Isotopic insights into the recharge dynamics of aquifers in the Chimborazo Volcanic Region (Riobamba, Ecuador)

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ABSTRACT Aquifers exploited in the Riobamba area, located in the southeastern sector of the Chimborazo volcano (Andean Ecuador), are essential in the drinking-water supply, which is strongly affected by climate change. Unconfined and semiconfined volcano-sedimentary aquifers are exploited through springs and wells in both rural and urban areas. The aim of this study is to identify the recharge areas of aquifers through an isotopic approach (δ 2 H and δ 18 O) in relation to the geological and hydrogeological context. 49 monitoring points including precipitation, surface waters, wells, springs and glacier ice from the Chimborazo glacier were analyzed over four different sampling campaigns (2020-2022 period), collecting 143 samples. Main physicochemical parameters were analyzed to better understand the recharge processes. Results highlight that precipitation and plausibly glacier ice melting of the Chimborazo glacier recharge groundwater. Differences in recharge areas between the aquifer groups (Chimborazo springs, Guano springs, Llio wells, Riobamba wells) were highlighted, with potential shallow and deep groundwater circuits in the study area. The probable Average Recharge Area Elevation (ARAE) of the aquifers extends broadly between 3,020 and 4,530 m a.s.l. Nevertheless, the main ARAE is potentially situated between 3,400 and 4,000 m a.s.l., based on the prevailing isotopic compositions and the dominant fracture permeability. Specifically, the Riobamba urban area aquifer is also recharged at lower altitudes, suggested by the presence of an anthropogenic footprint in the groundwater. This study clarified the groundwater recharge areas and processes, providing valuable knowledge for starting actions aimed at safeguarding these areas in a context particularly vulnerable to climate change and contamination.

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