Diel variations of phytoplankton and bacterioplankton production rates in four tropical lakes in the middle Rio Doce basin (southeastern Brazil).

Studies on phytoplankton production conducted in lakes of the middle Rio Doce basin demonstrated significant diurnal and seasonal variations with high phytoplankton production rates recorded in the morning hours during the dry periods. Bacterial production data for these lakes had not been recorded until now. The present study had as working hypothesis that bacterial production may contribute significantly to carbon fixation, particularly in lakes rich in organic matter and that this production varies diurnal and seasonally thus altering BP/PP ratios. In order to test this hypothesis the study had as objective to estimate phytoplankton and bacterioplankton production rates along with the concentrations of carbon, nitrogen, and phosphorus in two periods of the day (morning and afternoon) and in two seasons (dry and rainy), in four lakes, being two lakes within the Rio Doce State Park and two at its surroundings. Among the selected lakes, Lake Amarela showed the highest nutrient concentrations and highest bacterial production. The results allow to conclude that despite exhibiting lower values when compared with the ones recorded for phytoplankton production, bacterioplankton production is essential to the general metabolism of the lakes, particularly for those rich in organic matter and exhibiting oligo-mesotrophic conditions. [ABSTRACT FROM AUTHOR]