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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 s, Gloeocapsa, Dictyospaerium pulchellum, and Scenedesmus dominated intermediate water, where the light ranged from 36 to 216 μmol m s. Asterionella formosa Hassall and Mougeotia scalaris dominated near the bottom, where the light was below 36 μmol m s. In August, Microcystis and Selenastrum reinsch dominated surface water, where the light was above 18 μmol m s. Chroococcus, Chlorella, and Scendesmus quadricauda dominated intermediate water, where light ranged from 90 to 180 μmol m s. Anabaena spirioides and Pediastrum simplex dominated bottom water, where the light was below 90 μmol m s. 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. [ABSTRACT FROM AUTHOR]

The water quality of Erhai Lake is good as a whole, but its decreasing trend is not optimistic; the water ecosystem of Erhai Lake has changed dramatically, showing an obvious degenerating trend. The main reasons for the ecosystem degeneration are as follows: inflow pollution load exceeding the water environmental capacity, not favorable water habitat for the propagation of submerged plants, and the weak management for the lake basin. To prevent the degeneration of Erhai ecosystem, two key problems should be solved: one is to reduce the inflow pollution load to prevent the increase of nitrogen and phosphorus concentrations in the overlying water; and the other is to implement the ecosystem regulation, namely improve the stability and biodiversity of Erhai ecosystem by habitat improvement, ecological restoration and ecological regulation. In terms of the preventive measures against the Erhai ecosystem degeneration, the pollution source control in combination with ecosystem regulation should be taken as the focus. Pollution source control, habitat improvement, ecological restoration, ecological regulation and watershed management should be emphasized simultaneously. To be specific, the key tasks for preventing Erhai ecosystem degeneration include five points namely, the reduction of pollution loading into lake, adjustment of ecological fishery, restoration of submerged vegetation, watershed integrated management, and emergency treatment of water blooms. [ABSTRACT FROM AUTHOR]