Nitrogen-cycling process rates across urban ecosystems

• Published in: FEMS microbiology ecology 2016-12, Vol.92 (12), p.1
• Main Authors: Reisinger, Alexander J., Groffman, Peter M., Rosi-Marshall, Emma J.
• Format: Article
• Language: English
• Subjects: Ammonium; Aquatic ecosystems; Cycles; Denitrification; Ecology; Economic impact; Environmental aspects; Environmental impact; Environmental stress; Estuarine environments; Exports; Freshwater ecosystems; Freshwater pollution; Green infrastructure; Marine ecosystems; Marine pollution; Microbiology; Microorganisms; Mineralization; Nitrification; Nitrogen; Nitrogen cycle; Pollution; Pollution control; Reviews; Riparian forests; Runoff; Storm runoff; Stormwater; Stormwater management; Streams; Transformations; Urban areas; Urban environments; Urban forests; Urban studies; Urban watersheds
• ISSN: 1574-6941; 0168-6496; 1574-6941
• DOI: 10.1093/femsec/fiw198

Nitrogen (N) pollution of freshwater, estuarine and marine ecosystems is widespread and has numerous environmental and economic impacts. A portion of this excess N comes from urban watersheds comprised of natural and engineered ecosystems that can alter downstream N export. Studies of urban N cycling have focused on either specific ecosystems or on watershed-scale mass balances. Comparisons of specific N transformations across ecosystems are required to contextualize rates from individual studies. Here we reviewed urban N cycling in terrestrial, aquatic and engineered ecosystems, and compared N processing in these urban ecosystem types to native reference ecosystems. We found that net N mineralization and net nitrification rates were enhanced in urban forests and riparian zones relative to reference ecosystems. Denitrification was highly variable across urban ecosystem types, but no significant differences were found between urban and reference denitrification rates. When focusing on urban streams, ammonium uptake was more rapid than nitrate uptake in urban streams. Additionally, reduction of stormwater runoff coupled with potential decreases in N concentration suggests that green infrastructure may reduce downstream N export. Despite multiple environmental stressors in urban environments, ecosystems within urban watersheds can process and transform N at rates similar to or higher than reference ecosystems. Urban watersheds are made up of different types of ecosystems, with each ecosystem capable of decreasing nitrogen pollution via different microbial transformations that we reviewed across different urban ecosystem types.