Hydro-ecological analysis of a sacred lake watershed system in relation to land-use/cover change from Sikkim Himalaya

The hydrology and ecological linkages between Khecheopalri lake and its surrounding watershed (area: 12 km2) in Sikkim were investigated to assess the long-term impacts of land-use/cover change on the hydrology of the lake ecosystem and bog formation around the glaciated lake. Significant land-use/cover change occurred in the past 4 decades. The bog area expanded by 67%, while the area under agriculture land in the lake watershed grew by 63% between 1988 and 1997. Overland flow was highest on the bare land (4.77% of the precipitation) and lowest in areas of cardamom-based agroforestry (1.79%). Soil and nutrient losses were highest in the cultivated area and least in the cardamom agroforestry system. Sediment loads of 345 Mg year−1 were recorded at the lake inlet and of 316 Mg year−1 at the outlet. Annual soil loss from the lake watershed was 502 Mg km−2 and a net sediment deposition in the lake was 141 Mg year−1. The lake received high nutrient loads (organic carbon of 10.2 Mg year−1, total nitrogen of 1.01 Mg year−1 and total phosphorus of 0.51 Mg year−1) from soil erosion and overland flow. The pH, total phosphorus and bulk density of the peat increased from the lake towards the bog-forest edge. This reflects the trapping of sediments and nutrients around the bog forest margin, although their retention is limited. Agricultural practices should be minimized in the upper part of the watershed and agroforestry practices should be encouraged to maintain the health and longevity of the lake.