Nitrogen forms and dissolved organic matter optical properties in bulk rainfall, canopy throughfall, and stormwater in a subtropical urban catchment

Mary G Lusk; Paula Sanchez Garzon; Amanda Muni-Morgan

doi:10.1016/j.scitotenv.2023.165243

Nitrogen forms and dissolved organic matter optical properties in bulk rainfall, canopy throughfall, and stormwater in a subtropical urban catchment

Sci Total Environ. 2023 Oct 20:896:165243. doi: 10.1016/j.scitotenv.2023.165243. Epub 2023 Jun 30.

Authors

Mary G Lusk¹, Paula Sanchez Garzon², Amanda Muni-Morgan³

Affiliations

¹ Soil, Water, and Ecosystems Science Department, Gulf Coast Research and Education Center, University of Florida, Wimauma, FL, USA. Electronic address: mary.lusk@ufl.edu.
² Soil, Water, and Ecosystems Science Department, Gulf Coast Research and Education Center, University of Florida, Wimauma, FL, USA.
³ School of Natural Resources and Environment, Gulf Coast Research and Education Center, University of Florida, Wimauma, FL, USA.

PMID: 37394069
DOI: 10.1016/j.scitotenv.2023.165243

Abstract

The study of nitrogen (N) transformation in urban ecosystems is crucial in the protection of coastal water bodies because excess N may fuel harmful algae blooms (HABs). The purpose of this investigation was to study and identify the forms and concentrations of N in rainfall, throughfall, and stormwater runoff for 4 storm events in a subtropical urban ecosystem and to use fluorescence spectroscopy to evaluate the optical properties and expected lability of dissolved organic matter (DOM) in the same samples. The rainfall contained both inorganic and organic N pools, and organic N as nearly 50 % of total dissolved N in the rainfall. As water moved through the urban water cycle, from rainfall to stormwater and from rainfall to throughfall, it was enriched in total dissolved N, with most of the enrichment coming from dissolved organic N. Throughfall fluxes of total dissolved N were as high as 0.67 kg ha^-1, compared to 0.44 kg ha^-1 from rainfall, suggesting that the urban tree canopy can facilitate anthropogenic subsidies of N to the urban water cycle. Through analysis of sample optical properties, we saw that the throughfall presented the highest humification index and the lowest biological index when compared to rainfall, suggesting throughfall likely consists of higher molecular weight compounds of greater recalcitrance. This study highlights the importance of the dissolved organic N fraction of urban rainfall, stormwater, and throughfall and shows how the chemical composition of dissolved organic nutrients can change as rainfall is transformed into throughfall in the urban tree canopy.

Keywords: Dissolved organic matter; Dissolved organic nitrogen (DON); Stormwater; Throughfall; Urban ecosystems; Urban tree canopy.