ABSTRACT The stable isotopes of water (18O, 2H) and other hydrochemical properties were used to assess seasonal changes between sources of stream water and flow pathways in baseflow conditions for two headwater sub-catchments (∼3 km2) of the Jonkershoek, a mountainous catchment in the Western Cape of South Africa. The sub-catchments differ in land cover, one is dominated by indigenous fynbos vegetation and the other by pine plantation. Stream water, higher elevation springs, and lower elevation groundwater samples were collected monthly from January 2018 to January 2019, and were analysed for stable isotopes, electrical conductivity (EC) and pH. The stream water isotopic values resembled those of groundwater during the dry and wet seasons. Results indicated a steady contribution of spring discharge to streams during the dry season, with rainfall contribution less evident. Wet season flows were attributed to interflow including perennial and ephemeral springs. Spatial variations in EC between the sub-catchments were indicative of a greater proportional input from subsurface water, more evaporation and/or more mineral dissolution in the pine-dominated sub-catchment. The spatiotemporal variability in EC was significantly larger than for the stable isotopes. These findings enabled conceptualization of streamflow generation processes that can support strategic water resource management practices in this region.

中文翻译：

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结合使用稳定同位素和水化学特征来确定南非 Jonkershoek 流域的水流来源

摘要 水的稳定同位素 (18O, 2H) 和其他水化学性质被用于评估 Jonkershoek 的两个上游子集水区 (∼3 km2) 基流条件下溪流水源和流动路径之间的季节性变化，这是一个山区集水区在南非西开普省。子流域的土地覆盖不同，一个以本土蕨类植物为主，另一个以松树种植为主。2018 年 1 月至 2019 年 1 月，每月收集溪水、高海拔泉水和低海拔地下水样品，并分析稳定同位素、电导率 (EC) 和 pH 值。河水同位素值与旱季和雨季地下水的同位素值相似。结果表明，在旱季，春季流量对溪流的贡献稳定，降雨贡献不太明显。湿季流量归因于包括多年生和短暂泉水在内的互流。子流域之间 EC 的空间变化表明，在以松树为主的子流域中，来自地下水的更大比例输入、更多的蒸发和/或更多的矿物溶解。EC 的时空变异性明显大于稳定同位素。这些发现使水流生成过程的概念化成为可能，从而支持该地区的战略水资源管理实践。在以松树为主的子流域中更多的蒸发和/或更多的矿物溶解。EC 的时空变异性明显大于稳定同位素。这些发现使水流生成过程的概念化成为可能，从而支持该地区的战略水资源管理实践。在以松树为主的子流域中更多的蒸发和/或更多的矿物溶解。EC 的时空变异性明显大于稳定同位素。这些发现使水流生成过程的概念化成为可能，从而支持该地区的战略性水资源管理实践。