DOES THE NUTRIENT CONCENTRATION OF WATER ECOSYSTEMS AFFECT GROWTH RATES AND MAXIMUM PSII QUANTUM YIELD IN CALCIUM ALGINATE-ENCAPSULATED SCENEDESMUS OVALTERNUS AND CHLORELLA VULGARIS?
Aquatic ecosystems are susceptible to deterioration caused by eutrophication. Changes in the nutrient concentration may affect species physiology, making it a key factor in structuring communities. Phytoplankters have a short generation time and a fast response to environmental factors, which makes them a good model to address issues related to the effects of the trophic status on aquatic organisms. Our aim was to determine the changes in the growth and maximum PSII quantum yield of calcium alginate-encapsulated Scenedesmus ovalternus and Chlorella vulgaris incubated in aquatic ecosystems with different nutrient concentrations. We tested the following hypotheses: 1) alga with a greater capacity for nutrient absorption (C. vulgaris) would have the highest growth regardless of the environment nutrient concentration and 2) the concentration of nutrients positively affects the maximum PSII quantum yield in the two species. To test the hypotheses, S. ovalternus and C. vulgaris were immobilized in calcium alginate and cultured in wetlands with different nutrient concentrations. The growth of the two species differed between the wetlands; higher development was observed in the eutrophic environment. Significant differences were only recorded between the species in the eutrophic system, with greater growth in C. vulgaris. The hypereutrophic environment conditions were lethal for both species. The maximum quantum yield of PSII showed similar behaviour in both optimum nutrient conditions and limiting conditions. The nutrient concentration of the studied environments influenced the growth of the two species but not their maximum quantum yield of PSII, which seemed to be affected by factors other than nitrogen (N) and phosphorus (P) concentrations. C. vulgaris presented optimum growth only in the eutrophic system. The results showed that the growth rates of encapsulated algae could be a useful method for assessing changes, such as nutrient concentration, in the environmental conditions of the Sabana de Bogotá wetlands.