Chlorophyll ratio analysis of the responses of algae communities to light intensity in spring and summer in Lake Erhai

Abstract

Algae biomass and community structure can reflect the current situation of a lake, especially in response to changes in light intensity. The relationship between chlorophyll a (Chl a) and chlorophyll b (Chl b) ratio and the proportion of Chlorophyta within the algae community were analyzed in this study. Results showed that light was more intense in August than in March. Algae density in August was greater than in March. The concentration of Chl a and b was influenced by light intensity level. In March, Microcystis and Kirchneriella sp dominated surface water, where the light intensity was over 216 μmol m−2 s−1, Gloeocapsa, Dictyospaerium pulchellum, and Scenedesmus dominated intermediate water, where the light ranged from 36 to 216 μmol m−2 s−1. Asterionella formosa Hassall and Mougeotia scalaris dominated near the bottom, where the light was below 36 μmol m−2 s−1. In August, Microcystis and Selenastrum reinsch dominated surface water, where the light was above 18 μmol m−2 s−1. Chroococcus, Chlorella, and Scendesmus quadricauda dominated intermediate water, where light ranged from 90 to 180 μmol m−2 s−1. Anabaena spirioides and Pediastrum simplex dominated bottom water, where the light was below 90 μmol m−2 s−1. According to the mean value of Chlorophyta density and algae cell density in three different water levels, the ratio of Chlorophyta and algae community declined from March to August, ranging from 12.35–21.41 to 4.28–11.19 %. The mean value ratio of Chl b and Chl a in three different water levels showed the same tendency from March to August, ranging from 18.05–21.77 to 15.15–17.44 %. These variations in chlorophyll ratio and Chlorophyta ratio indicated that the structure of the algae community structure was influenced by differences in light intensity.