Atmospheric Inputs of Nitrogen, Carbon, and Phosphorus across an Urban Area: Unaccounted Fluxes and Canopy Influences

• Published in: Earth's future 2018-02, Vol.6 (2), p.134-148
• Main Authors: Decina, Stephen M., Templer, Pamela H., Hutyra, Lucy R.
• Format: Article
• Language: English
• Subjects: Air quality; Atmospheric deposition and throughfall; Atmospheric pollution deposition; Canopies; Deposition; Ecosystem services; Ecosystems; Environmental impact; Fluxes; Growing season; Nitrogen; Nutrient cycles; Nutrient loading; Nutrients; Organic carbon; Organic nitrogen; Organic phosphorus; Phosphorus; Runoff; Sewage; Soil permeability; Soil solution; Throughfall; Tree planting; Trees; Urban areas; Urban atmosphere; Urban biogeochemistry; Urban runoff; Urban tree canopy; Water quality
• ISSN: 2328-4277; 2328-4277
• DOI: 10.1002/2017EF000653

Rates of atmospheric deposition are declining across the United States, yet urban areas remain hotspots of atmospheric deposition. While past studies show elevated rates of inorganic nitrogen (N) deposition in cities, less is known about atmospheric inputs of organic N, organic carbon (C), and organic and inorganic phosphorus (P), all of which can affect ecosystem processes, water quality, and air quality. Further, the effect of the tree canopy on amounts and forms of nutrients reaching urban ground surfaces is not well‐characterized. We measured growing season rates of total N, organic C, and total P in bulk atmospheric inputs, throughfall, and soil solution around the greater Boston area. We found that organic N constitutes a third of total N inputs, organic C inputs are comparable to rural inputs, and inorganic P inputs are 1.2 times higher than those in sewage effluent. Atmospheric inputs are enhanced two‐to‐eight times in late spring and are elevated beneath tree canopies, suggesting that trees augment atmospheric inputs to ground surfaces. Additionally, throughfall inputs may directly enter runoff when trees extend above impervious surfaces, as is the case with 26.1% of Boston's tree canopy. Our results indicate that the urban atmosphere is a significant source of elemental inputs that may impact urban ecosystems and efforts to improve water quality, particularly in terms of P. Further, as cities create policies encouraging tree planting to provide ecosystem services, locating trees above permeable surfaces to reduce runoff nutrient loads may be essential to managing urban biogeochemical cycling and water quality. Key Points Atmospheric deposition is a substantial source of organic nitrogen, organic carbon, and phosphorus to urban ecosystems Inorganic phosphorus inputs in bulk deposition and throughfall were greater than sewage effluent inputs during the study period The tree canopy amplifies inputs to the urban ground surface, potentially increasing nutrient fluxes in runoff to nearby waterways