The impact of storm origin, local scavenging, and changing land use on rainwater Nitrogen content at a coastal Mid-Atlantic United States site

Jessica Irene Czarnecki, University of Delaware, School of Marine Science and Policy, Newark, DE, United States, Alina M Ebling, University of Delaware, School of Marine Science and Policy, Lewes, DE, United States, Nicole R R Coffey, University of Minnesota, Minneapolis, United States and Andrew S Wozniak, University of Delaware, School of Marine Science and Policy, Newark, United States
Abstract:
Inorganic (IN) and organic (ON) forms of nitrogen (N) are essential for primary and secondary production and can limit production in large parts of the ocean. When delivered in excess, N can promote eutrophication and degrade water quality in estuaries. Previous research (1990s) has found rainwater to contribute up to 25% of the N loaded to the Delaware Bay and its estuaries, but emissions policies and technologies and land use in the watershed has changed considerably since those estimates were made. Additionally, the dissolved ON (DON) component has been neglected despite its potential for fueling production in estuaries and oligotrophic portions of the ocean. The reactivity and potential impact of DON in aquatic systems likely depends on its specific molecular forms. Few studies, however, have assessed rainwater DON molecular compositional variability or its causal factors (e.g., airmass back trajectory (AMBT), season, local emission sources). A 25-year dataset from an NADP long-term monitoring site in Lewes, DE show total IN decreases to be due to a decrease in nitrate loads consistent with changes in emissions standards and policies since the 1990s. Rainfall collections from 2018-19 show highest amounts of DON and IN to be related to westerly and northwesterly AMBTs suggesting offshore transport of IN and ON to be higher than the bulk average values. Preliminary data from Fourier transform ion cyclotron resonance mass spectrometry measurements reveal marine AMBT DON (lower mean O/C content, higher relative peptide-like content) to differ from northwesterly AMBT DON (higher mean O/C content, higher relative condensed aromatic compound content) at the molecular level. These data demonstrate that DON quantity and quality depend on the emissions source region. The results of this work will give us a better understanding of rainwater N deposition both to watersheds of Sussex County, Delaware and to the coastal ocean beyond.

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