Flocculation of Riverine Sediment Draining to the Great Barrier Reef, Implications for Monitoring and Modeling of Sediment Dispersal Across Continental Shelves

Livsey, D. L.; Crosswell, Joseph R.; Turner, Ryan; Steven, Andrew D. L.; Grace, Peter R.

doi:10.1029/2021jc017988

Cited by 10 publications

(24 citation statements)

References 73 publications

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“…Livsey et al. (2022) observed settling velocities of O (1 mm s −1 ) once silts and clays have flocculated; this value is also suggested by Strom and Keyvani (2016) as a first approximation.…”

Section: Discussionmentioning

confidence: 55%

From Particles to Flocs: Revealing Where Flocculation Occurs in the Nearfield of a Negatively‐Buoyant River Plume in a Large Lake (Lake Geneva)

Piton,

Lemmin,

Bourrin

et al. 2024

JGR Oceans

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The dynamics of sediments entering lakes in river plumes is virtually unknown. This field study provides unprecedented evidence of the initiation and evolution of suspended sediment flocculation in the nearfield of the negatively‐buoyant Rhône River plume, flowing as interflow in the thermocline of stratified Lake Geneva. Sediment floc property changes (formation, size, composition, shape) with depth and distance from the mouth, were determined by combining digital holographic camera LISST‐HOLO data with full‐depth in situ profiles of particle size (LISST‐100X), density, turbidity, currents and water samples taken along the plume path. The total suspended matter volume of inflowing Rhône River waters (∼155 mg l−1) mostly consisted of clays (<4 μm), very fine silts (4–8 μm) and small contributions of microflocs (20–100 μm). This composition was also found in the interflow plume core. Above the plume, in the epilimnion, fine silts, microflocs and numerous phytoplanktonic organisms (∼200 μm) were observed, representative of the lake background. High levels of shear (15–27 s−1) and turbulence occurred in the shear layer that formed between the interflow bottom and the hypolimnion below. It was found that macroflocs only formed in this shear layer. In the hypolimnion, sediment load was the lowest and macroflocs (up to ∼300 μm) composed of inorganic particles were dominant. The size of the largest flocs was limited by the size of the smallest turbulent eddies determined by the Kolmogorov microscale. Floc 3D fractal dimensions of ∼2.1–2.5 suggest an intermediate shape complexity between marine snow and sludge flocs.

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Section: Discussionmentioning

confidence: 55%

From Particles to Flocs: Revealing Where Flocculation Occurs in the Nearfield of a Negatively‐Buoyant River Plume in a Large Lake (Lake Geneva)

Piton,

Lemmin,

Bourrin

et al. 2024

JGR Oceans

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“…V rms , MB, OBS, and particle size measurements from Livsey et al. (2022) were time‐averaged to one‐minute bursts when the profiling package and/or US‐P61 sampler was held at a constant depth. The one‐minute bursts, although exceeding the US‐P61 filling time, was chosen to improve the signal‐to‐noise ratio in acoustic backscatter (Thorne & Hurther, 2014) and particle size measurements (Mikkelsen & Pejrup, 2001).…”

Section: Methodsmentioning

confidence: 99%

“…Averaging of V rms , MB, OBS, M and particle size measurements was readily undertaken in the Chesapeake Bay and Brisbane River datasets with averaging time for all measurements set to the peristaltic pump filling times. V rms , MB, OBS, and particle size measurements from Livsey et al (2022) were time-averaged to one-minute bursts when the profiling package and/or US-P61 sampler was held at a constant depth. The one-minute bursts, although exceeding the US-P61 filling time, was chosen to improve the signal-to-noise ratio in acoustic backscatter (Thorne & Hurther, 2014) and particle size measurements (Mikkelsen & Pejrup, 2001).…”

Section: Data Processingmentioning

confidence: 99%

“…Salinity is used as an initial estimate of changes in n f as Livsey et al (2022) found that the log of ρ bulk decreased with the log of salinity (R 2 = 0.95, p-value <0.001, n = 21). The decrease in ρ bulk with salinity is thought to reflect a decrease in n f driven by an increase in marine-derived particulate organic matter offshore (Livsey et al, 2022). R 2 for the prediction of log 10 (a o ) from SCI dB for the Normanby River, Olive River, and Escape Estuary data combined (n = 244) is 0.62, while, adding log 10 (salinity) increased R 2 to 0.89 (n = 242).…”

Section: 1029/2022wr033982mentioning

confidence: 99%

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Combining Optical and Acoustic Backscatter Measurements for Monitoring of Fine Suspended‐Sediment Concentration Under Changes in Particle Size and Density

Livsey

Turner

Grace

2023

Water Resources Research

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Optical and acoustic backscatter measurements are routinely utilized to monitor suspended‐sediment concentration (M); however, both measurements are affected by changes in particle size and density. In this study, optical and acoustic backscatter measurements are combined to a single parameter, the sediment composition index (SCI), to quantify M, mean particle radius by number (ao), the fraction of sediment <20 μm by diameter (), and particle bulk apparent density (ρbulk). Data are analyzed from Chesapeake Bay and five rivers of Queensland, Australia. SCI is utilized to predict the ratio of M to acoustic backscatter under changes in ao and ρbulk (R2 ranged from 0.6 to 0.98 across all data sets) and combined with acoustic backscatter to predict estimates of M that are independent of changes in ao and ρbulk. SCI is proportional to log10(ao) and for SCI from acoustic backscatter measured at 6 MHz (R2 = 0.8 and 0.74, respectively, p‐value < 0.001, n = 133), while SCI(log10(ao)) and SCI() from acoustic backscatter measured at 2 MHz or lower are sensitive to changes in floc fractal dimension. Estimates of ρbulk from SCI are biased by changes in particle size (R2 is 0.1–0.5 across all datasets). This study builds upon recent work that derived SCI to quantify composition of sand and mud in suspension and demonstrates the utility of the approach in systems transporting flocculated silt and clay. Future research directions are discussed.

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“…Even more uncertainty is introduced when measuring ex situ, where sample collection (e.g., grab sampling, using Niskin bottles, or automatic samplers), sample storage (including storage duration and temperature), sample treatment (e.g., pre‐sieving, oxidation, or chemical dispersion) and transportation become necessary (Gartner et al., 2001). Many studies (Boss et al., 2018; Chakraborti et al., 2009; Czuba et al., 2015; Federal Interagency Sedimentation Project, 1941; Livsey et al., 2022; Phillips & Walling, 1995; Zhao et al., 2018) attempt to understand and quantify the individual uncertainties associated with each of the above‐mentioned choices. The LISST series of instruments developed by Sequoia (LISST‐100X/200X and LISST‐SL) are commonly used for in situ measurements.…”

Section: Introductionmentioning

confidence: 99%

The Impact of Flocculation on In Situ and Ex Situ Particle Size Measurements by Laser Diffraction

de Lange,

Sehgal,

Martínez‐Carreras

et al. 2023

Water Resources Research

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Accurate particle size distribution (PSD) measurements of suspended particulate matter (SPM) composed of flocs and aggregates are important to improve understanding of ecological and geomorphological processes, and for environmental engineering applications. PSDs can be measured in situ (in the field) using a submersible sensor, or ex situ (in the laboratory) using samples. The methodological choice is often guided by logistical factors, and the differences in PSDs acquired by in situ and ex situ measurements is of concern. In this study, a laser‐diffraction instrument (the LISST‐200X) was used to compare in situ and ex situ PSD measurements. Samples measured ex situ were stored for three consecutive weeks and measured each week in a laboratory using different stirrer speeds. We observed that ex situ measurements display a higher D50 (median particle size) than in situ measurements of the same sample (up to 613% larger, 112% on average). Our experiments show that the difference between in situ and ex situ measurements can be explained by flocculation of the riverine sediments during the first week of storage. During the subsequent ex situ measurements, the stirring results in a significantly lower D50. Ex situ measurements are therefore unsuitable for flocculated SPM. This study provides recommendations for optimizing PSD measurements by calculating the measurement times required to obtain robust PSD measurements (exceeding 3 min per sample), which are larger for field samples with coarser particles and wider PSDs.

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Flocculation of Riverine Sediment Draining to the Great Barrier Reef, Implications for Monitoring and Modeling of Sediment Dispersal Across Continental Shelves

Cited by 10 publications

References 73 publications

From Particles to Flocs: Revealing Where Flocculation Occurs in the Nearfield of a Negatively‐Buoyant River Plume in a Large Lake (Lake Geneva)

From Particles to Flocs: Revealing Where Flocculation Occurs in the Nearfield of a Negatively‐Buoyant River Plume in a Large Lake (Lake Geneva)

Combining Optical and Acoustic Backscatter Measurements for Monitoring of Fine Suspended‐Sediment Concentration Under Changes in Particle Size and Density

The Impact of Flocculation on In Situ and Ex Situ Particle Size Measurements by Laser Diffraction

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