Stable isotopic and geochemical data for inferring sources of recharge and groundwater flow on the volcanic island of Rishiri, Japan

An isotopic and chemical study was conducted on precipitation, spring water, streams, groundwater wells and submarine groundwater discharge (SGD) to constrain the recharge areas and flow paths of SGD. The isotopic values of precipitation were used to determine the local meteoric water lines (LMWLs) of Rishiri Island. The d-excess values of precipitation showed seasonal variation, with lows of 2.5‰ in the summer and highs of 24.2‰ in the winter. The d-excess values of spring water, streams, groundwater wells and SGD ranged from 12.5‰ to 23.0‰, indicating that the resulting waters were a mix of two seasons of precipitation. The isotopic composition of the groundwater wells sampled along the coast and SGD showed more negative values than that of the spring water sampled along the coast. This indicated that SGD recharged at high altitudes and flowed into the sea. The isotopic and chemical composition of SGD indicated unidirectional flow from land to sea.

► To constrain the recharge areas and flow paths of SGD in Rishiri Island.
► To determine the local meteoric water lines of Rishiri Island.
► An altitude effect of −0.12‰ per 100 m for δ18O was found.
► In temperate zone, the importance of winter precipitation in groundwater recharge.
► The submarine groundwater discharge (SGD) had a deeper flow system and longer flow paths than did spring water.