Assessing the impact of climate change on dissolved oxygen using a flow field ecosystem model that takes into account the anaerobic and aerobic environment of bottom sediments

Abstract

This study examines the potential impacts of climate change on Lake Biwa, Japan’s largest freshwater lake, with a focus on temperature, wind speed, and precipitation variations. Leveraging data from the IPCC Sixth Assessment Report, including CCP scenarios, projecting a significant temperature rise of 3.3–5.7 °C in the case of very high GHG emission power, the research investigates how these shifts may influence dissolved oxygen levels in Lake Biwa. Through a one-dimensional model incorporating sediment redox reactions, various scenarios where air temperature and wind speed are changed are simulated. It is revealed that a 5 °C increase in air temperature leads to decreasing 1–2 mg/L of dissolved oxygen concentrations from the surface layer to the bottom layer, while a decrease in air temperature tends to elevate 1–3 mg/L of oxygen levels. Moreover, doubling wind speed enhances surface layer oxygen but diminishes it in deeper layers due to increased mixing. Seasonal variations in wind effects are noted, with significant surface layer oxygen increases from 0.4 to 0.8 mg/L during summer to autumn, increases from 0.4 to 0.8 mg/L in autumn to winter due to intensified vertical mixing. This phenomenon impacts the lake’s oxygen cycle year-round. In contrast, precipitation changes show limited impact on oxygen levels, suggesting minor influence compared to other meteorological factors. The study suggests the necessity of comprehensive three-dimensional models that account for lake-specific and geographical factors for accurate predictions of future water conditions. A holistic approach integrating nutrient levels, water temperature, and river inflow is deemed essential for sustainable management of Lake Biwa’s water resources, particularly in addressing precipitation variations.