Relationship of isotopic variations with spring density in the structurally controlled springs and related geosystem services in Alaknanda Valley, Garhwal Himalaya, India.

As a traditional water source, springs are vital for Himalayan communities and it is essential to consciously focus on springs conservation. We report oxygen isotopes (δ18O) of spring water before, within, and after the tectonically active zones of the Alaknanda Valley, Uttarakhand. Higher variation of δ18O in the spring waters is found in highly tectonically disturbed zone i.e., Zone-2 with δ18O range - 4.9‰ to - 9.0‰ compared to tectonically less disturbed zones: Zone-1 and Zone-3 with δ18O value range - 7.9‰ to - 9.9‰ and - 7.4 to - 10.2‰ respectively. We hypothesize that the highly active thrust zones (Zone-2) with increased permeability compared to other Zones, manifested as greater spring density, results in higher water recharge in Zone-2. Very high to high spring density stretches are dominant in Zone-2 compared to Zone-1 and Zone-3. Stretches in Zone-2 with high spring density formed due to its highly tectonically active nature leads to the higher isotopic variation in Zone-2. The study also identifies the geosystem services provided by thrust zones as water resources to the local people and need of conservation modalities to manage the spring water resources in the thrust zones.