Mokua Retang A, Glenday Julia, Nel Jacobus, Butler Mike
Department of Environmental and Water Science, University of the Western Cape, Bellville, South Africa.
South African Environmental Observation Network, Fynbos Node, Newlands, South Africa.
Isotopes Environ Health Stud. 2020 Jun;56(3):238-259. doi: 10.1080/10256016.2020.1760861. Epub 2020 May 13.
The stable isotopes of water (O, H) 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 km) 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.
利用水的稳定同位素（氧、氢）和其他水化学性质，评估了南非西开普省山区Jonkershoek两个源头小流域（约3平方公里）基流条件下溪水水源与水流路径之间的季节性变化。这两个小流域的土地覆盖情况不同，一个以本土的硬叶灌木植被为主，另一个以松树种植园为主。从2018年1月至2019年1月每月采集溪水、较高海拔泉水和较低海拔地下水样本，并对其进行稳定同位素、电导率（EC）和pH值分析。在旱季和雨季，溪水的同位素值与地下水的同位素值相似。结果表明，旱季泉水对溪流的贡献稳定，降雨的贡献则不太明显。雨季径流归因于包括常年泉和临时泉在内的壤中流。两个小流域之间EC的空间变化表明，以松树为主的小流域中来自地下水的比例输入更大、蒸发更多和/或矿物溶解更多。EC的时空变异性明显大于稳定同位素的时空变异性。这些发现有助于对径流产生过程进行概念化，从而支持该地区的战略水资源管理实践。
