Effects of Extreme Summer Heat on Lake Kiba Water Quality in 2023

Abstract

At Lake Kiba in Komatsu City, Ishikawa Prefecture, COD, an indicator of water pollution, consistently exceeds the standard value of 3 mg/L, and in 1995 was the second highest in Japan. Previous studies have suggested that there is a correlation between COD and DOC and POC concentrations. The eight regular observations were made at Lake Kiba from June to October 2023 to measure water quality. In particular, DOC and POC concentrations increased significantly in August and September, suggesting an increase in phytoplankton. 2023 summer recorded the highest temperature ever recorded in Komatsu City (40 degrees), and August precipitation was the lowest in the past 10 years. Compared to summer season with the heavy rainfall of 2022, DOC and POC concentrations are higher approximately twofold in August 2023, which was both light rain and extremely hot, suggesting that temperature and rainfall had an effect on dynamics of dissolved and particular organic matter.