Riverine nitrate source and transformation as affected by land use and land cover

Xing Li; Y Jun Xu; Maofei Ni; Chunlin Wang; Siyue Li

doi:10.1016/j.envres.2023.115380

Riverine nitrate source and transformation as affected by land use and land cover

Environ Res. 2023 Apr 1:222:115380. doi: 10.1016/j.envres.2023.115380. Epub 2023 Jan 27.

Authors

Xing Li¹, Y Jun Xu², Maofei Ni³, Chunlin Wang¹, Siyue Li⁴

Affiliations

¹ Institute of Changjiang Water Environment and Ecological Security, School of Environmental Ecology and Biological Engineering, Key Laboratory for Green Chemical Process of Ministry of Education, Hubei Key Laboratory of Novel Reactor and Green Chemical Technology, Wuhan Institute of Technology, Wuhan, 430205, China.
² School of Renewable Natural Resources, Louisiana State University Agricultural Center, Baton Rouge, LA, 70803, USA; Coastal Studies Institute, Louisiana State University, Baton Rouge, LA, 70803, USA.
³ College of Eco-environmental Engineering, Guizhou Minzu University, Guiyang, China.
⁴ Institute of Changjiang Water Environment and Ecological Security, School of Environmental Ecology and Biological Engineering, Key Laboratory for Green Chemical Process of Ministry of Education, Hubei Key Laboratory of Novel Reactor and Green Chemical Technology, Wuhan Institute of Technology, Wuhan, 430205, China. Electronic address: syli2006@163.com.

PMID: 36716803
DOI: 10.1016/j.envres.2023.115380

Abstract

A mixed land use/land cover (LULC) catchment increases the complexity of sources and transformations of nitrate in rivers. Spatial paucity of sampling particularly low-resolution sampling in tributaries can result in a bias for identifying nitrate sources and transformations. In this study, high spatial resolution sampling campaigns covering mainstream and tributaries in combination with hydro-chemical parameters and dual isotopes of nitrate were performed to reveal spatio-temporal variations of nitrate sources and transformations in a river draining a mixed LULC catchment. This study suggested that point sources dominated the nitrate in the summer and winter, while non-point sources dominated the nitrate in the spring and autumn. A positive correlation was observed between proportions from sewage and land use index (LUI). However, negative correlations between soil nitrogen/nitrogen fertilizer and LUI were observed. With an increase of urban areas, the increased contribution from domestic sewage resulted in an increase of NO₃^- concentrations in rivers. Both urban and agricultural inputs should be considered in nitrate pollution management in a mixed LULC catchment. We concluded that the seasonal variations of nitrate sources were mainly affected by flow velocity conditions and agricultural activities, while spatial variations were mainly affected by LULC. In addition, we found a novel underestimation of dominated sources from Bayesian model because of mixing effect of isotope values from the tributaries to mainstream, however, high spatial resolution sampling can make up for this shortcoming. δ¹⁵N and δ¹⁸O values of nitrate indicated that nitrate originated from nitrification in soils. The nitrate concentrations and correlation between δ¹⁵N and 1/[NO₃^-] suggested little contribution of nitrate removal by denitrification. Thus, the nitrate reduction in the Yuehe River basin needs to be strengthened. The study provides new implications for estimation of nitrate sources and transformations and basis for nitrate reduction in the river with mixed LULC catchment.

Keywords: Dual isotopes; Mixed land use/land cover; Nitrate; Nitrogen transformation; Water quality.

Publication types

Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

Bayes Theorem
China
Environmental Monitoring / methods
Nitrates* / analysis
Nitrogen / analysis
Nitrogen Isotopes / analysis
Rivers
Sewage
Soil
Water Pollutants, Chemical* / analysis

Substances

Nitrates
Nitrogen Isotopes
Sewage
Water Pollutants, Chemical
Nitrogen
Soil