Isotopic exploration of eco-hydrological connectivity in the riparian zones of Southern Western Ghats, India

Understanding the route of precipitation through the soil-vegetation-atmosphere continuum is significant for partitioning evapo-transpiration (ET) into its components. The δ¹⁸O of water has been used in the present study to understand the eco-hydrological connectivity in the tropical humid Western Ghats, India. We conducted spatially distributed sampling of stream water, xylem, groundwater, root, and soil pore water. The results suggest that the vegetation mostly accessed water from the intermediate soil layer and not from the streams. Though the shallow roots exhibited enriched isotopic signatures due to the availability of evaporated soil water, the xylem water exhibited rather depleted signatures suggesting that the dominant uptake happened from the layers beneath the topsoil. While a significant Isotopic elevation effect (-0.09/100 m elevation) was observed in the stream water, the xylem water elevation effect was not significant. The major discontinuity of the Western Ghats, the Palghat Gap, exhibited the circulation of ¹⁸O enriched water in the soil-vegetation-atmosphere continuum due to the evaporative enrichment of source water and the subsequent abstraction by trees. The calculated leaf water enrichment at the evaporative site of the leaf (∆Le) and the ET fluxes recorded in the weighing lysimeters as well pointed towards the isotopic enrichment in the Palghat Gap. Additionally, the lysimeter ET flux and the mixing model-based partitioning of ET show the transpiration component to be 88%.