Autotrophic processes in meromictic Big Soda Lake

Daily rates of oxygenic photosynthesis (OP) by phytoplankton, anoxygenic photosynthesis (AP) by purple sulfur bacteria, and chemoautotrophic productivity (CP = dark CO, assimila-tion) were measured once each season in saline, meromictic Big Soda Lake. Total daily pro-ductivity and the relative importance of each autotrophic process varied with seasonal changes in vertical mixing, light availability, and the biomass of phototrophs. Daily productivity was highest (2,830 mg C.rnmz) and was dominated by OP in winter when the mixolimnion was isothermal, the biomass of phytoplankton was high, and the biomass of purple sulfur bacteria was low. During the summer-fall period of thermal stratification, phytoplankton biomass de-creased, a plate of purple sulfur bacteria formed below the oxycline, and daily rates of dark CO, assimilation (CP = 390-680 mg C.rnmz) exceeded phototrophic productivity (OP + AP = ZOO-370 mg C.rnmz). Total annual productivity was about 500 g C.me2, of which 60 % was produced by phytoplankton (mostly in winter), 30 % by chemoautotrophs (nitrifying and sulfur-oxidizing bacteria), and only 10 % by photosynthetic bacteria. All aspects of aquatic ecology relate, at least indirectly, to processes associate