The CADDIS Urbanization Module (PDF Version)

The CADDIS Urbanization Module (PDF version) URBANIZATION – The urban stream syndrome – Urbanization & biotic integrity – Catchment vs. riparian urbanization Riparian/Channel Alteration Wastewater Inputs Stormwater Runoff – Riparian zones & channel morphology – Combined sewer overflows (CSOs) – Effective vs. total imperviousness – Urbanization & riparian hydrology – Wastewater-related enrichment – Imperviousness & biotic condition – Stream burial – Reproductive effects of WWTP effluents – Thresholds of imperviousness Water/Sediment Temperature Hydrology Physical Habitat Energy Sources Quality – Heated surface runoff – Baseflow in urban – Channel enlargement – Terrestrial leaf litter – Conductivity – Temperature & biotic streams – Road crossings – Primary production & – Nitrogen condition – Water withdrawals & – Bed substrates & respiration – PAHs – Urbanization & transfers biotic condition – Quantity & quality of climate change – Biotic responses to DOC urban flows Urbanization is an increasingly pervasive land cover transformation that significantly alters the physical, chemical and biological environment within surface waters. The diagram above provides a simple schematic illustrating pathways through which urbanization may affect stream ecosystems. Riparian/channel alteration, wastewater inputs, and stormwater runoff associated with urbanization can lead to changes in five general stressor categories: water/sediment quality, water temperature, hydrology, physical habitat within the channel, and basic energy sources for the stream food web. This module is organized along these pathways (the nine shapes above), with subheadings for specific topics covered in greater detail. For an interactive version of this module, visit the CADDIS website (http://www.epa.gov/caddis). URBANIZATION Riparian / Channel Alteration Wastewater Inputs Stormwater Runoff Water / Sediment Quality Temperature Hydrology Physical Habitat Energy Sources What is urbanization? Urbanization refers to the concentration of human populations into discrete areas, leading to transformation of land for residential, commercial, industrial and transportation purposes. It can include densely populated centers, as well as their adjacent periurban or suburban fringes (Fig 1), and can be quantified in many different ways (Table 1). Example definitions used to classify areas as “urban” or “developed” include: • Core areas with population density ≥ 1,000 people per square mile, plus surrounding areas with population density ≥ 500 people per square mile (U.S. Census Bureau, for 2000 Census) • Areas characterized by ≥ 30% constructed materials, such as asphalt, concrete, and buildings (USGS National Land Figure 1. Urbanization map of the United States derived from city lights data. Cover Dataset) Urban areas are colored red, while peri-urban areas are colored yellow. Image created by Flashback Imaging Corporation, under contract with NOAA and NASA [accessed 7.16.09]. Why does it matter? Table 1. Common ways of quantifying urbanization • Urban development has increased dramatically in recent decades, and this increase is projected to continue. For MEASURE DESCRIPTION example, in the US developed land is projected to % Total urban area Area in all urban land uses increase from 5.2% to 9.2% of the total land base in the Area above some higher development next 25 years (Alig et al. 2004). % High intensity urban threshold • On a national scale urbanization affects relatively little Area above some lower development land cover, but it has a significant ecological footprint— % Low intensity urban meaning that even small amounts of urban development threshold can have large effects on stream ecosystems. % Residential Area in residential-related uses Area in commercial- or industrial-related % Commercial / industrial uses Key pathways by which urbanization alters streams % Transportation Area in transportation-related uses • Riparian/channel alteration – Removal of riparian Area of impervious surfaces such as roads, vegetation reduces stream cover and organic matter % Total impervious area parking lots and roofs; also called impervious inputs; direct modification of channel alters hydrology surface cover and physical habitat. Impervious area directly connected to • Wastewater inputs – Human, industrial and other % Effective impervious area streams via pipes; also called % drainage wastewaters enter streams via point (e.g., wastewater connection treatment plant effluents) and non-point (e.g., leaky Road density Road length per area infrastructure) discharges. Road crossing density # Road-stream crossings per area • Impervious surfaces – Impervious cover increases surface runoff, resulting in increased delivery of stormwater and Population density # People per area associated contaminants into streams. Household density # Houses per area Multimetric indices combining a suite of development-related measures into one Click below for more detailed information on specific topics index value [e.g., the USGS national urban Urban intensity indices intensity index (NUII), based on housing Catchment vs. density, % developed land in basin, and road The urban stream Urbanization & riparian density] syndrome biotic integrity urbanization URBANIZATION Riparian / Channel Alteration Wastewater Inputs Stormwater Runoff Water / Sediment Quality Temperature Hydrology Physical Habitat Energy Sources The urban stream syndrome Table 2. Symptoms generally associated with the urban stream syndrome Common effects of urbanization on stream ecosystems have STRESSOR CATEGORY SYMPTOM been referred to as the “urban stream syndrome” (Walsh et Water / sediment quality ↑ nutrients al. 2005a). Table 2 lists symptoms typically associated with the urban stream syndrome. Symptoms preceded by an ↑ toxics arrow have been observed to consistently increase (↑) or Δ suspended sediment decrease (↓) in response to urbanization, while symptoms Temperature ↑ temperature preceded by a delta (Δ) have been observed to increase, decrease, or remain unchanged with urbanization. Hydrology ↑ overland flow frequency As the urban stream syndrome illustrates, these streams are ↑ erosive flow frequency simultaneously affected by multiple sources, resulting in ↑ stormflow magnitude multiple, co-occurring and interacting stressors. As a result, identifying specific causes of biological impairment in urban ↑ flashiness streams, or the specific stressors that should be managed to ↓ lag time to peak flow improve condition, is difficult. Some communities are approaching this challenge by managing overall urbanization, Δ baseflow magnitude rather than the specific stressors associated with it—for ↑ direct channel modification (e.g., channel Physical habitat example, by establishing total maximum daily loads (TMDLs) hardening) for impervious surfaces, rather than individual pollutants. ↑ channel width (in non-hardened channels) ↑ pool depth Courtesy of USEPA ↑ scour ↓ channel complexity Δ bedded sediment Energy sources ↓ organic matter retention Δ organic matter inputs and standing stocks Many characteristics of urban Δ algal biomass development affect how the Modified from Walsh CJ et al. 2005a. The urban stream syndrome: current knowledge and the urban stream syndrome is search for a cure. Journal of the North American Benthological Society 24(3):706-723. expressed within a given system. These characteristics include (but are not limited to): Click below for more detailed information on specific topics • Location and distribution of development – catchment vs. riparian Catchment vs. The urban stream Urbanization & – upstream vs. downstream riparian syndrome biotic integrity – sprawling vs. compact urbanization • Density of development • Type of development and infrastructure – residential vs. commercial/transportation – stormwater systems – wastewater treatment systems • Age of development and infrastructure URBANIZATION Riparian / Channel Alteration Wastewater Inputs Stormwater Runoff Water / Sediment Quality Temperature Hydrology Physical Habitat Energy Sources Urbanization & biotic integrity Numerous studies have examined relationships between land use variables and stream biota, and shown that urban-related land uses can significantly alter stream assemblages. Land use variables considered include % urban land (in the watershed and in riparian areas), % impervious surface area (total and effective), road density, and other measures of urbanization. Photos courtesy of Noel Burkhead, USGS Biotic responses associated with these land use variables include (but are not limited to): ALGAE • ↑ abundance or biomass [Roy et al. 2003a, Taylor et al. 2004, Busse et al. 2006] Cosmopolitan] • other changes in assemblage structure (e.g., changes in – diatom composition) [Winter & Duthie 2000, Sonneman et al. 2001, Newall & Walsh 2005] BENTHIC MACROINVERTEBRATES • ↓ total abundance, richness or diversity [Endemic [Morley & Karr 2002, Moore & Palmer 2005, Walsh et al. 2007] ↑ forest cover PC1 ↓ forest cover • ↓ EPT (Ephemeroptera, Plecoptera, Trichoptera) ↓ urban intensity ↑ urban intensity abundance, richness or diversity [Morley & Karr 2002, Roy et al. 2003a, Riley et al. 2005, Walsh 2006] Figure 2. Plot of a measure of biotic homogenization [relative abundance of • ↑ abundance of tolerant taxa Appalachian highland endemic fishes – relative abundance of cosmopolitan [Jones & Clark 1987, Walsh et al. 2007] fishes] on the first axis of a principal components analysis of three catchment land use variables [1993 forest cover, forest cover change from

Load more