Spatial Variation in Denitrification and N_2O Emission in Relation to Nitrate Removal Efficiency in a N-stressed Riparian Buffer Zone

摘要

Spatial variability in hydrological flowpaths and nitrate-removal processes complicates the overall assessment of riparian buffer zone functioning in terms of water quality improvement as well as enhancement of the greenhouse effect by N_2O emissions.In this study, we evaluated denitrifica-tion and nitrous oxide emission in winter and summer along two groundwater flowpaths in a nitrate-loaded forested riparian buffer zone and related the variability in these processes to controlling soil factors. Denitrification and emissions of N_2O were measured using flux chambers and incubation experiments. In winter, N_2O emissions were significantly higher (12.4 mg N m~(-2) d~(-1)) along the flowpath with high nitrate removal compared with the flowpath with low nitrate removal (2.58 mg N m~(-2) d~(-1)). In summer a reverse pattern was observed, with higher N_2O emissions (13.6 mg N m~(-2) d~(-1)) from the flowpath with low nitrate-removal efficiencies. Distinct spatial patterns of denitrification and N_2O emission were observed along the high nitrate-removal transect compared to no clear pattern along the low nitrate-removal transect, where denitrification activity was very low. Results from this study indicate that spots with high nitrate-removal efficiency also contribute significantly to an increased N_2O emission from riparian zones. Furthermore, we conclude that high variability in N_2O:N_2 ratio and weak relationships with environmental conditions limit the value of this ratio as a proxy to evaluatethe environmental consequences of riparian buffer zones.