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<p>Dissolved organic carbon (DOC) is a critical component of aquatic carbon cycling and a key indicator of water quality in lake ecosystems. As the largest river-connected freshwater lake in China, Poyang Lake exhibits dramatic seasonal water level fluctuations (WLFs) and substantial spatial heterogeneity in hydrological connectivity. However, the drivers and mechanisms regulating DOC dynamics across its hydrologically distinct sub-lakes remain poorly understood. Based on quarterly monitoring data (2019–2022) from ten sampling sites in two typical regions—the relatively enclosed Cuoji Lake and the highly interconnected Nanji Wetland—this study investigated the spatiotemporal variations of DOC and identified the dominant controlling factors. Results showed that DOC concentrations in Cuoji Lake ranged from 0.54 to 4.61&#xa0;mg/L (mean: 2.46 ± 0.07&#xa0;mg/L) with significant seasonal fluctuations, peaking in the dry season (January: 3.52&#xa0;mg/L) and declining in the flood season (July: 2.58&#xa0;mg/L). In contrast, DOC in Nanji Wetland varied from 1.52 to 9.61&#xa0;mg/L (mean: 3.82 ± 1.72&#xa0;mg/L) without significant temporal variation. The correlation heatmap revealed no significant relationship between DOC and water level in either sub-lake, indicating that WLFs are not the dominant driver. Instead, hydrological connectivity, shaped by geomorphological enclosure, mediated DOC responses. Cuoji Lake’s seasonal DOC pattern was modulated indirectly by hydrological changes, while Nanji Wetland’s stability reflected a balance between allochthonous inputs and autochthonous production. Additionally, DOC was positively correlated with nutrients (NH<sub>4</sub><sup>+</sup>-N, PO<sub>₄</sub><sup>3−</sup>-P, TP), COD, chlorophyll a, and phytoplankton biomass, highlighting joint regulation by internal biogeochemical processes. These findings clarify the multi-factor regulation of DOC in hydrologically heterogeneous sub-lakes, emphasizing hydrological connectivity, organic matter sources, nutrients, and phytoplankton rather than water level as the main regulators shaping DOC dynamics in Poyang Lake’s sub‑lakes. The results provide scientific support for carbon cycling assessment and water quality management in large river-connected lakes.</p>

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Drivers of dissolved organic carbon in hydrologically distinct sub-lakes of Poyang Lake: the roles of hydrological connectivity, nutrients, and phytoplankton

  • 期刊论文

  • 发表日期：

    2026年7月11日

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  • Kuimei Qian,
  • Yuwei Chen,
  • Xueyang Zhang,
  • Shuya Wang,
  • Jinfu Liu,
  • Wei Li

摘要

Dissolved organic carbon (DOC) is a critical component of aquatic carbon cycling and a key indicator of water quality in lake ecosystems. As the largest river-connected freshwater lake in China, Poyang Lake exhibits dramatic seasonal water level fluctuations (WLFs) and substantial spatial heterogeneity in hydrological connectivity. However, the drivers and mechanisms regulating DOC dynamics across its hydrologically distinct sub-lakes remain poorly understood. Based on quarterly monitoring data (2019–2022) from ten sampling sites in two typical regions—the relatively enclosed Cuoji Lake and the highly interconnected Nanji Wetland—this study investigated the spatiotemporal variations of DOC and identified the dominant controlling factors. Results showed that DOC concentrations in Cuoji Lake ranged from 0.54 to 4.61 mg/L (mean: 2.46 ± 0.07 mg/L) with significant seasonal fluctuations, peaking in the dry season (January: 3.52 mg/L) and declining in the flood season (July: 2.58 mg/L). In contrast, DOC in Nanji Wetland varied from 1.52 to 9.61 mg/L (mean: 3.82 ± 1.72 mg/L) without significant temporal variation. The correlation heatmap revealed no significant relationship between DOC and water level in either sub-lake, indicating that WLFs are not the dominant driver. Instead, hydrological connectivity, shaped by geomorphological enclosure, mediated DOC responses. Cuoji Lake’s seasonal DOC pattern was modulated indirectly by hydrological changes, while Nanji Wetland’s stability reflected a balance between allochthonous inputs and autochthonous production. Additionally, DOC was positively correlated with nutrients (NH4+-N, PO₄3−-P, TP), COD, chlorophyll a, and phytoplankton biomass, highlighting joint regulation by internal biogeochemical processes. These findings clarify the multi-factor regulation of DOC in hydrologically heterogeneous sub-lakes, emphasizing hydrological connectivity, organic matter sources, nutrients, and phytoplankton rather than water level as the main regulators shaping DOC dynamics in Poyang Lake’s sub‑lakes. The results provide scientific support for carbon cycling assessment and water quality management in large river-connected lakes.