Identifying Changes to Stream Condition

caused by Urbanization

How understanding the responses can improve ecological risk characterization

----------------------------------------

James Coles – USGSThomas Cuffney – USGS

Cornell Rosiu – EPA

Denver

Portland

Dallas

Birmingham Atlanta

Raleigh

Milwaukee

BOSTON

Salt Lake City

Boston = NECBNew England Coastal Basins

Seattle

Sacramento

National Water-Quality Assessment (NAWQA) Program Urban Stream Studies

Setting up the Study Design

• Define homogeneous environmental setting.– minimize natural variability

• Determine watershed indicators of urbanization.– related to human presence

• Select sites to represent urban intensity gradient.– minimal to high levels of urbanization

• Establish consistent sampling reaches– 150 meters, riffles, riparian cover, stable channel

New England Study Sites

BOSTON

Develop an Index to measure

Urban Intensity

High Urban (100)Low Urban (0)

and which also corresponds to stream condition

Original (a priori) Index of Urban Intensity (UII) used 24 landuse and

demographic variables to characterize an urbanizing landscape.

• Infrastructure (Dams, Roadways, TRI sites)

• Land cover (Forest, Developed land)

• Census statistics (Population, Socioeconomic factors)

Perhaps an Index of Urban Intensity (UII)could be derived that is as effective,

but uses fewer than 24 variables

Revised UII

• Road Density– Expansion of Infrastructure

• Percentage of Buffer in Forest– Encroachment along riparian zone

• Percentage of Developed land– Change from natural landscape

• Population Density– Human presence on landscape

Comparing theUrban Intensity Indices (UII)

revised UII (4 variables)

a prioi UII (24 variables)

Comparing responses of Indicator Variables

between versions of the UII

Indicator VariableCategory

MetricsCompared

a priori UIIaverage

correlation

Revised-UIIaverage

correlation

• Water Chemistry 11 0.829 0.830

• Invertebrates 24 0.837 0.845

• Benthic Algae 12 0.756 0.743

• Fish 6 0.804 0.785

• Habitat 7 0.788 0.773

Overall Average 60 0.810 0.807

Impervious Surface Area (ISA) compared to

Revised and the a priori UII

revised - UII

NO

AA

IS

A

a priori UII

r2=0.982 r2=0.948

Impervious Surface Areacompared to

Urban Intensity (revised UII)

0 20 40 60 80 100

Urban Intensity

0

10

20

30

40

Percentage ISAY= 0.37X + 0.91R2 = 0.982

Invertebrate responses to urbanization (Urban Intensity scaled 0 to 100)

A B C D

0 20 40 60 80 100 Urban Intensity

30

40

50

60

70

80

90

100

Tot

al R

ich

0 20 40 60 80 100 Urban Intensity

0

10

20

30

40

EP

T R

ich

0 20 40 60 80 100 Urban Intensity

0

10

20

30

40

%R

ich

No

n In

sect

0 20 40 60 80 100 Urban Intensity

0

10

20

30

%R

ich

Mol

lusk

+C

rust

E F

0 20 40 60 80 100 Urban Intensity

0

10

20

30

40

GC

Ric

h

0 20 40 60 80 100 Urban Intensity

3

4

5

6

7

Ta

xa T

ole

ran

ce In

dex

Response of

Functional Group and Taxa Tolerance

Threshold Response Linear Response

Response of Water Quality to Urbanization

Parameters in WQ index:

- TKN- pH- Conductance- Alkalinity

0 20 40 60 80 100Urban Intensity

0

1

2

3

4

WQ

Inde

x (e

nric

hm

ent)

Improving Ecological Risk Assessments

The value of knowing the urban intensity of a site where contamination occurs.

(Is it urban intensity or the Superfund-site

that is affecting stream condition?)

Eastland Woolen Mill Site A Superfund Site in Corinna, ME.

-1 0 1 2 3 4 CA - Axis 1

-1

0

1

2

3

CA

- A

xis

2

25

2726

22

24

23

Reference(Lake)

Reference(River)

Correspondence Analysis, interpretation of the biplot :

The two sets of reference sites are distinct from the group that has the contaminated sites.

Contaminated

Urban Intensity used to define the expected condition

0 20 40 60 80 100

Urban Intensity

3

4

5

6

7

Ec

olo

gic

al

Co

nd

itio

n

T

axa

To

lera

nce

Ind

ex

This quadrant is the Problem Zone

Large dot represents the Nyanza

Superfund site. The Ecological

Condition metric indicates that

the cleanup was successful.

Developing Applications of the Urban intensity Index

Addressing the details • Variables used in an urban index can be somewhat

esoteric: Socioeconomic factors• The Urban Intensity Index is standardized over the

range of study sites, scaled 0 -100.• Results from a single study of 30 sites may be

tentative. Other data could be used to corroborate the Urban Intensity Index and the ecological responses.

Find regression coefficients to express the UII as equation

y = 12.5x - 13.6

0

20

40

60

80

100

0 5 10

Road Density (road km/ basin km2)

Ro

ad

De

ns

ity

(s

ca

led

)

y = 1.74x - 30.5

0

20

40

60

80

100

0 20 40 60 80

% Buffer (120 m Riparian Zone)

% B

uff

er

(scale

d)

y = 8.09x - 2.0

0

20

40

60

80

100

0 5 10 15

Population Density (# / HA)

Po

p D

en (

scal

ed)

y = 1.53x - 2.2

0

20

40

60

80

100

0 20 40 60 80% Developed Landcover

% D

evel

op

ed (

scal

ed)

Set up the equation to include the Landuse Variables

Urban Intensity = (ROAD*12.5)+(BUFF%*1.74)+(DEV%*1.53)+

(POP *8.09))*0.25)

• ROAD = road density [road length (km) / watershed area (km2)]

• BUFF% = percentage stream buffer not in forest landcover [MRLC level 1]

• DEV% = percentage watershed in developed landcover [MRLC level 1]

• POP = population density, people per hectare [U.S. census data]

Urban Intensity Indexmodeled vs. scaled

0 20 40 60 80 100

Urban intensity (scaled)

0

20

40

60

80

100

120

Urban Intensity modelY = 0.97X + 13.6

Intercept

EPA Region 1

New England WadeableStreamsProject

Regressions between response variables and the urban intensity index

Response RegressionVariable Coefficient (r2)_________________________________________________________________________________________________________

EPT Richness (-) 0.743

% Richness non-Insects (+) 0.837

Taxa Tolerance Index (+) 0.824

WQ Index (+) 0.834

__________________________________________________________

0 20 40 60 80 100Urban intensity

0

1

2

3

4

5

6

Taxa Tolerance(Expected)

Expected stream condition based on Urban Intensity of watershed

0 20 40 60 80 100Urban intensity

0

1

2

3

4

5

6

Taxa Tolerance(Expected)

Expected stream condition based on Urban Intensity of watershed

Acme Chemical Site

• Urban Intensity = 40

0 20 40 60 80 100Urban intensity

0

1

2

3

4

5

6

Taxa Tolerance(Expected)

Expected stream condition based on Urban Intensity of watershed

Acme Chemical Site

• Urban Intensity = 40• Stream Condition = 2.5

0 20 40 60 80 100Urban intensity

0

1

2

3

4

5

6

Taxa Tolerance(Expected)

Expected stream condition based on Urban Intensity of watershed

Acme Chemical Site

• Urban Intensity = 40• Stream Condition = 2.5

CONCLUSIONNo unacceptable ecological risk

0 20 40 60 80 100Urban intensity

0

1

2

3

4

5

6

Taxa Tolerance(Expected)

Expected stream condition based on Urban Intensity of watershed

Acme Chemical Site

• Urban Intensity = 40• Stream Condition = 4.5

CONCLUSIONStream condition may be affected bysite contamination.

Concluding Points

• Study currently being funded by EPA Region I (New England) to use this approach, which is expected to improve Ecological Risk Characterizations.

• Even a general awareness of the urban intensity of a basin is useful in making an interpretation of stream condition at a site.