Urbanization disturbs groundwater flow through the sealing of native soils with impervious surfaces and through modifications to the subsoil by constructed drainage and other infrastructure (trenches and excavations, e.g. water supply). The impact of these disturbances on groundwater contributions to urban streams (i.e. baseflow) is poorly understood. While high flows caused by impervious runoff to streams are a common focus of urban studies, the route taken by groundwater to become streamflow in urban landscapes is not generally considered. To assess the impact of urbanization on groundwater sources to streams, both rainfall and baseflow were sampled weekly for stable isotopes of water in two nearby streams—one draining a peri-urban catchment and the other draining a forested, natural catchment. In addition, to study the rate of groundwater discharge to the stream, monthly baseflow recession behavior was investigated. We found that baseflow in the forested catchment was constant in stable isotope values (δ¹⁸O = -5.73 ‰ ± 0.14 ‰) throughout the year. Monthly baseflow recession constants were close to 1 and had little variation (ranging 0.951-0.992), indicating a well-mixed groundwater store and long residence times. In contrast, the urban baseflow isotopic composition featured distinct seasonal variations (δ¹⁸O = -3.35 ‰ ± 1.20 ‰ from October to March and δ¹⁸O = -4.54 ‰ ± 0.43 ‰ from April to September) and high week-to-week variability in summer, reflecting a contribution of recent rainfall to baseflow. Recession constants were lower (ranging 0.727-0.955) with pronounced seasonal variations, suggesting shorter residence times and the likely presence of a variety of stores and pathways. These results provide evidence that the urban catchment has diversified groundwater pathways, and its groundwater storage is drained faster than that of the forested catchment. It highlights some of the subsurface hydrological consequences of urbanization. Restoring low-flow aspects of the flow regime through nature-mimicking stormwater management requires careful consideration of how the behavior of natural groundwater pathways can be restored or replicated using innovative stormwater control measures.

城市化通过密封不透水的原生土壤以及通过建造的排水系统和其他基础设施（沟渠和基坑，例如供水）对地下土壤的改性，扰乱了地下水的流动。这些干扰对地下水对城市河流（即基流）贡献的影响了解得很少。虽然不透水径流引起的高流量是城市研究的普遍关注点，但通常不考虑地下水成为城市景观中的水流的途径。为了评估城市化对地下水源向溪流的影响，每周对降雨和基流进行采样，以获取附近两条溪流中水的稳定同位素-一条排水到城郊集水区，另一条排水到有森林的自然集水区。此外，为了研究地下水向河流的排放速率，调查了每月底流的衰退行为。我们发现森林集水区的基流在稳定同位素值（δ全年为¹⁸ O = -5.73‰±0.14‰）。每月底流衰退常数接近于1，变化很小（范围为0.951-0.992），表明地下水储量充分混合，停留时间长。与此相反，城市基流同位素组成功能不同的季节性变化（δ ¹⁸ O = -3.35‰±1.20‰从十月到三月和δ ¹⁸ O = -4.54‰±0.43‰四月至九月）和高周与周夏季的多变性，反映了近期降雨对基流的贡献。经济衰退常数较低（范围为0.727-0.955），具有明显的季节性变化，表明停留时间较短，并且可能存在各种商店和途径。这些结果提供了证据，表明城市集水区的地下水路径多种多样，其地下水储存的排水速度比森林集水区的排水速度快。它强调了城市化的一些地下水文后果。通过模仿自然的雨水管理来恢复流态的低流量方面，需要仔细考虑如何使用创新的雨水控制措施来恢复或复制天然地下水路径的行为。