Optical Properties Of Dominant Species Of Phytoplankton In Typical Inland Lakes And Seas

In this study,three nanophytoplankton species of freshwater algae from Taihu Lake and 10 species of marine algae from the East China Sea were cultivated in the laboratory.The pigment composition and content of algae species were detected by high-performance liquid chromatography?HPLC?.The light absorption and scattering characteristics of each algae were measured using an instrument?ac-s,USA Wetlab Co.?.Through the processing and analysis of the pigment composition and concentration of each algae species,as well as their optical parameters,bio-optical models were established,and the effects of growth conditions on the physiological and optical properties of algae were explored.The absorption coefficient of algae has a power function relationship with chlorophyll concentration,which is in accordance with the power function model proposed by Bricaud,and the best fitting effect is near 440 nm and 674 nm.The blue-to-red band ratio?B/R?of marine algae used in this experiment is 1.659,and that of freshwater algae is 1.709.There is a negative correlation between particle size and B/R value.Comparing the absorption peak of the measured absorption spectrum with the absorption peak position of the pigment in the solvent recorded in the literature,it is found that the two correspond but do not completely match.Compared with the latter,the former shifts towards longer wavelength by about 2-10 nm,And the shift of the absorption peak in the blue band is larger than that in the red band.Chlorophyll a and chlorophyll c are the main pigments of marine species,and the auxiliary pigments are mainly fucoxanthin,diatoxanthin and peridinin,corresponding to their main absorption peaks,between 440 nm and 550 nm,and near 674 nm.The main pigments of freshwater green algae are chlorophyll a and chlorophyll b,and the auxiliary pigments are mainly lutein,Neoxanthin,etc.,corresponding to their main absorption peaks:440 nm,480 nm and 625 nm respectively.The diatoms have a high consistency of pigment composition,so the light absorption characteristics are also highly consistent.The coefficient of variation of the normalized model is less than 20%.The variation coefficient of the dinoflagellates normalization model is between 20%and 40%,reflecting the high diversity of dinoflagellates in pigment composition,cell morphology and particle size.There is no significant difference between the specific absorption coefficient of marine green algae Nannochloris sp.and the normalized model of freshwater green algae,and the consistency of pigment composition between freshwater algae and marine algae is high.The absorption characteristics of Zooxanthella sp.and Prorocentrum donghaiense in the East China Sea are very special,and they are quite different from the absorption characteristics of diatoms.However,the consistency of the light absorption characteristics of diatoms is not conducive to the identification of specific diatom algae species.The relative content of different pigments is related to the environmental conditions.The ratio of[Chl-(6]/[Chl-(8]of the Cyclotella cryptica under high light and carbon dioxide conditions differs from that of control group to the extent of more than100%.The relative content of microspheres was less than 10%affected by environmental conditions.Environmental conditions have a greater impact on[Chl-(6]/[Chl-(8]than on[Chl-(6]/[Caro].Environmental conditions also have an effect on the light absorption characteristics.Under different growth conditions,the specific absorption coefficient values of Rhodomonas sp.,Nannochloris sp.and Cyclotella cryptica vary between 20%and 50%.Such a difference may indicate that changes in absorption characteristics have a certain effect on quantitative inversion.There is also a power function relationship between the algae scattering coefficient and the chlorophyll a concentration.The sample fitting b₀ is less than the empirical value given by Loisel.The specific scattering coefficient of freshwater algae is between0.04-0.12 m²·mg^-1,and the specific scattering coefficient of seawater algae is between 0.02-0.10 m²·mg^-1.The scattering coefficient curve of diatoms at 450 nm to550 nm has a relatively stable slope,and there is a good linear correlation between the slope and particle size?²=0.839?.In addition,the morphology of intracellular pigments has a certain influence on the scattering characteristics,and cells with several small plasmids tend to have higher scattering efficiency.The coefficient of variation of the model is between 20-40%,the representativeness of diatom and microspheres is relatively good,but the accuracy of dinoflagellate model is low.Except that the specific scattering coefficient of Cryptomonas sp.is greatly affected by the environmental conditions,the specific scattering coefficient of Cyclotella cryptica and Nannochloris sp.under different growth conditions differs from the control group for about 20%,which has less effect on quantitative inversion.