Absorption properties of in-water constituents and their variation among various lake types in the boreal region

We studied the absorption properties of in-water constituents among 15 boreal lakes belonging to various lake types. One of the lakes was also monitored frequently during its growth season to reveal the seasonal variation of absorption properties. Within the studied lakes, CDOM absorption a(CDOM)(442) varied from 0.4 to 15 m(-1). CDOM was clearly dominating the absorption signal at low wavelengths, but even at the red-end of the spectra its contribution to total absorption was notable, varying from 48 to 99% of total absorption (excl. water) at 442 nm and from 5 to 86% at 665 nm. Slope of the CDOM absorption spectra S-CDOM(400-700) varied from 12.9 to 193 mu m(-1). Higher slopes were obtained when the wavelength range was extended to the UV-range (350700 and 300-700 nm). Non-linear relationships were noted between a(CDOM) and S-CDOM calculated over various wavelength ranges. Despite the significant relationship between DOC concentration and a(CDOM), almost fivefold variation was noted in DOC-specific CDOM absorption at 442 nm. This variation was clearly associated with concurrent changes in S-CDOM. Non-algal particulate absorption varied from 0.037 to 1.8 m(-1) at 442 nm, contributing <1 to 34% of total absorption at 442 nm and <1 to 27% at 442 nm. Slope of the NAP absorption spectra S-NAP(380-700) varied from 7.6 to 12.8 mu m(-1). Despite of the apparent covariation between weight of suspended particulate matter (SPM) and a(NAP), six-fold variation was observed in SPM-specific NAP absorption at 442 nm, which was mostly associated with organic content of the particle pool. Contribution of phytoplankton pigments ranged from 1 to 28% of total absorption at 442 nm, and 13 to 86% at 665 nm, respectively. Chlorophyll a (Chla) specific absorption of phytoplankton pigments varied from 0.012 to 0.038 m(2) (mg Chlar)(-1) at blue peak, and from 0.008 to 0.020 m(2) (mg Chla)(-1) at red peak. Observed values cluster around the low-end of the previously reported range, indicating a high package effect of phytoplankton cells in lakes. Observed variation was modeled as function of Chla (ranging from 1.8 to 95 mg m(-3)). Parameters and relationships presented in this study provide useful information for remote sensing of lakes, as well as for various ecological and geochemical applications. (C) 2014 Elsevier Inc. All rights reserved.