Cascade damming impacts on microbial mediated nitrogen cycling in rivers

Area of Science:

• Environmental Microbiology
• River Ecology
• Biogeochemical Cycling

Background:

• Rivers are crucial for nitrogen cycling, but damming, especially cascade damming, poses significant threats.
• Microbial roles in nutrient cycling are vital yet understudied in dam-affected river systems.

Purpose of the Study:

• Investigate microbial nitrogen (N) cycling functional biogeography in single-dammed and cascade-dammed rivers.
• Assess the impact of damming on N-cycling genes and microbial community structure.
• Understand the drivers of microbial functional changes in response to river regulation.

Main Methods:

• Utilized Geochip microarray to analyze microbial N-cycling genes.
• Compared N-cycling processes across single-dammed (Yarlung Tsangpo-Brahmaputra) and cascade-dammed (Lancang-Mekong) rivers.
• Examined relationships between gene abundance/composition and environmental factors (hydraulics, nutrients, geography).

Main Results:

• Nitrogen cycling processes were stimulated in reservoirs, inversely related to hydraulic retention time.
• Cascade damming hindered the recovery of N-cycling gene abundance downstream.
• N-cycling gene composition altered in single-dammed rivers but not cascade-dammed reaches.
• Cascade damming reduced N-cycling gene flow connectivity.
• Nutrients drove gene abundance in single-dammed rivers; geographical and physical factors influenced both abundance and composition in cascade-dammed rivers.

Conclusions:

• Cascade damming profoundly impacts river microbial functional biogeography and nitrogen cycling.
• Understanding these impacts is crucial for predicting microbial responses and biogeochemical feedbacks to river regulation.
• Findings inform strategies for protecting river ecosystems under increasing damming pressures.