Riparian wetlands, the transition zone between terrestrial and aquatic systems, play an important role in removing nitrogen (N) from runoff and improving river water quality. N can be removed or retained by riparian wetlands mainly through soil denitrification, plant uptake, soil storage, and microbial immobilization.

Soil denitrification is thought to be the most critical process for N removal, because it can permanently remove the N through reducing nitrate (NO₃^–) to gaseous products including nitrous oxide (N₂O) and dinitrogen (N₂).

Abiotic factors (soil properties, water quality, topography, etc.) and biological factors (functional microorganisms and vegetation) are closely related to the denitrification processes. However, the relative contribution of abiotic and biotic factors to riparian denitrification capacity remains elusive.

Under the supervision of Prof. LIU Guihua and associate prof. LIU Wenzhi , XIONG  Ziqian from Wuhan Botanical Garden analyzed the N removal capacity and its influencing factors in wetlands along the Han River.

The potential denitrification rate of the riparian wetland in the Han River was low. Denitrification rates showed distinct spatial and temporal variations, with higher values in August and April, but lower values in January. Riparian wetlands had higher soil denitrification rates than reservoir shoreline wetlands. The potential and unamended denitrification rates were positively correlated with edaphic conditions (moisture and carbon concentration), denitrifier abundance and plant species richness. Path analysis further revealed that edaphic conditions could regulate denitrification rates both directly and indirectly through their effects on denitrifier abundance.

The findings implied that ecological restoration such as revegetation and soil C amendment might effectively enhance the N removal capacity of wetlands along the Han River in the Yangtze River basin.

This research was funded in part by the National Natural Science Foundation of China and the Key Research Program of the Chinese Academy of Sciences. Relevant research results entitled “Edaphic conditions regulate denitrification directly and indirectly by altering denitrifier abundance in wetlands along the Han River, China” were published on Environmental Science & Technology online.

Path diagram depicting the direct and indirect effects of abiotic and biotic factors on soil potential denitrification rates (a) and unamended denitrification rates (b) (Image by XIONG Zhiqian)