Nitrogen cycling process rates across urban ecosystems.

Area of Science:

• Environmental Science
• Ecology
• Biogeochemistry

Background:

• Nitrogen (N) pollution impacts freshwater, estuarine, and marine ecosystems.
• Urban watersheds contribute excess N, altering downstream export through natural and engineered systems.
• Existing studies often focus on specific ecosystems or watershed-scale mass balances, limiting cross-ecosystem comparisons.

Purpose of the Study:

• To review urban nitrogen cycling across terrestrial, aquatic, and engineered ecosystems.
• To compare nitrogen processing rates in urban ecosystems versus native reference ecosystems.
• To contextualize N transformation rates within urban environments.

Main Methods:

• Literature review of urban nitrogen cycling studies.
• Comparison of N transformation rates (mineralization, nitrification, denitrification, ammonium/nitrate uptake) between urban and reference ecosystems.
• Analysis of N export potential from green infrastructure.

Main Results:

• Enhanced net N mineralization and nitrification rates were observed in urban forests and riparian zones compared to reference sites.
• Denitrification rates were highly variable but showed no significant difference between urban and reference ecosystems.
• Ammonium uptake was faster than nitrate uptake in urban streams; green infrastructure may decrease N export.

Conclusions:

• Urban ecosystems, despite stressors, can process nitrogen at rates comparable to or exceeding those in reference ecosystems.
• Understanding N transformations across diverse urban ecosystem types is crucial for managing N pollution.
• Green infrastructure shows promise for mitigating downstream nitrogen export from urban watersheds.