Bacterial Communities in Riparian Sediments: A Large-Scale Longitudinal Distribution Pattern and Response to Dam Construction

Abstract

Sediment microbes play major roles in riparian ecosystems; however, little is known about their longitudinal distribution pattern and their responses to dam construction, the most severe human disturbance in river basins. Here, we investigated the variability of sediment bacterial communities along a large-scale longitudinal gradient and between dam-controlled and dam-affected sites in riparian zone of the Lancang River, China. The abundance, activity and diversity of sediment bacteria gradually increased in a downstream direction, but were significantly lower in the dam-affected sites than in the dam-controlled sites. The bacterial community compositions differed significantly between the upper-middle-reach and downstream sites at all control sites, and also between the dam-affected and dam-controlled sites. In the cascade dam area, the relative importance of spatial distance and environmental heterogeneity for bacterial distribution differed between the dam-controlled and dam-affected sites. Spatial distance was the primary cause of variations in bacterial community in dam-controlled site. By contrast, the environmental heterogeneity had more control over the bacterial communities than did the spatial distance in dam-affected site. Network analysis showed that the bacterial community in the dam-affected sites had lower connectivity and stability when compared with that in dam-controlled sites. These results suggest the distinct variations in sediment bacterial community in dam-affected sites, which could enhance our understanding of potential ecological effects caused by dam construction.

Fungal community demonstrates stronger dispersal limitation and less network connectivity than bacterial community in sediments along a large river

“…A recent study on the Lancang River reported that the biogeographic pattern of bacterial community in riparian sediments largely differed between the upper‐middle reach sites and the downstream sites (Chen et al ., ). Similarly, both bacterial and fungal communities were significant different among the three river sections according to our NMDS and PERMANOVA results (Fig.…”

“…In the present study, spatial isolation might also contribute to dispersal limitation of microbial community. Our recent study reported the strong impact of dam construction on the relative importance of spatial distance for bacterial distribution in riparian sediments of Langcang River (Chen et al ., ). For the river sediment, water depth increased drag, which may restrict the mobility of microbial populations and exchange between sediment grains.…”

“…The upstream of the Jinsha River represents a natural river section due to the less anthropogenic disturbances, and the midstream and downstream sections are subject to anthropogenic impacts, such as cascade dam constructions on the river and industrial activities in the basin. The large‐scale riverine current and human activity along this large river provide the possibility of species dispersal and environmental selection, two factors that shape microbial communities in natural ecosystems (Martiny et al ., ; Chen et al ., ). As reported by Velimirov et al .…”

“…It is known that microbial diversity is significantly altered by varying geographical and environmental factors along a large river (Velimirov et al, 2011;Tian et al, 2018). Spatial variability of microbial composition from headwaters to the river mouth has been well demonstrated (Savio et al, 2015;Chen et al, 2018;Wang et al, 2018), but most previous studies only focused on one taxonomic group. Regarding bacteria and fungi in large rivers, one would expect that the spatial patterns of their diversities differed substantially among different river sections.…”

“…(), bacterial community in the midstream of the Danube River was obviously different from other river sections, which was mainly affected by the local environmental condition. Recent studies on the Lancang River found that the contribution of environmental heterogeneity to microbial community became more important than that of spatial distance in the dam‐affected area (Chen et al ., ; Chen et al ., ). It is reasonable to speculate that the ecological drivers and their contribution varied among different river sections.…”