Impact of functional microbes on nitrogen removal in artificial tidal wetlands in the Yangtze River estuary: Evidence from molecular and stable isotopic analyses

After decades of rapid development in the delta, the worsening water quality in the Yangtze River estuary has become a concern in China. To improve the situation, we explored the use of two tidal wetland mesocosms (PA and NP), by evaluating nitrogen removal performance, greenhouse gas emissions and underlying molecular mechanisms. Our results show the mesocosms removed ∼23.9% of TN from nitrate-dominated river water (1.20 mg L⁻¹), with PA twice effective as NP, which is consistent with the molecular and stable isotopic data. The emissions of methane (CH₄), carbon dioxide (CO₂) and nitrous oxide (N₂O) were low in the soil of both PA and NP, while integrated microbial analyses suggest nitrification was the major contributor of nitrite to anaerobic ammonium oxidation (anammox) and also the dominant ammonia removal pathway in the mesocosms, particularly PA. The simultaneous dissimilatory nitrate reduction to ammonium (DNRA), anammox, denitrification and nitrification had mainly contributed to the nitrogen removal and greenhouse gas emission reduction, with rates of 0.86–2.05, 11.94–24.38, 44.95–340.95, and 458.56–1046.91 nmol N₂ g⁻¹ dry soil d⁻¹, respectively. This study would expand our understanding of the nitrogen-cycling in tidal wetlands, helping develop a sustainable solution to the water pollution problem in the Yangtze River estuary.