Visualization of lake succession as indicated by macrophyte species composition and trophic levels in lakes subdivided by volcanic eruption at Akan Caldera, Hokkaido, Japan

Abstract

It is unfeasible to continuously observe ecological succession in lakes because of the long time-scales involved. Thus, the process has been inductively deduced by comparing many lakes with different succession states, or indirectly simulated by tracking studies of smaller water bodies, experiments using microcosms or mesocosms, and reconstruction of lake history by sediment analysis. However, the reality of succession processes in large lakes with slow succession is not well understood, and new approaches are needed. Theoretically, in a group of large and small lakes of similar ages and with similar initial and watershed environments the rate of nutrient accumulation in each lake depends on the ratio of lake size to the watershed area, and the lakes are predicted to evolve to different trophic levels over time. Here, we tested this hypothesis on the 10 lakes of varying sizes in Akan Caldera, Japan, which were formed thousands of years ago by fragmentation due to volcanic eruptions within the caldera. Topographic and water quality studies found that the ratio of lake size (area and volume) to accumulated watershed area, expressed logarithmically, had a positive linear regression with the total phosphorus concentration, an indicator of trophic level. The trophic levels of the lakes were diverse, including oligotrophic, mesotrophic, and eutrophic types in the traditional "lake type" classification based on total phosphorus and chlorophyll-a concentrations. Furthermore, 21 species of aquatic macrophytes were observed by a diving survey, and the species composition was classified into five groups corresponding to the trophic status of the lakes, indicating a conventional "hydrarch succession”. The diversity of water quality and aquatic vegetation in a group of lakes with similar origins paves the way for new comparative studies of lakes, including large lakes.

Seven Epithemia taxa (Bacillariophyta) from Lake Akan (Japan) and their salinity tolerances

“…2 ; 43°26′25.80″N, 144°5′6.70″E ), eastern Hokkaido, Japan, using 10-mL syringes. Lake Akan is an inland volcanic lake that serves as a habitat for rare algae such as Aegagropila linnaei Kützing (e.g., Wakana et al 2021 ). It has a salinity, pH, and temperature of 0‰, 8.0, and 21 °C, respectively (Table 1 ), with an electrical conductivity of 366 (μS/cm) and sand as the bottom sediment.…”