Bartwal Tanuja, Nautiyal Prakash
Aquatic Biodiversity Unit, Department of Zoology, Hemvati Nandan Bahuguna Garhwal University, (A Central University), Srinagar Garhwal, Uttarakhand, India.
Environ Monit Assess. 2025 Jun 6;197(7):738. doi: 10.1007/s10661-025-14162-8.
Large human habitations exist along the major glacier-fed Himalayan rivers. Over the years, the size of habitations and associated developmental activities has increased exponentially alongside pilgrimage and tourism. All these activities are sources of anthropogenic stress that have the potential to degrade river ecosystems. However, the long-term impacts of these stressors are barely known for the Himalayan rivers. Thus, we propose to examine long-term variation in the structure of the producer community over three decades as an indicator of ecosystem degradation. The Alaknanda sampled at Srikot was deemed suitable for these investigations. The sampling location in 2021-22 was the same as in previous studies conducted in 1991-92 and 2018-19, which made them comparable. The past naphrax mounts available for these periods were re-examined for historical species count to ensure taxonomic consistency in species identification. Species richness and diversity parameters increased over time, though not statistically significant between the years. However, notable variation occurred in the community dominant and their relative abundance, exemplified by Achnanthidium pyrenaicum (26-41%), Achnanthidium minutissimum (35-63%), and Achnanthidium latecephalum (19-50%) for the years 1991-92, 2018-19, and 2021-22, respectively. The assemblages persisted throughout the sampled months in 1991-92 but became inconsistent after three decades. The prevalence of community in each year was influenced by the gradient of ecological preferences. The observed variation in the community is likely driven by deficient discharge in the river stretch below the dam at Srikot, which enhances the impact of the organic load from the surrounding human habitations. This is the first study to examine the long-term variation in diatom community structure of the Himalayan river. Such long-term investigations are hence important for assessing ecosystem degradation and creating reference benchmarks for future ecological assessment. The study also demonstrates the use of historical mounts and diatom community structure, especially the persistence and dominance of sensitive taxa, as a key bioindicator in river health assessment.
喜马拉雅山脉主要冰川补给河流沿岸存在大型人类聚居地。多年来，聚居地规模及相关开发活动随着朝圣和旅游业呈指数级增长。所有这些活动都是人为压力源，有可能使河流生态系统退化。然而，这些压力源对喜马拉雅河流的长期影响几乎无人知晓。因此，我们建议研究三十年来生产者群落结构的长期变化，以此作为生态系统退化的指标。在斯里科特采样的阿拉克南达河被认为适合这些调查。2021 - 2022年的采样地点与1991 - 1992年和2018 - 2019年之前的研究相同，这使得它们具有可比性。重新检查了这些时期可用的过去硅藻载玻片，以统计历史物种数量，确保物种鉴定中的分类一致性。物种丰富度和多样性参数随时间增加，尽管各年份之间在统计学上不显著。然而，群落优势种及其相对丰度出现了显著变化，例如在1991 - 1992年、2018 - 2019年和2021 - 2022年，皮氏针杆藻（26 - 41%）、极小针杆藻（35 - 63%）和后头部针杆藻（19 - 50%）分别占优势。这些组合在1991 - 1992年的整个采样月份中持续存在，但三十年后变得不一致。每年群落的盛行受到生态偏好梯度的影响。观察到的群落变化可能是由斯里科特大坝下游河段流量不足导致的，这增强了周围人类聚居地有机负荷的影响。这是第一项研究喜马拉雅河硅藻群落结构长期变化的研究。因此，这种长期调查对于评估生态系统退化和为未来生态评估创建参考基准非常重要。该研究还展示了利用历史载玻片和硅藻群落结构，特别是敏感分类群的持续性和优势度，作为河流健康评估的关键生物指标。
