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

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 (b(m) and b(b.m)). Clay mineral particles, in the size range of 1-20 mu m, were the dominant form of minerogenic scattering, representing >75% of b(m) and b(b.m). Levels of b(m) and b(b.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 b(m) and b(b.m) was supported by the extent of optical closure obtained with paired bulk measurements of particulate scattering and backscattering coefficients (b(p) and b(bp)), and independent estimates of organic particle contributions based on empirical bio-optical models. Minerogenic particles dominated b(p) and particularly b(bp), and regulated spatial differences in the related common metrics of optical water quality, including turbidity and clarity. The b(bp):b(p) ratio was found to be a good predictor of the spatial differences in the relative contributions of minerogenic particles versus phytoplankton to scattering. (C) 2010 International Association for Great Lakes Research. Published by Elsevier B.V. All rights reserved.