Fig. 3

Seasonal changes in alpha diversity in Ace Lake. Line graph depicting Simpson’s index of diversity (alpha diversity) for the 120 metagenomes obtained from the three filter fractions (20–3 μm, dark blue line; 3–0.8 μm, pink line; 0.8–0.1 μm, light blue line) collected between 2006 and 2015 during summer (red shading), winter (blue shading), or spring (green shading). The data on the x-axis are arranged (from left to right) depth-wise from the upper to lower zone. The boxed area at the top of the figure provides an expanded view of the alpha diversity occurring between 0.9 and 1.0. Depths: U1, upper 1; U2, upper 2; U3, upper 3; I, interface; L1, lower 1; L2, lower 2; L3, lower 3 (see Additional file 1: Table S1 for specific information about sampled depths)