We investigated dissolved inorganic carbon (DIC) exchange associated with groundwater discharge and stream flow from two upstream catchments with distinct basement lithology (silicate vs. carbonate). The effects of catchment lithology were evident in the spring waters showing lower δ13CDIC and alkalinity (−16.2 ± 2.7‰ and 0.09 ± 0.03 meq L−1, respectively) in the silicate and higher values (−9.7 ± 1.5‰ and 2.0 ± 0.2 meq L−1) in the carbonate catchment. The streams exhibited relatively high δ13CDIC values, −6.9 ± 1.6‰ and −7.8 ± 1.5‰, in silicate and carbonate catchments, respectively, indicating CO2 degassing during groundwater discharge and stream flow. The catchment lithology affected the pattern of DIC export. The CO2 degassing from stream and groundwater could be responsible for 8–55% of the total DIC export in the silicate catchment, whereas the proportion is comparatively low (0.4–5.6%) in the carbonate catchment. We emphasize the importance of dynamic carbon exchange occurring at headwater regions and its variability with catchment lithology for a more reliable carbon budget in river systems
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