Microbial diversity, enzyme activity, metal contamination, and their responses to environmental drivers in an Indo-Burmese freshwater wetland.

Seasonal fluctuations can influence many biotic and abiotic parameters in wetland environments. Present research on wetlands do not serve as a comprehensive model for understanding these seasonal influences, especially in Northeast India, where wetland ecosystems remain understudied. That being, our study investigated the seasonal, spatial, depth-wise variations of enzyme activity (xylanase, invertase, and cellulase), microbial community, and heavy metal concentrations [chromium (Cr), cadmium (Cd), lead (Pb), and iron (Fe)] in the sediments of Deepor Beel. Our results show, seasons rather than sediment layers influence all parameters. Enzyme activities peaked during post-monsoon (POM), with xylanase showing highest activity throughout (0.01-132.94 mmole/min/g). Culture independent bacterial diversity study based on next generation sequence (NGS) analysis revealed a steady decrease in unique amplicon sequence variants (ASVs) from pre-monsoon (PRM) (31), followed by POM (22) and finally monsoon (MON) (2). Bacteria consistently outnumbered archaea throughout the study. Heavy metals peaked during PRM, with Fe reaching 1416-1200 mg/kg. Cr exceeded US EPA limit in all seasons, while Pb and Cd surpassed the limits during PRM and MON. Pearson's correlation showed that TC, TN, C/N ratio, and EC significantly influenced enzyme activity during PRM and POM. Correlations between microbial community and environmental parameters revealed enzyme activities, C/N ratio and TC to positively influence many microbial genera. In contrast, certain genera showed tolerance to elevated concentrations of Cd, Pb, and Fe. Our findings have considerable implications for predicting the dynamics of abiotic and biotic factors related to the carbon cycle as a consequence of seasonal change.