PRIMARY PRODUCTIVITY IN A DEEP SEWAGE STABILIZATION LAGOON

Primary productivity and production measurements and their relationshi p to observed variations in the concentrations of nutrients (N and P), CO2, pH, temperature, dissolved oxygen and solar radiation were studi ed in an 8 m deep sewage stabilization pond from October 1986 to Decem ber 1987. Two types of tests were carried out: short-term and long-ter m. The latter permitted the transformation of short-term measurements into daily measurements and the obtention of the relationship between the time of day and primary production. The measurement of primary pro duction was performed using the C-14 technique. The highest primary pr oductivity values were detected during the spring-summer period, which was characterized by high temperatures and an increased degree of sol ar radiation. The maximum value was obtained during June (14.38 mg C m g Chl-1 day-1) and was accompanied by: (a) a decrease in the concentra tion of nutrients (N and P) and CO2, (b) an increase in pH levels and dissolved oxygen concentrations and (c) a significant proliferation of cyanobacteria (which indicated a low organic loading).