Streams and rivers are now recognized to be sites of intense carbon (C) emissions, yet the lack of C emission estimates that integrate beyond individual river systems has slowed their inclusion in landscape C budgets. Here we apply empirical models of CO2 and CH4 concentrations and gas exchange continuously along entire fluvial networks to derive the total fluvial CO2 and CH4 emissions in large (3000 to 30,000 km2) watersheds located across the boreal biome of Québec (Canada). We assess how total fluvial network C emissions vary with landscape and climate properties, and compare their magnitude to other components of the landscape C budget. The total fluvial network emissions expressed as per unit watershed area ranged from 0.7 to 29.2 g C m-2 yr-1 for CO2, and 4-1780 mg C m-2 yr-1 for CH4, and neither was related to watershed area or drainage density. Rather, watershed slope and terrestrial net productivity were major drivers of the integrated network fluvial emissions. We also show that steeper watersheds had a greater proportion of emissions relative to downstream export of C from the watershed. Integrated fluvial emissions are of the same magnitude as the terrestrial C sink, yet these two fundamental components of the boreal landscape C budget are not tightly coupled.

中文翻译：

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魁北克北部寒带地区河流网络温室气体综合排放量的大小和驱动因素。

现在，溪流和河流被认为是大量碳（C）排放的地点，但是由于缺乏C排放量的估算，这些估算不能整合到各个河流系统之外，这减慢了它们纳入景观C预算的速度。在这里，我们应用了整个河流网络中连续的CO2和CH4浓度以及气体交换经验模型，以得出位于魁北克（加拿大）北部生物群落的大型（3000至30,000 km2）流域的总CO2和CH4排放量。我们评估了河流网络C的总排放量如何随景观和气候特性的变化而变化，并将其大小与景观C预算的其他组成部分进行比较。以单位流域面积表示的河流网络总排放量，对于CO2为0.7至29.2 g C m-2 yr-1，对于CH4为4-1780 mg C m-2 yr-1，两者均与流域面积或排水密度无关。相反，流域坡度和地面净生产力是综合网络河流排放的主要驱动力。我们还表明，相对于下游从集水区出口的碳，陡峭的集水区的排放比例更大。河流总排放量与地面C汇的幅度相同，但北方景观C预算的这两个基本组成部分并没有紧密耦合。