Water circulation and governing factors in humid tropical river basins in the central Western Ghats, Karnataka, India

Abstract

The narrow coastal strip to the west of the Western Ghats displays unique water characteristics in both tropical river basins investigated. For the smaller and hilly Swarna basin, the dense vegetation (wet canopies) could largely re-evaporate the (intercepted) rain, leading to no marked seasonal or altitude effect on the water isotope values within the basin. The larger Nethravati basin, which stretches farther into the foothills of the Western Ghats, receives winter monsoon water, and thus exhibits a clear seasonal variability in rainfall moisture sources. The degree of water vapor recycling in these wet tropical basins dominates the isotopic composition in this narrow coastal stretch of South India. An insight into the soil water contribution to the river water and groundwater, even in the rainfall-dependent tropical basins of South India, is provided in this study.

Seasonal freshwater flux estimation using mollusc from the tropical Mandovi Zuari estuary, Goa, India

“…We also calculated percentage of freshwater input into MZ estuary using d 18 O values measured in the Swarna river basin, which is in proximity to the MZ estuary that receives discharge from the river originating from the Western Ghat Mountains. The average d 18 O of river water during the month of November was À2.67% (Tripti et al 2016). Assuming the end member river water composition, our estimates yielded freshwater Cuxes for the month of July until January, varying from 72% to 12%, which is slightly different from the estimate described earlier in the text.…”

Evidence of elevation effect on stable isotopes of water along highlands of a humid tropical mountain belt (Western Ghats, India) experiencing monsoonal climate

“…The δ 2 H data compiled for the precipitation and surface water over the Indian subcontinent shows homogenous signature in southern part with relatively higher isotope ratio (δ 2 H > -20 ‰) than the north and northeast India due to larger influence of southwest monsoon (Hobson et al, 2012). The initial analysis on impact of climatic conditions on water budgeting and local moisture recycling in the central part of the Western Ghats through stable isotopes of rainwater, river water and groundwater have been reported in our earlier study (Tripti et al, 2016). This study is carried out to provide a spatial monitoring of water isotopes on a synoptic scale of the Western Ghats to account for the hydrological budgeting and monsoonal climate along the humid tropical high mountains.…”

“…These studies have reported that the precipitation of higher amount exhibits lower stable isotope ratio due to enrichment of lighter isotopes whereas the lower precipitation amount exhibits higher stable isotope ratio due to enrichment of heavy isotopes. However, this difference in the stable isotope ratios with precipitation amount tends to be smaller in the tropical ecosystems (Scholl et al, 2009;Tripti et al, 2016) although there is a large variability in precipitation amount. There are also studies reporting the reversed rainfall amount effect on the stable isotope ratios (i.e., a positive correlation of δ 18 O and δ 2 H with precipitation amount) of precipitation in the tropical region (Yadava et al, 2007).…”

“…(iii) The continental effect: This effect explains how the rainout system affects the isotopic composition of the rainfall and groundwater. The mean δ 18 O of groundwater in both across and along the region between eastern Arabian Sea coast and the western slopes of the Western Ghats is around -3 ± 0.5 ‰, and depicts the signature of homogeneous summer monsoon moisture input rather than that from the rainout history (Deshpande et al, 2003;Tripti et al, 2016). Recently the rain out effect has been reported for the west draining river basins of the Western Ghats where it is observed that the effect is limited only to the onset of summer monsoon and before the availability of excess moisture for undergoing recycling process (Tripti et al, 2018).…”

“…The winter monsoon rain derives moisture carried by the north-easterly winds moving from the Bay of Bengal, South China Sea and continental vapour sources to provide precipitation to the eastern and south-eastern parts of the Peninsular India (Mooley and Shukla, 1987). These two sources of moisture in the two monsoon seasons are known to have distinct stable isotope ratios (δ 18 O and δ 2 H) whose imprints are identifiable in the geographic distribution of isotopes in groundwater and surface water (Deshpande et al, 2003;Tripti et al 2016) and rain water (Lekshmy et al 2014;Warrier et al, 2010).…”