Lakes process a disproportionately large fraction of carbon relative to their size and spatial extent, representing an important component of the global carbon cycle. Alterations of ecosystem function via eutrophication change the balance of greenhouse gas flux in these systems. Without eutrophication, lakes are net sources of CO₂ to the atmosphere, but in eutrophic lakes this function may be amplified or reversed due to cycling of abundant autochthonous carbon. Using a combination of high-frequency and discrete sensor measurements, we calculated continuous CO₂ flux during the ice-free season in 15 eutrophic lakes. We found net CO₂ influx over our sampling period in 5 lakes (− 47 to − 1865 mmol m⁻²) and net efflux in 10 lakes (328 to 11,755 mmol m⁻²). Across sites, predictive models indicated that the highest efflux rates were driven by nitrogen enrichment, and influx was best predicted by chlorophyll a concentration. Regardless of whether CO₂ flux was positive or negative, stable isotope analyses indicated that the dissolved inorganic carbon pool was not derived from heterotrophic degradation of terrestrial organic carbon, but from degradation of autochthonous organic carbon, mineral dissolution, and atmospheric uptake. Optical characterization of dissolved organic matter revealed an autochthonous organic matter pool. CO₂ influx was correlated with autochthony, while efflux was correlated with total nitrogen and watershed wetland cover. Our findings suggest that CO₂ uptake by primary producers during blooms can contribute to continuous CO₂ influx for days to months. Conversely, eutrophic lakes in our study that were net sources of CO₂ to the atmosphere showed among the highest rates reported in the literature. These findings suggest that anthropogenic eutrophication has substantially altered biogeochemical processing of carbon on Earth.

相对于湖泊的大小和空间范围，湖泊处理的碳比例不成比例，代表了全球碳循环的重要组成部分。通过富营养化来改变生态系统功能会改变这些系统中温室气体通量的平衡。没有富营养化，湖泊是大气中CO _2的净来源，但是在富营养化湖泊中，由于丰富的原生碳循环，这种功能可能会被放大或逆转。结合使用高频和离散传感器测量，我们计算了15个富营养化湖泊在无冰季节的连续CO ₂通量。我们在采样期间发现了5个湖泊中的净CO ₂流入量（− 47至− 1865 mmol m ⁻²）和10个湖泊的净流出（328至11,755 mmol m ^-2）。在各个站点之间，预测模型表明最高的流出速率是由氮富集驱动的，而入流最好由叶绿素a的浓度预测。无论CO ₂流量是正还是负，稳定的同位素分析均表明，溶解的无机碳库并非源自陆地有机碳的异养降解，而是源自自生有机碳的降解，矿物溶解和大气吸收。溶解的有机物的光学表征揭示了一种自生有机物库。一氧化碳₂入潮与自养相关，而外排与总氮和流域湿地覆盖相关。我们的发现表明，开花期间初级生产者对CO _2的吸收可导致持续的CO ₂流入数天至数月。相反，在我们的研究中，富营养化的湖泊是大气中CO _2的净来源，在文献中报道的比率最高。这些发现表明，人为富营养化已大大改变了地球上碳的生物地球化学过程。