Abstract:

Aims: Headwater streams are important habitats for maintaining regional freshwater biodiversity, yet aquatic insect diversity in mountainous headwater streams and its responses to environmental factors remain insufficiently understood. This study aimed to characterize the community composition and diversity of aquatic insects along an altitudinal gradient in Tianma National Nature Reserve and to identify the major environmental factors associated with these patterns. 

Methods: From 2024 to 2025, aquatic insect communities were systematically surveyed at 10 sampling sites along an altitudinal gradient in Tianma National Nature Reserve. Community diversity was evaluated using species richness, the Shannon-Wiener diversity index, Margalef richness index, Simpson dominance index, and Pielou evenness index. Differences in community structure among altitudinal zones were assessed using analysis of variance and non-metric multidimensional scaling. Redundancy analysis was used to identify key environmental factors affecting community composition, and generalized linear models were applied to evaluate the responses of diversity indices to environmental gradients. 

Results: A total of 10,592 aquatic insect individuals were collected, representing 119 taxonomic units, 45 families, and 8 orders. Ephemeroptera, Trichoptera, Diptera, and Odonata were the dominant groups. Aquatic insect community structure differed significantly among altitudinal zones. Species richness, Shannon-Wiener diversity, and Margalef richness were higher in low-altitude (400–600 m) and mid-altitude (600–800 m) streams than in high-altitude streams (800–1,000 m). Redundancy analysis showed that altitude, water temperature, and the permanganate index were the key environmental factors associated with community structure. Generalized linear models further indicated that altitude and water temperature were the main factors influencing community diversity, while dissolved oxygen, total nitrogen, and water depth also played important roles. 

Conclusion: Altitudinal gradients significantly affected the composition and diversity patterns of aquatic insect communities in headwater streams by regulating thermal and hydrochemical conditions. These findings enrich baseline knowledge of aquatic insect diversity in headwater streams of the Dabie Mountains and provide scientific support for regional stream conservation, biodiversity monitoring, and management of nature reserves.

Key words: headwater stream, aquatic insects, community composition, species diversity, environment factor