Influence of season and storm trajectory on rainwater nitrogen composition
Date
2020
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Publisher
University of Delaware
Abstract
Inorganic and organic forms of nitrogen are of great biogeochemical importance to coastal waters. They are essential for primary and secondary production and, when delivered in excess, can promote eutrophication and degrade water quality. Much of the nitrogen delivered to coastal water bodies is influenced by anthropogenic activities (e.g., agriculture, land use, power plant and vehicle emissions). Previous research has found rainwater to contribute up to 25% of the nitrogen loaded to the Delaware Bay and its estuaries, but emissions policies and technologies and land use in the watershed have all changed considerably since those estimates were made. Additionally, the organic nitrogen component has long been disregarded despite its potential to contribute to nitrogen processes in our waterways. ☐ Organic nitrogen is thought to be particularly reactive in aquatic systems though its reactivity is likely dependent on its specific molecular structure. Few studies, however, have examined the molecular composition of organic nitrogen in rainwater and how that composition varies depending on storm characteristics (e.g., airmass trajectory, season, local emission sources). In this study we have observed decreases in the concentrations and fluxes of N and C in atmospheric wet deposition over the last 25 years in Sussex County, Delaware, with the major reductions observed for NO3- and DON which decreased by 64% and 55% since 1994. Seasonal and airmass back trajectory (AMBT) influences were observed for the concentrations and fluxes of these components. Concentrations of nitrate, ammonia, and dissolved organic carbon (DOC) were highest in Spring 2019. Dissolved organic nitrogen (DON) concentrations were highest in summer. Marine AMBT events showed the lowest nitrogen concentrations and fluxes of all AMBTs, and AMBTs passing through the Gulf of Mexico had the highest concentrations of all forms of nitrogen and DOC. Compositionally, DON was primarily composed of highly unsaturated aliphatic and peptide-like formulas which we speculate to be derived from a combination of secondary organic processes, biomass burning, and biological sources. Northwest AMBT samples were an outlier, containing high contributions from CHONS formulas that likely result from co-emission with inorganic sulfur along this AMBT. Season and AMBT could not completely explain the variations in concentrations and composition though; rainfall amounts and synoptic meteorology showed relationships with nitrogen and DOC concentrations, respectively.
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Keywords
Atmospheric Deposition, Nitrogen Deposition, Organic Nitrogen, Precipitation, Wet Deposition