Regional Sources and Seasonal Variability of Rainwater Dissolved Organic and Inorganic Nitrogen at a Mid‐Atlantic, USA Coastal Site. Issue 2 (8th February 2023)

• Record Type: Journal Article
• Authors: Czarnecki, J. I.; Levia, D. F.; Scudlark, J. R.; Ouyang, T.; Wozniak, A. S.
• Is Part Of: Journal of geophysical research. Volume 128:Issue 2(2023)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2023-02-08
• Subjects: rainwater -- dissolved organic nitrogen -- reactive nitrogen -- atmospheric deposition; Geobiology -- Periodicals; Biogeochemistry -- Periodicals; Biotic communities -- Periodicals; Geophysics -- Periodicals; 577.14
• DOI: 10.1029/2022JG007056
• Languages: English
• ISSNs: 2169-8953

Abstract

Abstract: Changes in anthropogenic activities have altered the speciation and concentration of inorganic reactive nitrogen (Nr ) delivered to coastal and oceanic waters with precipitation. Less is known about rainwater dissolved organic nitrogen (DON) despite its quantitative importance (>20% of Nr ) and potential contributions to primary and secondary production. We document decreases in rainwater nitrogen and carbon amounts between 1994 and 2019 in Delaware, USA with the major reduction observed for nitrate (64%) reflecting emissions technology improvements. [DON] in 2019 was 55% that of 1994, though only 2 years of data are available precluding any assessment of trends. Season, airmass back trajectory (AMBT), rainfall amount, and meteorology influenced Nr amounts in 2018–2019 rain. [DON], which peaked in Summer, had different seasonal patterns than inorganic Nr and dissolved organic carbon, suggesting a biological source. Marine AMBT events showed the lowest Nr abundances. AMBTs from the southwest had the highest concentrations of Nr and DOC partially due to low rainfall amounts. Characterization of the oxidized fraction of DON revealed abundant highly unsaturated aliphatic and peptide‐like formulas suggesting a combination of secondary organic, biomass burning, and biological sources. The large changes in Nr and DOC loads emphasize the dynamic nature of atmosphere to land/water fluxes due to the influence of anthropogenic processes with potential implications for coastal and oceanic water quality and ecology. Models of atmospheric deposition to watersheds and the ocean should be frequently reevaluated with current data to accurately assess inputs from changing atmospheric sources. Plain Language Summary: Despite its quantitative importance (>20% of rainwater reactive nitrogen (Nr )) and contributions to primary and secondary production in coastal and oceanic waters, temporal variability in dissolved organic nitrogen (DON) amounts and characteristics remains understudied. Here, we document reductions in rainwater nitrate (64%) and DON (55%) amounts in 2019 relative to 1994 in Delaware, USA. The nitrate reductions likely reflect improvements in anthropogenic emissions technologies. Only 2 years of DON data are available, unfortunately, precluding assessment of long‐term trends. Season, airmass back trajectory (AMBT), rainfall amount, and meteorology influenced Nr amounts in 2018‐2019 rain events. DON concentrations peaked in summer while inorganic Nr and dissolved organic carbon were highest in spring, suggesting a distinct biological source for DON. Marine AMBT events showed the lowest Nr abundances, and southwest AMBTs had the highest concentrations of Nr and DOC partially due to low rainfall amounts. Molecular analyses show DON to be primarily composed of compounds suggestive of biomass sources though Northwest AMBT rainwater showed evidence for the influence of anthropogenic inorganic sulfur co‐emissions. These results demonstrate the need to reevaluate Nr (and DON in particular) amounts and characteristics as the patterns of anthropogenic emissions change locally, regionally, and globally. Key Points: Mid‐Atlantic rainwater reactive nitrogen and dissolved organic carbon fluxes are significantly reduced over the last 25 years Rainwater dissolved organic nitrogen abundances are uncoupled from inorganic nitrogen and dissolved organic carbon Dissolved organic nitrogen compositional data and peak Summer abundance suggests a biological origin