Total Aquatic Carbon Emissions Across the Boreal Biome of Québec Driven by Watershed Slope

Abstract

AbstractInland waters emit large amounts of CO2 and CH4 to the atmosphere, partially offsetting the sequestration of carbon in terrestrial ecosystems. However, the incorporation of inland waters into landscape carbon budgets remains challenging, hampered by a lack of studies that consider both carbon gases and the variety of aquatic systems (streams, rivers, and lakes). Here we develop a whole‐network assessment of total aquatic carbon emissions for a set of large watersheds in boreal Québec, Canada. Expressed per unit watershed area, our estimates of total (CO2 + CH4) aquatic carbon emissions range between 11 and 38 g C m−2 yr−1 and cannot be predicted from the size of the watershed or the total surface area of aquatic systems. Rather, we show that total aquatic emissions vary across the boreal landscape of Québec as a function of the average slope of the watershed, which indirectly accounts for the configuration of aquatic networks, the physical forcing that influences gas exchange in fluvial systems, and the potential amount of soil carbon reaching aquatic systems. Total aquatic carbon emissions in boreal Québec are of the same range and magnitude of variation than other components of the boreal carbon budget and could offset terrestrial net ecosystem productivity by as much as 38%.