关键词: 亚热带湖泊, 水产养殖, 退养还湖, CO₂通量, 驱动因素

Abstract: Lakes are crucial for the global carbon cycle. The impacts of aquaculture and “pen removal and lake ecological restoration” on lake carbon source and sink functions remain unclear. We continuously monitored CO₂ fluxes in the aquaculture zones of East Lake Taihu during the aquaculture period (2018) and the ecological restoration period (2019-2020), to assess the effects of restoration on lake CO₂ flux and its driving factors. The results showed that, regardless of the aquaculture or restoration stage, seasonal variations of CO₂ fluxes followed a consistent pattern: net CO₂ uptake during the growing season (May-October) and near-zero fluxes during the non-growing season (December-March). Diurnal CO₂ flux patterns characterized by daytime uptake and nighttime release, which became more pronounced after restoration, with a significant increase in daytime uptake and a slight rise in nighttime emission. The reduction in external organic carbon input and the shift in dominant macrophyte communities from submerged plants to floating-leaf plants after restoration substantially enhanced net CO₂ uptake of East Lake Taihu, with growing-season CO₂ uptake increasing from 182.03 g CO₂·m^-2·a ^-1 in 2018 (aquaculture stage) to 384.17 and 629.19 g CO₂·m^-2·a ^-1 in 2019 and 2020, respectively. The diurnal CO₂ flux dynamics were primarily driven by solar radiation. Both light-use efficiency and photosynthetic capacity of aquatic plants improved after restoration. At the daily scale, CO₂ fluxes during the aquaculture period were regulated by temperature, solar radiation, and wind speed. After restoration, the effect of wind speed became insignificant, the temperature sensitivity (Q₁₀) of daytime uptake increased from 2.44 in 2018 to 3.16 in 2019 and 3.03 in 2020; and the Q₁₀ of nighttime emission declined from 10.20 in 2018 to 1.17 in 2019 and 5.14 in 2020. On the monthly scale, during the aquaculture phase, total nitrogen concentration was the primary controlling factor for lake CO₂ flux, while the normalized difference vegetation index (NDVI) was the primary controlling factor for diurnal lake CO₂ flux. After the cessation of aquaculture and the restoration of the lake, solar radiation and temperature became the primary controlling factors for lake CO₂ flux, and the sensitivity of diurnal lake CO₂ flux to changes in NDVI increased.

Key words: subtropical lake, aquaculture, pen removal and ecological restoration, CO₂ flux, driving factor