Hydrology and nutrient dynamics of a sacred lake in Sikkim Himalaya

Abstract

The hydrology and nutrient dynamics of a sacred lake in the western part of the Sikkim Himalaya were studied. The lake watershed has broad-leaved mixed forest and agriculture land, two perennial and five seasonal inlets, and one major outlet. Annual inflow was 1103×10⁶ l while outflow was 4279×10⁶ l. About 70% of its water was from subsurface flow and seepage. More than 50% of the discharge was recorded in August (peak rainy season month) and the least in March (lean month). Sediment flow to the lake was 346 Mg y^-1 and outflow 316 Mg y^-1. The remaining 30 Mg was deposited in the lake. High sediment runoff in the rainy season turned the lake turbid and caused expansion of the bog. The nutrient (dissolved oxygen, carbon dioxide, total-N, ammonium-N, phosphate-P and chloride) levels of the lake, inlets and outlet varied between seasons and sites. Plankton productivity ranged from 16 mg C m^-2 d^-1 in winter to 247 mg C m^-2 d^-1 in the rainy season. Its respiratory loss was 12 mg C m^-2 d^-1 in winter and 160 mg C m^-2 d^-1 in the rainy season. Religious activities, agriculture, cattle grazing and forestry in the watershed should be controlled for maintaining the longevity of the lake.