Winter ice regulates antibiotic resistance dynamics through seasonal genetic reservoirs across lake compartments.

Antibiotic resistance is a growing environmental and public-health threat, yet its seasonal dynamics in cold-region freshwater ecosystems remain poorly understood. Using year-round observations, metagenomic sequencing, and machine learning, we investigated antibiotic resistance genes (ARGs) across ice, water, and sediment in an ice-covered lake. Winter ice contained significantly higher abundances of ARGs, mobile genetic elements (MGEs), and microbial hosts than water and sediments. Driver analysis based on explainable machine learning showed that ARG dynamics in ice were primarily associated with MGEs, whereas ARGs in water and sediments were associated with host-related ecological processes and environmental conditions. During spring, ice-associated ARGs, MGEs, and their microbial hosts showed potential contribution to the water column, expanding resistance-risk hotspots and reorganizing associations among ARGs, MGEs, hosts, and virulence factors. These findings indicate that winter ice acts as a seasonal reservoir of antibiotic resistance, regulating spring antibiotic resistance dynamics and potential health risks.