Seasonal variation in stable isotope compositions of waters from a Himalayan river: Estimation of glacier melt contribution

Abstract

Stable isotopic compositions (δ18O and δD) in water samples collected from Parbati River in Himachal Pradesh, India, during 2002–2005 were measured to delineate the contributions from different sources in different seasons. A seasonal cycle with high δ18O and δD values (in ‰) during the spring (March to May; −9.2, −58.6), intermediate values during the winter (December to February; −10.1, −65.6), and low values during the south‐west monsoon (July to September; −10.9, −71.8) is observed. The d‐excess values (15.2 ± 2.1‰) are higher compared with the global meteoric waters indicating significant contribution (~26%) of moisture carried by western disturbances. Higher δ‐values during the spring are ascribed to enhanced contribution from snow melt. The lower δ‐values during the monsoon are due to various Rayleigh effects (altitude, continental, and amount effects) and large‐scale convection effect on rains. A three component‐mixing model using the isotopic data and some plausible end member isotopic values was applied to identify contributions to the river discharge from different sources such as groundwater or subsurface base flow, glacier/surface snow melt, and the monsoon rain. Meltwater from glacier and snow combines with the base flow in spring season. South‐west monsoon rain and glacier melt along with the base flow constitute the monsoon discharge. The post‐monsoon season and winter are dominated by groundwater contribution. About 80% of the discharge is contributed by glacier melts in spring season. In the rainy monsoon season, glacier/snow melt contributes ~41% of the discharge. The mean annual glacier melt contribution to the river water is estimated to be 44 ± 15%. The present estimate along with some previous studies suggest that glacier contribution to the river discharge increased from ~35% to 50% during the period 1990 to 2011. This is consistent with recent data on glacier retreats in the Himalayan region.

Did the Harappan settlement of Dholavira (India) collapse during the onset of Meghalayan stage drought?

“…More importantly, however, recent high‐resolution δ 18 O measurements of monsoonal precipitation at multiple stations across India clearly suggest that, contrary to normal belief, there is a negligible contribution of the amount effect in Indian monsoonal rain (Eastoe and Dettman, ; Midhun et al ., ). If so, the only plausible source(s) of depleted water can be the extra‐peninsular rivers and their tributaries of the Himalayan region where glacial meltwater can contribute to generate a river water δ 18 O of −12‰ (Lone et al ., ; Laskar et al ., ). Therefore, we propose that the highly negative δ 18 O values required to explain the Dholavira T. palustris record were due to inputs from such rivers to the Gulf water of the mangrove hosting the gastropods.…”

Moisture Sources for Precipitation and Hydrograph Components of the Sutri Dhaka Glacier Basin, Western Himalayas

“…A previous study based on stable water isotopes shows that the WDs contribute the maximum (>70%) to the total annual precipitation in the Kashmir valley (western Himalayas), which is more than the Indian Summer Monsoon (ISM) (<30%) [15]. In contrast, a study in the Parbati Basin, western Himalayas, shows that WDs contribute a maximum up to 30% to the annual precipitation [17]. These reports clearly indicate large spatial variability in annual precipitation over the western Himalayas, particularly during the WDs.…”

“…On the contrary, another study based on a stable isotopes study suggests that the snow/glacier melt contribution to the Beas River, Western Himalaya, is up to~50% [12]. A similar study in the Parbati River, a major tributary of the Beas River, has reported that glacier melt contributes up tõ 44% (±15%) [17]. A model-based water balance approach for other Himalayan rivers like the Sutlej, Ganga and the Chenab, estimates the annual snow and glacier melt contributions up to~60% (at Bhakra Dam),~28% (at Devpryag), and~49% (at Akhnoor), respectively [26,27].…”

“…Few studies have also been carried out to decipher moisture sources for precipitation over other parts of the Himalayan regions using d-excess and back trajectory analysis [12,15,16,20,28,59,60]. However, other studies in the lower region of the western Himalayas have reported a stronger influence of ISM with high spatio-temporal variability in the sources for precipitation over the western Himalayan region [12,17,28]. Our event-based back trajectory analysis of the major summer precipitation events shows that the air parcel comprises both ISM and WDs origins (Figure 7b).…”

“…Stable water isotope ratios of oxygen (δ 18 O) and hydrogen (δ 2 H), along with second order parameter, deuterium excess d − excess = δ 2 H − 8δ 18 O , have been widely used to trace moisture sources for precipitation, identify mixing water from various sources and to quantify their relative contributions [10,11]. Several isotope-based studies have been conducted in the Himalayan and polar regions to trace moisture sources and estimate the hydrograph components [12][13][14][15][16][17][18][19][20][21][22][23]. Moisture sources for precipitation over the central and eastern Himalayas are primarily derived from the Indian Summer Monsoon (ISM) during June-September, while moisture sources to the western Himalayas are predominantly derived from the Mediterranean region due to Western Disturbances (WDs) during winter (October-May) [6,24].…”