Chemical characteristics of pond waters within the debris area of Lirung Glacier in Nepal Himalaya

摘要

Water samples were analyzed from ponds developed within the debris-covered area of Lirung Glacier (28o 12.9’N, 86o 39.9’E; 4000 m a.s.l.) in the Himalayas of Nepal during the pre-monsoon to post-monsoon period of 1996. Major chemical species were classified into three groups based on their relationships relative to the sum of cations: conservative (SiO2, Ca2+, K+, and Alkalinity), semiconservative (Na+, Mg2+, and SO4 2-) and non-conservative (NH4 +, NO3 - and Cl-). The dominant processes determining the chemical composition of glacier pond water were sulfide oxidation coupled with carbonate dissolution and chemical weathering of aluminosilicate as indicated by the conservative and semi-conservative species. Calcium and alkalinity appeared as the dominant cation and anion, respectively, among all samples within the basin. Compared to the discharge waters at the outlet of the glacier, most of these pond waters have lower major solutes as well as alkalinity. The availability of fresh reactive minerals at the base of the glacier, coupled with higher temperature in discharge waters than in the ponds, may be the prime factors resulting in higher concentrations of most solutes in the discharge waters than in the ponds. In the ponds, higher concentrations of major solutes as well as alkalinity were observed in the monsoon than the pre-monsoon and post-monsoon seasons, suggesting the role of hydrolysis condition in chemical weathering rates. Ponds within the debris area of Lirung glacier in central Nepal Himalaya are likely to increase in importance if global warming accelerates the rate of glacial melting.