Abstract
A new ecosystem model was developed to predict the effects of pH variation on the microbial community in freshwater lakes by using the features of three existing models: an ecosystem model, a pH simulation model, and a cardinal temperature and pH model. Data for validation were obtained by conducting the following experiment. Circumneutral lake water, collected from Lake Inawashiro in Fukushima Prefecture, Japan, was mixed with acidic river water to prepare water samples with three pH values: 6.5, 5.5, and 4.5. Transparent acrylic tanks were filled with prepared water and placed in a sunny place for 24 days, during which time pH and dissolved oxygen content were continuously measured. The biomass of phytoplankton, zooplankton, and bacteria was measured on the first and last day. Hourly calculated values of pH and DO were in excellent agreement with observed values in the tanks. The simulation of the change in biomass of alkaliphilous, circumneutral, and acidophilous phytoplankton species for three different levels of pH over the course of 24 days also agreed with observations. The examination of fundamental model response also showed that the new ecosystem model is applicable to actual lake environments, where acidification or alkalization in pH is observed, by continuously changing the total alkalinity and incorporating sediment respiration.
