Relationship between land-use and sources and fate of nitrate in groundwater in a typical recharge area of the North China Plain

Shiqin Wang; Wenbo Zheng; Matthew Currell; Yonghui Yang; Huan Zhao; Mengyu Lv

doi:10.1016/j.scitotenv.2017.07.176

Relationship between land-use and sources and fate of nitrate in groundwater in a typical recharge area of the North China Plain

Sci Total Environ. 2017 Dec 31:609:607-620. doi: 10.1016/j.scitotenv.2017.07.176. Epub 2017 Jul 27.

Authors

Shiqin Wang¹, Wenbo Zheng², Matthew Currell³, Yonghui Yang⁴, Huan Zhao⁵, Mengyu Lv²

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. Electronic address: sqwang@sjziam.ac.cn.
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, 19A Yuquan Road, Beijing 100049, China.
³ School of Engineering, RMIT University, Melbourne 3001, Australia.
⁴ Key Laboratory of Agricultural Water Resources, Center for Agricultural Resources Research, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Shijiazhuang 050021, China.
⁵ Satellite Environment Center, Ministry of Environmental Protection, Beijing 100094, China.

PMID: 28763658
DOI: 10.1016/j.scitotenv.2017.07.176

Abstract

Identification of different nitrate sources in groundwater is challenging in areas with diverse land use and multiple potential inputs. An area with mixed land-uses, typical of the piedmont-plain recharge area of the North China Plain, was selected to investigate different nitrate sources and the impact of land use on nitrate distribution in groundwater. Multiple environmental tracers were examined, including major ions, stable isotopes of water (δ²H-H₂O, δ¹⁸O-H₂O) and nitrate (δ¹⁵N-NO₃^- and δ¹⁸O-NO₃^-). Groundwater was sampled from four land-use types; natural vegetation (NV), farmland (FL), economic forestland (EF) and residential areas (RA). A mixing model using δ¹⁸O and Cl^- concentrations showed that groundwater recharge predominantly comprises precipitation and lateral groundwater flow from areas of natural vegetation in the upper catchment, while irrigation return water and wastewater from septic tanks were major inputs in farmland and residential areas, respectively. Land use variation is the major contributing factor to different nitrate concentrations. In total, 80%, 49% and 86% of samples from RA, FL and EF, respectively exceeded the WHO standard (50mg/L NO₃^-), compared to 6.9% of samples from NV. Isotopes of δ¹⁵N-NO₃^- and δ¹⁸O-NO₃^- verified that nitrate in groundwater of the NV (with δ¹⁵N ranging from 1.7‰ to 4.7‰) was sourced from soil and precipitation. Examination of δ¹⁵N-NO₃^- vs δ¹⁸O-NO₃^- values along with multivariate statistical analysis (principle component and cluster analysis) helped identify sources with overlapping isotopic values in other land-use areas (where δ¹⁵N values range from 2.5‰ to 10.2‰). Manure and septic waste were dominant sources for most groundwater with high NO₃^- and Cl^- concentrations in both farmland and residential areas. The lack of de-nitrification and fact that the area is a recharge zone for the North China Plain highlight the importance of controlling nitrate sources through careful application of manure and fertilizers, and control of septic leakage.

Keywords: Land-use; Multivariate statistical analysis; Nitrate in groundwater; Nitrate source; North China Plain; Stable isotopes.