Method Of Phytoplankton Photosynthesis Activity Measurement In Situ And System Design

Eutrophication and drinking water safety is a hot issue in environmental science which has been concerned commonly at present. Excess proliferation of phytoplankton usually brings water into the "Harmful Algae Blooms, HABs" and "red tide", it do seriously harm to human health and economic sustainable development. Photosynthesis activity can represent phytoplankton growth state information, and is one of the most important parameters for "HABs" monitoring and early warning. There is no phytoplankton photosynthesis activity measurement method and equipment in situ. This paper studied on the phytoplankton photosynthesis activity measurement method in situ, and developed measurement system which based on chlorophyll fluorescence, and implemented the realtime, online measurement of phytoplankton photosynthesis activity.Acording to the research of spectral characteristics about phytoplankton fluorescence in vivo, we developed a measure system with pulse amplituded modulation(PAM) technology and saturated pulse method, obtaining the phytoplankton chlorophyll fluorescence characteristics and using the chlorophyll fluorescence as a probe in the photosynthesis process. The efficiency of phytoplankton photosynthesis process transfering light into chemical energy--hotosynthesis activity could be obtained.Phytoplankton chlorophyll fluorescence characteristics was studied under various light intensities and wavelength. This work could support in situ measurement system design of phytoplankton photosynthesis activity. Combined with fluorescence and light intensity, we got a excrete excitation spectrum, compared with3DEEM using Spectrophotometer (Hitachi F7000). Also, the absorbance at each wavelength was tested. The Photosystem H absorbance and fluorescence emission Yield could be obtained. Blue and red light could be used as measure light which were used to excit fluorescence at pigment level. The contrast test was did between phytoplankton in vivo and dead. The fluorescence Yield revealed difference between chlorophyll fluorescence and molecule fluorescence. The value of Photosynthesis activity in vivo could be obtained through the change of chlorophyll fluorescence Yield. With the principle of photosynthetic activity measurement, this paper proposed a in situ measurement method which based on chlorophyll fluorescence values Ft and Fm to get phytoplankton photosynthesis activity. A measure system in situ was designed in which LED and laser diode was used as excitation light sources and accomplished phytoplankton photosynthesis activity measurement real-timely. Then the designing details were shown, included hardware, software, optics and mechanic. The performances of system such as linearity, stability, repeatability were tested through phytoplankton samples prepared in laboratory. In order to improve the applicability of the instruments in practice, the variable gain amplifier was used to enlarge dynamic range with high sensitivity.Phytoplankton photosynthesis activity measurement system in situ was used in Chaohu lake for more than2months, We got the time series of photosynthesis phytoplankton activity measured in situ. The rising of activity value can forecast the "HABs" with other parameters. Also offline comparision analysis was did between our measurement in situ and instrument in laboratory. Results showed that the system in situ seemed very similarly when comparing with the Water PAM developed by WALZ. The correlation coefficient of cyanobacteria and green algae are0.9778and0.7768. The reliability of the in situ measurement system was shown in comparision experiment.