U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2006–3083

August 2006

National Water-Quality Assessment Program

Effects of Urban Development on Stream Ecosystems along the Front 

Range of the Rocky Mountains, Colorado and Wyoming

Printed on recycled paper

By Lori A. Sprague, Robert E. Zuellig, and Jean A. Dupree

The U.S. Geological Survey (USGS) conducted a study from 2002 

through 2003 through its National Water-Quality Assessment (NAWQA) 

Program to determine the effects of urbanization on the physical, chemical, 

and biological characteristics of stream ecosystems along the Front Range 

of the Rocky Mountains. The objectives of the study were to (1) examine 

physical, chemical, and biological responses at sites ranging from minimally to highly developed; (2) determine the major physical, chemical, and 

landscape variables affecting aquatic communities at these sites; and (3) 

evaluate the relevance of the results to the management of water resources 

in the South Platte River Basin.

How can urban development affect stream 

ecosystems?

As land areas urbanize, stream ecosystems can be 

substantially altered. Impervious surfaces—surfaces that are 

impenetrable to water, such as parking lots, rooftops, and 

paved roads—can prevent rainfall from infiltrating into soil 

and ground water, leading to increased runoff to streams. 

With rainfall moving to streams more quickly and in greater 

amounts, streamflow conditions can change more rapidly, 

the peak streamflows may be higher, and flooding may occur 

more frequently in urban areas (U.S. Environmental Protection Agency, 1997). Increased runoff to streams often leads to 

changes in water quality as well. Runoff can transport contaminants to streams from a variety of urban sources, including 

automobiles (hydrocarbons and metals); rooftops (metals); 

wood treated with preservatives (hydrocarbons); construction sites (sediment and any adsorbed contaminants); and golf 

courses, parks, and residential areas (pesticides, nutrients, 

bacteria) (Pitt and others, 1995). In addition, stream channels 

in urban areas can be straightened, deepened, and widened 

from their natural states to promote drainage and prevent 

flooding (Klein, 1979). Commercial, residential, and industrial 

development commonly involves soil disturbance, which can 

lead to increased movement of sediment to the stream, and the 

removal of vegetation on the streambank, which can lead to 

loss of sheltered areas and stream canopy cover (Jacobson and 

others, 2001). The loss of stream canopy cover in turn can lead 

to greater daily changes in stream temperature (Sinokrot and 

Stefan, 1993). 

These changes in stream hydrology, water quality, physical habitat, and stream temperature in urbanizing areas can 

have profound effects on aquatic communities of algae, invertebrates, and fish. Periods of high streamflow can eliminate 

some aquatic organisms, particularly in channelized streams 

where refuge (seclusion and rest) areas such as boulders and 

woody debris are lacking (Winterbourn and Townsend, 1991). 

In addition, higher streamflows are associated with increased 

movement of sediment to streams, which can affect aquatic 

communities by decreasing light penetration and photosynthesis and degrading stream-bottom habitat (Waters, 1995). 

Higher contaminant concentrations and stream temperatures 

can adversely affect growth, reproduction, species competition, and disease progression within aquatic communities 

(Fitzgerald and others, 1999; LeBlanc and others, 1997). 

How did the U.S. Geological Survey study the 

effects of urban development?

Most previous studies of stream ecosystems have focused 

on either pristine areas or highly developed areas; little is 

known about how the gradual progression of urban development between these two extremes affects stream ecosystems. 

To address this, the USGS conducted a study from 2002 

through 2003 through its NAWQA Program to determine the 

effects of urban development on the physical, chemical, and 

biological characteristics of stream ecosystems in the South 

Platte River Basin. The 28 study streams are located along the 

Front Range of the Rocky Mountains in the transition zone 

between the mountains and the plains. Study streams were 

chosen to represent (1) a wide range in the degree of urban 

development and (2) minimal natural variability due to factors 

such as geology, elevation, and climate, which can also affect 

stream ecosystems and therefore mask the effects of urban 

development. Stream locations that are strongly affected by 

wastewater-treatment-plant discharge were not included in this 

study. Because land use or population density alone often is 

not a complete measure of urban development, the degree of 

urban development in each drainage area was represented by 
Figure 1. Location and range of urban-intensity index values of 

the 28 study streams.

each stream for 4 to 6 weeks between May and June 2003 to 

concentrate trace levels of hydrophobic organic contaminants 

like polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs). The chemicals concentrated 

in the SPMDs were analyzed for concentration and potential 

toxicity. Biological characteristics included algae and invertebrate communities, measured once during June 2003, and 

fish communities, measured once during August 2003. In all, 

52 urban variables (including the urban intensity index), 153 

physical variables (including 53 habitat, 50 stream hydrology, 

and 50 stream temperature variables), 225 chemical variables 

(including 96 base-flow and 129 SPMD variables), and 75 

biological variables (including 19 algae, 30 invertebrate, and 

26 fish variables) were included in the study.

Major Findings

Commonly observed effects of urban development on 

physical, chemical, and biological characteristics of stream 

ecosystems, such as increased flashiness (more rapid rise and 

fall of stream levels during and after storms), higher and more 

frequent peak flows, increased concentrations of chemicals, 

and changes in aquatic communities, generally were not 

observed in this study. 

Physical Characteristics

Only one strong relation was found between the physical 

characteristics (stream hydrology, temperature, and habitat) 

and measures of urban development—decreases in stream 

temperatures occurred more rapidly as the percentage of 

high-intensity development near the stream increased (fig. 2). 

In urbanizing areas, inputs of ground water to the stream can 

decrease as more impervious surfaces are created. Because 

ground-water temperatures generally fluctuate less than stream 

temperatures, inputs of ground water can moderate stream 

temperatures; thus, with less ground water entering the stream, 

stream temperatures may be falling more quickly.

None of the hydrology variables were related to any of 

the fish variables, and only a small number of the hydrology 

variables were strongly related to a few of the invertebrate 

and algae variables—increased flashiness and higher peak 

streamflows were related to changes in algae and invertebrate 

communities associated with still-water habitats. During high 

streamflows, organisms living in still-water habitats can be 

carried downstream in faster moving water. When periods of 

high streamflow occur more often in flashier streams, it can be 

difficult for organisms that prefer still-water habitats to persist.

None of the habitat or stream-temperature variables were 

strongly related to any of the invertebrate, algae, or fish community variables.

Chemical Characteristics

Only two base-flow chemicals measured in August were 

strongly related to measures of urban development—sulfate 

concentrations increased in more rapidly growing areas and 

suspended-sediment concentrations decreased as housing age 

increased (fig. 2). The increasing sulfate concentrations may 

have been due to increased use of and runoff from impervious areas such as roads in urbanizing areas. The decreasing 

sediment concentrations may have resulted from stabilization 

of the land surface in older communities, where more mature 

a multimetric urban intensity index derived from 16 variables, 

including land use and land cover (such as developed area), 

infrastructure (such as road density), and socioeconomic (such 

as housing density) variables. Stream sites included in this 

study covered an urban land-use gradient from minimal development (urban intensity index = 0) to a very high degree of 

development (urban intensity index = 100) in the drainage area 

(fig. 1).

The objectives of the study were to (1) examine physical, 

chemical, and biological responses along the gradient of urban 

development; (2) determine the major physical, chemical, and 

landscape variables affecting the structure of aquatic communities; and (3) evaluate the relevance of the results to the management of water resources in the South Platte River Basin. 

Physical characteristics included habitat, measured once 

between July and August 2003, and stream hydrology and 

water temperature, measured on an hourly basis throughout the 

study. Chemical characteristics included nutrients, pesticides, 

major ions, and fecal bacteria, measured twice each during 

base-flow conditions in June and August 2003, and hydrophobic organics collected from semipermeable membrane devices 

(SPMDs). SPMDs are passive samplers that were placed in 

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North Fork Cache

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EXPLANATION

Urban Intensity Index

0–20

21–40

41–60

61–80

81–100

Base from U.S. Geological Survey digital data 1999 to 2004 

1:24,000 to 1:100,000 Albers Equal Area projection 

Standard parallels 29o30'N and 49o30'N 

Central meridian 104o00'W

Latitude of projection origin 23o00'N 

106o 105o 104o

41o

40o

39o

Saint Vrain

Crow Creek

WYOM ING

NEBRASKA

COLORADO
Figure 2. Relations between 52 urban variables, 225 chemistry variables, 50 hydrology variables, 53 habitat variables, 50 stream-temperature 

variables, 26 fish variables, 19 algae variables, and 30 invertebrate variables were examined. The strong relations are indicated in this 

diagram. ?, relations unknown. Fish photograph by Jeremy Monroe, Freshwaters Illustrated. Used with permission.

vegetation and lack of land disturbance from new construction 

may decrease the amount of sediment in runoff. 

In June, none of the base-flow chemicals were strongly 

related to any measure of urban development. Snowmelt 

runoff in the larger study streams originating in the mountains occurs during June, increasing streamflows throughout 

the month; smaller study streams originating in the plains 

have much lower streamflows during this month. This natural 

variability in hydrologic conditions likely contributed to the 

lack of clear relations between urban development and water 

chemistry in June. 

Of the 129 SPMD-based measures of concentration and 

potential toxicity, only 5 were detected often enough at the 

study sites to compare to measures of urban development. 

Three of those five (concentrations of the PAHs pyrene and 

fluoranthene and a measure of potential toxicity from a group 

of chemicals including PCBs, PAHs, dioxins, and furans) were 

strongly related to nearly one-half of the urban variables. The 

most important urban variable describing the pattern of the 

response in potential toxicity and PAH concentrations was 

distance from the stream site to the nearest road, indicating 

that automobile exhaust is most likely the largest source of the 

PAHs fluoranthene and pyrene in the study area. 

Automobile sources may be localized enough that the 

transport of PAHs to the study sites would have been minimally affected by water management (diversions, transfer 

between stream basins, and reservoir storage and release) 

upstream, whereas the transport of chemicals like nutrients 

and pesticides from more dispersed upstream sources may 

have been subject to greater disruption by water management. 

The stronger response of SPMD-based measures of PAH 

concentration and potential toxicity to urban development also 

may be a result of the SPMD deployment period; during the 

4-to-6 week deployment, the SPMDs were exposed to multiple 

storm-runoff events. In contrast, nutrient, pesticides, major 

ions, and fecal bacteria were measured on two single days 

during base-flow conditions. 

Although there were very few strong relations between 

chemistry variables and urban development, nutrient, pesticide, and major ion concentrations in base-flow were strongly 

related to biological community response (fig. 2). Fish 

communities were related to the amount of fine suspended 

sediment and chloride concentrations. Suspended sediment 

can damage stream habitat, clog gills, and bury eggs, factors 

that may have contributed to the observed decrease in the 

total number of fish species present as suspended-sediment 

concentrations increased. The amount of algae increased as 

total nitrogen and nitrite plus nitrate concentrations increased, 

likely because algae require nitrogen for growth. Invertebrate 

communities were related to total nitrogen, nitrite plus nitrate, 

and total herbicide concentrations. As nitrogen and herbicide 

concentrations increased, fewer sensitive invertebrate species 

were present, indicating that increased nutrient and herbicide 

concentrations adversely influenced invertebrate communities 

in the study streams.

Biological Characteristics

Only one fish variable was strongly related to measures 

of urban development—the percentage of fish that consume 

insects and plant material decreased as the percentage of 

housing over 60 years old increased (fig. 2). As previously 

described, fish communities also were related to the amount of 

fine suspended sediment and chloride concentrations. None of 

the algae or invertebrate variables was strongly related to any 

measure of urban development. Instead, also as described, the 

amount of algae was related to total nitrogen concentrations, 

nitrite plus nitrate concentrations, and the duration of high 

streamflows, and invertebrate communities were related to the 

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Fish 

y r t s i m e h C 

y g o l o r d y H 

Urbanization Other Factors

Algae Invertebrates 

Suspended 

 sediment

Sulfate 

Chloride 

Conductivity 

Nutrients

Pesticides 

PAHs

e r u t a r e p m e T 

Duration 

 of falling 

 temperatures 

Duration of 

 high flows 

Flashiness

Housing age 

Urban intensity index 

Land cover 

Population density 

Housing density

Road density 

Water management 

Agriculture 

t a t i b a H 
frequency of rising and falling streamflow, the duration of high 

streamflows, total nitrogen concentrations, nitrite plus nitrate 

concentrations, and total herbicide concentrations (fig. 2). 

How does the Front Range compare to other 

parts of the world?

Urban development has been established as a significant 

stressor on stream ecosystems in many parts of the world. In 

this study, the link between urban development and stream ecosystems was not found to be as strong in transition-zone streams 

along the Front Range of Colorado and Wyoming. Under 

natural conditions, aquatic communities in streams in the plains 

typically are more tolerant than those in less extreme habitats 

(Matthews, 1986), but historical records indicate that aquatic 

communities in these streams were more diverse before the 

advent of irrigated agriculture, localized pollution events, and 

water management (Jordan, 1891; Ellis, 1914). Human changes 

such as streamflow modifications and habitat alterations have 

occurred for nearly 150 years in the study area (Fausch and 

Bestgen, 1997, and citations within). Early surveys noted 

impaired aquatic communities in this region as early as 1900 

(Ellis, 1914), and historical evidence from the past 150 years 

indicates that several species no longer exist at certain locations (Kondratieff and Baumann, 2002; Cordeiro, 1999; Fausch 

and Bestgen, 1997; McCafferty and others, 1993). Present-day 

aquatic communities are composed primarily of tolerant species 

even in areas of minimal urban development; when development does occur, these communities may already be resistant to 

disturbance. The effects of urban development on stream ecosystems are stronger in other parts of the world, where development may occur in areas with previously undisturbed and more 

sensitive aquatic communities. 

In addition to the effects of historical stressors on aquatic 

community structure, it is possible that current (2006) watermanagement practices in the study basins are having an effect. 

In the absence of natural, unaltered hydrologic conditions, more 

sensitive taxa may be unable to reestablish in transition-zone 

streams. In addition, the movement and storage of water may 

lead to a disconnect between the land surface and streams, 

resulting in in-stream physical, chemical, and biological characteristics that are to some degree independent of land-cover 

characteristics.

The lack of a strong link between urban development and 

stream ecosystem response in transition-zone streams along 

the Front Range does not mean that urban development has no 

effect on stream ecosystems in this region. Rather, it is likely 

that these ecosystems are affected by multiple interacting stressors, including but not limited to urban development, agriculture, 

and water management. Maintenance or protection of stream 

ecosystems likely will involve supplementing the best management practices currently used in urbanizing areas with additional steps to mitigate the effects of other stressors that may be 

as or more important. Identifying the most important stressors 

ultimately will allow for better management of stream ecosystems in the face of continued urban development.

References Cited

Cordeiro, J.R., 1999, Distribution and habitat of freshwater mussels 

(Bivalvia: Unionoida: Unionidae) in Colorado: Natural history 

inventory no. 19, University of Colorado Museum, Boulder, 

Colorado, p. 56.

Ellis, M.M., 1914, Fishes of Colorado: Boulder, University Colorado 

Studies, v. 11, 136 p. 

Fausch, K.D., and Bestgen, K.R., 1997, Ecology of fishes indigenous 

to the central and southwestern Great Plains, in Knopf, F.L., and 

Samson, F.B., eds., Ecology and conservation of Great Plains vertebrates: New York, Springer-Verlag, Inc., p. 131–166. 

Fitzgerald, D.G., Lanno, R.P., and Dixon, D.G., 1999, A comparison of 

a sentinel species evaluation using creek chub (Semotilus atromaculatus Mitchill) to a fish community evaluation for the initial identification of environmental stressors in small streams: Ecotoxicology, 

v. 8, p. 33–48.

Jacobson, R.B., Femmer, S.R., and McKenney, R.A., 2001, Land-use 

changes and the physical habitat of stream—A review with emphasis 

on studies within the U.S. Geological Survey Federal-State cooperative program: U.S. Geological Survey Circular 1175, 63 p.

Jordan, D.S., 1891, Report of explorations in Colorado and Utah 

during the summer 1889, with an account of fishes found in each of 

the river basins examined: U.S. Fish Commissions Bulletin, v. 9, 

p. 1–40.

Klein, R.D., 1979, Urbanization and stream quality impairment: Water 

Resources Bulletin, v. 15, p. 948–963.

Kondratieff, B.C., and Baumann, R.W., 2002, A review of the stoneflies of Colorado with description of a new species of Capnia

(Plecoptera: Capniidae): Transactions of the American 

Entomological Society, v. 128, p. 385–401.

LeBlanc, R.T., Brown, R.D., and FitzGibbon, J.E., 1997, Modeling the 

effects of land use change on the water temperature in unregulated 

urban streams: Journal of Environmental Management, v. 49, 

p. 445–469.

Matthews, W.J., 1986, Physicochemical tolerance and selectivity of 

stream fishes as related to their geographic ranges and local distributions, in Matthews, W.J., and Heins, D.C., eds., Community and 

evolutionary ecology of North American stream fishes: Norman, 

Okla., University of Oklahoma Press, p. 111–120.

McCafferty, W.P., Durfee, R.S., and Kondratieff, B.C., 1993, Colorado 

mayflies (Ephemeroptera)—An annotated inventory: The Southwestern Naturalist, v. 38, p. 252–274.

Pitt, R.E., Field, R., Lalor, M., and Brown, M., 1995, Urban stormwater toxic pollutants—Assessment, sources, and treatability: Water 

Environment Research, v. 67, p. 260–275.

Sinokrot, B.A., and Stefan, H.G., 1993, Stream temperature dynamics—Measurements and modeling: Water Resources Research, v. 29, 

p. 2,299–2,312.

U.S. Environmental Protection Agency, 1997, Urbanization and 

streams—Studies of hydrologic impacts: EPA Report 

841–R–97–009, Washington D.C., 15 p.

Waters, T.F., 1995, Sediment in streams—Sources, biological effects 

and control: American Fisheries Society Monograph 7, 249 p.

Winterbourne, M.J., and Townsend, C.R., 1991, Streams and 

rivers—One-way flow systems, in Barnes, R.S.K, and Mann, K.H., 

eds., Fundamentals of aquatic ecology: Oxford, England, Blackwell 

Science Ltd., p. 230–242.

This fact sheet is based on the following report: Sprague, L.A., Zuellig, R.E., and Dupree, J.A., 2006, Effects of urbanization on stream 

ecosystems in the South Platte River Basin, Colorado and Wyoming, 

chap. A of Effects of urbanization on stream ecosystems in six metropolitan areas of the United States: U.S. Geological Survey Scientific 

Investigations Report 2006–5101–A, 139 p. 

URL: http://pubs.water.usgs.gov/SIR2006–5101A/