Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
8893745 | CATENA | 2018 | 10 Pages |
Abstract
The unsaturated zone is a significant feature of the nitrogen cycle in arid areas connecting atmospheric precipitation and surface water to groundwater. To measure NO3â, Clâ, and NH4+ concentrations, precipitation samples (39.9592°N, 94.3302°E) were collected at the western edge of the Mingsha sand dunes. Soil profiles were taken along the northern edge of the dunes to determine NO3â and Clâ concentrations and δ18O-NO3â and δ15N-NO3â levels in soil water. The mNO3â/Clâ, mNH4+/Clâ and NH4+-N/NO3â-N values in precipitation showed seasonal variations, reflecting the influence of distinct anthropogenic sources. The δ15N-NO3â and δ18O-NO3â of the LT profile ranged from 2.38 to 7.84â° and 14.72 to 57.5â°, respectively, and that of GC profile ranged from â 1.36 to 2.35â° and 5.07 to 21.3â°, respectively. These results suggest that the main sources of vadose zone nitrogen in the profiles are NO3â fertilizer and NH4+ in fertilizer and precipitation, all of which are influenced by agricultural sources. Obvious nitrification and the mixing of different sources were noted, but the profiles showed no evidence of denitrification. The findings of this study show that migration of NO3â and Clâ in the desert vadose zone is influenced by heavy rainfall events, vegetation, and evaporation. Heavy rainfall events promote leaching of NO3â and Clâ into the deep vadose zone, while evaporation at the surface prevents leaching and vegetation hinders the downward migration of NO3â and Clâ. Migration of NO3â-N and Clâ in sand dunes is affected by the solute gradient concentration difference of the soil water, moving from areas of higher concentrations to lower concentration. The NO3â-N and Clâ accumulations were 1.02 kg N haâ 1 and 3.45 kg haâ 1, respectively, throughout autumn. These were larger than could be attributed to the input flux of atmospheric precipitation, especially in the near-surface soil layer, likely illustrating the influence of atmospheric dry deposition.
Related Topics
Physical Sciences and Engineering
Earth and Planetary Sciences
Earth-Surface Processes
Authors
Shi Qi, Jinzhu Ma, Qi Feng, Fei Liu, Jianhua He, Heping Shu, Bing Jia,