Abstrakt
Major Ion Chemistry of River Bhagirathi and River Kosi in the Uttarakhand Himalaya
N. Semwal and J. S. Jangwan
The chemistry of river water is governed by supply of various elements from natural (chemical weathering and rain) and anthropogenic (sewage, mining effluents etc. ) sources. Major ions of glacial melt streams and sulphur spring, located in the Bhagirathi valley were studied separately to observe the contribution of these sources to the ionic abundance in River Bhagirathi. Ionic composition in glacial melt streams was found to be as; Mg > Ca > Na > K > NH4 (cations) and Cl > HCO3 > SO4 >NO3 (anions). On the other hand, sulphur spring water was characterized by high concentration values with altogether a different composition of cations i. e. Na > Mg > K > Ca > NH4, whereas, anion composition followed the same pattern as for glacial melt water. The average ionic composition of River Bhagirathi towards downstream was found to be as; Ca > Mg > Na > K > NH4 (Cations) and HCO3 > SO4 > Cl > NO3 (Anions). However, sulphate ion predominates over rest of the anions in the upstream i. e. in the Gangotri valley. Some local streams such as Nagun Gad and Syansu Gad, which contributes substantial quantity to River Bhagirathi in the downstream near Uttarkashi are characterized by high levels of HCO3 and Total Dissolved Solids (TDS). At two damming areas namely Maneri and Tehri, the concentration levels of cations and anions were increased as compared to flowing river stretch. These results were compared with ionic abundance of comparatively low altitude spring fed Himalayan River Kosi, where the ionic concentration levels were comparatively low at the origin and consistently increased towards downstream. The average ionic composition of River Kosi all through its length was similar as River Bhagirathi in the downstream reaches, which in fact is the composition of rain water over the Himalaya region. It is also observed during the study that biological life in the form of benthic fauna is also influenced by the ionic environment at sediment - water interface.
