Identifying groundwater anthropogenic disturbances and their predominant impact on microbial nitrogen cycling at a former contamination site adjacent to Baiyangdian Lake

Abstract

Groundwater ecosystems face increasing threat from declining water quality due to intensified urbanization, agricultural, and industrial activities. Accurately identifying anthropogenic disturbances remains challenging, and their effects on microbial nitrogen cycling are still largely unknown. Here, by collecting 64 groundwater samples from an aquifer beneath the Tanghe sewage reservoir in the North China Plain, we conducted a full-spectrum screening of 228 physiochemical indices, 47 nitrogen cycling genes (NCGs) and 2,182 metagenome-assembled genomes (MAGs) harboring NCGs. Unmix model identified antibiotic usage, industrial manufacturing, and agricultural practices as the predominant pollution sources, explaining 49.6% - 92.2% (averaged 81.0%) of the variations in aquifer attributes. These activities were primary drivers governing distributions of groundwater NCGs and NCG-hosts, with fragmented denitrification processes being prevalent. Antibiotic usage and industrial activities were probably associated with suppressed nitrogen cycling, while agriculture had a positive effect. Notably, we observed enhanced mutualistic interactions within NCG-hosts and increased enrichment of NCG-antibiotic resistance gene (ARG), NCG-mental resistance gene (MRG), and NCG-ARG-MRG co-hosts under high anthropogenic stresses, suggesting microbial adaptation to optimize nutrient and energy metabolism. This study provided new insight into how groundwater nitrogen cycling responds to anthropogenic disturbances, offering valuable information for developing groundwater management and pollution control strategies.