Effect of seasonal changes on cyanobacterial production and nitrogen-yield

A mixed culture of cyanobacteria (BGA) containingAulosira sp.,Aphanothece sp., andGloeotrichia sp. were grown throughout the year to assess the influence of seasonal variables on their biomass production and nitrogen (N)-yield under field conditions. The seasonal variables considered in this study, i.e., water temperature (maximum, minimum), solar radiation, sunshine hours, and rainfall, fluctuated widely. Attempts were made to establish a relationship between seasonal changes as independent variables and BGA productivity and N-yield as dependent variables. The analysis indicated that solar radiation was the prime factor. Estimates of BGA biomass production varied from 3.3 to 366.5 kg (dry wt)/ha/month, and N-yield ranged from 0.1 to 11.8 kg N/ha/month. The nitrogen accumulated during the study period was 71.2 kg N/ha. The variations explained by seasonal changes were 52.3 and 50.3% for biomass production and N-yield of BGA, respectively.