In mountainous headwater catchments, with their high variability of hydrological processes and catchment properties together with the limited spatial and long-term data, it remains unclear how the different spatiotemporal controls affect runoff generation during base and stormflow. In this doctoral thesis environmental tracers are used to identify sources contributing to baseflow, observe linkages between different landscape units and discern how rainfall becomes stormflow in a Swiss pre-alpine headwater catchment, the Zwäckentobel (4.25 km2), with high precipitation amounts (P>2000 mm y−1) and heterogeneous catchment properties. The spatially collected rainfall and its isotopic composition are used to test whether it is reasonable to assume that in small headwater catchments, there is spatially homogenous rainfall and isotopic composition, implying that one sampling location is sufficient. Important tracers in this thesis are the stable isotopes 2H and 18O. The collected water samples were analysed with a laser spectroscope. For this analysis it was tested how many measurements are needed to reduce the memory effect and obtain a desired accuracy. For the Zwäckentobel water samples it was sufficient to measure each sample six times while for highly depleted samples the memory effect was reduced only after seven to eight injections. The water samples collected during three snapshot sampling campaigns were analysed for their isotopic (δ2H) and hydrochemical components (Ca, DOC, AT, pH, SO4, Mg and H4SiO4)andcontainedusefulinformationonthedifferentsourcesandhelpedtoidentifythe flowpath of the water during baseflow. Although the six subcatchments had different landscape units, the inter- and intra catchment variability of the isotopic and hydrochemical components was generally small and statistically not significant. Streamwater samples at the subcatchment outlets were more similar to springs near the water divide than to groundwater from observation wells and wetlands. The wetlands, with 30-60% of the subcatchment area and large storage capacity, were less connected and acted as passive features with negligible contribution to baseflow runoff. In five subcatchments of the Zwäckentobel headwater catchment, rainfall and streamwater of 13 different rainstorms were sampled to perform a two-component isotope hydrograph separation. Pre-event water contributions based on δ18O or δ2H computations were similar. The pre-event water contributions of headwaters depended largely on rainfall (amount and intensity) and varied more between events than between catchments, despite clear differences in land cover between the catchments. With increasing rainfall amount, the proportion of rainfall in runoff increased and changed from pre-event to event water dominated. Antecedent wetness was not found to control the pre-event water contribution. The fact that catchment properties and antecedent conditions were only secondary factors in runoff processes, was mainly due to the dominant and frequent rainfall, which obscured a potential signal indicating differences in catchment properties. At the eight locations sequentially sampled rainfall revealed a spatial variability in total rainfall, rainfall intensity and its isotopic composition. The spatial variability in the isotopic composition varied from event to event. No clear relation between the isotopic composition and rainfall or altitude was observed. The isotope hydrograph separation results varied considerably depending on which temporal weighing technique or rain sampler was used. These results demonstrated that even in small catchments the spatial variability in the isotope composition of event rainwater has to be considered in hydrograph separation studies. When data from only one rain gauge are available, the location of the gauge might largely affect results and this source of uncertainty must be considered. The combination of long-term and spatially short-term hydrometeorological measurements, together with three baseflow sampling campaigns and event water sampling in different neighboring streams and multiple events, complemented each other and helped to overcome individual limitations. The results show the necessity and benefits of this spatially distributed dataset to derive and better understand controlling factors in runoff generation in a headwater catchment with high precipitation amounts and heterogeneous catchment properties.
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机译：在山区水源流域，由于其水文过程和流域性质的高度可变性以及有限的空间和长期数据，目前尚不清楚不同的时空控制如何影响基准流量和暴雨流量的径流产生。在本博士论文中，环境示踪剂用于识别造成基流的来源，观察不同景观单元之间的联系，并识别降雨如何在瑞士的阿尔卑斯山前水源地Zwäckentobel（4.25 km2）中形成高降雨量（P> 2000 mm y-1）和非均质集水性质。使用空间收集的降雨及其同位素组成来检验是否合理假设在小源头集水区存在空间均匀的降雨和同位素组成，这意味着一个采样位置就足够了。本论文中重要的示踪剂是稳定同位素2H和18O。收集的水样本用激光光谱仪分析。对于此分析，测试了需要多少次测量才能减少记忆效应并获得所需的精度。对于Zwäckentobel水样品，足够对每个样品进行六次测量，而对于高度消耗的样品，仅在注射七至八次后，记忆效应才会降低。分析了在三个快照采样活动中收集的水样的同位素（δ2H）和水化学成分（Ca，DOC，AT，pH，SO4，Mg和H4SiO4），并在不同来源上包含了有用的信息，并有助于识别基流期间水的流动路径。尽管六个子汇水区的景观单元不同，但是同位素和水化学成分的汇水区间和汇水区内部的差异通常很小，在统计上并不显着。在集水区出口处的溪水样本与分水岭附近的泉水更像，而不是与观察井和湿地的地下水相似。湿地面积为子汇水面积的30％至60％，存储容量较大，它们之间的连接较少，并作为被动要素，对基流径流的贡献可忽略不计。在Zwäckentobel上游流域的五个子集水区，对13种不同暴雨的降雨和溪流进行了采样，以进行两组分同位素水文法分离。基于δ18O或δ2H计算的赛前水贡献相似。尽管集水区之间的土地覆盖率存在明显差异，但源头事件发生前的水贡献在很大程度上取决于降雨（数量和强度），并且事件之间的变化大于集水区之间的变化。随着降雨量的增加，径流中降雨的比例增加，并且从事件前到事件水为主。未发现先行的湿度可控制赛前水的贡献。集水性质和前期条件只是径流过程中的次要因素，这主要是由于降雨占主导地位和频繁，这掩盖了表明集水性质差异的潜在信号。在八个地点，依次采样的降雨揭示了总降雨，降雨强度及其同位素组成的空间变异性。同位素组成的空间变异性随事件而变化。没有观察到同位素组成与降雨或海拔之间的明确关系。根据所使用的时间称重技术或雨水采样器，同位素水文法分离结果差异很大。这些结果表明，即使在小流域，事件水雨水同位素组成的空间变异性也必须在水位图分离研究中加以考虑。如果只有一个雨量计的数据可用，则该雨量计的位置可能在很大程度上影响结果，因此必须考虑这种不确定性来源。长期和空间短期水文气象测量的结合，以及三个基流采样活动以及在不同邻流和多个事件中的事件水采样，相辅相成，有助于克服个人的局限性。结果表明，这种空间分布数据集的必要性和好处是，可以得出和更好地理解具有高降水量和非均质集水性质的上游水源地径流产生的控制因素。
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