Quantifying tree dependency on imported water in artificial wetlands of arid regions: Insights from isotope analysis

Artificial wetlands in arid regions are characterized by high evaporation rates, artificially structured vegetation, and a higher proportion of non-drought-tolerant trees compared to natural wetlands. While these artificial wetlands play a crucial role in water resource management, ecosystem restoration, and environmental protection in arid regions, their water consumption patterns remain poorly understood. To address this knowledge gap, understanding the water use strategies of trees in artificial wetlands is critical for wetland ecosystem construction and efficient water resource utilization. In this study, we established a monitoring system to sample precipitation, groundwater, surface water, soil water, and the dominant tree species (willow) in the Zhangye artificial wetland in an arid region of China, and conducted hydrogen and oxygen stable isotope analyses. Our results reveal three key findings: (1) the dominant willow species primarily relies on soil water and groundwater as its main water sources, with their combined contribution exceeding 60 % across different seasons; (2) the artificially supplied water serves as the main source of soil water and groundwater in the Zhangye wetland; (3) water consumption of a single willow tree during the growing season reaches 432.5 mm, approximately three times the growing season precipitation, with total consumption by willows in the entire wetland system reaching 18.94 million m³ . Based on these findings, our study quantitatively assesses the dependence of trees in artificial wetlands on imported water and associated evapotranspiration losses in arid regions. We conclude that the current dominant tree species are excessively dependent on artificial water supply and have high evaporation rates. Consequently, we recommend that the current ecological forest structure should be re-evaluated, and moderately drought-resistant tree species with low evaporation rates should be selected to enhance wetland ecosystem resilience and reduce water resource consumption. This study provides quantitative quantitative evidence that willow water consumption is approximately three times the growing season precipitation and that groundwater and soil water contribute over 60 % to willow water sources in artificial wetlands of arid regions, revealing how artificial water introduction fundamentally alters tree water use strategies and offering insights for optimizing vegetation structure in water-limited ecosystems.