Light absorbing components in the Finger Lakes of New York

Abstract

Light absorbing constituents are important regulators of the underwater light field and the signal available for remote sensing of water quality. The spectral characteristics, magnitude and variability of the components of light absorption are documented and contrasted here for the broad range of conditions manifested in the 11 Finger Lakes of New York. The absorption coefficient, a (m -1 ), was partitioned according to the additive components of colored dissolved organic matter (a CDOM ), non-algal particles (a NAP ), phytoplankton (a Φ ), and water itself (a w ; known), using laboratory spectrophotometric protocols on near surface samples collected monthly in 2004. Bulk in-situ measurements included Secchi disc depth (SD), irradiance profiles to determine the diffuse attenuation coefficient (K d , m -1 ), and the beam attenuation coefficient at 660 nm [c(660)]. The average exponential slope values for CDOM (0.0175nm -1 ) and NAP (0.0121nm -1 ) were nearly equivalent to, and spectral features of aΦ were similar to, those reported by Babin et al. (2003b) for coastal marine waters around Europe. Order of magnitude differences in study average values of a CDOM , a NAP , and a Φ were observed amongst the study lakes. The largest component in each of the lakes, for the commonly adopted reference wavelength of 440 nm, was CDOM; it represented from 48 to 68 % of a amongst the study lakes. The a NAP and a Φ components were approximately of equal importance, with a NAP (440) exceeding a Φ (440) in 6 of the lakes. The value of a, from summation of the measured components, was a strong predictor of K d differences amongst the lakes, and it had significant relationships with average values of SD and c(660). The ratio of the watershed area to the lake volume was found to be a strong predictor of the major differences in both a CDOM (440) and a NAP (440) amongst the lakes indicating the importance of terrigenous inputs of these constituent.