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Groundwater from 10 production wells located in lowlands to highlands was investigated from July 2008 to February 2010 for chemical and isotopic compositions (delta O-18, delta H-2, and delta C-13(DIC)) to understand groundwater recharge processes and to assess geochemical conditions of groubdwater in the volcanic aquifers. The groundwater in lowlands had elevated concentrations of Cl and NO3 with greater seasonality when compared with those from higher areas, indicating that groundwater in the lowlands is affected by contamination. Based on delta O-18 values and altitudinal variations, groundwater was classified into two regional flow systems With different flow paths. The regional flow systems are likely connected from highland to lowland areas, considering consistent delta O-18 values and major ion contents throughout the seasons. Of the two regional flow systems, the wells clustered in one regional flow system showed low delta C-13(DIC) values (average - 14.3%0) and high P-CO2 (average 2.04 in -logP(CO2)), reflecting relatively high contribution of soil CO2 to groundwater. The other regional flow system with low P-CO2 (average 239 in -logP(CO2)), however, consisted of two highland wells with enriched delta C-13(DIC) value, -9.3% and two lowland wells with relatively depleted delta C-13(DIC) value, -13.7%.. These findings indicate that the two regional flow systems were mixed with local recharge from soil layers during recharge. The delta O-18 arid delta H-2 values in groundwater from the regional flow systems were not clearly consistent with the local meteoric Water line due to mixing of summer and dry season precipitation. The isotopic variations showed a phase lag and cyclic temporal patterns, suggesting that a considerable portion of groundwater was derived from fast recharge with short residence times on monthly time scales. This study suggests that groundwater in lowland areas in Jeju Island can be significantly contributed from highland areas, which was revealed by chemical and isotopic compositions, especially, altitude effect and seasonal variation of delta O-18 value. We expect that the knowledge on the volcanic aquifer system can be useful for management of groundwater resources including projects (e.g. artificial recharge technology) which has been carried out to mitigate water poverty over the world. (C) 2017 Elsevier B.V. All rights reserved.