Dissolved inorganic carbon export from carbonate and silicate catchments estimated from carbonate chemistry and δ13CDIC

This work presents a study of the dissolved inorganic carbon (DIC) exchange associated with groundwater discharge and stream flow from two upstream catchments with distinct basement lithologies (silicate vs. carbonate). The effects of catchment lithology were evident in the spring waters showing lower delta C-13(DIC) and alkalinity (-16.2+/-2.7 parts per thousand and 0.09+/-0.03 meq l(-1), respectively) in the silicate and higher values (-9.7+/-1.5 parts per thousand and 2.0+/-0.2 meq l(-1)) in the carbonate catchment. The streams exhibited relatively high delta C-13(DIC), -6.9+/-1.6 parts per thousand and -7.8+/-1.5 parts per thousand, 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. Therefore, the dynamic carbon exchange occurring at headwater regions and its possible variability with catchment lithology need to be examined for a more reliable carbon budget in river systems.