RESUMO
River ecological health assessments are the premise for protecting river biodiversity and curbing river water environment deterioration. To explore the river ecosystem health status and its response mechanism to water environmental factors in the middle reaches of the Yarlung Zangbo River, phytoplankton samples were collected during July and October 2021, and water environmental factors were measured. The phytoplankton species were identified, and their cell abundance and biomass were calculated. The phytoplankton integrity index was constructed to evaluate the ecological health status of the river. The temporal and spatial distribution characteristics of water environmental factors and phytoplankton community, as well as the correlation between P-IBI value and community parameters and water environmental factors were analyzed. The results showed that the difference in water environmental factors was not evident in time but was significant in space. The average cell abundance and biomass of phytoplankton were in the order of wet season>dry season and main stream>tributaries. Diatoms dominated the community, and pH and WT were the major water environmental factors driving the spatial and temporal distributions of phytoplankton. The ecological health status of the middle reaches of the Yarlung Zangbo River was "healthy to sub-healthy." The river health status was better than that of the dry season, and that of the tributaries was better than that of the main stream. EC, TUR, WT, NO3--N, and NH4+-N were the major water environmental factors affecting the ecological health status of the river reach, which could be affected by the direction and rate of phytoplankton community succession. It is involved in and affects the process of material circulation and energy flow of the river ecosystem, thereby driving the ecological health of the middle reaches of the Yarlung Zangbo River.
Assuntos
Ecossistema , Rios , Água , Biomassa , Nível de Saúde , FitoplânctonRESUMO
Eukaryotic microorganisms play an important role in the biogeochemical cycles of rivers. Dynamic hydrological processes in rivers are thought to influence the assembly processes of eukaryotic microbes, as well as affecting local geomorphology. These processes have not been extensively studied for eukaryotic river microbes in extreme environments on the Tibetan Plateau. This study used 18S rDNA gene amplification sequencing, a neutral community model, and a null model to analyze the spatial and temporal dynamics and assembly processes of eukaryotic microbial communities in the middle reaches of the Yarlung Zangbo River. We conducted analyses across wet and dry seasons, as well as varying altitudinal gradients. Our results showed that the diversity, structure, and taxonomic composition of eukaryotic microbial communities varied more with altitude than season, and the diversity of the communities first increased, then decreased, with increasing elevation. Distance-decay analysis showed that the correlation between eukaryotic microbial communities and environmental distance was stronger than the correlation between the microbial communities and geographical distance. Deterministic processes (homogeneous selection) dominated the construction of eukaryotic microbial communities, and water temperature, pH, and total phosphorus were the primary environmental factors that influenced the construction of eukaryotic microbial communities. These results expand our understanding of the characteristics of eukaryotic microbial communities in rivers on the Tibetan Plateau and provide clues to understanding the mechanisms that maintain eukaryotic microbial diversity in extreme environments.