Characterizations of individual suspended mineral particles in western Lake Erie: Implications for light scattering and water clarity

Abstract

Light-scattering attributes of minerogenic particles from the water column of the western basin of Lake Erie (13 sites, plus one from the central basin and one from Sandusky Bay), collected after a wind event, were characterized by scanning electron microscopy interfaced with automated image and X-ray analyses (SAX). SAX results specified scattering attributes for individual particles, including size and chemical composition, and were used in forward Mie theory calculations of minerogenic scattering and backscattering coefficients (bm and bb,m). Clay mineral particles, in the size range of 1–20μm, were the dominant form of minerogenic scattering, representing >75% of bm and bb,m. Levels of bm and bb,m were high in the western basin, apparently in part due to wind-driven sediment resuspension, and wide spatial variability was observed. The credibility of the SAX-Mie estimates of bm and bb,m was supported by the extent of optical closure obtained with paired bulk measurements of particulate scattering and backscattering coefficients (bp and bbp), and independent estimates of organic particle contributions based on empirical bio-optical models. Minerogenic particles dominated bp and particularly bbp, and regulated spatial differences in the related common metrics of optical water quality, including turbidity and clarity. The bbp:bp ratio was found to be a good predictor of the spatial differences in the relative contributions of minerogenic particles versus phytoplankton to scattering.