Historical Ecological State of a Mountain River: Developing Benchmarks for River Management and Restoration

Anthropogenic influences on alpine rivers are gradually increasing. Srinagar Garhwal, located on the banks of the Alaknanda River, a tributary of the Ganga, is one of the largest human settlements in the basin. A five-year study was planned to measure short-term changes in the ecological health of this river. For this work, we re-examined diatom mounts for 1991-92 (1st period) and 1995-96 (2nd period) and subjected them to species count for determining van Dam ecological categories. The tolerant N-autotroph, polyoxybiontic, βmesosaprobe, mesotrophic, and aquatic to aerophilic categories predominated in both periods, but their percentage increased considerably in the 2 nd period. A rise in the proportion of these categories, with the exception of polyoxybiontic, indicates deterioration of ecosystem health. Scrutiny of the categories indicated that only 9 taxa accounted for 21.6% of the polyoxybiontic category compared to 17 taxa for 20.6% of the tolerant N2 autotroph, which can also be used to enhance river health evaluation, especially in categories with few taxa accounting for a substantial percentage. This study will serve as a historical reference for the river health. The present growth of hydropower plants, together with numerous stressors, is increasing the source of disturbance, emphasizing the importance of having benchmarks for ecological states.