Feature analysis of phytoplankton pigments in Qinghai Lake

Abstract

The characteristics of pigments in phytoplankton in surface water, e.g., composition, spectral absorption and specific absorption, were examined based on in situ data collected during a field cruise in Qinghai Lake in August 2003. This study identified two pigments of chlorophyll (Chl), two pigments of photosynthetic carotenoids (PSC), and seven pigments of photoprotective carotenoids (PPC) in the samples. Our results show that (1) the amount of pigments in phytoplankton in Qinghai Lake can be sorted as Chl > PPC > PSC. Specifically, the phytoplankton mainly contains Chla and Zea which belong to Chl and PPC, and account for 64.72% and 21.84% in the total pigment, respectively. (2) The total pigment absorption of phytoplankton is largely determined by Chla and Zea, and therefore shows similar spectral characteristics (e.g., shape, peak position) among different samples with only slight variation(between 0.02 m−1 and 0.06 m−1 at 440nm) in the absorption. Moreover, the difference becomes insignificant when specific absorption (pigment absorption normalized by its concentration) is considered, i.e., spectral shape and peak position. This may suggest phytoplankton species change little across the lake. (3) Mean ratio of pigment absorption coefficient measured by the Quantitative Filter technique (QFT) to that by the High-Performance Liquid Chromatography (HPLC) were also examined. The ratio is 60.27% and 51.44% at around 440nm and 675nm, respectively, which suggests the package effect in the blue is much more obvious than that in the red. This also indicates existence of significant package effect from accessory pigments (e.g., carotenoids).