Quantifying lawn irrigation contributions to semi-arid, urban stream baseflow with water-stable isotopes
Date
2020
Authors
Fillo, Noelle K., author
Bhaskar, Aditi S., advisor
Bailey, Ryan T., committee member
Kampf, Stephanie K., committee member
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Abstract
In semi-arid cities, urbanization can lead to elevated baseflow during summer months. One potential source for the additional water is lawn irrigation. We sought to quantify the presence of lawn irrigation in Denver's summertime baseflow 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 the local tap water than precipitation or streamflow from nearby grassland watersheds. We expected the tap water to be distinctive due to local water providers importing much of their source water from high elevations. Thirteen urban streams and two grassland streams were selected for sampling. The thirteen urban watersheds ranged from 3.9 km2 - 63.3 km2 in drainage area and 22% - 44% in imperviousness. The two grassland watersheds had drainage areas of 3.7 km2 and 7.5 km2 as well as 1% and 5% imperviousness. 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 local water provider service areas. Wide spatial and temporal variation in isotopic composition was observed within the stream, tap and precipitation samples. Comparison of samples between nearby watersheds revealed that proximity did not imply similar isotopic values. Streamflow analysis focusing on summer 2019 revealed that the grassland watersheds flowed for 60% of the summer while urban watersheds flowed for 90% - 100% of the summer. A two end-member isotope mixing model using tap and precipitation end-members estimated that tap water contributed 61% - 97% of urban streamflow on specific days in late summer. After taking estimated contributions from infrastructure leakage into account, we conservatively determined the lawn irrigation return flows made up 4% - 75% of the modeled baseflow. Quantifying the contribution of lawn irrigation to urban baseflow will provide a basis for understanding how changes to lawn irrigation efficiency would affect water yield in the Denver metropolitan area.
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Subject
irrigation
lawn
water
isotopes
baseflow
urban