Efeito de diferentes níveis de enriquecimento por fósforo sobre a estrutura da comunidade perifítica em represa oligotrófica tropical (São Paulo, Brasil)

Abstract

Nutrient diffusing substrata (NDS) were used to determine the effect of added phosphorus on the periphyton development in a shallow reservoir (Lago do IAG, PEFI, São Paulo). Three treatments (n = 2) were designed: control (without phosphorous addition) and two levels of phosphorus addition (P1 = 0.1 M and P2 = 0.5 M KH2PO4). NDS surface was covered with a 20 μm mesh cloth for periphyton growth. Samplings were carried at 15, 20, 25 and 30 days of colonization. Biomass accumulation (organic matter, chlorophyll-a, total algal biovolume) and total algal density did not show significant response to nutrient addition. Seven species of chlorophytes and one of diatoms were closely associated to P availability. Periphyton nutrient status (P%, N%, N:P) demonstrated P-limitation as well as reinforced periphyton P retention capacity. Periphyton attributes were more sensible to P enrichment than to the different addition levels, indicating further N-limitation. Comparison with previous data indicated temporal (1996-2002) increase in the reservoir phosphorus availability, although P-limitation is still prevalent. Periphyton, on the basis of its nutrient status and species structure, was sensible to temporal shift on phosphorus availability and P-addition, reinforcing its potential as an evaluating tool for early signs of eutrophication.