Nitrogen transformation and microbial community interactions in hydrodynamic heterogeneous hyporheic zone sediment: Insights for ecosystem sustainability

Abstract

The hyporheic zone (HZ) plays a critical role in nitrogen transformation, yet the impact of hydrodynamic variability on microbial community dynamics within HZ sediments remains poorly understood. This study investigates how different hydrodynamic conditions affect microbial communities in HZ sediments using a simulation device to analyze groundwater-surface water interactions. Results indicate a significant reduction in nitrate (NO₃⁻) concentrations, with decreases of 93.81 % under upwelling (from 4.68 mg/L to 0.30 mg/L) and 91.05 % under downwelling conditions (from 6.2 mg/L to 0.55 mg/L). Concurrently, peaks in nitrite (NO₂⁻) concentrations were observed during denitrification processes (P < 0.05). High-throughput sequencing revealed diverse bacterial communities, predominantly consisting of Proteobacteria (40–46 % relative abundance) and Actinobacteria, with downwelling sediments exhibiting greater microbial richness (ACE index) compared to upwelling sediments (P < 0.05). The Shannon diversity indices showed mean values of 6.17 for downwelling and 5.81 for upwelling sediments. These findings demonstrate that hydrodynamic conditions significantly influence both microbial community structure and nitrogen transformation processes, underscoring the microbial role in biogeochemical processes of nitrogen cycling. Future research should examine the long-term effects of hydrological fluctuations on microbial dynamics in the HZ to enhance our understanding of ecosystem sustainability.