Hydrochemical and Isotopic Difference of Spring Water Depending on Flow Type in a Stratigraphically Complex Karst Area of South Korea

Abstract

Characterizing the subsurface flow in karstic areas is challenging due to distinct flow paths coexisting, and lithologic heterogeneity makes it more difficult. A combined use of hydrochemical, environmental isotopic, and hydrograph separation study was performed to understand the subsurface flow in a karst terrain where Ordovician carbonate rocks overlie Jurassic sandstone and shale along thrusts. Spring water collected was divided into Type Ⅰ (n = 11) and Ⅱ (n = 30) based on flow patterns (i.e., low and high discharge, respectively). In addition, groundwater (n = 20) was examined for comparison. Three Type Ⅱ springs were additionally collected during a storm event to construct hydrographs using δ18O and δD. As a result, Type Ⅱ had higher electrical conductivity, Mg2+, HCO3−, and Ca2+/(Na+ + K+) than Type Ⅰ and was mostly saturated with calcite, similar to deep groundwater. The hydrochemical difference between Types Ⅰ and Ⅱ was opposite to the expectation that Type Ⅱ would be undersaturated given fast flow and small storage, which could be explained by the distinct geology and water sources. Most Type Ⅱ springs and deep groundwater occurred in carbonate rocks, whereas Type Ⅰ and shallow groundwater occurred in various geological settings. The carbonate rocks seemed to provide conduit flow paths for Type Ⅱ given high solubility and faults, resulting in 1) relatively high tritium and NO3− and Cl−via short-circuiting flow paths and 2) the similar hydrochemistry and δ18O and δD to deep groundwater via upwelling from deep flow paths. The deep groundwater contributed to 83–87% of the discharge at three Type Ⅱ springs in the dry season. In contrast, Type Ⅰ showed low Ca2+ + Mg2+ and Ca2+/(Na+ + K+) discharging diffuse sources passing through shallow depths in a matrix in mountain areas. Delayed responses to rainfall and the increased concentrations of contaminants (e.g., NO3−) during a typhoon at Type Ⅱ implied storage in the vadose zone. This study shows that hydrochemical and isotopic investigations are effective to characterize flow paths, when combined with hydrograph separation because the heterogenous geology affects both flow paths and the hydrochemistry of spring water passing through each pathway.

Characterization of seasonal groundwater origin and evolution processes in a geologically heterogeneous catchment using geophysical, isotopic and hydro‐chemical techniques (Lough Gur, Ireland)

“…This indicates that calcium carbonate precipitation occurs which results in CO 2 evasion for most water samples as the p CO 2 is higher than atmospheric (Martinsen et al, 2020; Shin et al, 2011). Furthermore, during high flow periods many water compartments are super‐saturated for calcite and under‐saturated for dolomite which suggests dolomite dissolution to be a source of Ca 2+ , Mg 2+ and HCO 3 − particularly during periods of recharge (Han et al, 2010; Szramek et al, 2007; Yu et al, 2021). Under low flow conditions the elevated source of Mg 2+ (Figure 10) may be due to the partial dissolution of dolomite and accumulation of Mg 2+ due to incongruent weathering (Edmunds & Shand, 2009).…”

Bottled Mineral Waters as Unconventional Sampling in Hydro-Geological Research

“…In general, the chemical composition of water is determined by the natural environment from where it originates and it is mainly affected by the local (sometimes regional) geological and hydro-geological conditions. The primary natural influences on the chemical and isotopic composition of bottled water are (i) the water-rock interaction, (ii) the transit time, and (iii) the evaporation processes of groundwaters from the considered aquifers, e.g., [22,[37][38][39].…”

Karakteristik Hidrogeokimia dan Kualitas Air pada Mata Air Karst Selonjono Karst Gunungsewu Daerah Istimewa Yogyakarta

“…Kondisi akuifer kawasan karst yang didominasi oleh beberapa karakteristik porositas seperti diffuse (rongga antar butir batuan), fissure (retakan) dan conduit (lorong pelarutan berukuran cukup besar) telah menyebabkan kondisi hidrogeokimia yang unik dan sangat rumit (Yu et al, 2021). Mataair karst memiliki peranan yang sangat penting sebagai titik pengamatan atau pengambilan sampel air untuk mengevaluasi proses hidrogeokimia yang terjadi di dalam sistem hidrogeologi kawasan karst baik proses yang alamiah terjadi ataupun proses yang terjadi akibat dampak aktivitas antropogenik (Liu et al, 2007).…”