Parameterization of water component absorption in an inland eutrophic lake and its seasonal variability: a case study in Lake Taihu

Abstract

Water spectral absorption characteristics of eutrophic lakes are largely different from those of ocean and coastal waters. We therefore studied them with the aim of establishing an analytical model for inland water colour, to be used in remote sensing. Field measurements were carried out on 16 and 17 August 2006 (summer), 5 and 6 November 2006 (winter), and 29 and 30 March 2007 (spring) at 15 stations in northern Lake Taihu (China). Chromophoric dissolved organic matter (CDOM) absorption coefficients (a CDOM) are higher in summer than in spring and winter, with the ratios of a CDOM in spring, summer and winter being approximately 1 : 4.0 : 1.2 at both UV‐C and UV‐B. The spectral slope S CDOM values change with wavelength and season, and covary with CDOM concentration, as shown by regression analysis. For the CDOM absorption spectrum in the wavelength region 500–700 nm (important for water colour remote sensing), a linear method simulates better than an exponential method. Seasonal variations in non‐algal particulate (NAP) absorption (a NAP) at blue, green and red wavelengths show better consistency, in the order winter>spring>summer. The average S NAP is 0.0065±0.0009 nm−1, which is lower than that in other types of waters. Phytoplankton absorption (a ph) peak height changes with the season, with the pattern summer>winter>spring, and phytoplankton absorption spectra can be expressed with high accuracy by a quadratic model. CDOM absorption contributions in the three seasons are low compared to phytoplankton and NAP.