Tracer-based estimation of temporal variation of water sources: an insight from supra- and subglacial environments

Figures & data

Table 1. Detailed description of the Chhota Shigri Glacier.

Country, state	India, Himachal Pradesh
District	Lahaul & Spiti
Mountain range	Pir Panjal Range, Western Himalaya
Drainage system	Chandra River (Chenab-Indus River System)
Climate	Monsoon–arid transition zone
WGMS ID	2921
Latitude	32.19–32.28°N
Longitude	77.49–77.55°E
Snout position	~4050 m a.s.l.
Basin area	34.7 km^2
Glacierized area	15.5 km^2
Glacier length	9 km
Mean orientation	North
AWS altitude and location	4863 m a.s.l., on top of medial moraine
Mean annual temperature	−5.8°C
Annual precipitation	976 mm
Mean annual glacier-wide mass balance	−0.56 m w.e. year^−1
ELA0 (equilibrium line altitude)	~4950 m a.s.l.
AAR0 (area accumulation ratio)	~61%

Figure 1. Study area along with sample locations: (a) glacier ice surface, (b) supraglacial channel and (c) discharge measurement site (~3800 m a.s.l.) in the Chhota Shigri Glacier catchment.

Table 2. Detailed description (number of samples, sampling period and sampling frequency) of water source components (end members) and mixed components (glacial discharge) at Chhota Shigri Glacier.

Type	Sampling period (frequency)	Number of samples (n)
Water source component (end members)
Winter snow pack (450 cm)	Mid-June (one time only)	10
Glacial ice surface	July, August (monthly)	15
Supraglacial melt	Mid-June, July, August (monthly)	10
Subglacial melt	25 September to 4 October (diurnally)	15
Rainwater	Mid-June to 4 October (each rain event)	35
Water mixed component
Glacial discharge water	Mid-June to 4 October (diurnally)	Morning/Evening70/70
	Morning: 08:00 h/Evening: 18:00 h

Figure 2. Hydrological and meteorological observations at Chhota Shigri Glacier for the complete summer ablation season.

Figure 3. Box-and-whisker plots for (a) δ¹⁸O and (b) electrical conductivity of different types of water source and stream samples. The whiskers represent the 10th and 90th percentiles, while the box limits indicate the 25th and 75th percentiles, and the lines inside the box represent the median. R: rainfall; SP: winter snowpack; GS: glacier surface ice: SC: supraglacial channel water; MSTR: morning stream water; ESTR: evening stream water (where morning is 08:00 h and evening 18:00 h).

Figure 4. (a) Regression line (dashed green) between δ¹⁸O and δD values of rainwater samples (n = 35) at Chhota Shigri Glacier during the entire ablation season. Meteoric water lines (MWL) are as follows: dashed brown: Mediterranean MWL, dashed blue: Western Himalayan MWL, and solid black: global MWL. (b) Variation of d-excess and isotope (δ¹⁸O) in rainwater samples collected at the base station of Chhota Shigri Glacier (CS) during June–October.

Figure 5. Relationship between δD and δ¹⁸O values of glacier surface ice, winter snowpack and supraglacial meltwater collected during the monitoring period at Chhota Shigri Glacier.

Table 3. Parameters of the linear relationship between δ¹⁸O and δD for all types of end members (Chhota Shigri Glacier).

End member	n	Slope	Intercept	R^2
Winter snowpack	10	7.8	25	0.99
Glacial ice surface	15	6.3	3.6	0.77
Supraglacial melt	10	4.6	–17.5	0.70
Subglacial melt	15	4.5	–19	0.89
Rain	35	7.9	21.4	0.98

Table 4. Detailed summary of discharge data for stable isotopes and electrical conductivity during study period.

		δ^18O (‰)			δD (‰)
Scale	Time	Min.	Max.	Avg.	Min.	Max.	Avg.	EC avg. (µS/cm)	Streamflow	Air temp. avg. (°C)
Diurnal	Morning (08:00 h)	–15.3	–12.2	–14.1	–94.6	–74.9	–84.3	30	Low	1.05
	Evening (18:00 h)	–14.9	–11.1	–13.8	–96.3	–64.5	–82.7	20	High	2.2
Seasonal	Early ablation	–14.5	–14.1	–14.3	–96.9	–85.7	–88.7	25	Low	–0.8
	Peak ablation	–14.6	–11.3	–13.7	–92.6	–64.5	–81.9	30	High	4.4
	Late ablation	–16.1	–13.6	–14.5	–99.5	–82.8	–87.3	51.5	Very low	–0.7

Table 5. Parameters of the linear relationship between δ¹⁸O and δD for all stream water (Chhota Shigri Glacier).

Month	n	Slope	Intercept	R^2
June	35	5.2	–10	0.56
July	45	4.1	–26	0.73
August	10	6.1	4.6	0.96
September	35	5.5	–4.9	0.80
October	15	4.5	–19	0.89

Table 6. Statistical description of the tracers describing potential end members of stream water. SD: standard deviation.

Tracer	Statistical parameter	Supraglacial melt	Subglacial melt	Rain
δ^18O(‰)	Average	−13.7	−14.5	−10.0
	SD	0.289	0.558	3.679
EC(µs/cm)	Average	1.7	51.5	28
	SD	0.158	5.171	7.213

Figure 6. Rainfall–runoff characteristics the during ablation season at Chhota Shigri Glacier stream.

Figure 7. Mixing plot between δ¹⁸O (‰) and EC (µS/cm) of end members including average values of samples collected twice daily from main stream (morning: 08:00 h; evening: 18:00 h) during peak ablation.

Figure 8. Monthly variation of (a) morning δ¹⁸O (‰), (b) evening δ¹⁸O (‰), (c) morning EC (µS/cm), and (d) evening EC (µS/cm) in the glacier stream. The whiskers represents the 10th and 90th percentiles, while the box limits indicate the 25th and 75th percentiles and the line inside the box represents the median.

Figure 9. Temporal dynamics and comparison of monthly average values of tracers δ¹⁸O and EC in stream discharge samples taken consistently daily (morning: 08:00 h; evening: 18:00 h).

Table 7. Statistical differences among potential end members on the basis of tracers (δ¹⁸O and EC) performed with parametric t-test significant at α = 0.05.

End member	Tracer	t-test p value
Subglacial–Supraglacial	δ^18O	p = 0.02
	EC	p = 1.7421 × 10^−4
Rainfall–Supraglacial	δ^18O	p = 0.01
	EC	p = 0.001
Rainfall–Subglacial	δ^18O	p = 0.01
	EC	p = 1.5546 × 10^−4

Table 8. Previous studies that account for stable isotopes in hydrograph separation.

End member	Tracers	References
Glacial ice, surface runoff and groundwater	δ^18O	Maurya et al. 2011
Snowmelt, baseflow and rain	δ^18O and δD	Jeelani et al. 2013
Snowmelt, glacial melt and rainfall	δ^18O, EC	Penna et al. 2014
Snowmelt, glacial melt and groundwater	δ^18O and EC	Engel et al. 2016
Glacial melt and snowmelt	δ^18O,δD	Ohlanders et al. 2013
Snowmelt and baseflow	δ^18O and δD	St Amour et al. 2005
Channel precipitation, soil water and groundwater	δ^18O	DeWalle et al. 1988
Channel precipitation, soil water and groundwater	δ^18O	Swistock et al. 1989
Channel precipitation, soil water and groundwater	δD	McDonnell et al. 1991
Event water, groundwater and soil water	δ^18O	Buzek et al. 1995
Snowmelt, ice melt and rain	δ^18O	Rai et al. 2009
Snow/glacier, rain and baseflow	δ^18O	Ahluwalia et al. 2013

Table 9. Average (peak ablation) glacial end member (supraglacial and subglacial) contributions to glacial discharge based on tracer (δ¹⁸O and EC) data. The uncertainty is computed according to a Gaussian error propagation technique (Liu et al. 2004).

	End member component
Tracer	Supraglacial (%)	Subglacial (%)	Uncertainty
δ^18O (‰)	62.5	37.5	17%
EC (µS/cm)	68	32	1%

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