Sediment Bulk Density Research Articles

Retention and compartmentalization of lead and cadmium in wetland microcosms

This report describes results of a 14 month study of the fate of trace-metal contaminants in wetland microcosms. Duplicated wetland microcosms contained either cattail, Typha domingensis or duckweed, Lemma minor, as the dominant macrophyte. Each wetland microcosm received 14.6 cm/day of dilute landfill leachate amended with lead (measured average: 396 μg/l) and cadmium (measured average: 105 μg/l). At intervals of approximately 3 months, sediments and macrophytes were sampled and analyzed for heavy metal content. Differences between measured trace-metal concentrations in inflow and outflow samples indicated that approximately half of the added lead and cadmium were retained in wetland microcosms. Of the fraction removed from the water, less than half could be accounted for in calculated sediment and plant tissue concentrations, based on analysis. The apparent discrepancy in mass balance calculations probably arises from failure to accurately measure bulk density of sediment detritus floc, which contained a substantial amount of the trace metals. Measurement of sediment acid volatile sulfides (AVS), and comparisons of these concentrations to those of the added lead and cadmium, showed that nearly all of these trace metals were present in the sediments as sulfides, limiting bioavailability and toxicity of these elements. Results of analyses and a lack of overt biological effects suggest that in wetlands containing organic sediments, sediment chemistry dominates cycling of these trace metals. Plant accumulation is of secondary importance. Comparison of heavy-metal uptake by cattails and duckweed shows that duckweed, on a whole plant basis, accumulates lead and cadmium more effectively than does cattail. If plants were to be used in a biomass-harvesting process for metal bioremediation, duckweed appears to be a more suitable candidate than cattail because of high productivity and ease of harvesting, coupled with a significant bioaccumulation of lead and cadmium. Potential metal removal rates by duckweed are 3–8 mg Pb/m 2 day and 2–4 mg Cd/m 2 day.

A rapid technique to determine bulk density of fine-grained sediments by X-ray computed tomography

A rapid technique to determine bulk density of fine-grained sediments by X-ray computed tomography

Sediment stability on the western flanks of the Canary Islands

Sediment failures on the flanks of the Canary Islands are well documented but few geotechnical studies have been conducted. In this study the sedimentological and geotechnical properties (water content, grain specific gravity, bulk density, grain-size, consolidation and triaxial test data) of sediment recovered in cores from the submarine slopes of the island of La Palma, Canary Islands, NE Atlantic indicate that the sediment is heavily to lightly overconsolidated; the overconsolidation is considered to be apparent, in the absence of any evidence suggesting sediment erosion. Normalised strengths range from 0.53–0.77 for the carbonate-rich sediment. The sediment stability was semiquantitatively assessed. The sediment off La Palma is stable under drained and undrained static loading conditions at present, however, if affected by horizontal ground accelerations in excess of 15% of gravity the sediment will become unstable. Locally, on sediment waves for instance, slope angles may be greater thus enhancing the potential for sediment failure. Triggering can potentially be explained in terms of the likely magnitude and frequency of seismic accelerations, although other trigger mechanisms may have enhanced the failure potential of these sediments in the past. Steady state analysis indicates that all the sediments tested are state II type and are unlikely to result in disintegrative morphologies (e.g. debris flows) after initial failure. The sediment in the source region of the Canary Debris Flow must, therefore, have undergone transition from state II to state I type sediment perhaps brought about by a progressive style of failure during or after initial failure. This may be caused by a debris avalanche from the volcanic island flanks.

The stability of sublittoral, fine‐grained sediments in a subarctic estuary

ABSTRACTThe erodibility of natural estuarine sediments was measured in sit along a longitudinal transect of Manitounuk Sound, Hudson Bay, using the benthic flume Sea Carousel. Sedimentation processes along the transect varied from continuous, rapid, post‐glacial sedimentation in the inner Sound, to glacial outcrops and seabed reworking of the outer Sound. The grain size and physical bulk properties reflect changes in depositional environment and correlate with sediment erosion threshold stress (τc), erosion rate (E), erosion type and still‐water mass settling rate. There was a steady increase in τc (0·8–2·0 Pa) with distance down the Sound in parallel with the decreasing sedimentation rate (0·003–0·001 m yr−1) and increasing sediment bulk density (1650–2010 kg m−3). The near‐surface friction coefficient varied up to 68° in proportion to the clay content of post‐glacial material. Glacial sediments were characterized by variable results and generally higher friction coefficients. Seabed erosion in Sea Carousel began with surface creep of loose aggregates, pellets and organic debris. This was followed by Type I bed erosion at rates that varied between 0·0002 and 0·0032 kg m−2 s−1 (mean 0·0015). Type I peak erosion rate was inversely related to applied bed shear stress (τo). Type II erosion succeeded Type I, often after a broad transitional period. Simulations of suspended sediment concentration in Sea Carousel were made using four commonly used erosion (E) algorithms. The best results were obtained using Krone's dimensionless ratio relationship: E=M(τo/τc‐1). Simulations were highly sensitive to the definition of erosion threshold with sediment depth [τc(z)]. Small errors in definition of τc(z) caused large errors in the prediction of suspended sediment concentration which far exceeded differences between the methods tested.

A Rapid Technique to Determine Bulk Density of Fine-Grained Sediments by X-Ray Computed Tomography: RESEARCH METHOD PAPER

A Rapid Technique to Determine Bulk Density of Fine-Grained Sediments by X-Ray Computed Tomography: RESEARCH METHOD PAPER

Sedimentological study by using gammer-ray method for measuring wet bulk density of sediments

Sedimentological study by using gammer-ray method for measuring wet bulk density of sediments

Morphology of abyssal mudwaves at project MUDWAVES sites in the Argentine Basin

Abstract Extensive fields of mudwaves are present in the Argentine Basin. Mudwaves and water parameters at three sites were studied to provide detailed information on bathymetry, mudwave structure, sediment parameters and bottom water flow characteristics. Two sites, 5 and 6, are discussed in this paper. Crests of mudwaves at Site 5 on the north flank of the Zapiola Drift are oriented 45° anti-clockwise from the measured westward flow direction and migrate to the left of the flow direction. Mudwaves at Site 6 on the south flank of the Zapiola Drift are oriented 20° anti-clockwise from the inferred southeast bottom flow direction, and also migrate to the left of direction. Evidence from current meters and surface sediments suggests that the mudwaves at Site 5 are active today, while those at Site 6 have been active in the Holocene, but perhaps not within the last 100 years. Mudwave orientation anti-clockwise to mean flow, preferential sediment accumulation on the left wave flank, and apparent sediment accumulation on the wave crest agree with a model for mudwave growth presented by Blumsack and Weatherly (1989, Deep-Sea Research, 36, 1327–1339). Cross-wave asymmetry in sediment accumulation pattern is sufficient to cause a 10% change in surface sediment bulk density over the wave profile. The record of mudwave migration obtained from Sites 5 and 6 in the southern Argentine Basin and from Site 7 in the northern Argentine Basin suggests that bottom water flow has changed over a number of time scales during the last 200,000 years. Thus the analysis of abyssal bed forms can provide independent evidence about past changes in bottom flow.

Profundal Sediment Organic Content and Physical Character Do Not Reflect Lake Trophic Status, but Rather Reflect Inorganic Sedimentation and Exposure

An analysis of profundal sediment data from 83 north-temperate lakes shows that increasing inorganic sedimentation and exposure (or lake surface area) results in lower organic content and water content, and greater bulk density. Because sedimentation rates are unavailable for most lakes, we estimate sedimentation rates from readily available catchment sediment loads using a mass-balance model. The mass-balance estimate of sediment retention (per square metre of depositional zone) is an excellent predictor of measured inorganic sedimentation rates for a data set covering 19 lakes (R2 = 0.92). Multiple regressions are used to predict organic content, water content, and bulk density of profundal sediment from inorganic sedimentation rates and either exposure or lake surface area, which are surrogates for the energy of the depositional environment. These analyses explain 76, 74, and 66% of the between-lake variation in the three sediment parameters, respectively. Sediment organic content is not related to lake trophic status (chlorophyll a) and is negatively correlated with net organic matter sedimentation rates. The common occurrence of organic-rich sediments in oligotrophic shield lakes is, therefore, not a reflection of high organic matter inputs, but rather the extremely low inputs of mineral sediments to these lakes.

Nitrogen cycling in Louisiana Gulf Coast brackish marshes

Nitrogen fixation and nitrogen accumulation were measured in a Louisiana Spartina patens brackish marsh. Using the acetylene reduction technique calibrated with direct 15N2 assimilation, an equivalent of 90.0 µ g N g−1 yr−1 was fixed. Fixation was greater in the summer months and in the upper portion of the soil profile. Extractable ammonium increased with depth and was negatively correlated with ethylene production. Average ammonium concentration in the sediment was 39 µg NH4+-N g−1 sediment. Cesium-137 dating of the soil profile showed the marsh was vertically accreting at a rate of 0.60 cm yr−1. Calculations using vertical accretion rate, bulk density, and total nitrogen content of sediment indicate that the marshes are accumumating 7.2 g Nm−2 yr−1 thus serving as a major nitrogen sink. Measured nitrogen fluxes were incorporated with existing flux measurement in developing a nitrogen budget for the marsh.

Influence of pH on rheological properties of Al2O3 slips

The slip-casting technique is commonly used for the production of complex-shaped ceramic components. Various commercial powders have been used, which were characterized with respect to morphology, particle-size distribution and specific surface area. Alumina slips with 80% solid content were prepared with distilled water and ethanol as dispersing agent, with and without deflocculant. HCl and C4H13NO (tetramethylammonium hydroxide) were used for controlling the pH. Investigations into rheology, i.e. the dependence of viscosity and shear stress on shear rate, were performed. The slip, green and sedimentation bulk density were measured.

An Experimental Study of Well Control Procedures for Deepwater Drilling Operations

Summary A research facility has been designed and constructed to model thewell-control flow geometry present on a floating drilling vessel operating in 3,000 ft [914 m] of water. The main feature of thisfacility is a highly instrumented 6,000-ft [1829-m] well equipped with a packer and triple parallel flow tube at 3,000 ft [914 m] tomodel a subsea blow out preventer (BOP) stack with connecting subseachoke and kill lines. Several types of experiments were conductedin which gas kicks were simulated by the injection of nitrogen intothe bottom of the well. Alternative procedures studied andevaluated included techniques to compensate for chokeline frictional pressure loss during pump startup and techniques forhandling rapid gas-zone elongation when the kick reaches theseafloor. It was found that the demands placed on a choke operator during well-control operations in deep water were not as severe asanticipated from computer simulator studies and could be managedwith existing equipment by an experienced choke operator. Introduction In the late 1940's, the search for oil and gas accumulations firstmoved offshore to the shallow marine environment. Since that time, drilling operations have been extended steadily across thecontinental shelf. More recently, developments in the technologyfor drilling from floating drilling vessels have allowed exploratory drilling beyond the limits of the continental shelf andinto the relatively deep water of the continental slopes. In 1974, the first well was drilled in water deeper than 2,000 ft [610 in].1 By 1979, the water depth record was extended to 4,876 ft [1486in] on a well drilled offshore Newfoundland. More recent exploration offthe U.S. east coast extended the water depth record to 6,848 ft[2087 m]. Future plans in the Natl. Science Foundation's Ocean MarginDrilling Program call for scientific ocean drilling during the nextdecade in water depths of 13,000 ft [3962 m]. Like many other aspects of drilling operations, the problemof blowout prevention increases in complexity for floating drillingvessels operating in deep water. Several special well-control problems stem from greatly reduced fracture gradients and the use problems stem from greatly reduced fracture gradients and the use of long subsea choke and kill lines. Fig. 1 shows the approximateeffect of water depth on fracture gradients, expressed in terms ofthe maximum mud density that can be, sustained during normal drillingoperations. 4 Note that the maximum mud density that can be used withcasing penetrating 3,500 ft [1067 m] into the sediments decreases fromabout 13.9 lbm/gal [1666 kg/m3] on land to about 10.7 lbm/gal [1282 kg/m3]in 4,500 ft [1372 m] of water, and to about 9.8 lbm/gal [1174 kg/m3] in13,000 ft [3962 m] of water. These lower fracture gradients resultprimarily because the open hole must support a column of drilling fluid primarily because the open hole must support a column of drilling fluid that extends far above the mudline to the rig floor. This additionalcolumn weight is only partially offset by the seawater. An additional contributing factor is the relatively low bulk density of unconsolidated shallow marine sediments. The required vertical subsea choke and kill lines extendingfrom the BOP stack at the seafloor have two detrimental aspects. One difficulty arises because of the increased circulating frictional pressure loss caused by the great length of these lines. This frictional pressure loss can cause a significant increase inthe pressures occurring in the wellbore. The combination of highcirculating pressure losses in the chokeline and low wellborefracture gradients reduces the tolerance for error by the chokeoperator. A second difficulty results from rapid changes in hydrostaticpressure in the vertical chokelines when circulating a gas kick. pressure in the vertical chokelines when circulating a gas kick. Hydrostatic pressure falls quickly when gas exits the large casingand displaces mud from the relatively small-diameter chokeline. To maintain the bottomhole pressure (BHP) constant, there must be acorresponding increase in surface choke pressure to make up forthis decrease in hydrostatic pressure. Choke operation becomesmuch more difficult during this period, as rapid changes in controlpressure are required. This difficulty tends to increase with well pressure are required. This difficulty tends to increase with well depth because choke manipulation is based on surface drill pipepressure whose unsteady-state readjustment time increases with well pressure whose unsteady-state readjustment time increases with well depth and gas-kick volume. Evaluations of anticipated well-control problems for a givenset of deepwater conditions are often conducted by computer studiesthat predict the pressure response of a well for variousalternative procedures being evaluated. These studies have raisedquestions about the severity of the control problem faced by the choke operator. JPT p. 1239

Method for determining the dry bulk density of subaqueous sediments : Hobbs, C H J Sediment PetrolV53, N2, June 1983, P663–665

Method for determining the dry bulk density of subaqueous sediments : Hobbs, C H J Sediment PetrolV53, N2, June 1983, P663–665

Variation in the carbonate reactivity of deep-sea sediments: determination from flux experiments

Using a stirred-flow reactor, alkalinity flux from sediment into overlying seawater was measured as a function of dissolved carbonate ion concentration. Synthetic calcite powder and 10 deep-sea sediment samples ranging room 3 to 85% CaCO 3 content were used in the experiments. A diffusion-dissolution model analogous to the experimental conditions was developed to interpret the results. The experimental results depend on the total reactive surface areas of calcite and aragonite in the sediment, which are characterized by apparent rate constants k c and k a. The flux is approximately flux ≅ γ∥f c ( CO 3 2−)k c + f a ( CO 3 2−)k a ] 1 2 , where f c and f a symbolize the kinetic dependence of the calcite and aragonite on the dissolved carbonate ion concentration. The relationship of the functions to suspended particle kinetics is discussed. The coefficient, γ, depends on the sediment bulk density and porosity and on the ratio of carbonate ion to total CO 2 increase due to CaCO 3 dissolution. Variation of k c and k a between sediment samples shows the following: (1) The calcite reactive surface area is correlated with carbonate content between 0 and 60% CaCO 3. (2) The aragonite reactive surface area diminishes by an order of magnitude as water depth increases below the aragonite compensation depth (ACD). (3) A remnant aragonite standing crop persists below the ACD in sediment with > 20% CaCO 3. This may be due to mixing of the upper few centimeters by bioturbation, which results in the escape of a small fraction of the settling aragonite from dissolution. In the study the measured apparent calcite rate constant for a carbonate-rich sediment is two orders of magnitude lower than that determined from previous kinetic experiments on suspended sediment. Whether this is due to a diffusive boundary layer or other effects cannot be determined with certainty.

Small‐scale deformation structures and physical properties related to convergence in Japan Trench slope sediments

Diatomaceous mudstones, cored on DSDP legs 56/57 off Japan, contain numerous postdepositional veins, healed fractures, and microfaults. Beneath the forearc basin, these secondary structures occur only at depths greater than 620 m (Miocene) in a zone of normal faulting. Beneath the landward slope of the trench, however, they occur at depths as shallow as 250 m (Pliocene) in hemipelagic sediments which are inferred to blanket tectonically accreted deposits. The intensity of deformation in the trench slope deposits increases in a seaward direction. Bulk densities indicate that the trench slope deposits have not dewatered normally but are, above 400 m, more consolidated than sediment deposited on the deep sea terrace. A decline in sediment bulk density with increasing depth suggests that open fractures may exist in situ, perhaps induced and/or maintained by excess pore pressure. Below about 550 m, a normal pattern of increasing density with increasing depth may reflect fracture closure and consolidation under lithostatic load. We suggest that tectonic stress related to plate convergence has been communicated to the sediment on the landward Japan Trench slope, causing tectonic dewatering within the subduction complex and inducing pervasive but small‐scale veining, fracturing, and faulting in near‐surface (≤700 m) hemipelagic deposits. This deformation occurs in sediment which has not been subject to large tectonic movement and does not eradicate larger (50–100 m thick) structural/depositional units, which are apparent on seismic reflection records. The brecciation induced by deformation may reflect natural hydrofracturing under abnormally high pore pressures or opening of fractures formed earlier (at shallower depths) during the dewatering process. The overpressures may, in turn, locally reduce the sediment shear strength at shallow levels in the sediment column and induce downslope mass sediment movement.

Retention and fate of experimentally added mercury in a Massachusetts salt marsh treated with sewage sludge

A simple, rapid, precise and reproducible procedure is described for sample preparation, extraction and measurement of total mercury in peaty sediments, plants and animal tissues. Various amounts of a heavy metal containing dried sewage sludge were applied to experimental plots in a New England salt marsh. This treatment resulted in elevation of mercury levels in the surface 5 cm of the soil. Discrepancies in the bulk density of marsh sediments corresponded with interparticle spaces and detritus/mineral ratios in the peat matrix. Mass balance calculations showed that wetlands covered with tall Spartina alterniflora lost mercury considerable faster than higher marsh locations which retained virtually all mercury added. The shortest halflife of mercury calculated was four years. Grain size analyses of peat and sewage sludge suggested that mercury in the higher intertidal range remained associated with sludge components. Biochemical and physical processes affecting the dissipation of mercury from creek side sediments are discussed.

Bulk Density of Pelagic Sediments from the Equatorial Pacific Estimated from Carbonate Content, Age, and Subbottom Depth

ABSTRACT The bulk density of two sets of DSDP sediment samples from the central equatorial Pacific can be estimated using first and second order terms of carbonate percentage, depth below the seafloor and sediment age. The equations for the two data sets are essentially the same, and yield bulk density estimates that are comparable in accuracy to the experimental measurements.

Metal accumulation rates in the southeast pacific — errors introduced from assumed bulk densities

The common assumption that the in-situ dry bulk density of pelagic sediments is 0.7–0.75 g cm −3 can produce errors as great as 300–400% in metal accumulation rates. The best approach to obtain accumulation rates is to measure wet bulk density and water content. We show in this paper that if this is not possible, reasonable density and water content estimates in southeast Pacific sediments can be obtained from the CaCO 3 content of the sample. Although the specific equations derived in this paper do not apply to all areas of the ocean, the technique shown here can be used to take into account the special characteristics of any given sedimentary province and produce reasonable accumulation rate estimates.

Improved in situ gamma-ray transmission densitometer for marine sediments

The first-generation University of Illinois gamma-ray transmission densitometer, designed for the in situ measurement of sediment bulk density, was modified by incorporating in the detector probe (1) an Americium-241 alpha particle pulser and an anti-walk gain stabilization control to maintain better temperature stability and (2) a small power supply and a IC preamplifier to eliminate the need for a high-voltage coaxial cable between the detector and external signal conditioning electronics package. This second-generation Lehigh University system has been successfully deployed since 1971 in routine use from ships and submersibles in the Atlantic and Pacific Oceans and the Gulf of Mexico. Results are presented of system operations to (1) measure bulk density over the range of 1.2–1.8 Mg/m 3 in the Hudson Canyon, (2) penetrate 1.9 m into the seafloor in the San Diego trough and, (3) be lowered to a water depth of 3.6 km in the Gulf of Mexico.

Bulk Density--Water Content Relationship in Marine Silts and Clays

ABSTRACT Bulk density and water content are defined and then related to one another and to void ratio by 7 polynomial regression equations based on 1680 measured bulk density and water content values of water-saturated sediments from the Atlantic and Pacific Oceans and other areas. Theoretical relationships between bulk density, water content, and void ratio for specific gravities between 2.30 and 2.85 are demonstrated. The average specific gravity of 2.72 found for the data presented compares favorably to similar values reported in the literature. Use can be made of the regression equations to compute e log p sedimentation-compression curves entirely determined from the bulk density of water-saturated sediment measured nondestructively by laboratory or in situ nuclear transmission densitometers. In an example showing the consolidation of a fine-grained calcareous sediment from the Exuma Sound, Bahamas, the all-nuclear laboratory method compares favorably with the conventional, non-nuclear method of constructing e log p curves. The combination of suitable regression equations and the all-nuclear method is equally applicable to other fine-grained water-saturated sediments.

Theory of Nuclear Transmission Densitometry Applied to Sedimentology and Geotechnology

ABSTRACT A method of taking into account the changes in water content along the length of marine sediment cores analyzed by gamma ray attenuation is presented. Using previously established formulas, it is possible to choose calibration coefficients that will result in an error of less than 17 kg/m3 for the bulk density of most marine sediments while eliminating the task of estimating the water content of the sediment. Errors in bulk density due to errors in estimates of the chemical composition and grain density of the sediment are discussed.