Nitrate accumulation and leaching potential is controlled by land-use and extreme precipitation in a headwater catchment in the North China Plain

Wenbo Zheng; Shiqin Wang; Kangda Tan; Yuping Lei

doi:10.1016/j.scitotenv.2019.136168

Nitrate accumulation and leaching potential is controlled by land-use and extreme precipitation in a headwater catchment in the North China Plain

Sci Total Environ. 2020 Mar 10:707:136168. doi: 10.1016/j.scitotenv.2019.136168. Epub 2019 Dec 17.

Authors

Wenbo Zheng¹, Shiqin Wang², Kangda Tan³, Yuping Lei¹

Affiliations

¹ Key Laboratory of Agricultural Water Resources, Center for Agricultural Resources Research, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Shijiazhuang 050021, China.
² Key Laboratory of Agricultural Water Resources, Center for Agricultural Resources Research, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Shijiazhuang 050021, China; University of Chinese Academy of Sciences, Beijing 100049, China; Innovation Academy for Seed Design, Chinese Academy of Sciences, China. Electronic address: sqwang@sjziam.ac.cn.
³ Key Laboratory of Agricultural Water Resources, Center for Agricultural Resources Research, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Shijiazhuang 050021, China; University of Chinese Academy of Sciences, Beijing 100049, China.

PMID: 31869618
DOI: 10.1016/j.scitotenv.2019.136168

Abstract

Nitrate in groundwater is increasing in hilly areas of the world due to diverse land-uses and intensified anthropogenic activity. However, the key factors that control nitrate in groundwater as it leaches through the thin vadose zone are still poorly understood. In this study, the behavior of nitrate in the vadose zone during a normal year (2015) and a wet year (2016) were investigated in a cultivated farmland (FL) under wheat-maize double cropping and a field of natural vegetation (NV) in a headwater region of the Taihang Mountain. Water chemistry and N balances were quantified to estimate the accumulation and leaching of nitrate. Transport and fate of nitrate in the vadose zone were identified using stable isotopes of nitrate (δ¹⁸O-NO₃^-, δ¹⁵N-NO₃^-). Accumulation of NO₃^- was mainly in the shallow layer (0-50 cm) under both NV and FL in 2015. After large rain events (20-50 mm/day) during the rainy season in 2015, the leaching rates of NO₃^- at NV and FL sites were 86.04 and 9.61 kg/hm², respectively. The accumulation of NO₃^- decreased 30% and 7% at NV and FL, respectively. However, the leaching rates of NO₃^- were 63.8 and 22.63 kg/hm², and the accumulation of NO₃^- decreased 84% and 43% at NV and FL after extreme precipitation in 2016, respectively. Additionally, nitrate isotopes indicated that the different sources of nitrate in soil water were due to the land-use. However, nitrate isotopes showed that increased nitrate concentrations in groundwater at two sites in 2016 were due to the extreme precipitation. Accumulated high nitrate in surface soil in a normal year and leaching after extreme precipitation lead to increased nitrate concentration in groundwater, which poses a major threat in the future. The results are critical for informing land-use and water management when mitigating groundwater contamination in hilly area.

Keywords: Extreme precipitation; Headwater area; Land-use; Nitrate accumulation; Nitrate leaching.