Effect identification and analysis of tailwater on sediment denitrifier abundances and denitrification in an urban wetland

Abstract

Excessive anthropogenic nitrogen discharges have led to increasing nitrogen in aquatic systems, resulting in eutrophication problems. To address this problem, urban wetlands are used to remove nitrogen from wastewater treatment plant tailwater because of their efficient nitrogen removal capabilities. At the same time, high‑nitrogen tailwater can exert numerous impacts on the sediment denitrifier communities and denitrification of urban wetlands, and it is necessary to clarify this impact. In this research, we investigated denitrifier (nirK-, nirS- and nosZ-denitrifier) abundances and potential denitrification rate of 30 sediment samples from two urban wetland rivers in Haizhu National Wetland Park (China). One river called experimental river (ER) receives tailwater from a wastewater treatment plant, and the other called control river (CR) is unaffected by the tailwater. Moreover, we also determined the environmental variables to distinguish their relative effects on the variance of denitrifier abundances and denitrification rate in the two rivers. The results showed that the water quality was significantly different between ER and CR, while sediment property was not significant (p < 0.05). And it is unable to distinguish which has the greater denitrification rate between ER and CR. The redundancy analysis and path analysis indicated that riverine nutrient concentrations (e.g., ambient carbon and nitrogen) and physicochemical parameters (e.g., ambient temperature, dissolved oxygen and pH) were important determinants for denitrifier abundances and denitrification in ER and in CR, respectively. Furthermore, denitrifier abundances had an insignificant impact on denitrification in ER, but a considerable impact on denitrification in CR. The findings of this research can help to further understand how the tailwater affects sediment denitrifier communities and denitrification in urban wetland rivers, and to make better use of urban wetlands as a natural purification method.