Mill dams impact microbiome structure and depth distribution in riparian sediments

Area of Science:

• Environmental Microbiology
• River Ecology
• Soil Science

Background:

• River damming causes significant ecosystem fragmentation and alters sediment properties worldwide.
• Sediments above dams accumulate human-altered soil environments, with limited knowledge on microbial structure, depth distribution, and function.
• Understanding these microbial legacies is crucial for river ecosystem restoration.

Purpose of the Study:

• To compare microbial community structure and functional genes in riparian sediments above existing and breached milldams.
• To investigate the influence of depth (0-4m) on prokaryotic and fungal communities and nitrogen cycling genes.
• To assess the impact of dam removal on microbial diversity and ecological functions.

Main Methods:

• High-throughput sequencing of bacterial/archaeal and fungal communities.
• Analysis of functional genes (nitrification and denitrification) at various sediment depths.
• Comparison of microbial data with in situ denitrification enzyme assays.

Main Results:

• Significant location- and depth-dependent changes in microbial community structure were observed.
• Major prokaryotic phyla included Proteobacteria, Bacteroidetes, and Firmicutes; dominant fungi were Ascomycota and Basidiomycota.
• Ammonia-oxidizing genes (amoA) were highest at the surface, while denitrifying genes (nosZ) were present at depth, indicating potential for denitrification in deeper layers. Dam removal increased microbial diversity and nitrification.

Conclusions:

• Sediment stratification and watershed conditions are key factors influencing microbial communities and functional genes in dammed rivers.
• Dam removal positively impacts microbial diversity, richness, and nitrification rates.
• Findings offer valuable guidance for river restoration projects and understanding human impacts on soil microbiomes.