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3.3 Online monitoring of phytoplankton photoreaction curves using delayed fluorometer 
Delayed fluorescence technique and its application in the measurement of living phytoplankton
Abstract: This paper introduces a live phytoplankton online monitoring technology-delayed fluorescence measurement technology and DF algae delayed fluorescence measurement system based on delayed fluorescence technology. Living algae monitoring technology automatically records the biomass and composition of live phytoplankton by monitoring the delayed fluorescence of algae online, and is suitable for automatic online continuous monitoring of phytoplankton. Combined with the ecological factor parameters measured by other systems, the seasonal variation pattern of phytoplankton is analyzed as a function of the dynamic environment. Finally, the functional relationship between the ecological factors that change with the seasons and the growth of phytoplankton can be established, and the process of various blooms can be fully simulated, so as to prevent the occurrence of blooms. The application of delayed fluorescence technology in actual lake monitoring is also illustrated by the DF algae delayed fluorescence measurement system.
Key words: living phytoplankton; water bloom; delayed fluorescence; online monitoring
1 Introduction
When the water flow in a watershed is collected in a certain area, as the water flow slows down, the nutrients are gradually enriched, and the obvious growth of algae can be monitored under appropriate light and temperature, which is easy to cause bloom. Therefore, the formation of blooms is caused by the mass reproduction of living algae, and is affected by environmental factors such as water temperature, nutrient content, and radiation. At present, the water quality of the main rivers and lakes in China is generally deteriorating. The water blooms are frequent and the water quality monitoring task is very heavy.
Plants use light energy to synthesize the compounds needed for their own growth and to maintain metabolism. The antenna pigment in the plant receives sunlight and converts light energy into chemical energy. Chlorophyll plays a key role in the photosynthetic process. Like some substances, it emits light under light conditions. This light is called fluorescence. In living plants, both the excited state and the transient dark adaptation release fluorescence, the former releasing direct fluorescence and the latter releasing delayed fluorescence.
In the past 20 years, a large number of phytoplankton monitoring instruments based on fluorescence theory have appeared, mostly for rapid fluorescence measurement (Istvánovics et al. 2005). As early as 1931, Kautsky and Hirsch used rapid fluorescence monitoring for phytoplankton research. However, rapid fluorescence techniques measure all substances that release fluorescence, including dead phytoplankton and humus.
This article describes a living algae detection technology - delayed fluorescence technology, as well as live phytoplankton and ecological environment online monitoring system (DF). Delayed fluorescence technology can eliminate the influence of phytoplankton and humus on the measurement results, making the prediction and prevention of blooms more rapid and effective.
[1]
2 delayed fluorescence technology
In addition to fast fluorescence, fluorescence is also emitted when plants turn from light to dark, and this fluorescence is weaker and lasts longer, known as delayed fluorescence (DF), as found by Strehler and Arnold (1951). Although delayed fluorescence was found very early, it has not been taken seriously. Volkmar Gerhardt and his collaborators (1981) first developed delayed fluorescence spectroscopy. This technology has significant advantages over fast fluorescence technology.
Delayed fluorescence is produced by points and recombination caused by electron countercurrent (Gerhardt & Bodemer, 2000). Therefore, only cells with photosynthetic activity can delay fluorescence during labor, that is, delayed fluorescence is an exclusive characteristic of photosynthetic activity of living cells and an indicator of photosynthetic efficiency. Delayed fluorescence technology can effectively block the interference of resuspended, dead organisms and humus on measurement accuracy, and other fluorescence measurement techniques cannot be realized. This difference between delayed fluorescence technology and ordinary fast fluorescence technology can play a decisive role in shallow lakes or rivers, especially those that frequently resuspend and flood waves and introduce a certain amount of degraded algae or algae without photosynthetic function. The area of ​​the water body. Therefore, delayed fluorescence technology has gradually become a research hotspot in current water bloom monitoring.
The live phytoplankton and eco-environment online monitoring system (DF) is based on delayed fluorescence technology, which can measure two aspects of delayed fluorescence: delayed fluorescence kinetics, ie, the process of delaying fluorescence decay; delayed fluorescence spectroscopy, ie DF 0 with different excitations The change in the wavelength of the light source. These two measurement methods are used to measure the biomass and composition of living algae (the system workflow is shown in Figure 1).
Fig. 1 : Working schema of the DF spectrometer
The working system of the flowchart of FIG. 1
The Living Phytoplankton and Eco-Environment Online Monitoring System (DF) is used to monitor the delayed fluorescence of algae online and automatically record the photosynthetic biomass and composition of live phytoplankton, suitable for continuous and online monitoring of the number of natural phytoplankton (system online monitoring) as shown in picture 2).
Figure 2 Schematic diagram of DF system monitoring network distribution
Combined with other aquatic ecological factors such as hydrology, meteorology and optics, the seasonal variation pattern of phytoplankton is analyzed as a function of the dynamic environment. The final function between growing seasons with varying phytoplankton and ecological factors, can be sufficiently simulate various blooms process, accurate detection and algal bloom formation and demise, to achieve the purpose of preventing water bloom [ 1] .
3 delayed fluorescence technology application case:
3.1 On-line monitoring of Lake Balaton, Hungary - Studying the stability of phytoplankton communities in highly dynamic environments
In 2003-2004, the water ecological factors of Lake Balaton, such as water temperature, total radiation, vertical attenuation of light, internal P load, etc., were monitored, and cyanobacteria, green algae, Four algae species, diatom and cryptophyta, were monitored and the data were used to analyze the seasonal variation patterns of phytoplankton to simulate the occurrence of various blooms. The experimental results show that the above measured data can adequately simulate the formation and decay of various blooms.
The DF algae delayed fluorescence measurement system is capable of measuring four phytoplankton classifications (expandable to six species) and biomass, and optional enhanced community identification and photosynthetic rate-light curves; the detection limit is 0.1 μg Chl/L, and the sampling frequency is up to 6-10 times / hour, automatic online measurement or portable measurement in the field.
The DF algae delayed fluorescence measurement system monitors algae composition (class 4 algae) and biomass changes from March to October 2003 in Lake Balaton as follows, with a fine record of a cyanobacteria outbreak in August.
Seasonal variation pattern of phytoplankton in Lake Balaton in 2003
3.2 Relationship between delayed fluorescence and phytoplankton quantity and radiant energy utilization rate
Chlorella vulgaris is cultured under natural temperature and light conditions. During the culture, temperature, radiation and chlorophyll (Chl) content are measured, DF is detected (using DF algae delayed fluorescence measurement system), quantum efficiency (QE) and The radiant energy utilization efficiency ( ) index. Data analysis showed that the DF signal in the diurnal cycle was correlated with QE( ) and (r 2 =0.977, p<0.01).
Using DF algae delayed fluorescence measurement system to record photosynthesis of phytoplankton biomass and photosynthesis-light curve (PI ) and estimate primary productivity of phytoplankton in Lake Elken, Sweden, and Lake Balaton, Hungary Record the attenuation of the radiation in the vertical direction. Analysis shows that on-line detection of PI curves can significantly reduce the error in the estimation of primary productivity. This indicates that due to the resuspension of sediments and phytoplankton, in the superficial turbid lake water where the light changes rapidly, the variation with time scales of seasons or seasons also conforms to this law. This new theory has good prospects for studying the laws of primary productivity and long-term high-frequency monitoring of aquatic ecology.
Delayed fluorescence DF- light relationship curve
4 conclusion
The phytoplankton and eco-environment online monitoring system was used to monitor the time series data of photosynthetically sensitive algae, and the seasonal variation patterns of phytoplankton were analyzed as a function of dynamic changing environment, combined with the ecological factor parameters measured by other systems. Finally, a functional relationship between the ecological factors that change with the seasons and the growth of phytoplankton is established, so that the processes of various blooms can be fully simulated, thereby achieving the purpose of preventing blooms.
references:
[1]Istvánovics V., Honti M., Osztoics A., HM Shafik, Padisák J., Y. Yacobi and W. Eckert (2005) On-line delayed fluorescence excitation spectroscopy, as a tool for continuous monitoring of phytoplankton dynamics and Itsapplication in shallow Lake Balaton (Hungary). Freshwater Biology 50:1950-1970.
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[3] Honti M., Istvánovics V. and Osztoics A. (2007) Stability and change of phytoplankton communities in a highly dynamic environment ? the case of large, shallow Lake Balaton (Hungary). Hydrobiologia 581: 225-240.
[4] Honti M., Istvánovics V. and Kozma Zs. (2008) Assessing phytoplankton growth in River Tisza (Hungary). Verh. Internat. Verein. Limnol. 30(1): 87-89.
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