Multi-Metric Assessment of Trophic Status and Periphyton Responses in the Aripal Stream of Kashmir Himalaya

This study examined the environmental variables regulating periphytic algal assemblages on natural substrata in the Aripal Stream, Kashmir Himalaya, with particular emphasis on trophic dynamics and ecological responses to nutrient enrichment. A total of 72 species representing 48 genera were identified, among which Navicula sp., Diatoma sp., Cymbella sp., Pinnularia sp., Synedra sp., and Oscillatoria sp., exhibited the greatest species richness. Trophic assessment based on total phosphorus (TP) concentrations classified Sites I and II as mesotrophic, whereas downstream Sites III, IV, and V were categorized as eutrophic. Conversely, the Trophic State Index (TSI) derived from mean and maximum benthic chlorophyll-a concentrations predominantly indicated oligotrophic conditions across the study reach. Likewise, Autotrophic Index (AI) values ranging from 1.03 to 49.68 consistently reflected predominantly autotrophic conditions, suggesting a balanced relationship between primary production and organic matter decomposition. In addition, Siltation Index (SI) values ranging from 8.3 to 44.8 indicated relatively low sedimentation and erosion pressures within the watershed. A key outcome of the study was the pronounced divergence between nutrient-based and biological indicators of trophic status. Elevated TP concentrations at downstream sites suggested progressive eutrophication; however, benthic algal biomass and AI values continued to indicate oligotrophic to mesotrophic ecological conditions. This discrepancy underscores the limitations associated with the use of single physicochemical indicators for trophic assessment. The Sankey diagram further elucidated these relationships by demonstrating that downstream sites contributed strongly to eutrophic phosphorus signals, whereas chlorophyll-a-based trophic flows remained concentrated within oligotrophic categories. Collectively, the findings emphasize the ecological significance of integrating physicochemical and biological metrics for a more comprehensive evaluation of stream trophic status and ecosystem functioning.