Ecohydrological and hydrogeological dynamics of groundwater springs in Eastern Himalaya, India

Résumé fourni par la source

Groundwater springs are critical to achieving Sustainable Development Goals (SDG 6, access to clean water) in the Himalaya and remain highly vulnerable to climate change and land-use and land cover change. In a first from Eastern Himalaya, we analysed the relative controls of land-use, precipitation, soil properties, and hydrogeology on the diel and seasonal variability in three representative springs using high-frequency discharge monitoring. Kamrang spring is a high-discharge depression spring fed by a homogenous aquifer, whereas Mamley and Gaddi show dual-flow characteristics attributed to primary matrix-based flows and secondary conduit (karst) or unconsolidated storage-based flows, respectively. The first reports of strong diel fluctuations in springflows show significantly higher amplitude in the depression spring (22 ± 41 l min −1 ) than the fracture (15 ± 26 l min −1 ) and karst springs (12 ± 24 l min −1 ), attributed to evapotranspiration and hydrogeology, respectively. The forest spring (Gaddi, low soil hydraulic conductivity, K sat ) showed a faster response at intense precipitation (>30 mm h −1 ), whereas the agriculture springs (Kamrang and Mamley, high K sat ) showed the lowest lags at low-moderate intensities (<20 mm h −1 ). The depression spring showed high recharge potential, whereas the karst and fracture springs were constrained by their relatively smaller recharge area and low K sat , respectively. The per capita daily water availability was barely sufficient to support the minimum (20 l) and mandated (55 l) requirements for 30–70% and 2–47% of days a year, respectively. Thus, future precipitation intensification and land-use change will disproportionately impact the >5th-order karst and fracture springs. The study provides an integrated analytical framework for understanding Himalayan springs, which are critical for achieving SDG 6 (access to clean water) and a baseline for developing appropriate springshed models for effective management of freshwater ecosystems (SDG 15) against future climate change impacts (SDG 13), as well as informing the water security assessment in the Himalaya. • Characterising precipitation-discharge relationships in Eastern Himalayan springs. • Evidence of more than one aquifer governing a single spring discharge. • Significant diel springflow cycles induced by evapotranspiration and hydrogeology. • Future precipitation intensification will reduce net recharge to spring aquifers. • Karst and Depression springs are vulnerable to climate and land-use change.

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