Cold Temperature Effects on Long-Term Nitrogen Transformation Pathway in a Tidal Flow Constructed Wetland

The present study investigated long-term treatment performance and nitrogen transformation mechanisms in tidal flow constructed wetlands (TFCVVs) under 4, 8, and 12 degrees C temperature regimes. High and stable ammonium (NH4+ -N) removal efficiency (93-96%) was achieved in our TFCWs, whereas nitrate (NO3--N) was accumulated at different levels under different temperatures. Quantitative response relationships showed anammox/amoA, (narG+napA)/amoA, and (narG+napA)/bacteria were the respective key functional gene groups determining 4, 8, and 12 degrees C NO3--N reduction. Pathway analysis revealed the contribution of these functional gene groups along a depth gradient. In addition, denitrification process increased, while anammox process decreased consistent with a rise in temperature from 4 to 12 degrees C. Furthermore, cold temperatures exhibited different effects on anammox. and denitrification and their long-term acclimatization capacities changed with temperature.