evaluate the spatial relationships of Al and the elements that control its solubility in alpine soils. Organic C, exchangeable Al, silt and clay increased significantly (P

Particle size characteristics of suspended and bed sediments in the Rhône river

Abstract: Ten large volume water samples were taken from the Rhone River (Switzerland- France) in November 1989 for recovery of total suspended sediment by continuous flow centrifugation. The samples were freeze-dried and analysed for particle size, organic carbon, total nitrogen, and carbonate. For comparative purposes, four bed sediments collected in July 1989 are also described. The Rhone can be subdivided into three sections on the basis of the origins of the water. The first section is the Upper Rhone River draining into Lake Geneva. Waters are derived from glaciers, with low temperature and conductivity and high turbidity. Suspended sediment is coarse, has a bimodal distribution, and is low in both organic matter and carbonate. The second reach is from Lake Geneva to the confluence with the Saone at Lyon and has warmer water with higher conductivity and very low turbidity. Suspended sediment is higher in organic matter, with high carbonate originating from the lake. The final section is from Lyon to Aries, with warmer water and higher conductivity and turbidity due to modification by the Saone. Sediment is rich in organic matter, which may account for an observed decline in oxygen in the river waters downstream from Lyon. Carbonate in these sediments also decreases due to increased turbidity from the Saone. Suspended sediments other than from the Upper Rhone show a remarkable consistency in grain size, predominantly in the fine silts (mode 9-11 Jim). This consistency indicates a high degree of suitability for geochemical analysis. Bed sediments were bimodal throughout, with a dominant coarse population in two out of the four samples. Grain size statistical parameters could be easily explained by application of the theory of mixing of two major populations in the sand size (bed traction load) and the fine silt/clay size (suspended sediment load).

The Effects of Wind Transport on the Shapes of Quartz Silt Grains

Abstract: Wind-blown terrigenous silt is a common component in marine sediment, but it is often difficult to distinguish from fluvial silt. A field experiment was conducted in the Loess Plateau of China to determine the effect of eolian transport on the shapes of detrital quartz silt grains and to define grain-shape criteria for the recognition of eolian silt. The results show that eolian transport results in a rapid downwind increase in the roundness of quartz silt grains, and that this increase in roundness is apparently due to preferential transport, or shape-sorting, of more rounded grains. This capacity for shape-sorting distinguishes eolian from fluvial transport, which has no great effect upon the shapes of quartz silt grains, and provides a petrographic criteria for the distinction of t e eolian and fluvial silt components in marine sediments.

A model for predicting waves and suspended silt concentration in a shallow lake

Abstract: A wave model and a vertical silt model are developed for shallow lakes and both were applied to Lake Marken in the Netherlands. The results of the wave model serve as input for the silt model. The silt model calculates the suspended silt concentration at several depths at a certain location. The water column is divided in compartments and the suspended silt concentration can be divided into a maximum of seven fractions. It is also possible to divide the top layer of the lake bottom into 25 slices with different time-dependent soil-physical properties.

Sedimentology and Mineralogy of Jizan Shelf Sediments Red Sea, Saudi Arabia

Abstract: ABSTRACf. This study evaluates the texture, coarse fraction composition and mineralogical constituents of the bottom samples from the Jizan shelf, Red Sea, Saudi Arabia. Five sediment types were identified, namely muddy sand, sandy mud, silt, clayey silt and silty clay. It was found that most of the northern and central ~arts of the shelf are covered with muddy sediments, while the muddy sand and sandy mud sediments are restricted only to the southern part of the shelf and near shore areas. Based on the textural characteristics of the examined sediments, Jizan shelf environment can be divided into two energy zones: (a) low-energy zone, including most of the northern to middle shelf area; and (b) a moderate-energy zone, restricted to the southern part of the shelf and near shore areas. The detailed mineralogical investigation of the various size classes of Jizan shelf sediment!i revealed that they are of polygenetic origin. Two main sources of the shelf sediments were recognized, namely: (a) autochtonous materials which are derived from the degradation of recent she,lls of various fauna, erosion of submerged ancient sediments and sub-recent coastal sediments; and (b) allochtonous materials, which are derived from the onshore alluvium deposits by the action of intermittent streams.