Topography and land use effects on spatial variability of soil denitrification and related soil properties in riparian wetlands

Many rivers in the Yangtze River basin have suffered from excess nitrogen due to increased human activities in recent decades. Soil denitrification in riparian wetlands is a key process for removing nitrogen from polluted surface runoff and controlling eutrophication in river ecosystems. Currently, little is known about the influence of topography and land use on the riparian denitrification characteristics in the Yangtze River basin. In this study, we used the acetylene block technique to determine the spatial variability of the soil potential and unamended dentrification rates of 42 riparian wetlands in the Han River basin of China. The results indicated that riparian soils showed great spatial variation in potential denitrification, unamended dentrification and most of the measured physical and chemical properties. Both potential and unamended dentrification rates were positively associated with soil moisture, percentage of fine substrate, organic matter and nitrogen contents, but were negatively related to soil pH and bulk density. Agricultural riparian soils had unamended denitrification rates higher than forested riparian soils. Spearman correlation analysis also indicated that a topographic factor (i.e., elevation) had a negative effect on riparian denitrification rates. Our results suggest that both topography and land use can indirectly influence the soil denitrification rates in riparian wetlands. Low-elevation areas in the agricultural riparian zone are good candidates for wetland restoration or creation for nitrogen removal and water quality improvement in the Yangtze River basin.