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<p>Eutrophication and browning are two of the great issues causing degradation of freshwater ecosystems. While the ecological effects of each have been extensively studied, their interactive effects on the competition between submerged macrophytes and phytoplankton, a key dynamic in shallow lake stability, remain poorly understood. We used 30 mesocosms to simulate shallow lakes dominated by <i>Myriophyllum spicatum</i>, applying a factorial experiment crossing two nutrient conditions and five dissolved organic carbon (DOC) concentrations to assess their combined effects on the growth of these competing primary producers. In low to moderate DOC (2–16&#xa0;mg l<sup>–1</sup>) systems, high nutrient levels stimulated phytoplankton growth. Phytoplankton shading caused a significant decline in <i>M. spicatum</i> biomass and facilitated a shift from clear to murky waters. However, in systems with higher DOC, browning counteracted the stimulating effects of nutrients on phytoplankton and caused a decline in the biomass of both primary producers. The synergistic interaction of high nutrients and high DOC exacerbated ecosystem degradation. This study advances the alternative stable state theory by demonstrating how the interaction between eutrophication and browning nonlinearly regulates macrophyte–phytoplankton competition. Our quantitative findings provide a mechanistic basis for predicting regime shifts in shallow lakes and offer practical insights for pond and shallow lake management.</p>

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Eutrophication and allochthonous dissolved organic carbon input alter macrophyte–phytoplankton interactions in shallow lakes: a mesocosm experiment

  • 期刊论文

  • 发表日期：

    2026年7月7日

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  • Xinnan Zhang,
  • Dong Luo,
  • Ligang Xu,
  • Xiaolong Wang,
  • Gang Ge,
  • Lei Li

摘要

Eutrophication and browning are two of the great issues causing degradation of freshwater ecosystems. While the ecological effects of each have been extensively studied, their interactive effects on the competition between submerged macrophytes and phytoplankton, a key dynamic in shallow lake stability, remain poorly understood. We used 30 mesocosms to simulate shallow lakes dominated by Myriophyllum spicatum, applying a factorial experiment crossing two nutrient conditions and five dissolved organic carbon (DOC) concentrations to assess their combined effects on the growth of these competing primary producers. In low to moderate DOC (2–16 mg l–1) systems, high nutrient levels stimulated phytoplankton growth. Phytoplankton shading caused a significant decline in M. spicatum biomass and facilitated a shift from clear to murky waters. However, in systems with higher DOC, browning counteracted the stimulating effects of nutrients on phytoplankton and caused a decline in the biomass of both primary producers. The synergistic interaction of high nutrients and high DOC exacerbated ecosystem degradation. This study advances the alternative stable state theory by demonstrating how the interaction between eutrophication and browning nonlinearly regulates macrophyte–phytoplankton competition. Our quantitative findings provide a mechanistic basis for predicting regime shifts in shallow lakes and offer practical insights for pond and shallow lake management.