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| Spatiotemporal variability of different nitrogen forms in shallow groundwater of a small watershed in the subtropical region of China |
| Received:February 16, 2017 |
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| KeyWord:nitrogen;spatiotemporal variability;land use type;shallow groundwater;Xiangjiang River watershed |
| Author Name | Affiliation | E-mail | | JIAO Jun-xia | Zhengzhou University Environment Technology and Consulting Limited Company, Zhengzhou 450002, China
Research Center for Environmental Policy Planning & Assessment of Zhengzhou University, Zhengzhou 450002, China | | | ZHOU Jiao-gen | Key Laboratory of Agro-ecological Processes in Subtropical Region, Institute of Subtropical Agriculture, Chinese Academy of Sciences, Changsha 410125, China | zhoujg@isa.ac.cn | | YANG Wen | Hunan Normal University, College of Resources and Environmental Sciences, Changsha 410012, China | | | FENG Qing-yu | Agricultural and Biological Engineering Department, Purdue University, West Lafayette 47907, USA | | | ZHANG Man-yi | Key Laboratory of Agro-ecological Processes in Subtropical Region, Institute of Subtropical Agriculture, Chinese Academy of Sciences, Changsha 410125, China | | | LI Yu-yuan | Key Laboratory of Agro-ecological Processes in Subtropical Region, Institute of Subtropical Agriculture, Chinese Academy of Sciences, Changsha 410125, China | |
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| Abstract: |
| This study aimed at evaluating the spatial and temporal variability of different nitrogen(N) forms at the watershed scale. Shallow groundwater samples were taken at 200 locations under six different land use types(vegetable production, tea plantation, dry land, forest, double-rice cropping field, single-rice cropping field) across the headstream of the Xiangjiang River watershed in Changsha County, China. The concentrations of total nitrogen(TN), nitrate(NO3--N), and ammonium nitrogen(NH4+-N) were determined through continuous observation for one year(1/2011-12/2011) in shallow groundwater(80~130 cm) in the small watershed. The spatiotemporal variability of TN, NO3--N, and NH4+-N concentrations were analyzed using spatial analysis and geostatistical methods. The contents of TN, NO3--N, and NH4+-N in the shallow groundwater had strong spatial auto-correlation with nugget-to-sill ratios of 0.76%, 8.50%, and 4.41%, respectively. This means that structural spatial variance for TN, NO3--N, and NH4+-N played a dominant role across the studied watershed. Spatially, the TN, NO3--N, and NH4+-N ranged from 540~580 m. The monthly average concentrations of TN, NO3--N, and NH4+-N differed from each other in the shallow groundwater of the study area. The average concentrations of TN, NO3--N, and NH4+-N were 2.97, 1.12 mg·L-1, and 1.32 mg·L-1, respectively. The TN and NO3--N concentrations did not vary much; in contrast, the NH4+-N concentrations varied dramatically. The peak concentrations of TN and NH4+-N occurred in July 2011, but the NO3--N concentrations varied little and were stable over time. The spatial distributions of N concentrations in the shallow groundwater had close relationships with land use type. The concentrations of TN, NH4+-N, and NO3--N were highest under tea plantation, of medium value under rice cropping field, and lowest under forest land use types. |
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