河川の生物化学的酸素要求量の曜日・時間帯特異的な変動：群馬県南東部における調査事例

抄録

The biochemical oxygen demand (BOD) is widely used as an indicator of organic pollution in river water. Comparisons with environmental quality standards at environmental reference points in public water were conducted across Japan. In this study, we conducted consecutive 5-day weekday BOD measurements at four locations over four seasons in three rivers in the southeastern part of the Gunma Prefecture, to evaluate the day-of-the-week and parts-of-the-day-specific BOD variations. Although not statistically significant, higher BOD values were observed in the order—Thursdays, Wednesdays, Tuesdays, Mondays, and Fridays. The observed BOD was significantly higher in the afternoon than in the forenoon. In the study area, most of the previous BOD measurements for comparison with the environmental quality standard were conducted on Wednesday forenoon. Our study highlights the importance of understanding sampling design bias in BOD measurements to avoid overlooking possible over- or under-evaluation of water quality status.