Assessing catchment-scale groundwater discharge: Optimal tracers and factors analysis

Area of Science:

• Hydrology
• Environmental Science
• Geochemistry

Background:

• Streamwater-groundwater interactions (SGI) are vital for water resource management, particularly in arid regions.
• Large-scale SGI assessment is complex due to tracer variability and environmental conditions.

Purpose of the Study:

• To investigate SGI spatiotemporal variations and controlling factors in China's Loess Plateau (CLP).
• To quantify uncertainties in SGI estimation using various tracers.
• To provide insights for selecting effective tracers for SGI quantification.

Main Methods:

• Utilized multiple physicochemical and stable isotope tracers (δ²H and δ¹⁸O) across seven large watersheds in the CLP.
• Analyzed spatiotemporal variations and controlling factors of SGI.
• Estimated uncertainties in quantifying SGI using individual and combined indicators.

Main Results:

• Groundwater discharge into streamwater is the dominant SGI in the CLP, with mean discharge ratios ranging from 10% to 57%.
• Significant spatial variability in discharge ratios was observed across and within watersheds, influenced by loess thickness and vegetation.
• Individual tracers (isotopes or hydrochemicals) yield high uncertainties; combined approaches reduce SGI quantification uncertainties.

Conclusions:

• Groundwater discharge is a key component of river flow in the CLP, with significant regional and local variations.
• Loess thickness and vegetation cover are critical factors influencing groundwater discharge rates.
• Combining multiple tracers enhances the accuracy of SGI quantification, crucial for sustainable water resource management in arid and semi-arid environments.