Mineral N stock and nitrate accumulation in the 50 to 200 m profile on the Loess Plateau

A - Papers appearing in refereed journals

Jia, X., Zhu, Y., Huang, L., Wei, X., Fang, Y., Wu, L., Binley, A. and Shao, M. 2018. Mineral N stock and nitrate accumulation in the 50 to 200 m profile on the Loess Plateau. Science of the Total Environment. 633, p. 999–1006.

AuthorsJia, X., Zhu, Y., Huang, L., Wei, X., Fang, Y., Wu, L., Binley, A. and Shao, M.
Abstract

Nitrogen (N) stored in deep profiles is important in assessing regional and/or global N stocks and nitrate leaching risk to groundwater. The Chinese Loess Plateau, which is characterized by significantly thick loess deposits, potentially stores immense stocks of mineral N, posing future threats to groundwater quality. In order to determine the vertical distributions of nitrate and ammonium content in the region, as well as to characterize the potential accumulation of nitrate in the deep loess profile, we study loess samples collected at five sites (Yangling, Changwu, Fuxian, An'sai and Shenmu) through a 50 to 200 m loess profile. The estimated storage of mineral N varied significantly among the five sites, ranging from 0.46 to 2.43 × 104 kg N ha−1. Ammonium exhibited fluctuations and dominated mineral N stocks within the whole profile at the sites, except for the upper 20–30 m at Yangling and Changwu. Measured nitrate content in the entire profile at Fuxian, An'sai and Shenmu is low, but significant accumulations were observed to 30–50 m depth at the other two sites. Analysis of δ15N and δ18O of nitrate indicates different causes for accumulated nitrate at these two sites. Mineralization and nitrification of manure and organic N respectively contribute nitrate to the 0–12 and 12–30 m profile at Changwu; while nitrification of NH4+ fertilizer, NO3− fertilizer and nitrification of organic N control the nitrate distribution in the 0–3, 3–7 and 7–10 m layer at Yangling, respectively. Furthermore, our analysis illustrates the low denitrification potential in the lower part of the vadose zone. The accumulated nitrate introduced by human activities is thus mainly distributed in the upper vadose zone (above 30 m), indicating, currently, a low nitrate leaching risk to groundwater due to a high storage capacity of the thick vadose zone in the region.

KeywordsNitrate; Ammonium; Nitrate accumulation; Critical zone; The Loess Plateau
Year of Publication2018
JournalScience of the Total Environment
Journal citation633, p. 999–1006
Digital Object Identifier (DOI)doi:10.1016/j.scitotenv.2018.03.249
Open accessPublished as non-open access
FunderNatural Environment Research Council
Funder project or codeModelling and managing critical zone relationships between soil, water and ecosystem processes across the Loess Plateau
Output statusPublished
Publication process dates
Accepted21 Mar 2018
PublisherElsevier Science Bv
Copyright licenseCC BY
ISSN0048-9697

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