Aquatic carbon fluxes in a hemiboreal catchment are predictable from landscape morphology, temperature, and runoff

Aquatic networks contribute greenhouse gases and lateral carbon (C) export from catchments. The magnitudes of these fluxes exceed the global land C sink but are uncertain. Resolving this uncertainty is important for understanding climate feedbacks. We quantified vertical methane (CH4) and carbon dioxide (CO2) emissions from lakes and streams, and lateral export of dissolved inorganic and organic carbon from a hemiboreal catchment for 3 yr. Lateral C fluxes dominated the total aquatic C flux. All aquatic C fluxes were disproportionately contributed from spatially restricted areas and/or short-term events. Hence, consideration of local and episodic variability is vital. Temperature and runoff were the main temporal drivers for lake and stream C emissions, respectively. Whole-catchment aquatic C emissions scaled linearly with these drivers within timeframes of stable land-cover. Hence, temperature and runoff increase across Northern Hemisphere humid areas from climate change may yield proportional increases in aquatic C fluxes.

Automated summary

Aquatic networks play a crucial role in greenhouse gas emissions and carbon export from catchments, but the exact magnitudes of these fluxes are uncertain. It is important to resolve this uncertainty for a better understanding of climate feedbacks. Through a 3-year study, we measured vertical emissions of methane and carbon dioxide from lakes and streams, as well as lateral export of dissolved carbon from a hemiboreal catchment. Lateral carbon fluxes were found to dominate the total aquatic carbon flux, and were contributed mainly by localized areas and short-term events. Temperature and runoff were identified as the main drivers for C emissions from lakes and streams, respectively. Changes in temperature and runoff due to climate change in humid areas of the Northern Hemisphere may lead to proportional increases in aquatic carbon fluxes.