CHARACTERIZATION OF INORGANIC PARTICLES IN SELECTED RESERVOIRS AND TRIBUTARIES OF THE NEW YORK CITY WATER SUPPLY¹

Abstract

Individual particle analysis (IPA) by scanning electron microscopy interfaced with automated image and X-ray analyses was used to characterize inorganic particles in five reservoirs and four tributaries located within the Catskill and Delaware systems of the New York City water supply. Individual particle analysis provides combined elemental and morphologic characterizations. Results are presented in terms of particle projected area per unit volume (PAV), consistent with optical impacts, and partitioned into seven generic particle types according to composition. Minerals of terrigenous origins, particularly clay minerals, dominated the inorganic particle populations of all the study systems except one downstream reservoir. Higher PAV levels were observed in the Catskill system. Particle dynamics represented by PAV were driven primarily by runoff, while the reservoirs were also greatly influenced by the timing of sediment resuspension promoted by drawdown of the surface and fall mixing. The benefit of the serial configuration of the reservoirs in decreasing inorganic particles with progression downstream towards the city is demonstrated. The patterns in PAV levels among the study systems generally tracked those of more common metrics of impacts of suspensoids, including mass concentrations of suspended solids, turbidity, and Secchi disc transparency.

Suspended minerogenic particles in a reservoir: Light‐scattering features from individual particle analysis

“…SAX protocols-Sample preparation and analytical procedures for SAX characterizations have been described previously (Peng et al 2002;Peng and Effler 2005). Suspended particles were deposited onto polycarbonate membranes (25-mm diameter, 0.4-mm pore size) by pressure filtration and then carbon coated (thickness ,40 nm) before analysis.…”

“…Elemental composition of a particle is represented by its normalized elemental X-ray counts, that is, relative intensities. Particles were biogeochemically classified into seven generic types (Table 1) according to a scheme developed earlier for this reservoir and other local systems (Peng et al 2002): ''Organics,'' ''Clay,'' ''Si-rich,'' ''Quartz,'' ''Fe/Mn,'' ''Diatom,'' and ''Other'' (miscellaneous particles whose elemental X-ray composition does not fit into the criteria of one the specified types). The scheme is consistent with the mineralogy, geochemistry, and origins of particles for the study systems (Peng et al 2002.…”

“…Inorganic (or minerogenic) particles make substantial contributions to light scattering in many freshwater systems (Kirk 1985;Effler et al 2002b;Peng and Effler 2005) and Case 2 (coastal) waters (where the optical properties are influenced and often dominated by dissolved and particulate material of terrestrial origin other than algal cells with their retinue; Morel and Prieur 1977;Mobley et al 2004) and thus are important with respect to apparent optical properties (AOPs) and remote sensing (Woźniak and Stramski 2004). Partitioning of the total particle scattering coefficient (b(l); m 21 ), an inherent optical property (IOP), is often represented as the summation of organic (b o (l)) and minerogenic (b m (l)) components:…”

“…However, the populations (both the number of samples and the number of particles in each sample) characterized through such manual SEM techniques have been too small to advance the forward problem. SEM interfaced with automated X-ray microanalysis and image analysis (SAX) can assess PA i , d i , elemental Xray composition (thus the geochemical type and m i ), and shape for large numbers of inorganic particles over relatively short intervals (Johnson et al 1991;Peng et al 2002). This capability can support direct calculations of b m (l) (Eq.…”

“…1). Heretofore, applications of SAX have focused on either assessing origins of particles based on composition (Yin and Johnson 1984;Johnson et al 1991;Effler et al 1992) or establishing empirical relationships between the total projected area of inorganic particles per unit volume of water (PAV m ; the summation of PA i for N mineral particles) and AOPs (Effler et al 2002a,b;Peng and Effler 2005).…”