Stable Isotope Reveals Tap Water Source under Different Water Supply Modes in the Eastern Margin of the Qinghai–Tibet Plateau

Mingxia Du,Hongfei Meng,Rong Guo,Shengjie Wang,Mingjun Zhang,Cunwei Che

doi:10.3390/w11122578

Abstract

Based on 1260 tap water samples gathered monthly and 136 surface water samples collected seasonally in the eastern margin of the Qinghai–Tibet Plateau, the local tap water line, the basic spatiotemporal characteristics of tap water isotopes, and their indication for water source under different water supply modes were discussed, linking the local tap water supply and water source information. A new tap water isotopes data set based on dense sampling sites was established, which was reliable for the analysis of tap water isotope features, tap water supply management, and tap water sources. The main conclusions are: (1) The local tap water lines in Gannan and Longnan are δ2H = (7.06 ± 0.17) δ18O + (3.24 ± 1.75) (r2 = 0.81, p < 0.01) and δ2H = (5.66 ± 0.09) δ18O + (−8.12 ± 0.82) (r2 = 0.82, p < 0.01), respectively. (2) The annual mean δ2H and δ18O in tap water show an increasing trend from southwest to northeast. The seasonal differences of δ2H and δ18O in tap water in Gannan and Longnan are small. (3) The correlation of tap water isotopes with those in main source water is high, while that of isotopes in tap water with those in non-water source is low. Under the central water supply mode by local tap water company, tap water isotopes in Gannan where groundwater is the direct water source show weak connection with those in surface water and precipitation, and those in tap water in Longnan with surface water as main source water reveal good connection with isotopes in surface water. Under mixed water supply modes, tap water isotopes indicate that surface water is the main tap water source in Gannan and Longnan with multiple water sources.

Highlights

Under the mode of central water supply by local tap water companies, for tap water isotopes, weak connection can be seen in Gannan with isotopes in precipitation and surface water, while tap water isotopes in Longnan present better correlation with surface water isotopes
Correlation of tap water isotopes with isotopic composition of main water source is high, while that with isotopic composition of non-water source is low
Δ2 H and δ18 O in 1260 tap water and 136 surface water samples were analyzed to exhibit the spatiotemporal characteristics of tap water isotopes and their water source signals under different water supply modes

Summary

Introduction

Tap water isotopes are well proven to be essential indicators [1,2,3,4,5,6,7,8,9,10] for studies in many fields [10,11,12,13,14,15,16,17,18,19,20,21,22], including hydrology, ecology, climatology, forensic, and so on. Studies on isotopes in tap water [33,34] throughout the world are relatively few. The main research contents include basic features (e.g., spatial and temporal variations, local tap water line) of tap water isotopes, tap water source, the applicability of tap water to relevant fields, and so on. These studies have enriched the knowledge of tap water isotope features, tap water supply mode and management strategy of local water resources Their study areas have mainly involved the United States of America (e.g., the San Francisco Bay Area [31], the Salt Lake Valley of northern Utah [30], western and the whole United States [35,36,37]), South Africa [30], and China [34,38].

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