Hydrogeological responses in tropical mountainous springs

This study presents a hydrogeochemical analysis of spring responses (2013–2017) in the tropical mountainous region of the Central Valley of Costa Rica. The isotopic distribution of δ18O and δ2H in rainfall resulted in a highly significant meteoric water line: δ2H = 7.93·δ18O + 10.37 (r2 = 0.97). Rainfall isotopic composition exhibited a strong amount-dependent seasonality. The isotopic variation (δ18O) of two springs within the Barva aquifer was simulated using the FlowPC program to determine mean transit times (MTTs). Exponential-piston and dispersion distribution functions provided the best-fit to the observed isotopic composition at Flores and Sacramento springs, respectively. MTTs corresponded to 1.23 ± 0.03 (Sacramento) and 1.42 ± 0.04 (Flores) years. The greater MTT was represented by a homogeneous geochemical composition at Flores, whereas the smaller MTT at Sacramento is reflected in a more variable geochemical response. The results may be used to enhance modelling efforts in central Costa Rica, whereby scarcity of long-term data limits water resources management plans.

本研究针对哥斯达黎加中央谷地热带山区2013—2017年的泉水响应特征开展水文地球化学分析。降雨中δ¹⁸O与δ²H的同位素分布构建了极显著的大气降水线：δ²H = 7.93·δ¹⁸O + 10.37，决定系数r²=0.97。降雨同位素组成呈现显著的降水量效应季节性变化。本研究采用FlowPC程序对巴尔瓦含水层内两处泉水的δ¹⁸O同位素变化进行模拟，以确定其平均运移时间（mean transit times, MTTs）。其中，弗洛雷斯（Flores）与萨克拉门托（Sacramento）两处泉水分别以指数活塞模型与弥散分布函数的拟合效果最优，对应的平均运移时间分别为1.23±0.03年（萨克拉门托）与1.42±0.04年（弗洛雷斯）。弗洛雷斯泉水的平均运移时间更长，其地球化学组成均一性更强；而萨克拉门托泉水平均运移时间更短，地球化学响应也更为多变。本研究结果可用于完善哥斯达黎加中部的水文模拟工作，该区域因长期数据匮乏而制约了水资源管理规划的推进。