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<p>The underwater light environment is important for lake ecosystem function and structure. In the summer of 2023, the Yangtze River basin suffered an extreme drought, and Poyang Lake experienced its lowest water level since 1951. However, there remains&#xa0;a gap in understanding the impact of extreme drought on the underwater light environment. In this study, the underwater light environment in Poyang Lake was quantitatively investigated in late July 2023, and its influencing factors were explored. The results showed that the underwater light environment in Poyang Lake attenuated most drastically within the 0–0.4&#xa0;m depth range, where the underwater spectrum changes significantly, especially in the visible light range (400–700&#xa0;nm). With increasing depth, the proportion of red and green light increased, whereas that of blue light decreased rapidly. However, in regions with high Secchi depth (SD), even at 1.2&#xa0;m depth, blue light still accounted for 2.03–9.15%, forming a distinct underwater light environment. In other regions with low SD and high suspended solids (SS), blue light attenuated severely and red light became dominat. Although the red-to-blue light&#xa0;ratio varied across Poyang Lake, its maximum values were consistently distributed in the west. Attenuation of blue, green, and red light, as well as photosynthetically active radiation, in the four lake regions followed the order: northern &gt; western &gt; southern &gt; eastern, with blue light attenuating the most rapidly. In contrast to previous findings, SD was the key factor driving changes in the underwater light environment of Poyang Lake, followed by SS. Future efforts should prioritize enhanced monitoring of SD and the underwater light environment in Poyang Lake.</p>

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Extreme drought amplifies the dominant role of Secchi depth on the underwater light environment: evidence from Poyang Lake

  • 期刊论文

  • 发表日期：

    2026年1月30日

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  • Jianying Chao,
  • Xiaowen Lin,
  • Xiaodong Wu,
  • Jian Li,
  • Xuguang Ge,
  • Zhenni Gao,
  • Chenxin Zhong,
  • Zian Xiang,
  • Lishuai Zhang

摘要

The underwater light environment is important for lake ecosystem function and structure. In the summer of 2023, the Yangtze River basin suffered an extreme drought, and Poyang Lake experienced its lowest water level since 1951. However, there remains a gap in understanding the impact of extreme drought on the underwater light environment. In this study, the underwater light environment in Poyang Lake was quantitatively investigated in late July 2023, and its influencing factors were explored. The results showed that the underwater light environment in Poyang Lake attenuated most drastically within the 0–0.4 m depth range, where the underwater spectrum changes significantly, especially in the visible light range (400–700 nm). With increasing depth, the proportion of red and green light increased, whereas that of blue light decreased rapidly. However, in regions with high Secchi depth (SD), even at 1.2 m depth, blue light still accounted for 2.03–9.15%, forming a distinct underwater light environment. In other regions with low SD and high suspended solids (SS), blue light attenuated severely and red light became dominat. Although the red-to-blue light ratio varied across Poyang Lake, its maximum values were consistently distributed in the west. Attenuation of blue, green, and red light, as well as photosynthetically active radiation, in the four lake regions followed the order: northern > western > southern > eastern, with blue light attenuating the most rapidly. In contrast to previous findings, SD was the key factor driving changes in the underwater light environment of Poyang Lake, followed by SS. Future efforts should prioritize enhanced monitoring of SD and the underwater light environment in Poyang Lake.