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<p>Urban shallow lakes are crucial in regional carbon cycling, but their multi-interface exchanges and drivers remain poorly understood. This study examines Nianjia Lake, a typical urban shallow lake in Changsha, China, focusing on spatiotemporal distributions of DOC, DIC, POC, and PIC in water and sediments. Carbon fluxes at sediment–water and water–air interfaces were quantified with key drivers. Carbon fractions show spatial heterogeneity. DOC accumulates in mid-depth waters and porewater via sediment release and microbial mineralization of organic matter in the surface water. DIC increases downward due to organic-to-inorganic conversion through mineralization. POC and PIC concentrate in deeper zones, influenced by biological metabolism, settling, and sequestration. Patterns of the four carbon fractions varied significantly with water depth, pH, temperature, and nutrient concentrations, revealing differences in their transformation mechanisms. Sediment–water interface exhibits net DOC and DIC release, DIC dominant, driven by sediment organic matter mineralization modulated by depth and diffusion. water–air interface acted as a net CO<sub>2</sub> sink jointly regulated by nutrients, hydrodynamics, and biological metabolism. Nianjia Lake follows a coupled “sediment release–water-column transformation–atmospheric CO<sub>2</sub> uptake” pathway, acting as a net atmospheric CO<sub>2</sub> sink. Findings advance understanding of urban shallow lakes' roles in aquatic ecosystem carbon budgets and hydrological regulation.</p>

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Internal carbon cycling and CO2 emissions revealed by multiple carbon fractions in a subtropical urban shallow lake

  • 期刊论文

  • 发表日期：

    2026年8月4日

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  • Yishu Li,
  • Hai Xiao,
  • Dehua Mao,
  • Siyi Huang,
  • Yudong Sun

摘要

Urban shallow lakes are crucial in regional carbon cycling, but their multi-interface exchanges and drivers remain poorly understood. This study examines Nianjia Lake, a typical urban shallow lake in Changsha, China, focusing on spatiotemporal distributions of DOC, DIC, POC, and PIC in water and sediments. Carbon fluxes at sediment–water and water–air interfaces were quantified with key drivers. Carbon fractions show spatial heterogeneity. DOC accumulates in mid-depth waters and porewater via sediment release and microbial mineralization of organic matter in the surface water. DIC increases downward due to organic-to-inorganic conversion through mineralization. POC and PIC concentrate in deeper zones, influenced by biological metabolism, settling, and sequestration. Patterns of the four carbon fractions varied significantly with water depth, pH, temperature, and nutrient concentrations, revealing differences in their transformation mechanisms. Sediment–water interface exhibits net DOC and DIC release, DIC dominant, driven by sediment organic matter mineralization modulated by depth and diffusion. water–air interface acted as a net CO2 sink jointly regulated by nutrients, hydrodynamics, and biological metabolism. Nianjia Lake follows a coupled “sediment release–water-column transformation–atmospheric CO2 uptake” pathway, acting as a net atmospheric CO2 sink. Findings advance understanding of urban shallow lakes' roles in aquatic ecosystem carbon budgets and hydrological regulation.