Predicting phytoplankton assemblages growth and estimating critical N: P ratios with experimental nutrient additions in a drinking water reservoir of central China

Abstract

AbstractThe purpose of this study was to evaluate the effects of limiting nutrients and the N: P ratios on the growth of phytoplankton. In this study, we used the nutrient enrichment bioassays (NEB), Multivariate analysis of variance, and regression analysis. The results showed that the affected change of phytoplankton assemblages growth was the concentrations of nitrogen and phosphorous. During the same period, the response time of phytoplankton to the input of external nutrients was similar. The growth rates of phytoplankton were not persistent. This is related to the differences in environmental conditions, dominant species composition, and phytoplankton growth strategies. Different dominant species also had different response mechanisms to nutrient addition. The growth effect of phytoplankton in the preliminary experiment in the laboratory was more significant than that in the field experiment. Water temperature and light were also important environmental factors affecting the growth of phytoplankton. Multivariate analysis of variance showed that phosphorus addition alone had a more significant stimulation on phytoplankton growth than that of nitrogen, especially for Synedra. But addition of both nitrogen and phosphorus had the most stimulating effect on Cyanophyta and Chlorophyta. The phytoplankton had the maximum growth in TN: TP = 19.87, phytoplankton growth was promoted with 0.9 ∼ 13.59 mg/L TN and 0.02 ∼ 0.684 mg/L TP. When the total phosphorus in summer was greater than 0.04 mg/L, the possibility of algal bloom and will be greater. The linear regression fitted chlorophyll a and phosphorus well, and the regression equation was as follows: Log10(Chl.a) = 2.154 + 0.5103 × Log10(TP). The binary regression equation of chlorophyll a and nitrogen and phosphorus was as follows: Chl.a = 33.84 + 1.769TN + 123.9TP.

Keywords

• N: P ratios
• nutrient additions
• phytoplankton
• growth rate
• reservoir