Detection Research On Phytoplankton Community And CDOM Concentration Based On Fluorescence Data

Both phytoplankton and chromophoric dissolved organic matter?CDOM?are optical indicators for monitoring water quality in the marine environment.Detection of them is of great scientific significance for understanding the biogeochemical processes and aquatic ecosystems of seawater.There are few researches on the phytoplankton and CDOM fluorescence characteristics of offshore waters in China.In this study,we first developed a neoteric method to estimate phytoplankton communities and CDOM in the Bohai Sea?BS?,Yellow Sea?YS?and East China Sea?ECS?from in situ fluorescence spectra collected by the HS-6P and LIF instrument.Additionally,the phytoplankton communities and CDOM surface level and vertical spatial distribution were analyzed based on the in situ fluorescence spectra of surface and profile data.The main results are as follow:?1?The optimal band forms were confirmed through,i.e.,X1?i.e.,fl?700??,which means the fluorescence emission signal at 700 nm band)for Chlorophytes,Cryptophytes, Dinoflagellates,and Prymnesiophytes and X7?i.e.,[fl?700?+fl?550?]/[fl?550?/fl?700?], where fl?550?denotes the fluorescence emission signal at 550 nm band?for Chrysophytes and Diatoms.And through four function fittings,the linear model performed best for the Chlorophyte and Chrysophytes estimations,and the other four phytoplankton communities performed better under the power function.At the same time,each mode is validated by the leave-one-out method,and the inversion precision is high.?2?Two empirical CDOM fluorescence inversion algorithms were developed by analyzing the relationship between the spectra of HS-6P and LIF with CDOM.Subsequently,the two models were validated by field measured data.The coefficient R2 was greater than 0.8 ?p<0.001?,and the average relative error MRE was within 24%.And the accuracy of LIF model is better than that of HS-6P model.In addition,the R_rs???-based model was constructed through a linear regression analysis between the optimal band combination form X7=[R_rs?443?+R_rs?555?]/[R_rs?443?/R_rs?555?]and CDOM.Furthermore,this study compares and analyzes the inversion results of CDOM inversion algorithm based on fluorescence signal and remote sensing reflectance,and shows that the inversion accuracy of CDOM algorithm based on fluorescence signal is better than CDOM remote sensing algorithm.?3?The phytoplankton communities and CDOM surface and vertical spatial distribution of the study region were obtained by applying the field measurement fluorescence spectra surface and profile data.From the horizontal spatial distribution,the phytoplankton communities is uniformly distributed in the BS and YS,and the YS value is slightly higher than that in the BS.Large value of phytoplankton near the Yangtze River estuary in spring.And the diatom and Dinoflagellate is dominant algae in the BS,YS,and ECS.There is obvious regional difference in CDOM distribution.The CDOM value of BS is significantly higher than that of YS,and the nearshore is higher than offshore.From the vertical spatial distribution,the six algae showed relatively higher concentrations at the maximum layer of Chl a,and the concentration of Chlorophytes,Dinoflagellates and Cryptophytes is higher than that of Diatom,Prymnesiophytes,and Chrysophytes.The Chlorophytes, Prymnesiophytes,Dinoflagellates,and Cryptophytes showed a high concentration distributions at the maximum layer of Chl a,which may be affected by the ettrophic water area.The vertical spatial distribution of CDOM is uniformly distributed in winter.And the spatial distribution of CDOM value in the surface layer including the subsurface is lower than in the middle and lower layers.