Resumo

RAMIREZ-R., JOHN J.; GUTIERREZ, FERNANDO L.  e  VARGAS, ALEXANDER. Phytoplankton community response to artificial eutrophication experiments conducted in the La Fe reservoir, El Retiro, Antioquia, Colombia. Caldasia [online]. 2005, vol.27, n.1, pp.103-115. ISSN 0366-5232.

The addition of Nitrogen (Potassium Nitrate) at three concentrations [0 (µg.l-1 (No), 500 (µg.l-1 (N1), and 1000 (µg.l-1 (N2)], and Phosphorus (Potassium Phosphate acid) at four concentrations [0(µg.l-1 (Po), 10 (µg.l-1 (P1), 50 (µg.l-1 (P2) and 100 (µg.l-1 (P3)] to surface water samples contained in 2-litter plastic bags in the dam of La Fe reservoir were analyzed. Sampling was done on June, 6, 2001, and water samples were incubated on the surface for 14 days. Results were analyzed using Factorial anova type 3 x 4. Response variables analyzed were phytoplankton biomass, pigment ratio and suspended particle concentration. There was phytoplankton biomass increases in all of the treatments except in the first four. Anova of chlorophyll transformed logarithmically was significantly different for Nitrogen (α = 0.0290), but in treatments without Nitrogen, chlorophyll was absent. Anova was neither significantly different in chlorophyll concentration for Phosphorus (α = 0.9536), nor for double interaction (α = 0.7598). Anova for suspended particles was significantly different for Phosphorus (α = 0.0398), and for double interaction (α = 0.0162), but not for Nitrogen (α = 0.0607). The higher mean values were found in treatments where both nutrients were present, and the highest values were found in treatments in which both nutrients had the highest concentrations (N2P3). Significant phytoplankton biomass increase in bags with nitrates allows us to conclude that for the sampling day in the limnetic zone of La Fe reservoir, Nitrogen, and not Phosphorus, was the limiting nutrient. In treatments in which both nutrients were present, increase in chlorophyll was not pronounced. Total suspended particles was not the best criteria to evaluate the effects of the increase in phytoplankton community since zooplankton (highly abundant in the reservoir), an additional source of suspended particles, was not controlled.

Palavras-chave : Phytoplankton; nutrients; enrichment; controlled eutrophication; tropical reservoir.

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