The effect of particle size on the light attenuation coefficient of natural suspensions

Abstract

Laboratory calibration of a beam transmissometer by using natural sedimentary particles fractionated into seven size classes demonstrates that slopes of light attenuation vs. particle mass concentration regressions systematically vary with the size distributions of the particles. Suspensions with a mean particle size of 8.5 μm attenuate 660‐nm light 15 times more efficiently than suspensions of similar particles with a mean diameter of 48 μm. Theoretical calculations of attenuation, based on scattering by spherical particles with the measured size distributions, underestimate observed attenuation by factors of 2–4, apparently because the nonspherical shape and roughness typical of natural particles create an effective optical diameter larger than that for a sphere of equal volume. These laboratory results agree with the trend established from a survey of published field data showing that calibration slopes experience a steady increase from inshore high‐energy waters, where large particles are common, to offshore low‐energy waters, where large particles are rare.

Effects of upstream hydropower operation on riverine particle transport and turbidity in downstream lakes

“…Suspended particle concentrations (CL) were determined by the same procedure as for river samples. Since suspended matter in natural water consists of specific mixtures of different sizes and types of particles, calibration is required to determine CL based on in situ light transmission [Baker and Lavelle, 1984;Gordon et al, 1984;Hofmann and Dominik, 1995]. Light attenuation at 660 nm can unambiguously be related to particle concentrations assuming that the particle mixture is homogeneous and the attenuation by the water is constant [Boss et al, 2001].…”

230Th and 231Pa on GEOTRACES GA03, the U.S. GEOTRACES North Atlantic transect, and implications for modern and paleoceanographic chemical fluxes

“…In addition to increased particle loading, 197 bottom scavenging may also be affected by a change in particle composition. This section is also 198 well suited to test the hypotheses that 230 Th and 231 by transmissometer from CTD casts, which is, to first order, linearly related to particle 205 concentration (Bishop, 1986;Gardner et al, 1985), although the sensitivity of Cp to particle 206 concentration is known to vary with particle size and composition (Baker and Lavelle, 1984;207 Richardson, 1987). …”

North Atlantic Slope and Canyon Study; Volume 2

“…The error bars are ± 1 standard deviation of particle diameter or calibration Baker and Lavelle's experimental point at 106 ym where the mean diameter was estimated as the midpoint of the size range. The differences for natural sediment are probably due to differences in particle shape and the roughness of the natural sediment samples as discussed by Baker and Lavelle (1984).…”

“…(Sternberg and Creager, 1965;Drake and Cacchione, 1985;and Williams, 1985). Our laboratory calibrations of some of these sensors (presented in this paper) and those of Baker and Lavelle (1984) have shown that the proportionality constant between light attenuation A2-1 coefficient (c ) and suspended matter concentration (SMC) is a function of particle size. Therefore, a companion time series of suspended particle size is necessary to estimate SMC from these light transmission measurements.…”

“…Data from Baker and Lavelle (1984) are plotted using the symbols ( ) for natural sediment, ( Q ) for glass beads, and + for theoretical predictions. The error bars are ± 1 standard deviation of particle diameter or calibration Baker and Lavelle's experimental point at 106 ym where the mean diameter was estimated as the midpoint of the size range.…”