Oxygen evolution in a hypersaline crust: in situ photosynthesis quantification by microelectrode profiling and use of planar optode spots in incubation chambers

Net primary production and respiration were estimated in a hypersaline cyanobacterial mat colonizing a gypsum crust in the Eilat salterns, Israel. Two different approaches were used: in situ microprofiling with Clark-type O sub(2) sensors and application of optode sensor spots in incubation chambers. The net O sub(2) release rates of the mat phototrophs was high, with a maximum of 3.4 nmol O sub(2) cm super(-2) min super(-1) measured by microprofiling and 4.4 nmol O sub(2) cm super(-2) min super(-1) determined in the incubation chambers. The upper 2 layers of the mat as well as the overlying water quickly became O sub(2) saturated during the day. The respiration of the whole gypsum crust was also very intensive and corresponded to the O sub(2) produced by photosynthesis on a diurnal basis, which prevented most of the evolved O sub(2) from reaching the water. The results presented show that optode sensor spots are useful tools providing additional information about export and photosynthetic production rates of O sub(2) in hypersaline microbial mats.