Baltimore Ecosystem Study LTER

Debunking the Urban Legends of Human-dominated Ecosystems

Recent research in urban Baltimore challenges several assumptions about ecological processes in human-dominated ecosystems that could well have significant influence on management and policy.
* Natural processes are overwhelmingly corrupt by humans in urban ecosystems. In some cases we have found this to be true- however nitrogen retention in BES suburban watersheds amounted to 75%, a level similar to natural systems. And, while flux tower instruments showed a distinct rush-hour spike in carbon dioxide, carbon uptake rates in the urban forest is comparable to a natural deciduous forest.
* Poor people don’t care about environmental issues. BES research shows that environmental issues are important to all residents, regardless of socioeconomic status. A survey of 1,274 Baltimoreans found no significant difference for resident “awareness” or “concern for water or air quality” based upon household income.
* Urbanization spells doom for biodiversity. While nonnative species dominate many urban areas, we actually found new species, as well as pockets of rare species, and overall, a wide variance in levels of biodiversity across the urban matrix and areas in which native species rather than exotic species dominate animal communities. Indeed, elevated levels of diversity result in part from the presence of nonnative species.
* Environmental Inequities Affect Only Non-whites. Our work in Baltimore revealed that in areas near Toxic Releases Inventory (TRI) sites, whites made up 65% of the population, while in areas without a TRI facility, whites were 40%. Living close to work in the factories was once an amenity enjoyed mainly by whites and because racial composition of neighborhoods persists in Baltimore, many of the residences near the TRI sites that were white in the 1940s remain so today.
*Lawns are bad. BES LTER biogeochemical study plots in lawns show that nitrate leaching to groundwater, and nitrous oxide fluxes from soil to the atmosphere are low and comparable to forests. Moreover, lawn soil organic matter contents and microbial biomass were high and similar to forests. These results suggest that nutrient cycling in lawns is more complex than initially thought, and that their water quality effects are less negative than anticipated.
*Land Use Change from Agriculture to Urban Decreases Ecosystem Quality. BES research shows that nitrate and phosphate levels in streams are lower in dense urban areas than in suburban or agricultural areas (Fig 2). Much of the nitrogen and phosphorus in urban streams appears to come from leaking sanitary sewers, which can be fixed. Suburban areas with septic systems had stream nitrate levels similar to agricultural because septic systems discharge high amounts of nitrate by design. Also, agricultural practices reduce soil organic carbon (SOC). Our analysis suggests that SOC storage in urban ecosystems is highly variable, with both high and low SOC densities present in the landscape. The potential to increase carbon sequestration through supplemental watering or fertilization of urban landscapes exists for those soils with low SOC densities. Residential land did not usually approach the vegetative biomass of forest land, but – due to an increased density of woody plants and shrubs – it contained more aboveground biomass per unit area than agricultural landscapes. The ability to sequester carbon on urban lands must be accounted for in regional and global models.

This work has been submitted to Science by S.T.A. Pickett, J.M. Grove, P.M. Groffman, L.W. Band, C.G. Boone, G.S. Brush, W.R. Burch, Jr., M.L. Cadenasso, J. Hom, J.C. Jenkins, N. Law, C.H. Nilon, R.V. Pouyat, K. Szlavecz, P.S. Warren, and M.A. Wilson