Urban stream syndrome

Definition:

Urban stream syndrome describes the consistently observed ecological degradation of streams draining urban land.  Symptoms of the urban stream syndrome include a flashier hydrograph, elevated concentrations of nutrients and contaminants, altered channelmorphology, and reduced biotic richness, with increased dominance of tolerant species.

Examples:

The most obvious hydrologic changes associated with urbanization are the engineering of stream channels, in which natural features are replaced by concrete channels and streambank stabilization efforts designed to resist increased flood flows.  Extensive piped storm drainage networks often completely bypass riparian zones, channeling large amounts of water from impervious surfaces directly into streams, both quickly and with increased frequency.  A result of this altered hydrology is that incision or “downcutting” is a common feature of urban stream channels.  Downcutting results from large volumes of water scouring out sediment that has accumulated during agricultural activity and/or residential construction in the watershed.  Incision is especially marked in watersheds with old and/or stable urban land use, where there are few sources of sediment to replace material scoured by high flows.  There is therefore tremendous variability in the condition of urban streams, depending on historic patterns of development, redistribution of sediments within streams, and hydrogeologic conditions in the watersheds.  However, we suggest that, over time, urban watersheds move towards stable land use, with large amounts of impervious cover and low sediment production leading to stream incision in most locations.

Why important:

Urban stream syndrome alter multiple aspects of stream ecosystem structure and function; from biodiversity to nutrient retention.

For more information:

·         Groffman, P. M., D. J. Bain, L. E. Band, K. T. Belt, G. S. Brush, J. M. Grove, R. V. Pouyat, I. C. Yesilonis, and W. C. Zipperer. 2003. Down by the riverside: urban riparian ecology. Frontiers in Ecology and the Environment 1:315-321.

·         Kaushal, S. S. and K. T. Belt. 2012. The urban watershed continuum:  Evolving spatial and temporal dimensions. Urban Ecosystems 15:409–435.

·         Walsh, C. J., A. H. Roy, J. W. Feminella, P. D. Cottingham, P. M. Groffman, and R. P. Morgan. 2005. The urban stream syndrome: current knowledge and the search for a cure. Journal of the North American Benthological Society 24:706-723.

Contributed by BES Co-PI Dr. Peter Groffman

Urban grasslands

Definition:

Urban grasslands are ecosystems dominated by turf-forming species created and maintained by humans for aesthetic and recreational (not grazing) purposes.  We use this term, rather than “lawn” to signal that urban grassland ecosystems cover significant areas and have coherent patterns of ecosystem processes that can be evaluated with the same approaches used to study other ecosystem types e.g., forests, rangelands, prairies.  

Examples:

Suburban turfgrass now covers 10-16 million ha in the U.S., forming the nation’s largest irrigated crop. 

Why important:

While urban grasslands provide significant ecosystem services related to recreation and aesthetics, there are significant concerns about fundamental changes in ecological structure and function associated with lawns and other components of urban and suburban ecosystems.

For more information:

·   Groffman, P. M. and R. V. Pouyat. 2009. Methane uptake in urban forests and lawns. Environmental Science & Technology 43:5229-5235.

·   Groffman, P. M., C. O. Williams, R. V. Pouyat, L. E. Band, and I. Yesilonis. 2009. Nitrate leaching and nitrous oxide flux in urban forests and grasslands. Journal of Environmental Quality. 38:1848-1860.

·   Raciti, S. M., P. M. Groffman, and T. J. Fahey. 2008. Nitrogen retention in urban lawns and forests. Ecological Applications 18:1615-1626.

·   Raciti, S. R., A. J. Burgin, P. M. Groffman, D. N. Lewis, and T. J. Fahey. 2011a. Denitrification in suburban lawn soils. Journal of Environmental Quality 40:1392-1940.

·   Raciti, S. R., P. M. Groffman, J. C. Jenkins, R. V. Pouyat, and T. J. Fahey. 2011b. Nitrate production and availability in residential soils. Ecological Applications 21:2357-2366.

·   Raciti, S. R., P. M. Groffman, J. C. Jenkins, R. V. Pouyat, T. J. Fahey, M. L. Cadenasso, and S. T. A. Pickett. 2011c. Accumulation of carbon and nitrogen in residential soils with different land use histories. Ecosystems 14:287-297.

Contributed by BES Co-PI Dr. Peter Groffman

Hydrological drought

Definition:

Hydrological drought refers to deficiencies of water in some component of the hydrologic system, such as soil moisture, streamflow or groundwater or reservoir levels. 

Examples:

In urban watersheds we observe reduced groundwater levels, especially in riparian zones due to 1) reductions in the infiltration that feeds groundwater in uplands that are covered by impervious surface and 2) incision (deepening) or stream channels by either deliberate action or erosive storm flows.

Why important:

Riparian zones have been shown to have the ability to prevent the movement of pollutants from upland land uses into streams.  Hydrologic drought reduces this ability, particularly the capacity to support denitrification, an anaerobic process (wet soils) that converts nitrate, a common pollutant in urban watersheds, into nitrogen gas.

For more information:

·         Gift, D. M., P. M. Groffman, S. S. Kaushal, and P. M. Mayer. 2010. Denitrification potential, root biomass, and organic matter in degraded and restored urban riparian zones. Restoration Ecology 18:113-120.

·         Groffman, P. M., D. J. Bain, L. E. Band, K. T. Belt, G. S. Brush, J. M. Grove, R. V. Pouyat, I. C. Yesilonis, and W. C. Zipperer. 2003. Down by the riverside: urban riparian ecology. Frontiers in Ecology and the Environment 1:315-321.

·         Groffman, P. M., N. J. Boulware, W. C. Zipperer, R. V. Pouyat, L. E. Band, and M. F. Colosimo. 2002. Soil nitrogen cycle processes in urban riparian zones. Environmental Science & Technology 36:4547-4552.

·         Groffman, P. M. and M. K. Crawford. 2003. Denitrification potential in urban riparian zones. Journal of Environmental Quality 32:1144-1149.

·         Kaushal, S. S., P. M. Groffman, P. M. Mayer, E. Striz, and A. J. Gold. 2008. Effects of stream restoration on denitrification in an urbanizing watershed. Ecological Applications 18:789-804.

·         Mayer, P. M., S. K. Reynolds, M. D. McCutchen, and T. J. Canfield. 2007. Meta-analysis of nitrogen removal in riparian buffers. Journal of Environmental Quality 36:1172-1180.

Contributed by BES Co-PI Dr. Peter Groffman

Metropolis

Definition:

A centralized city, expressing concentrated political power, and adequately supported by local revenues based on an industrial or colonial economy, receiving resources and migrants from a vast hinterland or sphere of influence.  Metropolises were sometimes connected in linear arrays, such as that recognized in the Northeastern United states by Jean Gottman in 1961 as a megalopolis.

Examples:

London was the metropolis not only of the United Kingdom, but also of the British Empire.  New York is a metropolis based on finance and formerly on industry.  Baltimore as a metropolis was an industrial powerhouse in the first half of the 20^th century. 

Why Important:

The metropolis was the leading form of urbanization throughout the industrial and global imperial eras.  Although the term is sometimes still used to represent spatially broad urban regions, consisting of cities, suburbs, and exurbs, most metropolises have been altered in form since their heyday (Fig. 1). 

Figure 1. Metropolitan areas of the United States in 1950.  These dense urban areas lacked sprawling suburbs, and were highly centralized areas, mostly driven by industrial economies.  Connections between metropolitan areas was primarily by rail, and the intervening regions were agricultural, range, or wild lands.

Spatial diffusion resulting from the growth of private automobile transport, subsidies for dispersed housing and highway development, and lifestyle choices favoring suburbanization, and a diffusion of power and economic activity in space have all diluted the role of central cities that had formerly been identified as metropolises.   Furthermore, large cities now emerging or evolving in Asia and Africa may not exhibit a classic metropolis form, but establish new patterns of development.

For more information:

·         Borchert, J. R. 1967. American metropolitan evolution. Geographical Review 57:301-332.

·         Cronon, W. 1991. Nature's metropolis: Chicago and the great west. Norton, New York.

·         Gottmann, J. 1961. Megalopolis: the urbanized northeastern seaboard of the United States. The Twentieth Century Fund, New York.

·         Shane, D. G. 2011. Urban design since 1945 -- a global perspective. John Wiley & Sons, Ltd, Chichester UK.

·         Sterns, M. A. and W. M. Marsh. 1997. Editor's introduction. The decentered city: edge cities and the expanding metropolis. Landscape and Urban Planning 15:39-58.