Effect of organic fertilizer on plankton primary productivity in fish ponds

The effect of cattle organic fertilizer on plankton primary production and related variables was tested in six Bulgarian fish ponds situated close to the town of Plovdiv in Bulgaria. At the beginning of the experiment (16th of May 2004, about 10 days after filling with water) a suppression of plankton metabolism was observed and after that the ponds treated with manure demonstrated significantly higher productivity than the controls, especially during the transition to the autumn season when the water column was more regularly mixed. The other measured variables (Secchi disk readings, plankton chlorophyll-a and respiration, assimilation number per unit chlorophyll-a) did not show significant differences between the treated and control ponds.