Characterization of Dissolved Organic Nitrogen with Fluorescence Excitation-Emission Matrix Spectroscopy

and X-ray Photoelectron Spectroscopy

Bin Hua¹    John Yang¹    Fengjing Liu¹   Baolin Deng² 

Guocheng Zhu²     Jeffrey Hargrov¹  

¹Department of Agriculture and Environmental Sciences,

Lincoln University (MO), Jefferson City, MO 65102

²Department of Civil and Environmental Engineering,

University of Missouri, Columbia, MO 65211

Abstract

Dissolved organic nitrogen (DON) in surface waters plays an important role in nitrogen biogeochemical cycle, and is of major environmental concern when at elevated concentration levels. The occurrence, chemical structure, and transport of DON are not well understood due to the difficulties in DON characterization. This research aimed to demonstrate that fluorescence excitation-emission matrix (EEM) spectroscopy in conjunction with X-ray photoelectron spectroscopy (XPS) can be useful tools to identify DON sources in terrestrial water systems. Water samples were collected monthly from November 2011 to October 2012 at the Hinkson Creek, the Columbia landfill, and the Columbia constructed wetland system for waste water treatment, located in central Missouri near Missouri River. Statistical modeling of the fluorescence EEM spectra of the 168 samples revealed four components: one protein-like component, two humic/fulvic acid-like components, and one xenobioic-like component. The score loadings of the protein-like component were strongly correlated to the local land-use practice and precipitation, an understanding that could potentially be used for the DON source identification. The N 1s X-ray photoelectron spectra of dissolved organic matters isolated from various water sources also shed light on the DON origins. Nitrogen-containing compounds from primary croplands consisted of a mixture with oxidation states from –III to VI, while N compounds from the other sites were in more reduced forms. The oxidation states of N-containing compounds from the effluent of the wetland system suggested that oxidized species increased after the treatment.  This study demonstrates that EEM and XPS are advanced analytical technology that could help water quality assessment and DON monitoring and advance our knowledge of DON behaviors in terrestrial ecosystem.