Temporal and Spatial Variations of Freshwater Reservoir Ages in the Loire River Watershed

In order to map the freshwater reservoir effect (FRE) variability of the Loire River and its tributaries, spatial and temporal carbon isotope ( 13 C and 14 C) analyses of the dissolved inorganic carbon (DIC) were conducted. Sites were selected to represent the diversity of geological settings, soil type, and land use. Results show a large spatial variability of 14 C FRE ranging between 135 and 2251±30 yr, objectively correlated to DIC contents and alkalinity. Deeper investigations of the relationship between 14 C activity of DIC and environmental variables show that the geological substrate is the dominant factor in the 14 C reservoir effect, and far more influential than the river flow discharge.