Lakes and streams in mountain regions are important contributors to carbon (C) fluxes. However, detailed carbon balances of the stream-lake continuum are rare. Combining eddy covariance (EC) measurements of lake-atmosphere net ecosystem CO₂ exchange with measurements of fluvial C fluxes (dissolved organic C, DOC; particulate organic C, POC; dissolved inorganic C, DIC), and in-lake sedimentation, we here present a detailed annual C balance of an oligotrophic clearwater lake in the eastern European Alps. The C flux into the lake was 1522 Mg C year⁻¹ by DIC (93%), DOC (6%), and POC (0.7%). The largest C losses were fluvial exports (1595 Mg C year⁻¹) of DIC (93%), DOC (6%), and POC (0.8%), while sedimentation accounted for 7.3 Mg C year⁻¹. The residual of all fluvial and sedimentation fluxes revealed the lake as a net sink of atmospheric CO₂ of 77 Mg C year⁻¹. The EC measurement confirmed a small positive or negative contribution of atmospheric exchange to the lake C balance. In-lake transfer among C pools was only significant for the flux from DIC to POC (8.4 Mg C year⁻¹), which, following our model, is the transfer through primary production in summer. Fluvial DOC and DIC fluxes were controlled by discharge; POC retention and sedimentation depended on the meteorological season and in-lake residence time. Following our findings, we conclude that hydrology acted as the most important control for the C balance of this clearwater mountain lake by controlling inflow, outflow, and sedimentation fluxes.

中文翻译：

---

水文控制东欧阿尔卑斯山高山湖泊的碳质量平衡

山区的湖泊和溪流是碳（C）通量的重要贡献者。然而，河流-湖泊连续体的​​详细碳平衡很少见。将湖泊-大气净生态系统 CO ₂交换的涡度协方差 (EC) 测量与河流 C 通量（溶解有机 C、DOC；颗粒有机 C、POC；溶解无机 C、DIC）和湖内沉积的测量相结合，我们在这里展示了东欧阿尔卑斯山贫营养型清水湖的详细年度碳平衡。通过 DIC (93%)、DOC (6%) 和 POC (0.7%)，流入湖中的 C 通量为 1522 Mg C year ^-1。最大的 C 损失是DIC (93%)、DOC (6%) 和 POC (0.8%) 的河流出口（1595 Mg C 年^-1），而沉积占 7.3 Mg C 年^-1. 所有河流和沉积通量的残留表明该湖是大气 CO ₂的净汇，为 77 Mg C year ^-1。EC 测量证实了大气交换对湖 C 平衡的小的正或负贡献。C 库之间的湖内转移仅对从 DIC 到 POC 的通量（8.4 Mg C 年^-1)，按照我们的模型，这是通过夏季初级生产的转移。河流 DOC 和 DIC 通量受排放控制；POC 的滞留和沉淀取决于气象季节和湖内停留时间。根据我们的研究结果，我们得出结论，通过控制流入、流出和沉积通量，水文是该清水山湖 C 平衡的最重要控制因素。