OXYM instruments

The OXYM instruments are designed to measure photosynthetic oxygen production in aquatic phytoplankton or plants as well as respiration. The instruments use standard Clark electrodes (e.g. YSI).
The lab instruments can be equipped with one to five channels. Quartz tubes holding 50 ml each are inserted into a common water jacket made of UV transparent Plexiglas. Inside the quartz tube is a rotating magnetic stirrer individually activated by a small motor underneath. A Clark electrode is inserted bubble free from the top and connected to the controller (1 to 5 channels). The controller provides the polarization voltage for the electrodes (800 mV) and performs a two-step amplification of the signal before A/D conversion (12 bit).

The digitized signal is transmitted to the host computer via an RS 232 protocol to one of the serial ports. In addition the temperature inside the water jacket is measured as well as the incident irradiance from the light source. The water jacket can be connected to running water or a water bath to stabilize the temperature at a constant value. For field experiments a rugged diving instrument has been developed which holds e.g. a phytoplankton sample in a cuvette located at the top and which can be lowered into the water column.

A magnetic stirrer is installed inside the cuvette. In addition to the oxygen channel the instrument also measures temperature and light intensity and sends the signals to the controller box which in turn amplifies and digitizes the signals and forwards them to the host computer (laptop). The software includes a calibration module which allows to calibrate all sensors (temperature, light, oxygen). Since the oxygen solubility in water depends on temperature, salinity and hight above sea level (e.g. in alpine lakes) the calibration is corrected for these parameters.The software determines the actual oxygen concentration in each channel and calculates the slope, i.e. it determines the oxygen production or uptake over time. The number of measured points over which the signal is averaged as well as the number of points used for the slope determination can be chosen under user control. All relevant data are stored in ASCII files and can be used in EXCEl and other spreadsheet programs.