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- Title
Discerning the Concentration and Bi‐Directional Flux of Ammonia in an Urban Estuary Using the Relaxed Eddy Accumulation Method.
- Authors
Joyce, Emily; Balint, Sawyer; Walters, Wendell; Lichiheb, Nebila; Heuer, Mark; Myles, LaToya; Heikes, Brian; Hastings, Meredith
- Abstract
Narragansett Bay, the largest estuary in New England, is a heavily urbanized watershed impacted by deposition and runoff. Nutrient budgets and local policy rely on deposition data from a 1990 study that did not include any direct observations of dry deposition of gaseous ammonia (NH3(g)) and particulate ammonium (p‐NH4+) due to uncertainties in their flux direction and measurement difficulty. Recent work has shown that wet deposition of ammonium (NH4+) to the Bay has increased by a factor of 6 over the past three decades, leading to a 2.5‐fold increase in wet nitrogen (N) deposition. This documented increase in wet deposition of NH4+ is concurrent with managed nutrient reductions in urbanized estuaries but has potentially increased the impacts of atmospheric N deposition, including the dry deposition of NH3(g) and p‐NH4+. However, the lack of NH3(g) and p‐NH4+ measurements hinders our interpretation of this important N source. For the first time over Narragansett Bay, and to our knowledge over open water, dry (particulate and gas phase) total ammonia (NHx = NH3(g) + p‐NH4+) and the bidirectional NH3(g) flux were quantified using a relaxed eddy accumulation sampling technique. We find that dry deposition of NHx comprises 9.6% of total (wet + dry) N deposition. During the fall season, the dominant flux direction for NH3(g) is upward, which also has implications for urban air quality. We estimate that NH3(g) emitted from the Bay to the atmosphere makes up to 10% of the local NH3(g) emission budget for fall. Plain Language Summary: Estuaries around the world receive nitrogen from various sources, including from the atmosphere through rainfall (wet deposition) and gasses and particulates (dry deposition). Such is the case in Narragansett Bay, RI, where a scarcity of measurements hinders our understanding of how atmospheric nitrogen influences this system. Recent work has shown that wet deposition has increased by 2.5‐fold since 1990, driven by a 6‐fold increase in ammonium wet deposition. Gaseous ammonia is subjected to few emission regulations and is poorly understood because gaseous ammonia can flux upward and downward (bi‐directional). For the first time over Narragansett Bay, and to our knowledge over open water, dry deposition of total ammonia (gaseous ammonia + particulate ammonium) and the gaseous ammonia flux were quantified using a technique called relaxed eddy accumulation. We found that dry deposition of total ammonia made up 9.6% of total nitrogen deposition. The dominant flux direction of gaseous ammonia was upward (i.e., out of the water) during the fall season. Loss of nitrogen from the Bay to the atmosphere has implications for urban air quality. We estimated that gaseous ammonia emitted from the Bay to the atmosphere makes up to 10% of the local gaseous ammonia emission budget. Key Points: Dry deposition of gaseous ammonia and particulate ammonium comprises 9.6% of total nitrogen entering Narragansett Bay from the atmosphereThe dominant flux of gaseous ammonia is upward (out of the water) during the fall season when surface water concentrations are elevatedAmmonia released from Narragansett Bay to the atmosphere makes up to 10% of the local gaseous ammonia emission budget
- Subjects
NARRAGANSETT Bay (R.I.); NEW England; AUTUMN; URBAN watersheds; ATMOSPHERIC nitrogen; LOCAL budgets; ATMOSPHERIC deposition; ESTUARIES; AMMONIUM
- Publication
Journal of Geophysical Research. Biogeosciences, 2023, Vol 128, Issue 8, p1
- ISSN
2169-8953
- Publication type
Article
- DOI
10.1029/2023JG007414