URBANIZATION IMPACTS ON STREAM NUTRIENTCONCENTRATIONS IN THE SEATTLE REGION

Michael T. Brett,1 Sara E. Stanley,1 Giorgios Arhonditsis,1 David M. Hartley,2 Jonathan D. Frodge,2 & David E. Funke2

1Department of Civil & Environmental Engineering, Box 352700, University of Washington,

Seattle, WA 98195.

2King County Water & Land Resources, 201 South Jackson St #600,

Seattle, WA 98104-3854.

Land Cover

• 10 years, 17 streams, sampled monthly • Non-storm and storm samples

• 7 variables analyzed

King County Data

Land Cover Versus Stream Nutrients: Normal Flows

0

20

40

60

80

100

Geo

mea

n TP

(µg/

l)

0% 20%40%60%80%100%

Percent Urban Land Cover

r2 = 0.58

Total Phosphorus

0

10

20

30

40

50

Geo

mea

n SR

P (µ

g/l)

0% 20%40%60%80%100%

Percent Urban Land Cover

r2 = 0.56

Soluble Reactive Phosphorus

0

2

4

6

8

10

Geo

mea

n TS

S (m

g/l)

0% 20%40%60%80%100%

Percent Urban Land Cover

r2 = 0.03

Total suspended solids

0

1

23

4

5

6

Geo

mea

n tu

rbid

ity (N

TUs)

0% 20%40% 60%80%100%

Percent Urban Land Cover

r2 = 0.33

Turbidity

Tibbets

0

10

20

30

40

50

Geo

mea

n N

H 4 (µ

g/l)

0% 20%40%60%80%100%

Percent Urban Land Cover

r2 = 0.36

Ammonium

Tibbets

0

250

500750

1000

1250

1500

Geo

mea

n N

O 3 (µ

g/l)

0% 20%40%60%80%100%

Percent Urban Land Cover

r2 = 0.16

Nitrate

Change in Concentration: Storm/Normal Flow

0

2

4

6

8

10

12

14

TSS

(Sto

rm/N

orm

al F

low

)0% 20% 40% 60% 80% 100%

Percent Urban Land Cover

r2 = 0.09

Total Suspended Solids

Coal

0.0

0.5

1.0

1.5

2.0

2.5

3.0

TP (S

torm

/Nor

mal

Flo

w)

0% 20% 40% 60% 80% 100%

Precent Urban Land Cover

r2 = 0.03

Total Phosphorus

Coal

0.0

0.4

0.8

1.2

1.6

SRP

(Sto

rm/N

orm

al F

low

)

0% 20% 40% 60% 80% 100%

Percent Urban Land Cover

r2 = 0.51

Soluble Reactive Phosphorus

0.0

0.4

0.8

1.2

1.6

2.0

NO

3 (St

orm

/Nor

mal

Flo

w)

0% 20% 40% 60% 80% 100%

Percent Urban Land Cover

r2 = 0.67

Nitrate

0.0

0.5

1.0

1.5

2.0

2.5

NH 4

(Sto

rm/N

orm

al F

low

)

0% 20% 40% 60% 80% 100%

Percent Urban Land Cover

r2 = 0.18

Ammonium

0

2

4

6

8

Turb

idity

(Sto

rm/N

orm

al F

low

)

0% 20% 40% 60% 80% 100%

Percent Urban Land Cover

r2 = 0.11

Turbidity

Coal

55 ± 45%

67 ± 36%

244 ± 116%

184 ± 83%

1.0se

ason

al m

ean/

year

ly m

ean

Sum

mer

Fall

Win

ter

Sprin

g

Sum

mer

Nitrate & Ammonium

NH4

NO3

1.0

seas

onal

mea

n/ye

arly

mea

n

Sum

mer

Fall

Win

ter

Sprin

g

Sum

mer

Total & Soluble Reactive Phosphorus

SRP

TP

1.0

seas

onal

mea

n/ye

arly

mea

n

Sum

mer

Fall

Win

ter

Sprin

g

Sum

mer

TSS and Turbidity

Turbidity

TSS

2.0

0.50.50.5

2.02.0

Seasonal Fluctuations in Stream Constituent Concentrations

Average Average Percent Constituent Units Forested Urban Enrichment

Total Phosphorus µg/l 32.3 67.8 109%Soluble Reactive P µg/l 13.1 33.4 154%Total Nitrogen µg/l 1065 1412 33%Nitrate µg/l 840 1088 29%Ammonium µg/l 13.7 24.8 81%Turbidity NTUs 1.71 3.01 77%Total Susp. Solids mg/l 4.33 5.90 36%

Percent Urban Enrichment

Seattle streams Omernik (1976) Seattle For./ Seattle Urban/Constituent Forested Urban Forested Agri. Omernik's For.Omernik's Ag.

Total Phosphorus 32 70 35 135 0.92 0.52Soluble Reactive Phosphorus 13 35 14 58 0.94 0.61Total Nitrogen 1065 1404 885 4170 1.20 0.34

Dissolved Inorganic Nitrogen 862 1107 347 3190 2.48 0.35

Agricultural vs. Urban Enrichment

Averaged Overall Change in Urban Stream SRP Concentrations

25

30

35

40

45

50

55

60

Mea

n A

nnua

l SR

P co

nc. (

µg/l)

1980 1985 1990 1995 2000

y = -0.86x + 1747 r2 = 0.42

Urban stream SRP concentrations

800

900

1000

1100

1200

1300

Mea

n an

nual

nitr

ate

conc

. (µg

/l)

1980 1985 1990 1995 2000

y = -9x + 18950 r2 = 0.31

Urban stream nitrate concentrations

Conclusions:Urban streams are enriched with Phosphorus by about 100-150% and with Nitrogen by about 30-70%.

Stream TSS concentrations and Turbidity are more closely related to short term flow fluctuations than to land cover.

Forested streams export inorganic nitrogen and phosphorus during storms.

Stream phosphorus concentrations peak during the summer, and nitrogen and sediment concentrations peak during the winter.

The most urbanized streams have had a 36% decline in SRP and a 15% decline in nitrate concentrations during the last 20 years.

0.0

0.5

1.0

1.5

2.0

Sign

al/N

oise

TP SRP NO3 NH4 Turbid TSS

Constituent

Log10

Arithmetic