Water Contributors Identification to City Streams Using Multiyear
Analysis of Water Stable Isotopes
Water is scarce in semi-arid and arid areas where urban irrigation
consumes a large portion of city water. It is important to manage and
conserve water properly to meet the growing demand, especially in the
summer season. The purpose of this research is to identify the major
contributors to streamflow in the semi-arid Denver metropolitan area,
CO, USA, and analyze the temporal variation of streamflow sources using
two-year data. In this study, water-stable isotopes
(δ18O and δ2H) were used as the
tracer to identify the contribution of different sources such as tap
water, precipitation, or irrigation water in Denver urban streamflow.
Stream and tap water were sampled every other week and precipitation
samples were collected once a month. There were 13 urban and 6 grassland
streams, and tap water was collected from 6 different water providers.
The USGS real-time streamflow data and BaseflowSeparation function in R
package ‘EcoHydRology’ were used to select the baseflow condition in the
streams for sampling. Picarro L2130i Laser Water Isotope Analyzer was
used for oxygen and hydrogen isotope (δ18O and
δ2H) analysis of stream, tap, and precipitation water.
Results showed that precipitation samples were heavier in earlier
summertime than the late summer and 2019 showed greater variability than
2021. Tap samples showed temporal and spatial variability in
δ18O and δ2H values. Less
variability in tap isotopic data could be observed in 2021 than in 2019.
Centennial Water and Sanitation District showed a decreasing trend. In
the δ18O vs. δ2H plot, stream and
tap water followed local meteoric water line (LMWL) and global meteoric
water line (GMWL) well. But precipitation sample exhibited a slight
deviation from the LMWL and GMWL. The similar isotopic range in tap
water and stream water supported that tap water was the main source of
water during the summertime. In the future, the percent contribution of
different sources will be evaluated. Furthermore, the effect of reduced
urban irrigation by using efficient irrigation, landscape, or
conservation techniques will be analyzed to achieve water security for
sustainable urban development.