Wetlands play a vital role in removing nitrogen (N) from aquatic environments via the denitrification process, which is regulated by multiple environmental and biological factors. Until now, how denitrification rate responds to abiotic and biotic factors in wetlands under different hydrological conditions remain unclear.   

Researchers from CAS Key Laboratory of Aquatic Botany and Watershed Ecology, Wuhan Botanical Garden measured sediment potential denitrification rate (PDR) and unamended denitrification rate (UDR), and quantified denitrifier abundance in 36 stream, river, pond, and ditch wetland sites along the Dan River, a N–rich river in central China.    

Sediment denitrification rates significantly differed among streams, rivers, ponds, and ditches, with the ditches having the highest denitrification rates. Meanwhile, denitrification rates showed significant seasonality, and were negatively associated with water velocity and viscosity.    

Interestingly, PDR and UDR had positive relationships with N and carbon (C) availability in streams and rivers, but such correlations were not found in ponds and ditches. Furthermore, the relative nirS gene abundance, total C ratio, Reynolds number and interstitial space, could jointly estimate nitrate removal in wetlands with varying hydrologic regimes. 

These findings highlight that hydrological conditions, especially water velocity and hydrologic pulsing, play a nonnegligible role in regulating N biogeochemical processes in wetlands. 

This research was supported by the National Natural Science Foundation of China and Youth Innovation Promotion Association of Chinese Academy of Sciences. Dr. DENG Danli and Dr. PAN Yongtai are co-first authors, and Professor LIU Wenzhi and Dr. MA Lin are co-corresponding authors.  

The relevant research results have been published in Science of the Total Environment entitled “Seeking the hotspots of nitrogen removal: A comparison of sediment denitrification rate and denitrifier abundance among wetland types with different hydrological conditions”. 

A scaling analysis for estimating nitrate removal in wetlands with varying hydrologic regimes (Image by MA Lin)