The heterogeneity in landcover and geology in Precambrian Shield watersheds, along with regional differences in future climate projections, are anticipated to result in significant complexity in simulating streamflow and water resource variations. Tracer-aided hydrologic modeling supported by field-based stable isotope surveys offers a potentially powerful approach to investigate mesoscale streamflow generation processes and potential impacts of climate change in the region. We investigate the influence of landscape characteristics on catchment classification and the impacts of wetland connectivity on streamflow simulation in a forest-dominated Precambrian shield mesoscale watershed by applying the tracer-aided hydrologic model isoWATFLOOD for the 12,000 km2 Sturgeon-Lake Nipissing (SN) watershed in Northeastern Ontario. Clustering results show that the differences in wetland and lakes area, mean slope and elevation, glacialacustrine deposits were the main parameters influencing catchment classification. Moreover, a strong correlation between damping ratio (DR) and wetland area (%) was found, leading us to investigate the impact of changes in %connected wetland (CW) in streamflow simulation. Five models with different % CW (10%-50%) were set up and separately calibrated. The isoWATFLOOD models were calibrated using PA-DDS algorithm and two optimization objective functions: KGE for flow and ?18O. Results indicate that changes in %CW affect streamflow and ?18O simulations. All models could accurately simulate streamflow and stable isotope of ?18O across the watershed, but 40% CW had better baseflow simulations. Results suggest the model ability to represent hydrological processes accurately and support use of isoWATFLOOD to estimate the impacts of climate change on streamflow generation in the region.