[Characteristics of optical absorption coefficients and their differences in typical seasons in Lake Qiandaohu]

Absorption characteristics of total suspended particulate, phytoplankton and tripton in Lake Qiandaohu are presented based on the in situ data collected in winter (from December 2012 to February 2013) and summer (from July to August 2013). The mean values of total suspended particle absorption coefficients at 440 nm [a(p) (440)] in winter and summer are (0.20 +/- 0.07) m(-1) and (0.24 +/- 0.17) m(-1). Correspondingly, the mean values of a(p) (675) are (0.07 +/- 0.02) m(-1) and (0.10 +/- 0.07) m(-1). In winter the absorption spectra of total suspended particulate matters can be divided into two cases: the absorption spectra are similar to those of phytoplankton in the northwest lake and to those of tripton in other lake regions. In summer, the absorption spectra of total suspended particles are similar to those of phytoplankton from 400 nm to 700 nm. The mean values of phytoplankton absorption coefficients at 440 nm [a(ph) (440)] are (0.10 +/- 0.03) m(-1) in winter, and (0.17 +/- 0.14) m(-1) in summer. Accordingly, the mean values of a(ph) (675) are (0.05 +/- 0.02) m(-1) and (0.08 +/- 0.07) m(-1). The mean values of Chlorophyll-specific absorption coefficients (by the concentration of Chla) at440 nm a(*)(ph)(440) are (0.045 +/- 0.010) m2 x mg(-1) in winter and (0.039 +/- 0.013) m2 x mg(-1) in summer. At the same time, the mean values of a(*)(ph) (675) are (0.022 +/- 0.004) m2 x mg(-1) and (0.019 +/- 0.005) m2 x mg(-1). Significantly linear correlations are found between phytoplankton absorption coefficients and chlorophyll a concentration, trophic level index (TLI). Chlorophyll-specific absorption coefficients vary with the chlorophyll a concentrations following a power function. The tripton absorption coefficients exponentially decrease from 400 nm to 700 nm. The correlation between tripton absorption coefficients and inorganic particles is significant in winter, whereas, the correlation between tripton absorption coefficients and the concentrations of total suspended particles and organic particles are significant in summer.