Long‐term study of minerogenic particle optics in Cayuga Lake, New York

Abstract

The dynamics of light scattering by minerogenic particles in the upper waters of Cayuga Lake, New York, were characterized for the spring—autumn interval of 8 yr (1999–2006) at pelagic and nearshore sites with a scanning electron microscope interfaced with automated image and x‐ray analyses (SAX). SAX results were used to estimate the minerogenic scattering coefficient (bm) through Mie theory calculations. SAX—Mie supported a two‐component model for particulate scattering (bp) that included an organic component of scattering (bo), estimated from a bio‐optical model. The credibility of the bm estimates and the two‐component modeling approach was demonstrated through good closure of the modeling results with bulk values of bp (estimated from measurements of the beam attenuation coefficient at 660 nm). The average of the ratio bp : (bm + bo) was 1.03 (average relative error 19.4%). Two minerogenic particle types were important in regulating the dynamics of bm—clay minerals that increased in concentration in response to runoff events, and calcium carbonate precipitated mostly on small organic particles during short‐term late‐summer whiting events. bm was attributed to particles in the size range of 1–10 µm. Variations in bm dominated the overall variations in bp and Secchi disk depth; differences in bo explained well those observed in bp during dry weather intervals of low bm. Higher bm values, mainly associated with clay mineral particles, were observed at the nearshore site as opposed to the pelagic location; there was a positive linkage between these levels and tributary flow rate.