Abstract Documenting the changing sources of water during high streamflows following rainfall is important for understanding catchment behaviour. This study uses tritium (3H), major ion concentrations, and δ18O values to identify the sources of water that sustained streamflow in the upper Yarra and Latrobe catchments of southeast Australia over two high flow events in March 2016 and August 2016. The variations in geochemistry imply that direct contribution of rainfall to streamflow was minor. Rather, the baseflow that sustained the streams prior to the events was augmented by water derived from the soils or regolith. A two component mass balance based on 3H indicates that the soil/regolith water constituted 60–100% of total streamflow at the peak of the events. A mass balance based on silica yields similar estimates (50–70%). The 3H activities of the soil water imply residence times of up to six years. These are sufficiently long for evapotranspiration, dissolution of organic matter, and mineral weathering to increase the major ion concentrations above those of rainfall and for mixing to homogenise δ18O and δ2H values. This study helps resolve the paradox that the water contributing to high flow events in streams is commonly not rainfall but is unlikely to be only increased inflows of groundwater due to the time required for hydraulic loading to occur.

中文翻译：

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使用氚和其他地球化学示踪剂解决源头集水区的“旧水悖论”

摘要 记录降雨后高流量期间水源的变化对于了解集水区行为很重要。本研究使用氚 (3H)、主要离子浓度和 δ18O 值来确定在 2016 年 3 月和 2016 年 8 月的两次高流量事件中维持澳大利亚东南部雅拉上游和拉特罗布集水区水流的水源。地球化学的变化这意味着降雨对径流的直接贡献很小。相反，在事件发生之前维持河流的基流被来自土壤或风化层的水增强。基于 3H 的双组分质量平衡表明，在事件高峰期，土壤/风化层水占总流量的 60-100%。基于二氧化硅的质量平衡产生类似的估计值 (50–70%)。土壤水的 3H 活动意味着长达六年的停留时间。这些对于蒸发蒸腾、有机物溶解和矿物风化来说足够长，以将主要离子浓度增加到降雨量以上，并进行混合以均质 δ18O 和 δ2H 值。这项研究有助于解决这样一个悖论，即导致溪流中高流量事件的水通常不是降雨，而不太可能只是由于发生水力加载所需的时间而增加的地下水流入。