...Urban ecologists attribute the swell of interest in their discipline to multiple factors, including the realization that human actions are warming the planet, that people are migrating to cities in increasing numbers and evidence that the study of urban ecosystems provides important and practical insights.
One move in particular that spurred the field was the decision in 1997 by the US National Science Foundation (NSF) to include two cities — Baltimore and Phoenix, Arizona — in a group of more than 20 long-term ecological research (LTER) sites that it funds. The studies based on these sites "changed the way ecologists feel about working in urban situations", says Steward Pickett, an urban ecologist at the Cary Institute of Ecosystem Studies in Millbrook, New York, and director of the Baltimore LTER site.
The studies are offering up results. Among many findings, the Baltimore Ecosystem Study showed that urban streams — historically considered useless dead zones — retain nitrogen run-off from fertilizers, providing a valuable 'ecosystem service' by preventing the nitrogen from reaching other water courses where it can spawn damaging algal blooms.