Artificial destratification of a small tropical reservoir : effects upon the phytoplankton

The phytoplankton in a reservoir of 0.5 million m3, maximal depth 13.4 m, were studied over 4 years. The results were examined statistically by hierarchical fusion analysis based on the biomass of species. In the first 2 years the reservoir was strongly stratified for long periods; this was artificially eliminated in years 3 and 4 by aeration. In the unmanaged reservoir, chlorophyll-a reached a maximum during stratification with a shallow epilimnion. Cyanobacteria dominated the phytoplankton community during the warmer months of the year. The changing patterns of stratification and circulation in the unmanaged reservoir disrupted phytoplankton communities causing peaks of biomass. When the reservoir was mixed, diatoms became the dominant organisms until silica was depleted when cyanobacteria and chlorophytes replaced them. Average chlorophyll levels were 120 and 64 mg per m2 in the managed and unmanaged reservoir, respectively. There are 47 references.