Takeo Tsuchihara, Yuya Fukumoto, Katsushi Shirahata
Received 19 May, 2026
Accepted 12 August, 2026
Published online 16 October, 2026
Takeo Tsuchihara1), Yuya Fukumoto1), Katsushi Shirahata1)
1) Institute for Rural Engineering, National Agriculture and Food Research Organization, Japan
To evaluate shallow groundwater influence where conventional end-member definitions are hindered by unknown screened intervals, multiple environmental tracers were measured in shallow and deep irrigation wells. Non-negative matrix factorization-based end-member mixing analysis was applied to the collected dataset to extract two components associated with shallow and deep groundwater and evaluate the relative contribution of the shallow component in deep wells. The two components were labeled as the shallow and deep components, respectively, based on information from the shallow-well group, thereby reducing the arbitrariness that can arise when component labels depend on researcher interpretation. In the primary analysis using the full tracer set, the relative contribution of the shallow component in deep wells ranged from 0 to 51%, suggesting non-negligible shallow groundwater influence in some deep wells, potentially due to screened intervals extending into shallower zones and/or a hydraulic connection between aquifers. Additionally, principal component analysis identified indicators that distinguish between shallow and deep groundwater. Their characteristics were consistent with differences in relative contribution of the shallow component, supporting the hydrogeochemical plausibility of the estimated relative contributions. Overall, these results demonstrate that the proposed framework is useful for evaluating shallow groundwater influence and identifying indicators that characterize shallow and deep groundwater.
Copyright (c) 2026 The Author(s) CC-BY 4.0
