Physical, chemical, and biological Physical, chemical, and biological characteristics of streams in characteristics of streams in

urbanizing areas near Denver, urbanizing areas near Denver, ColoradoColorado

Lori SpragueLori Sprague Robert Zuellig Robert Zuellig HydrologistHydrologist EcologistEcologist

U.S. Geological SurveyU.S. Geological SurveyDenver, CODenver, CO

May 2006May 2006

U.S. Department of the InteriorU.S. Geological Survey

Study Objectives•• Determine the effects of Determine the effects of

urbanization on hydrologic, urbanization on hydrologic, geomorphic, chemical, geomorphic, chemical, habitat, and biological habitat, and biological conditionsconditions

•• Determine the most important Determine the most important urban stressors related to the urban stressors related to the responsesresponses

•• Compare these responses Compare these responses over a range of environmental over a range of environmental settings throughout the Nationsettings throughout the Nation

Population in the South Platte River Basin increased by about 670,000 people from

1990 through 2000, to over 2.8 million

Nebraska

Colorado

Wyoming

Denver

South Boulder CreekSouth Boulder Creek19371937

Photos courtesy of USFShttp://bcn.boulder.co.us/basin/gallery/sboulder50yrs.html

South Boulder CreekSouth Boulder Creek19871987

Water management

Photos from http://bcn.boulder.co.us/basin/gallery

Site Selection

• Environmental characteristics –homogeneous environmental framework controlled for “natural”sources of variability

• Urban intensity –sites represented a gradient of urbanization (urban intensity index)

BoulderBoulder HendersonHenderson

Castle RockCastle Rock

ParkerParker

DenverDenverIdaho SpringsIdaho Springs

LovelandLoveland

Estes ParkEstes Park

Fort MorganFort Morgan

Fort CollinsFort CollinsSterlingSterling

CheyenneCheyenne

GreeleyGreeley

KerseyKersey

JulesburgJulesburg

North PlatteNorth Platte

Nebraska

Colorado

Wyoming

0 20 40 km

Stream with high-level urban intensity Urban Intensity Index = 100

Stream with mid-level urban intensity Urban Intensity Index = 40

Stream with low-level urban intensity Urban Intensity Index = 3

Study Design

• Biological characteristicsalgae, invertebrates, fish (summer low flow)

• Physical characteristicshabitat (summer low flow), streamflow, water temperature (continuous for 1 year)

• Chemical characteristicsnutrients, pesticides, sediment, chloride, sulfate, bacteria (spring and summer base flow)

Time and flow integrated chemical parameters

• Semi-permeable membrane devices (SPMDs)

• Placed at all 28 sites for 4 weeks

• Sequesters hydrophobic organics

• Mimics bioaccumulation in fish

Fish InvertebratesAlgae

Che

mis

try

Hyd

rolo

gyH

abita

t

Tem

pera

ture

Urbanization

Conceptual model

Channelization, riparian clearingGreater extremes, more fluctuation

Pollutant generation, higher concentrationsFlas

hier s

tream

s, hig

her p

eak f

lows

Non

-nat

ive

spec

ies

Fish InvertebratesAlgaeC

hem

istr

y

Hyd

rolo

gy

Urbanization

Hab

itat

Tem

pera

ture

SedimentSulfate

Housing age

Population density

Base-flow chemistry• Suspended sediment related to housing age • Sulfate related to population density

Fish InvertebratesAlgae

Hyd

rolo

gy

Land coverRoad densityHousing age

Housing densityPopulation density

Urban intensity index

Urbanization

Hab

itat

Tem

pera

ture

PAHsChe

mis

try

Flashiness

SPMD chemistry• PAHs related to stream flashiness and many measures of urbanization • Variability in PAHs best explained by distance from stream to nearest road

Fish InvertebratesAlgae

Hyd

rolo

gyH

abita

t

Tem

pera

ture

Urbanization explained variability of SPMD chemistry well, but not variability of spring and summer base-flow chemistry

SedimentSulfate

PAHsChe

mis

try

Flashiness

Land coverRoad densityHousing age

Housing densityPopulation density

Urban intensity index

Urbanization

Fish InvertebratesAlgae

Hyd

rolo

gyH

abita

t

Tem

pera

ture

HabitatNo strong relations between habitat and urbanization

Che

mis

try

Urbanization

HydrologyNo strong relations between hydrology and urbanization

Fish InvertebratesAlgae

Hyd

rolo

gyH

abita

t

Tem

pera

ture

Water temperatureTemperatures related to high-intensity development near the stream

Duration of falling

temperatures

Che

mis

try

Land cover

Urbanization

Fish communities were related predominantly to housing age, fine suspended sediment, and chloride

Sediment

Chloride

Fish InvertebratesAlgaeC

hem

istr

y

Hyd

rolo

gyH

abita

t

Tem

pera

ture

Housing age

Urbanization

Algal biomass was related predominantly to conductivity, nutrients, pesticides, the duration of high flows, and stream flashiness

ConductivityNutrientsPesticides

Fish InvertebratesAlgaeC

hem

istr

y

Duration of high flows

Flashiness

Hyd

rolo

gyH

abita

t

Tem

pera

ture

Urbanization

Invertebrate communities were related predominantly to nutrients, pesticides, duration of high flows, and stream flashiness

NutrientsPesticides

Fish InvertebratesAlgaeC

hem

istr

y

Duration of high flows

Flashiness

Hyd

rolo

gyH

abita

t

Tem

pera

ture

Urbanization

SedimentSulfate

ChlorideConductivity

NutrientsPesticides

PAHs

?Water management

Other Factors

Fish InvertebratesAlgaeC

hem

istr

y

Duration of high flows

Flashiness

Hyd

rolo

gyH

abita

t

Tem

pera

ture Duration of

falling temperatures Land cover

Road densityHousing age

Housing densityPopulation density

Urban intensity index

Urbanization

Aquatic communities were related to chemistry and hydrology, but chemistry and hydrology generally were not strongly related to urbanization

Comparison – Total Pesticide Concentration

0.00

0.05

0.10

0.15

0.20

0.25

0 20 40 60 80 100Urban Intensity Index

Con

cent

ratio

n, μ

g/L

Denver

RaleighPortland

Atlanta

Con

cent

ratio

n, μ

g/L

Urban Intensity Index

0.0

0.5

1.0

1.5

2.0

2.5

0 20 40 60 80 100

Comparison – EPT Richness

RaleighPortland

Atlanta

05101520253035

0 20 40 60 80 100Urban Intensity Index

EP

T R

ichn

ess

Urban Intensity Index

Denver

EP

T R

ichn

ess

0

4

8

12

16

0 20 40 60 80 100

Comparison – EPT Richness

05101520253035

0 20 40 60 80 100Urban Intensity Index

EP

T R

ichn

ess

Conclusions• Aquatic communities were related to chemistry and hydrology,

but chemistry and hydrology generally were not strongly related to urbanization

• Commonly observed effects of urbanization (stream flashiness, increased chemical concentrations, fewer sensitive species) were not observed– Present-day aquatic communities are tolerant even in areas with

minimal development

– Water management?

• Does not mean urbanization is not affecting stream ecosystems– Likely multiple interacting stressors, including urbanization

– Protection of stream ecosystems may need to involve numerous strategies

CONTACT INFORMATION

Lori Sprague Robert Zuellig lsprague@usgs.gov rzuellig@usgs.gov

303-236-4882 x262 303-236-4882 x278

U.S. Geological SurveyColorado Water Science Center

Denver Federal Center Building 53 MS 415Denver, CO 80225