Karst conduit contribution to spring discharge and aquifer cross-sectional area

•Novel in situ measurements of groundwater fluxes in rock matrix and conduit zones.•Simple analytical solutions to identify flow contribution from conduit vs matrix.•Tested in Silver Springs, one of the largest springs in the world.•Conduits were a small fraction of the aquifer cross-sectional area.•Conduits contributed between 75 and 96% of the total groundwater flow.