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Characterization of autochthonously produced calcite particles, along with the associated heteronuclei, and evaluation of their effects on light scattering, are advanced for lacustrine waters. This is supported by (1) direct measurement of minerogenic particle populations from 12 northeastern U.S. lakes with scanning electron microscopy interfaced with automated image and X-ray analyses (SAX), and (2) application of the previously tested SAX−Mie-theory approach to resolve the contributions of calcite vs. allochthonous minerogenic particles to particulate scattering and backscattering coefficients ( bp and bbp), and (3) comparison with organic contributions estimated through empirical bio-optics models. Intervals of substantial contributions of calcite to bp and bbp, described as 'whiting events,' are demonstrated for these study lakes. Organic particles, apparently from two size ranges, likely corresponding to pico- and nanocyanobacteria, are found to serve as the primary heteronuclei for the calcite precipitation. The coating of these particles with calcite within the upper waters of the study lakes remained thin. The calculated relative increases in bbp were substantially more than for bp because of the greater effect of the higher refractive index (i.e., n) of calcite for the former. Differences in n values for calcite reported in the literature are a source of noteworthy uncertainty in associated bbp estimates. Nine years of spring−fall monitoring in Cayuga Lake, New York, documented major interannual variations in the whiting events with respect to timing, magnitude of the scattering signatures, and the sizes of heteronuclei. Whiting events can have major effects on commonly monitored optical features, including Secchi depth and remote sensing reflectance. [ABSTRACT FROM AUTHOR]

The particulate scattering and backscattering coefficients ( bp and bbp) were partitioned into the additive contributions of minerogenic ( bm and bb,m) and organic ( bo and bb,o) components for nearshore and pelagic areas of Cayuga Lake, New York, over a 7 month period in 2013. The analysis was based on paired measurements of (1) bulk bp and bbp, (2) light-scattering properties of mineral particles, with an individual particle analysis (IPA) technique, and (3) concentrations of chlorophyll a ([Chl]) and particulate organic carbon (POC), as two indices to quantify organic particle scattering. bm and bb,m were estimated through Mie theory calculations with IPA results as inputs. bo and bb,o were estimated with both system-specific and oceanic bio-optical models parameterized on [Chl] or POC. POC performed better than [Chl] as the index for both bo and bb,o. The averages of the ratios ( bm + bo) : bp and ( bb,m + bb,o) : bbp at 660 nm, were 1.02 and 1.03, respectively; the average relative errors were 18.2% and 15.6%. Multiple empirical bio-optical models developed for Case 1 oceanic waters (for bo and bb,o estimates) approached the closure performance of the system-specific relationships. In addition to systematically accounting for more bbp than bp, terrigenous minerogenic particles made greater contributions to both bp and bbp in the nearshore area proximate to tributary inputs than in pelagic waters. A strong positive dependency of the backscattering ratio ( bbp : bp) on the bm : bp ratio was observed for both nearshore and pelagic areas. [ABSTRACT FROM AUTHOR]

The role of suspended minerogenic particles in light scattering in eastern Lake Superior and Keweenaw Bay (11 sites) during July of 2006 was evaluated with an individual particle analysis technique (scanning electron microscopy interfaced with automated image and X-ray analyses, SAX), along with bulk measurements of particulate scattering and backscattering coefficients (bp and bbp) and chlorophyll a concentration ([Chl]). SAX measurements provided information on light-scattering attributes of minerogenic particles, including chemical composition and particle size distribution (PSD). The data were used in Mie theory calculations for estimations of minerogenic scattering and backscattering coefficients (bm and bb,m). The bay had higher concentrations of minerogenic particles and higher values of bm, bb,m, bbp, and the backscattering ratio (bbp : bp) than the pelagic sites. Minerogenic scattering was primarily attributable to clay mineral particles in the size range of 1-10 mm. The PSDs deviated from the (Junge) pattern of monotonic increase of particle numbers with decreasing particle size. The estimates of bm and bb,m combined with those of organic particulate components, as represented by empirical Case 1 bio-optical models, showed reasonably good closure with bp and bbp, supporting the credibility of the SAX-Mie approach. Variations in the bbp : bp ratio are strongly related to spatial differences in the relative contributions of phytoplankton vs. minerogenic particles to scattering, with higher values observed where the minerogenic component is more important. SAX can advance the understanding of optical variability by establishing the contributions of well-defined minerogenic constituents that strongly influence optical properties. [ABSTRACT FROM AUTHOR]