In semi-arid cities, urbanization can lead to elevated baseflow during summer months. One potential source for additional water is lawn irrigation. We sought to quantify lawn irrigation contributions to summertime baseflow in Denver, Colorado, USA using water-stable isotope (δ¹⁸O and δ²H) analysis of surface water, tap water, and precipitation. If lawn irrigation contributed significantly to baseflow, we predicted the isotopic composition of Denver's urban streams would more closely resemble local tap water than precipitation or streamflow from nearby grassland watersheds. We expected tap water to be distinctive due to local water providers importing source water from high elevations. Thirteen urban streams and two grassland streams were selected for sampling. None of the streams had high-elevation headwaters or wastewater effluent, and the grassland streams did not receive irrigation. Tap water was sampled from five water service areas. The grassland streams flowed for 60% of summer 2019 while urban streams flowed for 90%–100% of the summer. An isotope mixing analysis using tap and precipitation end-members over a two week antecedent period estimated that tap water contributed 65% ± 10%–93% ± 3% with a mean of 80% of urban baseflow on specific days in late summer. After taking contributions from infrastructure leakage into account, we estimated that lawn irrigation return flows made up 32% ± 10%–82% ± 21% of analyzed baseflow. Quantifying lawn irrigation contributions to urban baseflow provides a basis for understanding how changes to lawn irrigation efficiency would affect water yield in the Denver metropolitan area.

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基于水稳定同位素的草坪灌溉对半干旱城市基流的贡献

在半干旱城市，城市化会导致夏季的基流升高。额外水的一种潜在来源是草坪灌溉。我们试图使用水稳定同位素（δ ¹⁸ O 和 δ ²H) 地表水、自来水和降水分析。如果草坪灌溉对基流有显着影响，我们预测丹佛城市溪流的同位素组成将更接近当地自来水，而不是来自附近草地流域的降水或溪流。由于当地供水商从高海拔地区进口源水，我们预计自来水将与众不同。选取了 13 条城市溪流和两条草原溪流进行采样。没有一条溪流有高海拔源头或污水，草原溪流没有得到灌溉。自来水采样自五个供水服务区。草原溪流在 2019 年夏季的 60% 中流动，而城市溪流在夏季的 90%–100% 中流动。使用自来水和降水终端成员在两周前的同位素混合分析估计，自来水贡献了 65% ± 10%–93% ± 3%，在夏末的特定日子里，平均占城市基流的 80%。考虑到基础设施泄漏的影响后，我们估计草坪灌溉回流占分析基流的 32% ± 10%–82% ± 21%。量化草坪灌溉对城市基流的贡献为理解草坪灌溉效率的变化如何影响丹佛大都市区的水产量提供了基础。我们估计草坪灌溉回流占分析基流的 32% ± 10%–82% ± 21%。量化草坪灌溉对城市基流的贡献为理解草坪灌溉效率的变化如何影响丹佛大都市区的水产量提供了基础。我们估计草坪灌溉回流占分析基流的 32% ± 10%–82% ± 21%。量化草坪灌溉对城市基流的贡献为理解草坪灌溉效率的变化如何影响丹佛大都市区的水产量提供了基础。