Varying Ecological Successions in Lakes Subdivided by Volcanic Eruption at Akan Caldera, Japan

It is difficult to continuously observe ecological succession processes within lakes occurring over long-time spans. Thus, the process is generally shown as “lake types” or "hydrarch succession" reflected by trophic levels or differing aquatic vegetation, based on inductive inference by comparison of many lakes. Alternatively, long-term changes are simulated via microcosms or mesocosms in experimental systems, or lake history can be reconstructed by sediment analysis. Here, we try to demonstrate lake ecological succession processes over thousands of years by showing an example of lakes with diverse trophic levels and aquatic vegetation which were formed by segmentation inside Akan Caldera in eastern Hokkaido, Japan, due to volcanic eruptions. We found oligotrophic, mesotrophic, eutrophic and dystrophic lake systems in the caldera, despite similar ages and process of origin. Total water phosphorus concentration, defining trophic level, was significantly correlated with the ratio of accumulated watershed area to lake area and volume. Twenty-one species of aquatic macrophytes were classified into five groups clearly corresponding to respective or combinations of trophic level. This study is the first to visualize lake serial stages by documenting a series of trophic levels and associated aquatic vegetation groups as a result of differing eutrophication rates over time.