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<p>Understanding the drivers of long-term changes in phytoplankton limiting factors is crucial for effective eutrophication management in lakes. This study focuses on Taihu Lake—a large, shallow lake—over the period 2007–2023, during which substantial climate variability and watershed management occurred. This study aims to characterize the temporal evolution of the limiting factors that constrain the final yield of phytoplankton in the lake, and to identify the key drivers of these shifts, with particular focus on summer periods when environmental conditions are most favorable for achieving maximum algal biomass. We revised the trophic state index (TSIr) to suit the Taihu Lake case and analyzed the long-term total nitrogen (TN), total phosphorus (TP), Secchi depth (SD), and chlorophyll-<i>a</i> (Chl-<i>a</i>) data to track changes in algal biomass constraints. Results reveal a transition from a predominantly light-limited algal biomass in the early years to the increased nutrient limitation, particularly N and N&amp;P-co-limitation. This shift was evident in the evolving differences among TSIr sub-indices—TSIr(Chl <i>a</i>), TSIr(SD), TSIr(TN), and TSIr(TP). The observed transition was found primarily driven by sustained reductions in nutrient concentrations, especially TN, coupled with an improved light environment, as decreased wind speed reduced non-algal turbidity. The emergence of nutrient limitation re-established partially a positive coupling between Chl <i>a</i> and TN/TP in some areas of the lake, which differed from the decoupled patterns observed under light-limited conditions before 2020. Following this regime shift, continued TN and TP reductions post-2021 coincided with marked declines in Chl-<i>a</i> levels and bloom extent. Despite these improvements, Taihu Lake remains in a transitional phase, and light limitation remain to be dominant in most parts of the lake. Our ecosystem-scale study demonstrated that dual N &amp; P reduction is effective for treating shallow lakes. Furthermore, based on our results and by integrating reported thresholds from previous studies, we recommend TN concentrations of 0.69–0.80 mg/L and TP concentrations below 50 µg/L as preliminary control targets for shallow eutrophic lakes. These findings offer critical insights for algal bloom prevention and control in Taihu Lake and similar system.</p>

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From light to nutrient limitation: attributing cyanobacterial bloom transitions in Taihu Lake (2007–2023) through a limiting factor perspective

  • 期刊论文

  • 发表日期：

    2026年1月14日

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  • Shuzhan Ma,
  • Zihao Song,
  • Guangwei Zhu,
  • Yongjiu Cai,
  • Wei Zou

摘要

Understanding the drivers of long-term changes in phytoplankton limiting factors is crucial for effective eutrophication management in lakes. This study focuses on Taihu Lake—a large, shallow lake—over the period 2007–2023, during which substantial climate variability and watershed management occurred. This study aims to characterize the temporal evolution of the limiting factors that constrain the final yield of phytoplankton in the lake, and to identify the key drivers of these shifts, with particular focus on summer periods when environmental conditions are most favorable for achieving maximum algal biomass. We revised the trophic state index (TSIr) to suit the Taihu Lake case and analyzed the long-term total nitrogen (TN), total phosphorus (TP), Secchi depth (SD), and chlorophyll-a (Chl-a) data to track changes in algal biomass constraints. Results reveal a transition from a predominantly light-limited algal biomass in the early years to the increased nutrient limitation, particularly N and N&P-co-limitation. This shift was evident in the evolving differences among TSIr sub-indices—TSIr(Chl a), TSIr(SD), TSIr(TN), and TSIr(TP). The observed transition was found primarily driven by sustained reductions in nutrient concentrations, especially TN, coupled with an improved light environment, as decreased wind speed reduced non-algal turbidity. The emergence of nutrient limitation re-established partially a positive coupling between Chl a and TN/TP in some areas of the lake, which differed from the decoupled patterns observed under light-limited conditions before 2020. Following this regime shift, continued TN and TP reductions post-2021 coincided with marked declines in Chl-a levels and bloom extent. Despite these improvements, Taihu Lake remains in a transitional phase, and light limitation remain to be dominant in most parts of the lake. Our ecosystem-scale study demonstrated that dual N & P reduction is effective for treating shallow lakes. Furthermore, based on our results and by integrating reported thresholds from previous studies, we recommend TN concentrations of 0.69–0.80 mg/L and TP concentrations below 50 µg/L as preliminary control targets for shallow eutrophic lakes. These findings offer critical insights for algal bloom prevention and control in Taihu Lake and similar system.