Diatom communities in Himalayan river (Lower stretch of Alaknanda, Srinagar): Periodic variations in relative abundance

The mountain rivers are under anthropogenic stress, especially from habitations along the banks, exemplified by Srinagar Garhwal (Uttarakhand) situated on the banks of lower stretch of Alaknanda. The relative abundance patterns characterise a community and hence the ecosystem. In view of this, a study was designed to assess short and long -term response of benthic diatoms at 5-year and 30-year intervals. For this study we made species count by examining the diatom mounts of 1^st, 2^nd and 3^rd period (1991-92 19 95-96 and 2021-22) The 1^st and 2^nd periods were characterised by consistently high relative abundance of A. pyrenaicum and A. minutissimum . In contrast, 3 ^rd period is characterised by high relative abundance of A. pyrenaicum in January only and that of A. minutissimum and C. excisa from February to April. The relative abundance varies significantly (p=0.0043) in long-term interval. Flora varies conspicuously in these periods as some of the taxa exhibited restricted distribution; 5 of 54, 6 of 53 and 33 of 92 species in respective periods. Species diversity increases from 1^st to 3^rd periods and varies significantly for long-term interval. The variations in long-term interval reflect lack of stability in the ecosystem, possibly due to the flow modification (flooding and desiccation) caused by the power house. The temporal patterns of relative abundance and hence community structure over a period of time would be a suitable bench-mark for ecosystem integrity, and hence restoration.