Assessing the recharge process and importance of montane water to adjacent tectonic valley-plain groundwater using a ternary end-member mixing analysis based on isotopic and chemical tracers

Peng, Tsung-Ren; Zhan, Wen-Jun; Tong, Lun-Tao; Chen, Chi-Tsun; Liu, Tsang-Sen; Lu, Wan-Chung

Assessing the recharge process and importance of montane water to adjacent tectonic valley-plain groundwater using a ternary end-member mixing analysis based on isotopic and chemical tracers | Evaluation du processus de recharge et importance de l’eau de montagne dans les eaux souterraines d’une vallée tectonique adjacente à l’aide de la méthode EMMA (end-member mixing analysis) basée sur des traceurs isotopiques et chimiques Evaluación del proceso de recarga y la importancia del agua de la montaña para el agua subterránea adyacente a un valle tectónico utilizando un análisis ternario de mezclas de miembros extremos en base a trazadores químicos e isotópicos 利用以同位素和化學示蹤劑為基礎的三元端點混合分析評估山區地下水對鄰近構造谷地內地下水的補注及重要性 Avaliando o processo de recarga e a importância da água montanhosa para as águas subterrâneas tectônicas de vales adjacentes, utilizando uma análise de mistura de membro final ternário com base em traçadores isotópicos e químicos

2018

A study in eastern Taiwan evaluated the importance of montane water contribution (MC) to adjacent valley-plain groundwater (VPG) in a tectonic suture zone. The evaluation used a ternary natural-tracer-based end-member mixing analysis (EMMA). With this purpose, VPG and three end-member water samples of plain precipitation (PP), mountain-front recharge (MFR), and mountain-block recharge (MBR) were collected and analyzed for stable isotopic compositions (δ²H and δ¹⁸O) and chemical concentrations (electrical conductivity (EC) and Cl⁻). After evaluation, Cl⁻ is deemed unsuitable for EMMA in this study, and the contribution fractions of respective end members derived by the δ¹⁸O–EC pair are similar to those derived by the δ²H–EC pair. EMMA results indicate that the MC, including MFR and MBR, contributes at least 70% (679 × 10⁶ m³ water volume) of the VPG, significantly greater than the approximately 30% of PP contribution, and greater than the 20–50% in equivalent humid regions worldwide. The large MC is attributable to highly fractured strata and the steep topography of studied catchments caused by active tectonism. Furthermore, the contribution fractions derived by EMMA reflect the unique hydrogeological conditions in the respective study sub-regions. A region with a large MBR fraction is indicative of active lateral groundwater flow as a result of highly fractured strata in montane catchments. On the other hand, a region characterized by a large MFR fraction may possess high-permeability stream beds or high stream gradients. Those hydrogeological implications are helpful for water resource management and protection authorities of the studied regions.

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