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<p>Freshwater ecosystems in the Himalayas are increasingly threatened by climate change, hydrological instability, and invasive species, yet the long-term ecological trajectories after major disturbance events remain poorly understood. This study examines post-flood environmental changes in the Assi Ganga River, a glacial tributary of the Bhagirathi, more than a decade after the catastrophic 2012–2013 flood that wiped out native and invasive fish populations, including <i>Salmo trutta fario</i>. From 2023 to 2024, we carried out integrated monitoring of macroinvertebrate communities, fish populations, and physicochemical parameters across three altitudinal sites (S1–S3). Water temperature increased downstream by about 1.2 °C, dissolved oxygen levels dropped accordingly, and turbidity peaked during the monsoon season. Macroinvertebrates showed signs of partial recovery, with 42 taxa recorded and a 7.3% increase in total abundance. Fish communities included seven cold-water species, with native <i>Schizothorax</i> spp. displaying strong numerical recovery, and invasive <i>Salmo trutta fario</i> reappearing across sites, likely due to recolonization from upstream refuges. Multivariate analyses revealed that temperature, DO, turbidity, and alkalinity collectively influenced both macroinvertebrate and fish communities, indicating shared environmental filters. The resurgence of <i>S. trutta fario</i>, potentially aided by recovering macroinvertebrate prey, raises concerns about renewed competitive pressure on native snow trout. This research highlights the importance of integrated, multi-trophic biomonitoring to understand resilience, restructuring, and invasion pathways in Himalayan river ecosystems.</p>

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Integrated assessment of aquatic biota reveals ecological shifts and invasive trout reappearance in a post-flood Himalayan stream

  • 期刊论文

  • 发表日期：

    2026年3月13日

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  • Deepak Rana,
  • Nilay Singh,
  • Madhu Thapliyal,
  • Ashish Thapliyal

摘要

Freshwater ecosystems in the Himalayas are increasingly threatened by climate change, hydrological instability, and invasive species, yet the long-term ecological trajectories after major disturbance events remain poorly understood. This study examines post-flood environmental changes in the Assi Ganga River, a glacial tributary of the Bhagirathi, more than a decade after the catastrophic 2012–2013 flood that wiped out native and invasive fish populations, including Salmo trutta fario. From 2023 to 2024, we carried out integrated monitoring of macroinvertebrate communities, fish populations, and physicochemical parameters across three altitudinal sites (S1–S3). Water temperature increased downstream by about 1.2 °C, dissolved oxygen levels dropped accordingly, and turbidity peaked during the monsoon season. Macroinvertebrates showed signs of partial recovery, with 42 taxa recorded and a 7.3% increase in total abundance. Fish communities included seven cold-water species, with native Schizothorax spp. displaying strong numerical recovery, and invasive Salmo trutta fario reappearing across sites, likely due to recolonization from upstream refuges. Multivariate analyses revealed that temperature, DO, turbidity, and alkalinity collectively influenced both macroinvertebrate and fish communities, indicating shared environmental filters. The resurgence of S. trutta fario, potentially aided by recovering macroinvertebrate prey, raises concerns about renewed competitive pressure on native snow trout. This research highlights the importance of integrated, multi-trophic biomonitoring to understand resilience, restructuring, and invasion pathways in Himalayan river ecosystems.