Precipitation and groundwater stable isotope data from a peri-urban tropical volcanic catchment.

The study area (218 km2) is located on the northwestern part of the Central Valley of Costa Rica. The region is characterized by two well-defined seasons: dry (December to April) and wet (May to November). Daily precipitation samples (N=793) were collected from April 2021 to December 2022. Three passive rain collectors (Palmex Ltd., Croatia; Gröning et al., 2012) were installed at 938 m a.s.l (AC), 1,804 m a.s.l (AF), and 2,532 m a.s.l (VP). Precipitation and groundwater samples were stored below 6°C in 50 mL HDPE bottles with no headspace and plastic inserts to avoid evaporation. Samples were analyzed at the Stable Isotopes Research Group laboratory at the Universidad Nacional (Heredia, Costa Rica) using an IWA-45EP water analyzer (Los Gatos Research, Inc., California, USA). The precision was ±0.80‰ for d2H and ±0.08‰ for d18O (1sigma; 5 injections). Isotopic reference materials, USGS45 (d2H=−10.30‰, d18O=−2.24‰), USGS47 (d2H=−150.2‰, d18O=−19.80‰), and calibrated secondary standard PGW (d2H=−52.64 ‰, d18O=−8.20‰), were used for data normalization and quality control. 18O/16O and 2H/1H ratios are presented in delta notation relative to the VSMOW-SLAP scale and expressed as per mile (‰). Deuterium excess was calculated as d-excess= d2H - 8·d18O . Long-term d2H, d18O, and d-excess precisions are 0.29‰, 0.08‰, and 0.65‰, respectively.

本研究的研究区面积为218平方千米，地处哥斯达黎加中央谷地西北部。该区域具有两个界限清晰的季节：旱季（12月至次年4月）与湿季（5月至11月）。2021年4月至2022年12月期间，共采集793份日降水样品（样本量N=793）。研究人员在海拔938米（海平面以上，测点AC）、1804米（海平面以上，测点AF）以及2532米（海平面以上，测点VP）处安装了三台被动式降雨收集器（Palmex有限公司，克罗地亚；Gröning等，2012）。降水与地下水样品被存放于无顶空、带有塑料内衬的50毫升高密度聚乙烯（HDPE）瓶中，保存温度低于6℃，以避免蒸发。样品于哥斯达黎加国立大学（埃雷迪亚省）稳定同位素研究组实验室进行分析，所用仪器为IWA-45EP型水分析仪（美国加利福尼亚州Los Gatos Research公司）。分析精度方面，δ²H的精度为±0.80‰，δ¹⁸O的精度为±0.08‰（1σ；5次进样）。本次实验采用USGS45（δ²H=−10.30‰，δ¹⁸O=−2.24‰）、USGS47（δ²H=−150.2‰，δ¹⁸O=−19.80‰）以及经校准的二级标准物质PGW（δ²H=−52.64‰，δ¹⁸O=−8.20‰）用于数据归一化与质量控制。¹⁸O/¹⁶O与²H/¹H比值以相对于维也纳标准平均海水-南极融水标准（VSMOW-SLAP）的δ表示法形式呈现，单位为千分比（‰）。氘盈余值按公式d-excess = δ²H - 8×δ¹⁸O计算得到。长期分析精度方面，δ²H、δ¹⁸O以及氘盈余的精度分别为0.29‰、0.08‰与0.65‰。