Hydrobiologia 468: 213–232, 2002. © 2002 Kluwer Academic Publishers. Printed in the Netherlands. 213 Tripton, transparency and light penetration in seven New York reservoirs ∗ Steven W. Effler 1 , MaryGail Perkins 1 , Nicholas Ohrazda 1 , David A. Matthews 1 , Rakesh Gelda 1 , Feng Peng 2 , David L. Johnson 2 & Carol L.Stephczuk 3 1 Upstate Freshwater Institute, P.O. Box 506, Syracuse, N.Y. 13214, U.S.A. 2 Dept. of Chemistry, College of Environmental Science and Forestry, State University of New York, Syracuse, N.Y. 13210, U.S.A. 3 New York City Department of Environmental Protection, Valhalla, N.Y. 10295, U.S.A. Received 6 March 2001; in revised form 16 October 2001; accepted 19 November 2001 Key words: optics, attenuation coefficient, Secchi disc, turbidity, clay, reservoirs Abstract Temporal patterns and inter-system differences in the attenuation coefficient for scalar irradiance (K s ), Secchi disc transparency (SD), several measures of tripton, and chlorophyll a (Chl) are documented for the lacustrine zones of seven reservoirs (nine distinct basins) in New York (U.S.A.), based on a single year of comprehensive measurements. Analyses of these data and historic (12 years) observations of SD and Chl, including application of empirical and deterministic modeling frameworks, demonstrate that inorganic tripton is the primary attenuating constituent responsible for the substantial differences in K s and SD among these basins, and the major temporal variations observed in these optical characteristics in most of the study basins. These inorganic particles, of ter- rigenous origins, are supplied directly to the water column of these basins in inflows, particularly during runoff events, and through the sediment resuspension process. Comparison of the measures of tripton indicates electron- microscopy-based measurements performed somewhat better than gravimetric analyses in explaining the variations in K s and SD in the lower concentration systems. Increases in average SD values by factors of 2–5, compared to prevailing values, are predicted for the study basins with the deterministic model for the case of no tripton. Introduction The behavior of light in water, particularly its at- tenuation with depth, has important ecological and water quality implications. The extent of light pen- etration can be an important regulator of features of density stratification (Effler & Owens, 1985), and it establishes the vertical limit of primary production (e.g. photic zone; Vollenweider, 1974). The intensity of attenuation processes is widely quantified by dif- fuse light attenuation coefficients (K x ,m -1 ), based on measurements of irradiance with depth (Kirk, 1994). The visibility of submerged objects, as commonly measured with a Secchi disc (SD, m), is also regulated ∗ Contribution No. 203 of the Upstate Freshwater Institute. by attenuating processes (Tyler, 1968; Preisendorfer, 1986). Though K x and SD respond differently to the attenuating processes of absorption and scatter- ing (Effler, 1985; Kirk, 1994), and therefore changes in concentrations of attenuating constituents, the dis- tributions of these two variables are often correlated (Wetzel, 1983). Light attenuation is regulated by the composition and concentration of various attenuating constituents (Kirk, 1994), which include water itself, gelbstoff, phytoplankton, and tripton (Weidemann & Bannister, 1986; Kirk, 1994). Particulate constituents regulate light attenuation in the vast majority of inland waters (Davies-Colley & Smith, 2001). Differences in con- centrations of these constituents are responsible for the wide inter-system differences and dynamics within in-