Reforestation in the middle Yellow River has made groundwater recharge the main source of river water

The middle reaches of the Yellow River carry a substantial sediment load, impacting water quality and ecosystems downstream. Since the 1950s, soil conservation and 'Grain to Green' projects have altered hydrological conditions, yet groundwater-river interactions remain poorly understood. This study identifies water exchange between the Yellow River and groundwater in the Jinshan Gorge using major ion hydrochemistry and a revised ²²²Rn mass-balance method. Results indicate extensive hyporheic exchange, contributing an average of 44 % to the ²²²Rn balance, with rates ranging from 3.0 × 10^-5 to 1.40 × 10^-3 m³/(s·m). We identified four losing and seven gaining reaches, with the greatest losing rate reaching 1.95 × 10^-3 m³/(s·m) and infiltration depths of ∼100 m. Groundwater discharge, estimated at 88.19 m³/s, accounts for 80 % of the river's recharge, surpassing tributary contributions due to declining runoff linked to land use changes. Natural gas extraction and coal mining pose risks to groundwater quality, potentially degrading the Yellow River's water. Our findings highlight the increasing reliance on groundwater and its implications for river health under intensive human activities in the Loess Plateau.