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Estimation of the phytoplankton productivity and physiological state with the use of a submersible fluorometer probe
Diagnostics of the condition of water bodies is a topical problem. Phytoplankton forms the base of aquatic ecosystems and its activity determines their state and productivity. Concentration and photosynthetic activity of algal cells are characteristics of aqueous systems that are primarily affected by various environmental factors and antropogenic pollution. Hence, monitoring of these characteristics can be used to assess the state of an aqueous system as the whole.
Presently, parameters of chlorophyll fluorescence are widely used to assess the abundance and activity of phytoplankton. Methods for fluorescence registration are highly sensitive and allow fluorescence measurement to be conducted in the natural habitat of algae, without affecting their physiological state (Falkowski and Kolber, 1995; Geider et al., 1993; Green et al., 1994). Pump-and-probe fluorometer (Kolber et al., 1990) allows such fluorescence parameters as Fo and Fv/Fm to be measured (see Chlorophyll Fluorescence in vivo: A Theory. Constant and variable fluorescence).
Fo was shown to correlate with concentration chlorophylls and carotenoids and with biomass and cell number of microalgae in natural water bodies (Yentsch, Menzel, 1963; Lorenzen, 1966; Dieter, 1986; Keller, 1987), i.e., it is an indicator of phytoplankton abundance. We showed (Antal et al., 2001) that at natural phytoplankton concentrations, Fo as a rather accurate indicator of the fraction of light absorbed by pigments of algal cells in a unit of water volume, i.e., its value characterizes light absorbing capacity of phytoplankton, a fundamental characteristic of the light energy conversion in water bodies. Thus parameter Fo is used to calculate both phytoplankton concentration (by calibrating Fo vs chlorophyll or cells concentration, biomass) and light absorbing capacity which can be used for assessment the rate of photosynthesis.
Photosynthetic activity of phytoplankton is a function of the rate of the absorbed light energy conversion into energy of chemical bonds in reaction centers of photosystem II (RC PS II), which splits water, a process accompanied with O2 evolution. The Fv/Fm ratio was shown to characterize the efficiency of the photochemical energy conversion in PS II (Klughammer, 1992; Long et al., 1994) and to correlate with photosynthetic rates, measured by O2 evolution or CO2 fixation rate under various adverse effects on algal cells (Schreiber et al., 1995). Thus, the Fv/Fm ratio is an informative parameter which characterizes photosynthetic activity and can be used also to estimate the photosynthetic rate.
We suggest the method of assessment the vertical distribution of phytoplankton primary production by fluorescence parameters (Fo, Fv/Fm) and underwater irradiation (see Chlorophyll Fluorescence in vivo: A Theory. Calculation of phytoplankton primary production) (Antal et al., 1999; Antal et al., 2001).
A fluorometer (see PrimProd: system description and Technical specifications) was designed at the Biophysics Department of the Faculty of Biology (Lomonosov Moscow State University) for in situ measuring of chlorophyll fluorescence characteristics (Fo and Fv/Fm) using pump-and-probe technique. The fluorometer consists of a submersible probe, on-board power supply unit, cable-rope, and an IBM-compatible personal computer, which controls the measurement process using special software. With the use of cable-rope, the probe (9 kg) in a spherical case of 25 cm in diameter, can be submerged to a depth up to 150 m, i.e., to the lower limit of the photic layer in oligotrophic waters. The probe is equipped with a pressure (depth) sensor and provides for measurement of high resolution vertical profiles of phytoplankton distribution (Fo), its photochemical activity (Fv/Fm), as well as underwater irradiance and temperature. These characteristics are recorded automatically and the data are plotted on computer display (see Fig.) in real time as vertical profiles of characteristics measured and as time series in a single point or along the ship course. The complete vertical profile can be recorded within 10 min. A small size rechargeable battery (12 V) allows the fluorometer to be operated under field conditions from a small oar boat.
Using the fluorometer probe we studied the effect of various environmental, including antropogenic, factors on the abundance and photosynthetic activity of natural phytoplankton in various regions of the Black, Mediterranean, Baltic, White, Norwegian, and South China Seas, as well as in the Baikal and Issyk-Kul Lakes, and in the Moscow River. These studies showed that photosynthetic productivity and physiological state of algae can be assessed under environmental various conditions.
Data processing consisted mainly in plotting two-dimensional vertical and horizontal sections, three-dimensional maps, as well as time series of the abundance, photosynthetic activity, and productivity of phytoplankton communities, as well as temperature and optical characteristics of aquatic medium, which allowed characterize ecological state of the water bodies studied.
Further objective of our studies is to develop a system for continuous monitoring of the ecological condition of aqueous medium in different water bodies to forecast their changes and provide recommendations for rational nature management and conservancy. In addition to fluorometer probe, the equipment for monitoring may also include a complex of methods and devices developed in the Department of Biophysics for microfluorometric studies of individual cells to obtain information on the structure of microalgal populations, for measurement of delayed fluorescence and thermoluminescence of phytoplankton, as well as methods for biological testing of water quality.
We have many-year experience of cooperation with hydrobiologists, oceanologists, and ecologists from various countries and are ready to use our experience and designs for joint projects.
Team of engineers and researchers: Dr. Antal T.K., Prof. Venediktov P.S., Kazimirlo Yu.V., Prof. Matorin D.N., Prof. Pogosyan S.I., and Prof. Rubin A.B.
Address: Dept. of Biophysics, Faculty of Biology, MSU, 119899, Moscow, Russia
Phone: 7 (495) 939-3968
Fax: 7 (495) 939-1115