Spatio-temporal variations of nitrate pollution of groundwater in the intensive agricultural region: Hotspots and driving forces

Zhu, Xueqiang; Miao, Peng; Qin, Jimin; Li, Wanhong; Wang, Lei; Chen, Zhujun; Zhou, Jianbin. 2023 Spatio-temporal variations of nitrate pollution of groundwater in the intensive agricultural region: Hotspots and driving forces. Journal of Hydrology, 623, 129864. https://doi.org/10.1016/j.jhydrol.2023.129864

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Official URL: http://dx.doi.org/10.1016/j.jhydrol.2023.129864

Abstract/Summary

Nitrate (NO3−) pollution of groundwater is a persistent and widespread problem worldwide, particularly in intensive agricultural regions with high nitrogen (N) surplus. Identifying spatio-seasonal variations, drivers and sources of NO3− in groundwater is key to controlling this pollution. In this study, we monitored 175 wells in areas with different irrigation practices (dryland, well irrigation and canal irrigation) in an intensive apple-planting region over a year (September 2020–October 2021) in the southern Loess Plateau, China. The integration of hydrochemical analysis, deep soil profiles, NO3− isotopic composition and a Bayesian isotope mixing model (SIAR) was used to identify the hotspots and hot moments of groundwater NO3− pollution, and main NO3− sources. The results showed that average NO3− concentrations of three regions gradually decreased from north to south, following the order of dryland region (9 mg NO3 L−1) < well irrigation region (23 mg NO3 L−1) < canal irrigation region (94 mg NO3 L−1), and orchard > residential area ≈ cereal land. In the study region, 44% of groundwater exceeded the drinking standard of the World Health Organization (50 mg NO3 L−1). The intensive apple planting in the canal irrigation regions has caused groundwater NO3− pollution, and changed hydrochemical types from HCO3−Ca‧Mg to SO4‧Cl‧NO3-Ca‧Mg. In the canal irrigation region, NO3− in the vadose zone has migrated to groundwater. The hotspots of groundwater NO3− pollution (NO3− vulnerable zones) were identified at low-altitude loess tableland and alluvial plains with canal irrigation. Irrigation and precipitation accelerated soil NO3− deep migration. The hot moments of NO3− pollution in the irrigated region was the period from the wet season to the dry season; and the “hidden reactive N pool” in the deep vadose zone (>2 m) caused a time lag of NO3− reaching into groundwater. Chemical N fertilizer and manure N applied in apple orchards were the main contributing sources of groundwater NO3− pollution in the apple-planting region. Our study highlights the significant effect of apple-planting industry development on groundwater quality.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	https://doi.org/10.1016/j.jhydrol.2023.129864
ISSN:	00221694
Additional Keywords:	Groundwater, GroundwaterBGS
Date made live:	09 Aug 2023 16:04 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/535564

Item Type:

Publication - Article

Digital Object Identifier (DOI):

https://doi.org/10.1016/j.jhydrol.2023.129864

ISSN:

00221694

Additional Keywords:

Groundwater, GroundwaterBGS

Date made live:

09 Aug 2023 16:04 +0 (UTC)

URI:

https://nora.nerc.ac.uk/id/eprint/535564