Urban Ecosystems

, Volume 15, Issue 2, pp 409–435 | Cite as

The urban watershed continuum: evolving spatial and temporal dimensions

  • Sujay S. KaushalEmail author
  • Kenneth T. Belt


Urban ecosystems are constantly evolving, and they are expected to change in both space and time with active management or degradation. An urban watershed continuum framework recognizes a continuum of engineered and natural hydrologic flowpaths that expands hydrologic networks in ways that are seldom considered. It recognizes that the nature of hydrologic connectivity influences downstream fluxes and transformations of carbon, contaminants, energy, and nutrients across 4 space and time dimensions. Specifically, it proposes that (1) first order streams are largely replaced by urban infrastructure (e.g. storm drains, ditches, gutters, pipes) longitudinally and laterally within watersheds, (2) there is extensive longitudinal and lateral modification of organic carbon and nutrient retention in engineered headwaters (3) there are longitudinal downstream pulses in material and energy exports that are amplified by interactive land-use and hydrologic variability, (4) there are vertical interactions between leaky pipes and ground water that influence stream solute transport, (5) the urban watershed continuum is a transformer and transporter of materials and energy based on hydrologic residence times, and (6) temporally, there is an evolution of biogeochemical cycles and ecosystem functions as land use and urban infrastructure change over time. We provide examples from the Baltimore Ecosystem Study Long-Term Ecological (LTER) site along 4 spatiotemporal dimensions. Long-term monitoring indicates that engineered headwaters increase downstream subsidies of nitrate, phosphate, sulfate, carbon, and metals compared with undeveloped headwaters. There are increased longitudinal transformations of carbon and nitrogen from suburban headwaters to more urbanized receiving waters. Hydrologic connectivity along the vertical dimension between ground water and leaky pipes from Baltimore’s aging infrastructure elevates stream solute concentrations. Across time, there has been increased headwater stream burial, evolving stormwater management, and long-term salinization of Baltimore’s drinking water supply. Overall, an urban watershed continuum framework proposes testable hypotheses of how transport/transformation of materials and energy vary along a continuum of engineered and natural hydrologic flowpaths in space and time. Given interest in transitioning from sanitary to sustainable cities, it is necessary to recognize the evolving relationship between infrastructure and ecosystem function along the urban watershed continuum.


Land use change Sanitary city Urban sustainability Organic carbon Nitrogen Phosphorus Copper Lead Zinc Road salt Emerging contaminants Stream restoration Stormwater management Aging infrastructure 



Kaushal and Belt contributed equally to writing, conceptual design, and analysis of data. Research was supported by NSF Awards DBI 0640300, CBET 1058502, Baltimore Ecosystem Study LTER project (NSF DEB-0423476), ULTRA-EX Long-term Research 0948947, and Maryland Sea Grant Awards SA7528085-U, NA05OAR4171042, R/WS-2 and the U.S. Forest Service. This paper would not have been possible without the encouragement, support, and comments of Richard Pouyat. Steward Pickett provided helpful discussions and Peter Groffman, Paul Mayer, Claire Welty, and Andy Miller provided data and/or long-term collaborations over years. Chris Tripler provided valuable ideas and comments on a previous version of the manuscript. We are indebted to Bill Stack, Robert MaCauley, and Baltimore City Department of Public Works for sharing data, insights, and ideas. Katie Delaney-Newcomb provided synoptic data for 3 sampling dates along the Gwynns Falls. Dan Dillon and Melissa Grese assisted with field work.


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© Springer Science+Business Media, LLC 2012

Authors and Affiliations

  1. 1.Department of Geology & Earth System Science Interdisciplinary CenterUniversity of Maryland, College ParkCollege ParkUSA
  2. 2.USDA Forest Service, Northern Research StationBaltimore Field Station at University of Maryland Baltimore CountyBaltimoreUSA

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