Determining Size Distributions and Composition of Particles Suspended in Water: A New SEM–EDS Protocol with Validation and Comparison to Other Methods

Abstract

Knowledge of particle size distributions (PSDs) in seawater is important for understanding several facets of marine science, such as the behavior of light scattering in seawater, phytoplankton dynamics, and biogeochemical cycling. Here, a method has been developed to quantify the size distribution of particle suspensions and characterize their chemical composition utilizing a scanning electron microscope (SEM) coupled with an energy dispersive spectrometer (EDS) and applying image analysis techniques, including automatic thresholding. The method was validated by verifying the PSD and chemical composition of the Arizona Test Dust (ATD), which has a well-documented size distribution and chemical composition. Size distributions of ATD particles containing specific elements important in the marine environment, such as silicon, iron, calcium, aluminum, and potassium, were quantified. PSDs determined with the technique in field samples from coastal Long Island Sound and the remote South Pacific were compared with other sizing methods, including electroresistivity and laser diffractometry. Most accurate results for PSD determinations occurred when the particle mass loading on the filter was between 0.04 and 0.1 mg cm−2. With this in mind, immediate feedback in the field can be provided to prepare appropriate filtration sample volumes due to a linear relationship between the beam attenuation coefficient at 650 nm (c650) and the total suspended matter (TSM). Overall, the method presents two defining advantages in 1) minimizing user bias, because the majority of the analysis is automated, and 2) providing an elemental distribution in the context of a particle size distribution.

The optical volume scattering function in a surf zone inverted to derive sediment and bubble particle subpopulations

“…The influence was intermittent as might be expected, with periods showing a return to the background condition (Figure 7g). In specific size ranges with minimum radius in the range of 0.6 [ Groundwater et al , 2012] to 6 μ m [ Buonassissi and Dierssen , 2010], the Junge‐type power law model provided a reasonable fit to aggregate distributions, with slopes between 3 and 4, typical of natural oceanic distributions [ Kitchen , 1977; Buonassissi and Dierssen , 2010; Groundwater et al , 2012].…”

“…Aggregate particle size distributions from all subpopulations picked by the inversion also could be modeled well ( r 2 > 0.9) with the commonly observed Junge‐type power law distribution when minimum radii used in previous studies were considered. Slopes of the fit were consistent with values reported in the literature [ Kitchen , 1977; Buonassissi and Dierssen , 2010; Groundwater et al , 2012]. Moreover, available evidence suggests the correct subpopulations were picked by the inversion and that their relative concentrations fell within reasonable ranges.…”

Evidence for ubiquitous preferential particle orientation in representative oceanic shear flows

“…Both active and passive remote sensing rely on interpreting the signature of backscattered light from the ocean to detect algal biomass, “thin layers” with high phytoplankton concentration, suspended particle mass, and to quantify biological primary productivity (Platt and Satyendranath ; Stramski and Kiefer ; Twardowski et al ; Churnside et al ). Thus, characterizing oceanic particulates based on type, size, and shape has been the focus of a multitude of studies over the past several decades (Jackson et al ; Boss et al ; Twardowski et al ; Groundwater et al ; Twardowski et al ).…”

Particle size distributions and organic-inorganic compositions of suspended particulate matters around the Bohai Strait

“…However, the labor-costing and time-consuming measurement processes of these traditional methods hinder the studies of PSD and SPM compositions (Groundwater et al, 2012). Thus, increasing efforts have been made to estimate the size structure of SPM at a high spatial and temporal resolution with remote-sensing methods Nair et al, 2008;Qing et al, 2014), while these methods only provide PSD information in the surface layer of seawater.…”