Effects Of Suspended Sediment Concentrations Research Articles

Effect of suspended sediment concentration on the clearance and biodeposition rates of an Australian freshwater mussel (Hyriidae: Alathyria jacksoni)

Abstract Freshwater mussels are an ancient group of molluscs that are considered ecosystem engineers because of the many important functions they perform, including biofiltration and biodeposition. Associations between mussel declines and increased sedimentation are well documented, but the direct effects of suspended sediment (SS) concentrations on mussel functioning are poorly understood. This study investigated the effects of SS concentrations on the clearance and biodeposition rates of the Australian hyriid river mussel Alathyria jacksoni. Clearance rates of algae and sediment and biodeposition rates were measured in aquaria containing 3 L of aerated water for 1 hr, with six different concentrations of SS (bentonite clay: 0, 1, 10, 40, 100 and 300 mg/L). Clearance rates were estimated using flow cytometry and chlorophyll‐a with both methods giving similar results. Biodeposition rates were estimated by weighing the mussel biodeposits at the end of each trial. We found that SS concentrations did not have a significant effect on the clearance rates of algae, which ranged from 0.033 to 0.438 L mussel−1 hr−1, with an overall median of 0.118 L mussel−1 hr−1. By contrast, increasing SS concentrations had a significant effect on the clearance of sediment from the water column, with clearance rates peaking at 10 mg/L and declining thereafter. Clearance rates of suspended sediment ranged from 0.046 to 0.512 L mussel−1 hr−1, with an overall median of 0.182 L mussel−1 hr−1. We further detected a significant effect of SS concentration on the production of biodeposits, with inorganic and organic content in the biodeposits increasing as sediment concentrations increased. These results indicated that as SS concentrations increase, A. jacksoni rejects more inorganic and organic material in the form of pseudofaeces. This added maintenance work may result in an energetic cost to the mussel, and have potential consequences for growth, reproduction, and survival. Finally, population estimates of A. jacksoni in the lower Ovens River, Australia were combined with the clearance rates observed in the experiment, to estimate the potential impact mussel populations have in the clearance of total suspended matter from the open water of an unregulated south‐eastern Australian lowland river. A. jacksoni occurred patchily throughout the 35‐km section of the river surveyed, with an average overall mean and maximum density of 0.68, and 35 individuals/m, respectively. We estimate that under scenarios of 1 and 300 mg/L SS, the lower Ovens River mussel population can potentially clear up to 2–4 ML water/day, which equates to c. 1–2% of the average daily discharge in late summer, while transferring around 5.4–15.6 kg/day dry weight of organic material to the river bed. Increased SS concentrations negatively affect freshwater mussels around the world and many respond by reducing their clearance rates, but this was not the case for A. jacksoni. Instead, A. jacksoni increased production of inorganic and organic biodeposits rejecting more food particles in the form of pseudofaeces. For A. jacksoni and other species showing this response, the added energetic cost has the potential to impact growth rates, reproduction, and population dynamics.

Two-dimensional distribution of stream-wise mean velocity in turbulent flow with effect of suspended sediment concentration

Two-dimensional distribution of stream-wise mean velocity in turbulent flow with effect of suspended sediment concentration

Experimental study on the effect of sediment concentration on trapezoidal hydraulic jump

The effect of suspended sediment concentration on the characteristics of a hydraulic jump in a symmetrical trapezoidal channel was studied experimentally and compared with a classic jump. The first test series of the classical jump was performed in a rectangular flume, while the second series was conducted with two different trapezoidal side slopes. In both cases, the tests were conducted under clear water and with different concentrations (4, 8 and 12%) of fine sand of 0.22 mm as suspended sediment. The results of the tests showed that, with an increase in sediment concentration, the jump length ratio and the sequent depth ratio decreased and the energy dissipation increased. The present study considered three different sections (two sections of trapezoidal shape with side slopes of 60° and 75° and one rectangular section). A comparison of the results in flow with Fr1 = 10 for all three sections for a sediment concentration of 12% with clear water showed that the jump length ratio decreased by 14%, 22% and 18%, the sequent depth ratio decreased by 12%, 21% and 31% and the energy dissipation ratio increased by 9%, 12% and 11%, respectively. Some dimensionless relations for the prediction of jump characteristics were also developed.

The impact of short-term exposure to near shore stressors on the early life stages of the reef building coral Montipora capitata.

Successful reproduction and survival are crucial to the continuation and resilience of corals globally. As reef waters warm due to climate change, episodic largescale tropical storms are becoming more frequent, drastically altering the near shore water quality for short periods of time. Therefore, it is critical that we understand the effects warming waters, fresh water input, and run-off have on sexual reproduction of coral. To better understand the effects of these near shore stressors on Hawaiian coral, laboratory experiments were conducted at the Institute of Marine Biology to determine the independent effects of suspended sediment concentrations (100 mg l−1 and 200 mg l−1), lowered salinity (28‰), and elevated temperature (31 °C) on the successful fertilization, larval survival, and settlement of the scleractinian coral Montipora capitata. In the present study, early developmental stages of coral were exposed to one of three near shore stressors for a period of 24 h and the immediate (fertilization) and latent effects (larval survival and settlement) were observed and measured. Fertilization success and settlement were not affected by any of the treatments; however, larval survival was negatively affected by all of the treatments by 50% or greater (p > 0.05). These data show that early life stages of M. capitata may be impacted by near shore stressors associated with warming and more frequent storm events.

Impacts of turbidity on corals: The relative importance of light limitation and suspended sediments

As part of an investigation of the effects of water quality from dredging/natural resuspension on reefs, the effects of suspended sediment concentrations (SSCs) (0, 30, 100mgL−1) and light (~0, 1.1, 8.6molphotonsm−2d−1) were examined alone and in combination, on the corals Acropora millepora, Montipora capricornis and Porites spp. over an extended (28d) period. No effects were observed at any sediment concentrations when applied alone. All corals in the lowest light treatments lost chlorophyll a and discoloured (bleached) after a week. Coral mortality only occurred in the two lowest light treatments and was higher when simultaneously exposed to elevated SSCs. Compared to water quality data collected during large dredging programs and natural resuspension events (and in the absence of sediment deposition as a cause-effect pathway) these data suggest the light reduction associated with turbidity poses a proportionally greater risk than effects of elevated SSCs alone.

A data reconnaissance on the effect of suspended-sediment concentrations on dissolved-solids concentrations in rivers and tributaries in the Upper Colorado River Basin

The Colorado River is one of the most important sources of water in the western United States, supplying water to over 35 million people in the U.S. and 3 million people in Mexico. High dissolved-solids loading to the River and tributaries are derived primarily from geologic material deposited in inland seas in the mid-to-late Cretaceous Period, but this loading may be increased by human activities. High dissolved solids in the River causes substantial damages to users, primarily in reduced agricultural crop yields and corrosion. The Colorado River Basin Salinity Control Program was created to manage dissolved-solids loading to the River and has focused primarily on reducing irrigation-related loading from agricultural areas. This work presents a reconnaissance of existing data from sites in the Upper Colorado River Basin (UCRB) in order to highlight areas where suspended-sediment control measures may be useful in reducing dissolved-solids concentrations. Multiple linear regression was used on data from 164 sites in the UCRB to develop dissolved-solids models that include combinations of explanatory variables of suspended sediment, flow, and time. Results from the partial t-test, overall likelihood ratio, and partial likelihood ratio on the models were used to group the sites into categories of strong, moderate, weak, and no-evidence of a relation between suspended-sediment and dissolved-solids concentrations. Results show 68 sites have strong or moderate evidence of a relation, with drainage areas for many of these sites composed of a large percentage of clastic sedimentary rocks. These results could assist water managers in the region in directing field-scale evaluation of suspended-sediment control measures to reduce UCRB dissolved-solids loading.

Effects of suspended sediment concentration and grain size on three optical turbidity sensors

Optical turbidity sensors have been successfully used to determine suspended sediment flux in rivers, assuming the relation between the turbidity signal and suspended sediment concentration (SSC) has been appropriately calibrated. Sediment size, shape and colour affect turbidity and are important to incorporate into the calibration process. This study evaluates the effect of SSC and particle size (i.e. medium sand, fine sand, very fine sand, and fines (silt + clay)) on the sensitivity of the turbidity signal. Three different turbidity sensors were used, with photo detectors positioned at 90 and 180 degrees relative to the axis of incident light. Five different sediment ratios of sand:fines (0:100, 25:75, 50:50, 75:25 and 100:0) were also evaluated for a single SSC (1000 mg l-1). The photo detectors positioned at 90 degrees were more sensitive than sensor positioned at 180 degrees in reading a wide variety of grain size particles. On average for the three turbidity sensors, the sensitivity for fines were 170, 40, and 4 times greater than sensitivities for medium sand, fine sand, and very fine sand, respectively. For an SSC of 1000 mg l-1 with the treatments composed of different proportions of sand and fines, the presence of sand in the mixture linearly reduced the turbidity signal. The results indicate that calibration of the turbidity signal should be carried out in situ and that the attenuation of the turbidity signal due to sand can be corrected, as long as the proportion of sand in the SSC can be estimated.

Acceleration of Denitrification in Turbid Rivers Due to Denitrification Occurring on Suspended Sediment in Oxic Waters

High suspended sediment (SPS) concentration exists in many rivers of the world. In the present study, the effects of SPS concentration on denitrification were investigated in airtight chambers with sediment samples collected from the Yellow River which is the largest turbid river in the world. Results from the nitrogen stable ((15)N) isotopic tracer experiments showed that denitrification could occur on SPS in oxic waters and the denitrification rate increased with SPS concentration; this was probably caused by the presence of low-oxygen microsites in SPS. For the water systems with both bed-sediment and SPS, the denitrification kinetics fit well to Logistic model, and the denitrification rate constant increased linearly with SPS concentration (p < 0.01). The denitrification caused by the presence of SPS accounted for 22%, 38%, 53%, and 67% of the total denitrification in systems with 2.5, 8, 15, and 20 g L(-1) SPS, respectively. The activity of denitrifying bacteria in SPS was approximately twice that in bed-sediment, and the denitrifying bacteria population showed an increasing trend with SPS concentration in both SPS and bed-sediment, leading to the increase of denitrification rate with SPS concentration. Furthermore, the denitrification in bed-sediment was accelerated by increased diffusion of nitrate from overlying water to bed-sediment under agitation conditions, which accompanied with the presence of SPS. When with 8 g L(-1) SPS, approximately 66% of the increased denitrification compared to that without SPS was attributed to denitrification on SPS and 34% to agitation conditions. This is the first report of the occurrence of denitrification on SPS in oxic waters. The results suggest that SPS plays an important role in denitrification in turbid rivers; its effect on nitrogen cycle should be considered in future study.

Submerged hydraulic jump with sediment-laden flow

In this experimental study, the effect of suspended sediment concentration on the characteristics of a submerged hydraulic jump in a rectangular channel has been investigated, based on the sediment concentrations of 0.43%-16.15% and jet Froude numbers were in the range of 1.9-5. Two grain sizes, 0.15 and 0.03 mm (ρs=2.65 g/cm3) have been used in the experiments. Characteristics of the submerged hydraulic jump including the submergence depth at the gate, length of submerged hydraulic jump, energy dissipation, velocity, and concentration distribution have been studied in both smooth and rough beds. Results showed that the submergence depth at the gate and the energy dissipation were constant regardless of sediment concentration. However, in the presence of suspended sediment, the length of the submerged hydraulic jump is smaller than that of clear water flow. It was also found that suspended sediment increase flow resistance, as a result of decreased in the maximum flow velocity.

Effect of suspended sediment concentration on local scour around cylinder for clay–sand mixed sediment beds

Suspended sediments present in the flow are known to affect the flow resistance, velocity distribution and turbulent characteristics. Experiments were conducted in the laboratory flume to see the effect of suspended sediment concentration (SSC) on local scour around a cylindrical pier for a wide range of clay–sand mixed sediment beds for SSC up to 2700 mg/L. It has been observed that the effect of SSC on equilibrium scour hole parameters such as maximum equilibrium scour depth, and longitudinal and transverse extent of scour hole can be significant. Present data showed that the presence of SSC in the range 993–1332 mg/L can increase maximum equilibrium scour depth as much as 1.54 times compared to the clear water case. However, tests made for SSC in the range 2456–2700 mg/L showed that the maximum equilibrium scour depth reduced compared to that for SSC in the range 993–1332 mg/L, but these maximum equilibrium scour depths were still larger than that obtained for clear water. The effect of SSC on time variation of scour and equilibrium scour hole geometry was further investigated.

Effects of suspended sediment concentration and turbulence on settling velocity of cohesive sediment

Using a 5-MHz acoustic Doppler velocimeter (ADV), laboratory experiments were carried out to investigate the effects of suspended sediment concentration (SSC) and turbulence on the settling velocity (ws) of cohesive sediment. The measurement of ws with the Clay Bank sediment showed that ws increased non-linearly with SSC in the range of 300–700 mg L−1, and that turbulence can increase ws up to one order higher than ws for nonturbulent conditions. This turbulence effect can explain why ws derived by ADV is 1 to 3 orders higher than ws estimated by Owen tube where the ambient turbulence is totally blocked. When the turbulent shear stress was higher than about 0.14 Pa, however, it contributed to tear apart flocs and reduce ws. This study suggests that ADV is a useful tool to concurrently measure the instantaneous current velocities, SSC and ws in turbulence-dominant environments without breaking up flocs and disturbing ambient flow.

Effect of Suspended-Sediment Concentration on Nitrification in River Water: Importance of Suspended Sediment−Water Interface

High suspended sediment (SPS) concentrations exist in many Asian river systems. In this research, the effects of SPS concentration on nitrification in river water systems were studied. With orwithout introducing ammonium-oxidizing bacteria isolated from the water and sediment samples of the Yellow River, the microbially mediated nitrification rate increased with SPS concentration as described by the power function y = a x x(b), where y is the nitrification rate, x is the SPS concentration, and a and b are constants. With an indigenous ammonium-oxidizing bacteria, nitrification rate constants, i.e., K4 (micromax/Ks) values obtained from the Monod model, were 0.0016, 0.0036, 0.0040, 0.0063, 0.0066, 0.0071, and 0.0077 day(-1) microM(-1) for the systems with SPS concentrations of 0, 0.2 1.0, 5.0, 10, 20, and 40 g/L, respectively. The sorption percentage of NH4+-N increased with SPS concentration as a power function. Bacteria tend to attach onto SPS, and the maximum specific growth rate at the SPS-water interface was about twice that in the water phase. An increase of bacterial population and nitrification rate constant with SPS as a power function resulted in an increase of nitrification rate with SPS as a power function. Therefore, the high SPS concentration caused by erosion and bottom sediment resuspension and other factors will accelerate ammonium oxidation in many turbid river systems. This has useful implications for nitrogen removal from river systems.

Spectrally based remote sensing of river bathymetry

AbstractThis paper evaluates the potential for remote mapping of river bathymetry by (1) examining the theoretical basis of a simple, ratio‐based technique for retrieving depth information from passive optical image data; (2) performing radiative transfer simulations to quantify the effects of suspended sediment concentration, bottom reflectance, and water surface state; (3) assessing the accuracy of spectrally based depth retrieval under field conditions via ground‐based reflectance measurements; and (4) producing bathymetric maps for a pair of gravel‐bed rivers from hyperspectral image data. Consideration of the relative magnitudes of various radiance components allowed us to define the range of conditions under which spectrally based depth retrieval is appropriate: the remotely sensed signal must be dominated by bottom‐reflected radiance. We developed a simple algorithm, called optimal band ratio analysis (OBRA), for identifying pairs of wavelengths for which this critical assumption is valid and which yield strong, linear relationships between an image‐derived quantity X and flow depth d. OBRA of simulated spectra indicated that water column optical properties were accounted for by a shorter‐wavelength numerator band sensitive to scattering by suspended sediment while depth information was provided by a longer‐wavelength denominator band subject to strong absorption by pure water. Field spectra suggested that bottom reflectance was fairly homogeneous, isolating the effect of depth, and that radiance measured above the water surface was primarily reflected from the bottom, not the water column. OBRA of these data, 28% of which were collected during a period of high turbidity, yielded strong X versus d relations (R2 from 0·792 to 0·976), demonstrating that accurate depth retrieval is feasible under field conditions. Moreover, application of OBRA to hyperspectral image data resulted in spatially coherent, hydraulically reasonable bathymetric maps, though negative depth estimates occurred along channel margins where pixels were mixed. This study indicates that passive optical remote sensing could become a viable tool for measuring river bathymetry. Copyright © 2009 John Wiley &amp; Sons, Ltd.

The effects of suspended sediment concentration on turbulence in an annular flume

The effect of suspended sediment concentrations (SSC) on fluid turbulence in an annular flume was investigated. Flow speed was held constant at 0.57 m s−1, and the resulting turbulent conditions were recorded using a 3-D Acoustic Doppler Velocimeter (ADV) at height (z) of 8.5 cm above the bed. The suspended material was composed of a natural glacial clay made up of particles smaller than 6 μm. The SSC in the flume were increased from clear water to 4800 mg l−1 in nine discrete increments; temporal variations of SSC were monitored using three optical backscatter sensors (OBS) mounted in the flume wall at heights of 0.03, 0.10 and 0.20 m above the flume base. The results showed that turbulent intensity ( $$\overline { {q}^{2}}/ \overline {U} ^{2}$$ ) and energy dissipation rate (ɛ) did not change significantly between clear water and 200 mg l−1, but decreased by nearly 30% in the SSC range between 200 and 2400 mg l−1. Above 2400 mg l−1, no further decrease was observed. Analyses of the velocity variances over narrow frequency bands (0.2 Hz wide) from 0 to 12.5 Hz showed that most of the flow turbulent energy (~70–80%) was contained within the lower frequencies i.e. larger eddies, and that these eddies experienced the greatest decrease in energy due to turbidity. It is proposed that these patterns are the consequence of the increase in suspended sediment concentrations and of the vertical stratification of sediments for SSC >200 mg l−1.

The effect of suspended sediment concentration on the settling velocity of cohesive sediment in quiescent water

A laboratory study was carried to qualitatively investigate the effect of suspended sediment concentration C on the settling velocity w s of cohesive sediment in quiescent water. A bay mud sample was mixed with water in a cylindrical container, and three optical back scatterance sensors were then used to measure suspended sediment concentrations of the mud–water mixture at three levels every 15 s for 5 h while sediments were settling in the quiescent water. Based on the measured sediment concentrations, the settling velocities at different concentrations were derived from the depth-integrated mass balance equation. This study has found that the settling velocity w s is independent of C in the free settling regime of C<0.3 g/l, and then increases nonlinearly with C in the enhanced settling regime of 0.3< C<4.3 g/l, and finally decreases sharply with C in the hindered settling regime of C>4.3 g/l. The maximum settling velocity occurs at C≈4.3 g/l and is about nine times faster than the settling velocity in the free settling regime. A single empirical formula is also proposed to calculate the settling velocities at different sediment concentrations.

Oil Erosion in an Annular Flume by Seawater of Varying Turbidities: A Critical Bed Shear Stress Approach

Laboratory experiments were conducted in an annular flume using Hibernia crude oil to determine: (1) the critical shear stress ( τ c) necessary to remove stranded oil from a surface by resuspension and (2) the effect of suspended sediment concentrations (SSCs) on the oil erosion processes. Two types of erosion were evident: Type I––solution and erosion of soluble aromatics; and Type II––mass erosion of visible droplets. In particulate free seawater at 13 °C, the Type II erosion threshold τ cII is 5.0 Pa. This is equivalent to a mean current velocity ( U y ) of 0.55 m s −1. At U y values <0.55 m s −1, Type I erosion occurred as shown by the increase of oil concentrations without visible erosion of the oil surface. Temperature has a strong control on the threshold and rate of oil erosion: the threshold for Type I erosion at 4 °C was higher and erosion rate lower than at 13 °C. No Type II erosion was observed at 4 °C. SSCs also affects the entrainment of oil. Oil erosion was most efficient at moderate SSCs. At very high SSCs, turbulence suppression and drag reduction became effective and oil erosion rate decreased. SSC at 200–250 mg l −1 were observed to give maximum erosion efficiency and is therefore suggested as the optimal concentration for erosion and elimination of heavy crude oil at a water temperature of 13 °C.

Effect of suspended sediment concentration on the sediment to water partition coefficient for 1,3,6,8-tetrachlorodibenzo-p-dioxin

Determination du coefficient de partage K p dans un systeme eau-sediment par des mesures de centrifugation

Effects of suspended sediments on geochemical processes near the mouth of the Amazon River: examination of biological silica uptake and the fate of particle-reactive elements

The effects of suspended-sediment concentration on the biological uptake of silica and the chemical behavior of particle-reactive elements are examined for the continental shelf waters near the mouth of the Amazon River. Dissolved silica and suspended-sediment concentrations measured during periods of high and low discharge indicate that uptake of dissolved silica begins where the suspended-sediment concentration falls below 10–20 mg l 1. Near the mouth of the Amazon River the 10 mg l 1 turbidity contour and the region of initial silica uptake both occur 20–40 km farther offshore during periods of high discharge (May and June) than during periods of low discharge (October and November). The location of initial silica uptake along an across-shelf transect near the river mouth varies by as much as 20 km on a time scale of days to weeks, which is comparable to the seasonal variation. Silica uptake, chlorophyll a concentration, and suspended-sediment concentration are poorly correlated along this transect (correlation coefficients range from +0.03 to −0.3). The poor correlations may be a result of grazing by zooplankton. Phaeopigment:chlorophyll a ratios increase offshore from 0 to 0.7, which supports the hypothesis that zooplankton grazing may be responsible for the low chlorophyll concentrations in the low-turbidity offshore waters exhibiting extensive silica removal. Excess 210Pb inventories for box cores collected from an across-shelf transect just south of the river mouth range from 21 to 124 dpm cm 2, which are 2–10 times greater than the inventory supported by atmospheric supply and in-situ production in the overlying water column. Riverine supply and lateral transport from offshore waters are the main sources of excess 210Pb to the Amazon continental shelf. 210Pb and 234Th data indicate that the high particulate flux from the Amazon River scavenges particle-reactive species not only from river water and continental shelf water but also scavenges these elements from offshore open-ocean water which flows onto the shelf.