Effect of complex iron on the phosphorus absorption by two freshwater algae.

Iron plays an important role in physiological processes of microalgae and also affects the absorption of other nutrients by algae cells. Therefore, iron is one of the important controlling factors for algae bloom formation. This study investigated the effect of four kinds of complex iron (EDTA-Fe, ferric humate, ferric oxalate and ferric ammonium citrate) on the phosphorus absorption by two freshwater algae (Scenedesmus quadricauda and Anabaena flos-aquae). The results showed that the species and concentration of complex iron had a significant effect on the phosphorus uptake rate of S. quadricauda, but had only a slight effect on that of A. flos-aquae. The former exhibits positive influences on phosphorus absorption and was in the following order: ferric oxalate and EDTA-Fe > ferric humate and ammonium ferric citrate, and these effects depended on whether the presence of complex iron constitutes an environmental pressure for the growth of algal cells.

Effect of iron and phosphorus on the microalgae growth in co-culture.

Iron and phosphorus (P) are the important micro- and macro-nutrient for microalgae growth, respectively. However, the effect of iron and P on microalgae growth in co-culture associating with the formation of dominate algae has not been investigated before. In the current study, Anabaene flos-aquae, Chlorella vulgaris and Melosira sp. were co-cultivated under the addition of different initial iron and P to reveal the effect of iron and phosphorus on the growth of microalgae. The results showed that the mean growth rate of A. flos-aquae, C. vulgaris and Melosira was 0.270, 0.261 and 0.062, respectively, indicating that the A. flos-aquae and C. vulgaris algae are liable to be the dominant algae while the growth of Melosira was restrained when co-cultured. The ratio of Fe to P has a significant impact on the growth of microalgae and could be regarded as an indicator of algae growth. Microalgae showed a much more obvious uptake of iron compared to that of P. The information obtained in the current study was useful for the forecast of water quality and the control of microalgae bloom.