The Denitrification Efficiency of Two Types of Natural Wetlands in the Downstream of Yellow River and the Influencing Factors

For understanding the influence of different seasons and different types of natural wetlands on the efficiency of denitrification and the influencing factors, a first-order hydrodynamic model was constructed and an evaluation was made seasonally during 2019-2020 on the denitrification efficiency of two types of wetlands (i.e., artificially-enhanced natural wetland and ecologically-enhanced natural wetland) in Queshan reservoir. The results show tha: The denitrification rate constant (k) of the artificially-enhanced natural wetland (0.285±0.170) m·d^-1 was higher than that of the ecologically-enhanced natural wetland (0.144±0.143) m·d^-1 throughout the year. The concentration of nitrate in the Yellow River in non-flood season (3.86±0.61) mg·L^-1 was significantly higher than that in flood season (2.52±0.66) mg·L^-1. For both of the two types of wetlands, the denitrification rate constant k in flood season was significantly higher than that in non-flood season (P < 0.01). In non-flood season, temperature and dissolved oxygen also had significant impact on the performance of natural wetlands (P < 0.05). However, in flood season, only dissolved oxygen contributed to the denitrification (P < 0.05). As revealed in the results, by adopting alternatively mixed planting design in zones, the diversity and density of vegetation in artificially-enhanced natural wetland were increased, leading to higher denitrification efficiency. In the downstream of Yellow River, the concentration of nitrate and the denitrification efficiency of wetland have strong seasonal characteristics and the denitrification efficiency in flood season is relatively high. When the water diversion amount is 4×10⁵ m³·d^-1, the two types of wetlands can serve as buffer zones to support continuous and effective denitrification.