Groundwater inflows control patterns and sources of greenhouse gas emissions from streams

Abstract

Headwater streams can be important sources of carbon dioxide (CO 2 ) and methane (CH 4 ) to the atmosphere. However, the influence of groundwater-stream connectivity on the patterns and sources of carbon (C) gas evasion is still poorly understood. We explored these connections in the boreal landscape through a detailed study of a 1.4 km lake outlet stream that is hydrologically fed by multiple topographically driven groundwater input zones. We measured stream and groundwater dissolved organic C (DOC), CO 2 , and CH 4 concentrations every 50 m biweekly during the ice-free period and estimated in-stream C gas production through a mass balance model and independent estimates of aquatic metabolism. The spatial pattern of C gas concentrations was consistent over time, with peaks of both CH 4 and CO 2 concentrations occurring after each groundwater input zone. Moreover, lateral C gas inputs from riparian soils were the major source of CO 2 and CH 4 to the stream. DOC mineralization and CH 4 oxidation within the stream accounted for 17-51% of stream CO 2 emissions, and this contribution was the greatest during relatively higher flows. Overall, our results illustrate how the nature and arrangement of groundwater flowpaths can organize patterns of stream C concentrations, transformations, and emissions by acting as a direct source of gases and by supplying organic substrates that fuel aquatic metabolism. Hence, refined assessments of how catchment structure influences the timing and magnitude of groundwaterstream connections are crucial for mechanistically understanding and scaling C evasion rates from headwaters.

Stream metabolism controls diel patterns and evasion of CO2 in Arctic streams

“…litterfall or DOC; Demars, ; Roberts, Mulholland, & Hill, ). In our study, ER was strongly related to discharge (Figure S10), which has been reported elsewhere for other small northern streams (Demars, ; Lupon et al, ). These authors suggest that discharge could regulate the activity of stream heterotrophs through the delivery of terrestrial organic C. Consistent with this supply mechanism, previous work in the Miellajokka catchment has shown that DOC increases with discharge (Giesler et al, ).…”

“…This indicates that these streams mineralize substantial amounts of the organic C received from land that otherwise would have been exported downstream to lakes or marine systems. Our reported values of the contribution of aquatic NEP to CO 2 evasion are high compared to other studies of small streams in high latitudes (40%-75%; Lupon et al, 2019;Rasilo et al, 2016), and typically the largest contributions to date have been observed for considerably larger rivers (85%-97%; e.g. Cole & Caraco, 2001;Lynch, Beatty, Seidel, Jungst, & DeGrandpre, 2010).…”

Dynamics and potential drivers of CO2 concentration and evasion across temporal scales in high-alpine streams

“…In fact, groundwater has been shown to be important for the CO 2 dynamics in the streams in the Vallon de Nant catchment (RIC, AND, ANU) (Horgby et al 2019). Beyond our mountain streams, groundwater is now being increasingly recognized to drive CO 2 concentration and fluxes in various headwater streams (Duvert et al 2018, Lupon et al 2019. Because of the inherent link between gas exchange velocity and discharge, we found positive responses in k CO2 to q (100%, P<0.05) and F CO2 to increasing q , respectively (53%, P<0.05) ( Table S2).…”

Forest management influences the effects of streamside wet areas on stream ecosystems

“…This would also explain why the influence of VSAs on DOC in streams is temporally variable (Lupon et al. ) and the incongruencies among studies. Lupon et al.…”