Molecular characterization of dissolved organic nitrogen and phosphorus in agricultural runoff and surface waters

Yun-Ya Yang; Malak M Tfaily; Jared L Wilmoth; Gurpal S Toor

doi:10.1016/j.watres.2022.118533

Molecular characterization of dissolved organic nitrogen and phosphorus in agricultural runoff and surface waters

Water Res. 2022 Jul 1:219:118533. doi: 10.1016/j.watres.2022.118533. Epub 2022 Apr 30.

Authors

Yun-Ya Yang¹, Malak M Tfaily², Jared L Wilmoth³, Gurpal S Toor⁴

Affiliations

¹ Nutrient Management and Water Quality Group, Department of Environmental Science and Technology, University of Maryland, College Park, MD 20742, United States. Electronic address: yunyayang@gmail.com.
² Department of Environmental Science, University of Arizona, Tucson, AZ 85721, United States.
³ Department of Environmental Science and Technology, University of Maryland, College Park, MD 20742, United States.
⁴ Nutrient Management and Water Quality Group, Department of Environmental Science and Technology, University of Maryland, College Park, MD 20742, United States. Electronic address: gstoor@umd.edu.

PMID: 35533624
DOI: 10.1016/j.watres.2022.118533

Abstract

Agricultural runoff is a significant contributor to nitrogen (N) and phosphorus (P) pollution in water bodies. Limited information is available about the molecular characteristics of the dissolved organic N (DON) and P (DOP) species in the agricultural runoff and surface waters. We employed Fourier Transform-Ion Cyclotron Resonance-Mass Spectrometry (FT-ICR-MS) to investigate the changes in the molecular characteristics of DON and DOP at three watershed positions (upstream water, runoff from agricultural fields, and downstream waters). Across three watershed locations, more-bioavailable compounds (such as amino sugars, carbohydrates, lipids, and proteins) accounted for <5% of DON and 4-31% of DOP molecules, whereas less-bioavailable compounds (such as lignin, tannins, condensed hydrocarbons, and unsaturated hydrocarbons) were >95% of DON and 69-96% of DOP. Of the dissolved organic matter, runoff waters from agricultural fields contained the greatest proportion of DON formulas (20-25%) than upstream (18%) and downstream (13-14%) waters, indicating the presence of a greater diversity of DON species in the runoff. Various nutrient sources present in agricultural fields such as crop residues, soil organic matter, and transformed fertilizers likely contributed to the diverse composition of DON and DOP in the runoff, which were likely altered as the surface water traversed along the flow pathways in the watershed. The presence of more-bioavailable molecules detected in upstream compared to agricultural runoff and downstream waters suggests that photochemical and/or microbial processes likely altered the characteristics of DON and DOP compounds. The findings of this study increase our understanding of DON and DOP compounds lability and transformations in runoff and surface waters , which may be useful in quantifying the contribution of organic N and P sources to water quality impairment in aquatic ecosystems.

Keywords: Agricultural runoff; Dissolved organic nitrogen; Dissolved organic phosphorus; FT-ICR-MS; Surface waters.

MeSH terms

Agriculture
Dissolved Organic Matter*
Ecosystem
Nitrogen / analysis
Phosphorus* / chemistry

Substances

Dissolved Organic Matter
Phosphorus
Nitrogen