In the eutrophic Lake Kasumigaura in Japan, a trend of dissolved Si (DSi) concentration was detected over the last three decades, probably caused by the DSi release enhanced by an increase in sediment resuspension for the same period (Arai et al., Limnol., 13, 81–95, 2012). The present study described the long-term trends of the magnitude and seasonality of diatom blooms in the lake during 1981–2010 using the database and assessed the influencing factors for the trends by the numerical simulation of DSi and diatoms. The box model was developed based on the lake budgets (inflow, outflow, release and sedimentation) and the simple diatom growth model depending on DSi, temperature and light condition. As results, database analysis detected a long-term trend of increasing diatom abundance and a shift of blooming season from spring and autumn to the winter–spring period. Si could be regarded as a main nutrient factor limiting diatom growth by analyzing N:P:Si ratios. Our model simulation relatively well-reproduced the increasing trend and the shift of seasonality of DSi and diatoms, even though peaks of diatom blooms were underestimated in some years. Among input variables, the concentration of resuspended sediments radically increased. The model simulation with the input variables or parameters changed suggested as follows: (1) the recent DSi release from resuspended sediments enhanced diatom abundance and (2) the degradation of light condition caused by resuspension affected the shift of blooming season. These findings implicate the significance of the interactions between sediments and water to phytoplankton blooms.
展开▼
