| Abstract: | Spectral absorption coefficients of the total particulate, a
p(λ), nonalgal particulate, a
d(λ), and phytoplankton pigment, a
ph(λ), in the Pearl River estuary and its vicinity waters were determined using the quantitative filter technique. The particulate
absorption a
p(443) ranged from 0.04 to 1.82 m−1, with the corresponding a
ph(443) ranging from 0.016 to 0.484 m−1. Two typical spectral patterns are found for the total particulate absorption. For the first typical spectral pattern, the
total particulate absorption spectra are similar to that of nonalgal particulate, with values of absorption coefficient decreasing
with wavelength. In contrast, for the second spectral pattern the spectral absorptions by total particulate are very similar
to that of phytoplankton pigment. The spectral dependency of absorption by nonalgal particulate follows an exponential increase
toward short wavelengths, with an average slope of 0.012 ± 0.002 nm−1. The nonalgal absorption and the fraction of the nonalgal particulate absorption to the total particulate absorption exhibit
a distinct trend of decreasing with salinity of the surface water. Phytoplankton pigment absorption exhibits a clear trend
of increasing nonlinearly with chlorophyll a concentration. The relationships between the phytoplankton pigment absorption
and chlorophyll a concentration can be described by power law, with the determination coefficient r
2 of 0.82. But only weak relationships between a
p(λ) and chlorophyll a concentration are observed, with the determination coefficient r2 of 0.42. The relatively large scatter around a
p(443) versus chl-a relationship would be attributed to the effects of loading of the nonalgal particulate absorption. Our
analysis indicated that such relationships similar to that for Case I waters can be applicable to optically complex Case II
waters if the effects caused by nonalgal are corrected. The chlorophyll-specific absorption coefficients of phytoplankton
pigment are not constant, it increases with decreasing chlorophyll a level. To improve the accuracy of bio-optical algorithms
for remote sensing in coastal waters, further investigations on the variations of specific absorption of chlorophyll pigment
must be made. |
