Specific absorption characteristics of suspended particles in Lake Taihu and parameter analysis

Four field investigations were carried out in Lake Taihu in 2006 and 2007 to measure absorption coefficients of phytoplankton and non-algal particles. We used quantitative filter technology(QFT) ,which can further deduce specific absorption coefficients. At the blue light wavelength of 440 nm,aph varies from 0.008 m2·mg-1 to 0.268 m2·mg-1,while at the red light wavelength of 670 nm,the variation range is 0.004～0.098 m2·mg-1. Three types of specific absorption spectra with different characteristics were divided by the K-Mean algorithm. Type 1 spectra account for 61.0% of all spectra,while type 2 and 3 account for 12.2% and 26.8%,respectively. This implies that type 1 dominates the specific absorption spectra of phytoplankton in Lake Taihu. The package effect index Qa(675) decreases sharply when Chla concentration 50 mg·m-3,and slowly decreases when Chla concentration 50 mg·m-3. The variation of Qa(675) along with Chla can be simulated by a power function. At 440 nm,the specific absorption coefficients of non-algal particles range from 0.012×10-3 to 0.143×10-3 m2·mg-1,and the specific absorption spectra can be modeled with high accuracy,where S changes from 0.0049 to 0.0133 nm-1 with a mean of(0.0091±0.0029) nm-1. An exponential model can be used to simulate the relationship between aNAP and NAP concentrations with R2=0.502. The spatial and temporal changes of the specific absorption coefficients of phytoplankton and non-algal particles were also analyzed.