Abstract
Soil nitrification and denitrification are key nitrogen (N) removal processes in riparian wetlands in extremely arid regions, but the driving factors of the two N processes in these wetlands are still unclear. We measured soil nitrification and denitrification rates and related environmental properties in a typical riparian wetland in the middle reaches of the Heihe River, northwestern China. Our results showed that rates of soil nitrification and denitrification exhibited moderate variability, ranging from 52.77 to 221.18 μg kg−1 h−1 and 91.25 to 428.26 μg kg−1 h−1, respectively. Soil salinity was high, with mean electrical conductivity (EC) of 6.8 mS cm−1. Soil salinity and moisture were the key factors influencing nitrification and denitrification in this riparian wetland in an extremely arid region. Soil salinity exerted significant inhibitory impact on soil nitrification when EC was > 4.05 mS cm−1. Soil nitrification increased with an increase in soil moisture when soil water content < 27.03% and decreased with an increase in soil moisture when soil water content > 27.03%. Denitrification had a significantly negative relationship with soil salinity, and significantly positive relationship with soil moisture. The interaction of soil salinity and moisture played a central role in regulating soil denitrification. Based on these results, we propose that water consumption of riparian wetlands, and the planting of halophytes, should be increased to reduce soil salinity and increase soil moisture, which is essential for sustaining soil N removal function in riparian wetlands in extremely arid regions.
Highlights
Intensive agricultural practices in the arid northwestern regions of China led to N pollution of surface and groundwater [1]
We propose that water consumption of riparian wetlands, and the planting of halophytes, should be increased to reduce soil salinity and increase soil moisture, which is essential for sustaining soil N removal function in riparian wetlands in extremely arid regions
Riparian wetlands are ecologically important transition zones between terrestrial and aquatic ecosystems in extremely arid regions, and they play a critical role in the removal of nitrogen (N) pollution from farmland and groundwater to maintain the health of river ecosystems [2,3]
Summary
Intensive agricultural practices in the arid northwestern regions of China led to N pollution of surface and groundwater [1]. Riparian wetlands are ecologically important transition zones between terrestrial and aquatic ecosystems in extremely arid regions, and they play a critical role in the removal of nitrogen (N) pollution from farmland and groundwater to maintain the health of river ecosystems [2,3]. Nitrification and denitrification are the two major processes of N removal in wetlands [7]. Nitrification oxidizes ammonia (NH4 + -N) to NO3 − -N via nitrite (NO2 − -N) in oxygenated conditions; this process can remove NH4 + -N and provide substrate (NO3 − -N) for soil denitrification in wetlands [10]. Studies on soil nitrification and denitrification are essential for the understanding of N removal function in riparian wetlands in extremely arid regions
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