Long-term change in stream diatom assemblages in the Nepalese Himalaya

Gurung, Smriti, Jüttner, Ingrid, Vaughan, Ian ORCID: https://orcid.org/0000-0002-7263-3822, Chapagain, Prizma, Dhakal, Anubhuti, Thapa, Bhumika, Khatri, Kumar, Paudel, Pratima, Rai, Manita, Raut, Nani, Cox, Eileen J., Williams, David M., Ormerod, Steve J. ORCID: https://orcid.org/0000-0002-8174-302X and Jacobsen, Dean 2026. Long-term change in stream diatom assemblages in the Nepalese Himalaya. Hydrobiologia 10.1007/s10750-026-06327-4

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Abstract

Mountain ecosystems are sensitive to global change, but long-term data assessing effects for running waters are scarce. We, therefore, investigated changes in diatom diversity and assemblage composition using five surveys between 1992 and 2023 in streams across a 2,345 m altitudinal gradient in the Himalaya. Taxon richness tended to decline at high altitudes while peaking in the later years of the study. Among 75 species found, most were cosmopolitan—including the most abundant species which occurred across altitude. Navicula nielsfogedii and Gomphosinica chubichuensis had restricted distributions geographically and altitudinally and are potentially indicators of warming. The former increased through time at lower altitudes while the latter was restricted to the highest altitudes where it had declined by 2023. Gllvm models suggested that time, season, and altitude affected abundance and assemblage composition. Few species were more abundant at higher or lower altitudes, while many had wide altitudinal ranges and equal prevalence between seasons. Composition, nevertheless, changed with increasing altitude, reflecting changes in vegetation cover and stream chemistry and occurred through taxonomic turnover rather than nestedness. Compositional changes through time in both seasons were observed in most streams but were least pronounced above 3,500 m except in a glacier-fed stream.

Item Type:	Article
Date Type:	Published Online
Status:	In Press
Schools:	Schools > Biosciences Research Institutes & Centres > Water Research Institute (WATER)
Publisher:	Springer
ISSN:	0018-8158
Date of Acceptance:	15 July 2026
Last Modified:	15 Sep 2026 09:00
URI:	https://orca.cardiff.ac.uk/id/eprint/189595

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