Hydrogen and Oxygen Isotope Ratios of Groundwaters in Shallow Aquifers beneath the Alluvial Fan

概要

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Hydrogen and oxygen isotope measurements of river waters, spring waters of rainfall infiltration origin, and rice paddy waters collected in Toyama Prefecture have been used to deduce a mixing model for identifying sources of groundwater in the shallow aquifer beneath the alluvial fan. δD and δ18O values of the river water flowing on the fan depend on the average altitude of its catchment area. Their variations are limited throughout the year. The spring water from Kureha Hill can be regarded as a representative of rainfall infiltration, of which δD and δ18Ovalues are -49.3 and -8.8%0 in average, respectively. The rice paddy water irrigated by the main river flowing on the fan shows isotopic fractionations of ΔD =12.3‰ and Δ18O=2.6‰in average, caused by evaporation at its surface. A model based on intermixing of such source waters has been proposed to identify sources of groundwater in shallow aquifers beneath alluvial fans in Toyama Prefecture. Application of the model to groundwaters of Shogawa and Kurobegawa Fans has confirmed its validity.
Japanese Association of Groundwater Hydrologyの論文