Recharge sources and flow system of groundwaters in Osaka Basin, estimated from environmental isotopes and water chemistry

Abstract

Spatial distributions of stable isotopic ratios of oxygen and hydrogen, tritium concentrations, concentrations of nitrate-nitrogen and major water chemistry were investigated for the groundwaters shallower than -300m below sea level in the Osaka Basin in relation to groundwater tables, topography and hydrogeology to clarify the recharge sources and flow fields. The stable isotopic ratios of oxygen and hydrogen of groundwaters documented that groundwaters were recharged at the surrounding mountains, hills and plateaus of the Basin, and that the groundwaters transported nitric acids to -300m depth below the basin through aquifers. The flow velocities of recharge and migration through the aquifers are estimated roughly to be 2-9m/y and 0.1-1km/y in vertical and horizontal directions, respectively, in several recharge zones.