Assessment of system characteristics of Gangotri glacier headwater stream

Highlights: • River Bhagirathi remains under closed system from Gomukh to Gangotri, in which high p(CO₂) closed system dominates. • Sediment concentration and subglacial activities influence glacier system extend to downstream reaches as well. • Inter-annual variability of the discharge characteristics has direct bearing on the sediment transfer characteristics. • Sediment transfer characteristic is also linked with the development and progression of subglacial channel network. -- Abstract: The study examine the major ion chemistry and p(CO₂) variations of Ganga headwater stream for a stretch of 18 km from Gangotri glacier snout at Gomukh to Gangotri for characterising the open and closed system conditions and its temporal variations. The study has been carried out at three locations along the stream continuum, at the glacier snout (0 km), Bhojwasa (4 km) and Gangotri (18 km) covering three consecutive melt seasons from the year 2014 to 2016 and reveals the persistence of closed system conditions along the stream stretch. The year 2014 and 2016 melt seasons experience high p(CO₂) closed system conditions associated with high suspended sediment flux, whereas the year 2015 experienced low p(CO₂) closed system condition associated with low sediment flux suggesting in-stream sulphide oxidation during high sediment flux years and results into low values of the C-ratio. On the other hand, the melt season with low sediment flux such as the year 2015 showed dominance of HCO₃⁻ over SO₄²⁻ and higher C-ratio. The study shows that the headwater reach of River Bhagirathi from Gomukh to Gangotri has prevalence of high p(CO₂) closed system characteristics associated with high sediment flux and dominance of SO₄²⁻ during the seasonal peak flow. This is suggested as a unique characteristic of the meltwaters of the upper Bhagirathi basin.