Determination of absorption coefficients for chlorophyll a, phycocyanin, mineral matter and CDOM from three central Indiana reservoirs

Abstract

Absorption coefficients are used in semi-empirical and bio-optical models to estimate various optically active constituents in water. This study determines the mass-specific absorption coefficients of chlorophyll a (a*chl), phycocyanin (a*pc), minerals (a*m), and chromophoric dissolved organic matter (CDOM; a*CDOM) and the absorption coefficient for CDOM (aCDOM) for three central Indiana reservoirs. Absorption spectra were collected using a Shimadzu spectrophotometer equipped with a Spectralon coated integrating sphere. Quantitative measurements from either fluorometric (chlorophyll a, phycocyanin, CDOM) or weight-based (mineral) measurements were used to determine the mass-specific absorption coefficients tested in this study and an exponential function was used to estimate aCDOM. While a*chl showed minimum variability between reservoirs, a*pc, a*m, a*CDOM, and aCDOM showed statistically significant differences between reservoirs; however, for a*m, there was greater variation within each reservoir. Variability in a*CDOM and aCDOM between reservoirs was likely due to different inflows. All absorption coefficients fell within previously published ranges for each constituent examined, with the exception of a*pc. Differences in a*pc were likely due to different techniques used in extracting and estimating phycocyanin.