The CADDIS Urbanization Module
(PDF version)
Physical Habitat
- Channel enlargement
- Road crossings
- Bed substrates &
biotic condition
Hydrology
- Baseflow in urban
streams
- Water withdrawals &
transfers
- Biotic responses to
urban flows
Energy Sources
- Terrestrial leaf litter
- Primary production &
respiration
- Quantity & quality of
DOC
- Nitrogen
- PAHs
Water/Sediment
Quality
Temperature
- Heated surface runoff
- Temperature & biotic
condition
- Urbanization &
climate change
- The urban stream syndrome
URBANIZATION
Riparian/Channel Alteration
- Riparian zones & channel morphology
- Urbanization & riparian hydrology
- Stream burial
- Effective vs. total imperviousness
- Thresholds of imperviousness
Storm water Runoff
Wastewater Inputs
- Combined sewer overflows (CSOs)
- Wastewater-related enrichment
- Reproductive effects of WWTP effluents
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).
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URBANIZATION
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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 2.000 Census)
Areas characterized by > 30% constructed materials, such
as asphalt, concrete, and buildings (USGS National Land
Cover Dataset)
Why does it matter?
Urban development has increased dramatically in recent
decades, and this increase is projected to continue. For
example, in the US developed land is projected to
increase from 5.2% to 9.2% of the total land base in the
next 25 years (Alig et al. 2004).
On a national scale urbanization affects relatively little
land cover, but it has a significant ecological footprint-
meaning that even small amounts of urban development
can have large effects on stream ecosystems.
Key pathways by which urbanization alters streams
Riparian/channel alteration - Removal of riparian
vegetation reduces stream cover and organic matter
inputs; direct modification of channel alters hydrology
and physical habitat.
Wastewater inputs - Human, industrial and other
wastewaters enter streams via point (e.g., wastewater
treatment plant effluents) and non-point (e.g., leaky
infrastructure) discharges.
Impervious surfaces - Impervious cover increases surface
runoff, resulting in increased delivery of stormwater and
associated contaminants into streams.
Click below for more detailed information on specific topics
The urban stream
syndrome
Urbanization &
biotic integrity
Catchment vs.
riparian
urbanization
Figure 1. Urbanization map of the United States derived from city lights data.
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].
Table 1. Common ways of quantifying urbanization
MEASURE
DESCRIPTION
% Total urban area
% High intensity urban
% Low intensity urban
% Residential
% Commercial / industrial
% Transportation
Area in all urban land uses
Area above some higher development
threshold
Area above some lower development
threshold
Area in residential-related uses
Area in commercial- or industrial-related
uses
Area in transportation-related uses
% Total impervious area
Area of impervious surfaces such as roads,
parking lots and roofs; also called impervious
surface cover
% Effective impervious area
Impervious area directly connected to
streams via pipes; also called % drainage
connection
Road density
Road length per area
Road crossing density
# Road-stream crossings per area
Population density
# People per area
Household density
# Houses per area
Urban intensity indices
Multimetric indices combining a suite of
development-related measures into one
index value [e.g., the USGS national urban
intensity index (NUN), based on housing
density, % developed land in basin, and road
density]
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URBANIZATION
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The urban stream syndrome
Common effects of urbanization on stream ecosystems have
been referred to as the "urban stream syndrome" (Walsh et
al. 2005a). Tabie 2 Iists symptoms typically associated with
the urban stream syndrome. Symptoms preceded by an
arrow have been observed to consistently increase (i^) or
decrease (si,) in response to urbanization, while symptoms
preceded by a delta (A) have been observed to increase,
decrease, or remain unchanged with urbanization.
As the urban stream syndrome illustrates, these streams are
simultaneously affected by multiple sources, resulting in
multiple, co-occurring and interacting stressors. As a result,
identifying specific causes of biological impairment in urban
streams, or the specific stressors that should be managed to
improve condition, is difficult. Some communities are
approaching this challenge by managing overall urbanization,
rather than the specific stressors associated with itfor
example, by establishing total maximum daily loads (TMDLs)
for impervious surfaces, rather than individual pollutants.
Many characteristics of urban
development affect how the
urban stream syndrome is
expressed within a given system. These characteristics
include (but are not limited to):
Location and distribution of development
- catchment vs. riparian
- upstream vs. downstream
- sprawling vs. compact
Density of development
Type of development and infrastructure
- residential vs. commercial/transportation
- stormwater systems
- wastewater treatment systems
Age of development and infrastructure
Table 2. Symptoms generally associated with the urban stream syndrome
STRESSOR CATEGORY
SYMPTOM
Water/ sediment quality
1s nutrients
"f toxics
A suspended sediment
Temperature
"T temperature
Hydrology
Is overland flow frequency
'T erosive flow frequency
/tv stormflow magnitude
¦Is flashiness
^ lag time to peak flow
A baseflow magnitude
Physical habitat
"f- direct channel modification (e.g., channel
hardening)
'f channel width (in non-hardened channels)
¦Is pool depth
1s scour
4/ channel complexity
A bedded sediment
Energy sources
s|/ organic matter retention
A organic matter inputs and standing stocks
A algal biomass
Modified from Walsh CJ et al. 2.005a. The urban stream syndrome: current knowledge and the
search for a cure. Journal of the North American Benthological Society 24(3):706-723.
Click below for more detailed information on specific topics
The urban stream
Catchment vs.
syndrome
biotic integrity
urbanization
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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.
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]
other changes in assemblage structure (e.g., changes in
diatom composition)
[Winter & Duthie 2000, Sonneman et al. 2001, Newall & Walsh 2005]
BENTHIC MACROINVERTEBRATES
-i- total abundance, richness or diversity
[Morley & Karr 2002, Moore & Palmer 2005, Walsh et al. 2007]
4/ EPT (Ephemeroptera, Plecoptera, Trichoptera)
abundance, richness or diversity
[Morley & Karr 2002, Roy et al. 2003a, Riley et al. 2005, Walsh 2006]
1s abundance of tolerant taxa
[Jones & Clark 1987, Walsh et al. 2007]
other changes in assemblage structure (e.g., changes in
functional feeding groups)
[Stepenuck et al. 2002, Smith & Lamp 2008]
4/quality of biotic index scores
[Kennen 1999, Morley & Karr 2002, DeGasperi et al. 2009]
FISHES
4" abundance, biomass, richness or diversity
[Wang et al. 2003a, Bilby & Mollot 2008, Stranko et al. 2008]
other changes in assemblage structure (e.g., changes in
reproductive guilds)
[Stepenuck et al. 2002, Roy et al. 2007, Helms et al. 2009]
4' quality of biotic index scores
[Snyder et al. 2003, Miltner et al. 2004, Morgan & Cushman 2005]
1s biotic homogenization (replacement of more endemic,
specialist fishes with more broadly distributed, generalist
fishes)
[Scott 2006 (Fig 2), Walters et al. 2009]
Photos courtesy of Noel Burkhead, USGS
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Figure 2. Plot of a measure of biotic homogenization [relative abundance of
Appalachian highland endemic fishes - relative abundance of cosmopolitan
fishes] on the first axis of a principal components analysis of three catchment
land use variables [1993 forest cover, forest cover change from 1970s-1990s,
and urbanization intensity (normalized catchment building + road density)].
Sites with higher forest cover and lower urban intensity had more endemic taxa
(e.g., fishes such as the Tennessee shiner and the mottled scuipin, above left),
while sites with lower forest cover and higher urban intensity had more broadly
distributed, generalist taxa (e.g., fishes such as the redbreast sunfish and
central stoneroller, above right).
From Scott MC. 2006. Winners and losers among stream fishes in relation to land use legacies and
urban development in the southeastern US. Biological Conservation 127:301-309. Reprinted with
permission from Elsevier.
Click below for more detailed information on specific topics
Urbanization &
Catchment vs.
syndrome
biotic integrity
urbanization
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Catchment vs. riparian urbanization
Where urbanization occurs in the watershed can affect its
influence on stream ecosystems. Studies examining land use
variables and stream characteristics typically consider land
use at one (or more) of three general spatial scales:
Catchment - the entire catchment above the site
Riparian - the entire riparian area above the site
Reach - the riparian area for a relatively short distance
above the site
King et al. (2005) examined whether macroinvertebrate
assemblages in Coastal Plain, Maryland streams responded
differently to development in the watershed versus
development in areas closer to the focal site (Fig 3). They
found that where development occurs can significantly
influence its effects on benthic biota:
For% developed land in the watershed (Fig 3A), there
was an apparent threshold between 21-32% where the
probability of assemblage alterations increased rapidly;
once >32% of the watershed was developed, all
macroinvertebrate assemblages were affected.
When % developed land in the 250-m buffer was
considered (Fig 3B), this threshold shifted left and all
macroinvertebrate assemblages were affected once >22%
of land in the 250-m buffer was developed.
A similar pattern was seen when developed land in the
watershed was inverse-distance weighted (i.e.,
development closer to the focal site was weighted more
than development farther away; Fig 3C), with the
threshold for macroinvertebrate effects occurring
between 18-23%.
The relative importance of development at different scales
varies across studies (e.g., Sponseller et al. 2001, Wang et al.
2001, Morley & Karr 2002, Roy et al. 2007, Snyder et al. 2003,
Schiff & Benoit 2007), and likely depends, at least in part, on
the stressors considered (Allan 2004). For example, some
stressors associated with urbanization (e.g., changes in flow)
are highly dependent on catchment-scale processes, while
other stressors (e.g., changes in basal energy sources) are
more affected by reach-scale processes.
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Figure 3. Scatterplots of the threshold effect of developed land on
macroinvertebrate assemblage composition (Bray-Curtis dissimilarity
expressed as nonmetric multidimensional scale [nMDS] Axis 1 scores), for (A)
% developed land in watershed, (B) % developed land within 250-m radius
buffer of site, (C) % developed land in watershed weighted by its inverse
distance (IDW) to site. Dotted lines indicate the cumulative probability of an
ecological response to increasing % developed land. Sites within the
watershed-scale threshold zone of 21-32% developed land in (A) are
highlighted in black in all panels.
From King RS et a I. 2005. Spatial considerations for linking watershed land cover to ecological
indicators in streams. Ecological Applications 15(1):137-153. Reprinted with permission.
Click below for more detailed information on specific topics
Catchment vs.
riparian
urbanization
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Riparian / Channel
Alteration
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Riparian / channel alteration
Intact riparian zones, or vegetated areas adjacent to stream
channels, can serve several functions (Allan 1995), including:
Provide organic matter for stream food webs
Provide habitat (e.g., woody debris, bank vegetation)
Reduce bank and channel erosion
Moderate stream temperatures
Intercept and process groundwater nutrients and
pollutants
Urbanization typically reduces the extent and quality of
riparian areas, via the removal of native vegetation and the
development of near-stream areas (Fig 4). These alterations
can contribute to multiple instream stressors, including:
Water / sediment quality - 4/ nutrient uptake and
retention, /fv erosion of bank sediments (and associated
contaminants)
Temperature - ^ shading and thermal buffering
Hydrology - 4^ woody debris inputs, 4^ interception of
surface and groundwater flows
Physical habitat - iv erosion of bank sediments,
%]/ woody debris inputs
Energy sources - 4* leaf inputs, 1s algal biomass (due to
s|/ shading), 1s dissolved organic carbon
Direct modification of stream channels is common in urban
systems, and these direct alterations of channel morphology
often are the most damaging changes urban streams
experience (see the Physical Habitat module, as well as the
Physical Habitat section of this module).
Typical channel alterations in urban streams include:
Channelization (i.e., channel straightening)
Channel hardening or armoring (e.g., lining channels and
banks with concrete and riprap)
Creation of dams and impoundments
Stream piping and burial
Removal of riparian vegetation and
channel hardening in an urban stream
-+ Urbanization
Native understory stem frequency
Understory stem density
Native canopy stem frequency
Canopy tree stem density
Tree species richness
Canopy height
Dead trees
% Grass cover within 250 m
% Tree cover within 250 m
"oT
Figure 4. Spearman's rank correlations between riparian urbanization
(building area within 250 m radius of stream site) and riparian vegetation
characteristics, at 71 sites near Cincinnati, Ohio. Many of these characteristics
(e.g., riparian tree density and cover) showed negative relationships with
urbanization.
From Pennington DN et al. 2008. The conservation value of urban riparian areas for land birds
during spring migration: land cover, scale, and vegetation effects. Biological Conservation
141:1235-1248. Reprinted with permission from Elsevier.
Click below for more detailed information on specific topics
Riparian zones &
channel
morphology
Urbanization &
riparian hydrology
Stream burial
Courtesy of USEPA
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Riparian / Channel
Alteration
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Riparian zones & channel morphology
Forested riparian zones play a key role in determining stream
channel morphology. Their root structures can help stabilize
streambanks, and the woody debris they contribute to
streams can protect banks by absorbing flow energy.
Because urbanization often results in riparian alteration, it is
difficult to separate the effects of general watershed
urbanization (e.g., increased stormflows) on channel
morphology from those of riparian alteration. Hession et al.
(2003) tackled this issue, using a paired design that
considered forested and nonforested riparian reaches on
both urban and nonurban streams. They examined the
effects of urbanization and riparian vegetation on channel
morphology in 26 unchannelized mid-Atlantic streams (Fig 5),
and found that:
Urban streams were generally wider than nonurban
streams, especially for smaller streams.
Forested urban streams were generally wider than
nonforested (i.e., grassed) urban streams.
Differences between forested and nonforested reaches
(i.e., the vertical arrows in Fig 5) were generally similar for
urban and nonurban streamsillustrating that even in
urban systems, riparian vegetation influences channel
morphology.
In extrapolating these results to other sites, however, keep in
mind that relationships between riparian alteration and
channel morphology in urban streams depend upon
numerous other factors, including stream size, stream
gradient, surrounding geology, and riparian vegetation type.
Stream with reduced riparian
tree cover and an eroded
bank
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nonforested urban
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Forested urban
O Nonforested urban
Urban regressions
- Nonurban regressions
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Figure 5. Bankfull width in urban and nonurban streams, with forested and
nonforested riparian reaches, as a function of drainage basin area. Vertical
arrows indicate the effect of riparian vegetation on bankfull width in urban
and nonurban streams.
From Hession WC et a!. 2003. Influence of bank vegetation on channel morphology in rural and
urban watersheds. Geology 31(2):147-150. Reprinted with permission.
Click below for more detailed information on specific topics
Riparian zones &
channel
morphology
Courtesy of
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Riparian / Channel
Alteration
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Urbanization & riparian hydrology
Increased stormwater flows associated with urban
development can scour stream channels and increase
channel incision, especially in systems with limited sediment
inputs (e.g., highly impervious watersheds, which often occur
in older urban areas).
Channel incision and reduced infiltration (again, due to
impervious surfaces) act to lower riparian water tables (Fig
6), thereby altering riparian hydrology. For example,
Hardison et al, (2009) examined six Coastal Plain streams in
North Carolina, ranging from 3.8-36.7% catchment
impervious area. They found that:
Channel incision increased with total impervious area
(TIA).
The duration of shallow riparian groundwater
throughout the year decreased as TIA increased.
Sites with higher TIA had greater depths to riparian
groundwater (Fig 7).
(a)
Ftoodplain
Confining Unit
Floodplain
re*i
*
Confining Unit
Figure 6. Cross-sectional view of typical groundwater tables
(dotted lines) in (a) rural and (b) urban streams underlain by
a shallow confining unit.
This "urban riparian drought" can have significant
repercussions for the structure and function of riparian areas
(Groffman et al. 2002, 2003; Hardison et al. 2009), including:
Shifts in riparian vegetation from wetland to upland
species, or from diverse to limited size distributions
Changes in nitrogen uptake and cycling, such that urban
riparian areas may be sources of, rather than sinks for,
nitrate
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Figure 7. (a) Mean riparian zone groundwater depths, June 2006-June 2007,
for six sites varying in catchment impervious area (rural = 3.8-12.4% total
impervious area, urban = 22.1-36.7%). (b) Half-hourly riparian zone
groundwater depths, over the same period, at the most rural (Phillippi) and
most urban (Fornes) sites.
Figures 6 and 7 from Hardison EC et al. 2009, Urban land use, channel incision, and water table
decline along Coastal Plain streams, North Carolina. Journal of the American Water Resources
Association 45(4):1032-1046. Reprinted with permission.
Click below for more detailed information on specific topics
Urbanization &
riparian hydrology
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Stream burial
Headwater streams are key habitats in terms of aquatic
ecosystem structure and function, and they comprise a
significant portion of total stream miles. In urban
watersheds, however, these small streams often are filled in
or incorporated into storm sewer systems (i.e., piped),
altering hydroiogic connectivity and physical habitat within
the buried streams, as well as urban drainage networks. For
example:
Drainage density of natural channels was approximately
V* less in urban and suburban vs. forested catchments in
Atlanta, GA (Meyer & Wallace 2001).
Approximately % of all streams were buried in Baltimore
City, MD (Elmore & Kaushal 2008).
93% of ephemeral channel length and 46% of
intermittent channel length were lost to burial and piping
associated with urbanization in Hamilton County, OH (Roy
et al. 2009, Figs 8 and 9). As a result, drainage areas for
remaining ephemeral and intermittent channels were
larger in urban areas.
Interestingly, Roy et al. (2009) found that perennial channel
length actually increased with urbanization (Fig 8), although
approximately 40% of perennial channels originated from
pipes. This increase in perennial channel length was due at
least in part to increased baseflow stemming from reductions
in forest cover and evapotranspiration.
Click below for more detailed information on specific topics
Stream burial
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~ Forested
~ Urban
-1,276 km
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+260 km
(22%)
Ephemeral
Intermittent
Perennial
Figures. Total ephemeral, intermittent and perennial channel length within
Hamilton County, OH for forested vs. urban catchments. Ephemeral streams
are channels with distinct stream beds and banks that carry water briefly
during and after storms; intermittent streams are channels that carry water
during the wet season; perennial streams are channels that carry flow all
year. Numbers above bars indicate absolute and % different in channel length
between forested and urban catchments.
Forest
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Intermittent
Ephemeral
Figure 9. Conceptual representation of how urbanization affects headwater
streams in Hamilton County, OH. Dotted lines indicate ephemeral streams,
dashed lines indicate intermittent streams, solid lines indicate perennial
streams; shading indicates drainage area for each stream type.
Figures 8 and 9 from Roy AH et al. 2009. Urbanization affects the extent and hydroiogic
permanence of headwater streams in a midwestern US metropolitan area. Journal of the North
American Benthological Society 28(4):911-928. Reprinted with permission.
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What are wastewater inputs?
Urbanization often involves the input of wastewaters into
streams and rivers. Common wastewater sources in urban
streams include:
Wastewater treatment plant (WWTP) effluents -
permitted municipal sewage discharges (Fig 10), treated
to varying degrees (Table 3)
Industrial effluents - permitted discharges from
industrial facilities
Accidental or unpermitted discharges
Sanitary sewer overflows - wet weather overflows
resulting in direct discharge of domestic and other
wastewaters into streams and rivers
Combined sewer overflows (CSOs) - wet weather
overflows resulting in direct discharge of surface runoff
and domestic and other wastewaters into streams and
rivers
Sewer pipes - leakage from broken, blocked or aging
infrastructure
Septic systems - leachate from septic tanks (usually in
less densely developed areas)
Stressors associated with wastewater inputs
Numerous stressors may be associated with wastewater
inputs, including:
1s nutrients
[Giicker et al. 2006, Carey & Migliaccio 2009]
xj/ dissolved oxygen (Is biological oxygen demand)
[Ortiz & Puig 2007]
1s pathogens
[Gibson et al. 1998, Frenzel & Couvilliori 2002]
metals (e.g., copper, mercury, cadmium, lead, iron)
[Nedeau et al. 2003]
^ pharmaceuticals and personal care products
[Kolpin et al. 2002, Watkinson et al. 2009]
/{- toxics (e.g., PAHs, alkylphenols, pesticides)
[Kolpin et al. 2002, Phillips & Chalmers 2009]
1s dissolved solids (e.g., chloride, sulfate, specific
conductance)
[Hur et al. 2007, Rose 2007]
stream discharge
[Nedeau et al. 2003, Barber et al. 2006, Carey & Migliaccio 2009]
\ temperature
[Nedeau et al. 2003, Kinouchi 2007]
population
wastewater
1940
1968 1996
YEAR
2016
Figure 10. Historical and projected US resident population served by publically-
owned wastewater treatment facilities, and volume of wastewater flows
produced.
Adapted from USEPA. 2000. Progress in Water Quality: An Evaluation of the National Investment
in Municipal Wastewater Treatment US Environmental Protection Agency, Office of Water,
Washington DC. EPA-832-R-00-008.
WWTP discharge on
Fourmile Creek, IA
tB
tsi
Table 3. Typical treatment efficiencies of municipal sewage treatment for
specific pollutants
POLLUTANT
TYPICAL TREATMENT EFFICIENCIES
(% inflow concentrations)
Sewage ponds
Secondary
treatment
Advanced
treatment
Biological oxygen
demand
50-95
95
95
Nitrogen
43-80
50
87
Phosphorus
50
51
85
Suspended solids
85
95
95
Metals
Variable
Variable
Variable
Modified from Baker LA. 2009. New concepts for managing urban pollution. Pp. 69-91 in: Baker, LA
(ed). The Water Environment of Cities. Springer Science+Business Media, LLC.
Click below for more detailed information on specific topics
Combined sewer
Wastewater-
overflows (CSOs) related enrichment
Reproductive
effects of WWTP
effluents
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Wastewater Inputs
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What is a CSO?
A combined sewer system (CSS) is a wastewater collection
system that collects and transports sanitary wastewater
(domestic sewage, commercial and industrial wastewater)
and stormwater to a treatment plant in one pipe. During wet
weather, when capacity of the system is exceeded, it
discharges untreated wastes directly to surface waters-
resulting in a combined sewer overflow (CSO; Fig 11).
Because CSOs release untreated wastewater, they can
contribute pathogens, nutrients, organic carbon, toxic
substances and other pollutants to surface waters (Fig 12).
How prevalent are CSOs in the US (USEPA 2004)?
CSSs serve approximately 40 million people, in 772
communities (Fig 13).
828 NPDES permits authorize discharges from 9,350
CSO outfalls.
USEPA estimates that CSOs release approximately 850
billion gallons of untreated wastewater and
stormwater each year.
WARNING
C&E0
OVERFLOW
Courtesy of UStPA
Figure 13. Prevalence of combined sewer
systems (CSSs) in the United States
CSSs generally have not been constructed since the mid-20th
century, and efforts are underway to reduce CSOs in many
existing systems (e.g., by separating wastewater and
stormwater sewer systems).
Click below for more detailed information on specific topics
Combined sewer
waiter-
overflows (CSOs)
related enrichment
Down
spout
Storm
.drain
industrial
Wet Weather
CHOLESTEROL
CAFFEINE
TR1S (2-BUTOXYETHYL)
PHOSPHATE
(TBEP)
TRIS (2-CHLOROETHYL)-
GALAXOLIDE
PHOSPHATE
(TCPP)
4-NONYLPHENOE
DIETHOXYLATE
(NP2EO)
Figure 12. 2006 annual mass loads for six organic wastewater compounds
(OWCs) for the Burlington (VT) Main Wastewater Treatment Plant (filled bar),
combined sewer overflow (open bar), and two streams below CSO and WWTP
outfalls (striped bars). OWCs on top are highly removed during normal
wastewater treatment, while those on bottom are poorly removed.
From Phillips P & Chalmers A. 2009. Wastewater effluent, combined sewer overflows, and other
sources of organic compounds to Lake Champlain. Journal of the American Water Resources
Association 45(l):45-57. Reprinted with permission.
Dry Weather
Down
spout
Storm
Combined
Outfall pipe
Outfall pipe
to river
and
win sronn water
5e«erwp0TW *
to river
Figure 11. Schematic of a typical combined sewer system that discharges
directly to surface waters during wet weather.
From USEPA. 2004. Report to Congress: Impacts and Control of CSOs and SSOs. U.S.
Environmental Protection Agency, Office of Water, Washington, DC. EPA 833-R-04-001.
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Courtesy of USEPA
Wastewater-related enrichment of streams
WWTP effluents and other sources of domestic wastes (e.g.,
septic tanks) can subsidize stream ecosystems by increasing
nutrient and organic matter inputs to streams (Gucker et ai.
2006, Singer & Battin 2007). The amount of enrichment that
occurs depends upon the volume of waste discharged, as well
as the level of treatment that waste receives.
For example, Singer & Battin (2007)
estimated that sewage-derived
particulate organic matter (SDPOM)
inputs contributed mean annual
input fluxes of 108.3 g carbon (C),
21.7 g nitrogen (N) and 5.9 g
phosphorus (P) per day. On average, these inputs
represented a 34% increase in seston-bound C and a 29%
increase in seston-bound P (although these values were
highly variable). Resources in the wastewater-subsidized
reach also had higher nutritional quality: %C,%N and % P
content were many times greater in SDPOM than in natural
seston and benthic fine particulate organic matter (Table 4).
These subsidies were incorporated into higher trophic levels,
as macroinvertebrate secondary production increased in the
wastewater-influenced reach; this enrichment effect was
largely due to the response of gatherers and grazer/gatherers
(Fig 14). However, macroinvertebrate diversity and
evenness declined in the subsidized reach, indicating
enrichment also negatively affected community structure.
Click below for more detailed information on specific topics
Wastewater-
related enrichment
Table 4. Carbon, nitrogen and phosphorus contents of resources in reference
(top value) and wastewater-subsidized (bottom value) reaches of a third-
order Austrian stream.
RESOURCE
%C
% N
%P
Periphyton
5.9 ±3.7
8.0 ±5.0
0.8 ± 0.5
1.1 ±0.6
0.15 ± 0.14
0.26 ±0.15
Seston
0.6 ±0.2
1.0 ±0.3
0.1 ±0.04
0.1 ±0.05
0.021 ±0.01
0.035 ± 0.02
Benthic fine particulate
organic matter
0.2 ±0.1
0.2 ±0.1
0.02 ±0.01
0.02 ±0.01
0.01 ±0.004
0.009 ±0.004
Sewage-derived particulate
organic matter
2.1 ±0.8
0.4 ± 0.2
0.09 ±0.03
Modified from Singer GA & Battin TJ. 2007. Anthropogenic subsidies alter stream consumer-
resource stoichiometry, biodiversity, and food chains. Ecological Applications 17(2): 376-389.
800 -i
600 -
c "
¦B b
O Cjl
?!
= O)
400 -
200 -
Reference
Subsidized
i
"1==,
Jul
Sep
-ri-
Nov
Jan
Mar
May
Jul
300-
250-
c c
« "9 200 -
w (V
~o E
150-
== o> 100 -
to c
o s
50-
Reference
Subsidized
NS
i
j3
NS
NS
NS
A
Filt
Gath
Graz Gragath Pred
Shred
Figure 14. Daily macroinvertebrate secondary production in reference and
wastewater-subsidized reaches of a third-order Austrian stream, by (a) month
and (b) functional feeding group.
From Singer GA & Battin TJ. 2007. Anthropogenic subsidies alter stream consumer-resource
stoichiometry, biodiversity, and food chains. Ecological Applications 17(2):376-389. Reprinted
with permission.
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Reproductive effects of WWTP effluents
Municipal effluents often contain endocrine disrupting
chemicals (EDCs), which can mimic or interfere with normal
hormone signaling in aquatic animals and result in adverse
reproductive effects (Jobling & Tyler 2003), Standard
wastewater treatment practices typically are not effective at
removing these chemicals.
Examples of known or suspected EDCs found in WWTP
effluents include:
Natural hormones (e.g., 17(3-estradiol)
Synthetic hormones and other pharmaceuticals
(e.g., 17a-ethynlestradiol)
Pesticides (e.g., diazinon, lindane, atrazine)
Phthalates
Toxic metals (e.g., copper, mercury, cadmium)
Alkylphenols
Bisphenol A
white sucker
Catostomus commersoni
Courtesy of NY DEC
Vajda et al. (2008) examined the estrogenic effects of WWTP
effluent on white suckers in Boulder Creek, CO. They found
that intersex fishfish containing both ovarian and testicular
tissuecomprised 18-22% of the population downstream of
the WWTP outfall, but were not found upstream. Fish
downstream of the outfall also had altered sex ratios,
reduced sperm production, increased vitellogenin levels (a
protein associated with egg development in females), and
reduced gonad size (Fig 15).
Click below for more detailed information on specific topics
Reproductive
effects of WWTP
effluents
Upstream [///J Effluent
u o
Fall 2003
Spring 2004
B
100
] Absent fZ77l <25%
~Xa 50 to 75% |
~ 25 to 50%
I >75%
Upstream Effluent Upstream Effluent
Fall 2003 Spring 2004
Upstream l/WJ Effluent
Fall 2003
Spring 2004
Upstream V//\ Effluent
Fall 2003
Spring 2004
Figure 15. Evidence of reproductive impairment in white suckers collected
from sites upstream (upstream) and downstream (effluent) of the Boulder
WWTP on Boulder Creek, in terms of (A) % males, (B) sperm abundance in
males, (C) plasma vitellogenin concentrations in males, and (D) gonadosomatic
index in females.
From Vajda DW et al. 2008. Reproductive disruption in fish downstream from an estrogenic
wastewater effluent. Environmental Science & Technology 42:3407-3414. © 2008 American
Chemical Society. Reprinted with permission.
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Stormwater runoff & impervious surfaces
Perhaps the most defining characteristic of urban streams is
the increase in the amount and rapidity of stormwater or
surface runoff to those systems. Impervious surfaces
associated with urbanization reduce infiltration and increase
surface runoff (Fig 16), altering the pathways by which water
(and any associated contaminants) reach urban streams.
Common impervious surfaces include:
Roads
Parking lots
Rooftops
Driveways and sidewalks
Compacted soils
How does stormwater runoff affect streams?
It alters natural hydrology, generally leading to more
frequent, larger magnitude, and shorter duration peak
flows.
it alters channel morphology, generally leading to
changes such as increased channel width, increased
downcutting, and reduced bank stability.
It alters in-stream hydraulics, affecting biologically
important parameters such as water velocity and shear
stress.
It disrupts the balance between sediment supply and
transport, generally leading to increased sediment
transport capacity and channel erosion.
It increases stream temperatures, due to the transfer of
heat from impervious surfaces to stormwater runoff.
it increases delivery of pollutants from the landscape to
the stream. Pollutants commonly found in stormwater
runoff include:
sediment
nutrients
pesticides
wear metals
organic pollutants
oii and grease
Evapo-transpiration 40%
Shallow^1
Infiltration
25%
Forested
Runoff 10%
~
Deep
Infiltration
25%
Evapo-transpiration 38%
Runoff 20%
~
Shallow y Deep
Infiltration Infiltration
21% , r 21%
10-20% Imperviousness
Evapo-transpiration 35%
Runoff 30%
Evapo-transpiration 30%
Runoff 55%
Shallow,
Infiltration ee'}.
~no/ Infiltration
20/o X 15%
35-50% Imperviousness
Shallow, Deep
Infiltration [nflltratk)n
1#% 5%
75-100% Imperviousness
Figure 16. The shift in relative hydrologic flow in increasingly impervious
watersheds. Note the large increase in stormwater runoff as imperviousness
increases, at the expense of infiltration.
From Paul MJ & Meyer JL. 2001. The ecology of urban streams. Annual Review of Ecology &
Systematics 32:333-365. © 2001 by Annual Reviews. Reprinted with permission.
Click below for more detailed information on specific topics
Effective vs. total Imperviousness & Thresholds of
imperviousness biotic condition imperviousness
Courtesy of USEPA
Three common types of impervious surfaces in
urban watersheds: roads, roofs and parking lots
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bffective vs. total imperviousness
The effects of urbanization on stream ecosystems are largely
driven by impervious cover. There are two general ways to
quantify impervious cover:
Total impervious area (TIA) = all impervious area in
catchment
Effective impervious area (EIA) = impervious area in
catchment that is directly connected to stream channels
(i.e., precipitation falling on that area is effectively
transported to the stream)
Several methods can be used to determine EIA, with varying
levels of accuracy (Roy & Shuster 2009). They include:
Geographic information system data combined with
overlays of stormwater infrastructure
Published empirical relationships between TIA and EIA
(Alley & Veenhuis 1983, Wenger et al. 2008)
Field assessments
'/flllllVlVY
" 1
r ¦-
Many studies have found that EIA (also known as drainage
connection or directly connected impervious area) is a
better predictor of ecosystem alteration in urban streams.
For example, Hatt et al. (2004) showed that % connection
was more strongly related to water chemistry variables (e.g.,
conductivity, total phosphorus) than % total imperviousness,
during both baseflows and stormflows (Fig 17).
The strength of EIA relationships suggests that stormwater
management techniques aimed at disconnecting impervious
areas from stream channels can improve urban water quality
(Walsh et al. 2005b).
Click below for more detailed information on specific topics
Effective vs. total
imperviousness
14j
10-
~ 8-
g 6-
0
O 4 ¦
o » 'o
O
*
D
8 V"
2-
R=0.77 (0.77)
800,
R=0.91 (0.881
600:
A A
400-
>
E
.0
300-
A 0 *
/
CO
3
200.
0
0
\
\
«o
o
w
100-
R=0.71 (0.81)
Q.
U.
500-
100-
21
£
10-
1
R=0.£5 (0.67)
ra
A
X
z
200 -I
150
100 .
50
30
20
10
R=0.71 (0.80)
8
o X
»
't T" 1 I III
0 5 20 40 60 100
% Connection
RO.50 (0.44)
O
R-0.77 0.72)
R=0.48 (0.58)
Bg-^S
R|0.37 (0.47)
I iirr
R=0.66 (0.71)
f
0.1 2.5 10 2030 50
% Imperviousness
Figure 17. Relationships between geometric means of baseflow (close circles,
solid regression lines) and storm event (open circles, dashed regression lines)
concentrations and two impervious cover variables: % drainage connection
and % total imperviousness. R values provided as baseflow concentrations
(storm event concentrations). DOC = dissolved organic carbon; EC = electrical
conductivity; FRP = filterable reactive phosphorus; TP = total phosphorus; NH4+
= ammonium.
From Hatt BE et a I. 2004. The influence of urban density and drainage infrastructure on the
concentrations and loads of pollutants in small streams. Environmental Management 34(1):112-
124. Reprinted with permission from Springer Science+Business Media.
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Imperviousness & biotic condition
Total or effective impervious cover has been linked to
numerous changes in stream biotic assemblages. These
changes include (but are not limited to):
ALGAE
"t1 abundance or biomass
[Walsh et al, 2005b, Busse et al. 2006]
other changes in assemblage structure
[Walsh et al, 2005b]
BENTHIC MACROINVERTEBRATES
nJ/ total abundance, richness or diversity
[Walsh 2004, Moore & Palmer 2005, Utz et al. 2009]
sj/ EPT abundance, richness or diversity
[Walsh 2004, Walsh et al. 2005b, Schiff & Benoit 2007]
other changes in assemblage structure (e.g., changes in
functional feeding groups)
[Stepenuck et al. 2002, Wang & Kanehl 2003]
\]/ quality of biotic index scores
[Morley & Karr 2002, Walsh et al. 2005b, Schiff & Benoit 2007]
FISHES
\ abundance, biomass, richness or diversity
[Wang et al. 2001, Wang et al. 2003, Stranko et al. 2008]
other changes in assemblage structure (e.g., loss of
individual species, changes in reproductive guilds)
[Wenger et al. 2008 (Fig 18), Helms et al. 2009]
sj/quality of biotic index scores
[Wang et al. 2001, Wang et al. 2003]
Click below for more detailed information on specific topics
_Q
03
_Q
O
CD
o
c
CD
L_
D
O
o
O
tricolored shiner
Etowah darter
Photos courtesy of Noel Burkhead, USGS
(a) tricolored shiner
(b) speckled madtom
(c) Etowah darter
(d) bronze darter
% Effective impervious area
Figure 18. Occurrence probability of 4 fish species vs. impervious cover. Black
line represents response curve based on mean parameter estimate for
effective impervious area (ElA); gray lines represent response curves based on
5% and 95% values for parameter estimate for EIA. For three of the four
species (all but speckled madtom), occurrence probability was predicted to
approach zero at approximately 2-4% effective impervious cover.
From Wenger SJ et al. 2008. Stream fish occurrence in response to impervious cover, historic
land use, and hydrogeomorphic factors. Canadian Journal of Fisheries and Aquatic Sciences
65:1250-1264. © 200S NRC Canada or its licensors. Reproduced with permission.
Imperviousness &
biotic condition
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Thresholds of imperviousness
Relationships between impervious cover and measures of
stream condition, defined by either physical, chemical, or
biological parameters, can take several forms {Fig 19). When
the relationship is linear, any increase in imperviousness
results in a decrease in condition {Fig 19, yellow and Fig 20);
in other cases, there may be threshold values of impervious
cover above which condition either decreases rapidly (Fig 19,
green) or remains consistently low (Fig 19, blue and Fig 21).
impervious cover
Figure 19. Example relationships
between stream condition and
impervious cover: a linear
decline in condition (yellow); an
upper threshold switching to a
lower threshold (green); a
linear decline to a lower
threshold (blue).
Modified from Walsh et al. (2005a).
Example thresholds or critical levels of imperviousness
reported in the literature include:
PHYSICAL & CHEMICAL PARAMETERS
Consistent channel instability when EIA > 10% [Booth &
Jackson 1997]
Different geomorphic response patterns (e.g., in terms of
depth diversity, maximum pool depth) across sites with
< 13% VS. > 24% TIA [Cianfrani et al. 2006]
Consistently higher conductivity, dissolved organic
carbon, and filterable reactive phosphorus when EIA >
5%, 4%, and 1%, respectively [Walsh et al. 2005b]
Uniformly low summer baseflow when TIA > 40%
[Finkenbine et al. 2000]
BIOLOGICAL PARAMETERS
Consistently high algal biomass when EIA > 5%, low
diatom index value when EIA > 2% [Walsh et al. 2005b]
Sharp declines in macroinvertebrate diversity and
richness when TIA between 8-12% [Stepenuck et al. 2002]
Invertebrate taxa sensitive to impervious cover lost when
TIA between 2.5-15% in Piedmont streams and between
4-23% in Coastal Plain streams [Lltz et al. 2009]
Brook trout absent when TIA > 4% [Stranko et al. 2008]
Occurrence probability of three sensitive fish species
approaches zero when EIA between 2-4% [Wenger et al.
2008]
Sharp declines in fish IBI score and trout abundance when
EIA between 6-11%, consistently low values when EIA >
11% [Wang et a I. 2003]
o Agriculture
a Mixed-agriculture
~ Mixed-urban
o Urban
c 30
r2 = 0.70, P< 0.0001
20 40 60
Impervious surface (%)
80
Figure 20. Relationship between total macroinvertebrate richness and %
impervious surface cover in 29 headwater Maryland streams sampled in 2001.
Taxa richness declined linearly with increasing impervious cover.
From Moore AA & Palmer MA. 2005. Invertebrate biodiversity in agricultural and urban
headwater streams: implications for conservation and management. Ecological Applications
15(4):1169-1177. Reprinted with permission.
8*
§ 6
<
O 5-
w
4H
0.0
0.1
0.2 0.3
Proportion El
i
0.4
0.5
oo"
-i
0.1
i
0.2
0.3
0.4
i
0.5
Proportion Tl
Figure 21. SIGNAL scores (a biotic index) for macroinvertebrates in edge
habitats vs. (A) effective imperviousness (El) and (B) total imperviousness (Tl).
Solid lines are piecewise regressions, dashed lines are linear regressions; the
piecewise regression for El provided the best fit. Note that the threshold value
was 0.07 for El, approximately half the threshold value for Tl.
From Walsh CJ et al. 2005b. Stream restoration in urban catchments through redesigning
stormwater systems: looking to the catchment to save the stream. Journal of the North
American BenthologicalSociety 24(3):690-705. Reprinted with permission.
Click below for more detailed information on specific topics
Thresholds of
imperviousness
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Water/Sediment
Quality
Water & sediment quality in urban streams
Urbanization has been associated with
numerous impairments of water and
sediment quality, including:
1s dissolved solutes and
conductivity (Table 5)
1s suspended solids or turbidity
1s fecal bacteria
\ nitrogen and phosphorus (Table 5)
si/ dissolved oxygen
\ toxics (Table 5, Fig 22)
metals (e.g., Cd, Cr, Cu, Hg, Ni, Pb, Zn)
polycyclic aromatic hydrocarbons (PAHs)
polychlorinated biphenyls (PCBs)
pesticides (e.g., chlordane, chlorpyrifos, diazinon)
pharmaceuticals (e.g., antibiotics, hormones, anti-
depressants, ibuprofen)
other organic pollutants (e.g., caffeine, triclosan,
detergents, fragrances)
Exposure of aquatic organisms to these pollutants can result
in toxic effects, specific to each pollutant's mode of action.
The following pages focus on a few urban-specific water and
sediment quality issues in greater depth; in addition, more
detailed information on many of these parameters can be
found in CADDIS' individual stressor modules.
Click below for more detailed information on specific topics
Urbanization &
conductivity
Nitrogen in urban
streams
Table 5. Example water (Malibu Creek, Etowah River) and sediment (Charles
River and Stillwater River) quality differences between urban and non-urban
Stream sites [DIN = dissolved inorganic nitrogen; SRP = soluble reactive phosphorus].
LOCATION
[Reference]
PARAMETER
LEAST
URBAN SITE
MOST
URBAN SITE
Malibu Creek, CA
[Busse et al. 2006]
% Impervious
2
55
Conductivity (nS cm"1)
670
3060
SRP (ng L"1)
43
75
DIN (|ig L1)
30
521
Etowah River, GA
[Roy et al. 2003]
% Urban
5
61
Conductivity (fiS cm1)
21
172
SRP (|ag L1)
8
135
WH4-N (|ig L1)
0.6
2.0
Charles River and
Stillwater River, MA
[Chalmers et al. 2007]
% Urban
2
97
PAHs (mg kg"1)
1.2
32.5
PCBs (mg kg"1)
<0.1
0.3
Cr (ng g"1)
36
92
Pb (|ig g"1)
73
250
PAHs
c
.9?
o
cr
O
HI
CL
C
cd
CD
r2 = 0.80
0 5 10 15 20 25 30 35
Commercial, industrial, and transportation land use (%)
Figure 22, Overall sediment quality, as indicated by mean probable effect
concentration (PEC) quotient, vs. commercial, industrial and transportation
land use. PEC quotient = contaminant concentration/PEC for that
contaminant; at each site, PEC quotients for metals, chlorinated hydrocarbons,
and PAHs were averaged to determine mean PEC quotients.
From Chalmers AT et a I. 2007. The chemical response of particle-associated contaminants in
aquatic sediments to urbanization in New England, U.S.A. Journal of Contaminant Hydrology
91:4-25. Reprinted with permission from Elsevier.
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Urbanization & conductivity
Increases in conductivity or similar measures of ionic
strength (see the Ionic Strength module for further discussion
of different measurements) are among the most consistently
documented water quality changes associated with
urbanization, For example, Kaushal et al. (2005) examined
salinization of suburban and urban streams in Maryland.
They found that chloride concentrations exceeded
thresholds for sensitive freshwater taxa at sites with greater
than 40% impervious cover (Fig 23). In winter, chloride
concentrations reached peaks of nearly 25% the
concentration of seawater, and concentrations remained up
to 100 times higher than at forested and agricultural non-
impervious sites throughout the year.
This increase in dissolved solutes in urban streams has been
attributed to several sources, including:
Road salt and other deicing agents (in northern
regions)
Point source discharges (e.g., WWTP and industrial
effluents)
Leaky sewer and septic systems
Concrete weathering
Some studies have shown that urbanization-associated
changes in conductivity are related to shifts in biotic
assemblages. For example:
Roy et al. (2.003) found that specific conductance was a
significant predictor of invertebrate responses to
urbanization, negatively related to total invertebrate
richness, EPT richness, total invertebrate density, and
several benthic invertebrate indices.
Helms et al. (2009) found that streams with high
concentrations of total dissolved solids were dominated
by sunfish-based fish assemblages.
However, in many cases it is believed that conductivity is a
general indicator of overall urban impact, rather than a direct
cause of observed biotic effects.
i
.2
600
500
400
~ 1998
¦ 1999
2000
x 2001
* 2002
R2 = 0.81
Damage to Land Plants
Rural
20
Suburban
30 40
Urban
Percent Impervious Surface in Watershed
Figure 23, Relationship between impervious surface and mean annual
chloride concentration in Baltimore Long Term Ecological Research (LTER)
streams, 1998-2002. Dashed lines indicate thresholds for damage to certain
land plants and for chronic toxicity to sensitive freshwater taxa (U.S. EPA
1988).
From Kaushal SS et a I. 2005. Increased salinization of freshwater in the northeastern United
States. Proceedings of the National Academy of Sciences 102 (38):13517-13520. © 2005 National
Academy of Sciences, U.S.A. Reprinted with permission.
Courtesy of USEPA
Road salt and other deicers can contribute to elevated
stream conductivity in northern urban catchments.
Click below for more detailed information on specific topics
Urbanization &
conductivity
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Water/Sediment
Quality
Nitrogen in urban streams
One common water quality change associated with urban
development is an increase in nutrient concentrations,
especially nitrogen (Fig 24, Table 6). Wastewater inputs and
stormwater runoff both contribute to increased nitrogen
loading in urban catchments. Specific sources of nitrogen in
urban systems include:
Human wastes
- wastewater treatment plant effluents
- leaky sewer and septic systems
Atmospheric deposition
- vehicle exhaust
- other forms of fossil fuel combustion
Fertilizers applied to lawns and golf courses
Pet wastes
Landfill leachates
Legacy sources (e.g., development of agricultural land)
In addition, riparian alteration can affect nitrogen uptake
and cycling, and turn urban riparian areas into nitrogen
sources (Groffman et al. 2002, 2003).
Courtesy of USEPA
Although nitrogen loading to and export from urban streams
typically are elevated, many studies also have found relatively
high nitrogen retention [Groffman et al. 2004, Wollheim et
al. 2005 (Table 6)] in these systems. Pervious surfaces such
as lawns may act as nitrogen sinks in urban areas (Raciti et
al. 2008), and help to mitigate at least some nitrogen loading
increases. However, this mitigation may be limited as
fertilizers often are over-applied in urban systems.
4
B 3
0)
+¦>
TO
Forested
Suburban
Agriculture
0
07/24/98
02/09/99 08/28/99
03/15/00
Date
10/01/00 04/19/01 11/05/01
Figure 24. Nitrate concentrations in three streams draining completely
forested, suburban, and agricultural watersheds in Baltimore County, MD,
October 1998-October 2001.
From Groffman PM et a I. 2004. Nitrogen fluxes and retention in urban watershed ecosystems.
Ecosystems 7:393-403. Reprinted with permission from Springer Science+Business Media.
Table 6. Nitrogen budgets for an urban and a forested headwater stream in
Massachusetts, 2001-2002 water year.
PARAMETER
URBAN
FOREST
Total N loading
(kg km 2 y )
Wet deposition (DIN)
494
496
Dry deposition (DIN)
290
290
Net waste N
350
586
Fertilizer N
1443
395
SUM
2578
1767
River N exports
(kg km 2 y )
DIN (N03+ NH4)
333
7.5
DON
51.5
51.6
SUM
384.5
59.1
N retention
(%)
85
97
After Wollheim WM et al. 2005. N retention in urbanizing headwater catchments. Ecosystems
8:871-884.
Click below for more detailed information on specific topics
Nitrogen in urban
streams
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Water/Sediment
Quality
PAHs
Polycyclic aromatic hydrocarbons (PAHs) are common
pollutants in urban streams, resulting from numerous
transportation-related sources including oil leakage, vehicle
exhaust, tire and brake wear, and pavement erosion. Many
studies have shown that these compounds can adversely
affect stream biota (e.g., Maltby et al. 1995, Pinkney et al.
2004).
4
¦1
Pavement sealants are routinely applied to parking lots and
driveways to protect the underlying surfaces, and these
sealants can be significant sources of PAHs. For example:
PAH concentrations were 65 times higher in runoff from
coal-tar seal-coated parking lots versus unsealed parking
lots (Mahler et ai. 2005).
PAH concentrations in stream sediments were 3.9 to 32
mg kg-1 higher downstream of coal-tar seal-coated
parking lots versus upstream reference sites (Scoggins et
al. 2007).
Scoggins et al. (2007) examined the effect of these sealcoats
on benthic macroinvertebrate assemblages. They found that:
Average macroinvertebrate densities were 2 times
higher at sites upstream of seal-coated parking lots.
Chironomid density decreased at sites downstream of
seal-coated parking lots, whereas oligochaete density
usually increased.
Increases in pool habitat PAH sediment toxicity units
between sites upstream and downstream of seai-coated
parking lots explained decreases in macroinvertebrate
richness and density (Fig 25).
CO
CO
1 suggest
toxicity.
From Scoggins M et al. 2007. Occurrence of polycyclic aromatic hydrocarbons below coal-tar-
sealed parking lots and effects on stream benthic macroinvertebrate communities. Journal of
the North American Benthological Society 26(4):694-707. Reprinted with permission.
Click below for more detailed information on specific topics
PAHs
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Temperature
Urbanization & stream temperature
Urbanization often results in increased stream temperatures
(e.g., increased daily maximum temperature, increased
number of temperature exceedances), especially in summer.
This is due in part to the formation of urban heat islands, or
localized areas of heat storage (and warmer air
temperatures) near urban centers. Many other aspects of
urbanization also can contribute to stream warming:
Riparian alteration can
reduce canopy cover and
shading, increasing solar
radiation reaching the
water surface.
Wastewater inputs can
lead to the direct
discharge of warmer
effluents into stream and
rivers (Figs 26 and 27).
Stormwater runoff from warm impervious surfaces can
contribute heated surface runoff to surface waters, and
reduce cooler groundwater inputs via decreased
infiltration.
Lower baseflows can lead to shallower water and
standing pools, which warm quickly.
Physical habitat changes such as channel widening can
increase channel width;depth ratios, further reducing
riparian shading and increasing surface area for heat
exchange.
Certain best management practices (BMPs) for urban
streams, such as stormwater retention ponds, can
increase water retention time and warming, particularly
in unshaded systems.
Increases in water temperature also can affect other urban-
associated stressors, including:
Water / sediment quality - via decreased dissolved
oxygen saturation, increased ammonia toxicity, and
increased biotic uptake of toxic substances
Energy sources - via increased microbial respiration and
primary production
Elevated water temperatures can be stressful to aquatic
organisms, and may result in numerous lethal and sublethal
effects (e.g., death, increased disease susceptibility, and
decreased growth and reproduction). See the Temperature
module for further discussion of temperature as a cause of
stream impairment.
25
5 20
Year (Avg.)
¦O 1965(17.2)
o 1970(17.8)
-A 1975(18.3)
1985(18.9)
X--- 1995(20.6)
-k 2001 (21.7)
* 2004 (22.7)
Q.
1 2 3 4 5 6 7 8 9 10 11 12
Month
Figure 26. Monthly mean (plot) and yearly mean (legend) temperatures of
wastewater effluents from all treatment plants located in the central Tokyo
area, 1965-2004. Increases in effluent temperatures stem largely from
increased residential use of heated water.
From Kinouchi T. 2007. impact of long-term water and energy consumption in Tokyo on
wastewater effluent: implications for the thermal degradation of urban streams. Hydrological
Processes21:1207-1216. Reprinted with permission.
0.25
to
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CD
3
2
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CD
0.10
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c
0.05
0.00
0.5
0
1
2
1.5
Change in heat input from WWTPs
(TJ/day/year)
Figure 27. Change in wastewater heat effluent from wastewater treatment
plants vs. the rate of temperature increase in four stream segments (B-E) in
the Ara River system, central Tokyo. Kinouchi et al. (2007) contend that
increased wastewater effluent temperatures contribute to the thermal
degradation of effluent-receiving streams.
From Kinouchi T et al. 2007. Increase in stream temperature related to anthropogenic heat input
from urban wastewater. Journal of Hydrology 335:78-88. Reprinted with permission from
Elsevier.
Click below for more detailed information on specific topics
Heated surface
Temperature &
Urbanization &
runoff
biotic condition
climate change
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Temperature
JikL
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Heated surface runoff from impervious surfaces
Impervious surfaces absorb and store heat, which is then
transmitted to surface runoff during rainfall events. Several
studies have shown positive correlations between impervious
surface area and stream temperature (Wang et al. 2003,
Nelson & Palmer 2007, Imberger et al. 2008, Stranko et al.
2008).
Thompson et al. (2008) compared runoff temperatures from
asphalt and sod surfaces during 24 rainfall simulations (see
Fig 28 for one of these simulations). They found that:
Asphalt surfaces were more than 20°C warmer than sod
surfaces prior to rainfall simulations.
Initial asphalt runoff temperatures were roughly 10°C
warmer than sod runoff temperatures (35.0 vs. 25.5°C).
Asphalt runoff temperature decreased by an average of
4,1°C over the 1-hour rainfall simulation.
However, impervious surfaces do not always elevate stream
temperatures. Many factors influence whether impervious
surfaces generate heated surface runoff (Herb et al. 2008,
Thompson et al. 2008b), including:
Air temperature and humidity
Type of impervious surface (e.g., reflectance)
Solar radiation before and during rainfall
Rainfall intensity
Rainfall temperature
M 60
1:36 PM H
* 3:21 PM
Aaphat surface temperature
Asphalt lunoff temperature
Rainfall temperature
Asphalt runoff
Sod runoff
50
_ 40
Si
E
30
20
10
/
1:36 PM W
Soli sirfece temperalm
'¦* 3:21 PM
/
Sod runoff tempera! w
Rainfall temporal ire
Asphalt on off
Sod lunoff
50
40 -T
E
30 «
I
20 I
10
12:00 PM 1:00 PM
2:00 PM
3:00 PM
Time
4:00 PM 5:00 PM
0
6:00 PM
Figure 28. Temperature of (a) asphalt and (b) sod surface and runoff during
July 15, 2005 rainfall simulation; asphalt and sod runoff and rainfall
temperature are shown in both (a) and (b).
From Thompson AM et al. 2008. Thermal characteristics of stormwater runoff from asphalt and
sod surfaces. Journal of the American Water Resources Association 44(5):1325-1336. Reprinted
with permission.
Click below for more detailed information on specific topics
Heated surface
runoff
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Temperature
Temperature & biotic condition in urban streams
Biotic responses associated with increased temperatures in
urban streams include (but are not limited to):
BENTHIC MACROINVERTEBRATES
4/ total abundance, richness or diversity
[Sponseller et al. 2001]
4/ EPT abundance, richness or diversity
[Sponseller et al. 2001, Wang & Kanehl 2003]
4/quality of biotic index scores
[Wang & Kanehl 2003, Walters et al. 2009]
FISHES
\|/ abundance, biomass, richness or diversity
[Wang et al. 2003 (Fig 29), Stranko et al. 2008, Helms et al. 2009]
4" quality of biotic index scores
[Wang et al. 2003]
Coldwater fishes such as salmonids are among the taxa most
affected by temperature increases. For example, Runge et al.
(2008) found that the survival of stocked rainbow trout in the
Chattahoochee River, Georgia, was negatively related to the
amount of time water temperatures exceeded 20°C (Fig 30),
and that fish dispersed from warmer downstream reaches to
cooler upstream reaches.
It should be noted, however, that other studies have found
little or no relationship between water temperature and
biota in urban streams (Kemp & Spotila 1997, Waiters et al.
2009)and as with all urbanization-associated stressors, it
often is difficult to determine which of these often correlated
stressors is driving biotic responses.
# of species
# of individuals per 100 m
IStt-V .
10 15 20 25 30
15 20 25 30 35
Connected Imperviousness (%)
Figure 29. Relationship between % connected imperviousness and coldwater
fish species richness and abundance in 33 Wisconsin and Minnesota trout
streams.
From Wang L et a I. 2003. Impacts of urban land cover on trout streams in Wisconsin and
Minnesota. Transactions of the American Fisheries Society 132:825-839. Reprinted with
permission.
£ 0.6
500 1,000 1,500 2,000 2.500
Total number of exceedances per month
3.000
Figure 30. Estimates of monthly rainbow trout survival vs. number of
temperature exceedances at upstream (circles, dashed line) and downstream
(triangles, solid line) study reaches. An exceedance was defined as any 15-
minute interval in which temperature exceeded 20°C; numbers represent
months in which exceedances were recorded (e.g., 6=June).
From Runge JP et a I. 2008. Survival and dispersal of hatchery-raised rainbow trout in a river
basin undergoing urbanization. North American Journal of Fisheries Management 28:745-757.
Reprinted with permission.
Click below for more detailed information on specific topics
Temperature &
biotic condition
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Temperature
JikL
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Urbanizatiori & climate change
An increasing number of studies are considering the
potentially interactive effects of urbanization and climate
change on stream ecosystems (Palmer et al. 2009). Some
studies have focused on interactions between urbanization
and climate change-associated changes in precipitation and
runoff (Kaushal et al. 2008, Franczyk & Chang 2009, Han et al.
2009); others have examined interacting effects on stream
temperature.
Nelson & Palmer (2007) and Nelson et al. (2009) developed
models to predict the separate and combined effects of
urbanization and climate change on small mid-Atlantic
streams. They found that:
Water temperatures were highest under the scenario of
increased urbanization plus a warming climate, especially
in midsummer when there was heated runoff from
impervious surfaces (Fig 31).
Water temperatures exceeded the "good growth"
temperature maximum for coldwater fish species (28°C) on
an average of 49 days per 10-year period under the
urbanization plus climate change scenario, vs. 24 days per
10-year period in the urbanization alone scenario (Fig 32).
Water temperatures exceeded the "good growth"
temperature maximum for coolwater fish species (32°C)
only rarely, and only in the urbanization plus climate
change scenario.
Click below for more detailed information on specific topics
Urbanization &
climate change
35
u 30
10
May Jun Jul Aug
Date (year = 2090)
Sep
Figure 31. Projected maximum daily water temperatures for the year 2090
under four scenarios: baseline (B), urbanization (U), climate change (C), and
urbanization plus climate change (U+C).
From Nelson KC et a I. 2009. Forecasting the combined effects of urbanization and climate
change on stream ecosystems: from impacts to management options. Journal of Applied
Ecology 46:154-163. Reprinted with permission.
60
>.
to 40
.0
E
3
z
20 -
~ Baseline scenario
B Urbanization only
scenario
~ Climate change
only scenario
¦ Urbanization and
climate change
scenario
>y> J? J? <$> J^K J$> <$> <$
^ ^ ^ ^
Low average baseflow
High average baseflow
Figure 32. Predicted number of summer days with water temperatures > 28°C
(summed over a 10-year period), at 15 sites ranging from low to high average
baseflow, for four scenarios; baseline, urbanization, climate change, and
urbanization plus climate change.
From Nelson KC & Palmer MA. 2007. Stream temperature surges under urbanization and
climate change: data, models, and responses. Journal of the American Water Resources
Association 43(2):440-452. Reprinted with permission.
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Hydrology
r
Flow alteration in urban streams
Alteration of natural hydrologic regimes is a consistent and
pervasive effect of urbanization on stream ecosystems, as
discharge patternsthe amount and timing of water flow
through streamschange with urban development. Key
aspects of urbanization affecting hydrology may include:
4/ infiltration and surface runoff of precipitation
associated with impervious (and effectively impervious)
surfaces
/|s speed and efficiency of runoff delivery to streams, via
storm water drainage infrastructure
evapotranspiration due to vegetation removal
^ direct water discharges, via wastewater and industrial
effluents
infiltration due to irrigation and leakage from water
supply and wastewater infrastructure
-t water withdrawals and interbasin transfers
Commonly reported effects of urbanization on stream flow
regimes include (but are not limited to):
STORM FLOW
1s high flow frequency (Fig 33)
[Roy et a!. 2005, Schoonover et al. 2006, Brown et a!. 2009]
-f- high flow magnitude (Figs 33 and 34)
[Rose & Peters 2001, Burns et al. 2005, Schoonover et al. 2006]
^ flashiness or rapidity of flow changes (Fig 33)
[Roy et al. 2005, Schoonover et al. 2006, Chang 2007]
4, high flow duration
[Rose & Peters 2001, Poff et al. 2006, Chang 2007]
si' lag time (Fig 34)
[Arnold & Gibbons 1996, Changnon & Demissie 1996]
BASE FLOW
-4/ low flow magnitude (Fig 34)
[Finkenbine et al. 2000, Rose & Peters 2001, Kaufmann et al. 2009]
-f- low flow magnitude
[Burns et al. 2005, Riley et al. 2005, Poff et al. 2006]
^ low flow duration (Fig 34)
[Roy et al. 2005, DeGasperi et al. 2009]
These hydrologic changes can reduce habitat quality in urban
streams, and adversely affect stream biota. For example,
high flows can scour organisms and substrate from
streambeds, while low flows can reduce habitat area and
volume. See the Flow Alteration and Physical Habitat
modules for further details on biotic responses to these
changes.
>.
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UND
Aug Sep
Oct Nov Dec Jan
Date (2001-02)
Feb Mar
Figure 33. Stream runoff during a dry period (Aug 2001-Feb 2002) at three
study catchments: UND = undeveloped, MED = medium density residential
(1.6 houses ha1, 6% impervious), HIGH = high density residential (2.8 houses
ha1,11% impervious).
From Burns D et al. 2005. Effects of suburban development on runoff generation in the Croton
River basin, New York, USA. Journal of Hydrology 311:266-281. Reprinted with permission from
Elsevier.
01
£
A lag time
A high flow magnitude
A low flow duration
A low flow
magnitude
3
Time
Figure 34. Hypothetical hydrographs for an urban stream (yellow) and a rural
stream (green) after a storm, illustrating some common changes in stormflow
and baseflow that occur with urban development. Other changes are listed at
left.
Click below for more detailed information on specific topics
Baseflow in urban Water withdrawals
streams & transfers
Biotic responses
to urban flows
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Hydrology
r
Baseflow in urban streams
Urbanization generally results in increased magnitude and
frequency of peak flows, but baseflow effects typically are
more variable, with studies showing a range of responses in
urban streams [Lerner 2002, Brandes et al. 2005, Meyer
2005, Roy et al. 2005 (Fig 35), Poff et al. 2006],
Decreases in baseflow may result
from:
4- infiltration due to /fs impervious
surfaces
1s water withdrawals (surface or
ground)
These decreases may be offset,
however, by increases in baseflow
resulting from:
1s imported water supplies (i.e., interbasin transfers)
^ leakage from sewers and septic systems
T" leakage from water supply infrastructure
1s irrigation (e.g., lawn watering)
i"1 discharge of wastewater effluents
infiltration due to water collection in recharge areas
4- evapotranspiration due to \j/ vegetative cover
Urban-related increases in baseflow can be especially evident
in effluent-dominated systems, or streams and rivers in
which wastewater effluents comprise a significant portion of
baseflow volumes. For example:
Discharge from two wastewater treatment plants
accounted for at least 70% of river flow in the Bush River,
SC in Summer 2002 (Andersen et al. 2004).
Average effluent flow in the South Platte River, CO is 41%
total streamflow; during low flow conditions, this can
increase to 90% (Woodling et al. 2006).
As a result, changes in baseflow in these streams likely affect
water and sediment quality.
0.9 i
0.8
0.7 -
'ro
Q 0.6
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0.4
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350 -
300 -
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:> 200
o
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3
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50
0
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r2 = 0.54
1 1 1 1 1
0 5 10 15 20 25
% imperviousness
30
35
Figure 35. Linear regression models for baseflow variables showing highest
correlations with subcatchment imperviousness: (A) minimum daily
stage/mean daily stage during late spring; (B) maximum duration of low stage
<25th percentile during autumn. Of the nine baseflow variables tested across
five seasons, only these two variables showed relationships with r2 > 0.25,
and only in (B) was this relationship significant.
From Roy AH et a I. 2005. Investigating hydro logic alteration as a mechanism offish assemblage
shifts in urbanizing streams. Journal of the North American Benthological Society 24(3):656-
678. Reprinted with permission.
Click below for more detailed information on specific topics
Baseflow in urban
streams
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f
Hydrology
Water withdrawals & transfers
Water withdrawals and transfers associated with meeting
urban water demand can have significant repercussions for
stream systems. Their effects depend upon many factors,
including:
Where the water comes from
- Surface water vs. groundwater
- Within catchment vs. imported from another
catchment (i.e., water transfers)
- Direct intake from channel vs. from water supply
reservoir
- Small vs. large streams
Where the water goes
- Within catchment vs. exported to another
catchment (i.e., water transfers)
- Small vs. large streams
Freeman & Marcinek (2006) examined how surface water
withdrawals for municipal water supplies affected stream fish
assemblages in the Georgia Piedmont, using a withdrawal
index that represented the amount of water withdrawn on a
monthly average basis, relative to the 7-day, 10-year
recurrence low flow in those streams (7Q10). They found
that:
Richness of fluvial specialist fishes (e.g., many minnows
and darters) decreased as the amount of water withdrawn
increased (Fig 36).
This decrease generally occurred when permitted
withdrawal rates exceeded approximately 0.5-1 7Q10-
equivalent of water (Fig 36).
As water withdrawals increased, so did the probability
that sites would be classified as impaired based on their
Index of Biotic Integrity scores.
The type of water intake also was important, as reservoir
presence (along with withdrawal rate and drainage area)
were significant predictors of fluvial specialist richness.
Click below for more detailed information on specific topics
Water withdrawals
& transfers
to
QJ
*u
01
Q.
w»
0)
.Q
£
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Water intake structure for a water
supply plant on the Duck River, TN
h
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25 -
20 -
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;BJ .
¦ w*m I
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A
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^ BA
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A
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'4
A
A
A
A
A
0.00 0.50 1.00 1.50 2.00 2.50
Water withdrawal index
3.00
Figure 36. Richness estimates for (A) fluvial specialist and (B) habitat
generalist fishes vs. water withdrawal index values [ln(permitted monthly
average withdrawal / 7Q10)]. Squares indicate sites where water intake was
directly from channel; triangles indicate sites directly downstream from water
supply reservoirs. Data were collected in 28 Georgia streams used for
municipal water supplies, 2001-2003.
From Freeman MC & Marcinek PA. 2006. Fish assemblage responses to water withdrawals and
water supply reservoirs in Piedmont streams. Environmental Management 38(3):435-450.
Reprinted with permission from Springer.
Courtesy of Charlie Brenner
A New Orleans pump station that withdraws water
from the Mississippi River and transfers it to a
nearby treatment facility
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Hydrology
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m
esy of USEPA
Biotic responses to urban flows
Hydrologic changes associated with urbanization can directly
and indirectly affect stream biota in many ways. Effects may
include:
Direct scour and dislodgement from benthic surfaces due
to increased peak flows
Altered physical habitat
- changes in in-stream
hydraulic conditions (e.g.,
water velocity wetted
channel area and
duration)
- changes in channel
geomorphology
Life cycle disruption due to
changes in timing of flows
Other flow-associated alterations (e.g., increased
sediment, nutrient and contaminant delivery; changes in
food resources)
For example, Booth et al. (2004) examined how benthic index
of biological integrity (B-IBI) scores were related to two flow
metrics associated with urbanization:
TQmean = the fraction of a year that mean daily discharge
exceeds annual mean discharge
T0 5yr = the fraction of a multi-year period that a channel is
exposed to flows greater than the 0.5-year flood
For both TQmean and T05yt, low values indicate the prevalence
high discharge peaks that both rise and dissipate sharply
that is, increased flashiness and flow variability
Booth et al. (2004) found that:
TQmean anc' T0.5yr decreased as % total impervious area
increased, indicating that urban streams experienced
flashier hydrographs.
B-IBI scores increased asTQmean and T05yr increased,
indicating that macroinvertebrate biotic condition was
reduced in flashier streams (Fig 37a,b).
Sites with > 54% urban land cover fall below the main
trendline, indicating that macroinvertebrate biotic
condition was poorer than predicted by hydrologic
conditions alone (Fig 37c).
DQ
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¦
¦
¦ ¦
¦
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I
n = 15
0.25 0.30 0.35 0.40 0.45
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imean
50
30
10
o
o
o
o
o
° o
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n = 13
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30
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37
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53
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45,
o"89
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n = 15
0.25 0.30 0.35 0.40 0.45
TQ mean
Figure 37. Relationship between benthic index of biological integrity for
invertebrates and hydrologic variables TQmean(a, c) and T0 Syr (b). In (c), numbers
indicate % urban land cover (sites plotted as circles lacked land cover data).
Note that lower values for TQmean and T0 5 yr indicate higher flow variablity and
flashiness.
From Booth DB et al. 2004. Reviving urban streams: land use, hydrology, biology, and human
behavior. Journal of the American Water Resources Association 40(5):1351-1364. Reprinted with
permission.
Click below for more detailed information on specific topics
Biotic responses
to urban flows
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Physical Habitat
Physical habitat in urban streams
Urbanization can alter the geomorphologic and vegetative
structural features of stream channelsthat is, their physical
habitat.
Studies have reported many physical habitat alterations
associated with urbanization, including (but not limited to):
"Is direct channel modification (e.g., piping and burial)
[Elmore & Kaushal 2008, Roy et al, 2.009]
/fs channel enlargement
[Booth & Jackson 1997, Trimble 1997, Hession et al. 2003, Chin 2006,
Allmendinger et al. 2007]
"Is channel incision
[Booth & Jackson 1997, Hardison et al. 2009]
4" woody debris
[Finkenbine et al. 2000, King et al. 2005, Horwitz et al. 2008]
A geomorphologic units (Fig 38)
[Gregory et al. 1994, Riley et al. 2005, Shoffner & Royall 2008]
A streambed substrate composition (Fig 39)
[Finkenbine et al. 2000, Pizzuto et al. 2000, Walters et al. 2003, Roy
et al. 2005, Blakely et al. 2006]
4/habitat complexity
[Riley et al. 2005, Blakely et al. 2006, Gooseff et al. 2007]
See the Physical Habitat module for more general discussion
of physical habitat in streams (i.e., not just urban streams).
Click below for more detailed information on specific topics
Channel
enlargement
Road crossings
Bed substrates &
biotic condition
Natural streams
Urban streams
o
RUN
RIFFLE
POOL
Figure 38. Schematic representation of
the run, riffle and pool structure in two
natural & two urban streams in southern
California (the rectangle with an X in one
of the urban streams represents a
culvert). Urban streams had longer
habitat segments, higher percentages of
runs, & reduced habitat complexity.
From Riley SPD et a I. 2005. Effects of urbanization
on the distribution and abundance of amphibians
and invasive species in southern California streams.
Conservation Biology 19(6):1894-1907. Reprinted
with permission.
177771
Urban
Rural
Secondary
Mode
16-32 32-64 64-128 128-256 256-512 >512
Grain Size (mm)
Figure 39. Typical grain-size histograms from urban and rural catchments. The
frequency of < 2 mm particles more than doubled in urban streams. Rural
streams had a secondary sediment size mode at 8-16 mm; this secondary
mode was absent in urban channels, suggesting that these substrate sizes
were selectively removed from urban streams.
From Pizzuto JE et al. 2000. Comparing gravel-bed rivers in paired urban and rural catchments
of southeastern Pennsylvania. Geology 28(l):79-82. Reprinted with permission.
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Physical Habitat
Charinel enlargement with urbanization
Two key changes drive stream channel alterations in urban
systems:
f sediment supply initially, followed by 4^ sediment
supply over time
sediment transport capacity (i.e., stream discharge)
Early in urban development, soil disturbance commonly
increases sediment supply and leads to channel aggradation
(Wolman 1967, Chin 2006). Once development is more
established, imperviousness
and stream discharge
commonly increase and
sediment supply decreases,
leading to channel
degradation or incision
(Wolman 1967, Chin 2006).
Thus, streams in urban
catchments tend to widen and
deepen. Trimble (1997) observed this process in Borrego
Canyon Wash, CA (Fig 40), where erosion rates downstream
of an urbanizing area were 20 m3 m 1 yr1, versus 0.47 m3 m 1
yr1 at a less urbanized site. In lowland streams of western
Washington, Booth & Jackson (1997) found that channels
generally exhibited stability thresholds (below which there
was little or no bed and bank erosion) at 10% effective
impervious area, or at increased discharge such that 10-year
discharge in a forested catchment equaled 2-year discharge
under current catchment land use (Fig 41).
Channel enlargement is common but not universal in urban
streams. Whether channel enlargement occurs can depend
on several factors (Bledsoe & Watson 2001, Chin 2006,
Colosimo & Wilcock 2007), including:
Age and extent of urban development
Riparian condition
Connectedness of impervious areas and conveyance of
stormwaterto channel
Degree of channel entrenchment
Erodibility of bed and bank material
10
_i
m
Figure 40. Surveyed stream channel cross-sections taken downstream of an
urbanizing area on Borrego Canyon Wash, CA.
From Trimble SW. 1997. Contribution of stream channel erosion to sediment yield from an
urbanizing watershed. Science 278:1142-1144. Reprinted with permission from AAAS.
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O STABLE CHANNELS
X UNSTABLE CHANNELS
~ LARGE-LAKE SUBCATCHMENTS
GENERALLY STABLE CHANNELS
1 0-yr forested discharge =
2-yr current discharge
^XX
% X X
CENERALLY'UNSTABLE channels
xx
0 10 20 30 40 50 60
PERCENT IMPERVIOUS AREA IN CATCHMENT
Figure 41. Observed stable and unstable channels, plotted by % effective
impervious area in catchment and magnitude of simulated flow increases
(ratio of modeled 10-year forested to 2-year current or urbanized discharges).
From Booth DB & Jackson CR. 1997. Urbanization of aquatic systems: degradation thresholds,
stormwater detection, and the limits of mitigation. Journal of the American Water Resources
Association 33(5):1077-1090.
Click below for more detailed information on specific topics
Channel
enlargement
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Physical Habitat
Effects of road crossings
Roads can adversely affect stream ecosystems via multiple
pathways. Indirect effects include:
Altered stream discharge patterns due to increased
imperviousness and stormwater runoff
Increased contaminant loads due to accumulation on and
runoff from road surfaces
At road crossings, roads can directly impact stream
ecosystems, for example by altering channel geomorphology,
increasing sedimentation, and impeding fish and invertebrate
movement. In addition, stormwater drains often run along
roads, and road crossings frequently are points of stormwater
discharge to streams. Thus, road crossing density can be a
good predictor of stream biotic integrity, with biotic
condition decreasing as the number of road crossings
increases (Alberti et al. 2007, Carlisle et al. 2009).
However, not all road crossing types have the same effect.
For example, Blakely et al. (2006) examined how different
road crossing types affected movement of adult caddisflies in
New Zealand streams. They found that road culverts were
barriers to caddisfly dispersal: the number of adults caught
immediately upstream of culvert crossings was much lower
than the number caught at control sites downstream (Fig 42).
Bridges, which provided more open spans over streams, did
not inhibit movement. Fish movement has shown similar
bridge vs. culvert patterns (Benton et al. 2008).
Click below for more detailed information on specific topics
Road crossings
,M\
Example culvert (right) and
bridge (below) road crossings.
Photos courtesy of Tetra Tech
180
160J
140
^ 120
i 100
80
60-
40
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0
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Bridges Bridge Culverts Culvert
controls controls
Figure 42. Number of adult caddisflies caught directly upstream of bridges
and culverts (n = 8), vs. at control sites 50 m downstream.
From Blakely TJ et al. 2006. Barriers to the recovery of aquatic insect communities in urban
streams. Freshwater Biology 51:1634-1645. Reprinted with permission.
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Physical Habitat
Bed substrates & biotic condition
Urbanization typically affects both sediment supply and
transport capacity in streams, resulting in altered substrate
composition and stabilityboth of which are key factors
influencing stream biotic communities (see Sediment module
for further discussion of sediment as a stressor).
Many streambed substrate changes associated with urban
development have been linked to changes in biotic condition,
including:
1s fine sediment
[Hogg & Norris 1991, Morley & Karr 2002, Roy et al. 2005, Taulbee et
al. 2009, Walters et al. 2009]
1* embeddedness and armoring
[Borchardt & Statzner 1990, Biakely et al, 2006, Chin 2006, Walters
et al. 2009]
^ substrate stability
[Pedersen & Perkins 1986]
4" substrate complexity and heterogeneity
[Morley & Karr 2002, Biakely et al. 2006]
For example, Morley & Karr (2002) found that invertebrate
biotic integrity (B-IBI) scores and taxa richness metrics
increased with substrate size and roughness, but that these
substrate parameters decreased with urbanization (Table 7).
However, fine sediments are not always higher in urban
streams. Fines may be scoured from these systems as stream
discharge increases with impervious cover, resulting in
coarser, more armored streambeds (Chin 2006).
Sediment increases related to urbanization also can have
indirect effects on stream biota, via sediment-associated
contaminants. Urban sediments can contain high
concentrations of metals, organics, & other toxics, & these
compounds can adversely affect biotic condition (see Water
& Sediment Quality).
Increased erosion and sediment
runoff from disturbed soils.
Table 7. Spearmen rank correlation coefficients for associations of
urbanization and macroinvertebrate biotic condition parameters with
substrate measures. D16 and D50 refer to the substrate diameter below which
16% and 50% of particles are smaller, respectively; roughness was calculated
as the 84% particle diameter divided by bankfull depth. Coefficients in italics
had p < 0.10; coefficients in bold had p < 0.05.
PARAMETER
SUBSTRATE MEASURE
Die
d50
Roughness
Urbanization, n
17
17
17
% sub-basin
-0.20
-0.35
-0.60
% local
-0.12
-0.49
-0.70
Biotic condition, n
18
18
18
B-IBI
+0.27
+0.12
+0.51
Total taxa richness
+0.34
+0.17
+0.43
EPT richness
+0.59
+0.41
+0.50
dingers richness
+0.60
+0.39
+0.52
After Morley SA & Karr JR. 2002. Assessing and restoring the health of urban streams in the Puget
Sound basin. Conservation Biology 16(6):1498-1509.
Click below for more detailed information on specific topics
Bed substrates &
biotic condition
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Energy Sources
Urbanization & basal energy sources
There are two main sources of fixed energy that drive stream
food webs:
Organic carbon produced by photosynthesis outside the
stream, or allochthonous production
Organic carbon produced by photosynthesis within the
stream, or autochthonous production
Most streams rely on both allochthonous and autochthonous
energy, although the relative importance of each varies with
elevation, stream size and other factors. For example,
terrestrial carbon is more important in forested headwater
streams, whereas autochthonous carbon is more important
in open-canopied, mid-sized rivers.
Urbanization alters the energy sources available to stream
food webs, as well as the in-stream retention and storage of
those basal resources. Key changes associated with
urbanization are summarized at right; examples include:
Increased riparian deforestation, resulting in:
- increased light and algal production
- decreased terrestrial litter and wood inputs
Increased nutrient enrichment, resulting in increased algal
production and microbial respiration
Increased input of sewage-derived particulate organic
matter
Decreased algal biomass, due to scouring flows
Changes in the relative importance of physical vs.
biological factors in determining leaf decay rates
Changes in resources can result in changes in the consumer
community. For example invertebrate functional feeding
groups may change: reduced leaf litter may lead to few
shredder invertebrates; increased algal production may lead
to increased scrapers; and increased input of particulate
organic matter may lead to increased filterers. However,
these changes often are mitigated by concurrent changes in
habitat and water quality.
i -v - - v
=!£*,¦ <¦.,'/<- SSI
' ' "*' . .\\ ¦ '¦ : -v.-
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A
h *
*¦ .Jlir i.
^ ¦**.
-
urban
A conditions and inputs
1s light
1s temperature
nutrients
1s scouring flows
-l> natural carbon inputs
^ anthropogenic carbon
inputs
A responses
^ photosynthesis
"Is respiration
A decay rates
4/ carbon storage
Click below for more detailed information on specific topics
Terrestrial
leaf litter
Primary
production &
respiration
Quantity & quality
of DOC
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Energy Sources
Terrestrial leaf litter inputs & retention
Urbanization can alter terrestrial leaf litter inputs and
retention in several ways. Reported effects include:
\ leaf litter inputs resulting from riparian alteration and
stream burial
[Carroll & Jackson 2008]
1s leaf litter inputs due to increased horizontal delivery
(e.g., via stormdrains)
[Miller & Boulton 2005, Carroll & Jackson 2008]
A type and timing of inputs due to changes in riparian taxa
[Imberger et al. 2008, Roberts & Bilby 2009]
\ leaf litter retention due to scouring by high flows and
reductions in debris dams
[Paul & Meyer 2001]
Terrestrial leaf litter processing
Urbanization alters several variables that influence leaf decay
leading to variable effects of urban development on
decomposition rates. Reported findings include:
¦f leaf decomposition rates related to:
- physical abrasion by high flows
[Paul et al. 2006, Chadwick et al. 2006]
- /fv snails
[Chadwick et al. 2006]
- ^ microbial activity resulting from T" nutrient
concentrations and temperatures (Fig 43)
[Chadwick et al. 2006, Imberger et al. 2008]
leaf decomposition rates related to:
- ^ shredders
[Chadwick et al, 2006, Paul et al. 2006, Carroll & Jackson 2008]
- 4/ microbial activity
[Paul et al. 2006]
- metal contamination
[Woodcock & Huryn 2005, Chadwick et al. 2006]
0.08 "
A
:a
-0.06 "
r2 = 0.91
CD
u.
^0^ p = 0.003
1 0.04 -
O
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ro
0 0.02 "
o
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CD
oo
0.00 J
) 81
1
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£
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p = 0.003
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2
T3 «
r2 = 0.68
>, 2 "
_c
p = 0.04
<
£ o
^eo- ""0
i
0
1
5
i i i
10 15 20
El (%)
Figure 43. Pittosporum undulatum (closed circles) and Eucalyptus obliqua
(open circles) leaf breakdown rates (A) and microbial activity in leaves,
estimated by fluorescein diacetate (FDA) hydrolysis (B), vs. % effective
imperviousness (El). Breakdown rates and microbial activity increased with
% El for the more readily transformed leaf litter of introduced Pittosporum,
but effects on native Eucalyptus were minimal.
From Imberger SJ et al. 2008 More microbial activity, riot abrasive flow or shredder abundance,
accelerates breakdown of labile leaf litter in urban streams. Journal of the North American
BenthologicalSociety 27(3):549-561. Reprinted with permission.
Click below for more detailed information on specific topics
Terrestrial
Primary
leaf litter
respiration
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Energy Sources
Primary production & respiration
Primary production, or the fixation of inorganic carbon into
organic carbon (e.g., piant biomass), provides most of the
autochthonous carbon produced in streams. Algae are usually
the dominant stream primary producers, although other
plants (e.g., macrophytes, mosses) also may be important in
certain systems.
Effects of urbanization on algal biomass and primary
production may include:
\ primary production or algal biomass
(Fig 44, Table 8) resulting from:
- nutrients
- light and temperature
- \ grazers
\ primary production or algal biomass
resulting from:
- scouring due to high flows
- 1s fine sediment and 4/ sediment stability
- toxic pollutants
- 1s grazers
A assemblage structure
Many of the factors influencing primary production in urban
streams also affect respiration. Respiration does not always
show a clear pattern with urbanization, but often is
elevated in streams receiving wastewater discharges
(Giicker et al, 2006 [Table 8], Wenger et al. 2009). These
increases in respiration can lead to large oxygen fluctuations
and oxygen deficits in urban streams (Faulkner et al. 2000,
Ometo et al. 2000, Giicker et al. 2006 [Table 8]).
Click below for more detailed information on specific topics
Primary
production &
respiration
July 02
100-
10
CO
g
CO
I 100
Nov 02
10
"
\
<
0 5 20 40 60 80100
Percentage connection
0.1 2.5 10 2030 50
Percentage imperviousness
Figure 44. Median chlorophyll a at 16 Australian streams on 2 sampling dates,
vs. % drainage connection and % imperviousness; % connection (but not %
imperviousness) explained a significant amount of variation in chlorophyll a
in both sampling periods.
From Taylor SL et al. 2004. Catchment urbanisation and increased benthic algal biomass in
streams: linking mechanisms to management. Freshwater Biology 49:835-851. Reprinted with
permission.
Table 8. Gross primary production (GPP) and community respiration (CR24),
both measured in g 02 m 2 d1, at an upstream reference site and a
downstream wastewater-impacted site on a lowland stream in Germany.
SEASON
PARAMETER
UPSTREAM
DOWNSTREAM
SPRING
GPP
2
2
CR24
11
24
GPP:CR24
0.15
0.10
SUMMER
GPP
32
47
CR24
32
59
GPP:CR24
1.0
0.8
WINTER
GPP
0.1
< 0.1
CR24
6
18
GPP:CR24
0.01
< 0.01
Modified from Giicker B et al. 2006. Effects of wastewater treatment plant discharge on
ecosystem structure and function of lowland streams. Journal of the North American
Benthological Society 25(2):313-329.
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Energy Sources
Quantity & quality of dissolved organic carbon (DOC)
DOC can play an important role in many streamsfor
example, by providing a key energy source for stream food
webs via bacterial assimilation, or by influencing the
bioavailability of metals and other toxics.
Urbanization can affect both the quantity and quality of
DOC in streams. Point (e.g., wastewater discharges) and non-
point (e.g., impervious surfaces, turf grass) sources can
contribute DOC to urban streams. Riparian/channel
alteration can alter DOC inputs and processing. In many
cases, the quality of these DOC resources will vary.
For example, Harbott & Grace (2005) used bacterial
extracellular enzyme activity to examine how urbanization
affects DOC bioavailability. They found that:
DOC concentrations increased with catchment effective
imperviousness (El) (Fig 45)
The activity of individual enzymes varied with El, indicating
changes in DOC sources (and thus bioavailability) with
urban development
In less urbanized streams, DOC sources were more
diverse and more dependent on microbial detrital
material
- In more urbanized streams, DOC sources were
more dependent on peptides, perhaps due to
processing of filamentous algae
10 T
7.5
O)
O
O
o
5 H
2.5
-4.0 -3.0 -2.0 -1.0 0.0
log10(EI)
110
Figure 45. Relationship between catchment effective imperviousness (El) and
dissolved organic carbon (DOC) concentration in eight streams east of
Melbourne, Australia (r2 = 0.05, p = 0.051).
Reprinted with permission from Harbott EL & Grace MR. 2005. Extracellular enzyme response
to bioavailability of dissolved organic C in streams of varying catchment urbanization. Journal
of the North American Benthological Society 24(3):588-601.
Click below for more detailed information on specific topics
Quantity & quality
of DOC
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Han HJ, Allan JD, and Scavia D. 2009. Influence of climate and human activities on the relationship between watershed nitrogen input and
river export. Environmental Science & Technology 43:1916-1922.
Harbott EL and Grace MR. 2005. Extracellular enzyme response to bioavailability of dissolved organic C in streams of varying catchment
urbanization. Journal of the North American Benthological Society 24:588-601.
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labile leaf litter in urban streams. Journal of the North American Benthological Society 27:549-561.
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