Settling Of Suspended Particles Research Articles

An index concentration method for suspended load monitoring in large rivers of the Amazonian foreland

Abstract. Because increasing climatic variability and anthropic pressures have affected the sediment dynamics of large tropical rivers, long-term sediment concentration series have become crucial for understanding the related socioeconomic and environmental impacts. For operational and cost rationalization purposes, index concentrations are often sampled in the flow and used as a surrogate of the cross-sectional average concentration. However, in large rivers where suspended sands are responsible for vertical concentration gradients, this index method can induce large uncertainties in the matter fluxes. Assuming that physical laws describing the suspension of grains in turbulent flow are valid for large rivers, a simple formulation is derived to model the ratio (α) between the depth-averaged and index concentrations. The model is validated using an exceptional dataset (1330 water samples, 249 concentration profiles, 88 particle size distributions and 494 discharge measurements) that was collected between 2010 and 2017 in the Amazonian foreland. The α prediction requires the estimation of the Rouse number (P), which summarizes the balance between the suspended particle settling and the turbulent lift, weighted by the ratio of sediment to eddy diffusivity (β). Two particle size groups, fine sediments and sand, were considered to evaluate P. Discrepancies were observed between the evaluated and measured P, which were attributed to biases related to the settling and shear velocities estimations, but also to diffusivity ratios β≠1. An empirical expression taking these biases into account was then formulated to predict accurate estimates of β, then P (ΔP=±0.03) and finally α. The proposed model is a powerful tool for optimizing the concentration sampling. It allows for detailed uncertainty analysis on the average concentration derived from an index method. Finally, this model could likely be coupled with remote sensing and hydrological modeling to serve as a step toward the development of an integrated approach for assessing sediment fluxes in poorly monitored basins.

ДОСЛІДЖЕННЯ ВІДМІННОСТЕЙ ОРИГІНАЛЬНОГО ТА ДЖЕНЕРИЧНИХ ПРЕПАРАТІВ, ЩО МІСТЯТЬ БЕТАМЕТАЗОНУ ДИПРОПІОНАТ І БЕТАМЕТАЗОНУ НАТРІЮ ФОСФАТ

Мета роботи. Проведення дослідження, що дасть змогу виявити різницю між оригінальним і дженеричними препаратами, лікарські форми яких мають двофазний вміст бетаметазону (бетаметазону натрію фосфат у складі водного розчину і бетаметазону дипропіонат у вигляді суспензії в цьому розчині).Матеріали і методи. Використано оригінальний препарат бетаметазону натрію фосфату та бетаметазону дипропіонату у вигляді суспензії та його дженеричні аналоги, доступні на ринку України. Для оцінки кількості суспензії БМДП препаратів А, В, С, що перейшла у розчин 15 % водного ізопропанолу, нами була розроблена методика з використанням приладу «Лічильник числа та розміру часток в рідких середовищах» APSS-2000.Результати й обговорення. Здійснено візуальне вивчення механічної стабільності суспензій у запаяних ампулах, що показало різну швидкість осідання суспендованих часток у досліджуваних препаратах. Вивчено можливий вплив розчинника (розчину лідокаїну) на швидкість та ступінь осідання часток. Виявлено, що дженеричні препарати В і С суттєво відрізняються від оригінального препарату А за розподілом маси суспензії бетаметазону дипропіонату за розмірами часток. В оригінального препарату А основну масу суспензії БМДП складають частинки меншого розміру, ніж у дженериків.Розроблено методику для визначення розчинності, за допомогою якої виявлено, що суспензія оригінального препарату А за 130 хв експозиції на орбітальному струшувачі розчиняється майже повністю (99 %), тоді як у дженериків В і С за цей час переходить (розчиняється) у водно-ізопропанольну фазу відповідно, лише 66 і 53 % кристалічної маси БМДП. Показано, що динаміка розчинення суспензії БМДП досліджуваних препаратів може бути відстежена з використанням приладу «Лічильник числа та розміру часток в рідких середовищах» APSS-2000.Висновки. Встановлено, що оригінальний препарат та його дженерики мають суттєві відмінності в розподілі за розмірами часток. Розроблено методику визначення розчинності оригінального препарату та дженериків. Вказана різниця стосується суспензії бетаметазону дипропіонату: дженерики відрізняються від оригінального препарату тим, що мають інший розподіл часток за розмірами, і, як наслідок, іншу поведінку в розроблених тестах на розчинність.

Sediment Resuspension and Deposition on Seagrass Leaves Impedes Internal Plant Aeration and Promotes Phytotoxic H2S Intrusion.

HIGHLIGHTS: Sedimentation of fine sediment particles onto seagrass leaves severely hampers the plants' performance in both light and darkness, due to inadequate internal plant aeration and intrusion of phytotoxic H2S.Anthropogenic activities leading to sediment re-suspension can have adverse effects on adjacent seagrass meadows, owing to reduced light availability and the settling of suspended particles onto seagrass leaves potentially impeding gas exchange with the surrounding water. We used microsensors to determine O2 fluxes and diffusive boundary layer (DBL) thickness on leaves of the seagrass Zostera muelleri with and without fine sediment particles, and combined these laboratory measurements with in situ microsensor measurements of tissue O2 and H2S concentrations. Net photosynthesis rates in leaves with fine sediment particles were down to ~20% of controls without particles, and the compensation photon irradiance increased from a span of 20–53 to 109–145 μmol photons m−2 s−1. An ~2.5-fold thicker DBL around leaves with fine sediment particles impeded O2 influx into the leaves during darkness. In situ leaf meristematic O2 concentrations of plants exposed to fine sediment particles were lower than in control plants and exhibited long time periods of complete meristematic anoxia during night-time. Insufficient internal aeration resulted in H2S intrusion into the leaf meristematic tissues when exposed to sediment resuspension even at relatively high night-time water-column O2 concentrations. Fine sediment particles that settle on seagrass leaves thus negatively affect internal tissue aeration and thereby the plants' resilience against H2S intrusion.

A model of the vertical distribution of suspended sediment in the bottom layer of a natural water body

The paper suggests a stationary model of the vertical distribution of the concentration of suspended sediment in the bottom layer of a natural water body with a flat bottom. The model explains the concentration distribution, formed jointly by the settling of suspended particles and turbulent diffusion. The flow is assumed geostrophic above the bottom-influenced layer, while in the bottom layer the effect of turbulent diffusion by the large-scale turbulence constituent is assumed to dominate over the diffusion effect caused by the small-scale turbulence constituent. It is shown that for the characteristic diffusion length scale of the eddies much smaller than the height of the Ekman bottom boundary layer the model results in an analytic expression for the vertical distribution of the concentration of suspended sediment, which includes also the case with the presence of the lutocline. The model outcome is compared with the results of a laboratory experiment with sand-injected flume flow.

Water quality in a non-traditional off-stream polyethylene-lined reservoir

Annual water storage in a 5.3 ha, polyethylene-lined, off-stream irrigation reservoir in northern Alabama, USA, resulted in marked improvement in water quality. Results of three-year monitoring from June 1999 to May 2002 indicate that the relatively static conditions of the reservoir enhanced settling of suspended particles by 85% (from 14.4 to 2.1 mg TSS/L) that cleared the water and increased sunlight penetration. The organic and inorganic particles that settled to the bottom removed up to 88% of the nutrients and other chemical substances from the water. Nutrients remaining in the water column were rapidly assimilated by phytoplankton algae. With the basin sealed at the bottom and no runoff input there was limited opportunity for nutrients or other substances to enter the reservoir in quantities that would adversely affect water quality. Consequently, reservoir water was found to be of high quality and suitable as a raw water supply. Non-traditional, off-stream storage reservoirs such as described in this paper may be uniquely suited for agricultural irrigation and public water supply in regions such as southeastern US that experience relatively frequent drought conditions but have relatively abundant long-term annual rainfall.

Sediment Trapping and Transport in the ACE Basin, South Carolina

A study took place during May 1998 and May 1999 to examine the processes controlling localized accumulation of fine-grained sediments in the lower Ashepoo River. This region, referred to as the Mud Reach, is an area of muddy bottom sediments bounded by fine sands. The Mud Reach is located downstream of the landward extent of the salt intrusion where an estuarine turbidity maximum commonly occurs. Tidal time-series measurements made in the Mud Reach during May 1998, when river discharge was at a 10-yr high, showed high concentrations of suspended sediment (0.05–1 g I−1) during maximum tidal current velocity with concentrations in the bottom 30 cm exceeding 70 g I−1 (fluid mud). A correlation between salinity stratification and increased suspended sediment concentration suggests that inhibited vertical mixing enhances the settling of flocculated sediments to the bed. Measurements made during May 1999 show a two-order-of-magnitude decrease in the concentration of near-bed sediments. A decrease in river discharge during the 1999 observation period of more than 100 m3 s−1 suggests that changes in the hydrography and in the supply of sediments to the system both may be important factors in the trapping of fine-grained sediments in the region. The source of sediments is likely from muddy deposits in the Fenwick Cut, a man-made section of the Atlantic Intracoastal Waterway about 2 km north of the Mud Reach that connects the Ashepoo and Edisto Rivers. The Fenwick Cut appears to be an effective area for trapping sediments where shoaling has increased by 130% in the last decade. Current measurements show that flow velocities decrease through the Cut, likely allowing for the settling of suspended particles that form the thick deposits of unconsolidated mud observed during both years.

Experimental and in situ study of radiocaesium transfer across the sediment–water interface and mobility in lake sediments

Experiments have been carried out to study the uptake of radiocaesium by sediment cores from Esthwaite Water, Cumbria, UK in order to test models to describe the simultaneous uptake of radiocaesium from the water column and diffusion of activity within the sediment. A new, simplified method of simulating time dependent diffusion of tracers in sediments is developed and tested. Comparison of experimental with field measurements showed that rates of diffusion of activity which had been introduced by diffusion across the sediment–water interface (as in the present experiments) were approximately one order of magnitude greater than those determined from in situ Chernobyl and weapons test activity–depth profiles. Measured total solids–aqueous distribution coefficient ( K d t )) values in the experiments were ca. 2000 l kg −1, more than one order of magnitude lower than those measured in situ (ca. 7×10 4 l kg −1). Much better agreement, however, was observed between the exchangeable distribution coefficients ( K d e), measuring ‘mobile’ Cs, which were ca. 2000 l kg −1 in the experiments and ca. 4900 l kg −1 in the field. Modelling the removal of Chernobyl radiocaesium from Esthwaite Water showed that the majority of the activity was transported to the sediments by attachment to and settling of suspended particles. It is concluded that activity deposited on particulates (forming the majority of activity observed in situ) was more strongly bound to sediments than that introduced by direct diffusion across the sediment–water interface, leading to significantly different mobility of these two fractions of 137Cs in sediments. Model sensitivity analyses showed that removal of activity across the sediment–water interface is more strongly influenced by diffusion within the sediments than by the thickness of the benthic boundary layer.

Radiocaesium removal from European lakes and reservoirs: key processes determined from 16 Chernobyl-contaminated lakes

A study based on information from the scientific literature was carried out to identify the key processes which determine the initial radiocaesium activity concentration and its rate of removal in 16 different European lakes after the Chernobyl accident. Analysis and modelling of these data showed that a simple model, incorporating only dilution, lake flushing and settling of suspended particles, can explain 97% of the variation in initial activity concentrations in lakewater and 79% of the variation in 137Cs removal rates. On the basis of currently available data, incorporating a simple model for removal of activity by diffusion across the sediment–water interface did not improve model predictive power. It is shown that direct diffusion was of less importance in determining radiocaesium removal rates than particle settling. The potassium concentration of the lakewater was found to have a significant, negative, covariance with 137Cs removal rates. The relationship between [K +] and removal rate is shown to be quantitatively consistent with previous studies on the binding mechanism of 137Cs to particulates.

Marine Tailings Disposal Simulation

The disposal of mine tailings in deep water body requires comprehensive assessment of the potential environmental impacts, and estimates of the effective storage capacity of the bottom bathymetry for accommodating the anticipated volume of disposed tailings over the life of a mine. A mathematical simulation model was developed for this purpose to predict the distribution and long-term deposition patterns of tailings in a fjord. The model describes the mechanics of the tailings slurry flow along the bottom of the receiving water body and the settling of suspended particles, as well as the redistribution of the deposited sediments due to slumping of unstable slopes. Specific processes simulated in the model also include entrainment at the top of the density current, entrainment associated with internal hydraulic jumps in areas of changing bottom slopes, hindered settling and coagulation of suspended particles, and sediment deposition and bathymetric changes resulting from the deposition of large quantities of tailings. Long-term tailings deposition patterns are predicted by analyzing the flow of the tailings slurry in a series of time increments, from a few months to a year. The bathymetry is assumed to remain unchanged within each time increment, and the model first simulates the steady-state flow field for the tailings slurry along the bottom and the resulting deposition rates for several sizes of suspended particles. Then the estimated tailings deposition rates are combined with slope stability considerations to predict the new bathymetry of the receiving water body. Data from several operating marine tailings disposal systems were reviewed to assess the applicability of specific relationships used in the model. The model was calibrated using data from one of the most extensively studied marine tailings disposal systems, the Island Copper mine in Rupert Inlet of Vancouver Island, British Columbia. Comparison of simulated tailings deposition patterns in Rupert Inlet with data from field observations and measurements suggests that calibration of the model is satisfactory and provides confidence in the capability of the model to predict deposition patterns and suspended sediment concentrations for proposed mines.

Effect of saline groundwater on the aggregation and settling of suspended particles in a turbid Australian river

Laboratory studies have modelled the interaction of Darling River water and a saline groundwater intrusion. Kinetic measurements have shown that the rate determining step in water column clarification is the aggregation of small colloidal particles which then settle rapidly after reaching a critical diameter. Divalent cations (Ca 2+ and Mg 2+) are extremely effective in enhancing the rate of clarification by increasing the colloid stability factor. Three different phases have been observed in the cation-mediated removal of iron from solution: (i) rapid coagulation induced by the initial velocity shear resulting from solution mixing; (ii) a slower second-order iron removal, consistent with conventional aggregation kinetics; and (iii) a decrease in rate after 90% iron removal which is attributed to a lower iron content in the ultrafine colloid fraction. Specific interactions between the divalent cations and the organic coatings on the particles are proposed in order to explain the much higher rate of coagulation than expected on electrostatic grounds when compared with the monovalent Na + and K +. Water column clarification occurred more rapidly in these model laboratory studies than was observed in the Darling River weir pool. Iron removal rates in the river tend to be inhibited by hydrological effects. Turbulence inducing processes are required to mix the dense saline groundwater with the overlying water column and thus may ultimately limit the rate of turbidity reduction.

Biodeposition by a Fouling Community in the Indian River, Florida

Biodeposition rates were studied for a fouling community with a biomass of 6–10 kg per m2 dry wt including shells in which the barnacle Balanus eburneus was a dominant species. The fouling community filtered Indian River lagoon water containing 2–15 mg per 1 mud-size particles and deposited them as sand-size fecal pellets. Measurements of the fecal pellet flux by sediment traps indicated seasonal variations between 16.7 and 74.8 g per m2 per day. A significant correlation was found between fecal pellet flux and temperature (r=0.90; p<0.001). The average flux of fecal pellet deposition was four times greater than the average flux of suspended particle settling without biological influence. Suspended sediment concentration did not significantly affect the rate of biodeposition. Annual biodeposition was 18 kg per m2.