Influence Of Turbidity And CDOM On Classified Determination Of Phytoplankton Concentration With In-vivo Fluorescence Method And Its Correction

In vivo fluorescence method is widely used for in-situ measurement of phytoplankton concentration in water,with many advantages,such as simple operation,fast measurement,low cost,etc,which is one of the preconditions for the establishment of phytoplankton concentration monitoring and early warning system.However,in vivo fluorescence of phytoplankton is easily affected by its own physiological state and various environmental factors,such as fluorescence quenching,dissolved organic matter,suspended particles,etc,therefore the accuracy of measurement results cannot be guaranteed in practical application.In this paper,based on the discrete three-dimensional fluorescence technology,the influence of turbidity and colored dissolved organic matter(CDOM)on in vivo fluorescence spectrum and the classified measurement concentration of phytoplankton were studied,and a mathematical correction method for the classified determination of phytoplankton concentration was established,based on the analysis of relationship between influence and effect.The main research results are as follows:(1)By studying the influence of water turbidity on the discrete three-dimensional fluorescence spectrum of phytoplankton and the classified measurement concentration,it is found that the turbidity can enhance the phycocyanin fluorescence intensity of cyanobacteria,but weaken the fluorescence intensity of chlorophyll-a of chlorophyta.In accordance with the influence of turbidity on the discrete three-dimensional in vivo fluorescence,the chlorophyll-a concentration of cyanobacteria increases with the increasing of turbidity,which is measured by the in vivo fluorescence method,while the chlorophyll-a concentration of chlorophyta decreases with the increasing of turbidity,both of them show a good linear relationship.According to the influence-effect relationship of turbidity on phytoplankton concentration measurement,a mathematical correction method of turbidity influence is respectively established for different phytoplankton,namely turbidity compensation correction algorithm.With the turbidity correction of chlorophyta concentration,the relative error was reduced from-46.07--2.87%to-2.87-2.79%,which greatly improves the accuracy of measurement(2)By studying the influence of colored dissolved organic matter(CDOM)on the discrete three-dimensional fluorescence spectrum of phytoplankton and the classified measurement concentration,it is found that the CDOM can weaken the phycocyanin fluorescence intensity of cyanobacteria,and equally weaken the fluorescence intensity of chlorophyll-a of chlorophyta.In accordance with the influence of CDOM on the discrete three-dimensional in vivo fluorescence,the chlorophyll-a concentration of cyanobacteria and chlorophyta decrease with the increasing of CDOM concentration,which are measured by the in vivo fluorescence method,both of them show a good linear relationshipAccording to the influence-effect relationship of CDOM on phytoplankton concentration measurement,the mathematical correction method of CDOM influence,namely CDOM compensation correction algorithm,is respectively established for different phytoplankton.With the CDOM correction of cyanobacteria concentration,the relative error was reduced from-64.55?1.99%to-5.07?3.27%.while with the CDOM correction of chlorophyta concentration,the relative error was reduced from-54.57?-2.17%to-5.64?2.14%,which greatly improve the accuracy of measurement.