A bio-optical model for remote sensing of Lena water


Bio-optical measurements and sampling were carried out in the delta of the Lena River (Northern Siberia, Russia) during the high water run-off period between 26 June 2011 and 4 July 2011. The aim of this study was to determine the inherent optical properties of the Lena water, i.e. absorption, attenuation and scattering coefficients, during the period of maximum run-off. In this context CDOM (Colored Dissolved Organic Matter), total particle absorption, total suspended matter and phytoplankton-pigments were measured. CDOM was found to be the most dominant parameter affecting the optical properties of the river, with an absorption coefficient of 4.5–5 m−1 at 442 nm, which was almost four times higher than total particle absorption values at visible wavelength range during the first week of the campaign. This difference decreased over the following days when Total Suspended Matter (TSM) concentration increased. The wavelength dependent absorption spectra of the water constituents were characterized by determining the semi logarithmic spectral slope. Mean CDOM, and Detritus slopes, were 0.0149 nm−1(stdev = 0.0003, n = 18), and 0.0057 nm−1 (stdev = 0.0017, n = 19), respectively, values which are typical for water bodies with high concentrations of dissolved and particulate carbon. Mean total chlorophyll a, and total suspended matter, were also measured to determine the relationship between concentrations and optical properties. Mean chlorophyll a and total suspended matter were 1.821 mg m−3 (stdev = 0.734 n = 18) and 31.89 mg L−1 (stdev = 19.94) respectively. The light penetration depth (Secchi disc depth) was highly correlated with the suspended matter concentration with a maximum of 90 cm. We conclude that the bio-optical properties of the Lena River are rather complex because of the high CDOM and variable particle load which may change within a matter of days. Furthermore, the chlorophyll concentration constitutes a small fraction. Our results will improve the remote sensing protocols of the river and coastal waters in and around the Lena Delta and serve as a basis for characterizing the light climate with respect to primary production.
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